Homeostasis Flashcards
State how glucagon reaches liver cells.
Bloodstream
Glucagon —> (receptor) G-protein —> enzyme A —> second messenger B —> activated kinase enzymes —> enzymes cascade —> activated glycogen phosphorylase ^ATP^
Name enzyme A and second messenger B
A — adenylyl cyclase
B — cyclic AMP / cAMP
State the role of enzyme cascade.
Amplifies signal / expands message
State the function of the final enzyme in the pathway, glycogen phosphorylase.
Break down glycogen / glycogen —> glucose / glycogenolysis
A biosensor is used to measure blood glucose concentration to check that it is within the normal range.
Describe how a glucose biosensor is
Blood on strip inserted into biosensor;
Glucose oxidase;
Glucose —> gluconic acid and hydrogen peroxide;
Electric current / flow of e- / voltage;
Current proportional to glucose quantity / concentration ;
Digital / numerical reading on screen
GIve an example of a second messenger.
Cyclic AMP / cAMP
Explain why the lumen of the afferent blood vessel needs to be wider than the lumen of the efferent blood vessel.
To generate high blood pressure / hydrostatic pressure;
To force plasma / fluid through basement membrane / into the Bowman’s capsule / into lumen
Describe the roles of basement membrane and podocyte in the formation of the glomerular filtrate.
Basement membrane
Acts as a filter / filtration barrier;
Only named molecules / ions can pass through OR RBC / large proteins cannot pass through;
Podocyte
Has gaps / projections / pores;
Allows fluid / filtrate to pass into the lumen / Bowman’s capsule;
Produces basement membrane
Glucagon is synthesised by cells in the pancreas known as alpha cells. Glucagon binds to G-protein-coupled receptors in the cell surface membrane of liver cells. This results in the activation of G-proteins.
Adenylyl cyclase;
Formation of cyclic AMP / cAMP;
cAMP acts as a second messenger;
Activation of kinase;
Enzyme cascade;
Amplification of signal;
Glycogenolysis / gluceogenisis;
Glucose released into blood
Describe and explain the action of ADH on cells of the collecting duct when the water potential of the blood decreases.
ADH binds to cell membrane receptor of collecting duct cells;
G protein / adenylyl cyclase;
Cyclic AMP;
Protein kinase activated;
Vesicles fuse with cell membrane;
Aquaporins;
Collecting duct / cells/ membrane more permeable to water;
More water leavers lumen / nephron OR more water enters blood / medulla
What cells secrete the hormone insulin and glucagon.
Alpha and beta cells
Which part of the nephron
-contains cells that respond to ADH?
-is where podocyte cells are located?
-contains cells that are located in the medulla?
Distal convoluted tubule / collecting duct;
Bowman’s capsule;
Loop of Henl’e / collecting duct
Describe and explain how the cells of the proximal convoluted tubule are adapted to carry out selective reabsorption.
Microvilli / basal membrane folds increase / give large surface area;
For transport proteins;
Na+ and glucose / amino acids move / co-transported into cell from filtrate / lumen;
Na+ pumped out of cell to blood tissue / tissue fluid;
Via active transport
Many mitochondria for energy / ATP;
Suggest one effect on the circulatory system of a low concentration of ADH in the blood and explain why.
Blood volume / pressure decreases;
Low levels of ADH causes kidneys to excrete too much water, increasing volume of urine leading to a fall in blood pressure
Explain what is meant by homeostasis in a mammal and explain why it is important to maintain body temperature, blood glucose concentration and the water potential of blood.
Regulate internal environment;
Within narrow limits OR around optimum value;
High body temperature denatures enzymes;
Low body temperature does not allow maximum enzyme activity as enzymes require optimum temperature to work best
Describe and explain how the structures in the Bowman’s capsule and its associated blood supply are adapted to allow ultrafiltration to take place.
Afferent arteriole wider / has larger diameter then efferent;
Causes high blood /hydrostatic pressure in glomerulus / capillaries;
Pores / gaps in capillary endothelium;
Basement membrane acts as a filter;
Details of podocytes;
Basement membranes stops blood cells / large proteins OR allows urea / glucose / amino acid / ions / water
Describe the roles of ADH and the collecting ducts in osmoregulation.
Hypothalamus / osmoreceptors detects changes in water potential of blood;
Causes posterior pituitary gland;
To release ADH into blood;
ADH binds to receptors;
On cell surface membrane of collecting duct cells;
Stimulates enzyme cascade / phosphorylase enzyme produced;
Vesicles fuse with cell surface membrane;
Vesicles have aquaporins;
Collecting duct membranes more permeable to water;
Water moves down water potential gradient / by osmosis;
Into collecting duct cells / tissue fluid / blood;
Water potential of blood returns to set point
Explain how dip sticks function to test for glucose in a sample of urine.
Dip stick has immobilised enzymes;
Dip stick dipped in urine;
Glucose oxidase and peroxidase;
Glucose reacts to give hydrogen peroxide;
Hydrogen peroxide reacts with colourless substance;
To give colour change;
Compare with colour chart;
More glucose gives darker colour / colour intensity gives glucose quantity;
Doesn’t give current blood glucose concentration / not numerical / semi-quantitative
