Alimentary - diarrhoea Flashcards
What is the structure of the small intestines?
Duodenum - standard enterocytes
Jejunum - increased SA with taller and less villi
Ileum - move through is an increase in peyers patches (lymphoid tissue)
What is the structure of a cyrpt?
There are stem cells in the base that graduall migrate to the top and develop absorptive and digestive capacities, where they mature. They are shed after 3-5 days and become replaced.
How are carbs and proteins digested and absorbed?
Brush border enzymes on mature enterocytes are involved in final digestion.
ATP dependent for absorption and via diffusion across illi into lymph lacteals
How are fats digested and absorbed?
Updake of monoglycerides and free FA is via diffusion across the villi into lymph lacteals.
Where does most of the water reabsorption occur?
50% in jejunum
75% in ileum
Colon absorbs 90-95% delivered to the lumen
How is fluid absorbed in the SI?
Villus tip - absorbs sodium, glucose and amino acids on apical surface, sodium is pumped out on basolateral surface, water follows
Crypt base - stem cells have secretory cells with leaky intercellular junctions which allows sodium to leak back into lumen
What is the normal ratio of absorption and secretion in an animal?
Net absorption at tip>net secretion at crypt
What are the 4 basics mechanisms of pathogenesis of disease?
- Altered epithelial cell transport
- Altered structure/permeability of mucosa
- Osmotic effects
- Altered motility
What is altered epithelial cell transport?
Secretory diarrhoea.
Caused by some types of bacteria e.g. E Coli
They attach to villus epithelial and inject toxins into the cell preventing the sodium pump on the apical surface working leading to more sodium leaking out and fluid following into lumen.
Self-limiting as mature villous shed every 3-5 days
What is altered structure/permeability of mucosa?
Caused by cytotoxins, infiltration of cells into villi, lytic infection of villous epithelium cells by viruses or infection of cells in crypts
How do cytotoxins cause altered structure?
Caused by bacteria e.g. Salmonella
Leads to death of enterocytes, increasing permeability of lining so blood, fluid etc haemorrhage into the lumen.
Seen clearly with altered structure and can recover but may need supportive therapy
How does a infiltration of cells into villi cause altered structure?
Mass increase in cellularity leads to increase in width and decrease in height, leading to loss of surface area so enzymes are lost.
Caused by:
-Neoplasia (lymphoma) - mucosa infiltrated by neoplastic lymphoid cells (cobblestone gut) and distension
- Inflammation (lymphoplasmacytic enteritis) - IBD or inflammation due to bacteria
- Infection (Johnes disease) - paraTB infection survives in phagocytes and recruits more macrophages. Cobbling of villi seen due to mass infiltration
How does lytic infection of villous epithelium cells by viruses cause altered structure?
Caused by coronaviruses and rotaviruses
Replicate in villous epithelium leading to villous atrophy leading to a shorter villi.
Regenerated eventually.
How does lytic infection of stem cells in crypts cause altered structure?
Caused by parvovirus
Replicate in crypt epithelium damaging stem cells leading to mucosal collapse. Capacity for recovery is very poor
How do osmotic effects cause diarrhoea?
Abnormal osmotic gradient
A lack of brush border enzymes result in the accumulation of small osmotic solutes in the intestinal lumen that draws water into the lumen
e.g. Lactose intolerance in cats
