Unit 3.7 - Homeostasis and the kidney Flashcards
Homeostasis
The maintenance of a constant internal environment by negative feedback
What does homeostasis prevent?
Wild fluctuations beyond the optimal range
What does homeostasis allow to happen?
Cells and metabolism can function efficiently
Give some examples of factors that are maintained by homeostasis
Core body temperature
pH
Water potential of blood and body fluids
What should a human’s core body temperature be?
Approximately 37 degrees Celsius
What could happen to some of the factors that have an optimal level in our body and when?
May change due to changes in our activity or external environment
Does homeostasis keep factors at the optimal level all of the time?
The factors fluctuate about the set point
Explain the homeostatic mechanism that occurs when we exercise
Core body temperature rises
The body responds to bring the temperature down again by producing sweat which evaporated from the skin and uses energy to cool us down
What is the production of sweat when we’re hot an example of?
A homeostatic mechanism
What happens if our core body temperature gets too high?
Denatured enzymes
What happens if our core body temperature gets too low?
Metabolic reactions don’t happen fast enough, so metabolic processes in cells can’t be maintained
In what condition is the body kept during homeostasis?
Dynamic equilibrium
Why is the body described to be kept in “dynamic equilibrium”?
Constant changes occur but corrective mechanisms bring the internal environmental conditions back towards a set point
How are internal environmental conditions brought back towards a set point when changes occur?
Corrective mechanisms
Which system controls homeostatic responses?
The endocrine system
How does the endocrine system control homeostatic responses?
With hormones operating by negative feedback
What are the 4 stages involved in negative feedback?
Stimulus
Receptor
Co-ordination
Effector
Explain the negative feedback system for when the body temperature exceeds 37 degrees Celsius
Stimulus = body temperature exceeds 37 degrees Celsius
Receptor = nerve cells in skin and brain
Co-ordinator = temperature regulatory center in brain
Effector = sweat glands throughout the body
What does a receptor do during negative feedback?
Detects a deviation from the set point in the internal environment
What does a receptor do during negative feedback?
Sends instructions to the co-ordinator or controller
What does a co-ordinator or controller do during negative feedback?
Communicates with one or more effectors which make responses which are corrective
How does a co-ordinator communicate with effectors during negative feedback?
By hormones circulating in the blood or nerve impulse
Name for the “normal conditions” achieved by homeostasis?
The set point
How is negative feedback stopped once a factor has returned back to normal (the set point)?
The factor changing is monitored by the receptor and information is fed back to the effectors, which stop making the correction
What do homeostatic systems use to control their levels?
Negative feedback
Why is negative feedback called negative feedback? Give an example
It gives the opposite result to the stimulus
E.g - decrease in temperature = brings temperature up
2 main functions of the kidney
Excretion
Osmoregulation
Excretion
The removal of nitrogenous waste from the body
The removal of nitrogenous waste from the body
Excretion
Osmoregulation
The control of the water potential of the body’s fluids
The control of the water potentials of the body’s fluids
Osmoregulation
What is Osmoregulation an example of in the kidneys?
A homeostatic mechanism
What is an example of a homeostatic mechanism in the kidneys?
Osmoregulation
Why does excretion occur?
Due to metabolism
4 excretory organs used by the mammalian body to excrete compounds
Lungs
Kidneys
Skin
Liver
Compounds excreted by the lungs
CO2 and H2O in expired air
Compounds excreted by the kidneys
Urea, creatinine and uric acid in urine (all nitrogenous waste)
Compounds excreted by the skin
Urea in sweat
Compounds excreted by the liver
Bile pigments in faeces
What are urea, creatinine and uric acid in urine all examples of?
Nitrogenous waste
Main nitrogenous waste excreted by kidneys
Urea
Give a detailed explanation on why urea is the main nitrogenous waste from the kidneys
In our diet, we eat proteins
Proteins are digested and absorbed in the body in the form of amino acids (amino acids are needed to make proteins)
Generally, we have too much protein in our diets
Therefore, we have an excess of amino a acids
If we can’t use them, the body can’t store them
So, amino acids are processed in the liver
Liver cells remove the amino group in a process called deamination
The rest of the amino acid is used in respiration for energy or converted into carbohydrate or fat
The amino group is converted into ammonia, then idea, the mai excreted product
Can our bodies store amino acids?
No
Where are amino acids processed when we have an excess of them?
In the liver
Why do we have an excess of amino acids?
