Stomach Anatomy and Nerve Supply Quiz

Digestive System Overview

• Chemical digestion breaks down complex food molecules into their building blocks (water, acid, enzymes, and salts)
• Absorption primarily occurs in the small intestine, where nutrients are taken into the bloodstream or lipids into the lymphatic system
• Defecation removes undigested materials from the body

Regulatory Mechanisms

• Neural control: sensors in the stomach monitor expansion, food particle breakdown, liquid presence, and nutrient type, and can activate glands and muscle
• Two types of reflexes: short reflex (local stimulus and response) and long reflex (ANS and CNS reacting to stimuli outside the digestive tract)
• Hormonal control: gastrin stimulates gastric acid release, secretin stimulates bicarbonate release from the pancreas, CCK stimulates pancreatic enzyme and bile secretion, and gastric inhibitory peptide inhibits gastric secretion and slows gastric emptying and motility

Mouth, Pharynx, and Esophagus

• Mouth: oral cavity lined by cheeks, tongue, lips, and palate, capable of handling digestion and respiration simultaneously
• Tongue: involved in ingestion, mechanical and chemical digestion, swallowing, and vocalization
• Pharynx: propels food to the esophagus and lubricates food and passage
• Esophagus: propels food to the stomach, with upper and lower esophageal sphincters controlling food entry and acid reflux

Nerve Supply

• Enteric nervous system: runs from esophagus to anus, separated into myenteric and submucosal plexuses, responsible for motility and regulating digestive secretions
• Autonomic nervous system: extrinsically innervates the alimentary canal, with sympathetic nerves restricting enteric neurons and parasympathetic nerves increasing GI secretion and motility

Blood Supply

• Transports protein and carbohydrate to the liver via the hepatic portal system
• Delivers nutrients and oxygen to organs of the alimentary canal, with 25% of blood pumped entering arteries serving the intestines during rest and digestion

The Peritoneum

• Holds digestive organs in place, with parietal and visceral peritoneum regions
• Peritoneal cavity: space between parietal and visceral peritoneum

Digestive System Processes and Regulation

• Mouth: ingests, chews, and mixes food, beginning chemical breakdown of carbs and lipids
• Pharynx: propels food to the esophagus, lubricating food and passage
• Esophagus: propels food to the stomach, with upper and lower esophageal sphincters controlling food entry and acid reflux
• Deglutition (swallowing): movement of food to the stomach, with 4-8 seconds for solid food and 1 second for soft food and liquid, involving voluntary, pharyngeal, and esophageal phases

The Stomach

• Links the esophagus to the small intestine, responsible for digestion, contractions, and changing position and size
• Empty stomach is about half the size of a fist, can stretch to hold 4 liters, and has an additional oblique muscle to churn food
• Cardia, fundus, body, and pylorus regions, with gastric glands producing hydrochloric acid, pepsinogen, and mucous

Gastric Secretion

• Three phases: cephalic, gastric, and intestinal
• Cephalic phase: brief, stimulated by sight, smell, taste, or thought of food, with chemical secretion of mucous and no digestive enzymes

Feces and Defecation

• Feces: undigested food residue, unabsorbed substances, bacteria, old cells from GI mucosa, inorganic salts, and some water
• Valsalva maneuver: voluntary procedure to remove feces, increasing intra-abdominal pressure
• Feces in the anal canal opens the internal sphincter, giving the choice to open the external sphincter

Accessory Organs

• Liver: receives nutrients from the small intestine, processes nutrients, drugs, and toxins, and produces bile for emulsification of lipids in the small intestine
• Pancreas: exocrine and endocrine functions, producing bile and pancreatic lipase for digestion

Large Intestine

• Finishes absorption, forms feces, and eliminates it, with four regions: cecum, colon, rectum, and anal canal
• Bacterial flora: trillions of nonpathogenic bacteria live in the large intestine, facilitating digestion, absorption, and synthesis of certain vitamins

Digestion and Absorption

• Chemical digestion finishes carb and protein digestion in the small intestine
• Most lipids are undigested and require bile and pancreatic lipase
• Most water is absorbed through osmosis
• Mechanical digestion: haustral contractions, peristalsis, and mass movement in the large intestine