case 4 - PBL

Question 1

what is the chyme like in the colon

Answer 1

already very concentrated because most of the water has already been absorbed.

Question 2

what is the large intestine lined with

Answer 2

mucosa with crypts of Lieberkuhn

Question 3

what do these crypts contain

Answer 3

glands and mucus producing goblet cells

Question 4

what do these cells protect from

Answer 4

protect the intestinal wall from the plethora of anaerobic bacteria in the colon and from the pressure exerted on the walls by the concentrated chyme

Question 5

what else do the walls of the large intestine also contain

Answer 5

gastrointestinal lymphoid tissue (GALT)

Question 6

what does this GALT do

Answer 6

contributes to the body’s immune defences

Question 7

how much water does the colon help absorb from the lumen per day

Answer 7

400ml of wayer

Question 8

what is the consequence of chyme being concentrated

Answer 8

by the tie it reaches the colon, the colon must work against a larger osmotic pressure gradient than in the rest of the GI tract

the water must move against the gradient for osmosis

Question 9

what is there a net absorption of in the large intestine

Answer 9

sodium and chloride ions

Question 10

what are the three methods that sodium is absorbed via

Answer 10

sodium-hydrogen antiporter on the luminal membrane

epithelial sodium channels

enhanced by absorption of short chain fatty acids in the colon via specialised symporters

Question 11

how are chloride and bicarbonate absorbed

Answer 11

the movement of sodium into the plasma produces an electrochemical gradient to allow absorption of chloride

chloride ions are exchanged for bicarbonate ions

Question 12

how is water further absorbed

Answer 12

the absorption of these electrolytes creates an osmotic gradient to allow further absorption of water

Question 13

how is potassium absorbed

Answer 13

absorption of water along the length of the bowel concentrates potassium in the lumen

This provides an electrochemical gradient for the movement of potassium into the plasma

In the colon potassium may be absorbed or secreted depending on the remaining concentration in the lumen and the electrochemical gradient created by the active absorption of sodium

Secretion usually occurs when the luminal concentration of potassium ions is below 25mM

Question 14

how are vitamins and fats absorbed

Answer 14

short chain fatty acids, crucial B vitamins, such as B6, and B12, and vitamin K are produced by the digestion of chyme by the commensal microbial flora of the colon

Question 15

what are the 2 endocrine mechanisms used to regulate absorption in the GI tract

Answer 15

aldosterone
glucocorticoids

Question 16

explain the aldosterone endocrine mechanism

Answer 16

increases the net absorption of water and electrolytes by stimulating the basolateral sodium potassium ATPase.

this increases the electrochemical gradient and driving force for sodium absorption

it also increases transcription of epithelial sodium channels

Question 17

explain the glucocorticoid mechanism of absorption

Answer 17

(and somatostatin)
act to increase water and electrolyte absorption by increasing the action of the basolateral sodium-potassium ATPase

Question 18

what does the parasympathetic innervation promote in the intestines

Answer 18

promotes net secretion from the testes

Question 19

what does the sympathetic innervation promote in the intestines

Answer 19

promotes net absorption in the intestines

Question 20

what is the large intestine naturally separated into

Answer 20

segments known as haustrau

Question 21

along the course of the walls are groups of cells called what?

Answer 21

pacemaker cells

Question 22

what do these pacemaker cells do

Answer 22

send signals to the smooth muscle cells on the walls of the large intestine causing them to contract at regular intervals

Question 23

what did the contraction cause

Answer 23

the food to be churned in the intestine exposing the gut contents to a larger surface area of epithelium maximising absorption

Question 24

what does each group of cells control

Answer 24

a certain number of haustra

Question 25

what do the pacemaker cells closer to the ileum do

Answer 25

emit signals slightly faster than those towards the end of the length of the bowel

Question 26

what does this gradient allow for

Answer 26

gentle progression of bowel contents towards the rectum

Question 27

how often does mass movement occur

Answer 27

once or twice a day

Question 28

what does mass movement involve

Answer 28

a sudden, uniform, peristaltic contraction of smooth muscle of the gut which originates at the transverse colon and rapidly moves formed faeces into the rectum which is normally empty

Question 29

what is the result of this

Answer 29

the feeling of the urge to defecate

Question 30

this contraction may be stimulated when and what is this reflex called

Answer 30

The contraction may be stimulated by eating
When this occurs this is called the gastro-colic reflex.