Too much protein in our diets
Deamination
Remove the amino group from an amino acid
Process of removing the amino group from an amino acid
Deamination
What type of cells cause deamination?
Liver cells
What happens to the rest of the amino acid after deamination?
Used in respiration for energy or converted into carbohydrate or fat
What happens to the amino group removed from an amino acid after deamination?
The amino group is converted into ammonia, then urea, the main excreted product
Which system are the kidney part of?
The urinary system
Describe the location of the kidneys in the human body
Have 2 kidneys
One on each side of the back bone
Towards the back of the abdomen
Below the diaphragm
Describe the blood flowing from the heart to the kidneys
Oxygenated
High level of urea
How does oxygenated blood flow form the heart to the kidneys?
Via the aorta and renal arteries
Describe the blood returned to the heart form the kidneys
Deoxygenated
Lower levels of urea
Where is nitrogenous waste removed in the body?
The kidneys
How is blood returned to the heart from the kidneys?
Via the renal veins and vena cava
Explain how urine is passed out of the body
Urine containing a high concentration of urea is passed via the ureter to the urinary bladder for storage, until it is passed out of the body through the urethra
How is urine passed to the bladder and why?
Via the ureter
For storage
Through what is urine passed out of the body?
Through the urethra
What are kidneys inside and what is this?
Tough renal capsules
Fibrous connective tissue
Where is the blood from the renal artery filtered?
In the outer layer, the cortex, at the bowman’s or renal capsules
Where is the Bowman’s capsule located?
At the cortex
Where are the loops of Henle?
The medulla
What does the medulla contain?
The loops of Henle
The collecting ducts that carry urine to the pelvis
What do the collecting ducts in the medulla do?
Carry urine to the pelvis
What lead to the renal pelvis?
Calixes
What do calixes lead to?
The renal pelvis
What does urine travel down to reach the bladder?
The ureter
What does the renal artery do in the cortex?
Branches into narrow branches
Where does the renal artery branch into narrow branches?
In the cortex
What happens to blood in the cortex?
Blood is filtered to remove nitrogenous waste and excess water
Where is blood filtered to remove nitrogenous waste and excess water?
In the cortex
What happens to filtered blood once it’s been filtered in the cortex?
Travels through the renal vein to return to circulation
Where does blood travel down from the cortex to return to circulation after it’s been filtered?
Through the renal vein
Describe the network of blood vessels in the kidney
Very dense
Why is there such a dense network of blood vessels in the kidney?
All the blood in or system passes through the kidney many times a day
Where are most blood vessels found in the kidneys?
The cortex or the medulla
Where does the process of filtering out waste from blood happen?
In the cortex and the medulla
Nephron
One of the units used to filter blood
What are nephrons?
Millions of tubes in the kidneys
What is the nephron to the kidney?
The functional unit
Which part of the nephron are the bowman’s capsule and the proximal and distal consulates tubules present?
In the cortex
What are present in the cortex of the nephron?
Bowman’s capsule
The proximal and distal convoluted tubules
Which part of the nephron is found in the medulla?
The loop of Henle
Where is the loop of Henle found in the nephron?
In the medulla
What carries blood to the nephron?
An afferent arteriole (a branch of the renal artery)
What does an afferent arterials do?
Carries blood to the nephron
Afferent arteriole
A branch of the renal artery
What does the glomerulus contain?
About 50 parallel capillaries
What’s enclosed in the Bowman’s capsule?
Glomerulus
Wha encloses the Glomerulus in the nephron?
The Bowman’s capsule
Where is blood filtered exactly in the nephron?
The glomerulus
What happens in the glomerulus?
Blood is filtered
What does the tubule do after the glomerulus has filtered the blood?
Returns needed substances the the blood and removed waste
Where is filtered blood carried by an efferent arteriole to?
- a capillary network surrounding the proximal and distal convoluted tubules
-the vasa recta, a capillary network surrounding the loop of Henle
What is filtered blood carried by?
An efferent arteriole
Vasa recta
A capillary network surrounding the loop of Henle
The capillary network surrounding the loop of Henle
Vasa recta
Name for the fluid travelling through the nephron
Filtrate
Filtrate
Fluid travelling through he nephron
What happens to the content of the filtrate along the nephron?
Changes
When is filtrate called urine?
By the time it’s reached the renal pelvis
when is filtrate called urine instead?
By the time it’s reached the renal pelvis
Do nephrons exist individually?
