Kidney and Homeostasis C3 Flashcards
define homeostasis
maintenance of a constant internal environment within a living organism, irrespective of external conditions
why is homeostasis important?
so that cells can function efficiently and independently of fluctuations in the conditions of the external environment
therefore cells are provided with constant conditions, even during different levels of activity of the organism
give three examples of homeostatic control
regulation of blood glucose levels
regulation of solute potential eg water is lost via excretion, sweating and expiration
regulation of core body temperature and pH
what effect might a change in temperature and pH have on enzyme-catalysed reactions? why is this important for life?
changing temp. and pH can affect the rate of reactions
if these factors were affected by the environment, we would be restricted to very specific environments
this would increase competition for food and shelter
describe homeostatic control in 5 points
there is a set point which is desired level/norm at which system operates
nevertheless, changes in pH, temperature and solute potential take place and fluctuate around set point
(homeostasis uses negative feedback to return body to set point)
set point is determined by a control centre
deviations from set point are corrected by negative feedback so that set point is restored
give the role of negative feedback
uses detector/receptor -> monitors condition -> provides input to control centre/coordinator -> evaluates the information -> provides output to effector -> makes a response designed to take away deviation i.e. restore the set point/norm
define negative feedback
a reaction to a change in a system that negates (reverses) the first change
what does positive feedback do?
an effector increases a change
give two examples of positive feedback
oxytocin stimulates the contraction of the uterus at the end of the pregnancy and the contractions stimulate the production of more oxytocin, which increases the stimulus
when the skin is cut, the first stage of clot formation is that platelets adhere to the cut surface and also they secrete signalling molecules which attract more platelets to the site
what is thermoregulation?
restoration of core body temp. back to norm
where is the control centre of thermoregulation?
the hypothalamus in the brain
explain why a tall, thin swimmer is more likely to suffer from hyperthermia than a short, stout swimmer of the same body mass?
larger SA:V ratio
less insulation so loses more heat by conduction
give two functions of the kidney
nitrogenous excretion
osmoregulation
what is the difference between excretion and egestion?
excretion - removal from body of indigestible waste products
egestion - defaecation which is removal of unwanted material from digestive system
what is nitrogenous excretion?
amino acids can’t be stored and surplus amino acids which are not used for the synthesis of proteins and other nitrogenous compounds are deaminated in the mammalian liver
give 4 steps simply describing how nitrogenous excretion works
1- amine group is removed from amino acid
2- the removed amine group is converted to ammonia which is highly toxic
3- with the addition of CO2, urea which is less toxic is formed and transported in the blood plasma to kidneys
4- urea is removed by the kidneys and excreted in the urine
what is osmoregulation?
the control of water content and solute composition of body fluids eg blood, tissue fluid and lymph
give two ways humans gain water and three ways they lose water
gain:
food and drinks
respiration (metabolic water)
lose:
urination and egestion of faeces
sweating
exhalation - to keep exchange surfaces moisture
give the different labels of the human urinary system
kidneys
ureters
bladder
sphincter
urethra
what is the function of the kidneys?
filter waste products from the blood
what is the function of the ureters?
carries urine to the bladder
what is the function of the bladders?
stores urine prior to elimination
what is the function of the sphincters?
it is a muscle that allows conscious control of urine release
what is the urethra?
it transports urine outside of the body for elimination
what are vasa recta?
blood cells that run parallel to the loop of Henle
give the labels of the kidney
cortex
medulla
pelvis
tough fibrous capsule
ureter
renal vein
renal artery
give labels for the structure of the nephron inside the kidney
glomerulus
bowman’s capsule - glomerular capsular space, glomerular capillary
afferent arteriole
efferent arteriole
proximal convoluted tubule
distal convoluted tubule
loop of Henle
collecting duct
what is ultrafiltration?
filtration under pressure that separates small soluble molecules from the blood plasma
the small molecules like water, glucose, urea and salts are filtered from the knot of capillaries (glomerulus) to form a filtrate in the Bowman’s capsule
high hydrostatic pressure is generated in the glomerulus because the afferent arteriole diameter is wider than the efferent arteriole
what does the proximal convoluted tubule contain in the Bowman’s capsule?