Question 31

what is a haemorrhoid

Answer 31

swollen veins in your anus and lower rectum,

Question 32

what is an external haemorrhoid

Answer 32

these are under the skin around your anus
Itching or irritation in your anal region
Pain or discomfort
Swelling around your anus
Bleeding

Question 33

what is an internal haemorrhoid

Answer 33

lie inside the rectum. You can’t usually see or feel them, and they rarely cause discomfort. But straining or irritation when passing stools can cause:
Painless bleeding during bowel movements. Small amounts of bright red blood on toilet paper
A haemorrhoid to push through the anal opening resulting in pain and irritation

Question 34

what is a thrombosed haemorrhoid

Answer 34

if blood pools in an external haemorrhoid and forms a clot, it can result in:
Severe pain
Swelling
Inflammation
A hard lump near your anus

Question 35

what is blood when wiping generally caused by

Answer 35

bleeding in the lower GI tract, the rectum and anus

Question 36

what is the cause of bleeding in stools

Answer 36

bleeding that happens higher up in the digestive tract, may make stool appear black and tarry

Question 37

what are the possible causes for this

Answer 37

IBD
Ischaemic colitis
Bacterial infections
Diverticular disease
Anal tissue
Colitis
Angiodysplasia - this is a condition in which fragile, abnormal blood vessels lead to bleeding
Peptic ulcer
Polyps or cancer
Oesophageal problems

Question 38

what is hepatomegaly usually a sign for

Answer 38

of an underlying problem, such as liver disease, congestive heart failure or cancer

Question 39

what does leucovorin do

Answer 39

basically increases the levels of folic acid under conditions favouring folic acid inhibition. it is useful as an antidote to drugs which act as folic acid antagonists

Question 40

explanation of 5-HT3 receptor antagonists

Answer 40

Work on central serotonin receptors in the vomiting centre swell as peripheral serotonin receptors in the vagus nerve
Indicated for use against vomiting caused by acute gastroenteritis

Question 41

what is an example of a 5-HT3 antagonist

Answer 41

ondansetron

Question 42

explanation of H1 antihistamines

Answer 42

Used to treat and prevent nausea and vomiting induced by vestibular disturbances like vertigo and motion
Scopolamine is predominantly used to treat motion sickness

Question 43

what are some examples of H1 antihistamines

Answer 43

cyclizine, promethazine, and diphenhydramine, or antimuscarinics

Question 44

what are the dopamine antagonists and what are they indicated for

Answer 44

metoclopramide, most commonly used for postoperative nausea and motion sickness

Question 45

what is the drug used to suppress radiotherapy and chemotherapy nausea

Answer 45

neurokinin 1 -NK1

are relatively new medication class that can be used as antiemetics
Especially for suppressing radiotherapy and chemotherapy induced nausea and vomiting
Prevent nausea and vomiting after surgery
Should not be taken while pregnant or breastfeeding

Question 46

what is the antiemetic mechanism of action

Answer 46

is to block serotonin from interacting with the 5-HT3 receptor

Question 47

what is the mechanism of action - after it binds to these receptors

Answer 47

Drugs selectively bind to receptors in vomiting centre of the brainstem

Block signalling pathway

Inhibits stimulation of the GI tract, diaphragm and abdominal muscles.

Question 48

where are peripheral receptors found

Answer 48

the vagus nerve

Question 49

what is stimulated when someone is vomiting

Answer 49

the GI tract, abdominal muscles and the diaphragm

Question 50

when should NK1 not be taken

Answer 50

when breast feeding or pregnant