Topic 6 - Homeostasis

Question 1

What is homeostasis

Answer 1

control systems that keep your internal environment roughly constant to stop cell damage

Question 2

what happens to cells if blood glucose concentration is too low or too high

Answer 2

• too high - the water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis, the cells can shrivel up and die
• too low - cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy

Question 3

what is a negative feedback response

Answer 3

• change is counteracted to bring the level back to normal

Question 4

what is a positive feedback mechanism

Answer 4

• the change is amplified
• further increase the level away from the normal level

Question 5

When does bood glucose concentration level fall and rise

Answer 5

• rise - after eating food containing carbohdrates
• fall - after exercise

Question 6

what are the 2 hormones involved in blood glucose control

Answer 6

insulin
glucagon

Question 7

where is insulin and glucagon secreted from

Answer 7

• insulin - beta cells in the islets of langerhans in the pancreas
• glucagon - alpha cells in the islets of langerhans in the pancreas

Question 8

How does insulin work

Answer 8

• it lowers levels of blood glucose concentration when its too high
• Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells
• it increases the permeability of muscle cell membranes to glucose, so the cell take up more glucose. this involves increasing the number of channel proteins in the cell membranes
• insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen (glycogenesis)
• the cells are able to store glycoen in their cytoplasm, as an energy source

Question 9

what is glycogenesis

Answer 9

forming glycogen from glucose

Question 10

what is the name for forming glycogen from glucose

Answer 10

what is glycogenesis

Question 11

what does glucagon do

Answer 11

• rises blood glucose concentration levels
• glucagon binds to specific receptors on the cell membranes of liver cells
• glucagon activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis)
• glucagon also activates enzymes that are involved in the formation of glucose from glycerol and amino acids (gluconeogenesis)
• glucagon decreases the rate of respiration of glucose in cells

Question 12

how does adrenaline increase blood glucose concentration

Answer 12

• adrenaline is secreted from the adrenal glands when there is a low concentration of glucose in the blood, when youre stressed and exercising
• adrenaline binds to receptors in the cell membrane of liver cells
• it activates glycogenolysis
• it inhibits glycogenesis
• it also activates glucagon secretion and inhibits insulin secretion which increased glucose
• adrenaline gets the body ready for action by making more glucose available for muscles to respire

Question 13

what is the second messenger model for adrenaline and glucagon

Answer 13

• adrenaline and glucagon bind to their receptors and activate an enzyme called adenylate cyclase.
• activated adenlyate cyclase converts ATP into a chemical signal called cAMP
• cAMP activates an enzyme called protein kinase A.
• it activates a chain of reactions that cause glycogenolysis
• to produce glucose

Question 14

what is type 1 diabetes caused by

Answer 14

• The immune system attacks b cells in the islets of langerhans so they cannot produce insulin.

Question 15

How is type 1 diabetes treated

Answer 15

insulin injections
controlling sugar intake

Question 16

what causes type II diabetes

Answer 16

• usually acquired later in life and linked with obesity
• b cells dont produce enough insulin the body cells dont respond properly to insulin because insulin receptors dont respond properly.

Question 17

how can type II diabetes be treated

Answer 17

• eating healthy balanced diet
• loosing weight
• regular exercise

Question 18

how would you determine the concentration of a glucose solution

Answer 18

1. make serial dilutions
2. do a quantitative benedicts test on each solution
3. use a colorimeter to measure the absorbance of the benedicts solution remaining in each solution
4. use the results to make a calibration curve

Question 19

what is the function of the kidneys

Answer 19

• excrete waste products like urea
• regulate the water potential of the blood
• ultrafiltration
• selective reabsorption

Question 20

where, in the kidney, does ultrafiltration and selective reabsorption occur

Answer 20

nephrons

Question 21

what happens during ultrafiltration

Answer 21

• blood from the renal artery enters afferent arterioles in the cortex of the kidney
• each arteriole splits into a glomerulus - a bundle of capillaries looped inside the bowman’s capsule
• the efferent arteriole is smaller in diameter than the afferent arteriole, so blood in the glomerulus is at high pressure.
• the high hydrostatic pressure forces small moleucles like water and glucose out of the capillarie and into the bowman’s capsule
• the liquid and small molecules pass through 3 layers to get into the bowman’s capsule and enter the nephron tubules ( a capillary wall, a basement membrane and the epithelium with gaps called podocytes)
• larger molecules like proteins and blood cells stay in the blood

Question 22

what is the glomerulus

Answer 22

a bundle of capillaries inside the bowman’s capsule

Question 23

where is a nephron

Answer 23

in the cortex and medulla of the kidney

Question 24

list the structure of a nephron

Answer 24

• afferent/efferent arteriole
• glomerulus
• bowman’s capsule
• proximal convoluted tube (PCT)
• loop of henle
• distal convoluted tube (DCT)
• collecting duct

Question 25

what happens during selective reabsorption of glucose

Answer 25

* sodium ions are actively transported from the epithelial cells into the blood by tha sodium potassium ion pump * this creates a lower concentration of sodium ions in the epithelial cells compared to the lumen, so sodium inos diffuse down their gradient using a co transporter protein * this also binds to glucose, transporting glucose and sodium into the epithelial cells * the concentration of glucose is then higher in the epithilial cells compared to the blood so it moves down this concentration gradient via facilitated diffusion through a channel protein.

Question 26

how is the proximal convoluted tubule adapted for selective reabsorption

Answer 26

* microvilli * co transporter proteins * high number of mitochondria

Question 27

what is the function of the liver

Answer 27

makes urea

Question 28

what are water potential receptors called and where are they found

Answer 28

* osmoreceptors * hypothalamus of brain

Question 29

where is the cortex found on the kidney

Answer 29

outer layer of kidney

Question 30

what happens when you are dehydrated

Answer 30

* osmoreceptors in the hypothalamus detect a low water potential * the posterior pituitary glandis stimulated and releases more ADH into the blood * more ADH means that the distal convoluted tubule and collecting duct become more permeable so more water is reabsorbed into the blood by osmosis * a small amount of highly concentrated urine is produced and less water is lost

Question 31

where are osmoreceptors found

Answer 31

hypothalamus

Question 32

what happens when you are hydrated

Answer 32

* osmoreceptors in the hypothalamus detect high water potential * posterior pituitary gland releases less ADH into the blood * less ADH meas that the distal convolute tubule and the collecting duct become less permeable so less water is reabsorbed into the blood * a large amount of dilute urine is produced and more water is lost

Question 33

what happens to concentration of urine as the medulla is thicker

Answer 33

* longer loop of henle * sodium ion gradient is maintained for longer * more water reabsorbed from loop of henle by osmosis

Question 34

where is ADH secreted from

Answer 34

posterior pituitary gland

Question 35

explain how the concentration of filtrate changes through the loop of henle

Answer 35

* Concentration rises in descending limb because sodium ions enter and water is lost * Concentration falls in ascending limb because sodium ions (and chloride) ions actively removed * But water remains (in ascending limb) because its walls are impermeable to water