No
What does the efferent arteriole do?
Carries blood away from the glomerulus and divides up into many arteries
What leaves the blood when filtrate is formed?
Waste but also some useful materials like glucose
Why do we need selective re absorption?
To recover useful materials that left the blood when the filtrate was formed in the glomerulus
Where does selective reabsorption happen mainly?
In the proximal convoluted tubule
What happens mainly in the proximal convoluted tubule?
Selective re absorption
What is the loop of Henle mostly concerned with?
The osmotic potential of the blood
Ultrafiltration
Filtration under high pressure
Filtration under high pressure
Ultrafiltration
How many capillaries are in the glomerulus?
Numerous
Describe capillary walls
1 cell thick
Cells that make up capillary walls
Endothelial cells
What are the cells of the capillaries set on?
A basement membrane
What are between endothelial cells in the capillaries?
Fenestrations (pores)
Where are fenestrations in the capillaries?
Between endothelial cells
What do fenestrations in the capillaries do? Explain
Make the capillary semi-permeable
Don’t allow cells but allow small soluble molecules to leave the blood plasma (the rest can stay in the capillary)
What do fenestrations allow small soluble molecules to leave?
The blood plasma
How does blood arrive in the capillaries of the glomerulus?
From the afferent atriole
Why does the blood from the afferent arteriole to the glomerulus have a high pressure?
The afferent atriole has a wider diameter than the efferent atriole
The heart’s contraction increases the pressure of arterial blood
What does the high blood pressure to the glomerulus facilitate and why?
Facilitates ultrafiltration
High blood pressure forces filtrate out of the blood and into the nephron
What does glomerular filtrate contain?
Water
Glucose
Salts (e.g - sodium)
Urea
Amino acids
What do we want to do with the urea in globular filtrate?
Get rid of it as nitrogenous waste
How is blood entering the glomerulus separated from the bowman’s space?
By 3 layers
3 layers separating the blood entering the glomerulus from the Bowman’s space
Capillary walls
Basement membrane
Squamous epithelial cell layer of the Bowman’s capsule (podocytes)
What is the name for the tiny pores between the endothelial cells of the capillary walls in the glomerulus?
Fenestrations
Diameter of fenestrations
80nm
What do fenestrations in the capillaries of the glomerulus allow to happen?
Allow solutes to pass to the basement membrane
What is the selective molecular filter between the blood entering the glomerulus and the bowman’s space?
Basement membrane
What is the basement membrane known as in the glomerulus?
Selective molecular filter
Why is the basement membrane in the glomerulus known as the selective molecular filter?
It only allows small molecules to pass through
What type of molecules would be too large to pass through the basement membrane in the glomerulus?
Blood cells
Placelets
Large proteins such as antibodies
Extensions of podocytes
Pedicels
Type of cell layer of the Bowman’s capsule
Squamous epithelial cell layer
What do podocytes do?
Have extensions called pedicels, which wrap around a capillary, pulling it closer to the basement membrane. The gaps between the pedicels are called filtration slits
Filtration slits
Gaps between the pedicels of podocytes
What does the basement membrane behave as and what does this do?
As a molecular sieve
Stops larger molecules from entering the filtrate
What does the basement membrane stop large molecules from entering?
The filtrate
What do podocytes form?
The wall of the Bowman’s capsule
What form the walls of the Bowman’s capsule?
Podocytes
Explain how podocytes form filtration slits
Podocytes contain fingers tht plait together to form processes
Between the processes of the podocytes are the filtration slits
What do filtration slits allow to happen?
Allow the filtrate to pass through easily
Why do we need selective reabsorption?
After the literate is formed, the useful substances lost through ultrafiltration need to be re absorbed back into the blood plasma
What are also lost through ultrafiltration?
Useful substances like glucose
What is selective reabsorption?
The process by which useful substances such as glucose, amino acids and slats are re absorbed back into the blood plasma
Give some examples of substances reabsorbed back into the blood plasma through selective reabsorption
Glucose
Amino acids
Salts
Where does selective reabsorption take place?
The proximal convoluted tubule in the cortex
How does selective reabsorption happen in the proximal convoluted tubule in the cortex?
By facilitated diffusion and active transport
What is the nephron closely associated with?
Blood capillaries called the vasa recta
Where do reabsorbed substances from selective reabsorption pass from and to?
