Module 5 Section 1 - The Hormonal System

Question 1

What is the hormonal system?

Answer 1

The hormonal system sends information as chemical signals. It is made up of endocrine glands and hormones.

Question 2

What are endocrine glands?

Answer 2

Endocrine glands are groups of cells that are specialised to secrete hormones, eg the pancreas secretes insulin.

Question 3

What are hormones?

Answer 3

Hormones are chemical messengers. Many hormones are proteins eg insulin and some are steroids eg progesterone.

Question 4

What is the action of hormones?

Answer 4

1) A hormone is a first messenger because it carries the chemical message the first part of the way, from the endocrine gland to the receptor on the target cell.

2) when the hormone binds to its receptor it activates an enzyme in the cell membrane.

3) the enzyme catalyses the production of a signalling molecule. The signalling molecule is the second messenger because it carries the signal from the receptors to other parts of the cell.

4) signalling molecules activate a cascade (chain of reactions) inside the cell.

Question 5

When is adrenaline secreted?

Answer 5

It is secreted by the adrenal glands when there’s a low concentration of glucose, when you’re stressed and when you’re exercising.

Question 6

What is glycogenolysis?

Answer 6

This is the breakdown of glycogen to glucose. This is usually activated by adrenaline to make glucose more available for muscles to respire.

Question 7

How does adrenaline work?

Answer 7

1) adrenaline (first messenger) binds to specific receptors on the cell membranes of target cells.

2) when it binds to the receptors, the enzyme adenylyl cyclase is activated in the cell membrane.

3) activated adenylyl cyclase catalyses the production of cyclic AMP (second messenger).

4) cAMP activates a cascade of reactions to make glucose available to the cell by catalysing the breakdown of glycogen to glucose.

Question 8

Structure of the adrenal glands

Answer 8

They are endocrine glands found just above the kidneys. Each adrenal gland has an outer part called the cortex and the inner part called the medulla.

Question 9

Function of the cortex (adrenal gland)

Answer 9

The cortex secreted steroid hormones eg it secretes cortisol and aldosterone when you’re stressed. Their effects include:

• stimulating the breakdown of proteins and fats into glucose. The increases the amount of energy available so the brain and muscles can respond to the situation.
• aldosterone - increasing blood volume and pressure by increasing uptake of sodium ions and water by the kidneys.

-cortisol regulates the metabolism

Question 10

Function of the medulla (adrenal gland)

Answer 10

The medulla secretes catecholamine hormones eg secretes adrenaline and noradrenaline when you’re stressed. These act to make more energy available in the short term by:
- increasing heart rate and breathing rate causing cells to break down glycogen into glucose
- constricting some blood vessels so that blood is diverted to the brain and muscles.

Question 11

What is homeostasis ?

Answer 11

Homeostasis involves control systems that keep internal environment roughly constant. Keeping your internal environment constant is vital for cells to function normally and stop them from being damaged.

Question 12

Why is it important to control body temperature?

Answer 12

Temperature affects enzyme activity and enzymes control the rate of metabolic reactions.

Question 13

How does temperature affect the rate of metabolic reactions?

Answer 13

The rate of metabolic reactions increases when temperature increases. More heat means more kinetic energy, so molecules move faster. This makes a collision between the substrate and active site more likely.
The energy of the collisions also increase, so each collision is more likely to result in a reaction.

Question 14

What happens when body temperature is too high/low?

Answer 14

1) if temperature gets too high, the enzyme may denature. The enzyme molecule vibrates too much which breaks the hydrogen bonds that hold them in their 3D shape. The active site changes shape and can no longer bind to the substrate.

2) if body temperature is too low, enzyme activity is reduced slowing the rate of metabolic reactions. The optimum temperature is 37 degrees in humans.

Question 15

What is negative feedback?

Answer 15

The mechanism that restores the level to normal.
Receptors detect when a level is too high/low, and the information is communicated via the nervous or hormonal system to effectors.
The effectors counteract the change, returning levels to normal.

Question 16

What is positive feedback?

Answer 16

The mechanism that amplifies a change away from the normal level. It is not involved in homeostasis because it doesn’t keep internal levels constant.

Question 17

Example of positive feedback?

Answer 17

It occurs when a blood clot is formed after an injury.
1) platelets become activated and release a chemical, which triggers more platelets to be activated.
2) platelets quickly form a blood clot at the injury site.
3) process ends in negative feedback once the clot is formed.

Question 18

What are ectotherms?

Answer 18

Ectotherms are animals that cannot control their body temperature internally, they control it by changing their behaviour.
This means the internal temperature is dependant on their surroundings. They have a variable metabolic rate and generate very little heat themselves.

Question 19

Example of an ectotherm

Answer 19

A lizard is an ectotherm. When internal temperature drops, it moves to a warmer area such as a place with sunshine. When internal temperature increases, it moved to somewhere cooler like a burrow beneath sand.

Question 20

What are endotherms?

Answer 20

Endotherms are animals that control their body temperature internally by homeostasis, as well as altering their behaviour. This means the internal temperature is less affected by external temperature.
They have a constantly high metabolic rate to keep internal temperature constant and they generate a lot of heat from metabolic reactions.

Question 21

Example of an endotherm

Answer 21

An elephant is an endotherm. It’s temperature is mainly controlled internally by homeostasis, but it may also change its behaviour to control its temperature. For example it may wallow in mud or flap its ears to cool down.

Question 22

What mechanisms are used to reduce body temperature?

Answer 22

1) sweating - sweat is secreted by sweat glands. The water in sweat evaporates and takes heat from the body.
2) Hairs lie flat - when it’s hot, erector pili muscles relax so less air is trapped.
3) Vasodilation- arterioles near the surface of the skin dilate . More blood flows through capillaries so more heat is lost by radiation.

