Homeostasis

Question 1

What is the effect of high blood glucose concentration?

Answer 1

The water potential of the blood is reduced and water molecules diffuse out of cells into the blood by osmosis
This can cause cells to shrivel and die

Question 2

What is the effect of low blood glucose concentration?

Answer 2

Cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy

Question 3

What happens if blood pH is too high or low?

Answer 3

Hydrogen and ionic bonds break
The tertiary structure of enzymes changes shape so the active site changes shape
The substrate is no longer complementary to the active site and the rate of reaction decreases
A pH less than 7 is acidic so results in an influx of H+ ions

Question 4

What happens if body temperature is too high?

Answer 4

Hydrogen bonds break so the tertiary structure changes shape
So the active site changes shape
The substrate is no longer complementary to the active site
Rate of reaction decreases

Question 5

What is homeostasis?

Answer 5

Physiological control systems that maintain the internal environment within restricted limits

Question 6

What is a negative feedback mechanism?

Answer 6

Homeostatic systems involve receptors and effectors
Receptors detect when a change is too high or too low and the information is communicated via the nervous system or the hormonal system to effectors
The mechanism that restores the level back to normal is the negative feedback mechanism
Negative feedback only works within certain limits

Question 7

Why does homeostasis involve multiple negative feedback mechanisms?

Answer 7

More control over changes in the internal environment
It means you can actively increase or decrease a level so it returns to normal
One negative feedback mechanism results in a slower response and less control

Question 8

What does positive feedback do?

Answer 8

Amplifies the change
It’s useful to rapidly activate something e.g blood clotting after an injury
Though it can happen when a homeostatic system breaks down
It’s not involved in homeostasis because it doesn’t keep your internal environment stable

Question 9

Where are the hormones insulin and glucagon secreted from?

Answer 9

Clusters of cell sin the pancreas called the islets of Langerhans
Beta cells secrete insulin
Alpha cells secrete glucagon
They both act on effectors which respond to restore blood glucose concentration to the normal level

Question 10

What happens if blood glucose concentration is too high?

Answer 10

Beta cells secrete insulin, alpha cells stop secreting glucagon
Insulin binds to specific receptors on the cell membranes of liver and muscle cells
This increases the permeability of muscle cell membranes to glucose
This involves increasing the number of channel proteins in the cell membranes
Insulin also activates enzymes in the liver and muscle cells that convert glucose into glycogen, this is glycogenesis
Insulin also increases the rate of respiration of glucose, especially in muscle cells

Question 11

What is glycogenesis?

Answer 11

The conversion of glucose into glycogen

Question 12

What happens if blood glucose concentration is too low?

Answer 12

Alpha cells secrete glucagon, beta cells stop secreting insulin
Glucagon binds to specific receptors on the cell membranes of liver cells
This activates enzymes that break down glycogen into glucose, this is glycogenolysis
Glucagon also activates enzymes involved in the formation of glucose from glycerol (component of lipids) and amino acids, this is gluconeogenesis
Glucose decreases the rate of respiration of glucagon in cells

Question 13

What is glycogenolysis?

Answer 13

The break down of glycogen into glucose

Question 14

What is gluconeogenesis?

Answer 14

The process of forming glucose from non-carbohydrates

Question 15

How does insulin make glucose transporters available for facilitated diffusion?

Answer 15

Skeletal and cardiac muscle cells contain a channel protein called GLUT4
GLUT4 is a glucose transporter
When insulin levels are low it is stored in vesicles in the cytoplasm of cells
When insulin binds to receptors on the cell surface membrane it triggers the movement of GLUT4 to the membrane
Glucose is then transported into the cell by facilitated diffusion
through the GLUT4 protein

Question 16

How does adrenaline increase blood glucose concentration?

Answer 16

Adrenaline is a hormone secreted from your adrenal glands
Secreted when there’s a low concentration of blood glucose, when you’re stressed and during exercise
It binds to receptors in the cell membrane of liver cells
It activates glycogenolysis and inhibits glycogenesis
It also activates glucagon secretion and inhibits insulin secretion to increase glucose concentration

Question 17

How do glucagon and adrenaline act as a second messenger?

Answer 17

Adrenaline and glucagon can activate glycogenolysis inside a cell even though they bind to receptors on the outside of the cell
Adrenaline and glucagon bind to their complementary receptors and activate the enzyme adenylate cyclase
This converts ATP into a chemical signal called a ‘second messenger’
This second messenger is called cyclic AMP (cAMP)
cAMP activates an enzyme called protein kinase A which activates glycogenolysis

Question 18

What is type I diabetes?

Answer 18

The immune system attacks the Beta cells in the islets of Langerhans so they can’t produce insulin
After eating the blood glucose level rises and stays high, this is called hyperglycemia and can result in death if untreated
The kidneys can’t reabsorb all this glucose so some is excreted in urine

Question 19

How is type I diabetes treated?

Answer 19

With insulin therapy which has to be carefully controlled as too much can cause a dangerous drop in blood glucose levels
Eating regularly and controlling simple carbohydrate intake helps avoid a sudden rise in glucose

Question 20

What is type II diabetes?

