Chapter 16 - Homeostasis Flashcards
What is homeostasis
The maintenance of a constant internal environment within an organism
Why is homeostasis important
- Enzymes - It keeps the internal environment constant for metabolic reactions (which is controlled by enzymes)
- Water potential - maintenance of blood glucose level is essential for the maintenance of water potential which ensures cells function properly and avoid damage as they don’t shrink or burst
- Independence - if you can control your internal environment you are more independent of the changes in your external environment so organisms can have a wider geographical range
- It helps organisms respond and adapt to external changes.
how does negative feedback work
1) Receptors detect a change in one direction, like rising blood glucose.
2) Signals trigger effectors to produce responses that reverse the initial change, like releasing insulin to lower blood glucose.
3) Conditions return to their set range.
examples of negative feedback
Maintaining blood glucose concentration
Maintaining blood pH
Maintaining temperature
Water regulation
why is it important to maintain temperature and how is it achieved
Why it is important - Changes in temperature can impair enzyme action.
How it is achieved - Adjustments are made, for instance by sweating or shivering, to maintain the optimum temperature.
why is water potential important and how is it achieved
Why it is important - Too much or too little water in the blood and cells can cause cells to burst or shrink due to osmosis.
How it is achieved - Water is removed or reabsorbed from blood or tissue fluid to maintain the optimum water potential.
why is water regulation important and how is it achieved
Why it is important - Changes in pH can impair enzyme action.
How it is achieved - Adjustments are made to the acid-base balance in the blood to maintain the optimum pH.
why is Maintaining blood glucose concentration important
Glucose is needed for respiration, but too much glucose can affect water potential in blood and cells.
how does positive feedback occur
1) An initial change occurs, like the release of clotting factors after a blood vessel injury.
2) Effectors are stimulated and enhance the change, like more clotting factors being released.
3) The change continues until an endpoint is met, like a clot being fully formed.
what is positive feedback
positive feedback amplifies changes rather than reversing them
what does the endocrine system do
uses hormones to send information about changes in the environment around the body to bring about a designated response
what does the endocrine system consist of
the pancreas, adrenal glands, and the pituitary gland
how does hormones act as a chemical messenger
1) Hormones are produced by endocrine gland cells.
2) When stimulated, glands release hormones into the bloodstream.
3) The blood carries hormones to their target cells.
4) They attach to receptors on or inside the target cells.
The cells then respond to the hormones.
properties of non steroid hormones
- Water soluble (hydrophilic)
- Cannot diffuse across the phospholipid bilayer
- Bind to receptors on the cell-surface membrane of their target cells to activate second messengers
e.g adrenaline
properties of steroid hormones
- Lipid soluble (hydrophobic)
- Can diffuse across the phospholipid bilayer
- Bind to receptor molecules in the cytoplasm or the nucleus, forming a hormone-receptor complex that acts as a transcription factor
e.g oestrogen
difference between endocrine and nervous system
Signals
Endocrine sytem: Hormones
Nervous system: Nerve
Transmission
Endocrine system: By blood Nervous system: By neurones
Speed
Endocrine system: Slow Nervous system: Very rapid
Spread
Endocrine system: Widespread
Nervous system: Localised
Duration of effect
Endocrine system: Long Nervous system: Short
what does the second messenger model of hormone action do and what is the second messenger
The second messenger model of hormone action involves a hormone triggering the formation of a second messenger (cAMP) inside the cell, which activates enzymes to carry out a function.
second messenger = the next molecule which causes activation
how does adrenaline increase blood glucose (second messenger model of adrenaline)
1)nAdrenaline binds to complementary receptor on the cell-surface membrane of a liver cell.
2) The binding of adrenaline causes the protein to change shape, activating a G protein.
3) This activates the enzyme adenylate cyclase.
4) The activated adenylate cyclase converts ATP into cAMP.
5) cAMP acts as a second messenger, activating protein kinase via phosphorylation, amplifying the signal from adrenaline.
6) Protein kinases activate enzymes that catalyse the breakdown of glycogen into glucose (glycogenolysis)
7) Glucose moves out of liver cells by facilitated diffusion and into the blood through channel proteins.
8) This increases the blood glucose concentration so that more glucose can be delivered to body cells for respiration.
what are islets of langerhans
special cell clusters that produce hormones found in the pancreas
which cells do the islets of langerhans contains
- Beta (β) cells - They secrete the hormone insulin.
- Alpha (α) cells - They secrete the hormone glucagon.
what is negative feed back
when any deviation from the normal values are restored to their original level
where is the adrenaline hormone released from
the adrenal glands
What effect does adrenaline have on glucose levels?
