Topic 3.1 Homeostatsis & Kidneys Flashcards
a) Humans have 2 Kidneys. A tough _______ capsule covers each Kidney. Each recieves Kidney recieves blood at the ______ artery and returns to the general blood circulation from the _____ vein. The blood from the renal artery is filtered in the outer layer called the, ______ at the _______ capsule. The loops of henle are found in the ________regions as well as the _______ducts that carry the urine to the pelvis (the basin shaped complex of bones).
b) Name all of the parts of the NEPHRON in order:
Humans have 2 KIDNEYS. A tough renal capsule surrounds each. EachKIDNEY recieves blood from the renal artery. The blood exits the KIDNEY back into general circulation at the renal vein. The blood from the renal artery is then filtered in the outer layer called the, cortex at the bowman’s capsule. The loop of henle is found in the medulla region as well as the collecting ducts that carry urine to the pelvis.
b)
Bottom = afferent arteriole
Top = Efferent arteriole
Glomerulus
Bowman’s Capsule
Proximal Convoluted Tubule
Loop of Henle
Vasa Erecta (Capillaries that surround the loop of henle)
Distal Convoluted Tubule
Collecting Duct
a) What are nephrons put simply?
b) How does blood enter the nephron? Where does that blood then go - give a detailed trail (don’t talk about ultrafiltration or selective re-absorbtion yet)?
a) Nephrons are individual filtering units.
b) Blood enters the nephron in the afferent arteriole. The blood then gets divided into 50 different capillaries that make up the GLOMERULUS. The glomerulus is found encapsulated by the BOWMAN’S capsule. Filtered blood is then carried by an efferent arteriole which takes the blood to a capillary network that surrounds the PCT and the loop of henle (the network is collectively called the vasa erecta).
ULTRAFILTRATION - STEP 1:
a) Blood arrives in the capillaries of the ________ from the ________ arteriole (recall that the ________ arteriole brings ______, the _______ is then diverted into __ different capillaries which altogether form the ________). The _________ exhibits HIGH pressure. It can do this because the _______ arteriole has a wider diameter relative to the ______arteriole as well as the heart’s contractions.
The blood entering the _______ is seperated from the space inside the Bowman’s capsule. Between the blood and that space inside the Bowman’s capsule you’ll find __ layers.
1. The wall of the capillary, which is __ cell thick - __________ cells have pores between them allowing material to flow through except RBC and proteins. These pores are called __________ and they’re __ nm in diameter.
2. The basement membrane is an extracellular layer of proteins. It acts as a molecular filter and is a selective barrier - it acts as a sieve.
3. The walls of the Bowman’s capsule is made up of ___________ epithelial cells called _____________. Structures that extrude from each _________ main body wrap around the _________, allowing the __________’s main body to sit closer to the basement membrane of the __________. The structure that extrudes outwards are called _________. These ___________ have siltration slits in them!
a) Blood arrives in the capillaries of the glomerulus from the afferent arteriole (remember, the afferent arteriole brings the blood, the blood is then diverted into 50 different capillaries which altogether form the glomerulus). The glomerulus exhibits HIGH pressure.
It can do this because the afferent arteriole has a wider diameter relative the efferent arteriole as well as the heart’s contraction.
The blood entering the glomerulus is seperated from the space inside the Bowman’s capsule. Between the blood and that space insiede the Bowman’s capsule you have 3 layers.
1. The wall of the capillary which is ONE cell thick - endothelium cells that have pores between them allowing matreial to flow thorugh except for RBC and proteins which are far too large to fit through! These pores are called FENESTRAE - they’re 80nm in diameter…
2. The BASEMENT membrane is an extracellular layer of proteins. It is a MOLECULAR filter and is a selective barrier - i.e. it acts like a sieve.
