Digestive System 2 Flashcards
Describe the oesophagus?
A muscular tube about 25cm long, extending pharynx to stomach, travels posterior to the trachea, tube is normally empty with its lumen collapsed, and expands to accomodate food/water
Functions of the oesophagus?
Transport (travel time 5 seconds for food, 1 second for fluid, due to peristalsis)
Protection
No absorption, little secretion, no digestion
Differences in the oesophagus to the four layers of the gut tube?
- Epithelium of mucous membrane
- External muscle
- Serosa
What is the epithelium of the mucous membrane like?
- thick many layered (stratified squamous) with sacrificial outer layers for protection against abrasive fragments
- cells are replaced by division in basal layers, then slow migration outwards. Old cells are shed from the surface. Entire epithelium is renewed every 7 days
What is the external muscle in the oesophagus like?
Contains, in addition to the usual smooth muscle, some skeletal muscle in the upper third of the oesophagus to allow rapid contraction and voluntary control of swallowing
Does the oesophagus have a serosa?
No. Over most of its length the oesophagus does not lie in a body cavity, so lacks a serosa- instead, it is covered with a fibrous adventitia which attaches it to neighbouring organs eg trachea
What does the stomach look like?
A j-shaped bag on the left side, an enlargement of the gut tube. About 1.5 litre capacity
Function of the stomach?
Storage, since food can be eaten more quickly than it can be digested and absorbed
Regions of the stomach?
Four; cardia, fundus, body, pylorus
What’s at the outlet of the stomach?
A well developed muscular pyloric sphincter
What’s the stomach like when empty?
Lines with longitudinal folds
Differences in the stomach to the typical four layers of the gut tube?
- Epithelium of mucosa; forms many pits lined with mucus-secreting cells, plus gastric glands which open into pits
- External muscle; three layers rather than two (with addition of innermost oblique layer)
Functions of the stomach?
- Secretion of acid, enzymes, mucus (total volume 2-3 litres per day). Food+gastric juices= chyme
- Digestion of protein by pepsin (active form of enzyme)
- Absorption of water, ions, some drugs (aspirin, alcohol)
- Transport (mixing waves, every 20 seconds)
- Protection (against its own secretion and microbes)
Purpose of surface mucous cells?
To secrete insoluble alkaline mucus which protects the mucosa from acid and pepsin
Purpose of undifferentiated cells?
Stem cells dividing to generate new epithelium
Purpose of parietal cells?
To secrete HCl which kills microbes and living cells. Also secretes intrinsic factors, important for absorption of B12
Purpose of mucous neck cells?
Secrete soluble acid mucus at meal times
Purpose of chief cells?
Secrete pepsinogen (inactive form of pepsin) and gastric lipases. Pepsinogen is converted into the protein splitting enzyme pepsin by acid in the lumen of the gland
Purpose of gastric cells?
(Enteroendocrine)
Gastrin enters the bloodstream as a hormone, stimulates secretion of acid and pepsinogen, increases muscular contractions of stomach releases pyloric sphincter
What precedes chief cells?
Mucous neck cells then stem cells
Two parts of mucosa of stomach?
Gastric pit (upper) Gastric gland (lower)
What is the liver made of?
Epithelial cells (hepatocytes) derived from embryonic endoderm
What carries out liver function?
Hepatocytes
What are hepatocytes and what do they do?
Multitalented cells which perform more than 500 different metabolic functions, including: glycogen/glucose storage and release, recycling of red blood cells, bile synthesis and secretion, synthesis of plasma proteins and removal of toxins from blood
What do hepatocytes require?
Access to nutrient-laden blood drained from the intestinal wall
Access to oxygenated blood from the systemic circuit
Access to ducts which drain bile to the gall bladder
What do fenestrated endothelial cells of the liver sinusoid do?
Act as a filter and allow passage of the watery part of the blood (lymph) but exclude red blood cells
What in the liver is like a brick?
Hepatocytes
What is a plate of hepatocytes stacked together called?
Liver lobules-each lobule is hexagonal in cross-section, about 2mm long by 1mm wife
Where is outgoing bile from in the liver lobule?
Canaliculis leading into the bile duct
