01:377:213 Lecture Notes - Lecture 16: Gastrointestinal Tract, Salivary Gland, Digestion
I. Intro
A. The digestive system consists of:
1. The digestive tract
2. Accessory organs of digestion
B. Digestive tract
1. Oral cavity: mechanical processing, moistening with salivary secretions
2. Pharynx: throat, muscular propulsion of materials into esophagus
3. Esophagus: transport of materials to stomach
4. Stomach: chemical breakdown of materials by acid and enzymes,
mechanical processing by muscular contractions
5. Small intestine: enzymatic digestion and absorption of water, organic
substrates, vitamins and ions crosses the epithelium and goes to blood.
6. Large intestine: dehydration and compaction of indigestible materials in
preparation for elimination
C. Accessory organs of digestion
1. Teeth
2. Tongue
3. Salivary glands: secretion and lubricating fluid containing enzymes that
break down carbs
4. Pancreas: exocrine cells secrete buffers and digestive enzymes; endocrine
cells secrete hormones. Insulin is important for uptake of insulin to cells.
Insulin binds to receptors on tissues and uptake of glucose begins
5. Liver: secretion of bile for lipid digestion, storage of nutrients (liver
glycogen, very important for CNS function)(fats burn too quickly), many
other vital functions
6. Gallbladder: storage and concentration of bile
D. Glands:
1. secrete water,enzymes, buffers, and other components emptying things
into digestive tract. As food enters and passes along tract those secretions
prepare nutrients for absorption across digestive tract epithelium
2. Most important function: getting nutrient across epithelium to get to
tissues
E. Functions of the digestive system
1. Ingestion: occurs when foods and liquids enter digestive tract by mouth
2. Mechanical processing: most ingested solids undergo mechanical
processing before they are swallowed. Swirling, mixing add additional
motions.
3. Digestion : chemical and enzymatic breakdown of complex sugars, lipids,
proteins into small organic molecules that are absorbed by digestive
epithelium.
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