GI Anatomy Flashcards
Components of the GI system
Main: Mouth, esophagus, stomach, SI, LI, rectum, anus
Accessory organs: Salivary glands, GB, liver, pancreas
Layers of the GI tract
- Mucosa (innermost layer): epithelial cells with high rate of replication
- Submucosa
- Muscular propia
- Adventitia (outermost layer)
Mouth
Digestion of food (mechanisms):
- Mechanical: teeth, tongue, swallowing
- Chemical: enzyme secretions throughout the digestive tract
Ex. Salivary enzyme amylase breaks down carbs. from polysaccharides to disaccharides, and is inactivated by gastric acid
Esophagus
A muscular tube that is hollow, flexible, and lined with mucosa and stratified squamous epithelial cells; it lies behind the trachea and heart
Sphincters:
1. Upper esophageal sphincter: VOLUNTARILY prevents food from entering the trachea
- Lower esophageal sphincter (“cardiac sphincter”): INVOLUNTARILY prevents stomach acid/contents from refluxing into esophagus
Stomach
J-shaped hollow viscera (1.5 L capacity) with four parts: (1) Fundus, (2) cardia, (3) corpus (body), and (4) pylorus
Sphincters:
- Lower esophageal sphincter
- Pyloric sphincter: regulates gastric emptying into the duodenum
Functions of the stomach:
- Motor: Storage, mixing, and emptying
- Secretory: Exocrine and endocrine
- Digestion of proteins and lipids
- Absorption of water and ions
Peristalsis
Wave-like motions of smooth muscle that occur both in the esophagus and other parts of the GI tract
Function: Propel food and substances through the GI tract in one direction
Secretory functions of the stomach
EXOCRINE:
1. Gastric acid: production is regulated by the ANS and gastrin (pancreatic delta cells and stomach); consists mostly of HCl (pH 1.5-3)
- Intrinsic factor: a glycoprotein that absorbs vitamin B12 in the ileum (prevents anemia); secreted by PARIETAL cells
- Pepsinogen: converted to pepsin by gastric acid to break down proteins; secreted by CHIEF cells
ENDOCRINE: Gastrin (stimulates the release of gastric acid, gastric motility, pancreatic secretions, and GB emptying)
Stages of gastric acid secretion
Phases:
1. CEPHALIC: Gastric secretion occurs before food enters the stomach from the sight, smell, thought, or taste of food; PARASYMPATHETIC APs are carried by CN X (vagus) nerves to the stomach (which stimulate gastrin secretion)
- GASTRIC: Swallowed food and semi-digested protein (peptides and amino acids) activate gastric activity (about two-thirds of gastric secretion occurs during this phase); ingested food stimulates gastric activity in two ways: by (1) stretching the stomach and by (2) raising the pH of its contents
- INTESTINAL: The duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes; the duodenum initially enhances gastric secretion, but soon inhibits it
SI
Primary role: Absorb nutrients and minerals (approx. 20 ft. long)
Components: (1) Duodenum, (2) jejunum, and (3) ileum
Duodenum
Immediately after the stomach, and separated by the pyloric sphincter
Ampulla of Vater; opening to:
- Pancreatic duct: supplies exocrine enzymes amylase, lipase, protease (breakdown of carbs., fat, and protein); and bicarb (neutralizes acidic chyme)
- Common bile duct: supplies bile from GB/liver (breakdown of fat)
Functions:
- Chemical breakdown of chyme by enzymes
- Regulation of stomach emptying
- Mucus secretion
Jejunum and ileum
Attached to the posterior abdominal wall by mesentery; Function: Majority of absorption
JEJUNUM: Absorption of sugars, amino acids, and fatty acids
ILEUM: Absorption of nutrients left over from the jejunum (especially B12 by intrinsic factor and bile salts); it connects to the cecum of the LI
SI secretions
Main secretions:
1. Mucus: protects duodenum from enzymes, acidic contents, and friction
- Amylase: converts complex carbs. to simple sugars (secreted by the pancreas)
Other secretions:
- Aminopeptidase, peptidase, and enterokinase (protein breakdown)
- Sucrase, maltase, isomaltase, lactase, lipase (sugar breakdown)
LI
Primary role: Reabsorb water and minerals (approx. 5 ft. long)
Additional roles: Formation and storage of feces, maintain microbiome, bacterial fermentation, bacterial synthesis of vitamin K (clotting), and inflammation
Components: Cecum, ascending, transverse, descending, sigmoid
Autonomic nervous system and GI
- SNS: INHIBITORY; Decreases gastric secretions and gut motility, increases sphincter tone, and constricts blood vessels
- Parasympathetic nervous system: EXCITATORY; Increases gastric secretions and gut motility, decreases sphincter tone (allows passage of food and secretions), and dilates blood vessels (encourages blood flow to absorb nutrients)
Liver
Largest internal organ (with two lobes) located in the RUQ; the hepatic duct of each lobe join with the cystic duct to form the common bile duct
Functions:
1. Synthesis: Proteins (albumin), clotting factors, and bile
- Degradation: Insulin, bilirubin, ammonia (into urea), and meds.
- Metabolism: Carbs. (glycogen) and lipids
- Storage: Glucose, B12, vitamin D, K, iron and copper
- Immunity against infections
