Mr p bio 9 homeostasis

Question 1

what does a feedback loop do?

Answer 1

informs the receptor of the changes to the system brought about by the effector.

Question 2

what is negative feedback?

Answer 2

When there is a change away from the normal level/set point.​
Effectors act to opposes the change to bring the level back to norm/set point.

Question 3

what is positive feedback?

Answer 3

A change is amplified – a change causes further change – moves further away from the set point/norm.

Question 4

why is positive feedback not always involved in homeostasis?

Answer 4

it doesn’t keep your internal environment stable within restricted limits.

Question 5

why does homeostasis involve multiple negative feedback mechanisms?

Answer 5

for each factor being controlled.​
Having more than one mechanism gives increased control over changes in your internal environment.
Having multiple negative feedback mechanisms means you can actively increase or decrease a level so it returns to normal, rather than just control the factor in one direction.

Question 6

when does blood glucose level fall and rise?

Answer 6

Rises after eating food containing carbohydrates.​
Falls after exercise, as glucose is used in respiration for the release of energy.

Question 7

what hormones are used in blood glucose control?

Answer 7

Insulin and glucagon

Question 8

where are Insulin and glucagon secreted from?

Answer 8

a cluster of cells in the pancreas called the islets of Langerhans.

Question 9

how does insulin lower blood glucose?

Answer 9

1. binds to receptors on membranes of muscle and liver cells
   2.Increases membrane permeability to glucose so more glucose absorbed – by increasing no. of glucose carrier proteins in cell surface membrane
   3.Activates enzymes in muscle and liver cells that convert glucose into glycogen which is stored in cytoplasm – glycogenesis.
   4.Increases the rate of respiration of glucose in muscle cells.

Question 10

how does insulin’s process decrease blood glucose?

Answer 10

reduce the concentration of glucose in the cell so maintains the conc. gradient, meaning more glucose diffuses into the cell by facilitated diffusion.

Question 11

what is glycogenesis?

Answer 11

making glycogen from glucose in the liver

Question 12

how does glucagon increase blood glucose?

Answer 12

1. Binds to specific receptors on the membrane of hepatocytes and activates enzymes that hydrolyses glycogen to glucose – glycogenolysis
2. Activates enzymes involved in the formation of glucose from glycerol and from amino acids – gluconeogenesis.
   3.Glucagon decreases the rate of respiration of glucose in cells.

Question 13

what is glycogenolysis?

Answer 13

Hydrolysing glycogen in the liver to glucose

Question 14

what is gluconeogenesis?

Answer 14

making glucose from glycerol and amino acids in the liver

Question 15

name 3 differenes between a hormonal response + a nervous response

Answer 15

1.Hormones travel in the blood to target organs = slower response than nervous one.​
2.Also means response is widespread to all target organs/cells unlike localised nervous one.​
3.longer response as hormones broken down slower than neurotransmitters.

Question 16

when and where is adrenaline secreted?

Answer 16

Increased secretion from adrenal glands when blood glucose conc. is low/ stressed/ exercising.

Question 17

how does adrenaline increase blood glucose?

Answer 17

Binds to receptors on the cell membrane of hepatocytes and increases blood glucose levels by:​
1.Activating glycogenolysis.​2.Inhibiting glycogenesis .​
3.Activates glucagon secretion​
4.Inhibits insulin secretion.

Question 18

what is the second messenger model?

Answer 18

1.Adrenaline and glucagon bind to respective specific receptors, which activates enzyme called adenylate cyclase. ​
2.Activated adenylate cyclase converts ATP into a chemical called cyclic AMP (cAMP), which is a second messenger. ​
3.cAMP activates enzyme: protein kinase A. ​
4.Protein kinase A activates a cascade (chain of reactions) that hydrolyses glycogen into glucose.

Question 19

what is type one diabetes?

Answer 19

Person does not make insulin – usually from birth

Question 20

what is the role of glucose transporters in maintaining glucose levels?

Answer 20

glucose transporters are Channel proteins which allow glucose to be transported across the membrane.
When insulin binds to receptors on the cell surface membrane, triggers the insertion of channel proteins to the membrane so more facilitated diffusion of glucose into the cell can occur.

