41 animalnutrition text

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 41Chapter 41

Animal Nutrition


• Overview: The Need to Feed

• Every mealtime is a reminder that we are heterotrophs

– Dependent on a regular supply of food

Figure 41.1


• In general, animals fall into one of three dietary categories

– Herbivores eat mainly autotrophs (plants and algae)

– Carnivores eat other animals

– Omnivores regularly consume animals as well as plants or algal matter


• Regardless of what an animal eats, an adequate diet must satisfy three nutritional needs

– Fuel for all cellular work

– The organic raw materials for biosynthesis

– Essential nutrients, substances such as vitamins that the animal cannot make for itself


• Animals feed by four main mechanisms

Figure 41.2

Baleen

SUSPENSION FEEDERS

Feces

SUBSTRATE FEEDERS

BULK FEEDERS

FLUID FEEDERS

Caterpillar


• Concept 41.1: Homeostatic mechanisms manage an animal’s energy budget

• Nearly all of an animal’s ATP generation

– Is based on the oxidation of energy-rich molecules: carbohydrates, proteins, and fats


Glucose Regulation as an Example of Homeostasis

• Animals store excess calories

– As glycogen in the liver and muscles and as fat


• Glucose is a major fuel for cells

• Its metabolism, regulated by hormone action, is an important example of homeostasis

Figure 41.3

1 When blood glucose level rises, a gland called the pancreas secretes insulin,a hormone, into the blood.

Insulin enhances the transport of glucose into body cells and stimulates the liver and muscle cells to store glucose as glycogen. As a result, blood glucose level drops.

2

STIMULUS:Blood glucose

level risesafter eating.

Homeostasis:90 mg glucose/100 mL blood

STIMULUS:Blood glucose

level dropsbelow set point.

Glucagon promotesthe breakdown of

glycogen in theliver and the

release of glucoseinto the blood,

increasing bloodglucose level.

4

When blood glucose level drops, the pancreas secretes the hormone glucagon, which opposes the effect of insulin.

3


• When fewer calories are taken in than are expended

– Fuel is taken out of storage and oxidized


Caloric Imbalance

• Undernourishment

– Occurs in animals when their diets are chronically deficient in calories

– Can have detrimental effects on an animal


• Overnourishment

– Results from excessive food intake

– Leads to the storage of excess calories as fat

Figure 41.4

100 µm


Obesity as a Human Health Problem

• The World Health Organization

– Now recognizes obesity as a major global health problem

• Obesity contributes to a number of health problems, including

– Diabetes, cardiovascular disease, and colon and breast cancer


• Researchers have discovered

– Several of the mechanisms that help regulate body weight

• Over the long term, homeostatic mechanisms

– Are feedback circuits that control the body’s storage and metabolism of fat


• Several chemical signals called hormones

– Regulate both long-term and short-term appetite by affecting a “satiety center” in the brain

Figure 41.5

Produced by adipose (fat) tissue, leptin suppresses

appetite as its level increases. When body fat decreases,

leptin levels fall, and appetite increases.

LeptinPYY

Insulin

Ghrelin

Secreted by the stomach wall, ghrelin is one of the signals that triggers feelings of hunger as mealtimes approach. In dieters who lose weight, ghrelin levels increase, which may be one reason it’s so hard to stay on a diet.

The hormone PYY, secreted by the small intestine after meals,

acts as an appetite suppressant that

counters the appetite stimulant ghrelin.

A rise in blood sugar level after a meal stimulates the pancreas to secrete insulin (see Figure 41.3). In addition to its other functions, insulin suppresses appetite by acting on the brain.


• The complexity of weight control in humans

– Is evident from studies of the hormone leptin

• Mice that inherit a defect in the gene for leptin

– Become very obese

Figure 41.6


Obesity and Evolution

• The problem of maintaining weight partly stems from our evolutionary past

– When fat hoarding was a means of survival


• A species of birds called petrels

– Become obese as chicks due to the need to consume more calories than they burn

Figure 41.7


• Concept 41.2: An animal’s diet must supply carbon skeletons and essential nutrients

• To build the complex molecules it needs to grow, maintain itself, and reproduce

– An animal must obtain organic precursors (carbon skeletons) from its food


• Besides fuel and carbon skeletons

– An animal’s diet must also supply essential nutrients in preassembled form

• An animal that is malnourished

– Is missing one or more essential nutrients in its diet


• Herbivorous animals

– May suffer mineral deficiencies if they graze on plants in soil lacking key minerals

Figure 41.8


• Malnutrition

– Is much more common than undernutrition in human populations


Essential Amino Acids

• Animals require 20 amino acids

– And can synthesize about half of them from the other molecules they obtain from their diet

• The remaining amino acids, the essential amino acids

– Must be obtained from food in preassembled form


• A diet that provides insufficient amounts of one or more essential amino acids

– Causes a form of malnutrition called protein deficiency

Figure 41.9


• Most plant proteins are incomplete in amino acid makeup

– So individuals who must eat only plant proteins need to eat a variety to ensure that they get all the essential amino acids

Corn (maize)and other grains

Beansand other legumes

Essential amino acids for adults

Methionine

Valine

Threonine

Phenylalanine

Leucine

Isoleucine

Lysine

Tryptophan

Figure 41.10


• Some animals have adaptations

– That help them through periods when their bodies demand extraordinary amounts of protein

Figure 41.11


Essential Fatty Acids

• Animals can synthesize most of the fatty acids they need

• The essential fatty acids

– Are certain unsaturated fatty acids

• Deficiencies in fatty acids are rare


Vitamins

• Vitamins are organic molecules

– Required in the diet in small amounts

• To date, 13 vitamins essential to humans

– Have been identified


• Vitamins are grouped into two categories

– Fat-soluble and water-soluble

Table 41.1


Minerals

• Minerals are simple inorganic nutrients

– Usually required in small amounts


• Mineral requirements of humans

Table 41.2


• Concept 41.3: The main stages of food processing are ingestion, digestion, absorption, and elimination

• Ingestion, the act of eating

– Is the first stage of food processing


• Digestion, the second stage of food processing

– Is the process of breaking food down into molecules small enough to absorb

– Involves enzymatic hydrolysis of polymers into their monomers


• Absorption, the third stage of food processing

– Is the uptake of nutrients by body cells

• Elimination, the fourth stage of food processing

– Occurs as undigested material passes out of the digestive compartment


• The four stages of food processing

Figure 41.12

Piecesof food

Smallmolecules

Mechanicaldigestion

Food

Chemical digestion(enzymatic hydrolysis)

Nutrient moleculesenter body cells

Undigested material

INGESTION1 DIGESTION2 ELIMINATION4ABSORPTION3


Digestive Compartments

• Most animals process food

– In specialized compartments


Intracellular Digestion

• In intracellular digestion

– Food particles are engulfed by endocytosis and digested within food vacuoles


Extracellular Digestion

• Extracellular digestion

– Is the breakdown of food particles outside cells


• Animals with simple body plans

– Have a gastrovascular cavity that functions in both digestion and distribution of nutrients

Figure 41.13

Gastrovascularcavity

Food

Epidermis

Mesenchyme

Gastrodermis

Mouth

Tentacles

Mesenchyme

Food vacuoles

Gland cells

Flagella

Nutritivemuscularcells


• Animals with a more complex body plan

– Have a digestive tube with two openings, a mouth and an anus

• This digestive tube

– Is called a complete digestive tract or an alimentary canal


• The digestive tube can be organized into specialized regions

– That carry out digestion and nutrient absorption in a stepwise fashion

Esophagus

Mouth

Pharynx

Crop GizzardIntestine

Anus

Typhlosole

Lumen of intestine

Esophagus

Anus

Rectum

Mouth

CropGastric ceca

Anus

Intestine

Gizzard

Crop

Stomach

Mouth

Esophagus

Foregut Midgut Hindgut

(a) Earthworm. The digestive tract ofan earthworm includes a muscular pharynx that sucks food in through themouth. Food passes through the esophagus and is stored and moistened in the crop. The muscular gizzard, whichcontains small bits of sand and gravel, pulverizes the food. Digestion and absorption occur in the intestine, which has a dorsal fold, the typhlosole, that increases the surface area for nutrient absorption.

(b) Grasshopper. A grasshopper has several digestive chambers grouped into three main regions: a foregut, with an esophagus and crop; a midgut; and a hindgut. Food is moistened and stored in the crop, but most digestion occurs in the midgut. Gastric ceca, pouches extending from the midgut, absorb nutrients.

