1. Chapter 3 Digestions and Absorption
Kin 110
Chapter 3
Digestions and Absorption

2. Overview of Digestion and Absorption
Chapter 3
Gastrointestinal tract
Overview of Digestion (details discussed with each nutrient lecture)
Mechanical
Chemical
Overview of Absorption (details discussed with each nutrient lecture)
Circulation of nutrients
Regulation and influences on Digestion and Absorption

3. The Gastrointestinal Tract
Organization
Mouth  anus
Accessory organs
Salivary glands, liver, pancreas, gallbladder
Functions
Ingestion
Transport
Secretion
Digestion
Absorption
Elimination

4. The Digestive Tract Wall

5. Mouth:
chews and mixes food with saliva
Salivary Glands:
secrete enzymes & mucous
Pharynx & Esophagus:
passages for food
Stomach:
adds acid & enzymes
mixes, churns and grinds food
regulates entry of food into small intestine
Liver:
manufactures bile (required for fat digestion) ES
Pancreas:
secretes enzymes and buffers
secretes hormones
Gallbladder:
stores and releases bile
Pyloric Sphincter
Small Intestine:
primary site of digestion and absorption
Large Intestine:
reabsorbs water and minerals
contains bacteria which digest some food and synthesize some vitamins

6. Overview of Digestion
Digestion - the mechanical and chemical breakdown of foods into smaller units that can be taken across the intestinal epithelium into the body
Physical movement
Peristalsis
Waves of muscle contraction propelling food forward
Segmentation
Mixing contractions that do not propel food forward

7. Chemical Digestion: Enzymes
Definition
proteins that act as CATALYSTS to facilitate (speed up) chemical reactions
change molecules while remaining unchanged themselves
digestive enzymes break down molecules into smaller components via HYDROLYSIS
“hydro” = water
“lysis” = to burst or break apart
ENZYME

9. Chemical Digestion: Enzymes cont.
Examples
prefix indicates molecule the enzymes acts on
suffix “ase” indicates an enzyme
amylase
sucrase
lactase
maltase
pepsin
trypsin
peptidase
lipase
digest
proteins
digest carbohydrates
digests
lipids

10. Secretions of the Digestive Tract
Salivary Secretions
water, mucous, enzymes, buffers, lysozyme
Stomach (gastric) Secretions
hydrochloric acid, intrinsic factor, pepsinogen, gastric lipase, mucous, HCO3-, hormones (gastrin)
Liver & Gallbladder
bile

11. Secretions cont. Pancreatic Secretions Small Intestine
exocrine: enzymes & buffers (HCO3-)
endocrine: insulin, glucagon, & secretin, others
Small Intestine
exocrine: enzymes, mucous
endocrine & paracrine: CCK, motilin, others

12. Absorption
- movement of small units of food particles (after digestion) from the interior of the gut (lumen) into the blood stream or lymphatic system.
- Requires particles to be broken down by digestion, a large surface area to interact with particles and in some cases specialized transportation mechanisms to move particles across cell membranes

13. Large surface area facilitates absorption

14. Mechanisms of Absorption
passive (simple) diffusion
the unassisted movement of substances in or out of cells down a concentration gradient

15. Mechanisms of Absorption
facilitated diffusion
carrier proteins (transporters) in the cell membrane help move substances in or out of cells down a concentration gradient

16. Mechanisms of Absorption cont.
active transport
the movement of molecules into or out of cells against a concentration gradient using a transport protein
requires energy (ATP)

17. Mechanisms of Absorption cont.
endocytosis
the uptake of material by a cell through indentation and pinching off of part of the membrane to form a vesicle

18. Circulation of Nutrients
Vascular system
Lymphatic system

19. Transport of Nutrients
blood
direct absorption of glucose, fructose, galactose, & proteins, and small lipid molecules
travels directly to the liver
lymph
larger lipid molecules are too large to enter the blood directly
absorbed first into the lymph
enter the blood at the inferior vena cava

20. Transport of nutrients
Some nutrients travel freely in the blood (e.g. glucose, proteins).
Others are bound to protein transporters (e.g. lipids, vitamins, and minerals)

21. Regulation of GI Activity
Nervous system
Regulates GI activity
Local system of nerves
Central nervous system
Hormonal system
Increases or decreases GI activity

22. Regulation of GI Activity cont.
Endocrine (Hormonal) System

23. Influences on Digestion & Absorption
Psychological
taste, smell, presentation of food
Cephalic phase (see next slide)
Chemical
processing of foods and food preparation, medications
Bacterial
some may cause gastris, ulcers; others are beneficial

24. Cephalic Phase Responses

25. Nutrition and GI Disorders
Constipation
Hard, dry, infrequent stools
Reduced by high fiber, fluid intake, exercise
Diarrhea
Loose, watery, frequent stools
Symptom of diseases/infections
Can cause dehydration
Diverticulosis
Pouches along colon
High fiber diet reduces formation