It causes more glucose to be released from glycogen stores in the liver.
what is Glycogenolysis
Glycogen is converted back into glucose in liver and muscle cells
what is Gluconeogenesis
Glucose is produced from amino acids and fats in the liver
what happens when there is an increase in blood glucose levels
1) this rise is detected by beta cells in the islets of Langerhans
2) Beta cells then release insulin
3) causing cells become more permeable to glucose and enzymes are activated to undergo Glycogenesis
4) Glucose is then removed from the blood and stored as glycogen in cells
5) this results the blood glucose levels to return as normal
what is Glycogenesis
Glucose is converted into glycogen for storage, primarily in the liver
what happens if the blood glucose levels decrease
1) this decrease is detected by the alpha cells in the islets of Langerhans
2) Alpha cells will release glucagon and adrenal gland will release adrenaline
3) second messenger model occurs to activate enzymes to hydrolyse glycogen
4) Glycogenolysis occurs and the glucose is released back into the blood
5) Glucose levels return back to normal
how does insulin decrease blood glucose
1) insulin binds to receptors on the surface of target cells (liver cells), this changes the tertiary structure of the channel proteins, resulting in more glucose being absorbed by faciliated diffusion
2) the binding of insulin to the receptor causes intracellular chemicals to be released
3) this results in vesicles containing glucose protein channels to move towards the cell surface membrane AND fuse with the cell surface membrane
4) this allows more channel proteins to be incorporated into cell membrane so that more glucose is absorbed from the blood into cells
5) this activates enzymes which stimulates glycogenesis to occur in the liver
why does glycogenesis occur in the action of insulin when blood glucose levels are too high
this is because glucose is soluble so will dissolve into the cytoplasm of the cell causing water to move in by osmosis whilst glycogen is an insoluble store of glucose so doesn’t alter the osmotic pressure of the cell
how does glucagon increase blood glucose concentration (second messenger model of glucagon)
1) glucagon attached to glucagon receptors on the surface of target cells (liver cells)
2) when glucagon binds it causes an enzyme to be activated into adenylate cyclase and that enzyme catalyses the reaction to convert ATP into cyclic AMP (cAMP) (which is the second messenger)
3) cAMP activates an enzyme called protein kinase that can catalyse glycogenolysis (hydrolyse glycogen into glucose)
4) This activates enzymes to convert glycerol and amino acids into glucose (gluconeogenesis)
what is type 1 diabetes caused by
when the body is unable to produce insulin which could be a result of an autoimmune disease where beta cells were attacked leading to no insulin production and high blood glucose levels
what is type 2 diabetes caused by
when the receptors on the target cells lose their responsiveness to insulin or beta cells dont produce enough insulin due to obesity and poor diet results in
treatments for type 1 diabetes
- Regular insulin injections
- Use of an insulin pump providing continuous insulin administration.
- Pancreas transplants of healthy islet cells to enable some insulin production.
- Careful blood glucose monitoring and a diet balanced with insulin dosage.
- Exercise to help regulate blood glucose and insulin requirements.
treatments for type 2 diabetes
- Diet control to reduce sugar intake.
- Regular physical activity.
- Medications to increase cells’ sensitivity to insulin.
- Medications to stimulate more insulin production in cells.
- insulin therapy to manage blood glucose levels.
symptoms of diabetes and why they are caused
- excess urination = due to more water leaving the cell by osmosis so more urine is produced
- weight loss = less glucose is absorbed into cells so therefore more gluconeogenesis from lipids
- tiredness - less respiration due to less glucose in cell
- blurred vision - less blood flow to the retina so retina functions less well due to excess glucose
draw and label the structure of a kidney
labelled structures should include:
- Fibrous capsule - An outer membrane that surrounds and protects the kidney.
- The renal cortex - The outer region that contains Bowman’s capsules, convoluted tubules, and blood vessels.
- The renal medulla - The inner region with structures called pyramids that contain loops of Henle, collecting ducts, and blood vessels.
- The renal pelvis - The funnel-shaped cavity that collects urine into the ureters.