Answer 20

Occurs when beta cells don’t produce enough insulin
Or when the body’s cells don’t respond properly to insulin
Cells may not respond properly because the receptors on their membranes don’t work properly so cells don’t take up enough glucose
This results in a higher blood glucose concentration than normal

Question 21

How is type II diabetes treated?

Answer 21

A healthy, balanced diet that’s low in fat, salt and sugar
Weight loss
Regular exercise
Glucose-lowering medication can be taken if diet and exercise don’t help
Insulin injections may eventually be needed

Question 22

Name risk factors of type II diabetes

Answer 22

Usually acquired later in life
Often linked to obesity
Genetically linked
Lack of exercise, age and poor diet are contributing risk factors

Question 23

What do the kidneys do?

Answer 23

Excrete waste products such as urea
They regulate the water potential of the blood

Question 24

How is blood filtered at the start of the nephrons?

Answer 24

At the start of the nephron
Blood from the renal artery enters smaller arteries in the cortex of the kidney
Each arteriole splits into a structure called a glomerulus
This is where ultrafiltration takes place
High hydrostatic pressure in the glomerulus forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule
Pass through the basement membrane
Larger molecules (e.g. proteins and blood cells) can’t pass through so stay in the blood
Presence of pores in capillaries

Question 25

What is a glomerulus?

Answer 25

A bundle of capillaries looped inside a hollow ball called the Bowman’s capsule

Question 26

What is the difference between the afferent and efferent arteriole?

Answer 26

Afferent arteriole takes blood into the glomerulus
The efferent arteriole takes filtered blood away from the glomerulus
The efferent is smaller in diameter so the blood in the glomerulus is under high pressure

Question 27

What 3 layers does the glomerular filtrate pass through to get to the Bowman’s capsule and enter the nephron tubules?

Answer 27

The capillary wall
The basement membrane
The epithelium of the Bowman’s capsule

Question 28

What is selective reabsorption?

Answer 28

Takes place as glomerular filtrate flows along the proximal convoluted tubule (PCT), through the loop of Henle and the distal convoluted tubule (DCT)

Question 29

How is the PCT adapted to have a large surface area for reabsorption?

Answer 29

The wall of the PCT has microvilli for the reabsorption of useful molecules from the glomerular filtrate in the tubules into the blood (capillaries)

Question 30

How is glucose reabsorbed from the filtrate?

Answer 30

Along the proximal convoluted tubule by active transport and facilitated diffusion

Question 31

How is water reabsorbed from the filtrate?

Answer 31

Reabsorbed from the PCT, loop of Henle, DCT and collecting duct
Water enters the blood by osmosis because the water potential of the blood is lower than that of the filtrate

Question 32

What is urine usually made up of?

Answer 32

Water
Dissolved salts
Urea
Hormones
Excess vitamins

Question 33

What is osmoregulation?

Answer 33

The control of the water potential of the blood

Question 34

What happens if the water potential of the blood is too low?

Answer 34

The body is dehydrated
More water is reabsorbed by osmosis into the blood from the tubules of the nephrons
This means urine is more concentrated so less water is lost during excretion

Question 35

What happens if the water potential of the blood is too high?

Answer 35

The body is too hydrated
Less water is reabsorbed by osmosis into the blood from the tubules of the nephrons
Urine is more dilute
So more water is lost during excretion

Question 36

Where are osmoreceptors found?

Answer 36

In the hypothalamus

Question 37

What happens to ADH levels when you’re dehydrated?

Answer 37

Blood ADH rises
Water potential of the blood drops
This is detected by osmoreceptors in the hypothalamus
The posterior pituitary gland is stimulated to release more ADH into the blood
This means the DCT and the 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 38

What is ADH?

Answer 38

Antidiuretic hormone
It makes the walls of the collecting duct and DCT more permeable ot water

Question 39

What happens to ADH levels when you’re hydrated?

Answer 39

Water potential of the blood rises
This is detected by osmoreceptors in the hypothalamus
The posterior pituitary gland releases less ADH into the blood
DCT and collecting duct become less permeable so less water is reabsorbed into the blood via osmosis
A large amount of dilute urine is produced and more water is lost

Question 40

How does the loop of Henle maintain a sodium ion gradient?

Answer 40

At the top of the ascending limb sodium ions are actively transported into the medulla The ascending limb is impermeable to water so water stays inside the tubule
This creates a low water potential in the medulla because there’s a high concentration of ions
This means water moves out of the descending limb which is permeable to water, into the medulla by osmosis
This makes the filtrate more concentrated as the ions can’t diffuse out
The water in the medulla is reabsorbed into the blood through the capillary network
Na+ ions diffuse out of the bottom of the ascending limb into the medulla further lowering the water potential in the medulla
Water moves out of the DCT by osmosis and is reabsorbed into the blood
The volume of water reabsorbed is controlled by changing the permeability of the DCT and collecting duct by ADH

Question 41

How would a high concentration of glucose in glomerular filtrate result in a larger volume of urine

Answer 41

Glucose in filtrate lowers the water potential
So lower water potential gradient
Less water is reabsorbed by osmosis