Salt excretion Flashcards
Nephron
structural and functional unit of the kidney, responsible for filtering blood and producing urine. The end of the nephron is “claw” or “U” shaped with bowmans capsule in the middle of the U
Bowmans capsule
The end of a vertabrate nephron where primary urine is formed
Ultrafiltration
Ultra filtration takes place in the glomerulus of a bowmans capsule. The golmerulus has many branching blood channels surrounded by vascular endothelium. This endothelium is highly porous and made up of complex structures called podocytes, which give it its pores. Filtration occurs when filtration pressure is positive, pulling water and small molecules from the blood and into the nephron. The resulting fluid is called capsular fluid, aka primary urine
Filtration pressure
The sum of blood pressure minus Colloid pressure and capsular fluid pressure. Blood pressure tends to favor filtration while colloid and capsular fluid pressures tend to inhibit it, therefore filtration only will occur when filtration pressure is positive.
Formation of primary urine by solute secretion
Initially, concentration of solutes inside and outside of a nephron tube are the same, from diffusion. Energy from ATP is used to secrete solute X into the nephron tube from the blood. This causes water to enter the tube via osmosis. The increase in water within the tube dilutes the concentration of solute Y, in the blood. Solute Y outside of the tube then diffuses down its concentration gradient into the tube.
Amphibian nephrons and collection ducts
From the end of the nephron: Bowmans capsule connects to a slim tube called the neck. The neck feeds into a wide tube called the proximal convoluted tubule. The Proximal convoluted tubule then has a small thin section at the end called the intermediate segment. The intermediate segment feeds into the slightly wider (but still thinner than the PCT) distal convoluted tubule, which then becomes the collecting tubule, which feeds into the collecting duct. The collecting duct has many nephrons attached to it and feeds into the renal pelvis, then ureter.
Rapid urine flow in amphibians
Na+ and Cl- are reabsorbed in the proximal convoluted tubule but because it is freely permeable to water, the water leaves fast enough that the tubular fluid remains isosmotic to the blood. However in the distal convoluted tubule, it is barley permeable to water when the animal is in diuresis. So when Na+ and Cl- are reabsorbed here, the water cannot follow and the urine becomes highly diluted - resulting is rapid urine flow.
diuresis vs antidiuresis (4 each)
Diuresis:
-Distal convoluted tubule is poorly permeable to water
- large amount of water stays in the tube - resulting in lots of dilute urine
-causes high concentration of salts in blood plasma
-low amounts of ADH present
antidiuresis:
-Distal convoluted tubule is highly permeable to water
-only a small amount of water stays in the tube, resulting in small amounts of highly concentrated urine
-causes salt concentrations in the blood to remain unchanged
-high amounts of ADH present
ADH
Antidiuretic hormone - tells kidneys to release less water
kidney Structure
picture a kidney bean. The edge of the bean is the cortex, this is where the bowmans capsules are. Moving inward, is the medulla, where the tubular sections of the kidney are located. The tubular sections feed into the renal pelvis, which has many branches connecting the collection ducts to the ureter. The ureter is a single tube the flows out of the kidney
The renal papilla
Is a section of the medulla that projects into the renal pelvis when it is present. There is little to no development of this in freshwater species, some development of it in species that live on land, and it is highly developed in animals that live in areas with little to no rainfall. In the last case, it often extends into the ureter
Urine concentration and Medulla thiccness
the thiccer the medulla the higher an animals maximum urine concentration is. Remember the medulla is where the tube sections of the nephron are, so it makes sense because more densely packed medulla = more tubes = more concentrating ability
Loop of Henle
In humans, rather than an intermediate segment, we have something called a loop of Henle. These loops are where water reabsorption and therefore urine production happen within the kidney. The feature several segments, is the thick segment of the descending limb, which connects from the proximal convoluted tubule. This connects to the thin segment of the LoH which is where filtration occurs between the LoH and the vasa recta (blood vessels) but only one the descending side. back up is the thick segment of the ascending limb, which connects to the distal convoluted tubule.
nephron length and position
in animals like rodents with high urine concentrating abilities (UCA), they have many shorter nephrons that loop in the outer medulla, with very few extending into the inner medulla. In contrast, in animals with lower UCA, the length and position of the loops vary drastically. Additionally in carnivores, nephrons are very long, with loops all within the inner medulla
The single effect in the loop of Henle
The walls of the ascending limb are essentially impermeable to water. Active transport of NaCl out of the fluid in the ascending limb dilutes it’s fluid and concentrates the interstitial fluid (fluid between the loop). The descending loop has walls that are permeable to water, so the water osmosis’s out into the interstitial fluid, and some NaCl moves in via diffusion. This leads the fluid in descending loop to be highly concentrated, allowing NaCl to be reabsorbed into the blood. The single effect is the difference in osmotic pressure and [NaCl] between the ascending limb and the interstitial fluid.
osmotic pressure and medulla depth
Osmotic pressure increases with medulla depth
How is NaCl reabsorbed into the blood
The sodium potassium pump baby!!! The SPP pumps Na+ into the the blood with ATP because its just chill like that. This creates a positive charge in the blood, making Cl- flow down its electrochemical gradient from the tubule into the blood as well. The SPP really do be the GOAT
Bird kidneys
Bird kidneys are shaped like a lightbulb with the thick part being the cortex and the thin area being called the medullary cone. Nephrons in the cortex are loopless like in amphibians and nephrons in the cone are looped like mammals
Crayfish kidneys
They done have kidneys -they have antennal glands at the base of their antennae. It starts with the end sac which feeds into the sheet-like labyrinth. The Labyrinth feeds into the nephridial canal, which goes into the bladder. The bladder excretes urine through a small hole called a nephropore which is located near the antenna.
Botfly papilla
Botflies have 4 rectal papilla, which are shaped like boomerangs with two channels. The outer channel is surrounded on either side by epithelial cells and is an intercellular space. The inner channel flows bellow the epithelial cells of the outer channel and connects to the blood. There is also a junction where the two channels meet at the “peak” of the boomerang. outside of the boomerang is the rectal lumen
Botfly filtration
Water moves from the rectal lumen into the intercellular space (outer channel) through osmosis. The intercellular fluid flows towards the junction, then begins to flow towards the blood in the inner channel. As it flows, salts diffuse through the epithelial cells back into the intercellular space, causing the fluid in the inner channel to become more dilute before flowing into the blood.