From the proximal convoluted tubule
Into the blood plasma contained in the vasa recta capillaries
Which capillaries do the reabsorbed substances pass into after the proximal convoluted tubule during selective reabsorption?
The vasa recta capillaries
What does glomerular filtrate represent?
Things that have left the blood
Where is the basement membrane in the nephron?
Between the endothelial cells of the capillaries and the podocytes that form the Bowman’s capsule wall
How does blood enter the glomerulus?
Through the afferent arteriole
Where is filtrate formed?
In the glomerulus
What happens to the blood that isn’t filtered in the glomerulus?
Carries on through the efferent arteriole
What does the efferent arteriole do?
Splits up to form the capillaries of the vasa recta
Where does most of selective reabsorption occur?
In the proximal convoluted tubule
What type of cells does the proximal convoluted tubule have?
Cuboidal epithelium cells
List the ways in which the cells of the proximal convoluted tubule have adapted for selective reabsorption
Microvilli
Many mitochondria
Tight junctions between cells
Basal channels
Closely associated with the blood capillaries of the vasa recta
Purpose of the microvilli on the cells of the proximal convoluted tubule
Protrude into the lumen of the PCT to increase the surface area for selective reabsorption + absorb the contents of the filtrate for them to pass back into the blood
Where are the microvilli of the cells of the proximal convoluted tubule?
Protruding into the lumen of the PCT
What’s the purpose of the cells of the proximal convoluted tubule having many mitochondria?
Produces ATP for active transport
Purpose of the tight junctions between the cells of the proximal convoluted tubule
Hold neighbouring cells together closely to prevent molecules diffusing between adjacent cells (in either direction)
Purpose of the basal channels of the cells of the proximal convoluted tubule
Increase the surface area of the cell membrane at the basement membrane
What are the cells of the proximal convoluted tubule closely associated with?
The blood capillaries of the vasa recta
Are the materials that are reabsorbed into the blood via selective reabsorption absorbed back into the blood using the same processes?
No
Give 2 reasons why proteins are not reabsorbed back into the blood during selective reabsorption
-proteins are too large to be reabsorbed
-no specific transport proteins for them
How are salts reabsorbed during selective reabsorption?
Mainly active transport, but some facilitated diffusion
How are glucose and amino acids reabsorbed during selective reabsorption?
Cotransport with sodium ions into the cell
How is water reabsorbed during selective reabsorption?
Osmosis
How are urea and small proteins reabsorbed during selective reabsorption?
Facilitated diffusion
Why is some urea reabsorbed during selective reabsorption?
Is meant to be water but some is reabsorbed as it’s small enough to pass through channel proteins to be absorbed via facilitated diffusion
Summarise what happens during the reabsorption of glucose during selective reabsorption
Cotransport with sodium through a carrier protein at one end of the cell
What is the condition that has to be true for glucose to be cotransported?
Both glucose and sodium have to be present
What type of process is the cotransport of glucose with sodium?
Passive process
As cotransport is a passive process, what does it require?
A concentration gradient
Which concentration gradients do we need for the cotransport of glucose and sodium ions?
Concentration gradient needed for both glucose and sodium ions between the filtrate and the cytoplasm on the other side of the membrane
How do we obtain the concentration gradient for sodium for its cotransport with glucose?
Sodium is actively transported out through a sodium-potassium pump (sodium out, potassium in)
How do we obtain the concentration gradient for glucose for its cotransport with sodium?
Glucose leaves by facilitated diffusion into the blood down its concentration gradient
What do both the active transport of sodium and glucose leaving by facilitated diffusion ensure?
That the concentration of glucose and sodium ions in the cell is low
What undergoes the same process as glucose in the cotransport of glucose and sodium?
Amino acids
What happens to amino acids during the cotransport of glucose and sodium?
The same thing as the glucose (facilitated diffusion into the blood down its concentration gradient)
In what form is the Na+ for its cotransport with glucose?
NaCl
What ions are also present during the cotransport of glucose and sodium and why?
Cl- ions
Since Na+ is in the form of NaCl
What happens to the Cl- during the cotransport of sodium and glucose?
Pass straight through the channel proteins down a concentration gradient
What happens to H2O during the cotransport of sodium and glucose?
Passes straight through via osmosis
Which parts of the nephron does Osmoregulation take place?
Loop of Henle and collecting duct
What happens during ultrafiltration?
Lots of blood is filtered
What does how much water is taken back from ultrafiltration depend on?
