Human BiologySylvia S. Mader

Michael Windelspecht

Chapter 8 Part 1Digestive

System and Nutrition

Lecture Outline

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Points to Ponder1. What are the digestive system structures and their

functions?

2. Where does carbohydrate, protein, and fat digestion and absorption occur?

3. What are proteins, lipids, carbohydrates, minerals and vitamins needed for?

4. What is an essential vs. a nonessential nutrient?

5. What are the 3 accessory organs of digestion?

6. What is obesity and why is it a problem?

7. What is LDL and HDL?

8. What are the components of a healthy diet?

9. Name and explain 4 eating disorders.

What are the main steps in the digestive process?

Ingestion: intake of food by the mouth.

Digestion: mechanically or chemically breaking down

food into their subunits

Movement: food must be moved along the GI tract in

order to fulfill all functions.

Absorption: movement of nutrients across the GI tract

wall to be delivered to cell via the blood.

Elimination: removal of indigestible molecules.

8.1 Overview of digestion

What are the 4 major layers that make up the wall of the GI tract?

Mucosa: innermost layer that produces mucus that

protects the lining and also produces digestive enzymes.

Sub mucosa: 2nd layer of loose connective tissue that

contains blood vessels, lymphatic vessels, and nerves.

Muscularis: 3rd layer made of 2 layers of smooth muscle

that move food along the GI tract.

Serosa: outer lining that is part of the peritoneum.

8.1 Overview of digestion

Visualizing the layers of the GI tract

8.1 Overview of digestion

Lumencentral space containingfood being digested

Mucosainner mucous membranelayer modified accordingto the digestive organ

Submucosabroad band of looseconnective tissue thatcontains nerves, blood,and lymphatic vessels

Muscularistwo layers ofsmooth muscle

Serosathin, outermost tissuethat is the visceralperitoneum

nervesupply

lymphvessel

artery

vein

An overview of the digestive system

8.1 Overview of digestion

Livermajor metabolic organ:processes and stores nutrients;produces bile for emulsification of fats

Gallbladderstores bile from liver; sends it tothe small intestine

Pancreasproduces pancreatic juice: contains digestiveenzymes, and sends it to the small intestine;produces insulin and secretes it into theblood after eating

Digestive tract organs

Esophaguspassageway where peristalsis pushesfood to stomach

Stomachsecretes acid and digestive enzymefor protein; churns, mixing food withsecretions, and sends chyme tosmall intestine

Small intestinemixes chyme with digestive enzymesfor final breakdown; absorbs nutrientmolecules into body; secretesdigestive hormones into blood

Large intestineabsorbs water and salt to form feces

Rectumstores and regulates eliminationof feces

Mouthteeth chew food; tongue tastes andpushes food for chewing and swallowing

Pharynxpassageway where food is swallowed

Accessory organs

Salivary glandsecrete saliva: contains digestive enzymefor carbohydrates

Anus

What is the pathway that food follows?

1. Mouth2. Pharynx3. Esophagus 4. Stomach 5. Small intestine 6. Large intestine 7. Rectum 8. Anus

8.1 Overview of digestion

The mouth 3 pairs of salivary glands secrete salivary amylase that

begins carbohydrate digestion.

Tonsils at the back of the mouth and other lymphatic

tissues are important in fighting disease.

Contains teeth that begin the mechanical breakdown of food.

The tongue is covered in taste buds and also assists in the

mechanical breakdown and movement of food.

The tongue forms a bolus(mass of chewed food) and

moves it toward the pharynx.

8.2 First part of the digestive tract

Anatomy of the mouth 8.2 First part of the digestive tract

hard palate

soft palate

uvula

tonsil

incisors (2)

canine (1)

premolars (2)

molars (3)

Teeth 32 in adults used for mechanical breakdown of food

(20 deciduous teeth in babies).

Each tooth is made of a crown and a root.

A hard covering called enamel and dentin covers the

crown with an inner pulp area with nerves and blood

vessels.

