Iii test 1 study guide

Definitions of RDA, EAR, etc in intro lecture

innervations (there’s 2) of the GI tract

intrinsic and extrinsic

Intrinsic innervation

The enteric nervous system located within the GI tract wall itself (“in-house” semiautonomous nerve supply)

Extrinsic innervation

Nerves from outside the GI tract: the autonomic nervous system

Extrinsic innervation divisions

Parasympathetic nervous system (PNS)

Enhances motility and secretory activity

Sympathetic nervous system (SNS)

Inhibits motility and secretion

Layers of tissue surrounding the GI tract and their roles

Mucosa, Submucosa, Muscularis externa, Serosa (or adventitia in esophagus)

Mucosa role

Submucosa role

Contains connective tissue, blood vessels, lymphatic vessels, lymphoid tissue, and nerves; involved in blood flow and secretions

Muscularis externa role

Responsible for peristalsis and segmentation

Serosa (or adventitia in esophagus) role

Outer protective covering; serosa reduces friction with surrounding organs, while adventitia anchors the esophagus to nearby structures

3 layers of the mucosa

• Mucosal membrane — Inner lining

• Lamina propria — Connective tissue and lymphoid tissue for immune protection

• Muscularis mucosa — Thin smooth muscle layer that helps create folds and local movement of the mucosa

Location of the 2 plexuses + secretions/substances needed for digestion

Myenteric plexus (Auerbach’s plexus) location

Between muscle layers of muscularis externa

Submucosal plexus (Meissner’s plexus)

In the submucosa

Myenteric = muscle/movement

Submucosal = secretion

Secretions and substances needed for digestion

with source and function

Salivary amylase

Source: Saliva; Function: Begins carbohydrate/starch digestion

HCl (hydrochloric acid)

Source: Parietal cells of stomach; Function: Lowers pH, denatures proteins, activates pepsin

Pepsinogen

Source: Chief cells; Function: Inactive precursor of pepsin

Pepsin

Source: Activated by HCl; Function: Digests proteins

Gastric lipase

Source: Chief cells; Function: Begins fat digestion

Mucus

Source: Mucous/goblet cells; Function: Lubricates and protects GI lining

Intrinsic factor

Source: Parietal cells; Function: Needed for vitamin B12 absorption

Gastrin

Source: Stomach wall; Function: Stimulates HCl secretion

Secretin

Source: Duodenal wall; Function: Stimulates pancreas to release bicarbonate-rich juices

Bicarbonate

Source: Pancreas; Function: Neutralizes acidic chyme

CCK (cholecystokinin)

Source: Intestinal wall; Function: Stimulates gallbladder to release bile and pancreas to release enzymes

Bile

Source: Produced by liver and stored in gallbladder; Function: Emulsifies fats

Pancreatic enzymes

Source: Pancreas; Function: Digest carbohydrates, proteins, and fats

Trypsinogen

Source: Pancreas; Function: Inactive precursor

Trypsin

Source: Activated in small intestine; Function: Digests proteins

Brush border enzymes

Source: Enterocyte membrane; Function: Final digestion of nutrients

anatomy of the enterocyte (which border is which)

Apical border / brush border, Basolateral membrane, Tight junctions

Apical border / brush border

Faces the intestinal lumen/food; Contains microvilli and digestive enzymes for absorption

Basolateral membrane

Faces blood/interstitial fluid; Nutrients exit enterocyte through this side

Tight junctions

Between enterocytes; Regulate permeability between cells

• brush border = enterocyte membrane on lumen side

• Contains the glycocalyx and digestive enzymes

Differences between fat-soluble and water-soluble vitamins

Differences between fat-soluble and water-soluble vitamins

Fat-soluble vitamins depend on fat digestion and bile

Water-soluble vitamins dissolve in water and absorb more directly