colonic phase

Question 1

Function of colon

Answer 1

Absorption of water. Absorption of ions. Storage.

Question 2

Colon is separated from the small intestine by the………….. sphincter. Once beyond this sphincter chyme is called fecal material!

Answer 2

ileocecal

Question 3

The colon is subdivided into multiple anatomical zones. Along the length of the colon are 3 bands of longitudinal muscle called……………

Answer 3

taeniae coli

Question 4

Rectum function is storage of feces until it is appropriate to defecate. The rectum lacks………….. muscle. When………………. muscle contracts, rectal valves contract to aid in keeping feces in the rectum.

Answer 4

circular longitudinal

Question 5

The anal canal is surrounded by smooth muscle forming the internal sphincter. This is continuous with musculature of the rectum. Around the internal sphincter is the external sphincter which is made of…………. muscle.

Answer 5

skeletal

Question 6

Colon exhibits what two forms of mixing motility?

Answer 6

haustral contraction and short-duration contraction

Question 7

Mass movement propels feces caudally. The………………….. reflex enables packing of feces until appropriate time to defecate.

Answer 7

rectoanal

Question 8

Describe haustral contraction:

Answer 8

When the taeniae coli contract, the colon is squished into a series of bulging pouches called haustra. This is Long-duration (~60 sec) contraction of circular muscle, which kneads the feces to extract salt and water. Contraction moves the fecal material both retrograde and anterograde!

Question 9

Describe short-duration contraction:

Answer 9

Short-duration contraction (~8 sec) are contractions of circular muscle that also serve to mix feces.

Question 10

What system regulates haustral and short-duration contractions?

Answer 10

Both are locally regulated by the enteric system.

Question 11

Mass movement is a propulsive movement of fecal material toward the anus occurs 1-3 times daily. The…….. frequency, ………..amplitude contraction keeps fecal material in the colon for an extended period of about 48 hrs.

Answer 11

low high

Question 12

Muscle contraction in Mass movement is very large with wide bands of muscle strips involved in…………………. Each band is contract for an extended period of time.

Answer 12

cleaning sections of the colon fully

Question 13

Are slow waves involved in Mass movement?

Answer 13

No

Question 14

What induces mass movement?

Answer 14

Locally coordinated by the enteric nervous system for the most part. It can also be induced by long reflexes!

Question 15

Motility is modulated by what?

Answer 15

The ANS.

Question 16

………………………. stimulation stops movement. Stimulation of the vagal nerve induces greater motility in the……….. colon. Stimulation of the pelvic nerves does the same to the………….. colon.

Answer 16

Sympathetic proximal distal

Question 17

How do long reflexes influence mass movement?

Answer 17

• Orthocolic reflex is activated upon waking, leading to an urge to defecate in the morning. - Gastrocolic reflex, a long reflex, increases mass movement frequency in the colon, particularly in the sigmoid colon. Distention of the stomach as well as digestive products elicit gastrin release that induce movement. Additionally, CCK induces this movement. This give rise to the urge to defecate following a meal. - Colonocolonic reflex: contraction of one part of the colon induces relaxation of another.

Question 18

Describe colonocolonic reflex

Answer 18

When contraction of one part of the colon induces relaxation of another.

Question 19

Which reflex is activated upon waking, leading to an urge to defecate in the morning?

Answer 19

Orthocolic reflex

Question 20

The rectoanal reflex is responsible for what?

Answer 20

It prevents leakage and optimizes defecation to a point where the rectum has collected stool, and the time is appropriate.

Question 21

Describe the rectoanal reflex in detail:

Answer 21

• Normally the rectum contracts more frequently than the sigmoid colon and fecal matter is pushed retrogradely.
• Filling of rectum via mass movement transport relaxes the smooth muscle of the internal anal sphincter via VIP & NO from enteric inhibitory motor neurons (this is a local reflex).
• The external sphincter responds oppositely with increased rectal pressure increasing its tone.
• This rectoanal reflex prevents leakage and optimizes defecation to a point where the rectum has collected stool and to an appropriate time.

Question 22

Very important! What kind of control is the gastrocolic reflex?

Also, what is it due to?

Answer 22

Hormonal control AND a long reflex loop

Gastrin & CCK

Question 23

The rectum is not heavily innervated by sensory neurons, but the anus is! What does this mean?

Answer 23

The anus can distinguish between gaseous, solid, and liquids, and expulsion is regulated appropriately.

Question 24

Voluntary opening of the external sphincter is accompanied by……………. which changes/straightens the intestine. Furthermore, relaxation of the……………. muscle reduces the rectoanal angle.

Answer 24

squatting

puborectalis

in pic: 1 = puborectalis muscle

Question 25

Describe voluntary expulsion of flatus (gas):

Answer 25

the puborectalis muscle does not relax and there is no change in the rectoanalangle, and thus gas can pass without loss of feces.

Question 26

Additionally, defecation may be accompanied by a deep breath and exhalation against the………. glottis. This increases abdominal pressure.

What else can further increase pressure?

Answer 26

closed

Abdominal muscles can be contracted to further increase pressure.

Question 27

What release peptide YY?

Answer 27

Enterendocrine cells of the colon

Question 28

Enterendocrine cells of the colon release peptide YY in response to what?

Answer 28

Detection of unabsorbed nutrients particularly fat in the fecal material.

Question 29

What does peptide YY do?

Answer 29

• This hormone slows small intestine motility.
• This reflex is called the ileal break due to its function to give more time for nutrients to be absorbed by the intestine.

Question 30

Goblet cells in the colonic crypts secrete…………

Answer 30

mucus

Question 31

Enterocytes within the crypt secret……………via………….., and water follows.

What is the function of this?

Answer 31

Cl- via CFTR

Function is to induce movement of fluids in crypt and avoid stagnation.

Question 32

When it comes to NaCl absorption in the proximal colon, Na+ absorption is mediated by……………….. while Cl- absorption is mediated by…………………

Operation of the two results in maintenance of pH and electroneutrality. Export of both on the…………………. side draws water.

Answer 32

Na/H exchange

Cl-/bicarbonate exchange

basolateral

Question 33

Colonic bacteria convert residual dietary carbohydrates not absorbed in the small intestine into short chain fatty acids (SCFA). Then what happens?

Answer 33

• SCFA is pumped into enterocytes via SMCT1.
• SCFA feed enterocytes.

Question 34

The ENaC Na+ transporter is what brings Na+ into the cell (absorption). Describe this process.

Answer 34

• ENaC is regulated by aldosterone with acute high plasma K+ inducing release of aldosterone and insertion of ENaC. Consequent increase Na transport leaves the lumen negative driving higher secretion of K through apical K channels.
• Na/K pump transports Na+ out of cell on basolateral side.
• EMF moves Cl- paracellularly.
• Water follows.
• Mechanism active in distal portion of colon.