Jejunum and Ileum Flashcards
Describe the location and structure of the jejunum and ileum (simply)
Jejunum is found in upper left quadrant of abdomen. It has a thick intestinal wall. Has long vasa recata and few arcades
Ileum is found in lower right quadrant of abdomen. It has a thin intestinal wall. Has short vasa recta and lots of arcades
What is the blood supply to the intestines
Blood supply is via the superior mesenteric artery which splits into:
Jejunal and ileal arteries
Ileocolic, Right colic and Middle colic arteries - supply colon
Venous drainage is via superior mesenteric vein
What adaptations are there in the small intestine that allow for maximal absorption
Large surface area - mucosa folded into villi with the villi being covered in a brush border. Plicae circularis
Slow movement of contents - precise control in intestines
What cell types are found in the intestines
Enterocytes - absorptive cells. Have brush border and tight junctions between them
Goblet cells
Enteroendocrine cells
Stem cells - at base of crypts of Lieberkuhn
Paneth cells - produce antimicrobial peptides
What carbohydrates are broken down in the small intestine, what are they broken down into and what enzymes break them down
Starch -> glucose/maltose - amylase and isomaltase
Maltose -> glucose - maltase
Lactose -> glucose and galactose - lactase
Sucrose -> glucose and fructose - sucrase
Describe how CHOs are absorbed
N-K-ATPase on basolateral membrane creates concentration gradient
Na moves into the cell from the intestinal lumen down its concentration gradient via SGLT-1 along with glucose
GLUT2 transports glucose out of enterocyte so it can diffuse into the capillaries
Fructose enters enterocyte via GLUT5
Where does protein digestion start and by what enzyme
Protein digestion starts in the stomach by the action of pepsin which digests proteins into oligopeptides and amino acids
What major proteases are released from the pancreas and how do they work
Endopeptidases - break middle of peptide chains to produce shorter polypeptides. E.g. trypsin, chymotrypsin, elastase
Exopeptidases - break at ends of polypeptide chains to produce amino acids, dipeptides or tripeptides. E.g. carboxypeptidase (A&B)
How are amino acids, di- and tri-peptides absorbed in the intestine
Peptide transporter 1 - transports short peptides along with H+ into the enterocyte. H+ concentration gradient set up by NHE
Na-amino acids co-transporters - transport similar to glucose
How does oral rehydration work
Oral rehydration fluid contains a mixture of glucose and salt which stimulate maximum water uptake
Na uptake generates osmotic gradient -> water follows
Glucose uptake stimulates Na uptake
How does Na uptake differ in the small and large intestines
Na uptake on apical membrane is different:
In small intestines, Na is co-transported with other substances
In large intestines, Na channels induced by aldosterone aid water reabsorption
What channels drive water secretion
Cl channels
Name some causes of vitamin B12 deficiency
Terminal ileum problems
Lack of intrinsic factor
Hypochlorhydria
Inadequate intake of food
Inflammatory disorders of the ileum
What happens when a lactose intolerant person consumes lactose
Lactose cannot be absorbed by a lactose interolerant individual causing it to remain in the gut and create a high osmotic effect
This means water is not absorbed -> diarrhoea
Lactose is fermented in the gut producing flatus/bloating
What are the symptoms of IBS
Abdominal pain - often cramping
Bloating
Flatulence
Diarrhoea
Constipation
Rectal urgency