Question 20

what is type two diabetes?

Answer 20

Person makes insulin ​

Less receptors for Insulin (may still be some present)

Question 21

what do health advisors recommend to people with type 2 diabetes?

Answer 21

Recommend a diet low in fat, sugar and salt but high in grains, fruit and vegetables.

Regular exercise.

Lose weight if necessary.

Campaigns such as the NHS’s ‘Change4life’ aims to educate people

Question 22

how have some food companies responded to type 2 diabetes?

Answer 22

Some have attempted to make their products healthier e.g. using sugar alternatives instead of sugar and by reducing the sugar, salt and fat content of their products.
However, these companies want to make profit:
Don’t want to spend money on developing new, healthier alternatives.

Question 23

how many kidneys, where and how does blood enter?

Answer 23

2 kidneys

Each side of spinal cord

Blood enters through renal artery

Blood leaves through renal vein

Question 24

what is the role of the kidneys? (dont think mp)

Answer 24

We take in different volumes of water and amounts of ions every day Blood plasma and tissue fluid water potential is maintained at an optimum concentration Through osmoregulation

Question 25

what is the process of the excretion of waste products in the kidney?

Answer 25

Blood enters the kidney from the renal artery  capillaries in the cortex. As blood passes through the capillaries in the cortex, substances are filtered out of the blood into long tubules that surround the capillaries – ultrafiltration. Glucose, some water and some ions are reabsorbed back into the blood – selective reabsorption. Remaining unwanted substances pass along to the bladder to be extracted as urine.

Question 26

what are the nephrons?

Answer 26

The long tubules with the bundles of capillaries where the blood is filtered.

Question 27

before entering the Bowman's capsule, what does the liquid and small molecules have to pass through?

Answer 27

Capillary endothelium Basement membrane Epithelium of the Bowman’s Capsule.

Question 28

where does ultrafiltration occur?

Answer 28

Occurs between the glomerulus and the bowman’s capsule.

Question 29

what is the process of ultrafiltration?

Answer 29

Small molecules such as water, glucose, ions and urea are forced through the pores between capillary endothelium, basemen membrane and Bowman’s capsule epithelial cells (podocytes), to form filtrate in the Bowman’s capsule. Molecules are forced through because of a higher hydrostatic pressure in the glomerulus compared to the Bowman’s capsule (created due to the bigger afferent compared to the smaller efferent arteriole). Large molecules such as protein can’t pass through because they are too large and blocked by the basement membrane.

Question 30

where does selective reabsorption of the glomerular filtrate occur?

Answer 30

Proximal convoluted tubule Loop of Henle Distal convoluted tubule

Question 31

why does selective reabsorption need to occur?

Answer 31

A large amount of molecules forced out of blood at the Bowman’s capsule are useful and not waste. They must now be re-absorbed into the blood. Water is also reabsorbed here.

Question 32

in what 3 ways is the proximal convoluted tubule adapted to carryout selective reabsorption?

Answer 32

1) Many microvilli to increase surface area 2) Many mitochondria to produce ATP required for active transport of substances. 3) Many carrier proteins to enable active transport/cotransport.

Question 33

what is the process of glucose reabsorption in a healthy person?

Answer 33

Glucose is removed from the blood during ultrafiltration from the glomerulus into the Bowman’s Capsule in the kidneys. In healthy individuals, glucose is reabsorbed in the PCT using protein carriers - can be active transport or facilitated diffusion.

Question 34

why is glucose reabsorption different in diabetics?

Answer 34

large conc. of glucose in the blood and therefore in the filtrate. Not all glucose can be reabsorbed because there is saturation of the carrier proteins.

Question 35

what is the process of glucose reabsorption?

Answer 35

Na+ are actively transported out of the cells lining the PCT into the blood capillaries to reduce their sodium ion conc. This allows Na+ from the filtrate to move into the surrounding cells via facilitated diffusion BUT Na+ moves in with glucose/amino acid (co-transported).

