Homeostasis

Question 1

Insulin - detection by beta cells

Answer 1

High blood glucose concentration is detected by the beta cells in the pancreas

Question 2

Where are beta cells located

Answer 2

In the islets of Langerhans

Question 3

Secretion of insulin

Answer 3

Beta cells respond to high blood glucose concentration by secreting insulin into the blood which travels to liver and muscle cells

Question 4

Insulin: binding to muscle cells

Answer 4

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

Question 5

Glycogensis

Answer 5

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

Question 6

Importance of insulin

Answer 6

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

Question 7

Glucagon : detection by alpha cells

Answer 7

Low blood glucose concentration is detected by the alpha cells in the pancreas

Question 8

Where are alpha cells located

Answer 8

Islets of Langerhans

Question 9

Secretion of glucagon

Answer 9

Alpha cells respond to low blood glucose concentration by secreting glucagon into to the blood which travels to the liver cells

Question 10

Glycogenolysis

Answer 10

Glucagon binds to receptors on the liver cell membranes which stimulates the liver cells to produce enzymes that convert glycogen to glucose

Question 11

Gluconeogenesis

Answer 11

Binding of glucagon to liver cell membranes also causes the release of enzymes that form glucose from glycerol and amino acids

Question 12

How does glucagon affect the rate of respiration

Answer 12

Slows respiration rate in cells which slows the rate at which glucagon is used up

Question 13

Importance of glucagon

Answer 13

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

Question 14

Secretion of adrenaline

Answer 14

Secreted from the adrenal gland in response to low blood glucose concentration

Question 15

Adrenaline: binding to liver cells

Answer 15

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

Question 16

Primary messenger

Answer 16

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

Question 17

Secondary messengers

Answer 17

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

Question 18

Cyclic AMP

Answer 18

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

Question 19

Type I diabetes

Answer 19

Chronic health condition where sufferers cannot properly control their blood glucose concentration as they cannot produce insulin

Question 20

Cause of type I diabetes

Answer 20

Beta cells in the pancreas are attacked by the immune system and so become damage and no longer produce insulin

Question 21

Hyperglycaemia

Answer 21

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

Question 22

Treatment of type I diabetes

Answer 22

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

Question 23

Type II diabetes

Answer 23

Dont produce enough insulin or cannot respond to insulin

Question 24

Cause of type II

Answer 24

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

Question 25

Treatment of type II

Answer 25

Eating a healthy diet and exercising , in some cases medication is used to lower glucose levels or in rare cases , insulin injections are used

Question 26

Colorimetry

Answer 26

Used to identify the concentration of glucose in an unknown ‘urine’ sample

Question 27

Colorimetry: prepare urine samples

Answer 27

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

Question 28

Colorimetry : prepare the Calibration curve

Answer 28

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

Question 29

Colorimetry : use the colorimeter

Answer 29

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

Question 30

Colorimetry : record the results

Answer 30

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.

Question 31

Where does osmoregulation take place

Answer 31

Kidneys : absorb more or less water according to the water potential

Question 32

High water potential

Answer 32

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

Question 33

Low water potential

Answer 33

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

Question 34

Nephron : bowman’s capsule

Answer 34

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

Question 35

Nephron : afferent and efferent arterioles

Answer 35

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

Question 36

Nephron : Proximal convoluted tubule

Answer 36

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

Question 37

Nephron : loop of Henle

Answer 37

Produces a low water potential in the medulla of the kidney | Ascending limp is impermeable to water and descending is permeable

Question 38

Collecting duct

Answer 38

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

Question 39

Glomerular filtrate

Answer 39

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

Question 40

What does the filtrate contain

Answer 40

Water, amino acids, urea, glucose and inorganic ions

Question 41

Steps involved in the proximal convoluted tubule

Answer 41

1. NA+ ions are actively transported out of the PCT epithelial cells and into the blood by NA+ AND K+ pumps 2. 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 3. 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 4. 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

Question 42

How is water reabsorbed in the collecting duct

Answer 42

1. 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 2. Na+ continue to diffuse out at the bottom of the ascending limb 3. 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

Question 43

Antidiuretic hormone

Answer 43

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

Question 44

Osmoreceptors in the hypothalamus

Answer 44

Monitor blood water potential so if it increases, water diffuses into the osmorececptors and and the cells swell

Question 45

Osmoregulation : posterior pituitary gland

Answer 45

When osmoreceptors shrink this is detected by the this which releases ADH into the blood

Question 46

Aquaporins

Answer 46

Protein channels for water , they increase the permeability of the DCT and collecting duct which means more water is reabsorbed into the blood

Question 47

Urine and ADH

Answer 47

If more ADH is in the bloodstream then more water is reabsorbed from the nephron into the blood so the urine is more concentrated