ANAPHY DIGESTIVE THEORETICAL

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converts food into absorbable substances, recovers water and electrolytes, and eliminates unabsorbed material.

Digestive system

Digestion

breaks food down.

Absorption

moves substances across the intestinal epithelium into blood or lymph.

Small intestine

consists of the duodenum, jejunum, and ileum.

Large intestine

includes the cecum, colon, rectum, and anal canal.

Accessory glands

Salivary glands, liver, gallbladder, and pancreas contribute secretions. Food does not normally pass through these accessory glands.

Ingestion and mastication

Food enters and is chewed; Teeth reduce particle size

Propulsion

Contents move forward; Esophageal peristalsis

Mixing

Contents blend with secretions ; Intestinal segmentation

Secretion

Cells release useful substances ; Gastric acid or pancreatic bicarbonate

Chemical digestion

Enzymes split food molecules ; Amylase acts on starch

Elimination

Unabsorbed material leaves ; Defecation

Mucosa

protects, secretes, and absorbs

Submucosa

contains connective tissue, vessels, and nerves.

muscularis

mixes and propels contents.

Outer layer

either forms a smooth serosal surface or attaches an organ to nearby tissues.

Myenteric plexus

mainly regulates motility

Submucosal Plexus

mainly regulates secretion and local mucosal activity.

Enteric nervous system

Formed together by the myenteric plexus and submucosal plexus.

Parasymphatetic input

generally promotes digestive activity.

Sympathetic input

generally reduces it digestive activity

Local reflexes

respond to stretch and chemical conditions.

Parietal peritoneum

lines the abdominal wall.

Visceral peritoneum

covers organs.

Mesentries

support organs while providing routes for vessels, lymphatics, and nerves.

Teeth

cut and grind food, increasing the surface area available to enzymes.

Tounge

positions food and forms a bolus.

Saliva

provides water, mucus, buffers, and protective proteins.

Salivary amylase

begins starch digestion.

Major salivary glands

the parotid, submandibular, and sublingual glands.

voluntary phase of swallowing

phase in which the tongue pushes the bolus into the pharynx.

Pharyngeal phase of swallowing

mainly reflexive and protects the airway.

Esophageal phase of swallowing

peristalsis moves the bolus toward the stomach.

peristalsis

mainly propels contents forward.

segmentation

mainly mixes contents back and forth, increasing contact with secretions and the intestinal wall.

Sphincters

regulate passage between regions.

Rugae

folds that flatten as the stomach fills.

Stomach regions

cardia, fundus, body, and pylorus regions.

Stomach functions

stores food, mixes it with secretions, and releases chyme through the pyloric sphincter into the duodenum in controlled amounts.

Mucous cells

Main secretion: Protective mucus; Why it matters: Helps protect the lining.

Parietal cells

Main secretion: Hydrochloric acid and intrinsic factor; Why it matters: Acid supports pepsin activity; intrinsic factor supports vitamin B12 absorption.

chief cells

Main secretion: Pepsinogen and gastric lipase; Why it matters: Begins protein digestion after pepsinogen activation; contributes to fat digestion.

G cells

Main secretion: Gastrin; Why it matters: Stimulates gastric activity, including acid secretion.

Acid (Stomach)

helps denature proteins and activate pepsinogen to pepsin.

Pepsin

begins protein digestion.

Stomach mucosal protection

protects itself through mucus, bicarbonate near the surface, and an intact epithelial barrier.

cephalic phase

the sight, smell, taste, or thought of food stimulates preparation for digestion.

gastric phase

food and distension increase gastric activity.

intestinal phase

duodenal signals mainly slow secretion and emptying, allowing time to neutralize and process incoming chyme.

intrinsic factor

made in the stomach, but vitamin B12 absorption occurs in the terminal ileum.

Vitamin b12

over time, can impair DNA synthesis and normal blood cell production.

Small intestine

performs most chemical digestion and nutrient absorption.

Duodenum

receives chyme, bile, and pancreatic secretions.

jejunum

a major absorptive region.

ileum

continues absorption and is especially important for bile salt recovery and vitamin B12 absorption.

Circular folds, villi, and microvilli

increase the surface area.

Villi

projections of the mucosa containing blood capillaries and lymphatic lacteals.

Microvilli

projections of individual epithelial cells and form the brush borde

Brush boarders enzymes

including disaccharidases and peptidases, complete important digestion steps.

Liver

receives portal blood containing many absorbed nutrients.

Hepatocytes

process and store nutrients, produce bile, synthesize plasma proteins, and process substances for removal.

Gallbladder

stores and concentrates bile, then releases it through the biliary system into the duodenum.

Bile salts

emulsify fat and support micelle formation.

Bile

contains no digestive enzymes and does not itself hydrolyze triglycerides.

Exocrine pancreas

contributes digestive enzymes from acinar cells and bicarbonate-rich fluid from duct cells.

bicarbonate

neutralizes acidic chyme and creates suitable conditions for intestinal enzymes.

Pancreatic proteseas

secreted as inactive precursors, reducing the risk of digestion of pancreatic tissue.

Enteropeptidase

activates trypsinogen; trypsin then activates other precursors.

Gastrin

Main stimulus and source: Food-related signals and distension; gastric G cells; Main response: Increases gastric acid secretion and activity.

Secretin

Main stimulus and source: Acid in duodenum; intestinal S cells; Main response: Promotes bicarbonate-rich pancreatic and biliary secretion.

Cholecystokinin or CCK

Main stimulus and source: Fats and protein digestion products; intestinal I cells; Main response: Promotes pancreatic enzyme secretion and gallbladder contraction.

Intestinal hormones and neural signals

help slow gastric emptying.

Salivary and pancreatic amylase

Source or site of action: Mouth and small intestinal lumen; Main action: Digests starch into smaller carbohydrates.

Pepsin

Source or site of action: Stomach; Main action: Breaks proteins into smaller chains.

pancreatic proteseas

Source or site of action: Produced in pancreas; act in small intestine; Main action: Break proteins and peptides into smaller products.

Brush border disaccharidases

Source or site of action: Small intestinal epithelial surface; Main action: Produce absorbable monosaccharides.

Peptidase

Source or site of action: Brush border and inside absorptive cells; Main action: Complete peptide breakdown.

Pancreatic lipase

Source or site of action: Small intestine; Main action: Produces fatty acids and monoglycerides from triglycerides.

Glucose and galactose absorption

enter absorptive cells with sodium through cotransport.

Fructose absorption

enters by facilitated diffusion.

Carbohydrate transport to liver

These sugars leave the cells, enter intestinal capillaries, and travel through portal blood to the liver.

Lactase

splits lactose at the brush border.

Low lactase activity

unabsorbed lactose retains water and undergoes bacterial fermentation, which can produce watery stool, gas, and bloating.

Protein digestion

Pepsin starts protein digestion in the stomach. Pancreatic proteases continue the process in the small intestine. Brush border and intracellular peptidases produce amino acids.

Amino acid transport

Amino acids leave mainly through intestinal blood capillaries and portal circulation.

Fat emulsification

Bile salts and mixing disperse fat droplets.

Lipase

generates fatty acids and monoglycerides, which associate with micelles for delivery to the epithelial surface.

Chylomicrons formation

Inside the absorptive cell, long-chain lipid products are rebuilt into triglycerides and packaged with other lipids and proteins into chylomicrons.

micelles

carry lipid products within the intestinal lumen.

Shorter-chain fatty acids

can enter portal blood more directly.

Chylomicrons

form inside intestinal cells and transport absorbed lipids through lymph and blood.