The Gastrointestinal System Flashcards
What are the functions of the intestinal system?
→ Ingestion
→ Mechanical processing
→ Movement of food
→ Chemical digestion
→ Absorption
→ Excretion
→ Mechanical processes e.g. mashing
→ Digestion
What is the mucosa?
It is the inner lining of the digestive tract.
○ Mucous membrane – epithelium & lamina propria
What is the function of the Muscularis externa
Peristalsis
What is the serosa and its function?
Epithelium moistened by glandular secretions
Lamina propria contains blood vessels, smooth muscle cells, nerve endings, also contains secretory cells where appropriate –contains 2 sheets of muscle cells at 90 deg to each other (inner layer circular muscle, outer layer longitudinal muscle). Contractions in these muscles alter the shape of the lumen
Serosa is a serous membrane that covers most of the m. externa
What is the submucosa?
Submucosa – dense layer of connective tissue binding mucosa to muscularis externa. Also contains exocrine glands which secrete buffers and enzymes into gut lumen
muscularis externa also has two layers of muscles to move food along the digestive tract
What is the mesentery
A fold of membranous tissue that arises from the posterior wall of the peritoneal cavity and attaches to the intestinal tract. Within it are the arteries and veins that supply the intestine
What is the pharynx?
· Throat
· Shared by digestive & respiratory system
· Nasopharynx lined by ciliated columnar epithelium
○ Eustachian tube-from middle ear, opens into nasopharynx
○ Pharyngeal tonsil-adenoid
· Oropharynx
○ Epiglottis
○ Squamous epithelium
· Laryngopharynx
○ Connects to oesophagus
○ Squamous epithelium
What is the Oesophagus?
-25 cm long hollow muscular tube
-Transports solids/liquids from pharynx to stomach
-Enters abdominal cavity through oesophageal hiatus in diaphragm
-Mucosa & submucosa in large folds
-Squamous epithelium
What is the stomach?
- 4 functions
-Storage of food
-Mechanical breakdown of food
-Chemical breakdown of food
-Production of intrinsic factor
o Chyme is a mixture of ingested food and stomach
secretions
4 regions
-Cardia
-Fundus
-Body
-pylorus
Stomach- what is the region named the cardia?
Abundant mucous glands, secretions protect oesophagus from stomach acids/enzymes
Stomach- what is the region named the fundus?
Sits against the diaphragm
Stomach- what is the region named the body?
Mixing tank, gastric glands secrete acid/enzymes
Stomach- what is the region named the Pylorus
Pyloric sphincter regulates release of chyme into duodenum
What are rugae?
Stomach has lots of folds called rugae which allow it to expand. When the stomach is empty it contracts to a narrow muscular tube but can expand to accommodate 1.5 litres of material
What does the small intestine do?
Digests and absorbs 90% of the nutrients
Describe the structure of the villi.
-Extensive network of capillaries
-Carry nutrients via hepatic portal vein to liver
-Absorption of nutrients
-Villi are mobile-contractions of muscularis mucosae
-Increases absorption
-Goblet cells secrete mucus
-Lacteal transports material that cannot enter blood capillaries such as fatty acids. These combine with proteins and are then too large to diffuse into the bloodstream.
-Lacteals drain into the lymph system and this then enters the venous circulation at the left subclavian vein
What is the function of the pancreas?
- Produces digestive enzymes & buffers
What is the function of the large intestine?
- 10% absorption occurs here
- Reabsorption of water
- Bacterial residents produce vitamin K, biotin & B5
- Bilirubin converted to urobilin/stercobilin
What are the chemical events of CHO digestion and absorption?
- Salivary amylases break down starch into di and tri-saccharides
- Pancreatic a-amylase breaks down remaining complex CHO
- Maltase/sucrase/lactase in brush border convert disaccharides to monosaccharides
- Monosaccharides absorbed into bloodstream by facilitated diffusion & cotransport mechanisms
What are the chemical events of lipid digestion and absorption?
- Lingual lipase & pancreatic lipase
- Break down triglycerides into fatty acids & monoglycerides
- Bile salts improve digestion by emulsifying the lipid into tiny droplets
- Micelles form
- Diffusion of lipids across plasma membrane
- Chylomicrons diffuse into lacteal
What are the chemical events of protein digestion and absorption?
- Only occurs after food has been mechanically processed
- First protease to act is pepsin (pH 1.5-2.0)
- Pancreatic proteases – trypsin, chymotrypsin, elastase, carboxypeptidase
- Amino acids absorbed into bloodstream by facilitated diffusion & cotransport mechanisms
Proteins are complex structures so digestion is complex. Can only occur after the 3D structure of food has been disrupted eg chewing, action of HCl in the mouth and stomach
Carboxypeptidase removes C terminal amino acids regardless of what it is, so produces free amino acids
What are the chemical events of water absorption?
- Inactive process occurring along an osmotic gradient
- Osmotic equilibrium must be maintained
- Intestinal cells continuously absorb nutrients & ions
- Solute conc. in lumen decreases
- Causes water to move out of lumen into surrounding tissues
What are the chemical events of ion absorption?
- Na ions – absorbed by diffusion, co-transport or active transport
- Ca ions - active transport
- Lipid-soluble vitamins ADEK – absorbed from micelles with dietary lipids
- Water-soluble vitamins B & C – absorbed by diffusion across epithelium
- Exception vitamin B12 – is absorbed by active transport when bound to intrinsic factor
What are age related changes in the gastrointestinal system?
- Rate of proliferation of epithelial stem cells declines
- Smooth muscle tone decreases
- Cumulative damage to GIT
- Cancer rates increase
- Dehydration
