26in depth

Functions of digestive system

Ingestion, propulsion, mechanical digestion, chemical digestion, absorption, defecation; occurs throughout GI tract

Mucosa (function + location)

Inner layer; secretion, absorption, protection; lines lumen of entire GI tract

Submucosa (function + location)

Connective tissue with blood vessels and nerves; supports mucosa; deep to mucosa

Muscularis externa (function + location)

Smooth muscle for motility (peristalsis + segmentation); throughout GI tract

Serosa (function + location)

Outermost layer; reduces friction; covers abdominal organs

Peristalsis (what + where)

Wave-like contractions that propel food forward; esophagus → intestines

Segmentation (what + where)

Mixing contractions (no forward movement); mainly small intestine

Upper GI tract organs

Mouth, pharynx, esophagus

Lower GI tract organs

Stomach, small intestine, large intestine

Accessory organs

Salivary glands, liver, gallbladder, pancreas

Mechanical digestion (where)

Mouth (chewing) and stomach (churning)

Chemical digestion (where)

Mouth, stomach, mostly small intestine

Salivary amylase (function + location)

Begins carbohydrate digestion; secreted in mouth

Parotid gland (location + function)

Largest gland; watery saliva; near ear

Submandibular gland (location + function)

Produces most saliva; under jaw

Sublingual gland (location + function)

Mucus-rich saliva; under tongue

Deciduous teeth (what)

Baby teeth (20 total)

Permanent teeth (what)

Adult teeth (32 total)

Incisors (function)

Cutting food; front teeth

Canines (function)

Tearing food

Premolars (function)

Crushing/grinding

Molars (function)

Grinding

Pharynx (function + location)

Passageway for food; connects mouth to esophagus

Esophagus (function + location)

Transports bolus to stomach via peristalsis

4 regions of stomach (location + function)

Cardia (entry), fundus (storage), body (mixing), pylorus (emptying into duodenum)

Bolus (what + where)

Chewed food; formed in mouth

Chyme (what + where)

Semi-liquid acidic mixture; formed in stomach

Mucous cells (function + location)

Secrete mucus; stomach lining protection

Parietal cells (function + location)

Secrete HCl + intrinsic factor; stomach

Chief cells (function + location)

Secrete pepsinogen; stomach

G cells (function + location)

Secrete gastrin; pyloric region of stomach

Cephalic phase (what + trigger)

Stimulated by sight/smell/thought of food; prepares stomach

Gastric phase (what + trigger)

Triggered by food in stomach; increases acid/enzyme secretion

Intestinal phase (what + trigger)

Triggered by chyme in small intestine; slows stomach

Protein digestion (where + how)

Begins in stomach (pepsin); continues in small intestine

Carbohydrate digestion (where + how)

Begins in mouth; continues in small intestine

Fat digestion (where + how)

Mainly small intestine; bile + lipase

Nucleic acid digestion (where + how)

Small intestine; nucleases break down DNA/RNA

Small intestine (function + location)

Major digestion and absorption; between stomach and large intestine

Duodenum (function + location)

First part; chemical digestion; receives bile + pancreatic enzymes

Jejunum (function + location)

Middle part; most nutrient absorption

Ileum (function + location)

Last part; absorbs B12 + bile salts

Villi (function + location)

Increase surface area; small intestine lining

Microvilli (function + location)

Further increase absorption; on epithelial cells

Lacteal (function + location)

Absorbs fats; inside villi

Plicae circulares (function + location)

Folds that increase surface area and slow chyme; small intestine

Liver (function + location)

Produces bile, detoxifies, stores glycogen; upper right abdomen

Bile (function + location)

Emulsifies fats; produced in liver, acts in duodenum

Gallbladder (function + location)

Stores and concentrates bile; releases into duodenum

Pancreas (function + location)

Produces enzymes + bicarbonate; releases into duodenum

Acinar cells (function + location)

Secrete digestive enzymes; pancreas

Duct cells (function + location)

Secrete bicarbonate; pancreas

Pancreatic enzymes (function)

Amylase (carbs), lipase (fats), proteases (proteins), nucleases (DNA/RNA)

Bicarbonate (function + location)

Neutralizes acid; pancreas → duodenum

Gastrin (function + location)

Stimulates HCl secretion; stomach

Secretin (function + location)

Stimulates bicarbonate release; small intestine

CCK (function + location)

Stimulates bile release + pancreatic enzymes; small intestine

Large intestine (function + location)

Absorbs water, forms feces; from cecum to rectum

Cecum (location + function)

Beginning of large intestine; receives chyme from ileum

Colon (location + function)

Major part of large intestine; water absorption

Rectum (location + function)

Stores feces before elimination

Anal canal (location + function)

Final passage for feces

Haustra (function + location)

Pouches that segment colon; large intestine

Water absorption (where)

Large intestine

Defecation (what + where)

Elimination of feces; rectum → anus