The Digestive System

Setting Your Paper Up:

To organize this unit, we will be using the classic Cornell

Notes style. Please set your paper up accordingly

We will take a

moment to stop

after each stage

of digestion to fill

in the Key

Question Section!

The Cloaca Art exhibit by Wim

Delvoye

Artificial digestive

system

Feces at the end

were sold

The food begins at a long, transparent mouth, travels through a number of machine-like

assembly stations, and ends in hard matter which is separated from liquid through a

cylinder.Delvoye collects and sells the realistically smelling output, suspended in small

jars of resin at his Ghent studio. (Wikipedia)

Functions of the Digestive Tract

(aka Gastrointestinal Tract)

NOURISH the cells of the body

PHYSICAL AND CHEMICAL breakdown of food

Absorption of nutrients to the BLOODSTREAM

Removal of SOLID wastes

The Digestive System

Total length of the digestive tract in an adult human = 8m (approximately 26 ft)

Mouth (Oral cavity) Entry place for food

SALIVA secreted from salivary glands

SALIVARY AMYLASE begins to break down STARCH to simpler sugars

TEETH physically break food

Tongue rolls food into a smooth lump-like mass BOLUS

Tongue pushes bolus back during swallowing

The Pharynx, Epiglottis and

Swallowing

Food enters the PHARYNX

Need to prevent food from entering the TRACHEA which leads to the lungs

The EPIGLOTTIS is a flap of CARTILAGENOUS tissue

Covers the trachea during SWALLOWING to ensure that food does not enter the RESPIRATORY SYSTEM

Esophagus Tube that connects the

PHARYNX to the STOMACH

MOTILITY down the esophagus is achieved by PERISTALSIS

The two layers of smooth muscle (one layer circular, one layer longitudinal) that surrounds the esophagus work together to push food down the digestive tract

The Stomach

Physical and chemical DIGESTION occurs here

Other purpose: STORAGE site for food

Stomach (cont.)

Entry to stomach controlled by an ESOPHAGEAL SPHINCTER

The Esophageal Sphincter keeps the STOMACH closed (prevents acid from going up the esophagus HEARTBURN)

Stomach (cont.)

Has 3 MUSCLE

LAYERS (circular,

longitudinal, and

oblique layer

Foldings of stomach

wall = RUGAE

RUGAE allow the

stomach to expand

for STORAGE

Stomach (cont.) Gastric juice produced in GASTRIC PITS

Hydrochoric acid HCl (aq) – pH of 1-3 – begins to break down PROTEINSand kills bacteria

Pepsinogen – activated by the HCl to form PEPSIN – an ENZYME that breaks certain peptide bonds

Mucus – protects the stomach epithelum

GASTRIN: stimulate when food enters

which activates the stomach--motility

Stomach (cont.) The stomach MECHANICALLY

mixes the food

Very little ABSORPTION in the stomach (some water and salts, some medications and alcohol)

Between the stomach and the small intestine is another sphincter

The Small Intestine Main FUNCTIONS of the Small

Intestine : complete digestion and absorption of NUTRIENTS

Length of 5.5-6m (about 20 ft)

Has 3 regions: Duodenum, Jejunum, Ileum

Is in fact 4 times longer than the large intestine

Small intestine of a cat

1. What do you notice

about the room it

takes up in the

abdomen?

2. How long do you

think a cat’s

intestines are?

The Small Intestine (cont.)

VILLI to increase the SURFACE AREA

ENZYMES produced to continue breakdown of macromolecules

Carbohydrases (sucrase, maltase, lactase)

Peptidases (break down peptides even further)

Microvilli of small intestine

Duodenum There are cells on the

epithelium to detect the presence of ACIDIC chyme and FATTY chyme. They release REGULATORYhormones

There are DUCTS that attach ACCESORY organs to the duodenum. These accessory organs are: LIVER, GALL BLADDER, and PANCREAS

The Liver and Gall Bladder Liver Largest INTERNAL organ of

the human body Digestive function: produces

bile salts that are used to EMULSIFY fat

Storage of GLYCOGEN

Gall Bladder STORES bile When fatty substances enter

the duodenum, the gall bladder contracts and the bile enters the DUODENUM

The liver and gall bladder (con’t)

The Pancreas PANCREATIC fluid that contains

enzymes used for digestion

Trypsin and Chymotrypsin : proteases (breakdown proteins)

Pancreatic Amylase: CARBOHYDRASE (breaks down starch)

Lipase : digests FAT

Pancreas

Jejunum

LONGER than

Duodenum

Contains more

FOLDS than the

duodenum

Continues to break

down and ABSORB

food

Ileum

Slightly LONGER

than the Jejunum

Fewer and smaller

VILLI

Mostly just absorption

of NUTRIENTS

The Large Intestine SHORTER than small intestine

(1.5m, about 3.5 ft)

Function: concentrate and eliminate waste

Water and salts absorbed,

ANAEROBIC: houses bacteria

Has 3 regions (cecum, colon, rectum)

Caecum (or Cecum) and

Vermiform Appendix Caecum

First region of large intestine

In animals that digest plant materials, the caecum is much larger

Name four animals.

Vermiform Appendix

Vermiform = worm-like

Vestigial structure (lost function)

Why do you think we may have this????

An inflammed appendix

Colon and Rectum

Colon

SECOND region

Absorption of water and

salts

Storage of BACTERIA

MUCOUS cells along

length (lubrication

function)

Rectum

Storage of FECES until

they are eliminated

Even more mucous cells

Anus

Opening to the exterior of the

body for expelling feces

Opening is controlled by 2

sets of muscular

SPHINCTERS

One is INVOLUNTARY

(when rectum fills, signal is

sent to move the feces out)

Other is VOLUNTARY

Digestion - Review http://highered.mcgraw-

hill.com/sites/0072495855/student_view0/chapter26/animation_

_organs_of_digestion.html