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renal artery
Blood is being brought to the kidney by the renal artery from the posterior aorta. About 1/4 blood goes here then it is filtered.
renal vein
The blood supply leaving kidney. Will go back to the heart via the inferior vena cava.
ureter
Long tube that connects the kidneys to the urinary bladder
bladder
Stores urine. Has stretch receptors and when they are stimulated it signals you to urinate. Some osmoregulation can take place in non mammals
urethra
Tube from the urinary bladder to the outside world.
urine
Excreted from kidneys. Contains metabolic wastes (urea)
cortex
Outer layer of the kidney. Around the renal medulla. Capillary beds are found in this layer.
medulla
The inner layer of the kidney. Surrounded by the renal cortex.
nephron
The functional unit found in the kidney. Is a tubular transport epithelium. Is located in both the renal cortex and medulla. Has a blood supply.
collecting duct
Collects urine from several nephrons. Most reclaims water and NaCl.
juxtamedullary nephron
Is a special nephron that is in both cortex and medulla. This has a long loop of henle, that goes into the medulla. About 20% of nephrons (birds and mammals only). Allows urine to become very concentrated.
cortical nephron
Very short loop of henle that does not go into the medulla.
Bowman''s capsule
The structure in which the the filtrate is initially released into from the afferent arteriole, by the glomerulus. Is the beginning of a sealed tube so the filtrate must move along it to the proximal tubule.
proximal tubule
The tube leaving from the Bowman''s capsule. Is proximal because of its orientation to the Bowman''s Capsule.Organic molecules are only done here. (Ex: Amino acids, glucose). proximal because of its orientation to the Bowman''s Capsule.Organic molecules are only done here. (Ex: Amino acids
distal tubule
Is located farther away from the Bowman''s capsule and after the ascending loop of henle. Then connects to the collecting duct. Most reclaims water and NaCl.
loop of Henle
The decending and ascending loop after the proximal tubule. This dips down into the medulla of the kidney. Most reclaims water and NaCl.
afferent arteriole
The arteriole that moves into the Bowmans capsule.
glomerulus
A blind sac. That is sealed in one end with a capillary bed within it. The beginning of the nephron.
efferent arteriole
The ateriole that leaves the bowmans capsule.
peritubular capillaries
The efferent ateriole then breaks up after leaving the bowmans capsule into a capillary bed.
vasa recta
Capillary bed around the loop of henle. After the pertibular capillaries.
filtration
The process of moving fluid from a capillary bed though an epithelium layer. This filtration can be active or passive.
filtrate
"The fluid as it passes from a capillary bed into the kidney. Is very similar to blood plasma
secretion
Adding to the interstitial fluid (filtrate). Adding things we want to get removed. Only happens in proximal and distal tubules. Is a selective process. Requires some sort of active transport to move material into the filtrate. Is using selective protein channels or carrier proteins.
reabsorption
Requires energy and requires special proteins to move material out of filtrate. Since it has specific carrier proteins it is selective. Occurs all along the nephron, proximal and distal tubule, and the loop of henle. After different segments, different things are reabsorbed.
Amount of blood filtered per day
1100 - 1200 passes through the kidney per day ----> Of this about 180L ends up getting filtered. Most of the water filtered is put back into the blood. ------> 1.5L of urine is excreted per day.
Concentration of urine
Urine in mammals and birds can by hypertonic to interstitial fluids. This allows these mammals and birds to change the concentration of their urine based of their water needs.
Filtrate in proximal tubule. Process
The proximal tubule is a single layer thick of transport epithelium. The energy source for the transport here is done by the Na+/K+ pump located on the basal side of the epithelium. Pumps 3 Na out of the cell and 2 K into the cell. K+ channels on both side of the epithelium, can move out to either side of the membrane. Na is the main driving force, since when the filtrate is moved out of the glomerulus it has the same concentration of ions of the blood. The Na creates a gradient so the ions will move across. Now Na is low in the cell. Now in the apical side there are many Na+ cotransporters (Ex. glucose, amino acid). Glucose and amino acids are moved by via a transport protein (too large for channels) in the basal side. Cl- will follow an electrical gradient made by the movement of Na+, is moved via a electrical gradient. Nutrients (glucose/amino acids, organic molecules etc.) are moved via active transport. All of these ions, and organic molecules are moved into the interstitial space. These ions make the interstitial hypertonic, so water will rush into it. Outside of the proximal tubule is peritubular capillary bed.
Filtrate in decending loop of henle
Special cubodial epithelium that allows only water to move through it, via aquaporins. Na will not pass through. Around the cortex the osmolarity is about 300 mosm/L. In the interstitial fluid as you move into the medulla there is a steep salt gradient, up to 1200 mosm/L. Water can move out of into the area of 400 mosm/L, since water moves from hypotonic solutions to hypertonic, water will move out until it reaches equilibrium. This continues down the loop of henle until you reach the end of the decending loop at 1200 mosm/L. This process is concentrating the amount of Na+ in the filtrate. The water moves into the vasa recta, back into the blood.
Filtrate in the ascending loop of henle.
The filtrate is now very concentrated with Na+. Now water is not allowed to move back into the ascending loop of henle (no aquaporins). Salt can move out. Now as we go back up the ascending loop the osmolority of Na in the interstitial fluid begins to decrease. So the Na in the ascending loop of henle will move outward, until it reaches equilibrium. When you get about halfway through the ascending loop of henle there are active Na+/K+ ATPase to move the Na out. The solution when it reaches the end of the loop of henle is hypotonic due to the active transport of Na out of the filtrate. Some of the salt does not make it into the Vasa recta, will account for the salt ion gradient seen in the medulla.
Filtrate in the distal tubule
The mosm/L is now around 100, much less than the normal 300 in the blood. This section allows for more materials to be absorbed in this section, this can be done by various ATPase and channels.
Filtration in the collection duct
Where urine becomes concentrated. Recieves filtrate from many nephrons. As the filtrate moves down the collecting duct it has option to remove more water or leave water in the filtrate. If we are water stressed, the filtrate will interact with the salt gradient. This gradient can be used if we need more water. The aquaporins will allow water to leave, concentrating more urine. The number of aquaporins can be removed very quickly from the plasma membrane in the collecting duct. The most distal part will also allow urea to leave. Urea helps contribute to the concentration gradient found in the interstitial fluid in the medulla of the kidney. Urea came from the blood, urea maybe dilute in the beginning of the collecting tube but alot of water leaves so it concentrates the urea.
Variation of water concentration of the urine
Can be as concentrated as 1200 mosm/L if your water intake is low. Or can be as dilute as 100 mosm/L if you have too much water. DEPENDS ON THE PHYSIOLOGICAL CONDITION IN YOUR BODY.
Counter current exchange in kidney
The current runs opposite that of the filtrate. This is done so that the salt gradient (osmotic) created in the medulla of the kidney is not removed. As blood comes in from the vasa recta down the ascending loop of henle, its concentration is low and the (Na+ is only coming out on the ascending loop) filtrate is low. As it progresses farther down the ascending loop its concentration (Na+ only) will increase until it reaches 1200. Now this gradient will cause water (only water moves out of the descending loop of henle) that was removed to want to come back into the blood. Water coming in will continue to do so until it reaches equilibrium with the gradient outside. So water will continue to come in as it moves up the descending loop until it reaches 300. The moves to the renal vein. Sarah smells
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