(c) Bird. Many birds have three separate chambers—the crop, stomach, and gizzard—where food is pulverized and churned before passing into the intestine. A bird’s crop and gizzard function very much like those of an earthworm. In most birds, chemical digestion and absorption of nutrients occur in the intestine.Figure 41.14a–c


• Concept 41.4: Each organ of the mammalian digestive system has specialized food-processing functions


• The mammalian digestive system consists of the alimentary canal

– And various accessory glands that secrete digestive juices through ducts


IIeumof small intestine Duodenum of

small intestine

Appendix

Cecum

Ascendingportion of large intestine

Anus

Small intestine

Large intestine

Rectum

Liver

Gall-bladder

Tongue

Oral cavity

Pharynx

Esophagus

Stomach

Pyloricsphincter

Cardiacorifice

Mouth

Esophagus

Salivaryglands

Stomach

Liver

Pancreas

Gall-bladder

Large intestines

Small intestines

Rectum

Anus

Parotid glandSublingual gland

Submandibular gland

Salivaryglands

A schematic diagram of the human digestive system

Pancreas

Figure 41.15


• Food is pushed along the digestive tract by peristalsis

– Rhythmic waves of contraction of smooth muscles in the wall of the canal


The Oral Cavity, Pharynx, and Esophagus

• In the oral cavity, food is lubricated and digestion begins

– And teeth chew food into smaller particles that are exposed to salivary amylase, initiating the breakdown of glucose polymers


• The region we call our throat is the pharynx

– A junction that opens to both the esophagus and the windpipe (trachea)

• The esophagus

– Conducts food from the pharynx down to the stomach by peristalsis


• From mouth to stomach

Esophagus

Epiglottis down

Tongue

Pharynx

GlottisLarynx

Trachea

Bolus of food

Epiglottisup

To lungs To stomach

Esophageal sphinctercontracted

Glottis upand closed

Esophageal sphincterrelaxed

Glottisdown and open

Esophageal sphinctercontracted

Epiglottisup

Relaxedmuscles

Contractedmuscles

Relaxedmuscles

Stomach

Figure 41.16

1 When a person is not swallowing, the esophageal sphincter muscle is contracted, the epiglottis is up, and the glottis is open, allowing air to flow through the trachea to the lungs.

The swallowingreflex is triggeredwhen a bolus offood reaches thepharynx.

2

The larynx, theupper part of therespiratory tract,moves upward andtips the epiglottisover the glottis,preventing foodfrom entering thetrachea.

3

The esophagealsphincter relaxes,allowing thebolus to enter theesophagus.

4

After the foodhas entered theesophagus, the

larynx movesdownward and

opens thebreathingpassage.

5

Waves of muscularcontraction (peristalsis)

move the bolus down the esophagus

to the stomach.

6


The Stomach

• The stomach stores food

– And secretes gastric juice, which converts a meal to acid chyme

• Gastric juice

– Is made up of hydrochloric acid and the enzyme pepsin


• The lining of the stomach

– Is coated with mucus, which prevents the gastric juice from destroying the cells

Figure 41.17

Pepsin (active enzyme)

HCl

Parietal cellChief cell

Stomach

Folds of epithelial tissue

Esophagus

Pyloric sphincter

Epithelium

Pepsinogen

3

2

1

Interior surface of stomach.The interior surface of the

stomach wall is highly folded and dotted with pits leading

into tubular gastric glands.

Gastric gland. The gastric glands have three types of cells

that secrete different components of the gastric juice: mucus cells,

chief cells, and parietal cells.

Mucus cells secrete mucus,which lubricates and protects

the cells lining the stomach.

Chief cells secrete pepsino-gen, an inactive form of the

digestive enzyme pepsin.

Parietal cells secretehydrochloric acid (HCl).

1 Pepsinogen and HCIare secreted into thelumen of the stomach.

2 HCl convertspepsinogen to pepsin.

3 Pepsin then activatesmore pepsinogen,starting a chainreaction. Pepsinbegins the chemicaldigestion of proteins.

5 µ

m

Small intestine

Cardiac orifice


• Gastric ulcers, lesions in the lining

– Are caused mainly by the bacterium Helicobacter pylori

Figure 41.18

1 µ

m

Bacteria

Mucuslayer of stomach


The Small Intestine

• The small intestine

– Is the longest section of the alimentary canal

– Is the major organ of digestion and absorption


Enzymatic Action in the Small Intestine

• The first portion of the small intestine is the duodenum

– Where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and intestine itself

Figure 41.19

Liver Bile

Acid chyme

Stomach

Pancreatic juice

Pancreas

Intestinaljuice

Duodenum of small intestine

Gall-bladder


• The pancreas produces proteases, protein-digesting enzymes

– That are activated once they enter the duodenum

PancreasMembrane-boundenteropeptidase

Trypsin

Active proteases

Lumen of duodenum

Inactivetrypsinogen

Other inactiveproteases

Figure 41.20


• Enzymatic digestion is completed

– As peristalsis moves the mixture of chyme and digestive juices along the small intestine

Figure 41.21

Oral cavity,pharynx,esophagus

Carbohydrate digestion

Polysaccharides(starch, glycogen)

Disaccharides(sucrose, lactose)

Salivary amylase

Smaller polysaccharides,maltose

Stomach

Protein digestion Nucleic acid digestion Fat digestion

Proteins

Pepsin

Small polypeptides

Lumen of small intes-tine

Polysaccharides

Pancreatic amylases

Maltose and otherdisaccharides

Epitheliumof smallintestine(brushborder)

Disaccharidases

Monosaccharides

Polypeptides

Pancreatic trypsin andchymotrypsin (These proteasescleave bonds adjacent to certainamino acids.)

Smallerpolypeptides

Pancreatic carboxypeptidase

Amino acids

Small peptides

Dipeptidases, carboxypeptidase, and aminopeptidase (These proteases split off one amino acid at a time, working from opposite ends of a polypeptide.)

Amino acids

DNA, RNA

Pancreaticnucleases

Nucleotides

Nucleotidases

Nucleosides

Nucleosidasesandphosphatases

Nitrogenous bases,sugars, phosphates

Fat globules (Insoluble inwater, fats aggregate asglobules.)

Bile salts

Fat droplets (A coating ofbile salts prevents small drop-lets from coalescing intolarger globules, increasingexposure to lipase.)

Pancreatic lipase

Glycerol, fattyacids, glycerides


• Hormones help coordinate the secretion of digestive juices into the alimentary canal

Figure 41.22

Amino acids or fatty acids in the duodenum trigger the release of cholecystokinin (CCK), which

stimulates the release of digestive enzymes from the pancreas and bile

from the gallbladder.

Liver

Gall-bladder

CCK

Entero-gastrone

Gastrin

Stomach

Pancreas

Secretin

CCK

Duodenum

Key

Stimulation

Inhibition

Enterogastrone secreted by the duodenum inhibits peristalsis and acid secretion by the stomach, thereby slowing digestion when acid chyme rich in fats enters the duodenum.

Secreted by the duodenum, secretin stimulates the pancreas to release sodium bicarbonate, which neutralizes acid chyme from the stomach.

Gastrin from the stomach recirculates via the bloodstream back to the stomach, where it stimulates the production of gastric juices.


Absorption of Nutrients

• The small intestine has a huge surface area

– Due to the presence of villi and microvilli that are exposed to the intestinal lumen


• The enormous microvillar surface

– Is an adaptation that greatly increases the rate of nutrient absorption

Epithelialcells

Key

Nutrientabsorption

Vein carrying blood to hepatic portal vessel

Villi

Largecircularfolds

Intestinal wallVilli

Epithelial cells

Lymph vessel

Bloodcapillaries

Lacteal

Microvilli(brush border)

Muscle layers

Figure 41.23


• The core of each villus

– Contains a network of blood vessels and a small vessel of the lymphatic system called a lacteal


• Amino acids and sugars

– Pass through the epithelium of the small intestine and enter the bloodstream

• After glycerol and fatty acids are absorbed by epithelial cells

– They are recombined into fats within these cells


• These fats are then mixed with cholesterol and coated with proteins

– Forming small molecules called chylomicrons, which are transported into lacteals

Figure 41.24

Large fat globules are emulsified by bile salts in the duodenum.

1

Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles.

2

Fatty acids and mono-glycerides leave micelles and enter epithelial cells by diffusion.

3

Fat globule

Lacteal

Epithelialcells ofsmallintestine

Micelles madeup of fatty acids,monoglycerides,and bile salts

Fat dropletscoated withbile salts

Bile salts

Chylomicrons containing fattysubstances are transported out of the epithelial cells and into lacteals, where they are carried away from the intestine by lymph.