villi
what type of cells are surrounding the Bowman’s capsule?
squamous epithelial cells
what direction does the glomerular filtrate move in?
from glomerular capillary to lumen of Bowman’s capsule and into proximal convoluted tubule
what are podocyte cells?
inner layer of Bowman’s capsule which wrap around the capillaries of glomerulus
how is the blood in the glomerulus separated?
blood entering the glomerulus is separated from the space inside the Bowman’s capsule by two cell layers and a basement membrane
describe the movement of glomerular filtrate from top to bottom
the squamous endothelium has many gaps
the basement membrane acts as a molecular sieve during ultrafiltration
then we have podocyte cells
then the glomerular filtrate in the lumen of the Bowman’s capsule
there are squamous epithelial cells on the outer wall of Bowman’s capsule
what three ways are water and small soluble molecules filtrated by?
pores in the glomerular capillary wall
the basement membrane acting as a molecular sieve
filtered between the feet of the podocytes aka the epithelial cells of the Bowman’s capsule
what passes into the glomerular filtrate (has been mentioned before)?
amino acids
glucose
urea
water
salts aka Na+ Cl-
what remains in the blood plasma after ultrafiltration?
red blood cells
platelets
white blood cells
plasma proteins
summarise ultrafiltration in 4 points
1- there is a high hydrostatic pressure in the glomerulus due to the efferent arteriole having a narrower lumen than the afferent arteriole
2- due to this, high-pressure fluid containing water and small soluble molecules is forced out of the blood capillaries through the pores in the capillary walls, and then through the pores in the basement membrane
3- the basement membrane acts as a molecular sieve, allowing small molecules through like glucose, amino acids, urea, water and salts but preventing large molecules and cells through like red blood cells, platelets, white blood cells and plasma proteins
4- the small soluble molecules are then filtered through the feet of the podocyte cells and glomerular filtrate is formed in the Bowman’s capsule
what is selective reabsorption?
the process by which useful products, such as glucose and salts, are reabsorbed back into the blood as the filtrate flows along the nephron
the filtrate at the end of the proximal convoluted tubule is isotonic to blood plasma
give 4 products selectively reabsorbed
all of glucose
most of the mineral ions
most of water
urea
how are the different products selectively reabsorbed?
glucose - secondary active transport using a co-transport mechanism with Na+
mineral ions - active transport/co-transport
water - osmosis down a water potential gradient
urea - diffusion
give four adaptations in the proximal convoluted tubule for selective reabsorption
large surface area due to length and large number per kidney
cuboidal epithelial cells with microvilli to provide large surface area and basal channels
numerous mitochondria to provide ATP for active transport
tight junctions to prevent seepage of reabsorbed materials back into the filtrate and close association with peritubular capillaries
give the labels of a proximal convoluted tubule
apical microvilli
intrinsic proteins in the cell membrane
tight junctions
basal channels - allow build-up of substances so they can travel into the blood by diffusion
mitochondria
folded basal membrane - increases the surface area
capillary
what does the loop of Henle do?
concentrates Na+ in the tissue fluid of the medulla, decreasing the water potential gradient, causing an osmotic flow of water out of the collecting ducts and distal convoluted tubules
this water can then be reabsorbed into the bloodstream via the capillaries of the vasa recta. this concentrates the urine and makes it hypertonic to the blood lowering water potential
the loop of Henle prevents dehydration
describe the ascending limb
it is impermeable to water
since water can’t enter the a.l it goes into the blood
the thin part of the a.l is highly permeable to Na+ and Cl- which diffuse into the tissue fluid from the filtrate
the thick part of the a.l pumps Na+ by active transport into the tissue fluid
since Cl- is attracted to the Na+ (ionic), it follows the Na+
describe the descending limb
highly permeable to water
longer the loop of Henle, the lower the volume of water in urine
summarise the mechanism in the loop of Henle in 7 points
1- first part of loop is descending limb, second part is ascending limb
2- Na+ and Cl- are actively transported out of the filtrate in the ascending limb into the tissue fluid creating a lower water potential
3- the lower water potential of the medulla tissue fluid means that water leaves the descending limb by osmosis down a water potential gradient and can then move by osmosis into the capillaries of the vasa recta
4- the filtrate in the descending limb becomes more concentrated as it reaches the bottom of the loop of Henle due to the loss of water
Na+ and Cl- can also diffuse back into the filtrate near the bottom of the descending limb
5- as the filtrate passes up the ascending limb it becomes more diluted due to the loss of ions
6- an osmotic gradient is maintained down to the bottom of the loop of Henle
7- this is known as a hair-pin counter current multiplier effect
describe the osmolarity across the loop of Henle
as you go down water potential more positive
towards the bottom of the descending limb, water potential very negative
the loop of Henle very concentrated so water potential very negative
as you go up ascending limb, water potential becomes more positive
describe what happens in the collecting duct
as the loop of Henle creates a high Na+ concentration in the tissue fluid of the medulla, water will also leave the permeable collecting ducts by osmosis to be reabsorbed into the capillaries
what hormone affects the permeability of the collecting duct walls?
