Digestive system Flashcards
What are the 4 layers of the gut wall?
The mucosa
The sub-mucosa
The muscular externae
The serousa
What part of the gut in not intra-peritoneal?
The transverse colon- its retro-peritoneal
Anything superior to the diaphragm also.
Name the layers of the mucosa.
Epithelium
Lamina Propria
Muscularis Internae
What glandular secretion arises from the mucosa?
Mucous
What is the submucosa?
A layer of connective tissue that holds glands, arteries, veins and nerves.
What is the muscle arrangement in the muscularis externae?
Inner circular layer
Outer longtitudinal
What is the peritoneum?
The serousa that in invaginated by the gut. It consists of a connective tissue layer and simple squamous mesothelial cells.
What are the functions of the GI tract?
- Port of entry for food
- Mechanically disrupt food
- Temporarily store food
- Chemically digest food
- Kill pathogens
- Move food through it
- Absorb nutrients
- Eliminate watse
What things must we absorb from the GI tract?
Sugars Fatty acids Amino acids Minerals Vitamins
What is the role of the mouth?
Starts chemical digestion with amylases and lipase
physically disrupts with chewing.
What does saliva do?
Salvia is bacteriostatic , protects teeth, helps swallowing, protects the mouth and is alkaline. It is the first step in chemical disruption of our food.
Where are the fastest transit points in the GI system?
Oesophagus and rectum/ anus
Describe the muscularity though out the oesophagus.
Upper end is under voluntary control and contains skeletal muscle.
Lower down its smooth muscle which operates involunatrily.
This gives rapid peristaltic forces moving a food bolus to the stomach in 8-9 seconds even if upside down.
Describe the neural innervation of the oesophagus?
Sub-mucosal plexus
Myenteric plexus
What epithelium is normally found in the oesophagus?
Stratified squamous non-keratinised.
The oesophagus is not surrounded by serousa so what likes outside of the muscular externa?
Tunica adventitia.
Describe the chemical sorption of food in the stomach.
HCl gives pH of
Enzymes like pepsin break up food.
What roles does the stomach have?
Food store Receptive relaxation Rhythmic contraction Secretion of acid and enzymes Protection from self digestion - mucous secretion Make hypertonic chyme Control delivery of Chyme to duodenum
What are the macroscopic folds in the stomach called?
Rugae
How many layers of muscle are seen in the stomach’s muscularis externa?
3 layers of smooth muscle
Where do you find gastric pits?
Stomach
Whats the role of goblet cells in the stomach?
Secrete mucous to protect stomach from enzymatic degradation and pH damage. The mucous contains HCO3- to neutralise the H+.
Mucous is released in response to stretch, acidity and enzyme presence.
Alcohol and aspirin can harm these cells.
Outline the structure of the gastric pits.
The pit is at the top and island with mucous secreting cells.
The isthmus is the region of stem cell division to populate the gland by migrating up or down.
The parietal cells are spread from the isthmus down and secrete H+ into the lumen and HCO3- into local capillaries.
Chief cells around the base and are responsible for pepsinogen secretion.
Enteroendocrine cells include G cells and are found in the base of the pits and form the wider gastric mucosa that responds to hormonal control and secrete acid.
What is the duodenum?
C shaped proximal small intestine in close proximity to the pancreas.
What glands are found in the duodenum and whats their role?
Brunner glands secret bicarbonate rich mucous needed to neutralise the chyme.
What accessory organs are connected to the duodenum?
The liver via the gall bladder and biliary tree and the pancreas.
Whats the main roles of the duodenum?
Dilution - draw water in from ECF to make isotonic solution.
Neutralisation - Bile contains water, alkali and bile salts
- Pancreatic alkali
Degradation - Pancreas, liver and intestine make enzymes to complete chyme digestion.
What do enzymes from the pancreas and intestine do?
Cleave peptides
Cleave poly and mono saccharides
Breakdown and reform lipids
Break down nucleic acids
Where do we absorb nutrients and what kind of substance do we need in the GI tract to absorb?
Small intestine
Isotonic neutral solution
Is absorption active or passive?
Active
What do you need for good GI absorption?
Large surface area
Good contact time
Sufficient blood supply and drainage
Energy
In histology villi of the small intestine have a white lumen in the middle of them, what is this?
Lacteal which is a dilated lymphatic vessel.
What epithelial cell type is seen in the small intestine?
Simple columnar
What are the three areas of gut that make up the small intestine?
Duodenum, Jejunum and Ilieum
What is absorbed in the duodenum?
Iron
What is absorbed i the jejunum?
Sugars, AA, Fatty acids
What does the Ileum absorb?
Vit B12, bile acids and remaining nutrients
What else need to be absorbed after the ileum?
Water
Which anatomical structures form the large intestine?
Caecum, ascending colon, transverse colon, descending colon, sigmoid colon
Where do you find peers patches?
Small intestine
Where do you see crypts of Lieberkuhn?
Colon
How long is transit time in the large bowel?
20hrs to get water reabsorbed
Critical mass in the stretched rectum will give an urger to …… but higher centre control may initiate reverse ……
deficate
peristalsis
Why do we need bacteria in the colon?
Synthesis of Vit K, B12, thiamine and riboflavine.
break down bile salts
Convert bilirubin to non-pigmemented metabolite.
Where do we absorb most of the water from the GI tract?
Small intestine
How much water is exchanged in the GI tract?
14L
Why are diarrhoea and vomiting serious problems?
GI tract deals with a lot of water and its a delicate balance so if out of whack dehydration may occur or a systemic electrolyte imbalance.
How do we control motility and cut secretions?
Neural, paracrine and endocrine control
Which parts of the GI tract are under somatic control?
Mouth, upper 1/3 of oesophagus and then external anal sphincter.
The smooth muscle of the cut is controlled by post ganglionic plexus, where are they found?
Between muscle layers (myenteric plexus) and between the submucosa and the muscularis externa (submucosal plexus).
Give examples of paracrine substances in the GI tract.
Histamine - control acid secretion in the stomach
Vasoactive substances
What processed in the gut are controlled by hormones?
Secretion of acid in the stomach
Liver and pancreas alkali secretion
Enzyme secretions
What is the role of secretin?
Made by duodenum
Promotes HCO3- release from pancreas.
Promotes bile from liver.
Inhibits acid secretion in the stomach
What is the role of cholecystokinin?
Made by duodenum
Promotes pancreatic digestive enzyme release
Promotes bile release from gall bladder
Suppressed hunger
What is gastrin?
Made by G cells of the pyloric antrum of the stomach, the pancreas and the duodenum. Acts ti promote parietal cell HCl release.
