CHAPTER 25.1-25.7 & CHAPTER 26.1-26.4 Chapter 25.1 Digestive function: 1. Ingestion: the selective intake of food 2. Digestion: the mechanical and chemical breakdown of food into a form usable by the body 3. Absorption: the uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood or lymph 4. Compaction: absorbing water and consolidating the indigestible residue into feces 5. Defecation: the elimination of feces Mechanical digestion is the physical breakdown of food into smaller particles by cutting and grinding of the teeth and churning contractions of the stomach and small intestine. Chemical digestion is a series of hydrolysis reactions that break dietary macromolecules into their monomers: polysaccharides into monosaccharides, proteins into amino acids, fats into monoglycerides and fatty acids. And nucleic acid into nucleotides by digestive enzymes. Digestive tract : mouth pharynx esophagus stomach small intestine large intestine Accessory organs : teeth, tongue, salivary glands, liver, gall bladder, and pancreas Microscopic Anatomy: 4 layers, deep to superficial - Mucosa - Submucosa o Blood/lymph vessels and a nervus plexus - Muscularis Externa (responsible for the motility that propels food and residue through the digestive tract) o Circular and longitudinal - Serosa o Adventitia (fibrous connective tissue layer) Enteric Nervous System - Esophagus, stomach, and intestines have an Enteric Nervous System o Regulates motility, secretion and blood flow of the digestive tract - Nerve plexus o Submucosal Plexus Secretory activity (controls movement of the muscularis mucosae and glandular secretion of the mucosa o Myenteric Plexus Muscularis Externa GI tract motility (controls peristalsis and other contractions of the muscularis externa)
Peritoneum - Serous membrane - Mesenteries (hold organs) o Double layer Dorsal Ventral Greater omentum Lesser omentum - Functions o Provide passage for the blood vessels and nerves that supply the digestive tract, and contain many lymph nodes and lymphatic vessels o Holds organs: o Stores fat Digestive Tract Regulation - Short vs. Long Reflexes - Short Reflexes (Myenteric) o Intrinsic: capable of autonomous functions o Stretching or chemical stimulation of the digestive tract acts through the myenteric plexus to stimulate contractions in nearby regions of the muscularis externa (peristaltic contractions of swallowing) - Long Reflexes (Vasovagal) o Extrinsic o Acts through Autonomic nerve fibers that carry sensory signals from the digestive tract to the brainstem and motor commands back to the digestive tract Parasympathetic fibers of vagus nerve are important in stimulating motility and secretion by way of these long reflexes Chapter 25.2 Oral Cavity • Buccal cavity • Functions • Ingestion • Taste and sensory responses to food • Mastication (chewing) • First step for mechanical digestion • Chemical Digestion (starch is partially digested) • Swallowing, speech, and respiration • Salivary glands • Intrinsic and extrinsic salivary gland Esophagus • Long muscular tube
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- Summer '17
- Kyle Harris
- muscularis externa, gastric pits