16 - Homeostasis

Question 1

homeostasis

Answer 1

the maintenance of an internal environment within restricted limits in organisms

Question 2

conditions which need to be maintained in mammals

Answer 2

temperature, pH, water potential (osmoregulation), blood glucose concentration, cholesterol

Question 3

negative feedback mechanisms

Answer 3

the change produced by the control system leads to a change in the stimulus detected by the receptor, and turns the system off
the stimulus causes the corrective measures to be turned off

Question 4

hormones

Answer 4

produced in glands which secrete the hormone directly into the blood
carried in blood plasma to their target cells
are effective in very low concentrations
usually have widespread and long-lasting effects

Question 5

role of adrenaline in conversion of glycogen to glucose

Answer 5

1. adrenaline approaches transmembrane protein
2. adrenaline fuses to the receptor causing it to change shape on the inside of the membrane
3. this activates enzyme adenyl cyclase inside the membrane
4. the activated adenyl cyclase converts ATP to cyclic AMP, which acts as a secondary messenger
5. the cAMP activates the protein kinase enzymes
6. the active protein kinase enzyme catalyses the conversion of glycogen to glucose

Question 6

islets of Langerhans

Answer 6

groups of hormone producing cells in the pancreas

contains alpha cells (produce glucagon), and beta cell (produce insulin)

Question 7

glycogenesis

Answer 7

conversion of glucose to glycogen

when blood sugar levels are higher than normal the liver converts glucose from the blood into glycogen and stores it

Question 8

glycogenolysis

Answer 8

the breakdown of glycogen into glucose

when blood sugar levels are lower than normal

Question 9

gluconeogenesis

Answer 9

production of glucose from sources other than carbohydrates (eg. from glycerol and amino acids)

Question 10

when an insulin molecule binds with a receptor it causes:

Answer 10

1. the tertiary structure of the glucose transport carrier to change, meaning they change shape and open allowing more glucose into cells by facilitated
2. an increase in the number of carrier proteins responsible for glucose transport across membranes
3. activation of the enzymes that convert glucose to glycogen

Question 11

effect of glucagon

Answer 11

glucagon attaches to specific protein receptors on the cell membrane of liver cells
activates enzymes that convert glycogen to glucose
activates enzymes involved in gluconeogenesis

Question 12

type 1 diabetes

Answer 12

autoimmune condition, often inherited
immune system attacks and destroys beta cells, prevents sufficient insulin from being produced
without insulin blood glucose levels get too high
treated with insulin injections

Question 13

type 2 diabetes

Answer 13

not an autoimmune disease
body doesn’t produce enough insulin to deal with high blood glucose levels, or body’s cells do not respond
can be controlled with diet or tablets

Question 14

renal fibrous capsule

Answer 14

outer membrane for protection

Question 15

renal cortex

Answer 15

lighter coloured outer region consisting of renal capsules, convoluted tubules and blood vessels

Question 16

renal medulla

Answer 16

darker coloured inner region consisting of loops of Henle, collecting ducts and blood vessels

Question 17

renal pelvis

Answer 17

funnel shaped cavity which collects urine into the ureter

Question 18

renal artery

Answer 18

supplies kidney with blood from the heart

Question 19

renal vein

Answer 19

returns blood from the kidney to the heart

Question 20

renal Bowman’s capsule

Answer 20

cup shaped, surrounds a mass of blood capillaries known as the glomerulus

Question 21

proximal convoluted tubule

Answer 21

a series of loops surrounded by blood capillaries, walls made of epithelial cells which have microvilli

Question 22

loop of Henle

Answer 22

long, hairpin loop that extends from the cortex into the medulla, surrounded by blood capillaries

Question 23

distal convoluted tubule

Answer 23

series of loops surrounded by blood capillaries, walls of epithelial cells

Question 24

collecting duct

Answer 24

a tube into which several DCTs from a number of nephrons empty
becomes increasingly wide as it empties into the renal pelvis

Question 25

afferent arteriole

Answer 25

arteriole from the renal artery and supplies the nephron with blood
forms the glomerulus in the renal capsule

Question 26

glomerulus

Answer 26

knot of capillaries from which fluid is forced out the blood

Question 27

efferent arteriole

Answer 27

tiny vessel that leaves the renal capsule

smaller diameter than the afferent arteriole

Question 28

formation of glomerular filtrate

Answer 28

1. blood enters the kidney via the renal artery
2. this then divides into the afferent arteriole and glomerulus
3. water and all soluble components are forced out of the glomerulus
4. the pressure to do this is aided by the efferent arteriole leaving the glomerulus being narrower than the afferent arteriole entering
5. filtrate passes BETWEEN podocyte cells to enter renal capsule

Question 29

reabsorption of glucose

Answer 29

1. all glucose in the glomerular filtrate must be reabsorbed into the blood, however waste products like urea don’t need to be
2. glucose is reabsorbed in the process of co-transport from the epithelial cells of the proximal convoluted tubule to blood capillaries
3. sodium ions are actively transported from the epithelial cells into the blood, creating a low concentration of sodium ions in the epithelial cells
4. sodium ions therefore move in from the lumen of the proximal convoluted tubule by facilitated diffusion, carrying glucose with it
5. the glucose then diffuses into blood capillaries

Question 30

reabsorption of water in loop of Henle

Answer 30

1. in the ascending limb, Na+ are actively transported out into the interstitial space in medulla
2. this lowers water potential in interstitial space
3. ascending limb is impermeable to water, so water moves out permeable ascending limb by osmosis into medulla
4. water moves into capillaries in medulla by osmosis
5. at base of loop, Na+ diffuse out into medulla naturally lowering water potential of medulla further
6. water moves out DCT and collecting duct into low water potential medulla by osmosis

Question 31

loop of Henle as a countercurrent multiplier

Answer 31

Na+ leaving ascending limb increases down ascending limb because Na+ diffuses out of base of loop
water potential in interstitial space increases further down medulla
therefore interstitial fluid in medulla always has lower water potential than collecting duct