physiology of small intestine & accessory organs 2 Flashcards
what are the parts of the small intestine
- duodenum
- jejunum
- ileum
what are the parts of the large intestine
- caecum
- colon
- rectum
what does the mucosa secrete
- maltase and sucrase
- end and exopeptidase
what does the submucosa secrete
mucous to
- protect intestinal wall
- neutralise acidic chyme
what do both the submucosa and mucosa secrete
ions, water and mucous for lubrication and protection from enzymes
what is the function of villi
- folds of mucosa & submucosa increase surface area
- microvilli increase surface area further
- transport of nutrients
what does each villus have
- arteriole
- capillary bed
- venule
- lymphatic
what is in intestinal juices
water
mucous
enzymes
what stimulates and regulates secretion of intestinal juices
- stimulated by presence of chyme
- regulated by CCK and secretin
what starts the chemical digestion process
salivary amylase
stomach pepsin
what allows digestive process to be complete in small intestine
combined actions of
- pancreatic juice
- bile
- intestinal juice
what converts starch to disaccharides
pancreatic amylase
what converts disaccharides to monosaccarides
glycosidase
can monosaccharides be absorbed
yes
what catabolises polypeptides arriving from stomach
pancreatic trypsin and chymotrypsin
what completes digestion of proteins
peptidases released from glandular epithelium
where is most fat absorbed
jejunum
how do peptidases cleave peptides
- carboxypeptidases act at “carboxyl” end
- aminopeptidases act at “amino” end
- dipeptidases convert dipeptides to amino acids
how does bile help digest fat
fat globules in duodenum are coated with bile salts to create emulsion and disperse large fat globules into smaller entities.
what does emulsification allow in digestion of fats
breakdown of triglycerides by increasing the surface area for water soluble pancreatic lipases to act upon and produce monoglycerides and free fatty acids.
what is absorption in the small intestine
the process by which digestion products are transported across epithelial cells and into blood
where does almost all absorption occur
in the small intestine
how does general absorption through intestinal mucosa occur
active transport
diffusion
what are carbohydrates broken into in small intestine
monosaccharides
what are proteins broken into in small intestine
peptides and amino acids
what are fats broken into in small intestine
monoglycerides and free fatty acids
how are glucose and galactose (monosaccharides) absorbed
- absorbed into epithelial cell by co-transport with Na+ via sodium-glucose transporters
how do glucose and galactose (monosaccharides) enter blood
leave epithelial cell and enter blood by facilitated diffusion via glucose transporters (GLUTs)
how is fructose (monosaccharides) absorbed
absorbed into and leave cells by facilitated diffusion via GLUTs
how are peptides absorbed into small intestine
- uptake thought to be linked to H+ influx
- broken down to constituent amino acids inside epithelial cell
how are amino acids absorbed into small intestine
- uptake into epithelial cells by Na+-dependent co-transport (active)
- leave epithelial cell by facilitated diffusion
how are fats absorbed
monoglycerides and free fatty acids associate with bile salts to form micelles/emulsion and diffuse passively into cells
where do bile salts remain after fats are absorbed
remains in lumen of gut then re-cycled by enterohepatic circulation
where do lipids accumulate and how do they leave
lipids accumulate in the vesicles of the smooth ER epithelial cell
they leave the cell by fusing with the plasma membrane.
how do chylomicrons leave the intestine
in lymph since they are too large to enter the circulation immediately.
they are eventually delivered into venous circulation
what does the lymphatic system do
absorbs nutrients, electrolytes, fluid and protein from interstitial spaces.
chylomicrons too large to enter capillaries but lacteals have large pores.
removal of haemorrhaged red blood cells from tissue and invading bacteria
what are lymphatic vessels of the small intestine called
lacteals
what does the intestine act as to the lymphatic system
a lymphoid organ in addition to its absorptive role
where can lymphatic tissue be seen
close to epithelial surface and as large aggregates
does the lymphatic pathway cross the liver
no, allows nutrients/drugs are delivered into the systemic circulation close to the heart
can lymphatic system hold a large capacity
yes
when would drugs get involved in the lymphatic system
is solubility of drugs in triglycerides is around 50mg/ml or more
what allows lymphatic circulation
muscular movements of smooth muscle in walls of lymphatics pushing lymph along by peristalsis
where are electrolytes absorbed
along the intestine
how must fat soluble vitamins (A,D,E,K) be absorbed
in micelles (similar to fat)
how are water soluble vitamins (B,C) involved
by diffusion
how is vitamin B12 absorbed
it requires presence of intrinsic factor which is produces by stomach
