Lecture 3 - Secretions Flashcards
What does microbial digestion do?
- breaks down CHO fibers to VFAs
- synthesis of microbial protein from non-protein nitrogen such as urea
- synthesis of B vitamins
What are the end products of microbial digestion?
- volatile fatty acids = acetate, propionate, butyrate
4 requirements for microbial digestion
- fluid environment
- neutralized environment
- continuous removal of the end-products by absorption
- long retention time of digesta
SCFA absorption
- they are in acid form at neutral pH so they are not fat soluble
- protonate SCFA to neutralize them so they can diffuse down the gradient; H from hydration of CO2 or from Na/H exchange
- transporters found in small and large intestine
What are the 2 mechanisms for SCFA absorption?
- nonionic diffusion (majority)
- apical membrane SCFA-HCO3 exchange
What are 4 qualities of calves with failure of passive transfer have?
- lower body wt
- lower average daily gain
- higher vet costs
- reduced milk production
Neonatal colostrum absorption
- within 12-24 hrs of life
- leaky gut = when the gut is able to absorb via pinocytosis; this ability is lost over time
- absorbing IgG
What 4 things do we know about passive transfer?
- timing is important
- pinocytotic capacity is limited
- many factors affect colostrum quality
- pinocytosis is non-selective
What 4 things do we NOT know about passive transfer?
- what factors influence absorption timing
- how much total IgG can be absorbed
- if molecules other than IgG are absorbed through pinocytosis
- if molecule size/charge/polarity matters
Composition of salivary secretion
- buffer (HCO3-, H2PO4-_
- Na, Cl
- Amylase (except for ruminants and carnivores)
Fxn of salivary secretions
- moisten food to facilitate mastication and deglutition
- neutralize fermentation acids (ruminant)
Where is amylase produced?
acinus
How are salivary secretions controlled?
- flow rate increased by cholinergic stimulation
- salivary center in medulla; parasympathetic nervous system
- reflex stimulation from mechanoreceptors in mouth and stomach
6 fxns of the stomach
- store food
- produce HCl for denaturing proteins and DNA
- mechanical aspect of digestion for making lipid droplets smaller
- produce pepsinogen for protein digestion
- keep bacteria and pathogens out
- intrinsic factor produced in stomach needed for proper B12 absorption
Cheif cells
line stomach lumen and produce pepsinogen
Pepsinogen
used for protein digestion
Mucin producing cells
line stomach lumen and act as protection
Parietal cells
line fundus and corpus and are responsible for pH by producing HCl
ECL cell
line stomach lumen and are responsible for histamine
4 parts of glandular stomach
- esophageal part
- cardia
- fundus and corpus
- pylorus
Cardia
neutral area of where bacterial fermentation happens in non-glandular stomaches
2 gastric secretions
- HCl
- Pepsinogen
Active form of pepsinogen
pepsin
4 regulators of gastric secretions
- Acetylcholine
- Gastrin
- Histamine
- Somatostatin (-)
What protects the stomach from acid and pepsin?
- mucous layer
- mucous secreted by increase in cholinergic and mechanical stimulation
- bicarbonate secreted by epithelial cells gets trapped in mucous gel
Helicobacter Pylori
- main cause of ulcers in humans
- requires acid and increases stomach pH
- crosses the mucous layer of stomach and raises pH causing the mucin to de-gel and opens an opportunity for acid to enter epithelial cells and cause damage
Multifactorial causes of gastric ulcers in pigs
- nutritional
- physical diet
- management
- microbial (Helicobacter suis)
Pancreatic secretions
- proenzymes: amylase and trypsinogen
- bicarbonate (to neutralize small intestine pH)
- insulin
- glucagon
Mechanism of H2O sections
- sensory neurons recognize osmolarity, stretch and presence of nutrients
- Ach released and acts on G protein
- IP3 activated
- ER releases calcium
- calcium binds calmoudin
- Cl- transporter activated
- Cl- released and Na+ and water follow
Secretory Diarrhea
- PGE2 bidns receptor in response to damage and triggers cascade
- serotonin release triggered by toxins; calcium enters cell alonside serotonin triggering last 3 steps of cascade
- Cholera toxin binds G protein and won’t release = continued water secretion
- enterotoxigenic E. Coli binds G Protein
Viral Diarrhea
- associated with villous damage = reduced absorptive surface
