digestion and absorption Flashcards
what are the 4 stages of food processing
ingestion, digestion, absorption and elimination
what is ingestion
the act of eating or feeding
what are the 4 feeding mechanisms
filter feeding
bulk feeding
fluid feeding
substrate feeding
what are the layers of the gut
serosa, muscularis externa, submucosa, mucosa
what makes the serosa
connective tissue, longitudinal smooth muscle
what makes the muscularis externa
myenteric plexus, circular smooth muscle
what makes the submucosa
submucosa plexus, loose connective tissue with collagen and elastin fibres
what makes the mucosa
muscularis mucosa, lamina propria, epithelium
what does amylase breakdown in the mouth
starch
the tongue and the saliva manipulate food until it forms what shape
bolus
what receives the bolus of food
the pharnyx
what 2 passageways does the pharynx lead to
the trachea and the oesophagus
swallowing is carefully controlled to prevent food entering what
the trachea
how is food pushed along in the oesophagus
by peristalsis - muscular contraction - alternating waves of smooth muscle contraction
what is the sphincter
found at the end of the oesophagus and is a ring like valve of muscle that regulates passage of food into the stomach
what are the 2 roles of the stomach in digestion
storage
process food into a liquid suspension
what is the digestive fluid called that the stomach excretes
gastric juice - it mixes with food through the churning action
what is the mixture of ingested food and gastric juice called
chyme
How does the HCl of the gastric juice help liquefy food
it disrupts the extracellular matrix that binds cells together in meat and plants
how does the gastric juice help break down proteins
the low pH of the juice unfolds the proteins so that their peptide bonds become exposed.
the peptide bonds are then attacked by protease/pepsin, cleaving the proteins into smaller polypeptides.
which cells in the gastric glands produce the components of gastric juice
parietal cells
chief cells
how do parietal cells produce HCL
they use an ATP driven pump to expel hydrogen ions into the lumen.
They also diffuse chlorine ions into the lumen via their specific membrane channels
Thus HCL is only formed in the stomach
How do chief cells result in pepsin being released into the stomach
The chief cells release an inactive form of pepsin into the stomach called pepsinogen.
The HCl produced by the parietal cells converts pepsinogen into pepsin by clipping the molecule to expose the active site
Do HCl and pepsin form in the gastric glands
No - their components are released into the stomach from the glands and then they are transformed
how does pepsin activate pepsin
HCl activates some pepsin from pepsinogen then pepsin can also activate the pepsinogen with the same clipping action as HCl to form the active site
why don’t HCl and pepsin eat through the lining of the stomach
mucous is secreted by cells in the gastric glands to protect against self digestion
what are the 3 different types of cell kin the gastric glands
parietal
chief
mucous
what about the stomach enhances breakdown of food by gastric juices
muscular activity - series of muscular contraction and relaxation
how does churning facilitate chemical digestion
it mixes the food, bringing it all into contact with the gastric juices that are secreted by the lining of the stomach
what moves the contents of the stomach into the small intestine
peristaltic contractions
What does the sphincter, located at the stomach opening to the small intestine do
It allows only one squirt of chime into the small intestine at a time
what is heartburn
sometimes the sphincter at the top of the stomach allows some chime into the lower oesophagus which causes a burning sensation
most enzymatic hydrolysis of macromolecules form food occurs where
the small intestine
does the small of small intestine mean length or diameter
diameter
what forms the first 25cm of the small intestine
the duodenum
what happens in the duodenum
chyme mixes with digestive juices from the pancreas, liver, gallbladder and gland cells from the intestinal wall
what is triggered when chyme arrives in the duodenum
the production of the hormone secretin, which stimulates the pancreas to release bicarbonate
what does bicarbonate, released by the pancreas do to the chime from the stomach in the duodenum
the bicarbonate neutralises the chime and secretes numerous digestive enzymes into the small intestine
name some enzymes that the pancreas releases into the small intestine
trypsin and chymotrypsin that are produced in inactive forms. they become activated in the lumen of the duodenum in a similar way to pepsinogen in the stomach
some of the enzymes secreted by the epithelial lining if the duodenum are secreted into the lumen. where do the rest get secreted to
others are bound to the surface of epithelial cells
why are fats difficult to digest
the are insoluble in water so form large globules that cannot be attacked efficiently by the digestive enzymes
what is fat digestion stimulated by
bile salts
