Physiology Of The Intestines

Question 0

What happens in the duodenum?

Answer 0

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

Question 1

What are the secretions of the small intestine?

Answer 1

Protease
Carbohydrase
Secretin
Gastrin
CCK

Question 2

How much iron is consumed each day?

Answer 2

20mg

In haem or related pigments (Fe2+)

Question 3

What is required to dissolve the Fe complexes?

Answer 3

Gastric acid

Gastroferrin also dissolves them

Question 4

How is iron absorbed?

Answer 4

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

Question 5

What happens in the jejunum?

Answer 5

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

Question 6

What is starch made up of?

Answer 6

Amylose - straight chains with α-1,4 bonds

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

Question 7

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

Answer 7

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

Question 8

From what are α-amylases secreted?

Answer 8

Salivary glands

Pancreas

Question 9

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

Answer 9

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

Question 10

How is glucose absorbed from the small intestine?

Answer 10

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

Question 11

How is fructose absorbed?

Answer 11

Facilitated diffusion

Question 12

Function of pepsin?

Answer 12

Breaks down proteins into oligopeptides in the stomach

Breaks bond near aromatic amino acid side chains

Question 13

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

Answer 13

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

Question 14

How are amino acids absorbed?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

From where are amino acids absorbed in the gut?

Answer 16

All parts of the small intestine

Question 17

How are fatty acids absorbed?

Answer 17

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.

Question 18

How are water soluble vitamins absorbed?

Answer 18

Passive diffusion

Question 19

How much calcium is consumed and how much is absorbed?

Answer 19

6g consumed a day

700mg/day absorbed

Question 20

How is calcium absorbed?

Answer 20

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

Question 21

What is absorbed in the ileum?

Answer 21

Vitamin B12

Amino acids

Question 22

Where in the ileum is B12 absorbed?

Answer 22

Terminal ileum

Question 23

How is B12 absorbed?

Answer 23

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

Question 24

Clinical relevance of absorption of B12?

Answer 24

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

Question 25

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

Answer 25

About 16 hours

Question 26

What happens in the large intestine?

Answer 26

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

Question 27

What does the rectum do?

Answer 27

Stores and compacts faecal matter

Question 28

How does oral rehydration therapy work?

Answer 28

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.

Question 29

Why is segmenting done?

Answer 29

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

Question 30

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

Answer 30

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'

Question 31

How do pacemakers cause segmentation?

Answer 31

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

Question 32

What is the effect of segmenting and intestinal gradient?

Answer 32

Segmenting on its own just mixes the contents | Intestinal gradient causes the net movement of contents in a caudal direction

Question 33

What are taenia coli?

Answer 33

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

Question 34

What are the segments of the colon called?

Answer 34

Haustra

Question 35

How is Hautra shuttling done?

Answer 35

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

Question 36

How often does the peristaltic propulsive pattern happen?

Answer 36

Once or twice a day

Question 37

Where does the peristaltic propulsive pattern travel from and to?

Answer 37

From the transverse colon to the descending colon

Question 38

What does the peristaltic propulsive pattern do?

Answer 38

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

Question 39

What triggers the mass movement?

Answer 39

Gastrocolic reflex (eating) Time of day Thinking about it

Question 40

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

Answer 40

Internal - smooth muscle. Parasympathetic control relaxes it External - voluntary striated muscle. Voluntary control relaxes it

Question 41

How does the urge to defacate arise?

Answer 41

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

Question 42

How do you poo?

Answer 42

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