Anatomy and Physiology Chapter 23 – Digestive System.

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” IngestionPropulsion – this occurs by peristalsis

Figure 23.3 and CD Animation

Digestive System Physiology Overview

Mechanical digestion – this physically prepares food for chemical digestion

Chemical digestion – breaks large molecules into small molecules

AbsorptionDefication

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 amylaseLysozyme and IgA antibodies

Figure 23.9

Digestive TractTeeth – Figures 23.10 and 23.11

Digestive TractCavity 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 enzymeHydrochloric Acid (HCl) – function?

Gastric ulcers and Helicobacter pyloriTagamet 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 hoursCD AnimationVomitingStomach 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 foodAs food enters the small intestine from the

stomach, it is mixed with:bile (from the liver) - emulsifies fatpancreatic juice - contains digestive enzymes

and sodium bicarbonate

Figure 23.20


The surface area of the small intestine is roughly equal to the size of a tennis court!!!

How is that possible?Circular foldsVilli – finger-like projections of the mucosaMicrovilli – what are these?Figure 23.21

Anatomy of the Digestive Tract (cont.)Water soluble nutrients enter the blood

stream Lipid soluble nutrients enter lactealsAny material that is not digested and

absorbed moves on to the large intestine.Figure 23.21


Large Intestineabsorbs 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 likelihoodfiber decreases likelihood

Flatus Rectum and Anus - function to eliminate

undigested material (feces)3/4 water, 1/4 solid materialSolid material is largely bacteria from the large

intestineOver 1 billion bacteria in one gram of feces

Accessory Organs

Liver - largest organ in the bodyMicroscopic anatomy:

Hepatic arteries – oxygen rich bloodHepatic portal veins – these carry blood from

the GI tractHepatic ducts – bileCentral vein inferior vena cava

Figure 23.24

Accessory Organs (cont.)

Liver Functions:Bile productionStorage (usually short term)

Carbohydrates – glycogenFatVitamins – A, B12, D, E, and KCopper and iron

Nutrient InterconversionAmino acids and glycerol to glucoseFatty acids to phospholipids, etc.


DetoxificationThe liver removes toxic substances from the bloodAlcohol and ammonia

PhagocytosisSynthesis of Blood Proteins

Albumin, fibrinogen, heparin, clotting factors, etc.

Structure/function – Figure 23.24


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 bilegall stones - crystals of cholesterolFigure 23.20


The PancreasWhat does it do?

Endocrine and exocrine functionsSodium BicarbonateEnzymes:

pancreatic amylaseTrypsin, chymotrypsinlipase 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 DigestionBreaks macromolecules down into monomersCarbohydrates – How are these broken down?

Figure 23.33


Lactose intoleranceGlucose is absorbed via cotransport with Na+

It then enters into the bloodFigure from other text


Proteins – how are these digested?Figures 23.33 and 23.34


Proteins are also absorbed by cotransport with Na+

Figure from other text


Nucleic Acids – DNA and RNA are digested and absorbed

Figure 23.33


Lipids – fats, cholesterol, steroids, some vitaminsEmulsification by bileDigestion by lipase

Breaks triglycerides into fatty acids and glycerol

Figures 23.33 and 23.35


The fatty acids and other lipids then form micelles by associating with bile salts

The lipids can then enter the cells by simple diffusionFigure from other text


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


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 liverAs lipids are removed in adipose tissue VLDLLDLLDL 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


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)

Anatomy and Physiology Chapter 23 – Digestive System.

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