Question 36

what does urine consist of?

Answer 36

Usually made up of water, dissolved salts, urea and other substances such as hormones and excess vitamins. Urea is a waste product from the breakdown of amino acids in the liver. No glucose – normally actively reabsorbed back into the blood.

Question 37

what is osmoregulation?

Answer 37

Water must be kept at a constant level in the body. This means there is a constant amount of water in the blood and therefore a constant water potential. The kidneys regulate the water potential of the blood so the body has the correct amount of water – osmoregulation.

Question 38

how is water lost from the body?

Answer 38

Mammals excrete urea and other waste products in solution so water is lost through urination. Water is also lost in sweat

Question 39

why is most water reabsorbed at the proximal convoluted tubule?

Answer 39

Because all of the glucose is reabsorbed in the PCT. This lowers the water potential of the blood, so creates a water potential gradient. So water is reabsorbed by omosis

Question 40

where else is water reabsorbed othet than the pct?

Answer 40

Loop of Henle DCT Collecting duct

Question 41

what and where is the loop of henle?

Answer 41

located in the medulla and made up of two limbs, the ascending limb and the descending limb

Question 42

what are the differences between the a and d limbs in the loop of hemle and what do they do?

Answer 42

d- permeable to water and Na+ a- permeable to Na+ and Cl- (impermeable to water). The limbs control the movement of sodium ions so that water can be reabsorbed in to the blood.

Question 43

what is the process of water reabsorption?

Answer 43

1. Active transport of Na+ and Cl-ions out of ascending limb of the loop of Henle into tissue fluid of medulla. 2. Lowering water potential (increasing solute concentration) in medulla. 3/4. Water is moved out of filtrate in the descending limb of loop of Henle as descending limb is permeable to water but ascending limb impermeable (thick walls), into tissue fluid and into blood down water potential gradient. 5. Diffusion of Na+ and Cl-ions out of the ascending limb of the loop of Henle, producing concentration gradient needed for water reabsorption

Question 44

why do some animals have a longer loop of henle?

Answer 44

The longer the loop the greater the difference in concentration between A and D limbs This drives re- absorption of more water, so desert animals have longer loop of Henle

Question 45

what is the process of reabsorption in the distal convoluted tubule?

Answer 45

The cells of the DCT also have many microvilli and many mitochondrion, as they are adapted for activate transport of Na+ and K+. DCT adjusts the filtrate concentration by actively transporting Na+ and K+ into or out of the tubule. Causing more water to be reabsorbed if need be.

Question 46

what is the process of water reabsorption in the collecting duct?

Answer 46

Due to the increase in ion concentration in the medulla (all of the ions moving by diffusion and active transport into the tissue fluid) which caused the decrease in W.P. Water reabsorbed out of the collecting duct by osmosis and then ultimately back into the blood capillaries.

Question 47

what is the hormone involved in osmoregulation and what does it at on?

Answer 47

Anti Diuretic Hormone Acts on distal convoluted tubule and collecting ducts

Question 48

what is the process of releasing ADH?

Answer 48

Water potential decreases water moves out of osmoreceptors by osmosis cells decrease in volume sends signals to other cells in the hypothalamus send signal to posterior pituitary gland releases more ADH.

Question 48

how is WP monitored?

Answer 48

Water potential is monitored by cells called osmoreceptors in the brain called the hypothalamus

Question 49

what is the effect of ADH?

Answer 49

Binds to receptors on the plasma membrane of cells in the distal convoluted tubule and collecting duct. Proteins – aquaporins are inserted into the plasma membrane. Allows water to pass via osmosis, making the walls of the DCT and collecting duct more permeable  more water reabsorbed from the tubules into the medulla and into the blood by osmosis. This makes the urine more concentrated and lower volume.

Question 50

what happens when dehydration is detected?

Answer 50

WP of blood decreases. Detected by osmoreceptors in the hypothalamus. Posterior pituitary gland stimulated and releases ADH. DCT and Collecting duct are more permeable as aquaporins are inserted into the cell surface membrane. More water reabsorbed into the blood via tissue fluid by osmosis.