Homeostasis Flashcards
Insulin - detection by beta cells
High blood glucose concentration is detected by the beta cells in the pancreas
Where are beta cells located
In the islets of Langerhans
Secretion of insulin
Beta cells respond to high blood glucose concentration by secreting insulin into the blood which travels to liver and muscle cells
Insulin: binding to muscle cells
Insulin binds to receptors on muscle cell membranes which then stimulates them to insert more glucose channel proteins into the cell membrane so the rate of uptake of glucose by muscle cells increases and rate of respiration in the muscle cells increases
Glycogensis
Insulin binds to receptors on the liver cell membranes , they produce enzymes that convert glucose to glycogen which is stored in the liver cell’s cytoplasm
Importance of insulin
Important for maintaining optimum blood water potential - if blood glucose concentrations weren’t reduced by insulin then the water potential in the blood would decrease causing water to diffuse out of cells
Glucagon : detection by alpha cells
Low blood glucose concentration is detected by the alpha cells in the pancreas
Where are alpha cells located
Islets of Langerhans
Secretion of glucagon
Alpha cells respond to low blood glucose concentration by secreting glucagon into to the blood which travels to the liver cells
Glycogenolysis
Glucagon binds to receptors on the liver cell membranes which stimulates the liver cells to produce enzymes that convert glycogen to glucose
Gluconeogenesis
Binding of glucagon to liver cell membranes also causes the release of enzymes that form glucose from glycerol and amino acids
How does glucagon affect the rate of respiration
Slows respiration rate in cells which slows the rate at which glucagon is used up
Importance of glucagon
Important in increasing blood glucose concentration for survival , if blood glucose levels weren’t increased by glucagon then there wouldn’t be enough for respiration
Secretion of adrenaline
Secreted from the adrenal gland in response to low blood glucose concentration
Adrenaline: binding to liver cells
Induces two reactions in the liver cells :
Activation of glycogenolysis ( glycogen — glucose )
Inhibition of glycogenesis ( glucose — glycogen)
Also promotes the secretion of glucagon from the pancreas and inhibits secretion of insulin
Primary messenger
Messengers that do not enter the cell but instead exert an action on the cell membrane by binding to receptors and triggering a change within the cell e.g adrenaline and glucagon
Secondary messengers
Initiate and coordinate responses that take place inside a cell , usually activated by the binding of a primary messenger to a cell surface receptor e.g cyclic AMP
Cyclic AMP
The primary messengers -adrenaline or glucagon bind to receptors on the cell membranes of liver cells which activates an enzyme adenylate Cyclase which converts ATP to cyclic AMP
Cyclic AMP activates an enzyme called protein kinase A which triggers a cascade of reactions that result in glycogenolysis - breaks down glycogen into glucose
Type I diabetes
Chronic health condition where sufferers cannot properly control their blood glucose concentration as they cannot produce insulin
Cause of type I diabetes
Beta cells in the pancreas are attacked by the immune system and so become damage and no longer produce insulin
Hyperglycaemia
Eating causes the blood glucose concentration to increase and people with type I diabetes cannot produce insulin to counteract the increased levels of glucose so blood glucose level remains high
Treatment of type I diabetes
Insulin is injected regularly during the day or an insulin pump can be used
Too much insulin can cause a fall in glucose levels called hypoglycaemia so insulin therapy must be carefully monitored
Type II diabetes
Dont produce enough insulin or cannot respond to insulin
Cause of type II
Correlated with obesity ,lack of exercise, age and family history .
Develops when the beta cells in the pancreas no longer produce enough insulin or when muscle or liver cells stop responding to insulin
Treatment of type II
Eating a healthy diet and exercising , in some cases medication is used to lower glucose levels or in rare cases , insulin injections are used
Colorimetry
Used to identify the concentration of glucose in an unknown ‘urine’ sample
Colorimetry: prepare urine samples
Take three test tubes and label each with the name of the patient and add three cm^3 from each patient, add 2cm ^3 of benedict’s reagent and mix the contents of the tube
Colorimetry : prepare the Calibration curve
Label six test tubes 0 to 10 mmol dm ^-3 and dilute the glucose solution provide using distilled water to produce 5 additional concentrations : 0, 2, 4, 6, 8 , 10
Add 2cm^3 to each tube and mix the contents and add to the water baton
Colorimetry : use the colorimeter
Use the contents of the 0 mmol dm ^-3 glucose solution tube to calibrate the colorimeter to zero absorbance and place the remaining samples in cuvette s
Colorimetry : record the results
In a table and plot a graph of the absorbance of the known concentrations of glucose. Plot concentration of glucose on the x-axis and the absorbance on the y-axis.
