Diarrhoea - Anatomy and Pathophysiology Flashcards
Define Diarrhoea
A failure of fluid handling
What is the major function of the colon
To reabsorb water
Name the 2 major types of diarrhoea
1) Osmotic diarrhoea
2) Secretory diarrhoea
Explain Osmotic diarrhoea
Due to excess osmotically active particles in the lumen which inhibits normal water and electrolyte absorption
Explain Secretory diarrhoea
Gut mucosa secretes excess water into the lumen
Osmotic diarrhoea can be caused by ?
- Osmotic laxatives
- Inflammation w/in mucosa
- Excess solutes in the lumen
- Motility disorders
Secretory diarrhoea can be caused by ?
- Infective causes
- Cholera toxin
- Defects of specific electrolyte transport (e.g: Congenital chloride-losing diarrhoea)
How can infections cause diarrhoea ?
1) Damaging the mucosa
2) Infective organism producing toxins
Removing source of osmotically active particle by fasting stops osmotic diarrhoea. TRUE or FALSE
TRUE
Removing source of osmotically active particle by fasting stops secretory diarrhoea. TRUE or FALSE
FALSE. Fasting has no effect o secretory diarrhoea
Increased fluid secretion is due to 2 things. State them
1) Inherent abnormalities in enterocytes
2) Specific biological mechanisms involvig pathogen-produced factors such as Cholera toxins
Name 2 types of virus that cause diarrhoea
1) Rotavirus
2) Norovirus
Name 2 types of bacteria that cause diarrhoea
1) E.Coli
2) Salmonella
How many phases of movement of the GI tract are there and which is the most important ?
4 phases and Peristalsis is the most important
CFTR is the only ion pump that pumps ions downhill. TRUE or FALSE
TRUE
Name the protein that is mutated in Cystic fibrosis
CFTR
Give an example of bacteria that is a major cause of diarrhoea in patients on antibiotics
C.difficile
State the 3 steps of c.difficile in causing infection
1) Alteration of gut flora
2) C.difficile colonises flora
3) Growth and production of toxins
Pharmacological treatments for C.difficile in diarrhoea includes ? Name 3
1) Discontinue antibiotics
2) Metronidazole (contradicted in patients w/liver ad renal impairment)
3) Vancomycin (contradicted in patients with renal impairment)
Describe Cholera toxin action mechanism;
1) (CT) B subunits binds to GM1 receptor and A subunit is inserted through the host cell membane
2) Complex is endocytosed by target cell
3) Proton pumps acidify the endosomes causing dissociation of A and B subunits
4) A1 subunit has enzyme activity and breaks dow NAD into ADPR and nicotinamide
- ADPR covalently binds to a subunit of G protein
5) GTPase activity of a subunit is blocked therefore GTP binds to it and this complex activates adenylyl cylase
6) Incereased cAMP increases CFTR chloride pump activity therefore increases water secretion into gut lumen
