2 Homeostasis

Question 1

What is homeostasis?

Answer 1

Homeostasis is the maintenance of an internal environment within restricted limits in organisms. Involves trying to maintain the chemical make up, volume and other features of blood and tissue fluid within restricted limits.

Question 2

What is the importance of maintaining the right core body temperature?

Answer 2

• if body temp to high enzymes may become denatured. Enzymes molecules vibrate too much, which breaks hydrogen bonds that hold them in their 3D shape. Shape of enzymes active site change and no longer works as a catalyst. This means metabolic reactions less efficient .
• if body temp to low, enzyme activity reduced, slowing rate of metabolic reactions
• highest rate of enzyme activity at optimum temp about 37°c in humans.

Question 3

What is the importance of maintain blood pH?

Answer 3

• if blood pH too high or too low enzymes become denatured. Hydrogen bonds that hold them in their 3D shape broken, so enzymes active site changed and no longer works as catalyst, metabolic reactions less efficient.
• highest rate of enzyme activity happens at optimum pH- usually around pH 7 but some enzymes work best at other pHs eg stomach = low pH

Question 4

What is the importance of maintain blood glucose concentration?

Answer 4

• if blood glucose conc too high, water potential of blood reduced to point where water molecules diffuse out of cells into blood by osmosis. This can cause cells to shrivel up and die.
• if blood glucose conc to low, cells unable to carry out normal activities because their isn’t enough glucose for respiration to provide energy.

Question 5

How do control mechanisms work?

Answer 5

Optimum point, point at which system operated best. monitored by receptor, which detects any deviation from optimum point and informs coordinator, which coordinates info from receptors + sends instructions to an appropriate effector, which brings about changes needed to return system to optimum point. This return to normality creates a feedback mechanism

Question 6

What is negative feedback?

Answer 6

When the change in produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off. Having separate negative feedback mechanisms that control departures from the norm in either direction gives greater degree of homeostatic control. Because there are positive actions in both directions.

Question 7

What is positive feedback? (Not homeostasis)

Answer 7

Occurs when a deviation from an optimum causes changes that result in an even greater deviation from the normal.

Question 8

How is hypothermia an example of positive feedback?

Answer 8

• hypothermia is low body temp (below 35°)
• happens when heats lost from body quicker quicker than it can be produced
• as body temp falls brain doesn’t work properly and shivering stops, this makes body temp fall even more
• positive feedback takes body temp further away from normal level, and it continues to decrease unless action is taken.

Question 9

What are hormones?

Answer 9

• produced in glands, which secrete hormone directly into blood (endocrine glands)
• carries in blood plasma to target cells, which have specific receptors on their cell-surface membranes that are complimentary to a specific hormone
• effective in very low concentrations, but often have widespread and Lon lasting effects.

Question 10

Describe the second messenger model involving adrenaline.

Answer 10

• adrenaline binds to a transmembrane protein receptor within the cell-surface membrane of a liver cell
• causes protein to change shape on inside of membrane
• leads to activation of adenyl cyclase, this converts ATP to cyclic AMP(cAMP)
• cAMP acts as second messenger that binds to protein kinase enzyme, changing its shape + therefore activating it
• active protein kinase enzyme catalyses conversion of glycogen to glucose which moves out of liver by facilitated diffusion and into the blood, through channel proteins.

Question 11

What is the role of the pancreas in regulating blood glucose?

Answer 11

Pancreas produces enzymes ( protease, amylase and lipase) for digestion’s an hormones ( insulin and glucagon) for regulating blood glucose concentration.
Pancreas made up largely of cells that produce these enzymes. Scattered throughout these cells are the islets of langerhans.

Question 12

What do the cells of islets of langerhans include?

Answer 12

• α cells, which are the larger and produce glucagon

- β cells, which are smaller and produce the hormone insulin.

Question 13

What is the role of the liver in regulating blood glucose concentration?

Answer 13

Made up of hepatocytes and is where insulin and glucagon have their effect in the processes if; glycogensis, glycogenolysis, gluconeogenesis.

Question 14

What is glycogenesis?

Answer 14

The conversion of glucose into glycogen. When blood glucose conc. higher than normal liver removes glucose from blood and converts it to glycogen.

Question 15

What is glycogenolysis?

Answer 15

The breakdown of glycogen to glucose. When blood glucose conc. lower than normal, liver can convert stored glycogen back into glucose which diffuses into blood to restore normal blood glucose conc.

Question 16

What is gluconeogenesis?

