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3.7 - Homeostasis and The Kidney - Coggle Diagram
3.7 - Homeostasis and The Kidney
Homeostasis
- The maintenance of a constant internal environment by negative feedback.
Prevents wild fluctuations, beyond the optimal range, allowing cells and metabolism to function efficiently.
Core body temperature, pH and water potential
- may change due to changes in our activity or external environment, but they fluctuate around a set point.
Negative feedback
A receptor detects a deviation from the set point in an internal environment.
Receptor sends instructions to a co-ordinator.
Co-ordinator communicates with one or more effectors which make responses which are corrective.
The factor returns to normals, this is monitired by the receptor and infomation is fed back to the effectors, which stop makinf the correction.
Excretion
The removal of wastes produced by the body due to metabolism.
4 Excretory organs
Lungs
- Carbon Dioxide and water in expired air.
Kidneys
- Urea, creatinine and uric acid in urine.
Skin
- urea in sweat.
Liver
- Bile pigments in feaces.
The Kidney
2 main functions
Excretion
- The removal of nitrogenous waste from the body.
Osmoregulation
- The control of water potential of the bodily fluids.
Urea
Excess amino acids are
deaminated
in the liver,
1
. The amino group is removed and converted into ammonia (highly toxic) and then to urea (less toxic).
2
. Urea is removed by the kidneys.
Kidney Structure
Kidney is enclosed in a tough renal capsule.
Blood enters the kidney via the renal artery, and leaves the kidney via the renal vein.
The Nephron
Nephron is the functional unit of the Kidney.
Bowmans capsule
and the
proximal and distal convoluted tubules
are present in the cortex.
The
loope of Henle
is found in the medulla
Ultrafiltration
Filtration under pressure.
Small molecules
and ions are forced into the tubule as filtrate.
Large molecules
(proteins) and blood cells cannot pass into the tubule as they are too large filtrate.
Bowmans capsule and the capillary knot in the glomerulus are responsible for ultrafiltration.
High Hydrostatic pressure
is generated in the capillary knot as the blood capillaries narrow.
Blood enters the glomerulus via the
afferent arteriole
and leaves via the
efferent arteriole
.
The
afferent arteriole
has a wider diameter than the
efferent arteriole
; this narrowing generated a
high hydrostatic pressure
. This is provides the
driving force for ultrafiltration.
This provides the driving force for ultrafiltration.
Small molecules pass through the 3 filrtation laters and enters the bowmans capsule and tubule filtrate.
Glomerular filtrate
contains
Water
Glucose
Salts
urea
Amino Acids
The fine structure of the glomerulus and Bowman's capsule allows ultrafiltration to take place.
- Blood entering the glomerulus is separated from the Bowman's space by 3 layers
Capillary walls
The walls of the capillaries in the glomerulus is one cell layer thick this is called the
endithelium
. Tiny pores between cells, called
fenestration
, alloes soluted to pass to the basement membrane
Basement membrane
This is a
selective molecular filter
which only allows small molecules to pass through; blood cells, platelets and large proteins such as antibodies are too large
.
Squamous epithelial cell layer if the Bowman's capsule
Podocytes
have extensions, called
pedicels
, which wrap around a capillary, pulling is closer to the basement membrane. The gaps between the pedicels are called
filtration slits
Glomerular filtrate
The
high hydrostatic pressure
generated by the narrowing of the capillary in the capillary knot of the glomerulus, forcing small molecules through the
fenestrations
of the endothelial cells, through the selective molecular filter of the
basement membrane
and finally through the
filtration slits
of the pedicels into the Bowman's space.
Calculating filtration rate
20% of the blood that leaves the heart enters the kidneys. The rate at which fluid passes from the blood in the capillary knot (glomerulus) into the Bowman's space is the
filtration rate
This is calculated by:
% Blood filtered = volume of filtrate produced per minute/Volume of vlood entering kidneys per minute x 100
Selective reabsorption by the proximal convoluted tubule
Selective reabsorption
Process by which useful substances such as glucose, amino acids and salts are reabsorbed back into the blood plasma.
Takes place in the
convoluted tubule
By
facilitated diffusion
and
active transport
1 - Closely assiciated with blood capillaires called the
vasa recta
2 - Reabsorbed substances pass from the proximal convoluted tubule into the blood plasma contained in the vasa recta capillaries.
5 -
Basal Channels
also increase surface are of the cell membrane at the
basement membrane
. the cells are
closely associated with the blood capillaires
of the basa recta.
