case 4 - PBL Flashcards
what is the chyme like in the colon
already very concentrated because most of the water has already been absorbed.
what is the large intestine lined with
mucosa with crypts of Lieberkuhn
what do these crypts contain
glands and mucus producing goblet cells
what do these cells protect from
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
what else do the walls of the large intestine also contain
gastrointestinal lymphoid tissue (GALT)
what does this GALT do
contributes to the body’s immune defences
how much water does the colon help absorb from the lumen per day
400ml of wayer
what is the consequence of chyme being concentrated
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
what is there a net absorption of in the large intestine
sodium and chloride ions
what are the three methods that sodium is absorbed via
sodium-hydrogen antiporter on the luminal membrane
epithelial sodium channels
enhanced by absorption of short chain fatty acids in the colon via specialised symporters
how are chloride and bicarbonate absorbed
the movement of sodium into the plasma produces an electrochemical gradient to allow absorption of chloride
chloride ions are exchanged for bicarbonate ions
how is water further absorbed
the absorption of these electrolytes creates an osmotic gradient to allow further absorption of water
how is potassium absorbed
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
how are vitamins and fats absorbed
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
what are the 2 endocrine mechanisms used to regulate absorption in the GI tract
aldosterone
glucocorticoids
explain the aldosterone endocrine mechanism
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
explain the glucocorticoid mechanism of absorption
(and somatostatin)
act to increase water and electrolyte absorption by increasing the action of the basolateral sodium-potassium ATPase
what does the parasympathetic innervation promote in the intestines
promotes net secretion from the testes
what does the sympathetic innervation promote in the intestines
promotes net absorption in the intestines
what is the large intestine naturally separated into
segments known as haustrau
along the course of the walls are groups of cells called what?
pacemaker cells
what do these pacemaker cells do
send signals to the smooth muscle cells on the walls of the large intestine causing them to contract at regular intervals
what did the contraction cause
the food to be churned in the intestine exposing the gut contents to a larger surface area of epithelium maximising absorption
what does each group of cells control
a certain number of haustra
what do the pacemaker cells closer to the ileum do
emit signals slightly faster than those towards the end of the length of the bowel
what does this gradient allow for
gentle progression of bowel contents towards the rectum
how often does mass movement occur
once or twice a day
what does mass movement involve
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
what is the result of this
the feeling of the urge to defecate
this contraction may be stimulated when and what is this reflex called
The contraction may be stimulated by eating
When this occurs this is called the gastro-colic reflex.
what is a haemorrhoid
swollen veins in your anus and lower rectum,
what is an external haemorrhoid
these are under the skin around your anus
Itching or irritation in your anal region
Pain or discomfort
Swelling around your anus
Bleeding
what is an internal haemorrhoid
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
what is a thrombosed haemorrhoid
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
what is blood when wiping generally caused by
bleeding in the lower GI tract, the rectum and anus
what is the cause of bleeding in stools
bleeding that happens higher up in the digestive tract, may make stool appear black and tarry
what are the possible causes for this
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
what is hepatomegaly usually a sign for
of an underlying problem, such as liver disease, congestive heart failure or cancer
what does leucovorin do
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
explanation of 5-HT3 receptor antagonists
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
what is an example of a 5-HT3 antagonist
ondansetron
explanation of H1 antihistamines
Used to treat and prevent nausea and vomiting induced by vestibular disturbances like vertigo and motion
Scopolamine is predominantly used to treat motion sickness
what are some examples of H1 antihistamines
cyclizine, promethazine, and diphenhydramine, or antimuscarinics
what are the dopamine antagonists and what are they indicated for
metoclopramide, most commonly used for postoperative nausea and motion sickness
what is the drug used to suppress radiotherapy and chemotherapy nausea
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
what is the antiemetic mechanism of action
is to block serotonin from interacting with the 5-HT3 receptor
what is the mechanism of action - after it binds to these receptors
Drugs selectively bind to receptors in vomiting centre of the brainstem
Block signalling pathway
Inhibits stimulation of the GI tract, diaphragm and abdominal muscles.
where are peripheral receptors found
the vagus nerve
what is stimulated when someone is vomiting
the GI tract, abdominal muscles and the diaphragm
when should NK1 not be taken
when breast feeding or pregnant
