Anatomy and Physiology Chapter 23 – Digestive System

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

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

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

Digestive System - Anatomy Histology – Figure 23.6

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 (97-99.5%) salivary amylase Lysozyme and IgA antibodies Figure 23.9

Digestive Tract Teeth – Figures 23.10 and 23.11

Digestive Tract Cavity formation - Figure from other text

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

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 23.14 and 23.15

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

Digestion, Absorption, & Transport Proteins – how are these digested? Figures 23.33 and 23.34

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

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

Digestion, Absorption, & Transport Lipids – fats, cholesterol, steroids, some vitamins Emulsification by bile Digestion by lipase Breaks triglycerides into fatty acids and glycerol Figures 23.33 and 23.35

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

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

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

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?

Summary Table 23.2

Summary CD animation (Sm. Intestine)