11.3 Kidney and Osmoregulation Flashcards
Osmolarity
Refers to the solute concentration of a solution
Osmoregulators
Animals whose maintain a constant internal solute concentration (even when living in a marine environment with different osmolarity)
Osmoconformers
Animals whose internal solute concentration tends to be the same as concentration of solutes in the environment
Examples of Osmoregulators
All terrestrial animals, freshwater animals and some marine organisms (e.g. bony fish)
What is the Purpose of the Malpighian Tubule System?
The Malpighian tubule system in insects and the kidney carry out osmoregulation and the removal of nitrogenous wastes
Hemolymph
Animals that have a circulating fluid that combines characteristics of tissue fluid & blood
e.g. arthropods
Osmoregulation
Form of homeostasis where by concentration of hemolymph or blood (animals) with closed circulatory systems is kept within certain range
Control of solute concentrations in the body fluids
When Animals Break Down Amino Acids what is it’s Product?
When animals break down amino acids, the nitrogenous waste product is toxic and needs to be excreted
Waste product:
Insects - usually in form of uric acid
Mammals - urea
Malpighian Tubule System Process
Insects have Malpighian tubules. These are tubes that branch off from their intestinal tract.
Cells lining tubules actively transport ions and uric acid from hemolymph into lumen of tubules.
It draws water by osmosis from hemolymph through the walls of the tubules into lumen.
The tubules empty the lumen into gut.
The hindgut is where most of the water and salts are reabsorbed, while nitrogenous wastes are excreted with feces.
Parts of the Human Kidney
Cortex, medulla, renal pelvis
Renal artery, renal vein
Ureter
Renal Artery and Renal Vein
Renal Artery - Brings blood to the kidney
Renal Vein - Brings blood away from the kidney
Ureter
Carries urine from the kidney
Why is the Composition of Blood Different in the Renal Artery and Renal Vein?
The renal artery brings blood to the kidney from the body.
The kidney is responsible for removing substances from the blood that are not needed or harmful. The blood that leaves the kidney from the renal vein does not contain these substances.
Function of the Kidney
Both osmoregulation and excretion
Composition of Water and Salt in the Renal Artery and the Renal Vein
Renal Artery: Variable content
Renal Vein: Constant concentration
Osmoregulation in the kidney removes excess water and salt.
Composition of Unwanted Substances in the Renal Artery and the Renal Vein
Unwanted Substances - e.g. toxins, urea
Renal Artery: Present
Renal Vein: Not present
The kidneys filter out plasma
The filtrate contains all plasma substances except large protein molecules
The kidneys reabsorb specific substances in filtrate that are needed
Result: unwanted substances pass out of the body in urine
Composition of Oxygen, Carbon Dioxide and Glucose in the Renal Artery and the Renal Vein
Renal Artery: More oxygen, less carbon dioxide, more glucose
Renal Vein: Less oxygen, more carbon dioxide, less glucose
Oxygen: required by kidney metabolism
Carbon dioxide: waste product of metabolism
Glucose: used by kidney metabolism
Composition of Plasma Proteins in the Renal Artery and the Renal Vein
Renal artery + renal vein: same concentration in both
Plasma proteins are not filtered out by the kidney
The presence of plasma protein in the urine indicates abnormal function (looked in clinical exam of urine samples)
Blood in Capillaries in Many Tissues vs. the Glomerulus
The blood is capillaries are high pressure in many tissues. This pressure forces some plasma out through the wall to form tissue fluid.
The pressure in the glomerulus is particularly high and the capillary wall is particularly permeable. The volume of the forced out is much greater than other tissues.
Glomerular Filtrate
The fluid that is forced out from the Glomerulus
Solutes that are Filtered Out from the Capillaries of the Glomerulus
Substances in the glomerulus go through ultrafiltration. Most solutes are filtered out freely from blood plasma but almost all proteins are retained in the capillaries of the Glomerulus.
The permeability to larger molecules depends on their shape and charge. Almost all proteins are retained in the blood along with all blood cells.
Ultrafiltration
Separation of particles differing in size by a few nanometers
Three Parts of the Ultrafiltration System
Fenestrations, basement membrane, podocytes
If the substance passes all three parts, they become part of the glomerular filtrate.
Fenestrations
Gaps in the wall of the capillary
Fenestrations are between the cells in the wall of the capillaries.
They allow fluid to escape but not blood cells.
Basement Membrane
Separates capillaries
The basement membrane covers and supports walls of capillaries.
They are made of negatively charged glycoproteins that form a mesh.
This prevents proteins from being filtered out due to their size and negative charges.
Podocytes
Barrier through which waste products are filtered from blood
Podocytes form the inner wall of the Bowan’s capsule.
They have extensions that wrap around capillaries of the glomerulus.
They have many short branches called foot processes.
They have very narrow graps between the foot processes that help prevent small molecules from being filtered out.
Metabolic Pathways
Chains and cycles of reactions in living cells used to build up and break down biochemicals.
Metabolic pathways produce waste products that would be toxic if allowed to accumulate in cells and thus must be removed.
Excretion
The removal of potentially toxic waste products of metabolic pathways from the body
Where does glomerular filtrate into after it goes through ultrafiltration?
