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)
How is the endothelium of the capillary (fenestration) adapted to enable ultrafiltration
- Fenestration (the endothelium of the capillary)
* Between the cells in the wall of the capillaries
* Allow fluid to escape, but not blood cells
How is the basement membrane adapted to enable ultrafiltration?
- The basement membrane
* Covers and supports the wall of the capillaries
* Consists of fine mesh of collagen fibres and negatively-charged glycoproteins
* Prevents plasma proteins from being filtered out, due to their size and negative charges
How is the epithelial cells of the bowman’s capsule (podocytes) adapted to enable ultrafiltration?
- Podocytes (the epithelial cells of the Bowman’s capsule)
* the epithelial cells of the bowman’s capsule
* specialised shape - have many finger like projections called major processes
* on each major processes are minor proceses or foot processes
* These extensions wraps around the capillaries of the glomerulus
* the very narrow gaps between the foot processes help prevent small molecules from being filtered out of blood in the glomerulus
What are minor processes also known as?
Foot processes and/or pedicels
What determines if a particle is part of the glomerular filtrate?
If they pass through all 3 parts of the ultrafiltration system
* Fenestrations
* Basement membrane
* podocytes
Where does the glomerular filtrate then flow into?
the proximal convoluted tubule
How much of the filtrate must be reabsorbed into the blood?
Almost all
Where does most of the reabsorption of the filtrate occur?
In the first part of the nephrone - the proximla concoluted tubule
What happens by the end of the proximal tubule?
All glucose and amino acids and 80% of the water, sodium and other mineral ions have been absorbed
What is the method used to reabsorb sodium ions in the proximal convoluted tubule?
- active transport from filtrate to space outside the tubule
- then pass to peritubular capillaries
- pump proteins are located in oouter membrane of tubule cells
What is the method used to reabsorb chloride ions in the proximal convoluted tubule?
are attracted from filtrate to space outside the tubule because of charge gradient set up by active transport of sodium ions
What is the method used to reabsorb glucose and amino acid in the proximal convoluted tubule?
- co-transported out of filtrate into fluid outide the tubule by co-transporter proteins in outer membrane of tubule cells
- Sodium ions move down concentration gradient from outside tubule into tubule cells
- This provides energy for glucose to move at the same time to fluid outside the tubule
What is the method used to reabsorb water in the proximal convoluted tubule?
- pumping solutes out of filtrate and into the fluid outside the tubule creates a solute concentration gradeint
- Cause water to be reabsorbed from filtrate by osmosis
Which glomerular filtrate use a passive or active process to get reabrobed in the proximal convoluted tubule?
Passive
* Na+
* H2O
* Urea
Active
* Ions (e.g. Ca2+, Cl-)
* Amino acids
* Glucose
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)
What is the difference between endothelial cells and epithelial cells?
Endothelial cells
* cover the blood vessels inner surface
Epithelial cells
* cover outer surface of the internal organs and the body
How thick is the endothelium of blood capillary?
One cell thick
What allows the water to be reabsorbed by osmosis?
The active transport of mineral ions, glucose and amino acids across the apical membrane decreases the water potential of the cells lining the proximal convoluted tubule
* causing water to be reabsorbed by osmosis
Label the parts of a nephron
What is the basic functional unit of the kidney?
The nephron
What is the nephron?
- The tube with a wall consisting of one layer of cells
- This wall is the last ;ayer of cells that substances cross to leave the body - it is an epithelium
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 is the overall effect of the loop of Henle?
to create a gradient of solute concentration in the medulla
What is the energy to create the solute concentration gradient by the loop of henle is used up by what?
Is expended by wall cells in the ascending limb
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
What is meant by a countercurrent multiplier system?
Countercurrent system: Fluid flows in opposite directions
Multiplier system: causes a steeper gradient of solute concentration to develop in the medulla than would be possible with a concurrent system
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 relationship betwen the length of the loop of Henle with the water conservation in animals?
The longer the loop of Henle, the more water volume will be reclaimed
Animals adapted to dry habitats will often have long loops of Henle
Where are the loops of Henle found?
In the medulla
How are long loops of Henle accomodated?
The medulla must become relatively thicker
When is a solution hypotonic?
When the solute concentration is lower than that of normal body fluids
Where does the filtrate enter after the loop of Henle?
The distal convoluted tubule
What is the solute concentration when the filtrate enters. the distal convoluted tubule?
Its solute concentration is lower than that of normal body fluids - it is hypotonic
Why is the solution that enters the distal convoluted tubule hypotonic?
