Homeostasis Flashcards
Define homeostasis
Maintaining a constant internal environment despite external changes
Describe why temperature, ph and water potential must be kept the same
Temperature- enzyme reactions, proteins therefore two high equals denaturation, to low kinetic energy is to low
pH- enzymes again, pH effects bonding
Water potential - cells may shrink/ burst, relies on keeping glucose concentration the same
Define negative feedback and positive feedback
Negative feedback- system reverse the change (most homeostasis systems )
Positive feedback- response to the change exacerbates it e.g. Depolarisation
Give five methods used by animals to control temperature
Sweating
Vasoconstriction/ dilation - changes diameter of arterioles hence changes the volume of blood that meets the air
Shivering - metabolic heat
Raising hairs - traps layers of air, air acts as insulator
Behaviour - hide/ bask in sunlight
Define exo and extotherm
Exotherm - organisms that derive heat from metabolic processes
Ectotherm - acquire heat from environment
Give the three processes that occur in the liver to control blood concentration
Glycogenolysis - hydrolysis of glycogen into glucose
Gluconeogenesis - production of glucose from non carbohydrates sources
Glycogenesis - conversion of glucose to glycogen
Where and within which cells is insulin made? What is the role of these cells?
Pancreas
Islets of langerhans
Beta cells
Beta cells detect a rise in [glucose]
Describe how increased concentration of glucose leads ro insulin release.
K+ channels are open normally within beta cells
Where blood [glucose] is high glucose diffuses in
Respiration of glucose produces ATP
ATP closes the ATP gated K+ channels
K + accumulates and alters cell potential
Voltage gated Ca2+ channels open causing insulin vesicles to fuse to the outer membrane
Exocytosis
Describe what happens when insulin acts on Target cells.
Binds to target cells on the liver (muscles as well)
Activates tyrosine kinase
Which phosphorylates enzyme (activates them)
Enzymes: insert glucose transporters
Changed protein structure to allow more glucose in
Glycogenisis
Without insulin what would happen?
HYPERglyceamia
Causes organ failure
Lowers water potential leading to osmotic problems
When is glucogon released where from?
Released from alpha cells in the islets of langerhans from within the pancreas, released when [glucose] is very low
Describe the action of glucagon on its target cells, with reference to secondary messenger model
Binds to liver cells
Stimulates the G protein which in turn activates activates adenyl cyclase
Andeyl cyclase converts ATP into cAMP
cAMP is the secondary messenger ( secondary messenger model)
Activates an protein kinase which catalyses glycogen into glucose
What would occur without glucogon ?
Hypoglycaemia leading to comas
Other than Glucagon what other hormone causes [glucose] to rise?
Adrenaline
Describe the relationship between insulin and glucagon, what does this result in?
Antagonist pair of hormones
Fluctuates around an optimum point
Type 1 diabetes
What causes it?
Symptoms?
How can it be controlled?
Caused by an autoimmune disease where beta cells are attacked
Symptoms include : tiredness, increased thirst, blurred vision
Controlled : insulin injections, pancrease transplants
Type 2 Diabetes
What causes it?
What are the risk factors?
How can it be controlled
Glycoproteins lose responsiveness to insulin, or their is an inadequate supply
Risk factors : diet, ovesity, lack of exercise, family history
Controlled by : changing lifestyle, insluin injections, medication to reduces rate of glucose release
Where does osmoregulation occur?
The kidney
Describe the structure of nephron
Bowman’s capsules at the start - cup shaped with mass of blood capillaries known as the glomerulus which is…
Connected to the proximal convoluted tubule which is followed by…
Loop of henle - a hairpin loop extends from cortex into medulla, which rises again to meet the…
Distal convoluted tubules
Which finally reaches the collecting duct
Describe three blood vessels involved in osmoregulation
Glomerulus - fluid forced out
Afferent arteriole, stems from renal artery, supploes nephron with blood, enters bowmans capsule
Efferent arteriole, exits bowmans capsule and has a much smaller diameter which leads to an increased pressure to push fluid out
Describe ultrafiltration in the kidney
Blood enters kidney from renal artery, branches off into afferent arterioles to enter the bowman capsule
Divides into glomerulus ( many capillaries) that diverege at the efferent arteriole.
Efferent arteriole has a smaller diameter hence causes a build up of hydrostatic pressure, this pressure pushes out the glomerular filtrate.
There is resistance to ultrafiltration in the kidney from epithelial cells and the hydrostatic pressure of the renal capsule, what adaptations allow ultrafiltration to occur anyway
Podocyte cells which provide a surface for the glomerular filtrate to flow over
Endothelium of glomerular capillaries has gaps in
Where does selective reabsorbtion occur? Why here?
Proximal convoluted tubule
Large SA : V beause of microvilli and folded membranes
Many mitochondria for active transport
Describe the process of selective reabsorbtion
Na+ ions actively transported out of the proximal convoluted tubule convoluted tubule into the capillaries hence the Na+ is lowered
Co transport channels allow sodium to diffuse down the diffusion gradient with glucose and amino acids attached
What section of the nephron is responsible for water reabsorbtion?
The loop of henle
Describe the process of water reabsorption in the loop of henle
1) ascending limb actively pumps Na+ out
2) leads to decreased water potential in the medulla (ascending limb is thick and water impermeable )
3) filtrate becomes more concentrated down the descending limb, because this surface is more permeable
4) in ascending limb due to pumping water potential rises
5) the collecting ducts are permeable and water diffuses out and into capillaries to be carried away
Describe how a named hormone is released into the kidney to limit water loss
Lower water potential causes osmoreceptors in the hyper-thalamus to shrivel which triggers the release of antidiuretic hormone (ADH)
ADH is secreted into the capillaries after passing to the pituitary gland
Describe the action of ADH
Binds to receptors on the cell surface membrane of the distal convoluted tubule and collecting duct
Activates phosphorylase
Causes vesicles containing aqua porins to fuse to the plasma membranes to increase permeability.
More water leaves into capillaries and so less is lost in urine
