Lecture 6.2: The Intestines Flashcards
What are the 3 parts of small intestine?
Duodenum
Jejunum
Ileum
How long is the Duodenum?
25cm
How long is the Jejunum?
2.5m
How long is the Ileum?
3.5m
What are the 4 parts of the large intestine?
Cecum
Ascending Colon
Transverse Colon
Descending Colon
Cells of the Mucosa (5)
- Enterocytes
- Goblet Cells
- Paneth Cells
- Stem Cells
- Enteroendocrine Cells
What is the role of Enterocytes?
Absorption via microvilli (brush border)
What is the role of Goblet Cells?
Secrete mucus
What is the role of Paneth Cells?
Secrete defensins
Protect against infection and regulate the gut microflora
What is the role of Stem Cells?
Undifferentiated
New source of cells – turnover of cells~ 5days
What is the role of Enteroendocrine Cells?
In the crypts
Secrete a range of neuroactive compounds
Why are the 3 things intestinal motility is needed for to achieve?
- Mixing of luminal contents
- Ensuring that luminal contents contact with absorptive
surfaces - Ensuring forward movement of luminal contents
What is Segmentation? What is its role?
- Mixing and exposure to absorptive surfaces
- A discontinuous, alternate contraction and relaxation
of small intestine
What is Peristalsis? What is its role?
- Propulsion of liminal contents towards the anus
- Longitudinal followed shortly after by circular
contraction, longitudinal relaxes before circular muscle
– slow but steady wins the race!
Glucose then transported out of enterocyte via which GLUT transporter?
GLUT2
How is Fructose absorbed?
Via sodium independent facilitated diffusion via the GLUT5 carrier
Uptake of amino acids and peptides, what transport systems have been identified? (5)
- Neutral amino acids and methionine
- Cationic amino acids (arginine, histidine, lysine)
- Acidic amino acids (glutamate, aspartate)
- Proline
- Glycine
In what part of the small intestine are protein products principally absorbed?
Duodenum and Jejunum
How are lipids absorbed from the intestines?
- Pancreatic lipase results in the production of
monoglycerides and FFAs - These aggregate (with bile salts and phospholipids) to
form micelles - The micellar core (non-polar) also contains cholesterol
and fat soluble vitamins - Micelle ‘enters’ the brush border and contents diffuse
passively into the enterocytes (bile salts remain
outside – join the EHC) - Inside enterocytes TGs are reformed in the SER –
aggregate to form chylomicrons - These leave via exocytosis and ultimately enter
lacteals of villi which drain into venous circulation
How are lipids absorbed from the intestines?
- Pancreatic lipase results in the production of
monoglycerides and FFAs - These aggregate (with bile salts and phospholipids) to
form micelles - The micellar core (non-polar) also contains cholesterol
and fat soluble vitamins - Micelle ‘enters’ the brush border and contents diffuse
passively into the enterocytes (bile salts remain
outside – join the EHC) - Inside enterocytes TGs are reformed in the SER –
aggregate to form chylomicrons - These leave via exocytosis and ultimately enter lacteals
of villi which drain into venous circulation
What 2 oxidation states does iron exist in in the body?
Fe2+ (ferrous) and Fe3+ (ferric)
What reduces reduces Fe3+ to Fe2+? What effect does this have?
- Vitamin C
- It is less likely to form insoluble complexes
What reduces Fe3+ in the duodenum?
Reduced by the brush border enzyme ferric oxidoreductase
Fe2+ is taken up via the …… transporter
DMT1
How does iron leave the intestines?
- Leaves via the basolateral transporter ferroportin
(converted to Fe3+ and binds to transferrin in blood) * Removed from blood via RME - Binds to apoferritin to form ferritin
What transporters facilitate calcium uptake in the intestines?
Enter down a concentration gradient via TRPV5 and TRPV6 channels
How does calcium leave the intestines?
- Inside, Ca2+ binds to calbindin
- Moves to basolateral membrane and exists via a Ca2+
ATPase pump (sodium-calcium exchanger NCX1,
plasma membrane calcium exchanger PMCA1b)
B12 is released from….by pancreatic proteases
Haptocorrin
Poor absorption of vitamin B12 can be due to? (4)
- Stomach damage
- Autoimmune damage to secreting cells
- Gastritis/peptic ulceration
- Terminal ileum removed
Effects of B12 malabsorption
Leads to Pernicious anaemia - Red cell production compromised
What are Haustrations?
Small pouches caused by sacculation, which give the colon its segmented appearance
Process of Defecation (7 Steps)
- Stretch of the rectum initiates impulses in pelvic
cholinergic nerves - These transferred to the sacral spinal cord
- Subsequent transmission to higher centres allows the
decision to defecate (or not) - This is done by voluntarily relaxing the external anal
sphincter - The external anal sphincter is made of smooth muscle
- this relaxes as a response to distension
- Breathe in, closure of the glottis, increased
intrathoracic and abdominal pressure - Relaxation of pelvic floor muscles – faeces expelled
What is Transmural Inflammation?
Inflammation that causes the bowel wall to thicken and in some cases (but not all) the lumen to narrow
What are Bowel Adhesions?
They are irregular bands of scar tissue that form between two structures that are normally not bound together
What is the Erythrocyte Sedimentation Rate (ESR)?
- An ESR is a blood test that that can show if you have
inflammation in your body - If an ESR test shows that your red blood cells sink
faster than normal, it may mean you have a medical
condition causing inflammation