3. The walls of the BOWMAN’s capsule is made up of squamous epithelial cells called PODOCYTES. Structures that extrude from each podocyte’s main body wrap around the capillary, allowing the podocyte’s main body to sit closer to the basement membrane of the capillary. The structures which we talked about (that extrude outwards) are called pedicels. These pedicels have slits called filtartion slits.
a) The high b.p. forces the ______ and ______ through the __________ (the pores in the capillaries), through the __________ membrane and then thorugh the _________ _____ present in the pedicels. Therefore, they (the material) end up in the Bowman’s capsule. Filtration under high pressure is called ______________. __________ pressure builds-up inside the capillaries. ____________ pressure = pressure _______ by a _______.
b) What are the solutes contained in the water?
a) The high b.p. forces the solutes and water through the fenestrae (the pores in the capillaries), through the basement membrane and then thorugh the filtation slits present in the pedicels. Therefore, they end up in the Bowman’s capsule. Filtration under high pressure is called ultrafiltration. Hydrostatic pressure builds-up inside the capillaries. Hydrostatic pressure = pressure exerted by a liquid.
b)
Water
Gluecose
Salts
Urea
Amino Acids
a) The blood that _________ to the __________ arteriole is high in _________ and has a LOW ________ __________. Most of the ________ has left.
b) The basement membrane and podocytes have a WHAT charge? How does this impact the passage of WHAT ions into the Bowman’s capsule?
a) The blood that leaves to the efferent arteriole is high in protein (high protein concentration) and has a LOW water potential. Most of the water has left.
b) The basement membrane and podocytes have a NEGATIVE charge. This impacts the passage of negative ions into the Bowman’s capsule as it SLOWS them DOWN!
SELECTIVE REABSORPTION:
a) The _______ filtrate contains _______ that the body needs to eliminate, but also ________ molecules and ____, including gluecose, amino acids, Na+ ions and Cl- ions. Selective reabsorbtion (which is the _______ of _______ molecules and ions from the ________ filtrate in the nephron back into the bloodstream) is a process by which ________ products are reabsorbeed back into the general bloodstream as the glomerular filtrate moves through the nephron…
It all starts in the PCT - Proximal Convoluted Tubule.
1. The PCT is the ______ and ______ part of the nephron. It carries the filtrate from the Bowman’s capsule all the way to the loop of henle. The blood in the capillaries that __________ the ____ absorb the material, some ______ and most of the water, Na+ i and Cl- ions. The PCT has:
a) A large ____ because it is ______ and there are a million nephrons in the kidney.
b) Cuboidal epithelial cells in its walls. Their _____ is increased by the ________, about 1 micrometer long, facing the lumen, and invaginations called the ______ channels in the surface facing the ________ membrane and capillary.
c) Lots of ____________ inside the cells to provide ATP for _______ __________!
d) Close _____________ with the _________ ___________.
e) ______ junctions between cells of the ____ epithelium. These are multi-_________ complexes that ________ a cell, attaching it tightly to its __________. They prevent molecules from diffusing between ___________ cells or from the cell back into the __________ filtrate!
a) The glomerular filtrate contains wastes that the body needs to eliminate, but also useful molecules and ions, including gluecose, amino acids, Na+ ions and Cl- ions. Selective reabsorbtion (which is the uptake of specific molecules and ions from the glomerular filtrate in the nephron back into the bloodstream) is a process by which useful products are reabsorbeed back into the general bloodstream as the glomerular filtrate moves through the nephron…
It all starts in the PCT - Proximal Convoluted Tubule.
1. The PCT is the longest and widest part of the nephron. It carries the filtrate from the Bowman’s capsule all the way to the loop of henle. The blood in the capillaries that SURROUND the PCT absorb the material, some urea and most of the water, Na+ i and Cl- ions. The PCT has:
a) A large S.A because it is long and there are a million nephrons in the kidney.
b) Cuboidal epithelial cells in its walls. Their S.A is increased by the microvilli, about 1 micrometer long, facing the lumen, and invaginations called the basal channels in the surface facing the basement membrane and capillary.
c) Lots of mitochondria inside the cells to provide ATP for active transport!
d) Close association with the blood capillaries.
e) Tight junctions between cells of the PCT epithelium. These are multi-protein complexes that encircle a cell, attaching it tightly to its neighbours. They prevent molecules from diffusing between adjacent cells or from the cell back into the glomerular filtrate!
a) a) About 70% of the _______ in the glomerular filtrate are reabsorbed to the blood. Some reabsorbtion is _______, although almost all utilises ________ ________ by membrane pumps!
