Digestive System 2 Flashcards
What are the 3 parts of the small intestine from proximal to distal ?
- Duodenum- 25cm long
- Jejunum- 1m long
- Ileum- 2m long
What is the small intestine responsible for ?
The absorption of products of digestion into the blood and lymph
Describe the structure and organisation of the Duodenum
It forms a C-shape, wrapping around the head of the pancreas.
From top to bottom:
Superior part, descending part, horizontal part, ascending part.
Where is bile produced and stored ?
Produced by the liver and stored in the gall bladder
What does bile do ?
It is secreted continuously and acts as a surfactant and aids emulsification of fats within the chyme
What secretions from the pancreas enter the GI tract at the Duodenum?
Pancreatic juices and digestive enzymes are secreted intermittently
What happens when chyme enters the Duodenum?
- The sphincter guarding the Ampulla relaxes
- The gall blades contracts
- Bile and pancreatic juice exit into the duodenum and mix with the chyme
What is the principle site of nutrient absorption in the GI tract?
The jejunum and ileum
What is Peristalsis ?
Muscle contractions that move food through the digestive tract, controlled by Auerbach’s plexus
How are the jejunum and ileum specialised to increase surface area ?
- Plicae circularis (circular folds)- submucosa
- Villi- mucosa
- Microvilli- apical plasma membrane
What are Crypts of Lieberkuhn ?
Invaginations found between the villi, which contain stem cells that replace cells killed by the harsh environment in the small intestine
What are enterocytes ?
Intestinal absorptive cells specialised for breakdown and transport of small molecules derived from lipids, proteins and carbs
What is the effect of pernicious anaemia ?
There is an autoimmune attack on Parietal cells, leading to reduced production of intrinsic factor, so vitamin B12 cannot be easily absorbed in the ileum and defective erythrocytes form, causing anaemia
Where is the transition between the small and large intestine ?
Between the ileum and caecum
What is the entrance to the caecum guarded by ?
Ilio-caecal valve
How long is the large intestine?
1.6m
How is the large intestine structured from start to end ?
Appendix
Caecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
What is the main function of the large intestine ?
Absorption of ions and water
How many hours after eating does food reach the end of the large intestine? Then the rectum?
12 hours
24 hours into rectum
What happens when defecation is triggered?
- Contraction of the colon
- Relaxation of the involuntary anal sphincter
- Relaxation of the voluntary anal sphincter
What key histological transition occurs in the anal canal ?
From simple columnar epithelium of the intestines back to the stratified squamous non-keratinised epithelium