Answer 16

Production of glucose from sources other sources other than carbohydrate. When it’s supply of glycogen is exhausted, the liver can produce glucose from non-carbohydrate sources such as glycerol + amino acids.

Question 17

What happens if blood glucose concentration is too low?

Answer 17

Cells will be deprived of energy and die, brain cells are especially sensitive because they can only respire glucose.

Question 18

What happens if blood glucose concentration is too high?

Answer 18

It lowers water potential of blood + creates osmotic problems that can cause dehydration and be equally dangerous

Question 19

What factors influence blood glucose concentration?

Answer 19

• directly from diet in form of glucose absorbed following hydrolysis of other carbohydrates such as starch, maltose, lactose and sucrose
• from hydrolysis in small intestine/ glycogenolysis stored in liver + muscle cells
• from gluconeogenesis, which is production of glucose from sources other than carbohydrate

Question 20

How does insulin lower blood glucose when it’s too high?

Answer 20

• insulin binds to specific receptors on cell membranes of liver and muscle cells.
• increases permeability of muscle-cell membranes to glucose, so the cells take up more glucose. This involves increasing number of channel proteins in cell membranes.
• activates enzymes in liver + muscle cells that convert glucose into glycogen
• cells able to store glycogen in their cytoplasm, as an energy source
• also increases rate of respiration of glucose, especially in muscle cells

Question 21

How does glucagon raise blood glucose concentration when it’s too low?

Answer 21

• glucagon binds to specific receptors on cell membranes of liver cells
• glucagon activates enzymes in liver cells that break down glycogen into glucose by glycogenolysis
• glucagon activates enzymes involved in formation of glucose from glycerol and amino acids
• glucagon decreases rate of respiration of glucose in cells.

Question 22

Describe negative feedback mechanism to respond to a rise in blood glucose concentration.

Answer 22

• pancreas detects blood glucose conc. is too high
• β cells secrete insulin
• α cells stop secreting glucagon
• insulin binds to receptors on liver + muscle cells
• cells take up more glucose
• glycogenesis is activated
• cells respire more glucose
• less glucose in blood.

Question 23

Describe negative feedback mechanism to respond to a fall in blood glucose concentration.

Answer 23

• pancreas detects blood glucose concentration is too low
• β cells stop secreting insulin
• α cells secrete glucagon
• glucagon binds to receptors on liver cells
• glycogenolysis activated
• gluconeogenesis activated
• cells respire less glucose
• cells release glucose into blood

Question 24

How does adrenaline raise blood glucose concentration?

Answer 24

• adrenaline secreted by adrenal glands when low concentration of glucose in blood, when stressed, when exercising
• adrenaline binds to receptors in cell membranes of liver cells
• it activates glycogenolysis and inhibits glycogensis
• also activates glucagon secretion and inhibits insulin secretion, which increases glucose conc.
• adrenaline gets body ready for action by making more glucose available for muscles to respire.

Question 25

What is type 1 diabetes?

Answer 25

When the immune system attacks the β cells in the islets of langerhans so they can’t produce any insulin. After eating, blood glucose level rises + stays high- this called hyperglycaemia + can result in death if left untreated. Kidneys can’t reabsorb all this glucose, so some excreted in urine.

Question 26

What cause type 1 diabetes?

Answer 26

No one knows exactly, but scientists have found some people have a genetic predisposition to developing type 1 diabetes. They also think disease may be triggered by viral infection.

Question 27

How is type 1 diabetes treated?

Answer 27

With insulin therapy. Most people need regular insulin injections throughout day, but some people use an insulin pump to deliver insulin continuously instead. Insulin has to be carefully controlled because too much insulin can produce dangerous drop in blood glucose levels- called hypoglycaemia. Eating regularly + controlling simple carbohydrate intake helps avoid sudden rise in glucose.

Question 28

What causes type II diabetes ?

Answer 28

Usually acquired later in life than type I. Often linked with obesity + is more likely in people with family history of condition. Other risk factors include lack of exercise, age and poor diet

Question 29

What is type II diabetes?

Answer 29

Occurs when the β cells don’t produce enough insulin or when body’s cells don’t respond properly to insulin. Cells don’t respond properly because insulin receptors on their membranes don’t work properly, so cells don’t take up enough glucose. Blood glucose conc. higher than normal.

Question 30

How to treat type II diabetes?

Answer 30

Eating healthily, balanced diet, losing weight and regular exercise. Glucose-lowering medication can be taken if diet and exercise can’t control it. Eventually insulin injections may be needed.