antidiuretic hormone (ADH)
Describe the mechanism of how ADH hormone works in 4 points
ADH enables more concentrated urine to be formed:
1- ADH makes the plasma membranes of the distal convoluted tubule cells and collecting duct cells more permeable to water
2- ADH causes aquaporins (which are channel proteins for water) to become incorporated in the plasma membranes, from within the cytosol (which is the liquid phase of the cytoplasm)
3- water is reabsorbed by osmosis from the filtrate into the surrounding hypertonic tissue fluid and hence blood capillaries around the distal convoluted tubules and collecting ducts
4- the urine reaching the bottom of the collecting ducts has a concentration close to the concentration of the tissue fluid near the bottom of the loop, that is, hypertonic to the general body fluids
The volume of urine produced is small and concentrated
ADH presence makes collecting duct walls highly permeable to water and is the opposite to when no ADH presence
ADH is secreted when a person is dehydrated
Describe ADH’s role in negative feedback
Osmoreceptors in the hypothalamus detect changes in water
potential of the blood
A nerve impulse in initiated and cells in the posterior lobe of the pituitary gland secrete more or less ADH
ADH travels in the bloodstream and cells of the distal convoluted tubules and collecting ducts become more or less permeable to water
Describe the role of ADH when a person is dehydrated
Osmoreceptors in the hypothalamus detect a decrease in the water potential of the blood
Nerve impulses are sent to the posterior pituitary gland that releases more ADH
ADH travels in the bloodstream to the nephrons where it affects the cells of the collecting duct walls
The collecting duct walls become more permeable to water
Water therefore leaves the filtrate in the collecting duct by osmosis into the tissue fluid of the medulla
Water is then reabsorbed back into the bloodstream
This results in a small volume of concentrated urine being produced
what do different animals have in terms of the kidney?
they produce different forms of nitrogenous waste and have different lengths of the loop of Henle due to the environment in which they live
how are the kidneys of aquatic animals adapted?
they excrete ammonia which is highly toxic and is very soluble in water.
it can diffuse quickly across the gills of fish into the water where it is diluted to a non-toxic level
how are the kidneys of birds, reptiles and insects adapted?
they excrete uric acid which is a bit toxic and is almost insoluble in water
they use a lot of energy to excrete this waste but very little water is needed so their waste is light
therefore, these animals can survive in dry environments
how are the kidneys of mammals adapted?
we excrete urea
requires a lot of water but is less toxic than ammonia so body tissues can tolerate it in higher concentrations for short periods of time
how are the kidneys of desert animals adapted?
they survive with very little water
water is produced from the breakdown of food during respiration in the cells (metabolic water)
they may live in underground burrows which are cooler to reduce water loss by evaporation
why does the kangaroo rat have a longer loop of Henle than average? (it lives in desert regions)
longer loop of Henle means more ions can be pumped from the ascending limb into the medulla tissue fluid
this increases the concentration of ions in the tissue fluid, lowering the water potential
more water can be reabsorbed from the descending limb, distal convoluted tubules and collecting duct, resulting in a more concentrated, small volume of urine
what does the length of the loop of Henle relate to?
the typical availability of water in the environment
the longer the loop of Henle, the greater the water potential gradient in the medulla
what is the length of the loop of Henle, the position in the kidney and the reabsorption level for species that live in water like beavers?