4


The Large Intestine

• The large intestine, or colon

– Is connected to the small intestine

Figure 41.25


• A major function of the colon

– Is to recover water that has entered the alimentary canal

• The wastes of the digestive tract, the feces

– Become more solid as they move through the colon

– Pass through the rectum and exit via the anus


• The colon houses various strains of the bacterium Escherichia coli

– Some of which produce various vitamins


• Concept 41.5: Evolutionary adaptations of vertebrate digestive systems are often associated with diet


Some Dental Adaptations

• Dentition, an animal’s assortment of teeth

– Is one example of structural variation reflecting diet


• Mammals have specialized dentition

– That best enables them to ingest their usual diet

Figure 41.26a–c

(a) Carnivore

(b) Herbivore

(c) Omnivore

Incisors

Canines

Premolars

Molars


Stomach and Intestinal Adaptations

• Herbivores generally have longer alimentary canals than carnivores

– Reflecting the longer time needed to digest vegetation

Figure 41.27 Carnivore Herbivore

Colon(largeintestine)

Cecum

StomachSmall intestine

Small intestine


Symbiotic Adaptations

• Many herbivorous animals have fermentation chambers

– Where symbiotic microorganisms digest cellulose


• The most elaborate adaptations for an herbivorous diet

– Have evolved in the animals called ruminants

Figure 41.28

Reticulum. Some boluses also enter the reticulum. In both the rumen and the reticulum, symbiotic prokaryotes and protists (mainly ciliates) go to work on the cellulose-rich meal. As by-products of theirmetabolism, the microorganisms secrete fatty acids. The cow periodically regurgitates and rechews the cud (red arrows), which further breaks down thefibers, making them more accessible to further microbial action.

Rumen. When the cow first chews andswallows a mouthful of grass, boluses(green arrows) enter the rumen.

1

Intestine

2

Omasum. The cow then reswallowsthe cud (blue arrows), which moves tothe omasum, where water is removed.

3 Abomasum. The cud, containing great numbers of microorganisms, finally passes to the abomasum for digestion by the cow‘s own enzymes (black arrows).

4

Esophagus






Circulation and Gas Exchange


• Overview: Trading with the Environment

• Every organism must exchange materials with its environment

– And this exchange ultimately occurs at the cellular level


• In unicellular organisms

– These exchanges occur directly with the environment

• For most of the cells making up multicellular organisms

– Direct exchange with the environment is not possible


• The feathery gills projecting from a salmon

– Are an example of a specialized exchange system found in animals

Figure 42.1


• Concept 42.1: Circulatory systems reflect phylogeny

• Transport systems

– Functionally connect the organs of exchange with the body cells


• Most complex animals have internal transport systems

– That circulate fluid, providing a lifeline between the aqueous environment of living cells and the exchange organs, such as lungs, that exchange chemicals with the outside environment


Invertebrate Circulation

• The wide range of invertebrate body size and form

– Is paralleled by a great diversity in circulatory systems


Gastrovascular Cavities

• Simple animals, such as cnidarians

– Have a body wall only two cells thick that encloses a gastrovascular cavity

• The gastrovascular cavity

– Functions in both digestion and distribution of substances throughout the body


• Some cnidarians, such as jellies

– Have elaborate gastrovascular cavities

Figure 42.2

Circularcanal

Radial canal

5 cmMouth


Open and Closed Circulatory Systems

• More complex animals

– Have one of two types of circulatory systems: open or closed

• Both of these types of systems have three basic components

– A circulatory fluid (blood)

– A set of tubes (blood vessels)

– A muscular pump (the heart)


• In insects, other arthropods, and most molluscs

– Blood bathes the organs directly in an open circulatory system

Heart

Hemolymph in sinusessurrounding ograns

Anterior vessel

Tubular heart

Lateral vessels

Ostia

(a) An open circulatory systemFigure 42.3a


• In a closed circulatory system

– Blood is confined to vessels and is distinct from the interstitial fluid

Figure 42.3b

Interstitialfluid

Heart

Small branch vessels in each organ

Dorsal vessel(main heart)

Ventral vesselsAuxiliary hearts

(b) A closed circulatory system


• Closed systems

– Are more efficient at transporting circulatory fluids to tissues and cells


Survey of Vertebrate Circulation

• Humans and other vertebrates have a closed circulatory system

– Often called the cardiovascular system

• Blood flows in a closed cardiovascular system

– Consisting of blood vessels and a two- to four-chambered heart


• Arteries carry blood to capillaries

– The sites of chemical exchange between the blood and interstitial fluid

• Veins

– Return blood from capillaries to the heart


Fishes

• A fish heart has two main chambers

– One ventricle and one atrium

• Blood pumped from the ventricle

– Travels to the gills, where it picks up O2 and disposes of CO2


Amphibians

• Frogs and other amphibians

– Have a three-chambered heart, with two atria and one ventricle

• The ventricle pumps blood into a forked artery

– That splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit


Reptiles (Except Birds)

• Reptiles have double circulation

– With a pulmonary circuit (lungs) and a systemic circuit

• Turtles, snakes, and lizards

– Have a three-chambered heart


Mammals and Birds

• In all mammals and birds

– The ventricle is completely divided into separate right and left chambers

• The left side of the heart pumps and receives only oxygen-rich blood

– While the right side receives and pumps only oxygen-poor blood


• A powerful four-chambered heart

– Was an essential adaptation of the endothermic way of life characteristic of mammals and birds


FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS

Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries

Lung capillaries Lung capillariesLung and skin capillariesGill capillaries

Right Left Right Left Right Left Systemic

circuitSystemic

circuit

Pulmocutaneouscircuit

Pulmonarycircuit

Pulmonarycircuit

SystemiccirculationVein

Atrium (A)

Heart:ventricle (V)

Artery Gillcirculation

A

V VV VV

A A A AALeft Systemicaorta

Right systemicaorta

Figure 42.4

• Vertebrate circulatory systems


• Concept 42.2: Double circulation in mammals depends on the anatomy and pumping cycle of the heart

• The structure and function of the human circulatory system

– Can serve as a model for exploring mammalian circulation in general


Mammalian Circulation: The Pathway

• Heart valves

– Dictate a one-way flow of blood through the heart


• Blood begins its flow

– With the right ventricle pumping blood to the lungs

• In the lungs

– The blood loads O2 and unloads CO2


• Oxygen-rich blood from the lungs

– Enters the heart at the left atrium and is pumped to the body tissues by the left ventricle

• Blood returns to the heart

– Through the right atrium


• The mammalian cardiovascular system

Pulmonary vein

Right atrium

Right ventricle

Posteriorvena cava Capillaries of

abdominal organsand hind limbs

Aorta

Left ventricle

Left atriumPulmonary vein

Pulmonaryartery

Capillariesof left lung

Capillaries ofhead and forelimbs

Anteriorvena cava

Pulmonaryartery

Capillariesof right lung

Aorta

Figure 42.5

1

10

11

5

4

6

2

9

33

7

8


The Mammalian Heart: A Closer Look

• A closer look at the mammalian heart

– Provides a better understanding of how double circulation works

Figure 42.6

Aorta

Pulmonaryveins

Semilunarvalve

Atrioventricularvalve

Left ventricleRight ventricle

Anterior vena cava

Pulmonary artery

Semilunarvalve

Atrioventricularvalve

Posterior vena cava

Pulmonaryveins

Right atrium

Pulmonaryartery

Leftatrium


• The heart contracts and relaxes

– In a rhythmic cycle called the cardiac cycle

• The contraction, or pumping, phase of the cycle

– Is called systole

• The relaxation, or filling, phase of the cycle

– Is called diastole


• The cardiac cycle

Figure 42.7

Semilunarvalvesclosed

AV valvesopen

AV valvesclosed

Semilunarvalvesopen

Atrial and ventricular diastole

1

Atrial systole; ventricular diastole

2

Ventricular systole; atrial diastole

3

0.1 sec

0.3 sec0.4 sec


• The heart rate, also called the pulse

– Is the number of beats per minute

• The cardiac output

– Is the volume of blood pumped into the systemic circulation per minute


Maintaining the Heart’s Rhythmic Beat

• Some cardiac muscle cells are self-excitable

– Meaning they contract without any signal from the nervous system


• A region of the heart called the sinoatrial (SA) node, or pacemaker

– Sets the rate and timing at which all cardiac muscle cells contract

• Impulses from the SA node

– Travel to the atrioventricular (AV) node

• At the AV node, the impulses are delayed

– And then travel to the Purkinje fibers that make the ventricles contract


• The impulses that travel during the cardiac cycle

– Can be recorded as an electrocardiogram (ECG or EKG)


