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GI > Physiology Of The Intestines > Flashcards

Physiology Of The Intestines Flashcards

0
Q

What happens in the duodenum?

A

Bile and pancreatic secretions added
HCO3 added to neutralise chyme
Osmotic movement of water in
Absorption of iron

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1
Q

What are the secretions of the small intestine?

A 
Protease
Carbohydrase
Secretin
Gastrin
CCK
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2
Q

How much iron is consumed each day?

A

20mg

In haem or related pigments (Fe2+)

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3
Q

What is required to dissolve the Fe complexes?

A

Gastric acid

Gastroferrin also dissolves them

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4
Q

How is iron absorbed?

A 
Gastric acid dissolves iron complexes
Mucosal cells secrete transferrin
This binds Fe2+ in the lumen
Complex is endocytosed by cells
Once inside, Fe2+ is liberated and exporter to the blood where it binds again to transferrin
Taken to bone marrow for RBCs
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5
Q

What happens in the jejunum?

A

Absorption of carbohydrates, amino acids, fatty acids, vitamins, calcium, sodium, chloride and water

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6
Q

What is starch made up of?

A

Amylose - straight chains with α-1,4 bonds

Amylopectin - branched chains with α-1,6 bonds at branches

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7
Q

What breaks the α-1,4 bonds in starch and what is released?

A

α-amylase
Yields glucose and maltose from amylose
Yields α limit dextrins from amylopectins

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8
Q

From what are α-amylases secreted?

A

Salivary glands

Pancreas

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9
Q

Where is the final breakdown to glucose completed from carbohydrates and what enzymes are used?

A 
In the brush border 
Enzymes
-isomaltase breaks α-1,6
-maltase converts maltose -> glucose
-sucrase and lactase
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10
Q

How is glucose absorbed from the small intestine?

A

Gradient set up by Na-K-ATPase
Glucose absorbed over apical membrane via SGLT1 (can also transport galactose). Requires sodium
Glucose across basolateral membrane via GLUT2 transporter

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11
Q

How is fructose absorbed?

A

Facilitated diffusion

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12
Q

Function of pepsin?

A

Breaks down proteins into oligopeptides in the stomach

Breaks bond near aromatic amino acid side chains

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13
Q

What enzymes does the pancreas secrete into the duodenum which are involved in protein breakdown? Which bonds does each break?

A

Trypsin - bonds near basic side-chains
Chymotrypsin - bonds near aromatic side-chains
Carboxypeptidase - C terminal amino acids with basic side chains

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14
Q

How are amino acids absorbed?

A

Taken up by active and passive processes
At least 5 Na/amino acid co-transporters
Done just like glucose

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15
Q

How are di- and tripeptides absorbed from the small intestine?

A

Di/atripeptides are taken up by an active mechanism associated with active pumping of H+ into the lumen.
Return of H+ by co-transport with the peptide

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16
Q

From where are amino acids absorbed in the gut?

A

All parts of the small intestine

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17
Q

How are fatty acids absorbed?

A

Micelles generate a high surface area for the action of lipases
Lipases cleave fatty acids from glycerol
Micelles carry the products to the unstirred layer
Fatty acids are released and diffuse into the epithelial cells
Once inside, FAs are reconstituted into TAGs and expelled as chylomicrons.

18
Q

How are water soluble vitamins absorbed?

A

Passive diffusion

19
Q

How much calcium is consumed and how much is absorbed?

A

6g consumed a day

700mg/day absorbed

20
Q

How is calcium absorbed?

A

Enters cells in the duodenum by facilitated diffusion
Pumped out of basolateral membrane by Ca-ATPase
Requires 1,25-dihydroxyvitamin D/calcitriol
Stimulated by parathyroid hormone

21
Q

What is absorbed in the ileum?

A

Vitamin B12

Amino acids

22
Q

Where in the ileum is B12 absorbed?

A

Terminal ileum

23
Q

How is B12 absorbed?

A

Requires a co-factor called intrinsic factor which is secreted by the stomach mucosa

24
Q

Clinical relevance of absorption of B12?

A

Pernicious anaemia occurs with a B12 deficiency because B12 is needed for RBCs
Can be caused by stomach damage/terminal ileum removal

25
Q

How long does it take food to pass through the large intestine?

A

About 16 hours

26
Q

What happens in the large intestine?

A

Absorption of water and any remaining absorbable nutrients
Vitamins K, B12, thiamine and riboflavin created by bacteria
Sends indigestible matter to the rectum

27
Q

What does the rectum do?

A

Stores and compacts faecal matter

28
Q

How does oral rehydration therapy work?

A

Contains sodium and glucose
Glucose stimulates uptake of sodium and generates a water gradient
Uptake of sodium generates an osmotic gradient which water follows

Therefore glucose and NaCl combination stimulates maximum water uptake.

29
Q

Why is segmenting done?

A

Gently agitates food so that it can move slowly through the intestines for maximum absorption

30
Q

Talk about location of intestinal pacemakers and how often they go off

A

Located along the length of the small intestine
There is one for each section
Frequency of each pacemaker decreases from the duodenum to the jejunum
12 times a minute -> 8 times a minute
‘Intestinal gradient’

31
Q

How do pacemakers cause segmentation?

A

Each one drives a small section of the small intestine
Causes intermittent contraction of smooth muscle along its length
Contractions separate the small intestine into segments where muscle is contracted and not contracted

32
Q

What is the effect of segmenting and intestinal gradient?

A

Segmenting on its own just mixes the contents

Intestinal gradient causes the net movement of contents in a caudal direction

33
Q

What are taenia coli?

A

3 distinct longitudinal layers of smooth muscle which run the length of the colon.
Begin at the appendix
Merge at the rectosigmoid junction into a continuous layer around the rectum

34
Q

What are the segments of the colon called?

A

Haustra

35
Q

How is Hautra shuttling done?

A

Contraction of smooth muscle in the walls of Haustra shuffles contents back and forth, as absorption of water and NaCl forms faeces
Slowly moves towards sigmoid colon with control like segmenting

36
Q

How often does the peristaltic propulsive pattern happen?

A

Once or twice a day

37
Q

Where does the peristaltic propulsive pattern travel from and to?

A

From the transverse colon to the descending colon

38
Q

What does the peristaltic propulsive pattern do?

A

Rapidly forces faeces into the rectum which is normally empty
Causes the urge to defacate

39
Q

What triggers the mass movement?

A

Gastrocolic reflex (eating)
Time of day
Thinking about it

40
Q

What are the anal sphincters made up of and under what kind of control?

A

Internal - smooth muscle. Parasympathetic control relaxes it

External - voluntary striated muscle. Voluntary control relaxes it

41
Q

How does the urge to defacate arise?

A

Mass movement fills the rectum
Pressure receptors give you the urge
Rectal muscle then forces faeces towards the anus

42
Q

How do you poo?

A

Relax both sphincters
Intra-abdominal pressure increases, forcing expiration, causes expulsion of faeces
Voluntary control of external sphincter is overrides if rectal pressure becomes too high

GI (21 decks)

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