11.3 The kidney and osmoregulation Flashcards
What are osmoregulators and osmoconformers?
Osmoregulators maintain a constant internal solute concentration, even when living in marine environments with very difference osmolarities
Osmoconformers are animals whose internal solute concentration tends to be the same as the ocncentration of solutes in the environment
What is excretion?
The removal of metabolic waste products from the body
What is the difference between excretion and egestion?
Egestion - removal of faeces (undigested food that has never been absorbed into body cells
Excretion - The removal of metabolic waste products from the body
What products have to be excreted from the body?
- Urea
- CO2
- salts
- H20
- Mineral ions
- bile
What is the excretory products of the liver?
Bile and urea
What is the excretory products of the lungs?
CO2 and water vapour
What is the excretory products of the kidneys?
Urea is converted to urine
Urea ,H20, excess mineral ions
What is the excretory products of the skin?
Sweat
* H20, mineral ions, urea, ammonia
Why do waste products need to be excreted from the body?
- so they dont reach toxic concentrations
- Affect osmolarity and movement of water by osmosis
- so it doesnt take up space
Why must nitrogenous wastes be eliminated?
It is toxic in organism, so excess levels must be eliminated form the body
What is the type of nitrogenous waste in animals correlated to?
correlated with the evolutionary history of the animal and habitat
In what form do most aquatic animals excrete their nitrogenous waste? why?
Ammonia (NH3) - highly toxic but water soluble so it is suitable for animals living in aquatic habitats
In what form do most birds and reptiles excrete their nitrogenous waste?
Uric acid - required more energy to make but it is non-toxic and requires less energy and less water to egest from the body (egested as semi-solid paste)
Most osmoconformers live in salt water. What is the benefit of being an osmoconformer?
Minimise the movement of water in and out of cells by osmosis
WHat is hemolymph?
A circulating fluid that combines the characteristics of tissue fluid and blood
* Arthropods have them (Arthropods are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. )
What is osmoregulation?
Is a form of homeostasis whereby the concentration of hemolymph, or blood in the case of animals with closed circulatory systems, is kept within a certain range
What is the respective nitrogenous waste product of insects and mammals?
When animals break down amino acids:
Insects: Uric acid
Mammals: Urea
What are Malpighian tubules?
Tubes insected have that branch off from their intestinal tract
What is actively transported from the hemolymph into the lumen of the tubules?
Cells lining the tubules actively transport ions and uric acid from the hemolymph (analogous to blood and tissue fluid in mammals) into the lumen of the tubules
How is water drawn also from the hemolymph into the tubules?
By osmosis from the hemolymph through the walls of the tubules into the lumen
Where does the tubules empty their contents?
Into the gut
What happens in the hindgut?
Most of the water and salts are reabsorbed while the nitrogenous waste is excreted with the feces
What is the process of the mapighian tubule system?
- uric acid, Na+ and K+ are transported into the tubules and water follows by osmosis
- the tubules empty into the guy
- some ions are actively reabsorbed in the hindgut and some water follows
- dehydrated uric acid paste is released with other waste
What is kidney’s function?
Osmoregulation and excretion
Responsible for removing substances from the blood that are not needed or are harmful
What is the difference between the blood form the renal artery and the renal vein?
The composition of blood
Renal artery: through which blood enters the kidneys
Renal vein: through which blood leaves
What substances are present in higher amounts in the renal artery than the renal vein?
- Toxins and other substances that are ingested and absorbed but are not fully metabolized by the body (betain pigments in beets and also drugs)
- Excretory waste prodicts including nitrogenous waste products (mainly urea)
Others that are removed from blood by kidney that are not excretory products:
* Excess water (from cell repiration or absorbed from food in the gut)
* Excess salt (absorbed form food in the gut)
Why are water and salt not excretory products?
Because they are not produced by the body cells
Removal of excess water and salt is part of what?
Osmoregulation
The kidneys filter off about one fifth of what form the blood flowing through them?
one fifth of the volume of plasma
What does the filtrate from the blood in the kidney contain?
