1. Anatomy and Physiology
Chapter 23 – Digestive System

2. Digestive System - Anatomy
Digestive System vs. Digestive or Gastrointestinal (GI) Tract
What elements make up the GI tract?
Demo
What additional elements are there?
Teeth, tongue, gallbladder, liver, pancreas, and salivary glands

3. Digestive System
Physiology Overview – the digestive tract can be seen as a “disassembly line”
Ingestion
Propulsion – this occurs by peristalsis
Figure 23.3 and CD Animation

4. Digestive System Physiology Overview Figure 23.2
Mechanical digestion – this physically prepares food for chemical digestion
Chemical digestion – breaks large molecules into small molecules
Absorption
Defication
Figure 23.2

5. Digestive System - Anatomy
Histology – Figure 23.6

6. Digestive Tract The mouth:
Salivary glands are stimulated by food entering the mouth or even by seeing, smelling, or thinking about food
Saliva is composed of:
Water ( %)
salivary amylase
Lysozyme and IgA antibodies
Figure 23.9

7. Digestive Tract
Teeth – Figures and 23.11

8. Digestive Tract
Cavity formation - Figure from other text

9. Digestive Tract (cont.)
Pharynx
Esophagus
Heart burn – Figure 23.1

10. Digestive Tract (cont.)
Stomach – the temporary “storage tank”
Stomach size and amazing rugae!
The mucosa of the stomach contains gastric glands that produce mucus & gastric juice:
Pepsin - protein digesting enzyme
Hydrochloric Acid (HCl) – function?
Gastric ulcers and Helicobacter pylori
Tagamet and Zantac are proton-pump blockers
Figures and 23.15

11. Anatomy of the Digestive Tract (cont.)
The stomach mixes food with stomach juices
This produces chyme
Some lipid-soluble substances (like alcohol) are absorbed in the stomach, but most food is not
Food leaves the stomach in 2-4 hours
CD Animation
Vomiting
Stomach by-pass surgery – Figure 23.14

12. Anatomy of the Digestive Tract (cont.)
Small Intestine (or should it be called the “long intestine”?)
Major site of digestion and absorption of food
As food enters the small intestine from the stomach, it is mixed with:
bile (from the liver) - emulsifies fat
pancreatic juice - contains digestive enzymes and sodium bicarbonate
Figure 23.20

13. Anatomy of the Digestive Tract (cont.)
The surface area of the small intestine is roughly equal to the size of a tennis court!!!
How is that possible?
Circular folds
Villi – finger-like projections of the mucosa
Microvilli – what are these?
Figure 23.21

14. Anatomy of the Digestive Tract (cont.)
Water soluble nutrients enter the blood stream
Lipid soluble nutrients enter lacteals
Any material that is not digested and absorbed moves on to the large intestine.
Figure 23.21

15. Anatomy of the Digestive Tract (cont.)
Large Intestine
absorbs water, salts, minerals and some vitamins
~500 ml of chyme enter each day, but only 150 ml of feces is produced
stores undigested material until it is eliminated
Appendicitis – Figure 23.29

16. Anatomy of the Digestive Tract (cont.)
Polyps and colon cancer
fat consumption increases likelihood
fiber decreases likelihood
Flatus
Rectum and Anus - function to eliminate undigested material (feces)
3/4 water, 1/4 solid material
Solid material is largely bacteria from the large intestine
Over 1 billion bacteria in one gram of feces

17. Accessory Organs Liver - largest organ in the body
Microscopic anatomy:
Hepatic arteries – oxygen rich blood
Hepatic portal veins – these carry blood from the GI tract
Hepatic ducts – bile
Central vein  inferior vena cava
Figure 23.24

18. Accessory Organs (cont.)
Liver Functions:
Bile production
Storage (usually short term)
Carbohydrates – glycogen
Fat
Vitamins – A, B12, D, E, and K
Copper and iron
Nutrient Interconversion
Amino acids and glycerol to glucose
Fatty acids to phospholipids, etc.

19. Accessory Organs (cont.)
Detoxification
The liver removes toxic substances from the blood
Alcohol and ammonia
Phagocytosis
Synthesis of Blood Proteins
Albumin, fibrinogen, heparin, clotting factors, etc.
Structure/function – Figure 23.24

20. Accessory Organs (cont.)
Hepatitis is an infection of the liver
Cirrhosis – chronic inflammation of the liver (leads to the replacement of liver cells with connective tissue)
Gall Bladder - stores bile
gall stones - crystals of cholesterol
Figure 23.20

21. Accessory Organs (cont.)
The Pancreas
What does it do?
Endocrine and exocrine functions
Sodium Bicarbonate
Enzymes:
pancreatic amylase
Trypsin, chymotrypsin
lipase
Nuclease
Figure 23.20

22. Hormonal Control of the Digestive System
Table 23.1 and Figures 23.16, 23.25, and 23.28

23. Digestion, Absorption, & Transport
Chemical Digestion
Breaks macromolecules down into monomers
Carbohydrates – How are these broken down?
Figure 23.33

24. Digestion, Absorption, & Transport
Lactose intolerance
Glucose is absorbed via cotransport with Na+
It then enters into the blood
Figure from other text

25. Digestion, Absorption, & Transport
Proteins – how are these digested?
Figures and 23.34

26. Digestion, Absorption, & Transport
Proteins are also absorbed by cotransport with Na+
Figure from other text

27. Digestion, Absorption, & Transport
Nucleic Acids – DNA and RNA are digested and absorbed
Figure 23.33

28. Digestion, Absorption, & Transport
Lipids – fats, cholesterol, steroids, some vitamins
Emulsification by bile
Digestion by lipase
Breaks triglycerides into fatty acids and glycerol
Figures and 23.35

29. Digestion, Absorption, & Transport
The fatty acids and other lipids then form micelles by associating with bile salts
The lipids can then enter the cells by simple diffusion
Figure from other text

30. Digestion, Absorption, & Transport
Once inside the cells the fatty acids and glycerol are used to produce triglycerides again
These attach to proteins, cholesterol, and phospholipids to form chylomicrons
These then leave the cell and enter the lacteals
Figure from other text and Figure 23.36

31. Digestion, Absorption, & Transport
Chylomicrons eventually enter into the blood and go to the adipose tissue and liver
Low-Density Lipoprotein (LDL) vs. High-Density Lipoprotein (HDL)
VLDL leaves the liver
As lipids are removed in adipose tissue VLDLLDL
LDL then delivers lipids to other body cells
HDL is a protein which picks up any extra cholesterol and transports it back to the liver to make bile
Figure 24.22

32. Digestion, Absorption, & Transport
It is considered healthy to have high HDL and low LDL. Why?
What would be the problem with high LDL and low HDL?

33. Summary
Table 23.2

34. Summary
CD animation (Sm. Intestine)