The water levels in the body at the time
Describe how water level is controlled in the loop of Henle at the descending limb
The descending limb of Henle is permeable to water; water leaves by osmosis since the water potential in the tissue fluid surrounding the nephron is lower than the filtrate.
Na+ and Cl- ions enter the descending limb by facilitated diffusion
Describe how water level is controlled in the loop of Henle at the ascending limb
The ascending limb of the loop of Henle is not permeable to water but does allow Na+ and Cl- to leave by facilitated diffusion and then active transport
As the NaCl in the filtrate goes into the tissue fluid in the medulla, it decreases the water potential of the tissue fluid since there’s more solutes in it. This helps water leave.
Which limb of the loop do Henle is permeable to water?
Descending
Why does water leave the descending limb of the loop of Henle via osmosis?
Success the water potential in the tissue fluid surrounding the nephron is lower than the filtrate
How do Na+ and Cl- ions enter the descending limb of the loop of Henle?
Via facilitated diffusion
How do Na+ and Cl- ions leave the ascending limb of the loop of Henle?
By facilitated diffusion and then active transport
How is the water potential of the tissue fluid of the medulla decreased?
As the NaCl in the filtrate diffuses into the tissue fluid in the medulla, it decreases the water potential of the tissue fluid since there’s more solutes in it
How is water helped to leave the filtrate in the loop of Henle?
By NaCl diffusing into the tissue fluid in the medulla to decrease its water potential
What is the loop of Henle called?
A counter current multiplier
Why is the loop of Henle called a counter current multiplier?
Because the filtrate flows in opposite directions (a counter current) and the concentration of solutes in the filtrate increases towards the apex (is multiplied)
Why does the concentration of solutes in the loop of Henle increase towards?
The apex
What leads to a higher concentration of solutes at the apex of the loop of Henle?
Longer loop of Henle
What does a longer loop of Henle lead to?
A higher concentration of solutes at the apex
What do the numbers represent on Loop of Henle diagrams?
The concentration of solutes in the filtrate
At which point have most of the useful thing been reabsorbed back into the blood?
After the proximal convoluted tubule
What are most of the solutes left unabsorbed by the blood after the proximal convoluted tubule?
NaCl in water
Is there a change in concentration of the solutes in the proximal convoluted tubule? Why?
No, since there’s no concentration gradient
What happens to the concentration of solutes down the descending limb of the Loop of Henle? Why?
Increases
Water is diffusing out
Where does the concentration of solutes reach a maximum down the descending limb of the loop of Henle and why?
At the hair pin turn
Filtrate is most concentrated, with the lowest water potential
What happens to the concentration of solutes up the ascending limb of the loop of Henle?
Decreases
Why does the concentration of solutes decrease up the ascending limb of the loop of Henle?
Since the NaCl ions leave down their concentration gradient as they enter the tissue fluid via facilitated diffusion
Why does facilitated diffusion not occur for NaCl ions to leave the ascending limb of the loop of Henle all of the way up? What happens instead?
As the concentration of solutes decreases, it eventually reaches equilibrium with the tissue fluid in the medulla. Now, there’s no concentration gradient so NaCl is pumped out by active transport.
What does water do at the collecting duct in the nephron?
Diffuses out via osmosis
What does water diffusing out of the collecting duct in the nephron do?
Recovers the water in the filtrate
When is filtrate urine?
At the end of the collecting duct
What is filtrate at the end of the collecting duct?
Urine
What happens to the permeability of the walls of the collecting duct for water?
Can be changes due to a hormone
What is the length of the loop of Henle positively correlated with?
The need for water conservation in animals
Relationship between the length of the Loop of Henle and the need for water conservation in animals
Positively correlated
Describe the loop of Henle for an animal in a very wet enviornment
Shorter loop of Henle
Why does an animal have a shorter loop of Henle in a very wet environment?
No need to conserve water
Describe the loop of Henle of an animal in a very dry environment
Longer
Why do animals in very dry environments need longer loops of Henle?
For more water volume to be reclaimed
Explain why is is beneficial for an animal in a very dry environment to have a longer loop of Henle
Can have a higher concentration of solutes in the medulla tissue fluid
More water recovered in the loop of Henle and collecting duct
More blood leaves filtrate and enters blood
Causes more water in the blood
What are nitrogenous wastes?
The breakdown products of proteins and amino acids
What do different animals do in terms of nitrogenous waste?