short loH
doesn’t extend into medulla
minimal reabsorption
what are the symptoms of kidney failure?
unable to remove urea and the concentration can rise to toxic levels
bodily fluids can become very dilute
you can remain healthy with one kidney
fatigue, shortness of breath, nausea, confusion and coma
give 6 causes of kidney failure
auto-immune disease - where your immune system attacks itself
diabetes
kidney infections
road traffic accidents (physical trauma)
genetic conditions
raised blood pressure
what doe kidney problems almost always affect?
the rate at which blood is filtered in the Bowman’s capsule
what can treatments be used for?
to balance fluids in the blood and reduce the concentration of waste products
give 5 treatments for kidney failure
medication to control blood potassium and calcium levels - high blood K conc. could lead to heart arrhythmia, high Ca in the blood is linked to increased risk of heart disease and kidney stones
transplant
dialysis
reduce the intake of protein in diet to reduce urea formation
use of drugs to reduce blood pressure - inhibit/block angiotensin hormone which constricts blood vessels, cause dilation of blood vessels, reduce adrenaline to prevent it from increasing heart rate
describe the process of dialysis
it’s the process of removing excess water, inorganic ions and urea from the blood in people whose kidneys can no longer perform these functions naturally
the dialysate runs in counter-current flow next to the blood to be cleaned maintaining a concentration gradient
blood and dialysate are separated by a selectively permeable membrane to prevent loss of plasma proteins
replacement with fresh dialysate further maintains a concentration gradient
compare the concentrations of solutes and water potential between the blood and the dialysis fluid
glucose: same in both
sodium ions: high in blood, lower in D
amino acids: same in both
water: higher in blood, lower in D
urea: high in blood, non in D
what substances will diffuse out of the blood across the membrane to the dialysate and why?
inorganic ions, water and urea down their concentration gradient
why should the concentration of glucose be the same in dialysis fluid as that of the blood?
so that none diffuses out of the blood
why should the temperature of the dialysate be maintained at 37 degrees?
to increase the rate of diffusion
maintains the patient temperature
prevents temperature shock
describe a kidney transplant
the functions of the failing kidneys can be taken over by a single healthy kidney from a donor
the transplanted kidney should function normally in its new body, cleaning and balancing the blood, however it may only last 9 years
the kidney from the donor can be rejected since antigens on the donor organ differ from antigens on the cells of the recipient and the immune system is likely to recognise this
immunosuppressant medicines must be taken for the rest of their life
evaluate this statement: having a kidney transplant is not a good solution for those who have kidney failure as it may have complications.
true:
transplant lists are long
close matches could potentially be rejected
requires taking immunosuppressants
life-span of a transplanted kidney is limited - 1, 2 decades
the live donor is down one kidney - which increases stress on the remaining kidney, increasing the risk of further transplants in the future
false:
dialysis, on the other hand, is only a stepping-stone treatment and restricts an individual’s life
Aldosterone is released when blood pressure decreases. This results in a greater reuptake of sodium in the blood. What effect would this have on the blood pressure? Why?
The blood pressure would start to increase
Sodium ions reduce the water potential of blood
So more water enters the blood (from surrounding cells) by osmosis.
Describe in detail the effects of ingesting a large quantity of salt. State which hormones would be involved and whether their output would be increased or decreased.
The salt is absorbed into the blood. This makes the blood water potential very negative.
This is sensed by the cells within the hypothalamus.
Water begins to leave cells by osmosis.
This increases the blood volume and raises blood pressure.
The person is also likely to become thirsty, and consume more liquid which will also add to the blood volume.
The more water in the blood, the more dilute the salt, increasing the blood water potential.
The release of aldosterone will stop but there will be an increase in ADH.
Suggest what precautions a person who suffers from diabetes insipidus should take.
they should drink lots of water to replace the water lost in urine;
try to conserve water by not getting too hot and so reduce sweating;
avoid eating large amounts of salt.
Explain the symptoms of diabetes insipidus.
Large quantity of dilute urine à only a small quantity of the water is reabsorbed back into the blood.
Most leave the kidney in the urine as it passes through the collecting duct without being reabsorbed.
As the person is constantly losing water, they will feel thirsty, as the blood water potential will be very negative.
