6.4 homeostasis

Question 1

define homeostasis

Answer 1

the maintenance of an organisms internal environment

Question 2

define glucoregulation

Answer 2

keeping blood sugar levels constant

Question 3

define thermoregulartion

Answer 3

keeping body temperature constant

Question 4

define osmoregulation

Answer 4

keeping water and ion levels constant

Question 5

what is positive feedback

Answer 5

where a deviation from the normal conditions is amplified leading to further deviation, however this can lead to harmful and unstable conditions

Question 6

give example of positive feedback

Answer 6

oxytocin stimulates uterine contraction triggering a positive feedback reaction where more oxytocin is released leading to more contractions

Question 7

what is exocrine function

Answer 7

secretes digestive enzymes into pancreatic duct

Question 8

what is endocrine function

Answer 8

secretes hormones (insulin and glucagon) directly into blood

Question 9

3 ways to increase blood glucose levels

Answer 9

• digestion of carbohydrates
• breakdown of glycogen called glycogenolysis
• producing glucose from non-carbohydrate compounds called gluconeogenesis

Question 10

3 ways to decrease blood glucose levels

Answer 10

• when a demand for energy increases such as exercise respiration levels will increase and therefore glucose levels decrease
• lack of intake of carbohydrates/sugars
• glucose is converted and stored as glycogen by glycogenesis

Question 11

3 ways insulin affects target cells

Answer 11

1. vesicles containing glucose carrier proteins are stimulated to move and fuse with the cell membrane
2. more glucose is taken up by the cell
3. enzymes that convert glucose to glycogen are activated

Question 12

what is the difference between α and β cells

Answer 12

α cells - make glucagon
β cells - make insulin

Question 13

what do the pancreatic cells do

Answer 13

surround the small tubules which drain into the pancreatic duct. These produce the pancreatic juice made of amylase, tropomyosin and lipase

Question 14

what happens when there is a rise in blood glucose concentration

Answer 14

• detected by β cells in the islets of langerhans
• β cells secrete insulin into the blood
• insulin is detected by receptors on liver and muscle cells
• liver and muscle cells remove glucose from blood and convert glucose to glycogen
• glucose concentration falls

Question 15

what happens when there is a fall in blood glucose concentration

Answer 15

• detected by α cells in the islets of Langerhans
• α cells secrete glucagon into the blood
• glucagon detected by receptors on liver cells
• liver cells convert glycogen to glucose and release glucose into the blood
• glucose concentration rises

Question 16

where is adrenaline produced

Answer 16

arenal gland

Question 17

what does adrenaline do

Answer 17

increases metabolic rate preparing the body for fight or flight

Question 18

does adrenaline enter the cell

Answer 18

no

Question 19

describe the two messengers in adrenaline

Answer 19

first messenger is a hormone that transmits a signal around the body
second messenger is a molecule inside the cell which causes an affect

Question 20

what is the action of adrenaline (3 steps)

Answer 20

1. adrenaline approaches receptor site
2. adrenaline fuses to receptor forming a adrenaline-receptor complex and in doing so activates an enzyme inside the membrane
3. the activated enzyme converts ATP to cyclic AMP which is the second messenger activating other enzymes in turn converting glycogen to glucose

Question 21

describe type 1 diabetes

Answer 21

insulin dependant as the body cannot produce enough insulin. thought to be caused by the immune system attacking the insulin producing beta cells
type 1 can be controlled with regular insulin injections and the careful management of diet and exercise

Question 22

describe type 2 diabetes

Answer 22

insulin indépendant caused by glycoprotein receptors on the body cells losing their responsiveness to insulin or an inadequate supply of insulin from the pancreas
can be controlled by careful regulation of diet and exercise

Question 23

what is hyperglycaemia

Answer 23

occurs when the blood glucose concentration becomes too high. this can lower the water potential of the blood, causing osmotic problems such as dehydration as water is drawn out of cells

Question 24

what is hypoglycaemia

Answer 24

occurs when the blood glucose concentration becomes too low. this can occur when there is no store of glycogen causing cells to be deprived of energy