Excrete it in different forms
How are proteins converted into amino groups?
Proteins —> amino acids —> amino groups
How are nucleic acids converted into amino groups?
Nucleic acids —> nitrogenous bases —> amino groups
Different forms of excreting nitrogenous waste
Ammonia (NH3)
Urea
Uric acid
What animals excrete nitrogenous waste as ammonia?
Most aquatic mammals, including most bony fish
What animals excrete nitrogenous waste as urea?
Mammals, most amphibians, sharks and some bony fish
What animals excrete nitrogenous waste as uric acid?
Many reptiles (including birds), insects, land snails
Explain why aquatic mammals excrete ammonia directly as their nitrogenous waste
Excrete it directly into large amounts of water
Ammonia is the most soluble in water compared to other urea and uric acid, therefore a lot of water is needed to get rid of it, which is fine for aquatic mammals
What type of nitrogenous waste is the most soluble and what does this mean?
Ammonia
The most water is needed to get rid of it
How do aquatic mammals excrete nitrogenous waste?
As ammonia
How do mammals excrete nitrogenous waste?
Use energy to covert ammonia into less toxic urea, which is excreted in urine
How is urea excreted?
In urine
What is the most toxic - ammonia or urea?
Ammonia
How do we get urea?
Amino acids —> ammonia —> urea (in liver cells)
Give 2 reasons why urea is a better form of nitrogenous waste for mammals compared to ammonia
-urea is less toxic than ammonia
-urea is less soluble than ammonia, so less water is needed to get rid of it
How do birds and insects excrete nitrogenous waste?
Convert ammonia into uric acid
Disadvantage of producing uric acid as nitrogenous waste?
Required even more energy than producing urea
2 advantages of uric acid as nitrogenous waste
-insoluble in water
-can be excreted as a waster with little water loss
Do birds produce urine?
No
How does uric acid help keep much more water in the body compared to having urea as nitrogenous waste?
Uric acid is much less soluble
What does the fact that Uric acid is much less soluble than urea lead to?
It keeps more water in the body
Explain why having uric acid as nitrogenous waste is useful to birds
They need less water to get rid of nitrogenous waste = they’re lighter = it’s easier to fly
Explain why having uric acid as nitrogenous waste is advantageous for the fact that reptiles and birds lay eggs
As the embryo develops, it absorbs nutrients and produced nitrogenous waste
As this is in the form of uric acid, it ensures that the embryo isn’t poisoned in the egg
Why is water able to diffuse out of the collecting duct in the nephron?
It passes through the medulla, which has a low water potential
Where is water reabsorbed after it passes out of the collecting duct in the nephron?
Into the vasa recta
Why is filtrate urine at the end of the collecting duct?
More concentrated than blood
Name for concentration of solutes in the filtrates
Osmolarity
Osmolarity
Concentration of solutes in the filtrate
Why is the concentration of solutes in the filtrates referred to as Osmolarity?
Since it’s not just one compound
What does ADH stand for?
Antidiuretic hormone
What does ADH do?
Changes osmolarity
Where is ADH produced?
In the hypothalamus
Where is ADH secreted?
By the posterior lobe of the pituitary gland
Where is ADH stored?
In the pituitary gland
What does ADH increase the permeability of?
The cells of the collecting duct and distal convoluted tubule to water
What does increased permeability of the collecting duct and distal convoluted tubule due to ADH lead to?
More water is reabsorbed by osmosis
Results of the collecting duct walls being more permeable to water due to ADH
More water is reabsorbed from filtrate into the tissue fluid and into the blood
= lower volume of concentrated urine
Hormone that increases the permeability of the cells of the collecting duct and distal convoluted tubule
ADH
Where does water go when the collecting duct walls are more permeable to water due to ADH?
Reabsorbed form filtrate into the tissue fluid and into the blood
What does more water being in the blood lead to?
Lower volumes of concentrated urine
What are aquaporins?
Intrinsic protein channels which transport water across the phospholipid bilayer during osmosis
Intrinsic protein channels which transport water across the phospholipid bilayer during osmosis
Aquaporins
ADH
Anti diuretic hormone
Diuretic
Anything that increase urine quantities in the body
Example of a diuretic
Caffeine in tea and coffee
Anti diuretic
Hormones that suppress the production of urine (lower volume produced)
When does the blood water potential decrease?
When losing more water than normal (e.g - sweating, not drinking enough) and we become dehydrated
What detects low water potential levels of the blood?