Question 23

What mechanisms are used to increase body temperature?

Answer 23

1) shivering- muscles contract in spasms. More heat is produced from increased respiration.
2) hormones - they body releases adrenaline and thyroxine. These increase metabolism so more heat is produced.
3) much less sweat
4) hairs stand up- erector pili muscles contract so hair stands up and traps more air for insulation.
5) vasoconstriction- arterioles near the surface of the skin constrict so less blood flow through capillaries.

Question 24

How does the hypothalamus help control body temperature?

Answer 24

The hypothalamus receives information about internal and external temperature via thermoreceptors.
Thermoreceptors send impulses along sensory neurones to the hypothalamus which sends impulses along motor neurones to effectors.
The effectors respond to restore body temp to normal.

Question 25

Where are thermoreceptors found?

Answer 25

1) thermoreceptors in the hypothalamus detect internal temperature.
2) thermoreceptors in the skin (peripheral temperature receptors) detect external temperature.

Question 26

What is the normal concentration of glucose in blood?

Answer 26

90 mg per 100cm^3 of blood

Question 27

Structure and function of the pancreas

Answer 27

The areas of the pancreas that contain endocrine tissue are called the islets of Langerhans. They’re found in clusters around blood capillaries and they secrete hormones directly into the blood.

They are made up of alpha and beta cells. Alpha cells secrete glucagon and beta cells secrete insulin.

Question 28

How does insulin work?

Answer 28

It lowers blood glucose levels

1) it binds to receptors on the cell membranes of liver and muscle cells and increases the permeability of cell membranes to glucose

2) insulin also activates enzymes that convert glucose into glycogen.

3)insulin also increases respiration rate , especially in muscle cells.

Question 29

What is the process of converting glucose to glycogen called?

Answer 29

Glycogenesis

Question 30

How does glucagon work?

Answer 30

It raises blood glucose concentration

1) glucagon binds to receptors on the cell membranes of liver cells and activates enzymes that break down glycogen into glucose.

2) glucagon also promotes the formation of glucose from fatty acids and amino acids.

3) glucagon also decreases the rate of respiration in cell.

Question 31

What is the process of converting non-carbohydrates to glucose called?

Answer 31

Gluconeogenesis

Question 32

What is the structure of B cells at rest?

Answer 32

They contain vesicles of insulin. They have open potassium ion channels and closed calcium ion channels.
Potassium ions diffuse out the cell which make the inside of the cell membrane more negative than the outside.
The membrane is polarised.

Question 33

How does a B cell secrete insulin ?

Answer 33

1) when blood glucose concentration is high, more glucose enters B cells via facilitated diffusion. More glucose causes higher respiration rates, making more ATP.

2) The rise in ATP, causes the potassium ion channels to close. This means k+ ions build up inside the cell. This makes the inside of the cell less negative so the membrane become depolarised.

3) depolarisation triggers calcium ion channels to open, so Ca2+ diffuse into B cells. This causes vesicles to move to and fuse with the B cell plasma membrane, and release insulin by exocytosis.

Question 34

What is type 1 diabetes?

Answer 34

It is an autoimmune disease in which the body attacks and destroys the B cells in the islets of Langerhans. This means they don’t produce any insulin. The kidneys cannot reabsorb all this glucose, so some of it is excreted in the urine.

Question 35

Who does type 1 diabetes affect?

Answer 35

Type 1 diabetes usually develops in young adults and children. A person’s risk of developing type 1 diabetes is slightly increased is there’s a close family history of the disease.

Question 36

How to treat type 1 diabetes?

Answer 36

It is treated with insulin therapy. This could either be regular insulin injections throughout the day or an insulin pump, which delivers insulin via a tube inserted beneath the skin.

Some people have had successful islet cell transplantation where they receive healthy islet cells from a donor so they can produce some insulin.

People with diabetes need to regularly monitor blood glucose levels. A carefully planned diet can reduce the amount of glucose they are taking in. Exercise can also reduce this.

Question 37

What is type 2 diabetes?

Answer 37

Type 2 diabetes is when the body does not produce enough insulin or the body cells don’t respond properly to insulin. This is because their insulin receptors do not work.

Question 38

Who is likely to develop type 2 diabetes?

Answer 38

It is usually acquired later in life, and is linked to obesity. The risk is also increased in people from certain ethnic groups eg African or Asian and people who have close family history of type 2 diabetes.

Question 39

How to treat type 2 diabetes?

Answer 39

It is initially managed through lifestyle changes. Eating a balanced diet, exercising and losing weight can help prevent onset of type 2 diabetes and control the effects.

If it cannot be managed through lifestyle changes alone, medication may be prescribed.

Question 40

Examples of medication to treat type 2 diabetes

Answer 40

1) Metformin- acts on liver cells to reduce the amount of glucose they release into the blood. It also increases the cells’ sensitivity to insulin so more glucose can be taken up.

2) Sulfonylureas (eg gliclazide) - these stimulate the pancreas to secrete more insulin.

3) Thiazolidinediones (eg pioglitazone) - this makes body cells more sensitive to insulin.

Question 41

Why is producing insulin from GM bacteria better than extracting from animals?

Answer 41

1) it is cheaper than extracting it from animal pancreases
2) larger quantities of insulin can be produced from GM bacteria
3) GM bacteria makes human insulin so less likely to trigger allergic reactions or be rejected by the immune system.
4) some people prefer insulin from GM bacteria for ethical or religious reasons

Question 42

How to cure diabetes with stem cells?

Answer 42

Stem cells can be grown into B cells. This would then be implanted into the pancreas of a person with type 1 diabetes. This would mean the person could produce insulin as normal.