Biology 1A - Kidney biology Flashcards
what is the definition of homeostasis?
the maintenance of a constant internal environment
what are the most important features of our internal environment that needs to be kept constant?
- chemical composition (ions, glucose, etc.)
- blood pH (range 7.35-7.45)
- osmotic pressure = osmoregulation
- temperature ( regulated in birds and mammals but not fish and amphibia)
what are endotherms?
mammals and birds (regulate body temp)
what are ectotherms?
fish and amphibia ( typically don’t regulate the body temp but some use behavioural mechanisms to regulate it)
describe the features involved in thermoregulation.
(stimulus, Receptors, Control centre, Effectors, Response mechanisms)
- stimulus: temperature change
- receptors: skin and hypothalamus
- control centre: hypothalamus
- Effectors: skin blood vessels, sweat glands, hair (fur), Muscles
- response mechanisms:
- blood vessels constrict or dilate
- sweat produced or not
- piloerection
-shivering thermogenesis
what does it mean if a solution is HYPERosmotic to another?
contains MORE solutes and LESS water than the other solution.
what does it mean if a solution is HYPO-osmotic to another?
it contains less solutes and more water than the other solution
during osmosis where will water move?
from a high to low water concentration, therefore move out of a hypo-osmotic solution into a hyperosmotic solution.
what determines osmotic pressure?
a solution with few solutes in it (more water) will have LOWER osmotic pressure than one with many solutes
where will water move during osmosis in terms of osmotic pressure?
from a solution with low osmotic pressure to high osmotic pressure
what is osmolality/solute concentration?
no. of osmoles solute per litre of solution
what happens to cells when surrounded by a hypertonic
cells loose water
what happens to cells surrounded by an isotonic solution
equilibrium
what happens to cells when surrounded by a hypotonic solution
cells gain water
what are the important regulatory functions of the kidney?
- Removal of nitrogenous waste ( products of protein/ nucleic acid metabolism)
- Regulation of water content of the body (osmoregulation)
- Regulation of salt balance (body concentration of Na,K,Cl,Ca,Mg etc) (ionic regulation)
what happens when amino acids are metabolized?
the amino group is removed and forms ammonia
how is ammonia excreted? (nitrogenous wastes)
- ammonia/ ammonium
- urea
- Uric acid/ Guano
depending on the animal group, habitat, and the stage of development
describe ammonia
toxicity = high
metabolic cost = none
what has this form of nitrogenous waste = fish, amphibia, crocodiles, turtles
solubility (ml for 1g N) = 500 (high)
describe urea
toxicity = low
metabolic cost = some
what has this form of nitrogenous waste = sharks, mammals, turtles, some adult amphibia
solubility (ml for 1g N) = 50 (medium)
describe uric acid?
toxicity = very low
metabolic cost = high
what has this form of nitrogenous waste = birds, insects, reptiles
solubility (ml for 1g N) = 1(low)
where are kidneys located?
the back wall of the abdomen on either side of the body
2 of them
renal arteries connect them to the descending aorta and renal veins connect them to the inferior vena cava
what percentage of body weight do kidneys make up and how much cardiac output do they receive?
body weight = 1%
cardiac output received = 25%
because they control the chemical composition of blood in our body
what structures are in the kidney?
- nephron
- medulla
- cortex
- renal pelvis
- utterer
what are the two types of nephrons and what kind of urine do they produce?
- juxta-medullary = very concentrated urine
- cortical = less concentrated urine
approx. how many nephrons are in the human body?
2 million
in humans what type of nephron is more common?
85% cortical
15% juxta-medullary
what types of organisms have juxta-medullary nephrons?
only mammals and birds
reptiles and amphibians only have cortical
what are the parts of a nephron?
- bowman’s capsule
- glomerulus
- proximal tubule
- collecting duct
- loop of Henle (descending and ascending limb)
what is the function of Bowman capsule? (part of nephron)
- fluid moves by process of ultrafiltration
- the hydrostatic pressure of the blood plasma (blood pressure) forces fluid and solutes through the glomerular capillaries into the bowman’s capsule
- passive process - no energy
what passes into Bowman’s space?
myoglobin
egg albumin
haemoglobin
serum albumin
what is the diameter of molecule that cant pass through capillary
approx. 4.2nm
what prevents the movement of large molecules through capillaries?
- pores in endothelium =50-200 nm
- podocyte split-pores size = 4nm wide
what are podocyte split-pores
determine what can pass into the bowman’s space
what is hydrostatic force
liquid will exert force against the walls of whatever is containing it
why is blood pressure high in the glomerular capillaries?
- low resistance input pathway due to large diameter arteries and arterioles
- constriction of the arteriole increasing pressure
- High resistance due to many small thin capillaries in glomerulus, efferent arterioles and vasa recta
where are glomerular capillaries?
inside bowman’s capsule
what structures are in Bowman’s capsule?