All of the substances in plasma apart from large protein molecules
What does the kidney do to specific substances in the filtrate that the body needs?
They then actively reabsorb them
What is the result of actively reabsorbing specific substances in the filtrate that the body needs?
Unwanted substances pass out of the body in urine and those substances are only present in the renal artery but not the renal vein
What is the difference in the composition of blood in the renal artery and vein in terms of oxygen?
Blood leaving the kidney thorugh the renal vein is deoxygenated because kidney metabolism required oxygen
What are the differences between the composition of renal artery and vein in terms of carbon dioxide?
Renal vein also has a higher paertial pressure of carbon dioxie because this is a waste product of metabolism
What is the difference in the composition of blood in the renal artery and vein in terms of glucose?
- Normally glucose is filtered and then entirely reabsorbed
- But some are used by the metabolism of the kindey
- Therefore the concentration is slightly lower in the renal vein compred to the renal artery
What are the differences in oxygen, co2 and glucose in the renal artery and vein due to?
The metabolic activity of the kidney
What is not filtered by the kidney and what does it mean in terms of concentrations in both blod vessels?
Plasma proteins are not filtered by the kidney so should be present in the same concentration in both blood vessels
What does presence of plasma proteins in the urine indicate?
Abnormal function
What is the pressure of blood in capillaries?
High pressure
What does the high blood pressure in capillaries do to plasmas?
The pressure forces some of the plasma out through the capillary wall, to form tissue fluid
Why is the volume of fluid forced out of the glomerulus of the kidney 100x greater than in other tissues?
In the glomerulus of the kidney:
* pressure in the capillaries is particularly high
* capilary wall is partially permeable
* so volume of fluid force out is great
What is glomerular filtrate?
The fluid forced out of the glomerlus of the kidney
What are filtered out and what are retained in teh capillaries of the glomerulus?
Most solutes are filtered out freely from the blood plasma, but almost all proteins are retained in the capillaries of the glumerulus
What is ultrafiltration?
The separation of particles differing in size by a few nanometres and so is called ultrafiltration
* all particles with a relative molecular mass below 65,000 atomic mass units can pass through
What does the permeability to larger molecules depend on in the glomerulus?
their shape and charge
How is the high hydrostatic pressure of the blood in the glomerulus maintained?
The afferent arteriole has a wider diameter than the efferent arteriole, maintaining a high blood pressure
What is the importance of having a high pressure in the glomerulus?
To force small components out into the bowman’s capsule
What are some of the large components that are present in the blood going into the afferent ateriole that doesnt pass through the permeable wall?
- Plasma
- RBC and WBC
- Platelets
- Proteins
What do the renal artery split to form?
Many afferent arterioles, which lead to the glomerulus
What molecules are small enough to pass into the glomerular filtrate?
- Mineral ions
- Water
- Glucose
- Amino acids
- Urea
What does the basement membrane separate?
The capillaries (the white space at the left is the lumen of a capillary)
What are the gaps in the wall of the capillary referred to?
Fenestrations
What are the smaller projections from the membrane?
Podocyte foot processes
What do podocyte foot processes do?
Attach the podocytes (specialised epithelial cells) to the membrane
What do the podocytes function as?
A barrier through which waste products are filtered from the blood
Where is the filter in the kidney?
The filter is the barrier between the blood in the capillary and the lumen of the Bowman’s capsule
How many layers are their on the barrier that is the filter? What are they?
3
* Endothelium of the capillary
* The basement membrane
* The epithelial cells of the Bowman’s capsule
What are 3 parts to the ultrafiltration system?
- Fenestration (the endothelium of the capillary)
- The basement membrane
- Podocytes (the epithelial cells of the Bowman’s capsule)
Where does the glomerular filtrate then flow into?
the proximal convoluted tubule
What is the proximal convoluted tubule like?
