Chapter 16 homeostasis

Question 1

What is homeostasis

Answer 1

The regulation of the bodies internal conditions to maintain a stable environment of optimal conditions

Question 2

What does the body need to regulate

Answer 2

• body temperature (36 - 38)
• CO2 concentration (35 - 45 mmHg)
• blood pH (7.35 - 7.45)
• blood glucose level (75 - 95mg/dL)
• water balance

Question 3

what is negative feedback

Answer 3

If there is a change in the body’s internal environment then there will be a change to counteract this returning it to its optimum point

Question 4

What are the steps in glycogenesis

Answer 4

It is when glycogen is made from glucose

• when blood glucose is too high, insulin is released by the β cells in the pancreas
• insulin binds to the receptors on liver cells and muscle cells
• this increases the permeability of these cells so they take up more glucose
• insulin also activates the enzymes in the liver and muscle cells that convert glucose to glycogen

Question 5

what are the steps in glycogenolysis

Answer 5

it is when glycogen is broken down into glucose

• when the blood glucose concentration is too low the hormone glucagon is released by the α cells in the pancreas
• glucagon binds to the receptors on liver cells
• glucagon activates enzymes in the liver that break gown glycogen into glucose

Question 6

What are the steps in gluconeogenesis

Answer 6

making glucose from non-carbohydrates

• when blood glucose levels are still low after glycogenolysis
• glucagon activates enzymes that are involved in the formation of glucose from glycerol and amino acids

Question 7

How does insulin affect glucose transporters

Answer 7

• skeletal and cardiac muscles contain GLUT4 channel proteins.
• When insulin levels are low, GLUT4 is stored in vesicles inside the cytoplasm of cells
• when insulin binds to receptors on the cell surface membrane, it triggers the movement of GLUT4 to the membrane
• glucose can now be transported into cells via facilitated diffusion

Question 8

How does adrenaline affect blood glucose concentration

Answer 8

It increases blood glucose concentration

when there is low blood glucose levels or during stress or exercise adrenaline is secreted from the adrenal glands and binds to the receptors on liver cells.

This activates glycogenolysis and activates glucagon secretion
And inhibits glycogenesis and inhibits insulin secretion

Question 9

How does adrenaline and glucagon act as secondary messengers

Answer 9

They both have complementary tertiary structures to a receptor which activates the enzyme adenyl cyclase.
This converts ATP to cAMP (cyclic AMP) which is a secondary messenger
cyclic AMP activates an enzyme called protein kinase which causes a chain of reaction that convert glycogen to glucose

Question 10

What are the features of type 1 diabetes

Answer 10

It is an autoimmune disease where the immune system attacks the β cells in the islets of Langerhans to they cannot produce insulin.
This means after eating the blood glucose concentration stays high.
Type 1 diabetes can be treated with insulin injections throughout the day
Usually developed due to genetics in children

Question 11

What are the features of type 2 diabetes

Answer 11

when your β cells do not produce enough insulin or when your body cells do not respond properly to insulin causing blood glucose levels to e higher than normal
Can be treated by eating a healthy diet and exercise

Question 12

What is the function of the kidneys

Answer 12

to excrete waste products such as urea, excess salts and minerals.
They also regulate the water potential of the blood

Question 13

How is blood filtered into the nephrons

Answer 13

1. Blood enters the kidney through the renal artery and splits into smaller arterioles
2. Each arteriole enters a glomerulus which is a bundle of capillaries
3. The arteriole that takes blood into the glomerulus is called the afferent arteriole and the efferent arteriole takes blood away from the glomerulus
4. The efferent arteriole has a smaller lumen so the blood in the glomerulus has a high hydrostatic pressure
5. This forces small molecules such as glucose, lipids, amino acids into the Bowman’s capsule
6. Larger molecules such as red blood cells cannot pass through into the Bowman’s capsule so remain in the blood

Question 14

What are the steps in selective reabsorption

Answer 14

1. The useful substances have already passed out of the glomerulus and into the Bowman’s capsule due to the difference in hydrostatic pressure between the efferent and afferent arteriole
2. The epithelium of the microvilli that provide a large surface area for the reabsorption of useful materials
3. Glucose is reabsorbed via active transport and facilitated diffusion back into the blood

Question 15

What happens when the water potential of the blood is too low

Answer 15

More water is reabsorbed by osmosis into the blood. This means that the urine is more concentrated, so less water is lost during excetion

Question 16

What happens when water potential of the blood is too high

Answer 16

Less water is reabsorbed by osmosis into the blood. This means that the urine is more dilute, so more water is lost during excretion

Question 17

How does the loop of Henle maintain a sodium ion gradient

Answer 17

1. Energy from mitochondrion is used to actively transport sodium ions out of the ascending limb
2. This lowers the water potential in the medulla so water moves out of the descending limb by osmosis
3. At the base of the ascending limb sodium ions diffuse out further lowing the water potential of the medulla
4. Water moves out of the DCT into the medulla
5. Water moves out of the collecting duct by osmosis into the medulla

Question 18

How is the water potential of the blood monitored

Answer 18

It is monitored by osmoreceptors in the hypothalamus which can send signals to the posterior pituitary gland when the blood water potential is too high or too low causing the pituitary gland to release more ADH

Question 19

What happens to the levels of ADH when the blood water potential is too low

Answer 19

The blood ADH will rise overall

• The water potential of the blood is low
• This is detected by osmoreceptors in the hypothalamus
• The posterior pituitary gland is stimulated to release more ADH
• This makes the walls of the DCT more permeable so more water is reabsorbed into the blood via osmosis
• This causes a small amount of highly concentrated urine to be produced

Question 20

What happens to the levels of ADH when the blood water potential is too high

Answer 20

The blood ADH will fall overall

• The water potential of the blood is high
• This is detected by osmoreceptors in the hypothalamus
• The posterior pituitary gland is stimulated to release less ADH
• This makes the walls of the DCT less permeable so less water is reabsorbed into the blood via osmosis
• This causes a large amount of dilute urine to be produced