• The control of heart rhythm

Figure 42.8

SA node(pacemaker)

AV node Bundlebranches

Heartapex

Purkinjefibers

2 Signals are delayedat AV node.

1 Pacemaker generates wave of signals to contract.

3 Signals passto heart apex.

4 Signals spreadThroughoutventricles.

ECG


• The pacemaker is influenced by

– Nerves, hormones, body temperature, and exercise


• Concept 42.3: Physical principles govern blood circulation

• The same physical principles that govern the movement of water in plumbing systems

– Also influence the functioning of animal circulatory systems


Blood Vessel Structure and Function

• The “infrastructure” of the circulatory system

– Is its network of blood vessels


• All blood vessels

– Are built of similar tissues

– Have three similar layers

Figure 42.9

Artery Vein

100 µm

Artery Vein

ArterioleVenule

Connectivetissue

Smoothmuscle

Endothelium

Connectivetissue

Smoothmuscle

EndotheliumValve

Endothelium

Basementmembrane

Capillary


• Structural differences in arteries, veins, and capillaries

– Correlate with their different functions

• Arteries have thicker walls

– To accommodate the high pressure of blood pumped from the heart


• In the thinner-walled veins

– Blood flows back to the heart mainly as a result of muscle action

Figure 42.10

Direction of blood flowin vein (toward heart)

Valve (open)

Skeletal muscle

Valve (closed)


Blood Flow Velocity

• Physical laws governing the movement of fluids through pipes

– Influence blood flow and blood pressure


• The velocity of blood flow varies in the circulatory system

– And is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area

Figure 42.11

5,0004,0003,0002,0001,000

0

Aor

ta

Art

erie

s

Art

erio

les

Cap

illar

ies

Ven

ules

Vei

ns

Ven

ae c

avae

Pre

ssur

e (m

m H

g)V

eloc

ity (

cm/s

ec)

Are

a (c

m2)

Systolicpressure

Diastolicpressure

50403020100

120100806040200


Blood Pressure

• Blood pressure

– Is the hydrostatic pressure that blood exerts against the wall of a vessel


• Systolic pressure

– Is the pressure in the arteries during ventricular systole

– Is the highest pressure in the arteries

• Diastolic pressure

– Is the pressure in the arteries during diastole

– Is lower than systolic pressure


• Blood pressure

– Can be easily measured in humans

Figure 42.12

Artery

Rubber cuffinflatedwith air

Arteryclosed

120 120

Pressurein cuff above 120

Pressurein cuff below 120

Pressurein cuff below 70

Sounds audible instethoscope

Sounds stop

Blood pressurereading: 120/70

A typical blood pressure reading for a 20-year-oldis 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high.

1

A sphygmomanometer, an inflatable cuff attached to apressure gauge, measures blood pressure in an artery.The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery.

2 A stethoscope is used to listen for sounds of blood flow below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure.

3

The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed.

4

70


• Blood pressure is determined partly by cardiac output

– And partly by peripheral resistance due to variable constriction of the arterioles


Capillary Function

• Capillaries in major organs are usually filled to capacity

– But in many other sites, the blood supply varies


• Two mechanisms

– Regulate the distribution of blood in capillary beds

• In one mechanism

– Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel


• In a second mechanism

– Precapillary sphincters control the flow of blood between arterioles and venules

Figure 42.13 a–c

Precapillary sphincters Thoroughfarechannel

ArterioleCapillaries

Venule(a) Sphincters relaxed

(b) Sphincters contractedVenuleArteriole

(c) Capillaries and larger vessels (SEM)

20 m


• The critical exchange of substances between the blood and interstitial fluid

– Takes place across the thin endothelial walls of the capillaries


• The difference between blood pressure and osmotic pressure

– Drives fluids out of capillaries at the arteriole end and into capillaries at the venule end

At the arterial end of acapillary, blood pressure is

greater than osmotic pressure,and fluid flows out of the

capillary into the interstitial fluid.

Capillary Redbloodcell

15 m

Tissue cell INTERSTITIAL FLUID

CapillaryNet fluidmovement out

Net fluidmovement in

Direction of blood flow

Blood pressureOsmotic pressure

Inward flow

Outward flow

Pre

ssur

e

Arterial end of capillary Venule end

At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary.

Figure 42.14


Fluid Return by the Lymphatic System

• The lymphatic system

– Returns fluid to the body from the capillary beds

– Aids in body defense


• Fluid reenters the circulation

– Directly at the venous end of the capillary bed and indirectly through the lymphatic system


• Concept 42.4: Blood is a connective tissue with cells suspended in plasma

• Blood in the circulatory systems of vertebrates

– Is a specialized connective tissue


Blood Composition and Function

• Blood consists of several kinds of cells

– Suspended in a liquid matrix called plasma

• The cellular elements

– Occupy about 45% of the volume of blood


Plasma

• Blood plasma is about 90% water

• Among its many solutes are

– Inorganic salts in the form of dissolved ions, sometimes referred to as electrolytes


• The composition of mammalian plasmaPlasma 55%

Constituent Major functions

Water Solvent forcarrying othersubstances

SodiumPotassiumCalciumMagnesiumChlorideBicarbonate

Osmotic balancepH buffering, andregulation of membranepermeability

Albumin

Fibringen

Immunoglobulins(antibodies)

Plasma proteins

Icons (blood electrolytes

Osmotic balance,pH buffering

Substances transported by bloodNutrients (such as glucose, fatty acids, vitamins)Waste products of metabolismRespiratory gases (O2 and CO2)Hormones

Defense

Figure 42.15

Separatedbloodelements

Clotting


• Another important class of solutes is the plasma proteins

– Which influence blood pH, osmotic pressure, and viscosity

• Various types of plasma proteins

– Function in lipid transport, immunity, and blood clotting


Cellular Elements

• Suspended in blood plasma are two classes of cells

– Red blood cells, which transport oxygen

– White blood cells, which function in defense

• A third cellular element, platelets

– Are fragments of cells that are involved in clotting


Figure 42.15

Cellular elements 45%

Cell type Numberper L (mm3) of blood

Functions

Erythrocytes(red blood cells) 5–6 million Transport oxygen

and help transportcarbon dioxide

Leukocytes(white blood cells)

5,000–10,000 Defense andimmunity

Eosinophil

Basophil

Platelets

NeutrophilMonocyte

Lymphocyte

250,000400,000

Blood clotting

• The cellular elements of mammalian blood

Separatedbloodelements


Erythrocytes

• Red blood cells, or erythrocytes

– Are by far the most numerous blood cells

– Transport oxygen throughout the body


Leukocytes

• The blood contains five major types of white blood cells, or leukocytes

– Monocytes, neutrophils, basophils, eosinophils, and lymphocytes, which function in defense by phagocytizing bacteria and debris or by producing antibodies


Platelets

• Platelets function in blood clotting


Stem Cells and the Replacement of Cellular Elements

• The cellular elements of blood wear out

– And are replaced constantly throughout a person’s life


• Erythrocytes, leukocytes, and platelets all develop from a common source

– A single population of cells called pluripotent stem cells in the red marrow of bones

B cells T cells

Lymphoidstem cells

Pluripotent stem cells(in bone marrow)

Myeloidstem cells

Erythrocytes

Platelets Monocytes

Neutrophils

Eosinophils

Basophils

Lymphocytes

Figure 42.16


Blood Clotting

• When the endothelium of a blood vessel is damaged

– The clotting mechanism begins


• A cascade of complex reactions

– Converts fibrinogen to fibrin, forming a clot

Plateletplug

Collagen fibers

Platelet releases chemicalsthat make nearby platelets sticky

Clotting factors from:PlateletsDamaged cellsPlasma (factors include calcium, vitamin K)

Prothrombin Thrombin

Fibrinogen Fibrin5 µm

Fibrin clotRed blood cell

The clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Plateletsadhere to collagen fibers in the connective tissue and release a substance thatmakes nearby platelets sticky.

1 The platelets form a plug that providesemergency protectionagainst blood loss.

2 This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via amultistep process: Clotting factors released fromthe clumped platelets or damaged cells mix withclotting factors in the plasma, forming an activation cascade that converts a plasma proteincalled prothrombin to its active form, thrombin.Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM).

