16.1 - 16.7 Homeostasis Flashcards
Define homeostasis
The maintenance of an organisms internal environment within restricted limits
Explain why homeostasis is important with regards to proteins
- Enzymes and channel proteins
- Any changes to pH or temp can cause these to denature
- This affects the rate of biochemical reactions
Explain why homeostasis is important with regards to water potential
- Water potential of blood and tissue fluid
- Can cause cells to shrink and expand as water moves by osmosis
Explain why homeostasis is important with regards to glucose potential
- Effects water potential
- Needed for respiration
Explain why homeostasis is important with regards to the external environment
- Can better resist external changes such as weather and seasons
Give the steps of a control mechanism
- Receptor - Detects any deviation from the optimum point and informs the coordinator
- Coordinator - Coordinates information from receptors and sends information to effectors
- Effector - Causes changes to bring the system back to the optimum point
Define optimum point
The point at which the system operates best
Define positive feedback
When a deviation from an optimum causes changes that result in an even greater deviation
What factors may affect blood glucose conc?
- Diet - hydrolysis of carbohydrates
- Glycogenolysis
- Gluconeogenesis
Define glycogenesis
Conversion of glucose to glycogen
Define glycogenolysis
Breakdown of glycogen to glucose
Define gluconeogenesis
Producing glucose from sources other than carbohydrates e.g glycerol and amino acids
Where is glucagon produced?
- Pancreas
- Alpha cells of the islets of Langerhans
- a-cells are larger
Where is insulin produced?
- Pancreas
- Beta cells of the islets of Langerhans
- B-cells are smaller
Describe the action of insulin
- Binds to specific receptors on cell-membranes of target cells
- Increases cell uptake of glucose
- Activates enzymes involved in glycogenesis
- Decreases blood glucose conc
Describe how insulin increases a cells rate of absorption of glucose
- Change in the tertiary structure of the channel proteins
- Increased respiratory rate of cell
- Increases the number of channel proteins
Describe the action of glucagon
- Attach to receptor on the surface of liver or muscle cells
- Activates enzymes involved in glycogenolysis
- Activates enzymes involved in gluconeogenesis
- Increases blood glucose conc
Describe the action of adrenaline
- Released by the adrenal gland during stress or excitement
- Attaching to receptors on the surface of target cells
- Activates enzymes involved in glycogenolysis
Describe the second messenger model
How adrenaline causes an increase in blood glucose
- Adrenaline binds to protein receptors on the cell-surface membrane of a liver cell
- Causes protein receptor to change shape
- Activates adenylate cyclase enzyme
- This converts ATP to cyclic AMP
- Cyclic AMP then binds to protein kinase enzyme, changing its shape and activating it
- Protein kinase then catalyses glycogen to glucose
Describe the cause of Type 1 diabetes
- The body’s immune system attacks the beta cells of the islets of Langerhans
- This means the body is no longer able to produce insulin
Describe the causes of Type 2 diabetes
- Glycoprotein receptors on cells are lost or become less responsive to insulin
- May also be due to an inadequate supply of insulin from the pancreas
Describe how Type 1 diabetes can be controlled
- Monitor blood glucose with biosensors
- Insulin injections
- Control carbohydrate intake and exercise
Why must insulin be injected as opposed to taken orally?
- Insulin is a protein
- If taken orally it would be digested in the alimentary canal
Describe the primary method of controlling Type 2 diabetes
- Controlling carbohydrate intake and exercise
Describe alternative methods for treating Type 2 diabetes
- Insulin injections
- Injection of drugs that stimulate insulin production
- Drugs that slow the rate at which the body absorbs glucose from the intestine
Give the stages of osmoregulation
4
- Formation of glomerular filtrate by ultrafiltration
- Reabsorption of glucose and water by the proximal convoluted tubule
- Maintenance of a gradient of sodium ions in the medulla by the loop of Henle
- Reabsorption of water by the distal convoluted tubule and collecting ducts
Describe the formation of glomerular filtrate
- The efferent arteriole has a smaller diameter than the afferent arteriole
- Therefore, there is a build up of hydrostatic pressure within the glomerulus
- Water, glucose and mineral ions are pushed out of the capillary to form filtrate
- Blood cells and large proteins cannot pass across into the renal capsule as they are too large
How is it possible that water, glucose and mineral ions can move out of the capillaries to form glomerular filtrate?
