Digestion And Excretion Flashcards
structure of kidney
- kidney capsule is outside of kidneys tough and fibrous
- cortex is outer layer of the kidney has a vast blood supply
- medulla of kidney is the inner portion of the kidney, composed of collecting tubules that empty into the renal pelvis
- pelvic pyramid is where the collecting ducts of the nephrons drain into from the medulla
- Pelvis is the pyramids drain the urine into this hollow funnel shaped structure, which then leads to the ureter
- renal artery brings blood to the kidney and into the cortex
- Renal vein removes blood from kidneys from the vasa recta capillary network in the kidneys
what is nephron
each kidney contains between 1 and 2 million filtration units called nephrons
the parts of the nephron and the function
- Bowman’s capsule -Ultrafiltration
- PCT - reabsorption of water and glucose (selective reabsorption)
- loop of Henle maintains the gradient of sodium ions in the medulla
- DCT- reabsorption of water
- Collecting duct - reabsorption of water
what is ultrafiltration?
high hydrostatic pressure in glomerulus-as diameter of afferent arteriole (in) wider than efferent arteriole (out).
small substances e.g. water, glucose, ions, urea forced into glomerular filtrate. Large proteins remain in the blood
selective reabsorption in PCT
- here all glucose, amino acids and most of the water & ions are selectively reabsorbed. As the glucose & amino acids are reabsorbed, water will follow by osmosis, down the water potential gradient
- the cells of the proximal convoluted tubule contain many mitochondria to provide the ATP required for this process
- they are also covered in microvilli to increase the surface area to volume ratio for faster re-absorption
maintaining a gradient of sodium ions in the medulla by the loop of Henle
counter current multiplier system
1. in the ascending limb:
- Na+ actively transported out ( so filtrate conc. decreases)
- water remains as impermeable to water
- increases conc. of Na+ in medulla, lowering water potential
2. in the descending limb:
- water moves out by osmosis then reabsorbed by capillaries (so filtrate conc. increases)
-Na+ recycled so it diffuses back
Osmoregulation
- Control of water potential of the blood (by negative feedback)
~water moves out of the distal convoluted tubule and collecting duct by osmosis down a water potential gradient
~ controlled by ADH which increases their permeability
roles of the hypothalamus, posterior pituitary and ADH in osmoregulation
H: Contains osmoreceptors 0- detect blood water potential and produce ADH water potential low
PP: Secrete ADH into blood. Due to signal from hypothalamus
ADH: more secreted when blood water potential too low. Increases permeability of cells collecting duct and DCT to water, so increases water reabsorption back into the blood. so decrease volume & increases conc. of urine
how body responds top decrease in water potential/ dehydration e.g. caused by less water intake, increased sweating
- In hypothalamus:
- Osmoreceptors detect decrease in water potential
- So hypothalamus produces more ADH - Posterior pituitary gland secretes more ADH into blood
3,. ADH attaches to receptors on collecting duct
- increasing permeability of cells to water
-so more water reabsorbed from DCT/ collecting duct by osmosis
4.Urine = smaller vol, more conc.
how body responds to increase in water potential…
- Osmoreceptors->less ADH produced-> decreased permeability-> less water reabsorbed-> larger volume of dilute urine
digestive system
- stomach is large muscular sac that continues the mechanical and chemical digestion of food. Muscular walls churn the food the mechanically digest it. Contains HCI to kill any bacteria ingested. This is also the optimum pH for protease enzymes which start protein digestion
- Pancreas contains both exocrine glands ( secrete digestive enzymes endopeptidase pancreatic amylase and lipase into the duodenum via the pancreatic duct) and endocrine glands ( that secrete insulin & glucagon into the blood) to regulate glucose levels.
- Gall bladder: stores bile produced by the liver & releases it via the bile duct, then pancreatic duct into the duodenum. The bile has a pH of 8 to neutralise the stomach acid
-Duodenum is the first part of the small intestine. Site of neutralisation of the stomach acid using the bile from the gall bladder - ileum: part of the small intestine.
Microvilli-site of absorption of the products of digestion, which then move into the blood stream (glucose & amino acids)
or lymphatic system and removed - colon is site of water absorption
starch digestion
-salivary amylase (saliva) starch —> maltose
-pancreatic amylase (small intestine)
- brush border enzymes (maltase) maltose —> glucose
carbohydrate digestion
- starts in mouth with amylase converting starch to maltose
- In the duodenum, pancreatic amylase continues to hydrolyse the glyosidic bonds in starch to maltose
- Maltose is then hydrolysed to glucose by maltose enzymes embedded in the membrane of the epithelial cells lining the ileum
absorption of glucose
- sodium ions actively transported out of epithelial cells lining the ileum, into the blood by the Na+/K+ pump. Creating a conc. gradient of Na+( higher conc. of sodium in lumen than epithelial cell)
- As the sodium ions carried into the epithelial cell via a co transport carrier protein they carry glucose molecules with them
- creating a conc. gradient of glucose higher conc of glucose in epithelial cell than blood
- Glucose moves out of cell into blood by facilitated diffusion using carrier protein
Absorption of amino acids and protein digestion
- Amino acids are absorbed in the same way except instead of glucose amino acids are moved instead
- begins in stomach with pepsin, completed by team of diff enzymes in the lumen of small intestine and epithelium of sm intestines which break polypeptides into small small peptides into amino acids
