8. Functions of the Colon

Question 1

What are the 3 types of movements in colon smooth muscle?

Answer 1

Segmentation
Peristalsis
Mass movement

Question 2

What is segmentation?

Answer 2

Contractions of circular smooth muscle
Lumen closes over completely, pushing food along
Happens more in later part of colon

Question 3

What is mass movement triggered by?

Answer 3

After meals

Gastrocolic and duodenocolic reflexes

Question 4

What triggers the defaecation reflex?

Answer 4

Faeces in the rectum

Question 5

What is the intrinsic control of the defaecation reflex?

Answer 5

Caused by sensory inputs
Peristalsis in the descending and sigmoid colon and rectum
Relaxation of internal anal sphincter
Controlled by intramural reflexes

Question 6

What is the extrinsic control of the defaecation reflex?

Answer 6

Receptors feed into the sacral parasympathetics
Information is fed to the spinal cord
Parasympathetic efferents are activated
Peristalsis in colon and rectum
Relaxation of internal anal sphincter

Question 7

What is the conscious control of the defaecation reflex?

Answer 7

Pudendal nerves act on the external anal sphincter

Voluntary relaxation of sphincter and Valsalva manoeuvre

Question 8

What is the Valsalva manoeuvre?

Answer 8

Close the larynx and try to expire

Abdominal muscles contract

Question 9

Who lacks conscious control of defaecation?

Answer 9

Infants, cord and nerve injury, intellectual ability

Question 10

Describe secretion in the small intestine

Answer 10

Na+/K+ pump pumps Na+ into intracellular space
Na+/K+/2Cl- pump brings Na+ back in
K+ leaves through K+ leak channel
Cl- moves into lumen through CFTR
Na+ moves from intracellular space into lumen
Ion concentation causes water to move into the lumen

Question 11

Describe reabsorption in the small intestine

Answer 11

Na+/K+ pump causes a decreased concentration within the cell
Na+ reenters down concentration gradient bound to AAs or glucose
HCO3- and H+ made inside the cell
HCO3- moves into intercellular space
Na+/H+ pump moves H+ into lumen
H+ and HCO3- make H20 and CO2 in the lumen

Question 12

Why does the cholera toxin cause diarrhoea?

Answer 12

Activates the CFTR to cause excessive NaCl and water secretion

Question 13

How does oral rehydration therapy work?

Answer 13

Dehydration patient is given salt and glucose solution

Reabsorption mechanism in small intestine isn’t affected by toxins, so patient can absorb water

Question 14

Describe absorption in the colon

Answer 14

HCO3- secreted by the HCO3-/Cl- transporter
K+ secreted by electrochemical gradient
NaCl absorbed