Digestive System - Chapter 24

• hollow tube and associated glands

• most materials similar to human tissues:

• hydrolysis

absorption

pass through tube - "de-assembly line"

• transport (2)

6 Functional Activities

Tissue Layers of GI tract

1) Mucosa

2) Submucosa

3) Muscular

4) Serosa

Innervation:

Mouth and Pharynx

• lips and cheeks

• tongue -

• palate

• teeth and gums

incisors

molars

milk teeth

32 permanent teeth

wisdom teeth - 17-25

General Tooth

• crown

• root

• hollow core

• salivary glands

Esophagus

Swallowing

• mastication

• bolus

Stomach

• shape/function

• wall

1) many folds

2) gastric glands:

i) mucous - goblet cells

ii) HCl, pepsinogen (inactive form of pepsin), 5-HT, histamine, gastrin

other cells

HCl ---> v acidic (<2.0) --->

3 functions

secrete intrinsic factor

• mucosa normally resistent to low pH and pepsin

• ulcers

• chyme produced and expelled through pyloric sphinctor into

Small Intestine

• 20 ft long, 1 in wide

1) duodenum - 1 foot - digestion

2) jejunum/ileum - 19 ft - Absorption

villi -

• microvilli -

• also enzymes on cell membranes

Motility

• pacemaker potentials

• electrical synapses

• influenced by

Large Intestine

• 5 ft long

• 4 parts - ascending, transverse, descending, sigmoid

- ileocecal valve - prevents chyme backflow

appendix here

• terminal end - rectum and anus

anal sphinctor - keeps wastes inside

• tissue

Absorption of water

Mechanical activities

• chyme is squirted into lg intestine rhythmically - 15 mls/squirt

• rectum ---> increases pressure -->

Associated Glands

Liver

• largest internal organ - 3.5-4.0 lbs

• portal system

Functions:

1) detoxification

2) carbohydrate metab

3) lipid metabolism

4) protein synthesis

5) Bile salt synthesis

Gallbladder

Pancreas

Major Functions:

1) Blood glucose regulation - negative feedback

2) Digestive enzyme production

3) bicarbonate - neutralizes acid

Digestion and Absorption

Carbohydrates

1) begins in mouth

2) mainly in duodenum

3) microvilli enzymes

Proteins

1) begins in stomach

2) most in duodenum and jejunum

pancreas

RESULT:

1) free amino acids -

2) 2 or 3 a acids

Lipids

none until small intestine

2 processes:

1) emulsification

2) digestion

Neural and Hormonal Control

• automatic to some extent

Stomach

negative feedback