homeostasis Flashcards
what is homeostasis
homeostasis is the maintenance of a constant internal environment via physiological control systems
what are factors that are controlled by homeostasis
- temperature
- blood ph
- blood glucose concentration
what happens in the body when the temperature is too low
if it is too low then there is not enough kinetic energy for enzyme-substrate complexes to be formed
this means the rate of important biological reactions/ processes is too slow
what happens if body temperature is too high
is it is too high then enzymes will denature
the body will react to the deviation from normal and return the body back to normal temperature
what happens if ph deviates from the norm
if ph deviates from optimum, it causes enzymes to denature
what happens if blood glucose levels are too low
if it is too low then it leads to cell death as glucose is required for respiration (both aerobic and anaerobic)
what happens if blood glucose levels are too high
it leads to the blood water potential to decrease, s water leaves cells by osmosis
this increases the water potential of cells so water can move back into the cells causing it to burst
what is negative feedback
negative feedback restores systems back to their normal level when there is a change vai the nervous system
what are the stages of negative feedback
stimulus →receptor →CNS→effector→response
the receptor detects the change
it then sends the impulse along a sensory neuron to the CNS which contains a relay neurone
the impulse is then sent along a motor neurone to an effector that elicits a response
what is positive feedback
positive feedback:
when deviation from the optimum stimulus changes which results in an even bigger deviation from the optimum e.g. contractions during labour
contractions releases oxytocin which stimulates even more contractions
is positive feedback part of homeostasis
positive feedback is not involved in homeostasis because it does not keep your internal environment stable.
Positive feedback is useful to rapidly activate processes in the body
when else can positive feedback occur
positive feedback can also happen when a homeostatic system breaks down
for example, hypothermia is low body temperature.
It happens when the body has lost heat quicker than it can produce it. As the body temp falls the brain does not work properly and shivering stops. This makes body temp to fall even more
Positive feedback takes body temp further away from the normal and continues to decrease unless action is taken
what are factors that can influence blood glucose concentration
diet
exercise levels
insulin
adrenaline
glucogon
what is glycogenesis
excess glucose converted to glycogen by the liver only occurs when blood glucose levels are too high
glycogenolysis
breakdown of glycogen back to glucose in the liver when glucose levels are too low
what is gluconeogenesis
creates glucose from non- carbohydrates stores in the live e.g. amino acids and glycerol
it occurs when glucose levels are still too low despite glycogenolysis occurring
when is insulin secreted
insulin is secreted when beta cells in the Islets of Langerhans (which are in the pancreas) detect blood glucose levels that are too high
describe how insulin works to decrease blood glucose levels
- Insulin attaches to receptors on target cells and changes the tertiary structure of the channel proteins so more glucose is absorbed into the cells by facilitated diffusion
- more protein carriers are incorporated into the membranes so even more glucose is absorbed from the blood into the cells
- glycogenesis occurs - which is catalysed by activating enzymes once it is absorbed in the cells
why is glucagon produced
- glucagon attaches to receptors on the surface of target cells
- this stimulates adenylate cyclase to convert ATP into cyclic AMP (cAMP)
- cAMP acts as a second messenger model which contains 1 phosphate unlike three like ATP
- cyclic AMP activates an enzyme called protein kinase which hydrolysis glycogen to glucose→ so glycogen action stimulates glycogenolysis
- It can also activate enzymes involved in glyconeogensis
what is second messenger model
molecules inside a cell that transmit signals intracellularly from the binding of an extracellular molecule to a receptor
explain adrenaline action
- adrenaline attached to a receptor on the surface of a target cell
- this causes a G protein to be activated and to convert ATP to cAMP
- cAMP activated an enzyme that hydrolyses glycogen to glucose
this whole process is the flight or flight mechanism
what is type 1 diabetes
this occurs when the body is unable to produce insulin
this starts at childhood
most often, the results of an autoimmune disease where beta cells are attacked by antibodies
TREATMENT: insulin injections
what is type 2 diabetes
Receptors on target cells lose responsiveness to insulin and so it leads to a decrease in insulin sensitivity
This usually develops in adulthood due to obesity and poor diet → if you have too much glucose/ sugar in your blood due to diet, insulin works soo hard to decrease it your body becomes resistant to insulin
TREATMENT: regulating the uptake of carbohydrates, increasing exercise and sometimes insulin injections
What is the co tr of nlood water potential called
It is called osmoregulation
What is osomoregulation controlled by
Structures in the kidney called nephrons
Wht re the stages of osomoregulation
- Ultrafiltration 2. Selective reabsorption 3.loop of henle 4. Distal convulated table and collecting duct
Where does ultrafiltration occur
It occurs in the glomerus and the Bowman’s capsule
What happens during ultrafiltration
- Blood enters kidneys via the renal artery (which is the blood vessels that carries blood to the kidney) at a high pressure 2. The renal artery then divides jnk the afferent arterial then the glomerus 3. Water and soluble components are forced out of the glomerular (as the capillaries are small and entering the glomerulus at high pressures down a pressure gradient ito the Bowman’s capsule ) 4. The pressure gradient is aided by the efferent arteriolw leabing the glomerus being narrower than the afferent arteriole 5. Proteins are left behind in thr blood as they’re too large 6. The substances that move out the glomerulus capsule is card he glomerular filtrate
What occurs during selective reabsorption Selective reabsorption of substances from the glomerulus filtrate
- Glucose is reabsorbed by cotransport from epithelial cells of the proximal convoluted tube (PCT) to blood capillaries 2. This is carried out by actively transporting Na+ ions, creating a low Na+ concentration in the epithelial cells 3. Na+ are moved in from the PCT lumen by facilitated diffusion Minto the epithelial cells, which also brings in glucose 4. Glucose diffuses into blood capillaries
Why does glucose have to be reabsorbed
Glucose in the glomerular filtrate must be reabsorbed into blood for processes like respiration
What occurs at be loop of henle
- Na+ are ctively transported out of the ascending limb, creating a low water potential in the interstitial space (which is the same space ascending and descending limb) 2. The ascending limb is impermeable to water so water can only move out if the descending limb by osmosis into the interstitial space 3. There is high water potential now in the (I.S) and so water then energy blood capillaries by osmosis 3. At the hairpin of the loop Na+ ions naturally diffuse outbas water potential is at its lowest here.
What is the loop of heeled responsible for doing
It is involved with water reabsorption Forming urine and regulating urine volume
What occurs at the distal convoluted tube and collecting dut
- Water moves out the DCT and the coolecyih duct by osmosis 2. Collect runs parallel to the loop of the henlr so can concentration increases as you move down intj the medulla This means more water is reabsorbed into the blood by osmosis
Where is the medulla
The medulla is the bottom half od the nephron
What can alter collecting duct permeability
The hypothalamus Posterior pituitary gland Anti diuretic hormone (ADH)
Explain how hormones can alter the collecting duct of permeability
- Osmoreceptors in the hypothalamus detect blood water potential 2. When it falls, osmorecptors shrink causing the release of ADH 3. ADH travels to the posterior pituitary gland where its secreted into the blood 4. ADH then travels to the kidneysband binds to receptors on the surface of the collecting duct activates the enzyme phosphorylase 5. This causes vesicles containing aquporins to incorporate into the cell surface membrane 6. This increases water permeability and also urea permeability 6. Urea leaves the collecting duct, so water also leaves and is reabsorbed into the blood
Why do osmoreceptors shrink
Because water leaves the osmorecptors
What are aquaporins
These are channel proteins that allows the movement of water
