Tri B - Gastrointestinal System Flashcards
Name the parts of the digestive system
Mouth & pharynx
Oesophagus
Stomach
Small and large intestine
Accessory organs -
Teeth, tongue and salivary glands
Liver, gallbladder pancreas
What is the function of the GI tract?
Breakdown and absorption of food
Mechanical digestion = chewing swallowing
Chemical digestion = large molecules –> small molecules
Describe the process of absorption
Products of digestion
–> absorbed by epithelial cells in wall of gut
–> nutrients transferred to blood vessels
–> nutrients delivered to tissues
Describe the wall of the GI tract
Mucosa - inner layer of epithelium
Submucosa - connective tissue, vessels, glands
Muscularis - Smooth muscle layer
Describe the mucosa
Absorptive & secretory function
Lamina propria –> connective tissue, vessels, supportive
Muscularis mucosae - inner muscular layer
Describe the muscularis
Inner circular layer –> contraction narrows gut
–> outer longitudinal layer
contraction shortens the gut
What is the function of the mouth?
Food ground by teeth –> mastication
Food mixed with saliva
Tasting of food
What is the structure and function of the oesophagus?
Collapsible muscular tube
Transports food to stomach
Secretes mucus
Food propelled by peristalsis
What is the function of the lower oesophageal sphincter?
Controls entrance to stomach
Ring of smooth muscle
Prevents acid reflux
Describe peristalsis
Contraction and relaxation
Waves of contraction propels food
What is the function of the stomach?
Stores food
Mechanical and chemical digestion
Peristalsis
Describe the anatomy of the stomach
Cardia - mucus glands
Fundus and body - secretes HCl and enzymes
Pylorus - pyloric sphincter controls exit
Describe the cells of the stomach
Mucus surface & neck cells - secrete mucus
Parietal cells - secrete HCl - acidic environment
Chief cells - secrete pepsinogen & gastric lipase
Entereo endocrine cells - secrete gastrin
What is the function of the liver?
Metabolism of: Carbohydrates, lipids, proteins
Bile synthesis - extraction of bilirubin
Vitamin storage and activation of vitamin D
What is the function of the pancreas?
Secretes pancreatic juice –> buffers acidic chyme
Contains digestive enzymes: Pancreatic amylase
- Trypsin chymotrypsin
- Pancreatic lipase
Release of enzymes controlled by hormones; secretin, cholecystokinin
Describe the biliary system
Bile produced in liver, stored in gallbladder
Consists of water, bile salts, bile pigments, bilirubin
Control is hormonal - CCK
Stimulus is chyme in duodenum
What is the function of the small intestine?
Digestion and absorption of products and water
Describe the structure of the small intestine
Duodenum - mixes chyme with pancreatic and liver secretions
Jejunum - most digestion and absorption
Ileum - absorbs vitamin b12
Large surface area
1. long - 4.5-6.5m - circular folds
2. Villi - increase absorption
3. Microvilli - folds increase surface area
Describe the large intestine
Consists of: caecum, colon, rectum, anus
Completes food and water absorption
Forms and expels faeces
Presence of bacteria
Describe the journey of the products of digestion
Products of digestion
–> epithelial cells
–> blood or lymph
–> tissues
Describe the digestion of carbohydrates
Carbohydrates
–> digestion
–> polysaccharides
–> di- and tri- saccharides
–> monosaccharides (glucose, fructose, galactose)
Describe absorption of carbohydrates
Glucose and galactose absorbed by secondary active transport
Co-transported with sodium ions
Both have to bind to transport protein
Moves down concentration gradient
Describe the digestion of proteins
Proteins
–> peptides (by pepsin)
–>Amino acids (by pancreatic enzymes)
Describe absorption of proteins
Amino acids absorbed by secondary active transport with sodium or hydrogen ions
Some will share same transport systems
Describe the digestion of lipids
Triglycerides (fats)
–> monoglycerides and 2 fatty acids
Describe lipids
Hydrophobic molecules
Form large droplets with small surface area
Bile salts can speed up digestion and absorption
Describe the effect of bile salts on lipids
They emulsify fats to form smaller droplets
Products = 1. Short chain fatty acids
2. Long chain fatty acids
3. Monoglycerides
2 and 3 bind with bile salts forming micelles
Bile salts are amphipathic
They surround 2 and 3, keeping them soluble
Describe micelles
Move to fill brush border of intestinal epithelium
–> Long chain fatty acids and monoglycerides diffuse out
Describe what happens to fatty acids when they are inside the cell
Reform into triglycerides
Combine with cholesterol and proteins to form chylomicrons
Chylomicrons expelled from cell by exocytosis
Describe lacteals
Lymphatic vessels associated with villus, drain back into blood
Absorb nutrients from gut
–> used as fuel