3

Figure 42.17


Cardiovascular Disease

• Cardiovascular diseases

– Are disorders of the heart and the blood vessels

– Account for more than half the deaths in the United States


• One type of cardiovascular disease, atherosclerosis

– Is caused by the buildup of cholesterol within arteries

Figure 42.18a, b

(a) Normal artery (b) Partly clogged artery50 µm 250 µm

Smooth muscleConnective tissue Endothelium Plaque


• Hypertension, or high blood pressure

– Promotes atherosclerosis and increases the risk of heart attack and stroke

• A heart attack

– Is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries

• A stroke

– Is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head


• Concept 42.5: Gas exchange occurs across specialized respiratory surfaces

• Gas exchange

– Supplies oxygen for cellular respiration and disposes of carbon dioxide

Figure 42.19

Organismal level

Cellular level

Circulatory system

Cellular respiration ATPEnergy-richmoleculesfrom food

Respiratorysurface

Respiratorymedium(air of water)

O2 CO2


• Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases

– Between their cells and the respiratory medium, either air or water


Gills in Aquatic Animals

• Gills are outfoldings of the body surface

– Specialized for gas exchange


• In some invertebrates

– The gills have a simple shape and are distributed over much of the body

(a) Sea star. The gills of a sea star are simple tubular projections of the skin. The hollow core of each gillis an extension of the coelom(body cavity). Gas exchangeoccurs by diffusion across thegill surfaces, and fluid in thecoelom circulates in and out ofthe gills, aiding gas transport. The surfaces of a sea star’s tube feet also function in gas exchange.

Gills

Tube foot

Coelom

Figure 42.20a


• Many segmented worms have flaplike gills

– That extend from each segment of their body

Figure 42.20b

(b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gillsand also function incrawling and swimming.

Gill

Parapodia


• The gills of clams, crayfish, and many other animals

– Are restricted to a local body region

Figure 42.20c, d

(d) Crayfish. Crayfish and other crustaceanshave long, feathery gills covered by the exoskeleton. Specialized body appendagesdrive water over the gill surfaces.

(c) Scallop. The gills of a scallop are long, flattened plates that project from themain body mass inside the hard shell.Cilia on the gills circulate water around the gill surfaces.

Gills

Gills


• The effectiveness of gas exchange in some gills, including those of fishes

– Is increased by ventilation and countercurrent flow of blood and water

Countercurrent exchange

Figure 42.21

Gill arch

Water flow Operculum

Gill arch

Blood vessel

Gillfilaments

Oxygen-poorblood

Oxygen-richblood

Water flowover lamellaeshowing % O2

Blood flowthrough capillariesin lamellaeshowing % O2

Lamella

100%

40%

70%

15%

90%

60%

30% 5%

O2


Figure 42.22a

Tracheae

Air sacs

Spiracle

(a) The respiratory system of an insect consists of branched internaltubes that deliver air directly to body cells. Rings of chitin reinforcethe largest tubes, called tracheae, keeping them from collapsing. Enlarged portions of tracheae form air sacs near organs that require a large supply of oxygen. Air enters the tracheae through openings called spiracles on the insect’s body surface and passes into smaller tubes called tracheoles. The tracheoles are closed and contain fluid(blue-gray). When the animal is active and is using more O2, most ofthe fluid is withdrawn into the body. This increases the surface area of air in contact with cells.

Tracheal Systems in Insects

• The tracheal system of insects

– Consists of tiny branching tubes that penetrate the body


• The tracheal tubes

– Supply O2 directly to body cells

Airsac

Body cell

Trachea

Tracheole

TracheolesMitochondria

Myofibrils

Body wall

(b) This micrograph shows crosssections of tracheoles in a tinypiece of insect flight muscle (TEM).Each of the numerous mitochondriain the muscle cells lies within about5 µm of a tracheole.

Figure 42.22b 2.5 µm

Air


Lungs

• Spiders, land snails, and most terrestrial vertebrates

– Have internal lungs


Mammalian Respiratory Systems: A Closer Look

• A system of branching ducts

– Conveys air to the lungsBranch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole

Branch from thepulmonaryartery(oxygen-poor blood)

Alveoli

Colorized SEMSEM

50 µ

m

50 µ

m

Heart

Left lung

Nasalcavity

Pharynx

Larynx

Diaphragm

Bronchiole

Bronchus

Right lung

Trachea

Esophagus

Figure 42.23


• In mammals, air inhaled through the nostrils

– Passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs


• Concept 42.6: Breathing ventilates the lungs

• The process that ventilates the lungs is breathing

– The alternate inhalation and exhalation of air


How an Amphibian Breathes

• An amphibian such as a frog

– Ventilates its lungs by positive pressure breathing, which forces air down the trachea


How a Mammal Breathes

• Mammals ventilate their lungs

– By negative pressure breathing, which pulls air into the lungs

Air inhaled Air exhaled

INHALATIONDiaphragm contracts

(moves down)

EXHALATIONDiaphragm relaxes

(moves up)

Diaphragm

Lung

Rib cage expands asrib muscles contract

Rib cage gets smaller asrib muscles relax

Figure 42.24


• Lung volume increases

– As the rib muscles and diaphragm contract


How a Bird Breathes

• Besides lungs, bird have eight or nine air sacs

– That function as bellows that keep air flowing through the lungs

INHALATIONAir sacs fill

EXHALATIONAir sacs empty; lungs fill

Anteriorair sacs

Trachea

Lungs LungsPosteriorair sacs

Air Air

1 mm

Air tubes(parabronchi)in lung

Figure 42.25


• Air passes through the lungs

– In one direction only

• Every exhalation

– Completely renews the air in the lungs


Control of Breathing in Humans

• The main breathing control centers

– Are located in two regions of the brain, the medulla oblongata and the pons

Figure 42.26

PonsBreathing control centers Medulla

oblongata

Diaphragm

Carotidarteries

Aorta

Cerebrospinalfluid

Rib muscles

In a person at rest, these nerve impulses result in

about 10 to 14 inhalationsper minute. Between

inhalations, the musclesrelax and the person exhales.

The medulla’s control center also helps regulate blood CO2 level. Sensors in the medulla detect changes in the pH (reflecting CO2

concentration) of the blood and cerebrospinal fluid bathing the surface of the brain.

Nerve impulses relay changes in

CO2 and O2 concentrations. Other sensors in the walls of the aortaand carotid arteries in the neck detect changes in blood pH andsend nerve impulses to the medulla. In response, the medulla’s breathingcontrol center alters the rate anddepth of breathing, increasing bothto dispose of excess CO2 or decreasingboth if CO2 levels are depressed.

The control center in themedulla sets the basic

rhythm, and a control centerin the pons moderates it,

smoothing out thetransitions between

inhalations and exhalations.

1

Nerve impulses trigger muscle contraction. Nerves

from a breathing control centerin the medulla oblongata of the

brain send impulses to thediaphragm and rib muscles, stimulating them to contract

and causing inhalation.

2

The sensors in the aorta andcarotid arteries also detect changesin O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low.

6

5

3

4


• The centers in the medulla

– Regulate the rate and depth of breathing in response to pH changes in the cerebrospinal fluid

• The medulla adjusts breathing rate and depth

– To match metabolic demands


• Sensors in the aorta and carotid arteries

– Monitor O2 and CO2 concentrations in the blood

– Exert secondary control over breathing


• Concept 42.7: Respiratory pigments bind and transport gases

• The metabolic demands of many organisms

– Require that the blood transport large quantities of O2 and CO2


The Role of Partial Pressure Gradients

• Gases diffuse down pressure gradients

– In the lungs and other organs

• Diffusion of a gas

– Depends on differences in a quantity called partial pressure


• A gas always diffuses from a region of higher partial pressure

– To a region of lower partial pressure


• In the lungs and in the tissues

– O2 and CO2 diffuse from where their partial pressures are higher to where they are lower