Proximal convoluted tubule
What process occurs in the proximal convoluted tubule and how does its structure aid in this process?
Selective reabsorption occurs in the proximal convoluted tubule.
By the end, all glucose and amino acids and 80% of water, sodium and other minerals are absorbed.
Microvilli increases the surface area of reabsorption
Mitochondria produces ATP for active transport
The lumen contains the filtrate
How are sodium ions reabsorbed in the proximal convoluted tubule?
Active transport pumps Na+ ions from the proximal convoluted tubule cells to the capillaries
This generates a concentration gradient between the cells and the filtrate in the lumen
Na+ cells move from the lumen to the cells by facilitated diffusion down the concentration gradient
How are chloride ions reabsorbed in the proximal convoluted tubule?
Chloride ions are attracted from the filtrate to the space outside the tubule because of the charge gradient set up by the active transport of Na+ ions.
How are glucose and amino acids ions reabsorbed in the proximal convoluted tubule?
Glucose and amino acids and co-transported out of the filtrate and into the fluid outside tubule by co-transporter proteins in the outer membrane of the tubule cells
Na+ ions moving provides energy for glucose and amino acids to move the same time.
How are water ions reabsorbed in the proximal convoluted tubule?
Pumping solutes out of the filtration and into the fluid outside the tubule creates a solute concentration gradient. This causes the reabsorption of water from the filtrate to the proximal convolute tubule cells by osmosis.
Basic functional unit of the kidney
Nephron
Nephron
A tube with a wall consisting of one layer of cells
This is the last layer of cells substances cross to leave the body (epithelium)
Parts of the nephron
Bowman's capsule Proximal convoluted tubule Loop of Henlé Distal convoluted tubule Collecting duct
Blood vessels associated with the nephron
Afferent arteriole Efferent arteriole Glomerulus Peritubular capillaries Vasa recta Venules
Bowman’s capsule
Cup-shaped structure with a highly porous inner wall
Collects the fluid filtered from blood
Proximal convoluted tubule
High twisted section of the nephron
Cells in the wall have many mitochondria and microvilli projecting into the lumen of the tube
Transfers useful substances from the filtrate back into the blood by selective reabsorption
Loop of Henlé
Tube consisting of a descending limb (carries filtrate deep into the medulla) and an ascending limb (brings filtrate back out to the cortex)
Establishes high solute concentrations in the medulla so hypertonic urine can be produced
Distal convoluted tubule
Another highly twisted section of the nephron
Fewer, shorter microvilli and fewer mitochondria
Adjusts individual solute concentrations and the pH of the blood
Collecting duct
Wider tube that carries filtrate back through the cortex and medulla into the renal pelvis
Carries out osmoregulation by varying the amount of water reabsorbed
Overall effect of the loop on Henlé
To create a gradient of solute concentration in the medulla
Ascending limb of the loop of Henlé
The energy to create a gradient is expended by wall cells in the ascending limb.
Pump proteins pump out Na+ ions from the filtrate to the interstitial fluid (between cells in the medulla).
The wall is permeable to Na+ ions but impermeable to water.
Water is retained in the filtrate even through the fluid is hypertonic relative to the filtrate (higher solute concentration).
Descending limb of the loop of Henlé
The wall is permeable to water but impermeable to Na+ ions.
As filtrate flows down the descending limb, the increased solute concentration in the medulla causes water to be drawn out of the filtrate until it reaches the same solute concentration as interstitial fluid.
The fluid can therefore rise further and further until the maximum is reached.
The Loop of Henlé system is an example of what type of system and why?
Countercurrent multiplier system
Countercurrent - the fluids flow in opposite direction
Multiplier - causes a steeper gradient concentration in the medulla in comparison to a concurrent system
The length of the loop of Henlé
The length of the loop of Henlé is positively correlated with the need for water conservation.
The longer the loop, the more water volume reclaimed.
E.g. animals adapted to dry habitats have long loops of Henlé
To accommodate long loops, the medulla bust become relatively thicker.
Function of antidiuretic hormone (ADH)
To control reabsorption of water in the collecting duct
Filtrate that enters the distal convoluted tubule
The solute is hypotonic - lower than normal body fluids
This is because proportionately more solutes than water pass out of the filtrate through the loop of Henlé
Low blood solute concentration
Relatively little water is reabsorbed as the filtrate passes the distal convoluted tubule and the collecting duct
The walls have an unusually low permeability to water and thus, a large volume of urine is produced with a low solute concentration.
This results in a increase in solute blood concentration.
High blood solute concentration
The hypothalamus of the brain detects this and causes the pituitary gland to secrete antidiuretic hormone.
Antidiuretic hormone causes the distal convoluted tubule and the collecting duct to be more permeable to water.
Most water in the filtrate is reabsorbed.
As filtrate passes down the collecting duct, it flows deep into the medulla where the solute concentration of the interstitial fluid is high.
Water continues to be reabsorbed along the whole length of the collecting duct and the kidney produces a small volume of concentrated urine.
This results in a reduction in solute blood concentration.
Kidney and osmoregulation
The action of the kidney plays a role in osmoregulation as it helps keep relative amounts of water and solutes in an appropriate level
