Homeostasis- B19 Flashcards
What is homeostasis?
Maintaining the body’s internal environment(temperature, pH, water potential, glucose levels) within restricted limits
What is the set point?
The desired level or the norm at which the system operates
What is negative feedback?
-When there is a change away from the normal level/set point.
-Effectors act to oppose the change to bring the level back to norm/set point.
What is positive feedback?
A change is amplified - a change causes further change- moves further away from the set point/norm
What does it mean for homeostasis to involve multiple feedback mechanisms?
-having more than one mechanism gives increased control over changes in your internal environment
-having multiple negative feedback mechanisms means you can actively increase or decrease a level so it returns to normal, rather than just control the factor in one direction
-having one negative feedback mechanisms means gives a slower response and less control
Why do we need to keep a constant temperature?
Low temperatures means little kinetic energy so chemical reactions involving enzymes in the body slow down which result in death. Vice versa
Why do we need to keep blood water potential constant?
If our blood has a lower WP then our tissue fluid water will move by osmosis into our blood and this will cause tissues to dehydrate. If blood WP is too high, RBCs may swell and burst
Why do we keep blood pH constant?
pH affects the amount of hydrogen ions and this can cause the tertiary structure of enzymes(and other proteins) to change
Why do we need to keep blood glucose levels constant?
Dissolved glucose in large amounts can effect the WP of the blood.
What are the structures within the islets of langerhans and what do they do?
-beta cells - secrete insulin
-alpha cells - secrete glucagon
-capillaries into which hormones are secreted
What is the action of insulin?
-lowers blood glucose conc. by binding to receptors on the membranes of muscle and liver cells(hepatocytes)
1)increases membrane permeability to glucose so more glucose is absorbed - by increasing the number of (GLUT4) glucose carrier proteins in the cell surface membrane
2)activates enzymes in muscle and liver cells that convert glucose into glycogen which is stored in the cytoplasm - glycogenesis
3)increases the rate of respiration of glucose in muscle cells
-both 2 and 3 reduce the concentration of glucose in the cell so maintains the conc. gradient, meaning more glucose diffuses into the cell by facilitated diffusion
What are glucose transporters?
-channel proteins which allow glucose to be transported across the membrane
-skeletal and cardiac muscle contain a glucose transporter called GLUT4
-when insulin levels are low, GLUT4 is stored in vesicles in the cytoplasm
-when insulin binds to receptors on the cell surface membrane, triggers the insertion of GLUT4 to the membrane so more facilitated diffusion of glucose into the cell can occur
What is the action of glucagon?
-raises blood glucose conc.
1)binds to specific receptors on the membrane of hepatocytes and activates enzymes that hydrolyses glycogen->glucose - glycogenolysis
2)activates enzymes involved in the formation of glucose from glycerol and from amino acids - gluconeogenesis
3)glucagon decreases the rate of respiration of glucose in cells
What process does insulin instigate?
glycogenesis - making glycogen from glucose in the liver
What process does glucagon instigate?
-gluconeogenesis - making glucose from glycerol and amino acids in the liver
-glycogenolysis - hydrolysing glycogen in the liver to glucose
Difference between hormonal and nervous response.
-hormones travel in the blood to target organs
=slower response than a nervous one
-also means the response is widespread to all target organs/cells unlike the localised nervous one
-tends to have a longer response as hormones are broken down slower than neurotransmitters
What hapens when there is a rise in blood glucose conc.?
beta cells secrete insulin]
alpha cells stop secreting glucagon
What happens when there is a fall in blood glucose conc.?
beta cells stop secreting insulin
alpha cells secrete glucagon
What does adrenaline do?
-increased secretion from adrenal glands when blood glucose conc. is low/stressed/exercising
-binds to receptors on the cell membrane of hepatocytes and increases blood glucose levels by:
1)activating glycogenolysis
2)inhibiting glycogenesis
3)activates glucagon secretion
4)inhibits insulin secretion
What is the second messenger model?
-adrenaline and glucagon activate glycogenolysis/gluconeogenesis by binding to receptors
-this activates an enzyme on the inside of the cell membrane, which then produces a chemical known as a second messenger
-the second messenger activates other enzymes in the cell to bring about the response
Explain the process of the second messenger.
-adrenaline and glucagon bind to their respective specific receptors, which activates an enzyme called adenylate cyclase
-activated adenylate cyclase converts ATP into a chemical messenger called cyclic AMP(cAMP), which is a second messenger
-cAMP activates an enzyme called protein kinase A
-protein kinase A activates a cascade(a chain of reactions) that hydrolyses glycogen into glucose
What is type 1 diabetes?
-insulin dependent
-person doesn’t make insulin - usually from birth
-autoimmune response - body attacks beta cells
-immune system attacks beta cells in the iselts of langerhans, so they can’t produce insulin
-after eating, blood glucose levels rise and stay high - hyperglycaemia
-the kidneys can’t reabsorb all this glucose, so some of it is excretes in the urine
What are the treatments for type 1 diabetes?
-insulin therapy
-regular injections throughout the day or delivered by a pump to continuously deliver insulin
-must be controlled carefully because too much can cause hypoglycaemia -low blood sugar levels
-eating regularly and controlling simple carbohydrate intake can help avoid sudden rises in glucose levels
What is type 2 diabetes?
-insulin independent
-person makes insulin
-less receptors for insulin(may still be some present)
-can sometimes be linked to inadequate supply of insulin
-acquired later in life
-beta cells produce insulin but cells don’t respond to insulin because the receptors on their membranes don’t function properly, so less glucose is absorbed into cells
-causes hyperglycaemia