Inhaled air Exhaled air

160 0.2O2 CO2

O2 CO2

O2 CO2

O2 CO2 O2 CO2

O2 CO2 O2 CO2

O2 CO2

40 45

40 45

100 40

104 40

104 40

120 27

CO2O2

Alveolarepithelialcells

Pulmonaryarteries

Blood enteringalveolar

capillaries

Blood leavingtissue

capillaries

Blood enteringtissue

capillaries

Blood leaving

alveolar capillaries

CO2O2

Tissue capillaries

Heart

Alveolar capillaries

of lung

<40 >45

Tissue cells

Pulmonaryveins

Systemic arteriesSystemic

veinsO2

CO2

O2

CO 2

Alveolar spaces

12

43

Figure 42.27


Respiratory Pigments

• Respiratory pigments

– Are proteins that transport oxygen

– Greatly increase the amount of oxygen that blood can carry


Oxygen Transport

• The respiratory pigment of almost all vertebrates

– Is the protein hemoglobin, contained in the erythrocytes


• Like all respiratory pigments

– Hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body

Heme group Iron atom

O2 loadedin lungs

O2 unloadedIn tissues

Polypeptide chain

O2

O2

Figure 42.28


• Loading and unloading of O2

– Depend on cooperation between the subunits of the hemoglobin molecule

• The binding of O2 to one subunit induces the other subunits to bind O2 with more affinity


• Cooperative O2 binding and release

– Is evident in the dissociation curve for hemoglobin

• A drop in pH

– Lowers the affinity of hemoglobin for O2


O2 unloaded fromhemoglobinduring normalmetabolism

O2 reserve that canbe unloaded fromhemoglobin totissues with highmetabolism

Tissues duringexercise

Tissuesat rest

100

80

60

40

20

0

100

80

60

40

20

0

100806040200

100806040200

Lungs

PO2 (mm Hg)

PO2 (mm Hg)

O2 s

atur

atio

n of

hem

oglo

bin

(%)

O2 s

atur

atio

n of

hem

oglo

bin

(%)

Bohr shift:Additional O2

released from hemoglobin at lower pH(higher CO2

concentration)

pH 7.4

pH 7.2

(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4

(b) pH and Hemoglobin Dissociation

Figure 42.29a, b


Carbon Dioxide Transport

• Hemoglobin also helps transport CO2

– And assists in buffering


• Carbon from respiring cells

– Diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs


Figure 42.30

Tissue cell

CO2Interstitialfluid

CO2 producedCO2 transportfrom tissues

CO2

CO2

Blood plasmawithin capillary Capillary

wall

H2O

Redbloodcell

HbCarbonic acidH2CO3

HCO3–

H++Bicarbonate

HCO3–

Hemoglobinpicks up

CO2 and H+

HCO3–

HCO3– H++

H2CO3Hb

Hemoglobinreleases

CO2 and H+

CO2 transportto lungs

H2O

CO2

CO2

CO2

CO2

Alveolar space in lung

2

1

34

5 6

7

8

9

10

11

To lungs

Carbon dioxide produced bybody tissues diffuses into the interstitial fluid and the plasma.

Over 90% of the CO2 diffuses into red blood cells, leaving only 7%in the plasma as dissolved CO2.

Some CO2 is picked up and transported by hemoglobin.

However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed bycarbonic anhydrase contained. Withinred blood cells.

Carbonic acid dissociates into a biocarbonate ion (HCO3

–) and a hydrogen ion (H+).

Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thuspreventing the Bohr shift.

CO2 diffuses into the alveolarspace, from which it is expelledduring exhalation. The reductionof CO2 concentration in the plasmadrives the breakdown of H2CO3 Into CO2 and water in the red bloodcells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4).

Most of the HCO3– diffuse

into the plasma where it is carried in the bloodstream to the lungs.

In the HCO3– diffuse

from the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3.

Carbonic acid is converted back into CO2 and water.

CO2 formed from H2CO3 is unloadedfrom hemoglobin and diffuses into the interstitial fluid.

1

2

3

4

5

6

7

8

9

10

11


Elite Animal Athletes

• Migratory and diving mammals

– Have evolutionary adaptations that allow them to perform extraordinary feats


The Ultimate Endurance Runner

• The extreme O2 consumption of the antelope-like pronghorn

– Underlies its ability to run at high speed over long distances

Figure 42.31


Diving Mammals

• Deep-diving air breathers

– Stockpile O2 and deplete it slowly






The Immune System


• Overview: Reconnaissance, Recognition, and Response

• An animal must defend itself

– From the many dangerous pathogens it may encounter in the environment

• Two major kinds of defense have evolved that counter these threats

– Innate immunity and acquired immunity


• Innate immunity

– Is present before any exposure to pathogens and is effective from the time of birth

– Involves nonspecific responses to pathogens

Figure 43.1 3m


• Acquired immunity, also called adaptive immunity

– Develops only after exposure to inducing agents such as microbes, toxins, or other foreign substances

– Involves a very specific response to pathogens


• A summary of innate and acquired immunity

INNATE IMMUNITY Rapid responses to a

broad range of microbes

ACQUIRED IMMUNITYSlower responses to

specific microbes

External defenses Internal defenses

Skin

Mucous membranes

Secretions

Phagocytic cells

Antimicrobial proteins

Inflammatory response

Natural killer cells

Humoral response(antibodies)

Cell-mediated response(cytotoxic lymphocytes)

Invadingmicrobes

(pathogens)

Figure 43.2


• Concept 43.1: Innate immunity provides broad defenses against infection

• A pathogen that successfully breaks through an animal’s external defenses

– Soon encounters several innate cellular and chemical mechanisms that impede its attack on the body


External Defenses

• Intact skin and mucous membranes

– Form physical barriers that bar the entry of microorganisms and viruses

• Certain cells of the mucous membranes produce mucus

– A viscous fluid that traps microbes and other particles


• In the trachea, ciliated epithelial cells

– Sweep mucus and any entrapped microbes upward, preventing the microbes from entering the lungs

Figure 43.3

10m


• Secretions of the skin and mucous membranes

– Provide an environment that is often hostile to microbes

• Secretions from the skin

– Give the skin a pH between 3 and 5, which is acidic enough to prevent colonization of many microbes

– Also include proteins such as lysozyme, an enzyme that digests the cell walls of many bacteria


Internal Cellular and Chemical Defenses

• Internal cellular defenses

– Depend mainly on phagocytosis

• Phagocytes, types of white blood cells

– Ingest invading microorganisms

– Initiate the inflammatory response


Phagocytic Cells

• Phagocytes attach to their prey via surface receptors

– And engulf them, forming a vacuole that fuses with a lysosome

Figure 43.4

Pseudopodiasurroundmicrobes.

1

Microbesare engulfedinto cell.

2

Vacuolecontainingmicrobesforms.

3

Vacuoleand lysosomefuse.

4

Toxiccompoundsand lysosomalenzymesdestroy microbes.

5

Microbialdebris isreleased byexocytosis.

6

Microbes

MACROPHAGE

Vacuole Lysosomecontainingenzymes


• Macrophages, a specific type of phagocyte

– Can be found migrating through the body

– Can be found in various organs of the lymphatic system


Adenoid

Tonsil

Lymphnodes

Spleen

Peyer’s patches(small intestine)

Appendix

Lymphaticvessels

Masses oflymphocytes andmacrophages

Tissuecells

Lymphaticvessel

Bloodcapillary

LymphaticcapillaryInterstitial

fluid

Lymphnode

• The lymphatic system

– Plays an active role in defending the body from pathogens Interstitial fluid bathing the

tissues, along with the white blood cells in it, continually enters lymphatic capillaries.

1

Figure 43.5

Fluid inside thelymphatic capillaries,called lymph, flowsthrough lymphaticvessels throughoutthe body.

2

Within lymph nodes,microbes and foreignparticles present in the circulating lymphencounter macro-phages, dendritic cells, and lymphocytes, which carry out various defensive actions.

3

Lymphatic vesselsreturn lymph to theblood via two large

ducts that drain intoveins near the

shoulders.

4


Antimicrobial Proteins

• Numerous proteins function in innate defense

– By attacking microbes directly of by impeding their reproduction


• About 30 proteins make up the complement system

– Which can cause lysis of invading cells and help trigger inflammation

• Interferons

– Provide innate defense against viruses and help activate macrophages


Inflammatory Response

• In local inflammation, histamine and other chemicals released from injured cells

– Promote changes in blood vessels that allow more fluid, more phagocytes, and antimicrobial proteins to enter the tissues


• Major events in the local inflammatory response

Figure 43.6

Pathogen Pin

Macrophage

Chemical signals

CapillaryPhagocytic cells

Red blood cell

Bloodclottingelements

Blood clot

Phagocytosis

Fluid, antimicrobial proteins, and clotting elements move from the blood to the site.Clotting begins.

2Chemical signals released by activated macrophages and mast cells at the injury site cause nearby capillaries to widen and become more permeable.