Dental caries (cavities) occur when bacteria metabolize

sugars and produce acids, so limiting sugar intake and

brushing teeth reduces these.

8.2 First part of the digestive tract

Anatomy of a tooth8.2 First part of the digestive tract

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root

crown

enamel

dentinpulpgum

jawbone

root canal

periodontalmembrane

cementum

The pharynx and esophagus

• Pharynx: is a cavity between the mouth

and esophagus that serves as a

passageway for food (and air).

• Esophagus: is a long, muscular tube that

carries food to the stomach.

8.2 First part of the digestive tract

How do we swallow food?• Voluntary phase:

– The beginning of food being swallowed from the mouth

into the pharynx.

• Involuntary phase:

– Once the food is in the pharynx swallowing becomes a

reflex action perform automatically.– The epiglottis covers the voice box to make sure food

is routed into the esophagus.– Food moves down the esophagus through peristalsis

(rhythmic contraction).

8.2 First part of the digestive tract

How do we swallow food?

8.2 First part of the digestive tract

Soft palate closesoff nasopharynx.

Larynx rises andepiglottis coversglottis.

Lower gastroesophagealspincter relaxes andfood enters stomach.

hard palate food bolusnasopharynx

softpalate

a. Swallowing

trachea(airway)open

Esophagusis closed.

epiglottis

esophagusopens

b. Peristalsis

esophagus

peristalticwave

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glottis

bolus

stomach

Health focus: Heartburn Occurs when acids from the stomach pass into the

esophagus (acid reflux).

Burning sensation in the esophagus.

Chronic heartburn is called gastro esophageal reflux disease (GERD).

Tips for decreasing heartburn:

Avoid high fat meals.

Don’t overeat.

Eat several small meals rather than the standard 3 larger meals

each day.

Exercise lightly.

8.2 First part of the digestive tract

The stomach

• The stomach is an enlarged part of alimentary

canal and receives food from esophagus.

• The stomach like J shape with a thick wall.

• Mucous membrane lining stomach contains

folds called rugae.

• Folds disappear as stomach fills with food.

o Its structure is divided into 4 main region:

o Funds: bulge o Body : largest region o Antrum:o Pylorus : pyloric

sphincterso It has two sphincters:Cardiac sphincter.Pyloric sphincter.

Function of stomach

store food, start digestion of proteins

controls movement of chyme into the small intestine.

Mixing of the food in the stomach produces Chyme.

Mixing movement mainly occurs in the Antrum.

Controlled emptying of gastric content into

duodenum.

HCl SecretionHCl Secretion gives the stomach a pH of 2 which

activates pepsin and helps kill bacteria found in food.

Anatomy of the stomach8.3 The stomach and small intestine

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Mucosa layerhas rugae.

Muscularis layerhas three layersof muscle.

lower gastroesophagealsphincter

cells that secretegastric juice

d. How the stomach empties

esophagus

lower gastroesophagealsphincter

pyloricsphincter

a. Stomach

gastric pit

gastric gland

b. Gastric glands

pyloricsphincter

SEM 3,260xgastric pitc. Gastric pits in mucosa

c: © Dr. Fred Hossler/Visuals Unlimited

The small intestine Averages 6m (18 ft) in length

Enzymes secreted by the pancreas into the small intestine

digest carbohydrates, proteins, and fats.

Bile is secreted by the gallbladder into the small intestine to

emulsify fats.

Digested food is absorbed through large surface area

created by numerous villi (finger-like projections) and

microvilli.

Amino acids and sugars enter the capillaries while fatty acids and glycerol enter the lacteals (small lymph vessels).

8.3 The stomach and small intestine

Anatomy of the small intestine

8.3 The stomach and small intestine

Small intestine

Section of intestinal wall

lumen

lymphnodule

villus

lacteal

Villi arteriole

lymphaticvessel

venule

gobletcell

bloodcapillaries

microvillivillus

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(villi): © Manfred Kage/Peter Arnold/Photolibrary; (microvilli):Reprinted from Medical Cell Biology, Charles Flickinger, copyright 1979, with permission from Elsevier.