To start, there are both ______ ions in the epithelial cells and the PCT’s _________. _______ions in the epithelial cells move _____ and ______ the ________ via active transport. This creates a ____________ ___________ whereby there are less ions (____ ions) in the __________cell now, and so via __________ diffusion of the _____ions from the PCT’s lumen move into the epithelial cells. The transport proteins can also transport ________ alongside ___ions. Thus, they’re _______________ proteins. Then once they’re in the __________ cell, they can flow down their _________ __________ into the _________.
As a result of substances moving _______ the epithelial cell, the water __________ in the epithelial cells __________! The water potential of the lumen _________! This constitutes to a water potential _________. So water moves ______ the cell (epithelial cells) via _______.
The entry of gluecose and amino acids alongside the _______ ions is called _________ active-transport. It’s __________ because it’s not using energy from the ___ directly, but uses energy from the __________________ gradient of _____ ions from the lumen into the cell, which was generated by active t. of the _____ ions into the capillary!
a) About 70% of the salts in the glomerular filtrate are reabsorbed to the blood. Some reabsorbtion is passive, although almost all utilises active t. by membrane pumps!
To start, there are both Na+ ions in the epithelial cells and the lumen. Na+ ions in the epithelial cells move out and into the capillary via active transport. This creates a conc. grad. whereby there are less ions (Na+ ions) in the epithelial cell now, and so via facillitated diffusion of the Na+ ions from the PCT’s lumen move into the epithelial cells. The transport proteins can also transport gluecose alongside Na+ ions. Thus, they’re co-transport proteins. Then once they’re in the epithlial cell, they can flow down their conc. gradient into the capillary.
As a result of substances moving into the epithelial cell, the water potential in the epithelial cells decrease! The water potential of the lumen increases! This constitutes to a water potential gradient. So water moves into the cell (epithelial cells) via osmosis.
The entry of gluecose and amino acids alongside the Na+ ions is called secondary active-transport. It’s secondary because it’s not using energy from the ATP directly, but uses energy from the electrochemical gradient of Na+ ions from the lumen into the cell, which was generated by active t. of the Na+ ions into the capillary!
a) a) About ____% of the water in the __________ filtrate is ___________ by the blood passively, by __________, as reabsorbed ions ______ the water potential of the ______.
About ___% of the UREA and small proteins in the glomerular filtrate is reabsorbed back to the blood by _________. SO much water has been lost from the glomerular filtrate that their concentration there is high. As a result, the conc. grad. down which they diffuse is steep.
a) About 90% of the water in the glomerular filtrate is reabsorbed to the blood passively, by osmosis, as reabosrobed ions lower the water potential of the blood.
About 50% of the UREA and small proteins in the glomerular filtrate is reabsorbed back to the blood by diffusion. SO much water has been lost from the glomerular filtrate that their concentration there is high. As a result, the conc. grad. down which they diffuse is steep.
The GLUECOSE threshold:
a) Gluecose is an energy source the body would be disadvantaged if it were lost to urine. Under normal cicumstances, the PCT reabsorbs all of the gluecose that’s present in the glomerular filtrate. If the concentration of gluecose in the filtrate is too HIGH, however, there may be too few transport molecules in the membrane s of the PCT allowing all of the gluecose to be absorbed. In that case, gluecose passes thorugh the LOOP of HENLE and be lost in urine.
The conc. of gluecose may be very HIGH because:
- The pacreas secretes too little insulin (type I diabetes).
- The response of liver cells to insulin is reduced because insulin receptors in the surface membranes are damaged (type II diabetes or gestational diabetes, which occurs in some women during pregnancy).
The GLUECOSE threshold:
a) Gluecose is an energy source the body would be disadvantaged if it were lost to urine. Under normal cicumstances, the PCT reabsorbs all of the gluecose that’s present in the glomerular filtrate. If the concentration of gluecose in the filtrate is too HIGH, however, there may be too few transport molecules in the membrane s of the PCT allowing all of the gluecose to be absorbed. In that case, gluecose passes thorugh the LOOP of HENLE and be lost in urine.
The conc. of gluecose may be very HIGH because:
- The pacreas secretes too little insulin (type I diabetes).
