Summary of chapter 66 from Guyton & Hall Physiology Medical Physiology 14 Edition
Pulmonary Ventilation and circulation
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Guyton Hall Medical Physiology 14 Edition
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CHAPTER 65
Secretory Functions of the Alimentary Tract
1. Secretory Glands in the GI Tract Have Two Main Jobs
• Digestive Enzymes: Break down food and are secreted throughout most of the digestive system, from the mouth to
the ileum (last part of the small intestine).
• Mucus Secretion: Mucous glands produce mucus to lubricate and protect the lining of the digestive tract, from the
mouth to the anus.
2. Secretion Responds to Food
• The body secretes just the right amount of digestive juices needed for the type and amount of food present.
• Some enzymes and secretions change depending on the type of food.
3. Types of Glands in the Digestive Tract
• Mucous (Goblet) Cells: Found on the surface of the digestive lining; they release mucus in response to irritation.
, • Crypts of Lieberkühn: Located in the small intestine; they are pits that contain cells for secretion.
• Tubular Glands: Found in the stomach and upper duodenum; they secrete acid, enzymes, and other substances.
• Complex Glands: Includes the salivary glands, pancreas, and liver, which are located outside the digestive tract.
These glands release their secretions (e.g., enzymes, bile) through ducts into the tract.
4. How Glands Get Stimulated
• Local Stimulation: When food touches the gut lining, it activates:
1. Direct contact: Stimulates mucus release.
2. Enteric Nervous System: Local nerve reflexes triggered by:
▪ Tactile (touch) stimulation.
▪ Chemical irritation.
▪ Stretching of the gut wall.
• Nervous System Regulation:
1. Parasympathetic Nervous System:
▪ Boosts secretion rates, especially in glands in the upper digestive tract (e.g., salivary glands, stomach
glands).
▪ Also affects some glands in the large intestine.
, 2. Sympathetic Nervous System:
▪ Can slightly increase secretion, but it also reduces blood flow to the glands, which may decrease
secretion if parasympathetic signals are active.
• Hormones: Certain hormones, released in response to food, regulate secretion (e.g., gastric juice increases when
food enters the stomach).
5. Mechanism of Secretion by Gland Cells
• How Secretions Are Made:
1. Nutrients from blood enter the gland cell.
2. Mitochondria in the cell use energy (ATP) to create secretions.
3. Secretions are synthesized in the endoplasmic reticulum and modified in the Golgi complex.
4. Secretory vesicles store the material until a signal (nerve or hormone) triggers their release via exocytosis.
• Water and Electrolytes: These are secreted along with enzymes to help flush them out of the glands and into the
digestive system.
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