Gastrointestinal Flashcards
Ingestion
Acquisition of nutrients
Digestion
Mechanical and chemical breakdown of ingested food
Propulsion
Movement of food through GI tract (peristalsis and segmentation)
Secretion
Release of mucin, water, acid, and enzymes into the lumen of the digestive system
Absorption
Transport of nutrients from the digestive system to the circulatory system
Defecation
Elimination of feces
Parietal Peritoneum
Lines inner surface of body wall; is attatched to abdominal and pelvic walls; secretes peritoneal fluid and stores fat
Visceral Peritoneum
Wrapped around the organs within the Intraperitoneal space
Mesenteries
Folds of peritoneum that support the intraperitoneal GI tract organs; contains vessels, nerves and lymphatics
Intraperitoneal Organs
Organs suspended into the peritoneal cavity that are movable and contain mesenteries
Retroperitoneal Organs
Organs not suspended into the peritoneal cavity that are immobile and lack mesenteries
Hepatic Portal System
A network of veins that carries blood from the GI trct and spleen to the liver
Esophagus
Hollow 25cm muscular tube connecting the pharynx tto the stomach
Liver
Removes and adds compounds to the blood as it circulates through the lobule
Gallbladder
- Concentrates bile produced by the liver - absorbs Na+ and Cl- and water by osmosis
- Stores up to 450mL of bile (12hrs worth)
- Releases bile upon stimulation (PNS & CCK)
Pancreas
Produces hormones and enzymes
Epithelial cells sense the contents of the GI lumen via,
- Chemoreceptors
- Osmoreceptors
- Stretch receptors
Steps of Swallowing
- Bolus in mouth and upper esophageal sphincter is closed
- Glottis moves upward and closes and Epiglottis moves dowward and covers glottis
- Upper esophageal sphincter opens
- Wave of peristalsis travels along esophagus and upper esophageal sphincter closes
- Lower esophageal sphincter opens
- Secondary wave of peristalsis in esophagus.
Coordination of Muscular Contractions in Peristalsis
- Contraction of circular muscles behind food mass
- Contraction of longitudinal muscles ahead of food mass
- Contraction of circular muscle layer forces food mass forward.
Frequency and Amplitude of Peristalsis
Regulated by:
- Body temp and metabolic activity
- ENS and ANS
- Hormones eg. CCK
ENS
- Intrinsic
- Extrinsic
ANS
- Parasympathetic
- Sympathetic
Phases of Digestion
- Cephalic phase
- Gastric phase
- Intestinal phase
Cephalic Phase
Prepares stomach for food:
- Short (min)
- Mechanism: neural
- Actions: stimulation of mucus, enzyme and acid production –> increased volume of gastric juice
Gastric Phase
Stomach acts on food:
- Long (3-4hrs)
- Mechanisms: Neural, hormonal, local
- Actions: Chemical and mechanical digestion
Stomach
- Mechanical digestion and mixing of Proteins (HCl, Pepsinogen) and Fats (Gastric lipase)
- Storage 50mL-1.5L
- No absorbtion (except aspirin and alcohol)
Layers of Stomach Muscularis Externa
- Inner oblique
- Middle circular
- Outer longitudinal
Regions of Small Intestine
- Duodenum
- Jejunum
- Ileum
Small Intestine
The longest component of the GIT, Begins at pyloric sphincter and ends at ileocecal valve
Function:
- Digestion
- Absorbtion
Duodenum
‘C’ shaped tube
- Mixing bowl
- Chyme with bile and pancreatic secretions
- Longitudinal and circular smooth muscle
- Mucous membrane lining to buffer stomach acid
Secretions in Duodenum
Secretin and CCK control:
- Gastric emptying
- Accessory organs (Pancreas, gallbladder, liver)
Exocrine Pancreas Contains…
- Digestive enzymes
- Digestive enzymes as zymogens (inactive)
- Lipases and bile salts are pH sensitive
Digestive Enzymes
- Proteolytic enzymes
- Pancreatic lipase
- Pancreatic amylase
Digestive Enzymes as Zymogens (Inactive)
- Trypsinogen is activated by enteropeptidase
- Trypsin then activates other symogens
Lipases and bile salts are PH sensitive
- CF (Insufficient alkali)
- Gastrinomas (Excess acid production)
- Staeterrhea = fatty stools
Hepatic Portal System
- Liver recieaves all blood that passes through the stomach and intestines
- Metabolising gatekeeper (liver detox fads)
- Nutrient rich and oxygen poor
Detailed Functions of the Liver
- Metabolism of: carbohydrates, lipids, proteins
- Storage of vitamins and minerals
- Processing of drugs and hormones
- Phagocytosis of RBC, WBC and bacteria
- Makes bile
Bile Acids
Synthesised from cholesterol
Bile Contents
- Bile acids
- Water
- Ions
- Cholesterol
- Phospholipids
- Bilirubin
Gallstones
Crystallisation of bile
Jejunum and Ileum
Primary sites of absorption
Absorption of Electrolytes With Monosaccharides and Amino Acids
- All uses secondary active transport
- Nutrient absorption matched by Na+ absorption
- Matched to water absorption via osmosis
Large Intestine
- Extends from ileocecal sphincter to anus
- Tonic contraction of longitudinal muscles form pouches
4 Divisions of Large Intestine
- Caecum
- Colon
- Rectum
- Anal canal
Colon Physiology
- Storage
- Absorption of water and electrolytes
- Gablet cells (Mucous lubricate faeces and secrete HCO3)
- Bacteria ferment undigested carbohydrates and produce acid
Bacteria Support Immune and Antioxidant Functions
- > 700 species in large intestine
- Bacterial gas = N2, CO2, CH4, H2, H2S
- approx. 30% faecal mass is bacteria
Colon Motility
- Low Frequency segmentation (mixing)
- Mass movements - contraction wave toward distal colon
Defacation Reflex
- Mass movements (faecese to rectum)
- Distention
- Internal sphincter relaxes
- Colon contracts
- External anal sphincter controls defecation
