Digestion

Copy everything in red

The Digestive System’s Function

• As food passes through the digestive system, it gets broken down distributing its nutrient value to the body

• The function of each organ of the digestive system is to help convert foods into simpler molecules that can be absorbed and used by the cells of the body

The Digestive System Structures• The digestive system includes:

– Mouth– Pharynx– Esophagus– Stomach– Small intestine– Large intestine

• Major accessory structures that add secretions to the digestive system include:– Salivary glands– Pancreas– Liver

Mouth

Salivary glands

Stomach

Pancreas (behind stomach)Large intestine

Small intestine

Rectum

Gallbladder (behind liver)

Liver

Esophagus

Pharynx

Figure 38–10 The Digestive System

Mouth & Salivary Glands• Teeth

– Protected by enamel– Chewing begins the process of mechanical

digestion = physical breakdown of large pieces of food into smaller pieces (cutting, tearing, crushing)

• Saliva– Secreted by salivary glands– Moisten food making it easier to chew– Begins the process of chemical digestion =

Amylase (digestive enzyme) chemically breakdown large starch molecules into smaller sugar molecules

– Lysozyme enzyme fights infection

Pharynx

• Remember from the Respiratory System:

• The pharynx (throat) is a tube in the back of the mouth that passes both air and food

• Epiglottis (flap of tissue) covers the trachea to ensure food continue to move along digestive tract

Esophagus• Food tube• Bolus (chewed clump of food) moves along

by contractions of smooth muscle surrounding the esophagus = peristalsis

• Cardiac sphincter closes esophagus after food has passed into the stomach preventing stomach contents from moving back into the esophagus (heart burn occurs when stomach acid splashing into the esophagus)

Stomach• A large muscular sac made of smooth muscle

that mechanically and chemically digests food• Chemical digestion occurs as gastric glands in

the stomach lining secrete mucus to protect the inner wall while pepsin and hydrochloric acid break down protein– Ulcers = a hole in the stomach wall caused by a

bacterial infection that eats away at the lining of the stomach

• Mechanical digestions occurs as the stomach muscles contract to churn and mix stomach fluids producing a mixture = chyme– Pyloric valve opens allowing chyme to flow from the

stomach into the small intestine

Duodenum

• More chemical digestion of chyme occurs in the duodenum (the first part of the small intestines)

• Chyme mixes with enzymes and digestive fluids from the pancreas and the liver (accessory structures)

Pancreas

• A gland that produces hormones that regulate blood sugar levels

• Produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids

• Produces sodium bicarbonates (a base) that neutralizes stomach acid

Liver

• Produces bile = “detergent” dissolving fat droplets

• Bile is stored in the gallbladder

Liver

Gallbladder

Duodenum

Bile duct

Pancreas

Pancreatic duct

To small intestine

Figure 38–13 The Liver and the Pancreas

Section 38-2

Small Intestine• Made of three parts: duodenum, jejunum, and

ileum• Where chemical digestion is completed• The folded surfaces are covered with villi = small

fingerlike projections that increase the surface area of the small intestines for greater absorption of nutrients

• The products of carbohydrate or protein digestion are absorbed into capillaries in the villi and microvilli

• Undigested fats are absorbed by lymph vessels = lacteals

Small Intestine Villus

Circular folds

Villi

Epithelial cells

Capillaries

Lacteal

Vein

Artery

Figure 38–14 The Small Intestine

Section 38-2

The Digestive EnzymesKNOW THIS CHART

Site

Mouth

Stomach

Small intestine(from pancreas)

Small intestine

Site

Mouth

Stomach

Small intestine(from pancreas)

Small intestine

EnzymeEnzyme Role in DigestionRole in Digestion

Section 38-2

Salivary amylase

Pepsin

Amylase

Trypsin

Lipase

Maltase, sucrase, lactase

Peptidase

Breaks down starches into disaccharides

Breaks down proteins into large peptides

Continues the breakdown of starch

Continues the breakdown of protein

Breaks down fat

Breaks down remaining disaccharides into monosaccharides

Breaks down dipeptides into amino acids.

Large Intestine• Food entering large intestine is basically

nutrient-free, mainly made of water, cellulose (fiber), and other indigestible substances

• Removes water left in the chyme by absorbing it across the large intestine wall– If water removal is inefficient, diarrhea occurs and can

be dangerous due to the loss of salts and water

• Intestinal bacteria help with digestion– The appendix is believed to have formerly stored

bacteria to assist with cellulose digestion

• Solid concentrated waste (feces) is excreted through the rectum

Excretion

Copy everything in red

Excretion

• Excretion = the process by which wastes are eliminated from the body

• The excretory system includes:– Lungs: excrete gaseous carbon dioxide from

cellular respiration– Rectum: excrete solid undigested remains

from food– Skin: excretes excess water, salts, urea– Kidneys and accessory organs

The Urinary System

• The urinary system rids the blood of wastes produced by the metabolism of nutrients and controls blood volume by removing excess water produced by body cells.

• The urinary system includes: – Kidneys– Urinary bladder– Connecting tubules:

• Ureter • Urethra

Kidney (Cross Section)

Cortex

Medulla

Vein Artery

Kidney

Ureter

Urinary bladder

Urethra

The Urinary SystemDRAW & LABEL THIS

Section 38-3

Kidneys

• Most people have 2 kidneys located on either side of the spinal column on your lower back

• Ureters = tubes that carry urine from each kidney to the urinary bladder

• Urinary bladder = saclike organ that stores urine until it can be excreted

• The kidneys filter blood by removing urea, excess water and other wastes collected as urine and the clean filtered blood returns to circulation

Kidney Structure

• Inner part = renal medulla

• Outer part = renal cortex

• Functional units of the kidney = nephrons

• About 1 million nephrons in each kidney

• Each nephron has its own arteriole (small artery), venule (small vein), and network of capillaries to filter blood

Kidney Nephron

Cortex

Medulla Renal artery

Renal vein

Ureter

To the bladder

Bowman’s capsule

Glomerulus

Capillaries

Collecting duct

To the ureter

Loop of Henle

Artery

Vein

Figure 38–17 Structure of the Kidneys

Section 38-3

FILTRATION…REABSORBTION…SECRETION

Urine

• The material that remains = urine containing urea, salts, water and other substances

• The loop of Henle conserves water and minimizes the volume of urine

• Urine is stored in the urinary bladder until it can be released from the body through a tube = urethra

Kidney Function

• The kidneys maintain homeostasis by: – Regulating the water content of the blood

(blood volume)– Maintaining blood pH– Removing waste products from the blood