- The response of liver cells to insulin is reduced because insulin receptors in the surface membranes are damaged (type II diabetes or gestational diabetes, which occurs in some women during pregnancy).
Reabsorbtion of water:
a) A major challenge for terrestrial organisms is preventing dehydration. Large volumes of water CANNOT be lost towards urine.: so much of it is therefore reabsorbed back into the blood as the glomerular filtrate moves thorugh the nephron. About 90% is filtered at the PCT. Some of the water is absorbed at the DCT (found in the cortex) and the loop of henle (found in the medulla region of the kidney). About 5% is reabsorbed back in from the collecting duct.
b) The PCT and loop of Henle always absorb the same amount of water from the glomerular filtrate - i.e. it’s a FIXED number. The DCT and the collecting tube however are special because they can vary the amount of water absorbed by making their membranes more or less permeable to water - it all depends on the body’s level of hydration.
c) Mechanism of Water Reabsorbtion:
The filtrate enters the descending limb of the loop of henle and moves down into a hairpin bend and up into the ascending limb.
The walls of the ascending limb are IMPERMEABLE to water. They actively transport Na+ and Cl- ions out of the glomerular filtrate into the tissue fluid in the medulla. A longer loop of henle means more ions can be exported out into the medulla! As a result of the transport of these ions into the medulla, the medulla now has a LOW water potential. As the filtrate climbs from the bottom of the hairpin, it contains progressively fewer ions. It becomes increasingly DILUTE and its water potential rises (remember that it contains progressively fewer ions becasue those ions are being exported out of the loop of henle.
The walls of the descending limb are PERMEABLE to water, and slightly permeable to Na+ and Cl- ions.
- As the glomerular filtrate flows DOWN the descending limb, water diffuses OUT, by osmosis. Water moves into the medulla region which has a LOW water potential. From there (i.e. from the medulla) it moves into the vasa erecta (the capillaries surrounding the loop of henle).
- At the same time, some Na+ ions and Cl- ions diffuse into the descending limb from the medulla region.
As the glomerular filtrate flows down the descending limb, it contains progressively less water and more ions and so at the bottom of the hairpin, the filtrate is at its most concentrated, with the lowest water potential.
Having 2 limbs of the loop running side by side, with the fluid flowing down in one direction and up in the other direction enables the maximum concentration to be built at the apex of the loop. This mechanism is called counter-current multiplier - this is because flow in the two limbs is in the opposing directions (Counter-current) and the concentration of solutes is increased (multiplied) leading up the ascending limb!
d) The collecting duct runs back into the medulla, psasing through the region of low water potential. Water therefore diffuses out of the collecting duct by osmosis, down a water potential gradient. The longer the loop of henle , the LOWER the water potential in the medulla and therefore, the more water leaves the collecting dut via osmosis. The filtrate becomes more concentrated than the blood.
Reabsorbtion of water:
a) A major challenge for terrestrial organisms is preventing dehydration. Large volumes of water CANNOT be lost towards urine.: so much of it is therefore reabsorbed back into the blood as the glomerular filtrate moves thorugh the nephron. About 90% is filtered at the PCT. Some of the water is absorbed at the DCT (found in the cortex) and the loop of henle (found in the medulla region of the kidney). About 5% is reabsorbed back in from the collecting duct.
b) The PCT and loop of Henle always absorb the same amount of water from the glomerular filtrate - i.e. it’s a FIXED number. The DCT and the collecting tube however are special because they can vary the amount of water absorbed by making their membranes more or less permeable to water - it all depends on the body’s level of hydration.
c) Mechanism of Water Reabsorbtion:
The filtrate enters the descending limb of the loop of henle and moves down into a hairpin bend and up into the ascending limb.
The walls of the ascending limb are IMPERMEABLE to water. They actively transport Na+ and Cl- ions out of the glomerular filtrate into the tissue fluid in the medulla. A longer loop of henle means more ions can be exported out into the medulla! As a result of the transport of these ions into the medulla, the medulla now has a LOW water potential. As the filtrate climbs from the bottom of the hairpin, it contains progressively fewer ions. It becomes increasingly DILUTE and its water potential rises (remember that it contains progressively fewer ions becasue those ions are being exported out of the loop of henle.