How are nutrients digested and transported out of the small intestine?

8.3 The stomach and small intestine

+carbohydrate

pancreatic amylase

cell ofintestinalvillus

maltase

glucose

pH = basic

blood capillary

a. Carbohydrate digestion

b. Protein digestion

blood capillary

pH = basic

protein

peptides

trypsin

peptidase

amino acids

bile salts fat globules

emulsificationdroplets

lipase

monoglyceridesand freefatty acids

chylomicron

c. Fat digestion

lymphaticcapillary

pH = basic

What are the major digestive enzymes?

8.3 The stomach and small intestine

The three accessory organs

8.4 Three accessory organs and regulation of secretions

• Pancreas

• Liver

• Gallbladder

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gallbladder

common bile duct

duodenum

a.

bile

common hepatic duct

pancreatic ductpancreas

pancreaticjuice

centralvein

bile canals

branch ofhepaticartery

branch ofhepatic

portal veinbile ductb.

The pancreas• Fished-shaped spongy organ behind the stomach• Functions of the pancreas:

1. Secretes enzymes into the small intestine• Trypsin: digests proteins.• Lipase: digests fats.• Pancreatic amylase: digests carbohydrates.

2. Secretes bicarbonate into the small intestine to neutralize stomach acids

3. Secretes insulin into the blood to keep blood sugar levels under control

8.4 The accessory organs and regulation of secretions

The liver and gallbladder

• Large metabolic organ that lies under the diaphragm and is

made of 100,000 lobules.Function:1. Filters blood from the GI tract thus acting to remove poisons

and detoxify the blood.2. Removes iron, vitamins A, D, E, K and B12 from the blood and

stores them.3. Stores glucose as glycogen and breaks it down to help retain

blood glucose levels.4. Makes plasma proteins and helps regulate cholesterol levels by

making bile salts.5. Makes bile that is then stored in the gallbladder to be secreted

into the small intestine to emulsify fats.6. Breaks down hemoglobin.

8.4 The accessory organs and regulation of secretions

Liver disorders• Hepatitis:

– Inflammation of the liver– Caused by Hepatitis A, B, and C– This can lead to liver damage, cancer and/or death

• Cirrhosis:

– The liver becomes fatty and eventually this tissue is replaced by fibrous scar tissue.

– Seen in alcoholics and obese people.– This can lead to liver failure in which the liver

cannot regenerate as fast as it is being damaged.

8.4 The accessory organs and regulation of secretions

How do hormones control digestive gland secretions?

8.4 The accessory organs and regulation of secretions

gallbladder liver

stomach

pancreas

blood vessel

duodenum

gastrinCCK

secretin

The large intestine• Includes the cecum, colon, rectum

and anal canal• Larger in diameter but shorter than

the small intestine• The cecum has a projection known

as the appendix that may play a role in fighting infections

• Functions to:

1. Absorb water to prevent

dehydration.

2. Absorbs vitamins (B complex and

K) produced by intestinal flora.

3. Forms and rids the body of feces through the anus.

8.5 The large intestine and defecation

vermiformappendix

orifice ofappendix

transverse colon

ascendingcolon descending

colon

smallintestine

cecum

anal canal

internal anal sphincter external anal sphincter

anus

sigmoid colonrectum

Disorders of the colon and rectum

1. Diarrhea: increased peristalsis and water is not reabsorbed due

to either an infection or nervous stimulation.

2. Constipation: condition when feces are dry and hard that may

be controlled with water and fiber.

3. Hemorrhoids: enlarged and inflamed blood vessels of the anus

due to chronic constipation, pregnancy, aging, and anal

intercourse.

8.5 The large intestine and defecation

To understand weight and nutrition we first

have to understand nutrients

• Nutrients are a component of food that is needed

to perform a physiological body function.

• Nutrients include: CarbohydratesProteinsLipidsMineralsVitamins

8.6 Nutrition and weight control

Any question?

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