Digestion 2: eosphagus to liver Flashcards
What is the general appearance/location of the oesophagus
It is a 25cm long muscular tube from the pharynx to the stomach. Dorsal to the trachea. Has collapsed lumen when empty which stretches to accomodate food
What are the major functions of the oesophagus and what major differences in the oesophagus tunic layers reflect this
Function:
1. Protection: Epithelium:
This is stratified squamous epithelium for protection against abrasive fragments of food.
-gets regenerated by basal layers, renewed each week
- Transport: Has an additional layer to smooth muscle of skeletal muscle in the upper third of the oesophagus to allow rapid contraction and voluntary swallowing.
- – Has a fibrous adventitia which attaches it to trachea etc
Describe the general structure of the stomach including 4 regions
J shaped bag with 1.5 litre capacity.
Has 4 regions:
1. Cardia: Entrance containing Mostly mucous glands
2. Fundus (top above cardia) and
3. Body : (main section) that both secrete acid, enzymes and mucous
4. Pylorus Exit with mostly mucous glands.
What are the interesting muscle features of the stomach (not related to differences in the tunic)
There is an thickening of the internal circular smooth muscle at the exit of the stomach called the Pyloric sphincter. This controls the rate and volume of chyme exiting.
The walls are also lined with transient longitudinal folds called rugae, only present when empty.
What are the major functions of the stomach and what major differences in the stomach tunic layers reflect this
Primary function is storage
Epithelium of mucosa form many pits lined with mucus secreting cells, and glastic glands which open into the gastric pits. This helps with the
1. Secretion of acid, enzymes and mucus making chyme
2. Digestion of proteins by pepsin
3. Absorption of water, ions, and some drugs
4. Protection: against its own secretions and microbes
There is the addition of an innermost oblique layer of smooth muscle to the Muscularis externa to generate mixing waves - 5. Transport
What are the cells in the gastric pit and neck of the stomach and what is their function
- Surface mucous cells
-> they secrete insoluble alkaline mucus which protects the mucosa from acid and pepsin
Neck : Mucous neck cells : secrete soluble acid mucous at mealtimes
What are the cells in the gastric glands of the stomach (from lumen to base) and what is their function
- Undifferentiated stem cells which divide to create new epithelium
- Parietal cells that secrete H+ and Cl- to sterilise the food and acidify the environment –> allow activation of enzyme digesting protein. It also secretes intrinsic factor which is important for absorption of vit B12~ and therefore RBC haematopoesis.
- Chief cells: secrete Pepsinogen and gastric lipase
Pepsinogen is converted into pepsin by the acid in the gland lumen. - Gastrin cells: release hormone gastrin into the blood stream which stimulates secretion of acid and pepsinogen, increases muscular contractions of the stomach and relaxes the pyloric sphincter
What stimulates gastrin cells and are they exocrine or enterendocrine
They are enteroendocrine and are stimulated by stomach distension and change in pH when you eat food
What are the two cells of the gastric pit that produce products for digestion and how do they stop autodigestion
The parietal cells -produce the acid HCl and intrinsic factor. To stop autodigestion: secretes HCl as H+ and Cl- ions
The chief cells secrete pepsinogen and gastric lipase but it stop autodigestion: by secreting a precursor to the protein digesting Pepsin enzyme that is only activated in the lumen of the gland.
Also autodigestion is stopped by alkaline mucous of the surface mucous cells which protects from the acid and the pepsin
List the main functions of the liver
- Synthesis of bile salts for emulsifying lipids
- Metabolism of carbs, protein and lipids (glycogen storage and release)
- Phagocytosis of rbc, wbc and some bacteria.
- Storage of vitamins/ minerals+ activation of vit D
- detoxifying drugs
What cells carry out the functions of the liver and what do they require to do this
Hepatocyte which are the epithelial cells from embryonic endoderm do all the functions.
They require:
1. access to nutrient laden blood drained from the intestinal wall
2. access to oxygenated blood from the systemic circuit
3. Access to ducts which drain bile to the gall bladder
How are the hepatocytes placed in relation to the blood spaces around them
Hepatocytes are arranged in lins (plates) extending from the central vein of the lobule. There are sinusoidal capillaries in between them and they are very dilated (>1 RBC) and leaky.
What is between the hepatocyte and the blood in the sinusoidal capillaries (from hepatocyte side) and the function of these features
- hepatocyte microvilli-> for increasing SA for transport,
- The lymph space of Disse (contains filtered lymph)
- Endothelial cell of the sinusoid–> fenestrated to exclude RBC from blood plasma.
How are the hepatocytes placed in relation to the bile spaces around them
The bile produced by the hepatocytes go to Bile canaliculi which are small tunnels between the tight junctions of neighbouring hepatocytes. The canaliculi lead to ductules, ducts and then common hepatic duct
Describe the structure of a liver lobule
This is hexagonal stack of plates of hepatocytes, with a central vein in the centre and branches of the hepatic artery and hepatic portal vein on the outer border. These feed towards the central vein. However the bile produced by the hepatocytes will drain away from central vein into a tributary of the central duct on the outer border.