- ureter
- renal vein and artery
- renal pelvis
draw and label the nephron structure
This should include labels:
- renal capsule/bowmans capsule with glomerulus
- proximal tube
- loop of henle
- distal convulated tube
- collecting ducts
- efferent and afferent arteriole
- ascending and descending tube
where is the nephron found
medulla
function of the nephron
- filters the blood to remove waste and selectively reabsorb useful substances back into the blood
what does urine contain
- water
- dissolved salts
- urea
- small substances e.g hormones and excess vitamins
why does the urine not contain proteins, blood cells and glucose
proteins and blood cells - too large to be filtered out of the blood
glucose - all glucose is absorbed at the selective reabsorption stage in the PCT (proximal convoluted tubule)
how does filtering and reabsorption occur (steps of making urine)
Stage 1) Ultrafiltration - due to high hydrostatic pressure water and small molecules are forced out of the glamorous into the renal capsule
Stage 2) Selective reabsorption - occurs in the proximal convoluted tubule
Stage 3 + 4) The loop of henle -maintains a sodium gradient so water can be reabsorbed by the blood
Stage 5 + 6) Distal convoluted tubule (DCT) and collecting duct - water moves out DCT and collecting duct to return back to blood, collecting duct then carries the remaining liquid to ureter
Steps of ultrafiltration
1) blood enters through afferent arteriole and this splits into smaller capillaries which make up the glomerulus, causing high hydrostatic pressure of blood
2) Water and small molecules e.g glucose and mineral ions are forced out the capillaries and forms the glomerulus filtrate through gaps in the capillary endothelium and through basement membrane
3) Large proteins and blood cells are too big to fit through the gaps in the capillary endothelium so remain in the blood
4) The blood leaves via the efferent arteriole
adaptions of the proximal convoluted tubule
- microvilli - provide a large surface area for reabsorption
- lots of mitochondria - provides energy for active transport
process of selective reabsorption
1) The concentration of sodium ions in the PCT cell decrease as the sodium ions are actively transported out of the PCT epethilial cells into the blood in the capillaries
2) Due to the concentration gradient, sodium ions diffuse down the gradient from the lumen of the PCT into the cells lining the PCT, this is also an example of co transport as the proteins which transport sodium ions in carry glucose with it
3) the glucose can then diffuse from the PCT epithelial cell into the bloodstream
4) All the glucose is REABSORBED
properties of ascending and descending limb
ascending - walls are impermeable to water and has thicker walls
descending - walls are permeable to water and the walls are thinner
how is the sodium ion gradient maintained by the loop of Henle
1) Mitochondria in the walls of the cells provide energy to actively transport sodium ions out of the ascending limb of the loop of Henle into the interstitial space
2) The accumulation of sodium ions outside the nephron in the medulla lowers the water potential
3) In the descending limb water diffuse out by osmosis into the interstitial space and the water is then reabsorbed into the blood
4) At the base of the ascending limb some sodium ions are transported out by diffusion since the solution is dilute due to all the water that has moved out
Process of reabsorption of water at the DCT and collecting duct
DCT = distal convoluted tubule
1) Due to all the sodium ions being actively transported out of the loop of Henle when the filtrate reaches the DCT it is very dilute
2) The filtrate moves into the DCT and collecting duct
3) This causes more water to diffuse out of the DCT and collecting duct
4) Whatever filtrate remains in collecting duct forms urine
suggest how the length of the loop of henle will differ for as desert animal compared to a human and explain why?
- Desert animals will have a longer loop of henle
- the longer the loop of henle the surface area increases causing more sodium ions to be actively transported out, so a more negative water potential is created, resulting in more water being reabsorbed into the blood and very concentrated urine
why is homeostasis of water potential (osmoregulation) important
- if blood has too low water potential (hypertonic) - too much water will leave the cell and move into the blood by osmosis, causing cells to shrivel (crenation)
- if blood has too high a water potential (hypotonic) - too much water will move from the blood into the cells by osmosis, causing the cells to burst (lysis)
what causes hypertonic and hypotonic blood
hypertonic - too much sweating, not drinking enough water, lots of iron in diet
hypotonic - drinking too much water, not enough salt in diet
what is the role of the hypothalamus
- changes in the water potential of the blood are detected by osmoreceptors found in the hypothalamus
what happens when the water potential of the blood is too low
1) water leaves the osmosreceptors by osmosis, causing them to shrivel
2) This stimulates the hypothalamus to produce more ADH
3) ADH then moves to the posterior pituitary gland and from there it is released into the blood where it travels to the kidneys
4) DCT and collecting duct become more permeable to water
5) so more water is reabsorbed into the blood and less water is lost in the urine
6) water potential of the blood returns to normal
what happens when the water potential of the blood is too high
1) water enters the osmosreceptors by osmosis
2) this stimulated the hypothalamus to produce less ADH
3) ADH then moves to the posterior pituitary gland and from there it is released into the blood where it travels to the kidneys
4) DCT and collecting duct become less permeable to water
5) so less water is reabsorbed into the blood and more water is lost in the urine
6) water potential of the blood returns to normal
what happens when ADH reaches the kidneys
1) when ADH reaches the kidney it causes an increase in the permeability of the walls of the collecting duct and distal convoluted tube to water
2) this means that more water leaves the nephron and is reabsorbed into the blood so urine is more concentrated
How does ADH increase the permeability of the DCT and collecting duct to water
1) ADH binds to the receptors on the cell membrane of the collecting duct and DCT
2) when bound, it activates a phosphorylase enzyme in the cells
3) Phosphorylase causes the vesicles containing aquaporins (channel proteins) to fuse with the cell membrane and the aquaporins embed into the membrane
4) this causes more water to leave the DCT and collecting duct via the aquaporins and be reabsorbed into the blood
what are aquaporins
protein channels for water to pass through
