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Summary A2 CCEA Biology - Chapter 1 - Homestasis and the Kidney
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Homeostasis and the Kidney mindmap for the CCEA GCE exam board
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• Solute potential = more negative, which is detected by osmoreceptorsin the hypothalamus.
• posterior lobe of the pituitary body releases more ADH into blood. The ascending limb secretes Na ions and CI ions into the medulla by active transport. NaCI
• walls of DCT and collecting duct become more permeable - aquaporins builds in the interstitial fluid in the medulla, creating a very negative solute potential. As a
(special channel proteins) which helps make the walls of the collecting result of the ions leaving the ascending limb, the filtrate in it becomes progressively more
duct more permeable. Blood develops a higher solute potential dilute and is hypotonic by the time it reaches the top of the ascending limb. The met result
• more water is reabsorbed from the collecting ducts back into blood. (less negative), less concentrated, and is of the very negative water potential in the medulla, caused by the high conc. NaCI, and the
• the net result is that solute potential of blood returns to normal detected by osmoreceptors in the permeability of the descending limb walls, is that water is osmotically removed along the
(becomes less negative) and a smaller volume of hypertonic urine is hypothalamus, less ADH is released, the length of the descending limb. The filtrate in the descending limb becomes progressively
produced. walls of the collecting ducts become less more conc. as you descend (aided by Na and CI ions entering the descending limb by diffusion,
• negative feedback- as blood conc. Changes the solute potential goes permeable and less water is realosorbed until at the very bottom it is hypertonic to blood. The cuboidal epithelial cells in the
back to normal; as the blood conc returns to normal the release of ADH back into blood, produce a large volume of ascending lib are rich in mitochondria which provide the ATP necessary to pump the Na and
reduces, returning to normal levels. hypotonic urine (dilute). Cl ions into the medulla. Water that leaves the descending limb by osmosis enters the vasa
recta and is removed from the medulla causing little effect on the solute potential of the
interstitial fluid. The osmotic differences bet ween the descending and ascending limb at any
By sweating, not drinking enough, or eating a salty meal. one level are small , but the cumulative effect over the length of the limbs is significant,
When drinking a hypotonic liquid. alongside the filtrates in the limbs travelling in opposite directions is described as the
countercurrent multiplier effect. The length of the loop of henlé affects the ability to
S + P = When blood is too concentrated When blood is too dilute reabsorb water and concentrate liquid in the collecting duct as well as water conservation
More negative solute potential Higher solute potential - less negative The collecting duct is where water regulation takes place. Most in a species. The longer the loop of henlé, the more water can be reabsorbed as a longer loop
Plasma - Filtrate = Net filtration force
water is reabsorbed in the pct, the process is passive and the allows the medulla to have an even more negative potential.
exact amount that is reabsorbed can't be controlled.
Solute potential is represented by plasma
Reabsorption in the collecting ducts can be controlled by
proteins as there are plasma proteins in the
ADH is produced in the hypothalamus and is varying the permeability of the collecting duct walls. The
blood in the glomerular capillaries but not in
secreted into the posterior lobe of the antidiuretic hormone (adh) is crucial in this process as it can
the filtrate. The filtrate has a less negative
pituitary gland where it is stored. The solute control the degree of permeability of the collecting duct walls.
solute potential than the blood in the The walls of the descending limb are thin and
glomerulus. Although the difference in solute potential of the blood is monitored by permeable to water. The ascending limb walls
potential opposes filtration,it is insignificant osmoreceptors in the hypothalamus. are much thicker and impermeable to water
Controls balance of water in the body.
when compared to the differences in
hydrostatic pressure across the basement The pressure potential (hydrostatic pressure) of the blood is much greater than
membrane; which promotes filtration. The net Loop of Henlé To create the very conc. Interstitial fluid in the medulla, which facilitates
the back pressure (hydrostatic pressure) created by the filtrate in the nephron. the osmotic removal of water from the collecting ducts.
filtration pressure causes fluid to move from
Enables mammals to produce hypertonic urine
the glomerular capillaries.
There is an outer cortex and an inner medulla in the
Hydrostatic pressure forces water and small molecules kidney. The medulla is sub-divided into a number of
through as well as water potential an each side of the Osmosregulation
The blood entering the glomerulus is under high pyramids whose apices protrude into the pelvis.
membrane. For filtration to occur the water potential in the A kidney contains millions of microscopic tubules called
hydrostatic pressure. Due to:
glomerular capillaries (blood) must exceed the water potential nephrons. The nephron is the functional unit of the
• Renal arteries are wide, short and relatively
close to the heart. in the bowman's capsule (glomerular filtrate) → the kidney.
• the efferent arteriole is larger than the glomerular filtrate must have a more negative water
potential
Homeostasis & the kidney
.
afferent arteriole.
There are three layers that separate plasma from Homeostasis - The maintenance of steady states within the body
filtrate: Filtration force
Excretion - is the removal of toxic waste products
from the body as a byproduct of metabolic processes
• capillary endothelium- consists of a single layer
of squamous endothelium cells with pores
bet ween them. Ultrafiltration - plasma in the glomerulus is filtered into bowman's
• the inner wall of bowman's capsule which Blood Blood Capillary endothelium
Pore in capillary capsule, only substances below a certain size so the filtrate contains
consists of podocytes which are footed cells endothelium
useful substances as well as toxic substances.
=
with spacious gaps bet ween them called Basement membrane
Reabsorption - useful substances are reabsorbed back into blood and it occurs
filtration slits ↑
/
·
as it passes along the nephron and collecting duct.
• the effective filter - the basement membrane of Podocyte
the glomerular capillaries. Glomerular filtrate
Most useful blood products are reabsorbed back into blood mainly along the proximal
convoluted tubule, glucose and amino acids are small enough to pass through the basement
Adaptations of the PCT membrane but too valuable to be lost in the urine they are selectively reabsorbed by
• Microvilli - increases SA for carrier proteins facilitated diffusion and active transport. As they are actively reabsorbed into blood,
• Carrier proteins - in cell surface membrane needed FD and the osmotic effect created causes over 70% of the water in the filtrate to re-enter the
AT of specific molecules. blood capillaries passively by osmosis. Small plasma proteins which may have passed
The epithelial cells of the pct have
• Mitochondria - many mitochondria, high respiration, high through the basement membrane are reabsorbed by pinocytosis. The reabsorption reduces
high levels of metabolic activity and
energy release. solute potential in both the reabsorbing epithelial cells of the tubule and the blood in the
continually carry out energy
capillaries creating the osmotic gradient required for the reabsorption of water.
demanding process such as AT. At the
Some urea passes from the nephron back into the blood by diffusion. Glucose and amino
end of the pct the filtrate is isotonic
acids can be absorbed by facilitated diffusion as long as the concentration gradient
with blood plasma.
permits. Active transport is necessary to ensure that all the glucose is reabsorbed from
the nephron back into the capillary net work.
Further regulation of blood composition takes place in
the DCT. The pt and ionic composition of the blood in
the capillaries surrounding the tubule are adjusted
and some toxic substances eg. Creatinine (a byproduct
of muscle metabolism), are secreted from the blood for
disposal.
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