Question 25

what is the renal medulla

Answer 25

darker coloured inner region made of the hoops on Henle

Question 26

what is the renal pelvis

Answer 26

funnel shaped cavity that collects urine into the ureter

Question 27

what is the ureter

Answer 27

a tube that carries urine to the bladder

Question 28

what is the renal artery

Answer 28

supplies kidney with blood from the heart via the aorta

Question 29

what is the renal vein

Answer 29

return blood to the heart via the vena cave

Question 30

what is the renal (Bowmans) capsule

Answer 30

the closed end at the start of the nephron. it surrounds a mass of blood capillaries

Question 31

what is the proximal convoluted tube

Answer 31

a series of loops surrounded by blood capillaries. its walls are made of epithelial cells which have micro villi

Question 32

what is the loop of Henle

Answer 32

a long hairpin that extends from the cortex into the medulla of the kidney and back again

Question 33

what is the distal convoluted tube

Answer 33

a series of loops surrounded by blood capillaries, before the loop of henle

Question 34

what is the collecting duct

Answer 34

a tube which a number of distal convoluted tubules from a number of nephrons empty

Question 35

what are the three steps of kidney regulation

Answer 35

1. ultrafiltration
2. selective reaborbtion
3. osmoregulation

Question 36

how is glucose, ions, water and urea reabsorbed

Answer 36

glucose - all reabsorbed
ions - some reabsorbed
water - some reabsorbed
urea none reabsorbed

Question 37

7 steps of ultrafiltration

Answer 37

1. occurs in the Bowmans capsule
2. renal artery brings blood to the kidney , this splits into each arteriole each feeding a different nephron
3. arterioles split into numerous capillaries forming a knot called the glomerulus
4. this is surrounded by the Bowmans capsule
5. arteriole leading into the glomerulus is wider than the one leading increasing blood pressure
6. this high pressure forces plasma out of the blood by ultrafiltration
7. once the blood is filtered in this way only blood cells and the large plasma proteins remain in the blood and continue into the proximal convoluted tubes

Question 38

4 steps of selective reabsorbtion

Answer 38

1. glucose diffuses into cells which line the proximal convoluted tubule. microvilli increase the surface area for efficient absorbtion
2. the glucose is actively transported out of cells into the intercellular spaces. ATP supplied by mitochondria
3. once in the intercellular spaces the glucose diffuses through the walls of the capillaries and is transported away by the blood
4. active transport of glucose out of these tubule cells maintains a concentration gradient so more glucose is able to diffuse out of the tubule fluid

Question 39

what happens when rise in water potential

Answer 39

• change detected by osmoreceptors in hypothalamus
• pituitary gland released less ADH
• less ADH so decreases permeability of collecting ducts so less water reabsorbed
• dilute urine

Question 40

what happens when decrease in water potential

Answer 40

• change detected by osmoreceptors in hypothalamus
• pituitary gland releases more ADH
• ADH increases permeability of collecting ducts so more water reabsorbed
• concentrated urine

Question 41

initial 4 steps of osmoregulation in nephron

Answer 41

1. Na+ and Cl- ions are actively pumped out of the ascending limb. the ions accumulate in the interstitial fluid lowering the water potential. water cannot counter the lower ψ as the calls of the ascending limb are impermeable
2. water is drawn out of the deciding limb and into and into the interstitial fluid by osmosis. making the fluid in the descending limb more concentrated
3. by the time the fluid has reached the bottom of the descending limb it has lost water and it concentrated, the fluid surrounding the bottom of the loop is also very concentrated because of the accumulation of Na+ and Cl- ions
4. the fluid then enters the ascending limb, as it moved up the ascending limb sodium ions are actively pumped out of it (step one)

Question 42

second 4 steps of osmoregulation in nephron

Answer 42

5. the fluid at the top of the ascending limb is very dilute
6. the fluid empties into collecting ducts which pass through very concentrated medullary regions
7. ADH causes the walls of the collecting duct to become permeable to water by initiating the aquporins to bind to the cells allowing water to be drawn out by osmosis into the membrane
8. by drawing water out the fluid in the collecting duct is very concentrated. the concentration of the urine can be controlled by regulating the permeability of the collecting duct

Question 43

what does the size of the loop of hence mean

Answer 43

the longer the loop of hence the more concentrated the urine will be.