Option D.2 Digestion Flashcards
Where is food taken into in mammels?
alimentary canal (gut)
What is the alimentary canal?
long tube with muscular wall;
food is held in lumen and digested there
What are the glands called that release digestive enzymes?
exocrine glands; where secretory cells are arranged
What are major exocrine glands release?
gastric glands in stomach; exocrine glands in pancreas;
What fluid is secreted onto food to aid digestion in gut?
digestive juice (bunch of enzymes)
Is the secretion of digestive juice continuous?
No. Coordination regulated by nervous hormonal mechanisms that ensure secretion:
- when/where required
- volume and composition of juice is appropriate to food
What is an example of digestive juice secretion regulated by nervous/hormones?
- sight/smell of food causes brain to send nerve impulses via vagus nerve from medulla;
- gastric gland cells in stomach wall are stimulated;
- Gastric juice from gastric glands
- if receptors in stomach wall detects peptides/distension of stomach, impulses to brain
- brain responds by sending impulse to secrete gastrin in nearest duodenum;
What is chyme?
when food is mixed with gastric juice and churned by muscle action
Describe the mechanism of secretion control in the stomach
- sight/smell of food causes brain to send nerve impulses via vagus nerve from medulla;
- gastric gland cells in stomach wall are stimulated;
- Gastric juice from gastric glands
- includes HCl;
- makes optimum pH for protease enzymes (pepsin)
- if receptors in stomach wall detects peptides/distension of stomach, impulses to brain
- brain responds by sending impulse to secrete gastrin in nearest duodenum;
- gastrin stimulates secretion of acid and pepsinogen
- when stomach pH falls to 3.5 gastrin secretion slows (at pH 1.5 it stops);
- protein acts as buffer so when protein present pH falls more slowly
- chyme starts entering duodenum only if low in protein, contains glucose and fatty acids
- if chyme not low in protein, it stimulates lining of duodenum to secrete intestinal gastrin (more gastric juice for more protein digestion;
- gut wall releases secretin and cholecytokinin
- decreases gastric juice secretion
- hormones continue to control secretion in duodenum (pancreatic juice)
What hormones are involved in intestial secretion?
gastrin, enterogasterone, secretin, CCK-PZ
How can stomach acid secretion be reduced?
secretin and CCK-PZ released;
proton pump inhibitor drugs can also b used which which treat symptoms of low pH;
How do proton pump inhibitor drugs work?
surpresses gastric acid production by inhibiting the activity of proton pumps;
raises pH of stomach; may also encourage growth of gut microflora (suseptible to bacterial colonization)
Although the stomach is strongly acidic there is a bacterium that can survive there?
Helicobacter pylori
Where does gastrin come from and what is its effect?
stomach wall;
- stimulates production of hydrochloric acid by partiel cells and pepsinogen by chief cells, and gastric juices
where does enterogasterone come from and what is its effect?
stomach wall;
- slows flow of gastric juice
- slows exit of fats from stomach
Where does secretin come from and what is its effect?
small intestine;
- stimulates the pancreas to release hydrogen carbonate ions to neutralise acidic chyme (partly digested food) from stomach
Where does CCK-PZ come from and what is its effect?
small intestine;
- stimulates the release of bile from gall bladder
- release of pancreatic enzymes into small intestine
What is the effect of having helicobacter pylori survive?
attaches to receptors on plasma membrane of stomach muscosa under muscus lining;
protected by mucus (of inner lining of gut);
hydrogen ions are neutralized by hydrogecarbonate ions and amonnium ions that the bacterium produced;
persistent presence on exterior of cells causes immune system to sensitize;
antibodies produced in vicinity of infection; killer cells accumulate;
defences cannot reach invading cells on exterior of membrane, they are ineffective
What is the relationship between ulcers and H. pylori?
Ulcers were supposed to be caused by H. pylori.;
H.pylori found in patients with ulcers;
antimicrobial drugs are used to kill bacteria and remove H.pylori infection; provides long term relief of symptoms and cure ulcers;
produces toxins that cause inflammation of stomach lining;
can cause stomach cancer
What is the epithelium layer of the small intestine called?