Where does osmoregulation take place
Kidneys : absorb more or less water according to the water potential
High water potential
More water must be lost by excretion to return the water potential to normal , the blood reabsorbs less water from the kidneys. The urine is more dilute and water potential in the blood decreases
Low water potential
Less water must be lost by excretion so the blood reabsorbs more water from the kidneys so the urine is more concentrated and water potential in the blood increases
Nephron : bowman’s capsule
Beginning of the tubules that make up the nephron .
Surrounds a network of capillaries called the glomerulus : first step of filtration of the blood to form urine takes place in the bowmans capsule which produces the glomerular filtrate
Nephron : afferent and efferent arterioles
Blood flows into the glomerulus through the afferent arteriole and out of the glomerlus out through the efferent arteriole
The afferent arteriole is much wider than the efferent arteriole
Nephron : Proximal convoluted tubule
PCT is the site of selective reabsorption,
After the glomerular filtrate has been produced in the bowman’s capsule, glucose and water are reabsorbed into the bloodstream through the PCT
Nephron : loop of Henle
Produces a low water potential in the medulla of the kidney
Ascending limp is impermeable to water and descending is permeable
Collecting duct
Water is reabsorbed into the blood through the collecting duct.
The amount of water that is reabsorbed depends on the water potential of the blood : if blood water potential is low , more water is reabsorbed. If blood water potential is high then less water is reabsorbed
Glomerular filtrate
Takes place in the bowmans capsule
The afferent arteriole is much wider than the branch that exists which creates a high blood pressure in the glomerulus - this high pressure causes the fluid and its solutes to be forced out of the capillary ( pressure filtration.
The fluid flows through the pores in the capillary endothelium and then the smaller molecules filter through slit pores in the basement membranes.
The substances pass between epithelial cells of the bowmans capsules
What does the filtrate contain
Water, amino acids, urea, glucose and inorganic ions
Steps involved in the proximal convoluted tubule
- NA+ ions are actively transported out of the PCT epithelial cells and into the blood by NA+ AND K+ pumps
- Active transport of NA+ ions causes the concentration of Na+ ions inside the epithelial cells to decrease so they diffuse into the epithelial cells by co transporter proteins which allows glucose and amino acids to be transported aswell
- As glucose and amino acids are co transported into the PCT, the concentration increases so they diffuse down the concentration gradient into the blood - the blood pressure is high so they are carried away quickly which maintains a steep concentration gradient
- The moment of Na+ ions, glucose and amino acids into the blood stream cause the water potential to decrease in the blood and increase in the PCT so it diffuse out by osmosis
How is water reabsorbed in the collecting duct
- Na+ ions are actively transported out of the top of the ascending limb into the surrounding tissue fluid in the medullla which causes the solute concentration of the medulla to increase and the water potential to decrease however the ascending limb is impermeable to water
- Na+ continue to diffuse out at the bottom of the ascending limb
- The descending limp is permeable to water which means that water inside the tubule can diffuse out because there is a lower water potential in the medulla so it is absorbed by the blood stream - this creates a high solute concentration and and low water potential in the tissue fluid surrounding the collecting duct which causes water diffuse out
Antidiuretic hormone
ADH influences the permeability of the distil convoluted tubule and collecting duct so controls how much water is reabsorbed
Binds to the receptors on the cell membrane of epithelial cells of the distal convoluted tubule and the collecting duct : when it binds, containing aquaporins fuse with the cell membrane
Osmoreceptors in the hypothalamus
Monitor blood water potential so if it increases, water diffuses into the osmorececptors and and the cells swell
Osmoregulation : posterior pituitary gland
When osmoreceptors shrink this is detected by the this which releases ADH into the blood
Aquaporins
Protein channels for water , they increase the permeability of the DCT and collecting duct which means more water is reabsorbed into the blood
Urine and ADH
If more ADH is in the bloodstream then more water is reabsorbed from the nephron into the blood so the urine is more concentrated
