Biology: Homeostsis (last section)

Question 1

What is the definition of homeostasis?

Answer 1

maintenance of constant internal conditions.

Question 2

why is homeostasis important in living organisms?

Answer 2

• enzymes are sensitive to temp. change so it must be kept constant to keep them working efficiently.
• changes to water potential of the blood can cause to shrink or expand (cell lysis) so it must be kept constant.
• they must keep internal conditions the same despite external conditions changing.

Question 3

what is negative feedback?

Answer 3

when the intensity of the stimulus reduces the extent of the response. causes corrective measures to be turned off

Question 4

what is positive feedback?

Answer 4

deviation from an optimum causes changes that result in a greater deviation from the normal.

Question 5

how is negative feedback used to control blood glucose?

Answer 5

• fall in blood glucose detected.
• glucagon secreted from ‘a’ cells in the pancreas.
• it converts glycogen into glucose in the liver.
• blood glucose at optimum concentration reduces the stimulation of ‘a’ cells.

Question 6

what are hormones and what do they do?

Answer 6

• produced in glands.
• carried in the blood plasma to target cells.
• are effective in low concentrations, often have widespread and long-lasting effects.

Question 7

how is the second messenger model used in the secretion of adrenaline.

Answer 7

• adrenaline binds to a protein receptor on the cell surface of the liver.
• causes protein to change shape on the inside of the membrane.
• the change in protein shape activates the enzyme adenyl cyclase, which converts ATP to cyclic AMP (cAMP)
• the cAMP acts as a second messenger that binds to the protein kinase enzyme, changing its shape and activating it.
• the protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cell by facilitated diffusion.

Question 8

which cells do the islets of Lanerghans contain, state their purposes.

Answer 8

‘a’ cells: larger cells which produce glucagon.

‘b’ cells which are smaller and produce insulin.

Question 9

what are the 3 processes which take place in the liver and are responsible for regulating blood sugar? describe each process.

Answer 9

• Glycogenesis: the conversion of glucose into glycogen
• Glycogenolysis: the breakdown of glycogen into glucose.
• Gluconeogenesis: the production of glucose from sources other than carbohydrate. when there’s no carbohydrate, the liver can produce glucose from glycerol and amino acids.

Question 10

which factors can influence blood glucose concentration?

Answer 10

• diet
• hydrolysis of glycogen (glycogenolysis)
• breakdown of glycerol and amino acids (gluconeogenesis)

Question 11

where is adrenaline produced and how does it raise the blood glucose concentration?

Answer 11

-adrenal glands

• attaches to surface of target cells.
• activates enzymes which break down glycogen into glucose.

Question 12

what are the types of diabetes, describe each.

Answer 12

TYPE 1:
-body can’t produce insulin, can be the result of an autoimmune response whereby the body’s immune system attacks its own cells.

TYPE 2:
-glycoprotein receptors lose their responsiveness to insulin. can also be due to an inadequate supply of insulin from the pancreas.

Question 13

how are each of the types of diabetes controlled?

Answer 13

TYPE 1:

• controlled by injections of insulin.
• blood glucose monitored using biosensors.

TYPE 2:
-regulate diet and exercise.

Question 14

what is the structure of the kidney? describe each part.

Answer 14

• fibrous capsule: outer membrane that protects the kidney
• cortex: light-coloured outer region made up of bowman’s capsuled, convoluted tubes and blood vessels.
• medulla: inner region made up of loops of Henle, collecting ducts and blood vessels.
• renal pelvis: collects urine into the ureter.
• ureter: carries urine to the bladder.
• renal artery: supplies the kidney with blood from the heart via the aorta.
• renal vein: returns blood to the heart via the vena cava.

Question 15

what is the structure of the nephron? describe each part.

Answer 15

• bowman’s capsule: closed end at the start of the nephron. surrounds the glomerulus.
• proximal convoluted tubule: series of loops surrounded by blood capillaries. its walls are made up of epithelial cels with microvilli.
• loop of Henle: a long, hairpin loop which extends from the cortex and into the medulla.
• distal convoluted tubule: a series of loops surrounded by blood capillaries.
• collecting duct: a tube into which a number of distal convoluted tubules from a number of nephrons empty. it empties into the pelvis of the kidney.

