Homeostasis Flashcards
What is homeostasis?
the way the body maintains constant internal environment during changes externally
What are some of the internal factors at homeostasis maintains?
- pH
- temperature
- blood glucose concentration
- water potential
- ion content
Why is maintaining water potential important?
maintains water potential to ensure that cells don’t burst
Why is maintaining ion content important?
it effects osmotic potential of blood
Why is maintaining temperature and pH important?
effect the rate of enzyme controlled reactions
Why is maintaining blood sugar level important?
effects water potential of blood and availability of respiratory substances
What is negative feedback?
A feedback mechanism that inhibits the original stimulus and reverses the change in conditions, restoring the optimum point
What is the general process of negative feedback?
- stimulus detected by sensory receptor
- they send electrical impulses to nervous or endocrine system
- message is then sent to effectors which are either glands or muscles
How is blood sugar paintained when glucose levels increase?
- Beta cells act as receptors and detect ↑ in blood glucose levels
- They then secrete insulin into blood plasma (in surrounding capillaries)
- Insulin binds to glycoprotein receptors on membrane of body cells (Red blood cells for example)
- Tertiary structure of channel proteins changed allowing more glucose to be transported in
- This ↑ amount of channel proteins which are released by vesicles
- Enzymes activated
- This allows glycogenesis to occur, converting glucose to glycogen and fat
- This results in ↑ glycogen, ↑ glycogenesis in muscle and liver, ↑ in respiratory rate, and ↑ fat
How is blood sugar maintained when glucose levels decrease?
- Alpha cells acts as receptors and detect ↓ in blood glucose levels
- They then secrete glucagon into the blood plasma (in the surrounding capillaries)
- Glucagon binds to the glycoproteins receptor on the membrane of target cells (liver cells)
- This activates a protein to become adenylate cyclase and converts ATP into cyclic AMP (cAMP)
- cAMP activates the enzyme protein kinase, which hydrolyses glycogen into glucose
- other enzymes converts glycerol and amino acids into glucose (gluconeogenesis)
- this ↑ glucose levels back to normal
How is the blood water potenial controlled?
through osmoregulation in the kidney
in the nephron
What is osmoregulation?
control of water and salt content
What are the stages of osmoregulation?
- untrafiltration
- selective reabsorption (of glucose and water)
- maintaining dradient of sodium in the loop of henle
- reabsorption of water by the distal convoluted tubule and collecting ducts.
Descibe ultrafiltration.
- a high hydrostatic pressure is made as it enters the (because efferent is narrower than afferent)
- This pushes water, urea and glucose into the Browman’s capsule through the pores of the epithelium of capillaries and the basement membrane
- Proteins stay in as they are too large to pass through
- Glucose is then reabsorbed into the blood and the other substances flow into the ureter as urine
glucose is reabsorped in selective reabsorption
Describe Selective Reabsorption.
- sodium actively transports into the blood from the epithelial cells of the proximal convoluted tube (PCT)
- this ↓ the concentration of sodium in the epithelial cells
- this establishes a concentration gradient, causing the sodium ions in the PCT lumen to move into the epithelial cells via facilitated diffusion
- then co-transport of sodium with another substance (glucose) occurs, which moves sodium and said ion into the blood
Describe what happens in the descending loop of the henle.
- fluid descends
- water potential ↓ because the walls are more permeable to water (therefore they leave into tissue fluid via osmosis) and sodium and chloride ions diffuse in the tubules from the tissue fluid
Describe what happens in the ascending tube of the loop of henle.
- fluid ascends towards cortex
- water potential ↑ because sodium and chloride ions diffuse into the tissue fluid at the base, then as the fluid gets higher it actively transports out. The walls are also not permeable to water, therefore there is no water loss via osmosis
Describe how water is reabsorpted.
- first active transport occurs in the diastol convoluted tube in order to readjust the sodium consentration
- fluid reaches the duct and at this point it has a high water potential
- It is then carried to the medulla, which contains a high amount of salt (has a low water potential)
- The fluid then moves into the surrounding tissue down the water potential gradient by osmosis
- It then moves into the capillaries by osmosis and thus water has been reabsorbed
What hormone effects the amount of water being reabsorpted?
ADH
anti-dieuretic hormone
How is the nephron adapted for untrafiltration
- the epithelium of capillaries have a large amount of pores, which increases surface for molecules ,urea and glucose, to diffuse out, and they are very thin, creating a short diffusion path
- the basement membrane is made up of collagen and glycoprotein fibres, which are negatively charged, thus repelling the negatively charged large proteins
- Epithelium of Renal Capsule is up of podocytes, which have extensions that wrap around the capillaries of the glomerulus and interlink with neighbouring cells, leaving filtration slips in between, these are thin so it controls what can pass through it
How is the nephron adapted for selective reabsorption?
- contains microvilli on epithelial cells, which increases the surface area for transport of sodium and glucose
- it contains a lot of co-transport proteins, which Increases rate of co-transport
- it has a high number of mitochondria, which increases rate of respiration, which makes more ATP for active transport
What is the movement across the loop of henle called?
the hairpin countercurrent multiplier system
Where are osmoreceptors found?
the hypocampus of the brain
How is ADH released?
if the water potential is too low
- when stimulated a action potential is sent down the axon
- this causes the ADH to be released into the capillaries
- it then runs through the posterior pituitary gland before reaching the collecting duct
How does ADH work?
it effects the collecting ducts permiablility to water and thus controlls the amount of water reabsorption
Where is ADH stored?
neurosensory cells produce ADH in their cell body and then stores in the posterier pituitary gland terminal bulb until needed
What happens when there is too little water?
- ADH is released
- it then binds to the ADH receptors on the collecting duct walls
- this causes the enzyme phosphorylase to be released, which causes vescicles containing aquaporins to fuse with the membrane
- when they fuse with the membrane, aquaporins are inbedded in it, thus making it more permiable to water
- this means more water moves into the surrounding cells
urine is concentrated
What happens when there is too much water?
- less ADH is produced
- this causes the membrane to fold inwards in order to make more vescicles
- this causes it to lose aquaporins, thus making it less permiable to water
- this means less water is reabsorbed
urine is less concentrated
How is blood sugar paintained when glucose levels decrease?
- Alpha cells acts as receptors and detect ↓ in blood glucose levels
- They then secrete glucagon into the blood plasma (in the surrounding capillaries)
- Glucagon binds to the glycoproteins receptor on the membrane of target cells (liver cells)
- This changes the teritary shape of the protein and activates it so it becomes adenylate cyclase and converts ATP into cyclic AMP (cAMP)
- cAMP activates the enzyme protein kinase, which hydrolyses glycogen into glucose
- other enzymes converts glycerol and amino acids into glucose (gluconeogenesis)
- this ↑ glucose levels back to normal
What is the secondary messenger model?
when another molecules causes activation (for example cAMP)
Describe the effect of adenaline on glucose levels.
second messenger model
- Glucagon binds to the glycoproteins receptor on the membrane of target cells
- This changes the teritary shape of the G-protein and activates it and converts ATP into cyclic AMP (cAMP)
- cAMP activates the enzyme protein kinase, which hydrolyses glycogen into glucose
- other enzymes converts glycerol and amino acids into glucose (gluconeogenesis)
- this ↑ glucose levels
What effect does adrenaline have on glucose levels?
increases glucose levels
especially during the fight or flight response
How is hydrostatic pressure made in Ultrafiltration?
- afferent arteriole is wider than the efferent artierole but the volume of blood passing through remains the same just in a smaller space
- blood is straight from the aorta