The walls of the descending limb are PERMEABLE to water, and slightly permeable to Na+ and Cl- ions.
- As the glomerular filtrate flows DOWN the descending limb, water diffuses OUT, by osmosis. Water moves into the medulla region which has a LOW water potential. From there (i.e. from the medulla) it moves into the vasa erecta (the capillaries surrounding the loop of henle).
- At the same time, some Na+ ions and Cl- ions diffuse into the descending limb from the medulla region.
As the glomerular filtrate flows down the descending limb, it contains progressively less water and more ions and so at the bottom of the hairpin, the filtrate is at its most concentrated, with the lowest water potential.
Having 2 limbs of the loop running side by side, with the fluid flowing down in one direction and up in the other direction enables the maximum concentration to be built at the apex of the loop. This mechanism is called counter-current multiplier - this is because flow in the two limbs is in the opposing directions (Counter-current) and the concentration of solutes is increased (multiplied) leading up the ascending limb!
d) The collecting duct runs back into the medulla, psasing through the region of low water potential. Water therefore diffuses out of the collecting duct by osmosis, down a water potential gradient. The longer the loop of henle , the LOWER the water potential in the medulla and therefore, the more water leaves the collecting dut via osmosis. The filtrate becomes more concentrated than the blood.
Osmoregulation:
a) Osmoregulation is the homeostatic function that maintains concentrations of enzymes and metabolites, so that the reactions within cells occur at a constant and appropriate rate. To maintain the osmotic properties of their tissues and fluids, mammals must balance water gain with water loss. Humans gain most of their water externally. About 10%, however, is ‘metabolic water’ released by the body’s reactions.
In the same way as other homeostatic mechanisms, osmoregulation operates by negative feedback: the hypothalamus at the base of the brain, is the receptor, as its osmoreceptors monitor solute potential of the blood. It is also the co-ordinator, as it signals the effector, the posterior lobe of the pituitary gland, to release stored ADH. This returns the system to normal if it deviated too far by changing the behaviour of the walls of the DCT and the collecting duct - i.e. making them more or less permeable.
Diuresis is the production of large volumes of dilute urine. A diuretic, such as alcohol, is a compound that causes the production of large volumes of urine. As its name suggests, ADH causes the production of a small volume of concentrated urine.
Negative feedback controls the volume of water reabsorbed. It restores the normal water potential if the blood is diluted or becomes more concentrated. A fall in water potential of the blood may be caused by:
- Reduced water intake
- Sweating
- Intake of large amounts of salt.
Kidney Failue and its Treatment:
a) The major roles of the kidney are excretion and osmoregulation. If they fail, the body is unable to remove urea, so its concentration increases to TOXIC levels. The body is unable to also remove excess water and so body fluids raise in volume and are diluted compromising key metabolic reactions.
Causes of KIDNEY FAILURE:
- Glomerulosclerosis is the scarring of the tiny filtering units called glomeruli. This causes the loss of protein into urine. Those proteins help fluids stay within the blood vessels. Without them, fluid leaks into the nearby tissue and causes swelling.
- High b.p. - this damages the capillaries of the glomeruluspreventing ultrafiltration from occuring. Conversely, LOW b.p. also prevents ultrafiltration.
b) The body can remain healthy with just one kidney. There may be a slight loss of kidney function later in life but life span is normal. If both are comprimised, however, then as a result treatments must aim to remove/ reduce the concentration of waste products and control the volume of body fluids, to regulate the solute concentration.
- Reducing the intake of certain nutrients - this reduces urea formation.
-Using drugs to reduce b.p: Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers reduce the effect of angiotensin, which is a hormone that constricts blood vessels, increasing the pressure of the blood within. Calcium channel blockers dilate blood vessels and reduce b.p. Furthermore, beta blockers reduce the impact of adrenalin, one effect of which is increased b.p. as the heart rate increases.
- The concentration of dissolved potassium and calcium ions are normally maintained by a balance of absorbtion in the small intestine and by selective reabsorbtion by the nephrons.
> A HIGH K+ conc. in the blood is treated with a combination of gluecose and insulin. If untreated, it leads to heart arrhythimias so intravenous calcium is used in addition, to stabalise heart muscle membranes