Osmoregulators
What are osmoregulators?
Specialised cells in the hypothalamus in the brain
When do osmoregulators detect blood water potential changes?
When blood flows through the hypothalamus in the brain
What do osmoregulators do once they detect blood water potential changes?
Send a nerve impulse to the pituitary gland
What do pituitary glands do once they receive nerve impulses from osmoregulators?
Secrete ADH into the blood
What secrete ADH into the blood?
The posterior lobe of the pituitary gland
What effects does ADH have?
Increases the permeability of the walls of the collecting duct + distal convoluted tubule to water
Triggers a feeling of thirst
How can we tell from our urine if we’re dehydrated?
Darker urine = more concentrated —> sign of dehydration
What is the pituitary gland?
A type of endocrine gland
Give a detailed description of how the ADH hormone works
ADH is transported in the blood from the pituitary gland to the kidneys
ADH attaches to receptors in the cel wall of the collecting duct
Receptors stridulate aquaporin versicles to move towards the membrane of the cells of the collecting duct
As aquaporin pores are inserted into the cell membrane, there’s an increased number of channels, so an increasing flow of H2O out of the tubule and so the permeability of the collecting duct increases
More water possess from the lumen of the collecting duct (since the water potential of the filtrate is higher than the cells of the walls of the collecting duct) into the cells in the cell wall of the collecting duct and into the blood via osmosis
= ADH makes the collecting duct more permeable to water
What does ADH do to the collecting duct?
Makes it more permeable to water
Where are receptors for ADH to attach to?
In the cell wall of the collecting duct
What do receptors in the cell wall of the collecting duct?
Stimulate aquaporin vesicles to move towards the membrane of the cells of the collecting duct
What stimulates aquaporin vesicles to move towards the membrane of the cells of the collecting duct?
Receptors
What happens as aquaporin pores are inserted into the cell membrane of the cells of the walls of the collecting duct?
Increased number of channels
Increasing flow of H2O out of the tubule
What happens as ADH makes the collecting duct more permeable to water?
More water passes from the lumen of the collecting ducts into the cells in the cell walls of the collecting duct and into the blood via osmosis
Why are the cells in the walls of the collecting duct the only ones to react in the presence of ADH?
As they contain aquaporins that can be absorbed into the membrane
Give a detailed description of the kidneys response to water deprivation (Osmoregulation)
- Low water levels (low water potential) in the blood caused by water deprivation
- Detected by osmoreceptors in the hypothalamus
- Nerve impulses are sent to the pituitary gland (endocrine gland)
- The pituitary gland secretes the hormone ADH (anti diuretic hormone)
- ADH carried in the bloodstream to kidneys
- Increased ADH levels in kidney increases permeability of wall of the collecting duct and distal convoluted tubule to water
- Water leaves the collecting duct and distal convoluted tubule by osmosis due to the low water potential in the medulla
- This results in a small volume of more concentrated urine being produced
Why is more concentrated urine produced during Osmoregulation - the kidneys response to water deprivation?
Water leaves the collecting duct and distal convoluted tubule by osmosis due to the low water potential in the medulla
This results in s a sell volume of more concentrated urine being produced
Explain what will happen if the water levels in the blood become too high?
The opposite occurs…
The osmoregulators will detect the high blood water potential
The pituitary glands released less ADH
Thirst suppressed
Decreased permeability of walls of the collecting duct and distal convoluted tubule to water
Less water reabsorbed from kidney tubules
Large volumes of dilute urine forms
What forms in terms of urine when the water levels in the blood become too high and why?
Large volumes of dilute iurine
Less water reabsorbed from kidney tubules since there’s a decreased permeability of the walls of the collecting duct and the distal convoluted tubule from kidney tubules with less ADH being released by pituitary glands
Explain why Osmoregulation is a homeostatic mechanism
Stimulus: low water potential in the blood
Receptor: osmoreceptors in hypothalamus
Co-ordinatior: hypothalamus
Effector: pituitary gland (releases the hormone)
What is the effector in a homeostatic mechanism usually?
A gland or a muscle
Can we live healthily with one kidney? How do you know?
Yes
People often donate one of their kidneys as kidney donors
What can a kidney do if there’s only one healthy kidney?
Can grow in size in order to work as hard as 2 kidneys
Why will treatment be needed if both kidneys fail?