- Bowman’s space
- mesangial cells
- glomerular capillaries
- podocytes
what arterioles enter and exit Bowman’s capsule?
enter = afferent arteriole
exit = efferent arteriole
what promotes filtration from glomerular capillaries into Bowman’s capsule?
glomerular hydrostatic pressure = 55 mmHg
promotes movement of fluid and molecules out of plasma into Bowman’s capsule
what opposes filtration from glomerular capillaries into Bowman’s capsule?
- capsular hydrostatic pressure = 15 mmHg,
hydrostatic force in Bowman’s capsule - glomerular colloid osmotic pressure = 30 mmHg, osmotic pressure in capillaries
what is the net filtration pressure in Bowman’s capsule?
net hydrostatic pressure = glomerular hydrostatic pressure - capsular pressure (hydrostatic force in Bowman’s capsule)
net filtration pressure = net hydrostatic pressure - glomerular colloid osmotic pressure
= 10 mmHg
what is glomerular filtration rate?
how much of the blood plasma is filtered into kidney tubules per minute
what type of excretion do kidneys show?
selective
what does selective excretion mean?
the kidney does not excrete everything that goes into the nephron, some of it is reabsorbed back into the body
what do both the mechanisms that form urine from ultrafiltrate involve?
active transport (except for the movement of water)
what does active transport allow?
the flow of substances against concentration gradient
what is tubular reabsorption?
a mechanism involved in forming urine from ultrafiltrate
reabsorption of water and solutes back into the body from glomerular filtrate
what is secretion?
a mechanism involved in forming urine from ultrafiltrate
some substances (drugs, excess salts) are actively secreted into the tubule to be lost in urine
what are the two mechanisms to form urine from ultrafiltrate?
- reabsorption
- secretion
what does active transport involve?
- protein embedded in the membrane of a cell
- protein is specific and can move particular molecules (inside to outside tubule)
- ATP causes a conformational change of protein allowing to move molecule across membrane.
where are the proximal and distal tubules located?
proximal = just after Bowman’s capsule
distal = just after loop of Henle
what occurs in the proximal and convoluted tubules?
reabsorption and secretion of substances by active transport
water passively leaves by osmosis
describe the osmolality of the solution inside the kidney nephron?
because lots of solute is taken out, a higher proportion of water in the solution inside the nephron, solution is hypo-osmotic to surrounding interstitial fluid
(allows loss of water by osmosis)
what is the renal threshold mechanism
- how kidneys regulate the concentration of a substance in the blood
- it sets a limit on the amount of each substance to reabsorb, as reabsorption in an active transport mechanism it has a maximum rate it can work at and when max is exceeded the excess appears in urine
what is the renal glucose threshold?
180mg/100ml
what is a sign of diabetes mellitus
if glucose is secreted in the urine
what is the minimum requirement of urine to be produced a day to rid the body of urea?
0.5L per day
how do mammals conserve water?
by producing urine with a higher osmotic pressure (more solutes) than the blood
do we produce hyper or hypo-osmotic urine too the blood?
hyper osmotic (contains more solutes and less water)
what is the medulla of the kidneys osmotic pressure?
maintained at high osmotic pressure/osmolality providing the force for recovering water by osmosis
how does the loop of henle aid water reabsorption?
via a counter current multiplier system
describe the process of .counter current heat exchange.
- arteries carrying warm blood are in close contact with veins carrying cooler blood
- heat from the arteries is reabsorbed by the vein
- as the blood in the veins nears the centre it is almost as warm as the body core
what does counter current heat exchange do?
traps heat in bodies core and reduces heat loss to extremities, but no heat can be added to the system
how does the counter current multiplier work?
a simple counter current multiplier:
- hairpin loop
- active transport of solute (NaCl) from one side to the other (Y to X)
- permeability to solute in X
- salt is continually lost by active transport up tube Y, so concentration drops as you go up Y
- salt is constantly reabsorbed by X, so concentration increases down X
- creates a longitudinal gradient of NaCl with highest at tip of hairpin
after Bowman’s capsule describe the order of apperatus?
- proximal tubule (in cortex)
- descending limb of loop of henle (in medulla)
3.thin segment of ascending limb of loop of henle (in medulla) - thick segment of ascending limb ( in medulla)
- distal tubule (in cortex)
- collecting duct (in medulla)
what occurs in the ascending limb of the loop of henle (the driving force)Henle
- NaCl is actively transported out of thick segment (wall not permeable to water)
- more NaCl leaves the thin segment of the ascending limb by facilitated diffusion ( wall not permeable to water
- increased concentration of NaCl in fluid in the medulla with greatest concentration at bottom of medulla/loop
what happens in the descending limb of the loop of Henle (osmotic response)
- water leaves by osmosis drawn by the increasing NaCl concentration in the interstitial fluid in the medulla ( wall not permeable to NaCl)
- water movement occurs until the osmotic pressure in the tubule equals that of the interstitial fluid in the medulla
- get an increasing NaCl gradient in the descending limb of the loop
what occurs in the collecting duct of the loop of Henle
- more NaCl leaves
- some urea also leaves helping maintain high osmotic pressure in the medulla
-water leaves by osmosis
what does isosmotic mean?
