Nutritional management Flashcards
How do you calculate apparent digestability, and why do we calculate the apparent digestabilty not true digestability ?
Why do we calculate the apparent digestability
- the difference between ingested dry matter and faecal dry matter does not accurately describe the digestability of feed
- Faecal dry matter includes microbes, lipids, minerals and bile pigments which were not absorbed
- requires adjustments to achieve the true digestability of feed
Describe the digestion of proteins (four steps)
Digestion of proteins
Protein intially denatured loss of complex structure quanternary, tertiary and secondary to primary polypeptide chain - PH, heat, strong salt solution or organic solvents. Allows proteases to attch to the straightened structure.
- heating, PH and strong salt solution or organic solvents in the stomach hydrolyse peptide bonds
- Pepsinogen - pepsin in stomach denatures proteins
- small intestine polypeptides - oligopeptides small intestinal lumen (trypsin)
- brush border of intestinal lumen contains a number of proteases which hydrolyse the oligopeptides to amino acids and di tri peptides
The eventual product prior to absorption is di tri peptides and amino acids
Different proteases target different amino acid sequences
mouth Describe the digestion of carbohydrates ?
Carbohydrates are classified by the number of sugar units linked together by glycosidic bonds.
Mouth - amylase (except dogs and cats)
stomach - salivary amylase until deactivation by HCL
Small intestinal lumen - acini cells secrete pancreatic juice containing amylase which hydrolyses starch and oligosaccharides.
Small intestinal brush border - brush border enzymes anchorded to the cell membrane maltase, lactase and sucrase hydrolyse the alpha 1-4 and beta 1-6 bonds of oligosaccharides.
Why can mammals digest starch but not cellulose ?
Starch is digestible with an alpha 1-4 glycosidic bond
Cellulose has a beta 1-4 glycosidic bond which orientate glucose units alternately in up and down positions forming straight chains of glucose units. These straight chains are able to form hydrogen bonds with adjacent cellulose chains forming a stable crystalline structure.
Describe the absorption of amino acids di tri pepetides and sugar monomers ?
Absorption of amino acids, monosaccharides and B group vitamins mostly occurs in the jejunum, but also duodenum and ileum.
- seconadry active transport Na+/K+ pump
- bile salts and vitamin B12 mostly absorbed in the ileum
These nutrients diffuse across the interstitual space and into capillaries where they enter the mesenteric vein then the hepatic portal vein and then the liver.
What are the products of the reticular - rumen ?
Fermenatation system with plant fibre, protein and sugars as the primary substrates =
product microrganisms, organic acids and gas as the end product.
Formed via oesophageal tissue.
Name the four layers making up the wall of the gastrointestinal tract ?
lumen
1 = mucosa
2= submucosa
3= muscularis externa
4 = serosa
What are the intestinal cells of Cajal ?
pacemaker cells located between the circular and longitudinal muscle of the gastrointestinal tract
regulate slow wave peristaltic activity of the GIT tract
Describe the mucosal layer ?
The mucosal layer
First layer made of three distinct tissue layers
- Epithelium - columnar epithelial cells
- Laminar propria - glands, blood and lymph vessels
- Muscularis mucosae - smooth muscle cellsthat change the shape of the mucosal surface locally.
Describe the submucosa layer ?
Submucosa
second layer
Consist of a layer of connective tissue that contain tubular glands
Submucosal plexus = nerve cells which provide neural input into glandular tissue as one component of control of secretory processes..
Describe the muscularis externa ?
Muscularis externa ?
third layer = Consist of an inner layer (luminal side) circular and outer layer of longitudinal muscle
- circular muscle contraction causes the lumen to narrow
- longitudinal muscle contraction causes the lumen to expand
- coordinated movement of these two muscle layers result in segmentation and peristalsis.
Myenteric plexus = A network of nerve cells that communicates with the submucosal plexus coordinating motility and secretory processes of the GIT.
What organ in the GIT tract has an additional oblique muscle layer ?
Stomache
Additional muscle layer that provides a twisting action to help grind food into a smooth paste.
What are teniae coli and Haustra ?
Teniae coli are bands of longitudinal muscle in the human and horse caecum.
The teniae coli contract to form haustra that assist with mixing and reabsorption of water, fermentation of acids, salts to form faecal balls.
Describe the serosa layer of the GIT ?
The outermost layer of the gastrointestinal tract.
Consist of connective tissue covered by a single layer of cuboidal epithelial cells called the visceral peritoneum.
secretes a fluid for lubrication
What are smooth muscle cells connected by ?
gap junctions
What is a long reflex arc, and a short reflex arc?
Long reflex arc
- integrates the central nervous system in neuronal signaling
- eg central nervous system signal to the salivary glands a meal is on its way
Short reflex arc
- neuronal signalling occurs entirely within the enteric nervous system
- eg stretching of the rectal wall signals the internal anal sphincter to relax allowing for defaecation
What do the lymphatic vessels do?
The lymphatic vessels collect leaked fluids and proteins from the interstitual fluid from digestive organs and transport the fatty products of digestion as chyle.
Occurs directly to the subclavian vein bypassing the liver.
Thoracic duct = primary lymphatic vessel
chyle = fat rich lymphatic fluid.
What is the advantage/ disadvantage of having all water soluble nutrients transported to the liver before the rest of the body?
Liver
Advanatage
- absorbed nutrients quickly converted to metabolites that are ready for use
- toxins neutralised
Disadvantage
- some drugs are neutralised
- some compounds become more toxic
What is the advantage/ disadvantage of having fatty compounds absorbed by the GIT bypass the liver.
Liver
Advantage
- reduces metabolic load on the liver
Disadvantage
- lipid soluble toxins enter the circulation and can accumulate in adipose tissue. (DDT, dioxin)
Only the GIT and liver can package and process triglycerides.
Describe the digestion of fats ?
Digestion of fats
- bile emulsification into smaller fat droplets
- lipases break the ester bonds forming two free fatty acids and one monoacylglycerol for each triglyceride
- product diffuse across enterocyte cell membrane within the brush border.
The free fatty acids and monoglycerol are reformed into chlomicrons leaving the enterocyte via exocytosis.
Describe the digestion of Ca2+ ?
The cellular plasma concentration of Ca2+ is tightly regulated
Calcitriol (vitamin D3)
- acts to increase the the production of both calcium binder and transport proteins
- increase uptake of Ca2+ across the apical membrane
- the pressence or absence of transporter binding proteins regulate the uptake and intracellular transport of calcium
Describe the digestion of minerals and claudins ?
Digestion of minerals
Intracellular route
- active transport Na+/K+
- absorption usually complete
- small and large intestine
- regulated by transporter and binding proteins
- Na+, K+ CL-, SO4 2-
Paracellular route
- diffusion down a concentration gradient
- jejunum and ilieum
- claudins
- Ca2+, Mg2+
- Claudins - tight gap junction proteins open/close gated pores for regulation of Ca2+ uptake by the paracellular pathway.