- single cell thick
- connected by tight junctions -> function to create a thin tubular surface with no gaps
- Large number of mitochondria within thhese tubule cells, as reabsorption involves active transport
What are substances actively transported across?
The apical membrane (membrane of tubule cells facing the tubular lumen)
What do substances passively diffuse across?
the basolateral membrane (membrane of tubule cells facing the blood)
Label the parts of a nephron
Bowman’s capsule annotation
A cup shaped structure with a highly porous inner wall, which collects the fluid filtered from the blood
Proximal convoluted tubule annotation
A highly twisted section of the nephron, with cells in the wall having many mitochondria and microvilli projecting into the lumen of the tube
Loop of Henle annotation
A tube shaped like a hairpin, consisting of a descending limb that carries the filtrate deep into the medulla of the kindey, and an ascending limb that brings it back out to the cortex
Distal convoluted tubule annotations
Another highly twisted section, but with fewer, shorter microvilla and fewer mitchondria
Collecting duct annotations
A wider tube that carries the filtrate back through the cortex and medulla to the renal pelvis
Blood vessel annotations
associated with the nephron are blood vessels. Blood flows through them in the following sequence:
* Afferent arteriole - brings blood from the renal artery
* Glomerulus - a tight, knot-like, high pressure capillary bed that is the site of blood filtration
* Efferent arteriole - a narrow vessel that restricts blood flow, helping to generate high pressure in the glomerulus
* Peritubular capillaries - a low-pressure capillary bed that runs around the convoluted tubules, absorbing fluid from them
* Vasa recta - unbranched capillaries that are similar in shape to the lops of henle, with a descending limb that carries blood deep into the medulla and an ascending limb bringing it back to the cortex
* Venules - carry blood to the renal vein
What happens in the ascending limb of the loop of Henle?
- sodium ions are pumped out of the filtrate to the interstitial fluid (fluid between the cells in the medulla)
- Water is retained in the filtrate even though the interstitial fluid has a higher solute concentration
What is permeable and impermeable in the descending and ascending limb?
Descending
* Permeable to water
* Impermeable to Na+ ions
Ascending
* Na+ ions are actively pumped out into interstitual fluid
* Impermeable to water
How does the solute concentration or osmolarity change as you go down the descending limb?
Increase
What is the normal tissue lfuid osmolarity and what is the maximum?
Normal - 300mOsm
Max - 1200 mOsm
What causes H2O to move out of the descending limb and collecting duct?
Na+ are actively transported out of the ascending limb, making the interstitual fluid more concentrated (higher osmolarity/lower water potential)
* and so water moves from a lower concentration (the descending limb) to an area with a higher solute concentration (the interstitual fluid) due to the Na+ being pumped out from the ascending limb
* Why the loop of Henle is so important, in order to get the H2O out from the descending limb, the ascending limb needs to pump Na+ out
Why is the vasa recta also a countercurrent system?
- prevents the blood flowing through this vessel from diluting the solute concentration of the medulla, while still allowing the vasa recta to carry away the water removed from filtrate in the descending limb, together with some sodium ions
- the vasa recta blood network that surrounds the loop of Henle flows in the opposite direction (counter-current)
This means that salts released from the ascending limb are drawn down into the medulla, further establishing a salt gradient
the red is the vasa recta
How could the loop of Henle be adapted to conserve more water?
The longer the loop of henle, the more water can be reabsorbed
What is the difference in the epithelial border between the PCT and DCT?
Proximal convoluted tubule - has a brush border consisting of microvilli to increase surface area for reabsorption
Distal convoluted tubule - has no brush border - only absorbs Na+
Why does the concentratin of urea rise as the fluid passes along the distal convoluted tubule?
Water is reabsorbed from the filtrate along the nephron but urea is not reabsorbed therefore the concentration of urea increases
Why does the concentration of sodium stay constant as the fluid passes along the PCT?
Both water and Na+ are reabsorbed from the PCT at the same rate in equal amounts
Why does the glucose concentration drop in the PCT?
All glucose is selectively reabsorbed in the PCT?