equal water concentration
what is the osmolality of urine compared to the medulla and blood?
isosmotic to medulla
hyperosmotic to the blood
describe osmolality around the loop of henle
- fluid in Bowman’s capsule = osmolality of blood plasma
- water and salts reabsorbed along convoluted tubule but osmolality still the same
- osmolarity increases to maximum at the hairpin of the loop of Henle Due to loss of water by osmosis in descending limb
what does loop of Henle maintain?
global NaCl gradient in medulla
where is concentrated urine produced?
collecting duct
why is water lost by osmosis in the collecting duct?
due to global NaCl gradient in the medulla
describe the physiology of kidney function in desert mammals
- need to conserve water
- only have juxta-medullary nephrons
-very long loops of henle meaning lots of NaCl pumps and can produce minute quantities of very concentrated urine ( hyperosmotic to blood)
describe the physiology of kidney function in reptiles?
- only have cortical nephrons , so can only produce isosmotic urine
- epithelium of cloaca ( urogenital opening) reabsorbs water so that semi solid uric acid paste is excreted
- kidneys not their only organ of osmoregulation
describe the physiology of kidney function in freshwater fish
- freshwater fish are hyperosmotic to their surroundings, so suffer loss of salts and an inundation of water
- have a diluting kidney that produces a large amount of very dilute urine
- salts are reabsorbed in proximal tubules of nephrons
- no loops of Henle
- they don’t drink and additional salt is taken up at the gills
describe the physiology of kidney function in salt water marine animals?
- they are hypo-osmotic to their surroundings (in danger of gaining salts and dehydrating)
- constantly drink seawater
- excrete monovalent ions at the gills
- kidneys play only minor role in osmoregulation
- kidney nephrons lack glomeruli and Bowman’s capsule
- main function of kidneys is to produce small volume of urine to regulate divalent ions (gills perform more osmoregulatory funtions)
describe the control system for dehydration in humans:
(stimulus, receptors, control centre, effectors, response mechanism)
- stimulus = dehydration, rise in osmolarity of plasma
- receptors = osmoreceptors in hypothalamus and carotid artery
- control centre = hypothalamus and within carotid artery
- effectors = antidiuretic hormone (ADH) released from posterior artery
- response mechanism = increase in water reabsorption in collecting ducts
what is ADH in birds, reptiles, fish and amphibians?
arginine vasotocin
what does ADH induce?
aquaporins
describe the effect of ADH
- acts on kidney increasing the permeability of the collecting ducts
- ADH binds to receptors on the basal membrane of the collecting ducts
-triggers insertion of proteins (aquaporins) onto apical membranes
-serve as water channels and lead to formation of hyperosmotic urine
what does dehydration stimulate?
- release of ADH from posterior artery
- thirst
why do dessert animals have long loops of Henle?
aid water retention
If a human was dehydrating/overheating what two systems work against each other and how
- maintaining water balance - release of ADH leads to thirst and water retention by production of tiny amount of hyperosmotic urine to the blood, constitutes high amount of recovery of water entering the nephrons
- maintaining temperature balance - excessive sweating to cool body, thickening of blood and straining of heart eventually leading to death by heart failure
why shouldn’t you drink sea water?
for every 1000ml of seawater you drink you produce 1350ml of urine due to addiction of urea
we can only excrete approx. 6g of Na per litre but seawater contains around 12g per litre
how does alcohol induce dehydration
-it is diuretic meaning stimulates urine production
- ethyl alcohol inhibits release of ADH
- causes imbalance of
describe the control system for over hydration?
- large fluid intake reduces osmotic concentration of the blood
- decreased stimulation of osmoreceptors in hypothalamus inhibits release of ADH
- increase in blood volume stimulates stretch receptors in aorta and carotid arteries further inhibiting ADH release
- causes lack of thirst, collecting ducts less permeable to water, more urine produced
what is a consequence of overhydration?
accumulation of water on the brain:
- osmotic forces pushing water into brain cells
- cells squashed against skull causing brain damage
what effect does ecstasy have on water intake?
- ecstasy causes you to feel dehydrated and take on large amounts of water
- increases levels of ADH which decreases volume of urine excreted
-can lead to cell damage
what is diabetes insipidus?
lack of ability to produce ADH or kidneys do not react to ADH
results in excessive thirst and production of lots of urine
risk of dehydration and salt imbalances
what is a test of diabetes insipidus?
reduce fluid intake and test for more concentrated urine. if diabetic you cant produce more concentrated urine
