This is the new specification notes for the Biology A2 Unit 1, I achieved an A in this unit as well as overall. They are very condensed but still have all the information required for the unit which makes them perfect to use as revision notes.
As a student doing the new revised spec - especially ...
Homeostasis and kidney
Homeostasis is the maintenance of constant or steady state Excretion is the removal of
conditions within the body. toxic waste of metabolism
A control system with sensors(receptors) provides Osmoregulation is the
information allowing the monitoring of a factor, usually in control of water potential of
the brain. body fluids
If the receptors show a deviance from a set point then a
corrective mechanism brings changes to return the factor
back to its normal level
It is a negative feedback system, bringing the factor to its set
point causes the corrective mechanism to be tuned off
preventing over-correction.
This can be under nervous or hormonal control
Ultrafiltration- occurs through 3 layers
Endothelium of capillary- very thin and porous, proteins too
big
Basement membrane of capillaries- meshwork of fibres that Epithelial cells of PCT have high metabolic activity In the collecting duct, water is regulated.
small molecules can fit through e.g. water and small solutes to carry out energy demanding processes-active Antidiuretic hormone(ADH) is crucial
Epithelium of the renal capsule- Podocytes, each cell has transport Produced in the hypothalamus and secreted into posterior lobe of pituitary
foot like extensions that interlink with neighbouring cells to Large amount of protein carrier molecules for body. Solute potential of blood is monitored by osmoreceptors in the
increase surface area, leaving small filtration slits selective reabsorption (Facilitated+active) hypothalamus
Factors affecting rate Microvilli-increase surface area for absorption If blood is too concentrated- solute potential becomes more negative and is
Hydrostatic pressure- if high more fluid lost from blood Large amount of mitochondria-provide ATP for detected by osmoreceptors in hypothalamus. Posterior lobe of pituitary body
Pressure of the glomerular filtrate- back pressure on blood active transport releases more ADH into blood. Causes walls of DCT and collecting duct to
vessels, normally lower than blood pressure Vasal invaginations to increase surface area become more permeable-aquaporins open in collecting ducts (more permeable)
Solute potential - of blood is less negative than that of Capillaries lie close to cells lining PCT reducing More water is reabsorbed into blood, this means it returns to normal and a
filtrate due to loss of soluble substances into bowmans diffusion distance smaller volume of concentrated urine is produced.
capsule Further regulation takes place in DCT and ionic/pH This is negative feedback as it returns to normal the release of ADH reduces
Blood pressure- higher blood pressure=greater rate of of capillaries are adjusted returning to normal
filtration The ascending limb secretes Na+ and Cl- ions into medulla by active
Vasodilation of afferent arteriole- increases pressure in transport resulting in salt building up in medulla and creating a very Cuboidal epithelial cells in ascending are rich in
glomerulus negative solute potential. The filtrate becomes more dilute and becomes mitochondria (ATP)
Vasoconstriction of efferent arteriole- increases pressure hypotonic to blood. The net result of the very negative water potential in Water that leaves the descending limb by osmosis
the medulla due to the Na+ and Cl- and the permeability of descending enters vasa recta, no effect on solute potential of
Loop of henle involved in creation of hypertonic urine limb means that water is osmotically removed along the length of the interstitial fluid (countercurrent multiplier effect
Descending limb- thin and permeable to water descending limb. The filtrate becomes more concentrated down the due to osmotic difference between descending
Ascending limb- thick and impermeable to water but descending limb aided by the reabsorption of Na+ and Cl- in descending and ascending limbs+running in opposite
permeable to salts limb by diffusion directions.
The longer the loop of henle the more water that can be At the bottom of the loop the filtrate is hypertonic.
reabsorbed - more negative solute potential in interstitial
fluid
Biology A2 1 Page 1
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