what do bile salts act as
emulsifiers that break apart fat and lipid globules
which organ secretes bile
the liver
bile salts are a major component of what
bile
where is bile stored and concentrated
the gallbladder
as well ass digestion what else does bile production contribute to
the destruction of red blood cells that are no longer fully functional
where do the contents of the duodenum got to
jejunum and ileum (by peristalsis)
what are the 3 parts of the small intestine
duodenum
jejunum
ileum
in what part of the small intestine does nutrient absorption occur in
the jejunum and the ileum linings
what are the projections on the small intestine lining called
villi
what are the microscopic projections in each epithelial cell within each villi
microvilli
where do the microvilli face
the intestinal lumen
what is the brush border
the side by side microvilli give the intestinal epithelium a brush like appearance hence the name
why is the increased surface area due to the villi beneficial
it allows for increased rate of nutrient absorption
is transport across the epithelial cells of the intestine passive or active
both - it depends on the nutrient
e.g. fructose moves by facilitated diffusion down its concentration gradient from the lumen of the small intestine into the epithelial cells. from there it exits the basal surface and is absorbed into blood vessels or capillaries at the core of each villus
which nutrients get pumped against their concentration gradient into the epithelial cells of the tissues
amino acids, small peptides, vitamins and most glucose molecules
the capillaries and veins that carry nutrient rich blood away from the villi converge into what
the hepatic portal vein - a blood vessel that leads directly to the liver
where does the blood travel from the liver
the heart then to other tissues and organs
why might blood leaving the liver have a very different nutrient balance compared to the blood that entered it
it converts many organic nutrients into different forms for use elsewhere
the arrangement allows the liver to remove any toxic substances before they can circulate broadly
what is the product of hydrolysis of fat by lipase in the small intestine
fatty acids and a monoglyceride (glycerol joined to a fatty acid)
fatty acids and monoglycerides are absorbed by what
intestinal epithelial cells
what happens when the fatty acids and monoglycerides are absorbed by the epithelial cells of the intestine
they reform to make triglycerides again. they then become coated in phospholipids, cholesterol and proteins, forming globules called chylomicrons
once they exit the small intestine where do the chylomicrons go
the lacteal - a vessel at the core of each villus - part of the lymphatic system
which organ system is the lacteal part of
the lymphatic system
what is the clear fluid contained within the network of vessels of the lymphatic system
lymph
lymph containing the chylomicrons passes into the larger vessels of the lymphatic system and eventually into larger veins that return the blood directly to what
the heart
in addition to absorbing nutrients the small intestine recovers two things - what are they
water and ions
water is reabsorbed into the small intestine by what method of transport
osmosis - when sodium and other ions are pumped out of the lumen
Which organ does the alimentary canal end with
the large intestine - which includes the colon, cecum and rectum
what shape is the junction that joins the small intestine to the large intestine
T shaped
where does the colon lead to
the rectum and the anus
why is the cecum important
for fermenting ingested material - especially in mammals that eat a large amount of plant material
do humans have a small cecum compared to other mammals
yes
the appendix is a finger shaped extension of what
the cecum
which process does the colon complete that began in the small intestine
water recovery
once the water has been recovered from the colon what is left over
feces - the waste of the digestive system, that become increasingly solid as they get moved along the colon by peristalsis
if the lining of the colon is irritated, less water may be reabsorbed resulting in what
diarrhoea
what occurs when the feces moves along the colon too slowly
constipation - too much water reabsorbed and the feces becomes too compact
the undigested material in feces includes cellulose - why is this beneficial
it helps move food along the alimentary canal
what contributes to one third of the dry weight of feces
bacteria living on unabsorbed organic material in the colon
by products of colon bacteria digestion are what
gases - methane and hydrogen sulphide
gases and ingested air are expelled through the anus as what
flatulence - farts
what is another name for parietal cells
oxyntic cells
what type of cells produce saliva
acini cells
how are the actions of the stomach in digestion regulated
by the endocrine cells that produce histamine and serotonin hormones to promote digestion and somatostatin hormone to inhibit digestion
g cells stimulate the release of what
gastrin