Question 16

which blood vessels are associated with the nephron? describe the function of each.

Answer 16

• afferent arteriole: supplies the nephron with blood.
• glomerulus: knot of capillaries from which fluid is forced out of the blood.
• efferent arteriole: tiny vessel which leaves the renal capsule, causes an increase in blood pressure within the glomerulus.

Question 17

how is filtrate formed within the glomerulus?

Answer 17

-the diameter of the afferent arteriole is greater than that of the efferent arteriole, causes a build up of hydrostatic pressure in the glomerulus which forces filtrate (glucose and mineral ions) out.

Question 18

how are the epithelial cells of the proximal convoluted tubules adapted for reabsorption?

Answer 18

• microvilli provide a large surface area.
• infoldings at bases increase surface area.
• mitochondria provide ATP for active transport.

Question 19

what is the process of reabsorption?

Answer 19

• sodium ions are actively transported out of the cells lining the PCT into blood capillaries which carry them away. sodium ion concentration is lowered.
• sodium ions diffuse down a concentration gradient from the lumen of the PCT into the epithelial lining cells by facilitated diffusion.
• co-transport carries other molecules into the cells along with sodium ions.
• these molecules that have been co-transported into the PCT then diffuse into the blood. glucose and other valuable molecules are reabsorbed as well as water.

Question 20

what are the 2 regions of the loop of Henle? what do they do?

Answer 20

DESCENDING LIMB:

• narrow
• highly permeable to water.

ASCENDING LIMB:

• wider
• thick walls which are impermeable to water.

Question 21

describe how the loop of Henle acts as a counter-current multiplier.

Answer 21

1) sodium ions actively transported out of the ascending limb using ATP provided by mitochondria.
2) this creates a low water potential in the region of the medulla between the 2 limbs (interstitial space). the thick walls of the ascending limb means that no water can escape by osmosis.
3) the walls of the descending limb are permeable so water passes out of the filtrate by osmosis to the interstitial space. water enters the blood capillaries in this region and is carried away.
4) the filtrate progressively loses water as it moves down the descending limb as the water potential decreases. water potential is at its lowest at the tip of the hairpin.
5) at the base of the ascending limb, sodium ions diffuse out of the filtrate and as it moves up the ascending limb, these ions are actively pumped out. the water of the filtrate increases.
6) In the interstitial space, there’s a gradient of water potential with the highest in the cortex and the lowest in the medulla.
7) the collecting duct is permeable to water and so, as the filtrate moves down it, water passes out by osmosis. the water goes to the blood vessels which occupy this space then is carried away.
8) water potential is lowered as water passes out of the filtrate. it’s also lowered in the interstitial space so it ensures that there’s always a water potential gradient drawing water out of the tubule.

Question 22

what is the role of the DCT and how does it carry out this function?

Answer 22

• makes final adjustments to water and salts that are reabsorbed and to control the pH of the blood by selecting which ions to reabsorb.
• the permeability of its walls become altered by hormones.

Question 23

how does the body respond to a fall in water potential of the blood?

Answer 23

• osmoreceptors in the hypothalamus detect the fall in water potential and shrink due to water being lost.
• causes the hypothalamus to produce a hormone called antidiuretic hormone (ADH)
• ADH passes to the posterior pituitary gland, from where it’s secreted into the capillaries.
• ADH passes into the kidney, it increases the permeability to water of the cell-surface membrane of the cells that make up the DCT and CD.
• ADH binds to specific protein receptors, activating an enzyme called phosphorylase.
• causes vesicles within the cell to fuse with the cell surface membrane.
• these vesicles contain plasma that have numerous water channel proteins. they fuse with the membrane and make it more permeable.
• ADH increases the permeability of the CD to urea.
• moe water leaves the CD by osmosis, down a water potential gradient, and reenters the blood.
• osmoreceptors send signals to the thirst centre of the brain, encourages the individual to find more water.
• osmoreceptors detect the increase in water potential and send fewer impulses to the pituitary gland.
• reduces the release of ADH. the permeability of the CD to urea returns to its normal state.