Because proportionately more solutes than water have passed out of the filtrate as it flows through the loop of Henle in the medula
In the loop of Henle, does more water or solute get passed out of the filtrate?
More solute passes out of the filtrate
How does the solute concentration of the blood affecct the amount of water reabsorbed?
If the solute conc. of the blood is too low, relatively little water is reabsorbed as the filtrate passes on through the distal convoluted tubule and the collecting duct
What is reabsorbed in the distal convoluted tubule?
Mineral ions (mosly sodium ions) by active transport
How does producing large amounts of urine help increase the solute concentration of the blood?
When solute concentration is low in the blood, little water is reabsorbed and because the distal convoluted tubule has a low permeability to water, a large volume of urine is therefore produced, with a low solute concentration, and as a result the solute conc. of the blood is increased
What happens if the solute concentration. is too high in the blood?
The hypothalamus of the brain detects this and cause the pituitary gland to secrete a hormone - antidiuretic hormone or ADH
* ADH causes the walls of the distal convoluted tubule and collecting duct. tobecome much more permeable to water and most of the water in the filtrate is reabsorbed.
* Also helped by the solute conc. gradient of the medulla. Filtrate passes down the collecting duct where the solute conc. of the interstitual fluid is high. Water continues to be reabsorbed for the whole length of the collecting duct. = kidney produces a small volume concentrated urine
What happens if the solute concentration. is too high in the blood?
The hypothalamus of the brain detects this and cause the pituitary gland to secrete a hormone - antidiuretic hormone or ADH
* ADH causes the walls of the distal convoluted tubule and collecting duct. tobecome much more permeable to water and most of the water in the filtrate is reabsorbed.
* Also helped by the solute conc. gradient of the medulla. Filtrate passes down the collecting duct where the solute conc. of the interstitual fluid is high. Water continues to be reabsorbed for the whole length of the collecting duct. = kidney produces a small volume concentrated urine
How does the kidney help keep the relativ amounts of water and solutes in balance (i.e. how is it osmoregulating)?
Too low
* little water is reabsorbed
* Large volume of urine is produced with low solute conc.
* Increase solute conc. of blood
Too high
* ADH produced
* Increase permeability of DCT and collecting duct
* Most water reabsorbed
* even more water is reabsorbed in the collecting duct due to solute concentration gradient
* produce small volume of concentrated urine
* Decrease solute conc. of blood
What does the permeability of the collecting duct depend on?
Conc of ADH
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?
What is dehydration + how does it arise
Condition that arises when more water leaves the body than comes in
* exercise
* insufficient water intake
* diarrhoea
Can lead to the disruption of metabolic processes
What are the symptoms of dehydration?
- Water is necessary to remove metabolic wastes so can lead to tiredness and lethargy due to decreased efficiency of muscle function and increase tissue exposure. tometabolic wastes
- Blood pressure can fall due to low blood volume
- increases in heart rate
- Body temperatyre regulation may be affected because of inability to sweat
What is overhydration?
- less common
- over consumption of water
- dilution of blood solutes
- can occurs when large amounts of water are consumed after intense exercise without replacing the electrolytes lost at. the same time
- makes body fluids hypotonic and can result in the swelling of cells due to osmosis
- headache
- nerve function disruption
What are some treatment options for kidney failure?
- Hemodialysis
* Using. adialysis machine to filter the blood of a patient then returning to the patient via a vein
* Can take several hours
* risk of infection and other complications - Kidney transplant
* A living donner can survive with one functional kidney
* greater independence. ofmovement and freedom to travel compared to a dialysis
* organ can be rejected by recipient’s body’s imune system (numerous lymphocytes will infiltrate the kidney tissue)
What is urinalysis?
A clinical procedure that examines urine for any deviation from normal composition
How does a urine test strip work?
The strip contains 3 test areas designed to change colour to indicate a positive or negative result after being dipped in urine
The test indicates the pH, protein level and glucose level
What does high levels of glucose and protein in the urine indicate?
diabetes
What can high protein levels in the urine indicate?
damage to the kidneys as these do not get through ultrafiltration in a healthy kidney
How is monoclonal antibody technology based test strips used?
To test for traces of banned and controlled drugs
What does it mean when white blood cells are seen in a microscopic examination of urine?
can be a sign of urinary tract infection
What does it mean when red blood cells are seen in a microscopic examination of urine?
sign that there is a kidney stone or a tumour in the urinary tract
