The Gastrointestinal Tract Flashcards
What are the 3 key processes in digestion
Mechanical digestion, chemical digestion and microbial digestion
What is the mechanical digestion
Digestion via mastication and muscular movements from mouth to anus
What is chemical digestion
Hydrolysis by enzymes
What is microbial digestion
Digestion via enzyme produced by gut microorganisms in colon
What is the gross structure of the GI tract
- muscular tube with central lumen, with 4 major layers
What are the 4 major layers of the digestive tract
Mucosa, submuscisa, muscularis externa and serosa
What is the Mucosa layer
Epithelial cells
What is the submucosa
Connective tissue beneath mucosa containing large blood vessels, lymphatic vessels and exocrine glands
What is the muscularis externa
Layer beneath submucosa that is dominated by smooth muscle in two layers (circular layer and longitudinal layer) involved in mechanical processing of molecules
What is the serosa
Layer of visceral peritoneum that covers muscularis externa, dense network of collagen fibres that firmly attaches digestive tract to adjacent structures
How many pairs of salivary glands are there in the mouth
3
What regulate saliva production in the mouth
Acetylcholine secretion/ parasympathetic stimulation
What enzymes are secreted by the salivary glands
Salivary alpha amylase and lingual lipase
Which salivary gland secretes salivary alpha amylase
Parotid gland
Which salivary gland secretes lingual lipase
Von ebners gland
What regulates the passage of food in the oesophagus
Epiglottis and cardiac sphincter
What is peristalsis
Rhythmic contraction of smooth muscle
Why is peristalsis important in the oesophagus
Ensures one way movement of food from mouth to stomach
What do chief cells secrete in the stomach
Gastric lipase and pepsinogen (zymogen)
What do parietal cells secrete in the stomach
Hydrogen and chloride ions (gastric acid as passively followed by water)
What regulates gastric acid secretion in the stomach
Histamine, gastrin and acetylcholine (from vagus nerve)
What is the gastric pit
Invagination in the stomach where specialised cells are located
What are the specialised cells in the stomach
Parietal cells, chief cells and G cells
How is pepsinogen activated (into pepsin)
HCL secreted by parietal cells cleaves pepsinogen secreted by chief cells to pepsin (active form)
What are the digestive accessory organs
The Liver and pancreas
What stimulates the secretion of bile (liver) and pancreatic digestive enzymes (pancreas)
CCK and secretin
What is the key function of the liver in digestion
Synthesis of bile salts from cholesterol
What is the function of the gall bladder
Storage of bile acids
What stimulates the release of CCK
Food entering the duodenum
What two cells types are in the pancreas
Exocrine (enzymes) and endocrine (hormones)
What are the cells in the pancreas that secrete digestive enzymes
Acinar cells
What are the crypts of lieberkuhn
Intestinal crypts at base of villi in the small intestine
What are CBC stem cells
Stem cells located at base of villi (crypts of lieberkuhn) that differentiate into specialised epithelial cells
What are paneth cells
Specialised epithelial cells at base of villi that have immune function
What are enterocytes
Specialised epithelial cells
What are enteroendocrine cells
Specialised epithelial cells
that secrete hormones
What are goblet cells
Specialised epithelial cells that secrete mucus
What are tuft cells
Specialised epithelial cells with immune function
What is the hepatic portal vein
Transports blood from GI tract, pancreas, gallbladder and spleen to liver to supply metabolic substrates and for detoxification of ingested toxins
What is the caecum
Small pouch on the right side of ascending colon that is a reservoir for chyme
What is the appendix
Tube like structure connected to caecum that is a reservoir for beneficial gut bacteria to repopulate gut flora and immune system
What is the Ilecocaecal valve
Valve separating small and large intestine
What are the three main components of the large intestine
Ascending, transverse and descending colon
What are the three components of the small intestine
Duodenum, jejunum and ileum
What is the function of the large intestine
Microbial digestion of nutrients not digested and absorbed in the small intestine ( e.g. dietary fibre)
What is the symbiotic relationship in the large intestine
We provide environment for growth and nutrients and gut microorganism facilitate digestion of beta bonds
What is the rectum
Long chamber at the end of the descending colon that descending colon does
What stimulates defaecation
Entry of stool into rectum
What is the anus
Anal sphincter regulates stool leaving the body (egestion)
What does the central core of chylomicrons contain
Triacylglycerides and cholesterol esters
What does the outer membrane of chylomicrons contain
Phospholipid monolayer, free (unesterified) cholesterol and apoproteins
How are lipids absorbed in the small intestine
- bile salts from liver coat fat droplets and emulsify them
- pancreatic lipase and co-lipase break down fats into monoglycerides and FA stored in micelles
-monoglycerides and fatty acids move out of micelles and diffuse into epithelial cells, cholesterol is transported into cells - absorbed fats reassemble and combine with cholesterol and protein in chylomicrons
- chylomicrons are removed by the lymphatic system
What is the difference between the apical and basolateral membrane the epithelial cells of the small intestine
Apical- facing lumen of small intestine
Basolateral- facing hepatic portal vein
How is glucose absorbed in the small intestine
-Na+ bind to SGLUT1 (sodium dependent glucose transporter) on apical membrane enabling glucose/galactose to bind and be cotransported into the entereocyte
- Glucose is transported out of cell to hepatic portal vein by GLUT2
-Sodium potassium pump actively transports Na+ out of cell by exchange with k+ (energy dependent)
Why is fructose absorption not energy dependent
sodium independent GLUT5 transported transports fructose into cell instead of SGLUT1 so Na+/K+ pump not need
How are amino acids absorbed in the small intestine
Na+ dependent AA transporter on apical membrane co transports AA with Na+ into cell
X Na+/K+ pump maintains Na+ concentration gradient (energy dependent)
Facillitative AA transfer on basolateral membrane transports AA to hepatic portal vein
How are di and tripeptides absorbed in the small intestine
- Hydrogen-dependent di- and tri-peptide transporter (PepT1) on apical membrane cotransports
- energy dependent as Na+/ H+ pump (apical membrane) removes H+ from cell and then Na+/K+ pump (requires ATP) actively transports Na+ out of cell (basolateral membrane)
- Intracellular peptidases hydrolyse do and tripeptides → amino acids
-Facilitative amino acid transporter on basolateral
membrane, AA enter hepatic portal vein