3 - Cells lining the wall of the proximal convoluted tubule are
highly specialised cuboidal epithelial cells
Specialised cuboidal epithelium cell has
microvilli
protruding into the lumen of the PCT to increase surface are for selective reabsorbtion.
4 - Many mitochondria producing ATP from active transport.
Tight junctions between cells to hold neighbouring cells together closely to prevent molecules diffusing between adjecent cells.
Molecules are reabsorbed
Salts - mainly active transport
Glucose and amino acids - Contransport with sodium iron into the cell
Water - Osmosis
urea and small proteins - Facilitaed diffusion
The Glucose Threshold
Glucose usually all reabsorbed by the PCT and re-enters the blood stream via the
vasa recta
If the concentration of glucose inthe filtrate is too high intrinsic transport proteins may become limiting.
Meaning that not all glucose will be reabsorbed.
Glucose will remain in the filtrate and pass out of the body in urine.
Reabsorbed of water by the loop of Henle
1- Filtrate leaves the PCT and enters the descending limb.
2 - The descending limb is permeable to water,
water leaves the filtrate and enters and blood by osmosis, down a water
potential gradient
3 - At the same time Na+ and Cl- ions diffuse into the descending limb from the medulla.
4 - Medulla = low water potential which is maintained by the ascending limb of the loope of henle.
4 - Expelling Na+ and cl- by facilitated diffusion and then active transport.
5 - As water leaves the descending limb by osmosis the filtrate becomes more concentrated, reaching maximum concentration at the apex of the loope
6 - The **ascending limb is impermeable to water, but is permeable to Na+ and cl- initially Na+ and cl- leaves the ascending limb by facilitated diffusion.
7 - but later as the concetration of solutes decreases, active transport takes the expulsion of Na+ and c;- iinto the tissue fluid of the mesulla.
Osmoregulation
- Control of body fluid water potential by negative feedback
This is a type of homeostasis
Under hormonal control
3 -
Osmoreceptors
in the hypothalamus detect a decrease in blood plasma water potential.
A signal is sent to the posterior lobe of the pituitary gland which releases a hormone
ADH
into the bloodstream.
4 -
ADH
is carried to the kidneys and binds to receptor proteins on the wall of the collecting duct and distal convoluted tubule.
5 -
Aquaporins
are added to the cell membranes of the effectors allowing more water to be reabsorbed by osmosis.
This increases the water potential of the blood back towards the set point.
The information is fed back to the hypothalamus and less ADH is produced
6 -
ADH increases the permeability of the collecting duct and distal convoluted tubule
allowing more water to be reabsorbed; urine produced will be more concentrated and a lower volume.
Increasing the permeability of cell membranes using aquaporins
1 -
ADH
binds to
ADH receptor proteins
in the phospholipid bilayer of the cell membrane.
2 - Vesicles containing aquaporins fuse with cell membrane - increasing the number of availiable aquaporins for osmosis.
3 - This increases with permeability of the cell membrane to water, allowing more water to be reabsorbed into the blood plasma of the vasa recta capillaires.
4 - This is reversible, when ADH is released from the receptors the cell membrane folds, forming aquaporin vesicles, this reducing the number if aquaporins and reducing permeability
Kidney failure and treatment
1 - Treatment will be needed to balance fluids in the blood and remove waste.
2 - Medication can be taken to control blood potassium and calcium levels.
3 - A low proteins diet will be reduced the need for deamination in the liver and less urea will be produced.
Dialysis
Haemodialysis
Removes waste products and excess salts from blood
2 - Blood is taken from the artery in the arm and is passes through thousands of long narrow strands of selectively permeable dialysis tubing
3 - The fibres surrounded by dialysis fluid.
4 - Wastle products pass our of the blood plasma, through the pores in the dialysis tbing, into the dialysis fluid.
5 - The fluid flows in the opposite direction to the flood (counter-current flow) and is continously replaced to maintain steep concentration gradients.
Kidney transplant
A donar donates a kidney to the patient.
The donar and patient must have
compatible tissue types and blood groups
To reduce the risk of rejection post-transplant the patient must take
immunosuppressants drugs
for the rest of their lives.
Nitrogenous waste disposal in other organisms
Fish
-Excrete ammonia into the surrounding water by diffusion across their gills
Birds and insects
Produce uric acid. It is non-toxic and very little waters needed for excretion - this requires water loss.
Mammals
Produce urea, which requires ATP, but is less toxic than ammonia