1 Chemokines released by various kinds of cells attract more phagocytic cells from the bloodto the injury site.

3 Neutrophils and macrophagesphagocytose pathogens and cell debris at the site, and the tissue heals.

4


Natural Killer Cells

• Natural killer (NK) cells

– Patrol the body and attack virus-infected body cells and cancer cells

– Trigger apoptosis in the cells they attack


Invertebrate Immune Mechanisms

• Many invertebrates defend themselves from infection

– By many of the same mechanisms in the vertebrate innate response


• Concept 43.2: In acquired immunity, lymphocytes provide specific defenses against infection

• Acquired immunity

– Is the body’s second major kind of defense

– Involves the activity of lymphocytes


Antigen-binding sitesAntibody A

Antigen

Antibody BAntibody C

Epitopes(antigenicdeterminants)

• An antigen is any foreign molecule

– That is specifically recognized by lymphocytes and elicits a response from them

• A lymphocyte actually recognizes and binds

– To just a small, accessible portion of the antigen called an epitope

Figure 43.7


Antigen Recognition by Lymphocytes

• The vertebrate body is populated by two main types of lymphocytes

– B lymphocytes (B cells) and T lymphocytes (T cells)

– Which circulate through the blood

• The plasma membranes of both B cells and T cells

– Have about 100,000 antigen receptor that all recognize the same epitope


B Cell Receptors for Antigens

• B cell receptors

– Bind to specific, intact antigens

– Are often called membrane antibodies or membrane immunoglobulins

Figure 43.8a

Antigen-bindingsite

Antigen-binding site

Disulfidebridge

Lightchain

Heavy chains

Cytoplasm of B cell

VA B cell receptor consists of two identical heavy chains and two identical light chains linked by several disulfide bridges.

(a)

Variableregions

Constantregions

Transmembraneregion

Plasmamembrane

B cell

V

V

CC C

C

V


Antigen-Binding site

chain

Disulfide bridge

chain

T cell

A T cell receptor consists of one chain and one chain linked by a disulfide bridge.

(b)

Variableregions

Constantregions

Transmembraneregion

Plasmamembrane

Cytoplasm of T cell

T Cell Receptors for Antigens and the Role of the MHC

• Each T cell receptor

– Consists of two different polypeptide chains

Figure 43.8b

V V

C C


• T cells bind to small fragments of antigens

– That are bound to normal cell-surface proteins called MHC molecules

• MHC molecules

– Are encoded by a family of genes called the major histocompatibility complex


• Infected cells produce MHC molecules

– Which bind to antigen fragments and then are transported to the cell surface in a process called antigen presentation

• A nearby T cell

– Can then detect the antigen fragment displayed on the cell’s surface


• Depending on their source

– Peptide antigens are handled by different classes of MHC molecules


Figure 43.9a

Infected cell

Antigenfragment

Class I MHCmolecule

T cellreceptor

(a) Cytotoxic T cell

A fragment offoreign protein(antigen) inside thecell associates withan MHC moleculeand is transportedto the cell surface.

1

The combination ofMHC molecule andantigen is recognizedby a T cell, alerting itto the infection.

2

1

2

• Class I MHC molecules, found on almost all nucleated cells of the body

– Display peptide antigens to cytotoxic T cells


• Class II MHC molecules, located mainly on dendritic cells, macrophages, and B cells

– Display antigens to helper T cells

1

2

Figure 43.9b

Microbe Antigen-presentingcell

Antigenfragment

Class II MHCmolecule

T cellreceptor

Helper T cell

A fragment offoreign protein(antigen) inside thecell associates withan MHC moleculeand is transportedto the cell surface.

1

The combination ofMHC molecule andantigen is recognizedby a T cell, alerting itto the infection.

2

(b)


Lymphocyte Development

• Lymphocytes

– Arise from stem cells in the bone marrow


• Newly formed lymphocytes are all alike

– But they later develop into B cells or T cells, depending on where they continue their maturation

Figure 43.10

Bone marrow

Lymphoidstem cell

B cell

Blood, lymph, and lymphoid tissues(lymph nodes, spleen, and others)

T cell

Thymus


Generation of Lymphocyte Diversity by Gene Rearrangement

• Early in development, random, permanent gene rearrangement

– Forms functional genes encoding the B or T cell antigen receptor chains


DNA ofundifferentiatedB cell

DNA of differentiatedB cell

pre-mRNA

mRNA Cap

B cell

B cell receptorLight-chain polypeptide

Intron

Intron

Intron

Variableregion

Constantregion

V1V2 V3

V4–V39

V40 J1 J2 J3 J4 J5

V1 V2V3 J5

V3 J5

V3 J5

V C

C

C

C

C

Poly (A)

Figure 43.11

Deletion of DNA between a V segmentand J segment and joining of the segments1

• Immunoglobulin gene rearrangement

Transcription of resulting permanently rearranged,functional gene2

RNA processing (removal of intron; addition of capand poly (A) tail)3

4 Translation


Testing and Removal of Self-Reactive Lymphocytes

• As B and T cells are maturing in the bone and thymus

– Their antigen receptors are tested for possible self-reactivity

• Lymphocytes bearing receptors for antigens already present in the body

– Are destroyed by apoptosis or rendered nonfunctional


Clonal Selection of Lymphocytes

• In a primary immune response

– Binding of antigen to a mature lymphocyte induces the lymphocyte’s proliferation and differentiation, a process called clonal selection


• Clonal selection of B cells

– Generates a clone of short-lived activated effector cells and a clone of long-lived memory cells

Figure 43.12

Antigen molecules

Antigenreceptor

B cells thatdiffer inantigenspecificity

Antibodymolecules

Clone of memory cells Clone of plasma cells

Antigen moleculesbind to the antigenreceptors of only oneof the three B cellsshown.

The selected B cellproliferates, forminga clone of identicalcells bearingreceptors for theselecting antigen.

Some proliferatingcells develop intoshort-lived plasmacells that secreteantibodies specificfor the antigen.

Some proliferating cellsdevelop into long-livedmemory cells that canrespond rapidly uponsubsequent exposureto the same antigen.


• In the secondary immune response

– Memory cells facilitate a faster, more efficient response

An

tibo

dy

con

cen

tra

tion

(arb

itra

ry u

nits

)

104

103

102

101

100

0 7 14 21 28 35 42 49 56

Time (days)Figure 43.13

Antibodiesto A

Antibodiesto B

Primaryresponse toantigen Aproduces anti-bodies to A

2Day 1: First exposure toantigen A

1 Day 28: Second exposureto antigen A; firstexposure to antigen B

3 Secondary response to anti-gen A produces antibodiesto A; primary response to anti-gen B produces antibodies to B

4


• Concept 43.3: Humoral and cell-mediated immunity defend against different types of threats

• Acquired immunity includes two branches

– The humoral immune response involves the activation and clonal selection of B cells, resulting in the production of secreted antibodies

– The cell-mediated immune response involves the activation and clonal selection of cytotoxic T cells


• The roles of the major participants in the acquired immune response

Figure 43.14

Humoral immune response Cell-mediated immune response

First exposure to antigen

Intact antigensAntigens engulfed and

displayed by dendritic cellsAntigens displayed

by infected cells

Activate Activate Activate

Gives rise to Gives rise to Gives rise to

B cellHelperT cell

CytotoxicT cell

Plasmacells

MemoryB cells

Active and memory helperT cells

Memory cytotoxic

T cells

Active cytotoxic

T cells

Secrete antibodies that defend againstpathogens and toxins in extracellular fluid

Defend against infected cells, cancer cells, and transplanted tissues

Secretedcytokinesactivate


Helper T Cells: A Response to Nearly All Antigens

• Helper T cells produce CD4, a surface protein

– That enhances their binding to class II MHC molecule–antigen complexes on antigen-presenting cells

• Activation of the helper T cell then occurs


• Activated helper T cells

– Secrete several different cytokines that stimulate other lymphocytes


• The role of helper T cells in acquired immunity

Figure 43.15

After a dendritic cell engulfs and degrades a bacterium, it displays bacterial antigen fragments (peptides) complexed with a class II MHC molecule on the cell surface. A specific helper T cell binds to the displayed complex via its TCR with the aid of CD4. This interaction promotes secretion of cytokines by the dendritic cell.

Proliferation of the T cell, stimulatedby cytokines from both the dendritic cell and the T cell itself, gives rise toa clone of activated helper T cells(not shown), all with receptors for thesame MHC–antigen complex.

The cells in this clonesecrete other cytokines that help activate B cellsand cytotoxic T cells.