To balance fluids
To remove waste
Reasons for kidney failure
Bacterial disease
Injury
Inherited condition (kidneys may get worse with age)
List the different cations taken against kidney failure
-medication taken to control blood potassium and calcium levels (kidneys normally do this)
-low protein diet —> will reduce the need for deamination in the liver and less urea will be produced
-drugs taken to reduce blood pressure
-dialysis and a kidney transplant
Why is medication taken during kidney failure?
To control blood potassium and calcium levels, which kidneys usually do
What type of diet are those with kidney failure expected to go on and why?
Low protein
Will reduce the need for deamination in the liver + less urea will be produced
What does a haemodialysis column do?
Gets rid of excess water from the blood like kidneys would
What is the rest of the machinery apart from the haemodialysis column, used during haemodialysis, used for?
As a sophisticated pump that pumps blood from the arm of the patient to the haemodialysis column and back into the patient’s body
Dialysis fluid name
Dialysate
Purpose of dialysate during haemodialysis
Pumped through the machine and through the column to remove waste from the body, which diffuses into the dialysate
Haemodialysis
When a dialysis machine removes waste products and excess salts form the blood
Where is blood taken from during dialysis?
An artery in the arm
Where does blood travel through once it’s been taken from an artery in the arm during haemodialysis?
Is passed through thousands of long narrow strands of selectively permeable dialysis tubing
What are dialysis fibres surrounded by?
Dialysis fluid
Where do waste products pass from and to during haemodialysis and how?
Out of the blood plasma, through the pores in the dialysis tubing, into the dialysis fluid
How is clean blood returned to a patient during haemodialysis?
Through a vein
How frequently is haemodialysis carried out?
3 days a week, with each session lasting 4 hours
why does each haemodialysis session have to last 4 hours?
To allow the whole volume of blood in the body to pass through to complete dialysis
What else diffuses into dialysis fluid apart from waste and why?
Water to remove excess water from the blood to avoid oedema
What does dialysis fluid leave the top of the haemodialysis column with?
Waste and excess water from the blood
What are the ways in which a dialysis machine makes filtration more efficient?
Counter current flow between blood and dialysis filter through the haemofilter
Dialysis fluid is continuously replaced
Blood flows through hundreds of thin, hollow membrane fibres
Temperature at about 40 degrees Celsius
Dialysis fibres made out of a semi-permeable membrane
Why is the counter current flow between blood and dialysis fluid important?
Ensures that the concentration gradient of urea between blood and dialysis fluid is maintained along the length of the filter
Why is dialysis fluid continuously replaced during haemodialysis?
To maintain a steep concentration gradient
Why is it beneficial that blood flows through hundreds of thin, hollow membrane fibres during haemodialysis?
Provides a large surface area for dialysis to occur
Why is a temperature of about 40 degrees used during haemodialysis?
Maximum possible
Higher than body temperature
Prevents temperature shock
Why is it important that dialysis fibres are made out of a semi-permeable membrane?
Large enough for urea to diffuse out
Too small for proteins + blood cells to leave the blood
What does a patient have to do when kidneys fail?
Undertake dialysis regularly
Why can someone be forced to undertake dialysis for the rest of their life?
Since there’s a shortage of kidneys for kidney transplants
What do the mitochondria in the cells of the proximal convoluted tubule do?
Produce ATP for active transport (not energy)
What is the most toxic type of nitrogenous waste and what needs to be done therefore?
Ammonia
Needs to be diluted
What needs the least amount of water for excretion - ammonia or urea?
Urea
When is the most amount of water lost - with urea or ammonia?
Ammonia
What can be stored the best- ammonia or urea and why?
Urea
Less toxic
What does ADH do in terms of aquaporin?
Makes more aquaporin insert into the membrane
What are we describing everything occurring on when explaining the effects of ADH?
The membrane of the collecting duct
what type of gland is the posterior lobe of the pituitary gland?
endocrine gland
endocrine gland
secretes the hormone directly into the blood
exocrine gland
secretes hormones via a duct
where in the brain is the pituitary gland?
the base
give the negative feedback loop of osmoregulation
stimulus = different water potential levels in the blood
detector = osmoregulators in the hypothalamus
coordinator = hypothalamus
effector = posterior lobe of the pituitary gland
key word when talking about osmoregulation
negative feedback
what does the rate of water réabsorption into blood depend on?
water potential gradient
number of aquaporins
What does ADH do in terms of aquaporin?
Inserts more aquaporin into the membrane