- The inner layer of the renal capsule is made of podocytes (a type of cell that has spaces between them)
- Endothial cells of the glomerular capillary have gaps between them
Describe how the proximol convoluted tubules are adapted to reabsorb substances into the blood
Epthelial cells have:
* Microvilli for large surface area
* Infoldings at their base for large surface area
* High density of mitochondria to provide ATP for active transport
Describe how glucose is reabsorbed
- Na+ are actively transported out of the cells lining the proximal convoluted tubule into blood capillaries
- Therefore, Na+ conc of these cells decreases
- Na+ move from the lumen of the proximal convoluted tubule into the epithelial cells via facillitated diffusion. This co-transports other molecules as well.
- Co-transported molecules then diffuse into blood
Describe how the distal convoluted tubule is adapted for absorption
- Cells have microvilli and many mitochondria
The main role of the distal tube is to make the final adjustments and control pH of blood
Describe ADH
- Antidiuretic hormone
- ADH can alter the number of aquaporins so can control water loss
Describe what may cause a rise in solute concentration/decrease in water potential
- Too little water being drank
- Excessive sweating
- Large amounts of ions being taken in
Describe what may cause a fall in solute concentration/rise in water potential
- Drinking too much water
- Salts used in metabolism or excreted not being replaced in the diet
Describe how a fall in water potential results in ADH reaching the kidneys
- Water is lost from osmoreceptors in the hypothalamus via osmosis
- Osmoreceptors shrink
- This causes the hypothalamus to produce ADH
- ADH is secreted from the posterior pituitary gland into the cappillaries
- Transported to kidneys in the blood
Describe how ADH prevents water potential from getting any lower
- Increases the cell surface membranes permiabiltiy to water in the distal convoluting tubule and the collecting duct
- Increases the permiability of the collecting duct to urea so urea passes out and the water potential around the duct decreases
Therefore, more water leaves the collecting duct, via osmosis, and renters the blood
Describe how ADH increases the permiability of cell surface membranes to water
Distal convolute tubule and the collecting duct
- Binds to specific protein receptors on cell-surface membrane
- Activates an enzyme called phosphorylase
- This causes vesicles to fuse with the cell surface membrane
- Vesicles contain a piece of plasma that has many aquaporins so this causes cell to become more permiable to water
Describe how a fall in water potential is resolved
After the action of ADH has prevented any further decrease
- Osmoreceptors send nerve impulses to the thirst centre of the brain
- Osmoreceptors detect rise in water potential and send fewer impulses to pituitary gland
- Reduces release of ADH and the permiability of the collecting duct to water returns to normal
Describe the response to a rise in water potential
- Detected by osmoreceptors in the hypothalamus
- Increase the frequency of nerve impulses to the pituitary gland to reduce the release of ADH
- Less ADH leads to a decrease in the permiability of the collecting ducts to water and urea
- Water potential in the blood falls
- Osmoreceptors detect this and ADH is increased back to normal levels
Describe what happens in the descending limb of the loop of Henle
Due to low water potential in the interstitial space between the two limbs…
* Walls are thin and very permiable to water so water moves out via osmosis
* Water enters the capillaries and is carried away
* Some Na+ move in by diffusion
* The filtrate progressively loses water potential down the limb
Describe what happens in the ascending limb of the loop of Henle
- Sodium ions are actively transported out using ATP
- This creates a low water potential in the interstitial space between the two limbs
- Water does not move out via osmosis as the walls are thick and impermiable to water
Describe what happens in the collecting duct
- In the interstitial space between the ascending limb and the collecting duct, there is a a water potential gradient
- Higher water potential in the cortex, lower moving into the medulla
- As filtrate moves down the collecting duct, water passes out by osmosis
- As both water potentials are decreasing, water moves out for the full length of the collecting duct
Describe how the secretion of ADH effects the urine produced
- Permeability of collecting duct and distal tubule to water is increased
- More water moves out and into the blood stream via osmosis
- Smaller volume of urine
- Urine is more concentrated