Cell-mediatedimmunity(attack on

infected cells)

Humoralimmunity

(secretion ofantibodies byplasma cells)

Dendriticcell

Dendriticcell

Bacterium

Peptide antigen


TCR

CD4

Helper T cell

Cytokines

Cytotoxic T cell

B cell

1

2 3

1

2 3


Cytotoxic T Cells: A Response to Infected Cells and Cancer Cells

• Cytotoxic T cells make CD8

– A surface protein that greatly enhances the interaction between a target cell and a cytotoxic T cell


• Cytotoxic T cells

– Bind to infected cells, cancer cells, and transplanted tissues

• Binding to a class I MHC complex on an infected body cell

– Activates a cytotoxic T cell and differentiates it into an active killer


Cytotoxic T cell

Perforin

Granzymes

CD8TCR

Class I MHCmolecule

Targetcell Peptide

antigen

Pore

ReleasedcytotoxicT cell

Apoptotictarget cell

Cancercell

CytotoxicT cell

A specific cytotoxic T cell binds to a class I MHC–antigen complex on a target cell via its TCR with the aid of CD8. This interaction, along with cytokines from helper T cells, leads to the activation of the cytotoxic cell.

1 The activated T cell releases perforin molecules, which form pores in the target cell membrane, and proteolytic enzymes (granzymes), which enter the target cell by endocytosis.

2 The granzymes initiate apoptosis within the target cells, leading to fragmentation of thenucleus, release of small apoptotic bodies, and eventual cell death. The released cytotoxic T cell can attack other target cells.

3

1

2

3

Figure 43.16

• The activated cytotoxic T cell

– Secretes proteins that destroy the infected target cell


B Cells: A Response to Extracellular Pathogens

• Activation of B cells

– Is aided by cytokines and antigen binding to helper T cells


• The clonal selection of B cells

– Generates antibody-secreting plasma cells, the effector cells of humoral immunity


21

3

B cell

Bacterium

Peptide antigen


TCR

Helper T cell

CD4

Activated helper T cell Clone of memory

B cells

Cytokines

Clone of plasma cellsSecreted antibodymolecules

Endoplasmicreticulum of plasma cell

Macrophage

After a macrophage engulfs and degradesa bacterium, it displays a peptide antigencomplexed with a class II MHC molecule.A helper T cell that recognizes the displayed complex is activated with the aid of cytokines secreted from the macrophage, forming a clone of activated helper T cells (not shown).

1 A B cell that has taken up and degraded the same bacterium displays class II MHC–peptide antigen complexes. An activated helper T cellbearing receptors specific for the displayedantigen binds to the B cell. This interaction,with the aid of cytokines from the T cell,activates the B cell.

2 The activated B cell proliferatesand differentiates into memoryB cells and antibody-secreting plasma cells. The secreted antibodies are specific for the same bacterial antigen that initiated the response.

3

Figure 43.17


Antibody Classes

• The five major classes of antibodies, or immunoglobulins

– Differ in their distributions and functions within the body


• The five classes of immunoglobulins

Figure 43.18

First Ig class produced after initial exposure to antigen; then its concentration in the blood declines

Most abundant Ig class in blood; also present in tissue fluids

Only Ig class that crosses placenta, thus conferring passive immunity on fetus

Promotes opsonization, neutralization, and agglutination of antigens; less effective in complement activation than IgM (see Figure 43.19)

Present in secretions such as tears, saliva, mucus, and breast milk

Triggers release from mast cells and basophils of histamine and other chemicals that cause allergic reactions (see Figure 43.20)

Present primarily on surface of naive B cells that havenot been exposed to antigens

IgM(pentamer)

IgG(monomer)

IgA(dimer)

IgE(monomer)

J chain

Secretorycomponent

J chain

Transmembraneregion

IgD(monomer)

Promotes neutralization and agglutination of antigens; very effective in complement activation (see Figure 43.19)

Provides localized defense of mucous membranes byagglutination and neutralization of antigens (seeFigure 43.19)

Presence in breast milk confers passive immunity onnursing infant

Acts as antigen receptor in antigen-stimulated proliferation and differentiation of B cells (clonal selection)


Antibody-Mediated Disposal of Antigens

• The binding of antibodies to antigens

– Is also the basis of several antigen disposal mechanisms

– Leads to elimination of microbes by phagocytosis and complement-mediated lysis


• Antibody-mediated mechanisms of antigen disposalBinding of antibodies to antigens

inactivates antigens by

Viral neutralization(blocks binding to host)

and opsonization (increasesphagocytosis)

Agglutination ofantigen-bearing particles,

such as microbes

Precipitation ofsoluble antigens

Activation of complement systemand pore formation

Bacterium

Virus Bacteria

Solubleantigens Foreign cell

Complementproteins

MAC

Pore

Enhances

Phagocytosis

Leads to

Cell lysis

MacrophageFigure 43.19


Active and Passive Immunization

• Active immunity

– Develops naturally in response to an infection

– Can also develop following immunization, also called vaccination


• In immunization

– A nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory for that microbe


• Passive immunity, which provides immediate, short-term protection

– Is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk

– Can be conferred artificially by injecting antibodies into a nonimmune person


• Concept 43.4: The immune system’s ability to distinguish self from nonself limits tissue transplantation

• The immune system

– Can wage war against cells from other individuals

• Transplanted tissues

– Are usually destroyed by the recipient’s immune system


Blood Groups and Transfusions

• Certain antigens on red blood cells

– Determine whether a person has type A, B, AB, or O blood


• Antibodies to nonself blood types

– Already exist in the body

• Transfusion with incompatible blood

– Leads to destruction of the transfused cells


• Recipient-donor combinations

– Can be fatal or safe

Table 43.1


• Another red blood cell antigen, the Rh factor

– Creates difficulties when an Rh-negative mother carries successive Rh-positive fetuses


Tissue and Organ Transplants

• MHC molecules

– Are responsible for stimulating the rejection of tissue grafts and organ transplants


• The chances of successful transplantation are increased

– If the donor and recipient MHC tissue types are well matched

– If the recipient is given immunosuppressive drugs


• Lymphocytes in bone marrow transplants

– May cause a graft versus host reaction in recipients


• Concept 43.5: Exaggerated, self-directed, or diminished immune responses can cause disease

• If the delicate balance of the immune system is disrupted

– The effects on the individual can range from minor to often fatal consequences


Allergies

• Allergies are exaggerated (hypersensitive) responses

– To certain antigens called allergens


• In localized allergies such as hay fever

– IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells


• The next time the allergen enters the body

– It binds to mast cell–associated IgE molecules

• The mast cells then release histamine and other mediators

– That cause vascular changes and typical symptoms


• The allergic response

Figure 43.20

IgE antibodies produced in response to initial exposure to an allergen bind to receptors or mast cells.

1 On subsequent exposure to the same allergen, IgE molecules attached to a mast cell recog-nize and bind the allergen.

2 Degranulation of the cell,triggered by cross-linking of adjacent IgE molecules, releases histamine and other chemicals, leading to allergysymptoms.

3

1

2

3

Allergen

IgE

Histamine

GranuleMast cell


• An acute allergic response sometimes leads to anaphylactic shock

– A whole-body, life-threatening reaction that can occur within seconds of exposure to an allergen


Autoimmune Diseases

• In individuals with autoimmune diseases

– The immune system loses tolerance for self and turns against certain molecules of the body


• Rheumatoid arthritis

– Is an autoimmune disease that leads to damage and painful inflammation of the cartilage and bone of joints

Figure 43.21


• Other examples of autoimmune diseases include

– Systemic lupus erythematosus

– Multiple sclerosis

– Insulin-dependent diabetes


Immunodeficiency Diseases

• An inborn or primary immunodeficiency

– Results from hereditary or congenital defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses


• An acquired or secondary immunodeficiency

– Results from exposure to various chemical and biological agents


Inborn (Primary) Immunodeficiencies

• In severe combined immunodeficiency (SCID)

– Both the humoral and cell-mediated branches of acquired immunity fail to function


Acquired (Secondary) Immunodeficiencies

• Acquired immunodeficiencies

– Range from temporary states to chronic diseases


Stress and the Immune System

• Growing evidence shows

– That physical and emotional stress can harm immunity


• Acquired Immunodeficiency Syndrome (AIDS)

• People with AIDS

– Are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse


• Because AIDS arises from the loss of helper T cells

– Both humoral and cell-mediated immune responses are impaired


• The loss of helper T cells

– Results from infection by the human immunodeficiency virus (HIV)

1µmFigure 43.22


• The spread of HIV

– Has become a worldwide problem

• The best approach for slowing the spread of HIV

– Is educating people about the practices that transmit the virus

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