Mucosa (with goblet cells)
What do the goblet cells do?
secrete mucus (lubricating secretion); protects from mechanical damage
In the structure of a villi in the small intestine, what is the surface of the cells called that face the lumen?
apical surface
What is the basal surface?
surface of cells in small intestine that face blood vessels
What are structural features of the small intestine that aid absorption?
villi & microvilli increase surface area , mitochondria, pinocytotic vesicles, basal channels, tight junctions
What are pinocytotic vesicles?
they take up fluid or release tiny vesicles across plasma membrane of cell;
What are basal channels?
are channels between epithelium cells and below junctions
What are tight junctions?
bind together the individual epithelium cells, so that only way into tissues is through epithelium;
What must digested material pass through to reach capillary or lacteal vessel?
microvilli of epithelial cells
What does the epithelium contain to support the absorption in endothelium
lots of mitochondria for active transport
What parts of the structure of the epithelium of a villi are adapted to absorption?
tight junctions - ensure that most materials pass into blood vessels only the epithelial cell;
microvilli - their brush order increases surface area
mitochondria - lots of mitochondria give lots of ATP for active transport
pinocytic vesicles - large number for absorption of food by endocytosis
apical surface & and basal surface - have different protein for material transport
How are monosaccharides transported into the epithelial cells?
active transport (secondary pumps)
How does fructose enter the epithelial cell?
facilitated diffusion
How are disaccharides transported into epithelial cells?
Must be broken down by enzyme, active transport (as monosaccharide)
How are short chain peptides transported into epithelial cell?
- attach to specific protease of membrane that make their transport like amino acids; amino acid actively transported into epithelium
What passes the epithelium through simple diffusion?
short chain fatty acid; vitamins
What does the epithelium absorb through facilitated diffusion?
fructose (hydrophilic)
What passes into the epithelium through active transport?
amino acids; mineral ions; glucose
What does pinocytosis also draw into the epithelium?
small drops of liquid from the ileum
What are chylomicrons?
triglycerides coated with protein forming spherical masses
What happens to material that our body cannot absorb?
egested (fraction of food never leaves our body)
What does material contain that we cannot absorb/that is egested?
contains INSOLUBLE/DIETRY FIBRE
What are examples of insoluble fibres?
cellulose, pectin and lignin
Why can our body not absorb cellulose?
do not have cellulase enzymes
If we cannot absorb insoluble fibres, are not important?
add bulk;
stimulates movement of chyme through gut;
prevents constipation;
speeds up excretion;
slows absorption of glucose (no diabetes II);
reduce desire to eat
reduces risk of colon/bowel cancer;
Do soluble or insoluble fibres absorb water?
soluble
What do mammals use to digest cellulose (don’t have cellulase)?
fungi and bacteria that produce cellulase to break down cellulose
what is commensalism?
microorganisms that do not have any effect on us like bacteria that develop in large intestine
What products are egested as feces?
excretory products, unabsorbed water, undigested fibre
How do soluble fibres help us?
slow down rate of digestion; helps contraction of intestinal muscles;
How does high water content in intestine affect movement of fecal matter?
increase
What kind of relationship does rate of transit of materials through large intestine and fibre content have?
positively correlated; rate of movement increase as fibre content increases
What foods contain dietry fibres?
whole grain bread/cereal; vegetables (cabbage/salad)
How is cholera caused?
infection by bacterium vibrio choleria; acquired from faece- contaminated drinking water
What happens normally when vibrio choleria enters body?
gets killed by acids
What happens if vibrio choleria reaches intestine?
attaches to epithelium membrane;
releases toxin to bind to receptor on intestinal cells;
cascade effect;
loss of ions from cells;
outflow of water/body loses lots of fluid (osmosis);
watery diarrhoea; water drawn from blood to replace loss;
death through dehydration
What is the B part of a cholera enterotoxin?
binding protein; attaches the toxin to a glycolipid on intestine epithelial cell
What is part A of a cholera enterotoxin?
enzyme; activates plasma membrane of epithelial cell; causes secretion of chloride ions into lumen; cells can’t take up sodium
