Intestines Flashcards
What processes take place in the small intestine?
Digestion
Absorption - by secondary active transport and diffusion
What are the 2 phases of intestinal digestion?
Luminal - enzymes and bile salts within the lumen
Membranous - enzymes on surface of intestinal cells
What are the 4 layers of the intestines/
Mucosa
Submucosa
Muscular
Serosa
What cells are found in the epithelium of the SI?
Goblet cells
Enteroendocrine cells
Paneth cells
Enterocytes
What do goblet cells do?
Produce mucous for lubrication and protection
Secrete HCO3
What do enteroendocrine cells do?
Control digestion via hormones
What do paneth cells do?
Defence against microbes
What do enterocytes do? What is a key feature to them? What type of digestion phase is this and why?
Absorb products via transporter proteins
Microvilli
Membranous - luminal enzymes would be absorbed
What is distension?
The accumulation of gas or fluid in the abdomen
What is the gastro-ideal relflex?
Motility increases after feeding
Ileo-colic sphincter relaxes to allow SI contents to LI
What motility is found in the SI?
Segmental and peristaltic
At end of SI - no segmental, peristaltic only
What is the migrating myo-electric complex?
When a contraction reaches the ileum, a new one begins in the duodenum
Which neurotransmitter contracts and inhibits smooth muscle?
Contracts and inhibits smooth muscle
What happens to longitudinal and circular muscle behind chyme?
Longitudinal relaxes
Circular contracts
Which cells are the pacemaker cells? Where are they? Which NS innervates them?
Interstitial Cajal cells
Stomach
Enteric NS
Which bonds are indigestible by mammalian enzymes, so go onto microbial fermentation in the LI?
Beta glycosidic bonds
Describe the absorption and digestion speed of maltose, which one is the limiting factor?
Fast digestion
Slow absorption - limiting factor
Describe the digestion and absorption of lactose, which is the limiting factor?
Slow digestion - limiting factor
Fast absorption
Which enzyme do ruminants have none of?
Sucrase
Describe the Maltase and lactase levels in neonates and adults
High maltase adults, little lactase
High lactase neonate, little maltase
Which transporter transports glucose and galactose in the SI? Is this active or passive? Symport or antiport?
Na/glucose cotransporter = SGLT1
Active - secondary AT
Symport
How is fructose absorbed in the SI?
Facilitated diffusion via GLUT5
What happens to carbohydrates in the bloodstream?
Go to liver via hepatic portal vein and stored as glycogen
Or continue circulation
Carnivores have high CHO. Therefore lots of which transporter?
SGLT1
Describe the presence of SGLT1 throughout rumen development
High before rumen develops
Once developed, almost negligible
If there is lactose in the SI and no lactase, what happens?
Osmotic force decreases water absorption in the LI
Diarrhoea
How are proteins absorbed and by which transporter?
Di or tri peptides
H+ cotransporter
What is the main source of protein for ruminants?
Their own microflora
In the large intestine, what does lactic acid cause?
Drop in pH
Upsets microbial balance, gas and distension
Lactate is poorly absorbed - diarrhoea
What is the final stage of carbohydrate absorption? What size molecules are absorbed? How many enzymes are required?
membranous phase
monosaccharides only
Few enzymes - only few monosaccharides
What is the final stage of protein absorption? What size molecules are absorbed? How many enzymes are needed and why?
Luminal phase
Mono/Di/tri peptides
Many - 20 amino acids
What are the similarities between carbohydrate and protein digestion?
Both transport via secondary active transport
Both use cotransporter s
Both require sodium gradient
If a neonate absorbs an intact protein, what does it stimulate?
Immune response
Which animals need colostrum as they do not get antibodies through the placenta?
Pigs, horses, ruminants
What enables neonates to absorb antibodies from colostrum?
Epithelial cells in SI are permeable to intact proteins
Stomach produces less HCl
Fewer pancreatic enzymes
Trypsin inhibitor
Which type of animals have high and low fat diets?
Carnivores high, herbivores low
What is the main source of fats?
triglycerides
Where are lipase concentrations high and low?
Low in mouth/ stomach
High in pancreas
How are fats digested and absorbed
Liver produces bile - emulsifiers fats and forms aggregates called micelles
Micelles absorb monoglycerides and fatty acids, return through microvilli to lumen and repeat
Where do monoglycerides and fats re-esterify?
Endoplasmic reticulum
what are the two routes for water absorption?
Paracellular - via tight junctions
Transcellular - via cell membranes - luminal membranes contain aquaporins for osmosis
Most water is reabsorbed from digestive secretions in which part of the intestine? Except which animal?
SI
Horse - LI
Why is sodium an important mineral in the intestines?
Provides energy for secondary active transport
How are sodium and chlorine absorbed?
Diffusion
Cotransporter
Why is it important HCO3 is reabsorbed
To prevent metabolic acidosis
Phosphate is absorbed as which molecule? What does it act as?
HPO4, 2-
Rumen buffer
Which iron molecule is poorly absorbed? How is it absorbed instead?
Fe3+
Fe2+ by cotransporter
What are the functions of the LI?
Microbial fermentation, absorption of water and ions
Horses are what kind of fermenter? What do they also use the LI as?
Hindgut
Energy source
are there digestive enzymes in the LI?
No- microbes only
What are the products of microbial fermentation
VFAs - acetate, propionate, butyrate
What type of motility takes place in the SI?
Mass movement only
What molecules are absorbed in the LI?
VFAs
Cl
Na
water
What hormone increases sodium absorption in the LI?
Aldosterone
Nearly all water in the LI is reabsorbed. Why does diarrhoea occur?
Stress/nutrition overload/infection
Increased water content causes distension and decreases motility, leading to less water absorption
What is the treatment options for diarrhoea?
IV - maintain BP, restore ions, HCO3 to counteract metabolic acidosis.
Oral rehydration - containing NaCl to increase osmotic gradient between lumen and blood
Stress can cause diarrhoea by the strong activation of which nervous system?
Parasympathetic
What is constipation? What is the treatment?
Abnormal accumulation of material in the gut
Dry food expands GI tract
Fluids, paraffin oil (lube), enemas
Describe the process of defaecation
Terminal colon and rectum contract
Inner anal sphincter muscle (autonomic) relaxes
Outer anal sphincter muscle relaxes
Abdominal muscles help mass evacuation
What type of smooth muscle is the inner and outer anal sphincter
Inner - smooth
Outer - striated
Which animals do not have conscious control of their outer anal sphincter
Horses
Ruminants
