14- hormonal communication

Question 1

what is an endocrine gland?

Answer 1

It’s a group of cells that are specialised to secrete chemicals- these chemicals are hormones, and are secreted directly into the bloodstream.

Question 2

How is hormone release triggered?

Answer 2

This can occur as a result of a change in concentration of a particular substance e.g. blood glucose conc, or as a result of another hormone or nerve impulse.

Question 3

What are target cells?

Answer 3

Once secreted, the hormones are transported in the blood plasma all over the body. They diffuse out of the blood and bind to specific receptors for that hormone, found on the membrane or cytoplasm of cells in the target organs, known as target cells.

Question 4

How do steroid hormones work?

Answer 4

They’re lipid soluble, so can pass through the lipid components of a cell membrane and bind to steroid hormone receptors to form a hormone- receptor complex. The receptors may be present in the cytoplasm or the nucleus, depending on the hormone. The hormone-receptor complex formed acts as a transcription factor which in turn facilitates or inhibits the transcription of a specific gene. e.g. oestrogen

Question 5

What is a non-steroid hormone?

Answer 5

They’re hydrophilic so cannot pass directly through the cell membrane. Instead, they bind to specific receptors on the cell surface membrane of the target cell. This triggers a cascade of reaction mediated by chemicals called second messengers. e.g. adrenaline

Question 6

Give 8 characteristics of the hormonal system.

Answer 6

Communication is by chemicals called hormones.
Transmission is by the bloodstream.
Transmission is usually relatively slow.
Hormones travel to all parts of the body, but only target organs respond.
Response is widespread.
Response is slow
Response is often long lasting
Effect may be permanent and irreversible.

Question 7

Give 8 key features of the nervous system.

Answer 7

Communication is by nerve impulses.
Transmission is by neurones
Transmission is very rapid
Nerve impulses travel to specific parts of the body
Response is localised
Response is rapid
Response is short lived
Effect is temporary and reversible.

Question 8

What are the adrenal glands?

Answer 8

They’re two small glands that measure approx. 3cm high and 5 cm long. They’re located on top of each kidney and are made up of 2 distinct parts, surrounded by the capsule.

Question 9

What are the 2 parts of the adrenal glands?

Answer 9

Adrenal cortex- outer region of the glands. This produces hormones that are vital to life, e.g. cortisol and aldosterone.
Adrenal medulla- the inner region of the glands. This produces non-essential hormones e.g. adrenaline- helps the body react to stress.

Question 10

What are the 3 main types of hormones produced by the adrenal cortex?

Answer 10

Glucocorticoids
Mineralocorticoids
Androgens

Question 11

What are glucocorticoids?

Answer 11

Include cortisol which helps regulate metabolism by controlling how the body converts fats, proteins and carbohydrates into energy. It also helps to regulate blood pressure and cardiovascular function in response to stress.
Another glucocorticoid hormone released is corticosterone. It works with cortisol to regulate the immune system and supresses inflammatory reactions. The release of these hormones is controlled by the hypothalamus.

Question 12

What are mineralocorticoids?

Answer 12

The main one produced is aldosterone which helps control blood pressure by maintaining the balance between salt and water concentrations in the blood and bodily fluids. Its release is mediated by signals triggered by the kidney.

Question 13

What are androgens?

Answer 13

Small amounts of male and female sec hormones are released. Their impact is relatively small compared with the larger amounts of hormones e.g. oestrogen and testosterone, released by the ovaries or testes after puberty, but they are still important, especially in women after the menopause.

Question 14

What hormones are produced by the adrenal medulla?

Answer 14

They’re released when the sympathetic nervous system is stimulated.
Adrenaline- This increases the heart rate, sending blood quickly to the muscles and brain. It rapidly increases blood glucose conc. levels by converting glycogen to glucose in the liver.
Noradrenaline- works with adrenaline in response to stress, producing effects such as increased HR , widening of pupils, widening of air passages in the lungs, and the narrowing of blood vessels in non-essential organs (resulting in higher blood pressure)

Question 15

What are the 2 main functions of the pancreas?

Answer 15

Exocrine gland- to produce enzymes and release them via a duct into the duodenum
endocrine gland- to produce hormones and release them into the blood.

Question 16

Explain the role of the pancreas as an exocrine gland.

Answer 16

Most of the pancreas is made up of exocrine glandular tissue. This tissue is responsible for producing digestive enzymes and alkaline fluids known as pancreatic juices. The enzymes and juice are secreted into ducts which eventually lead to the pancreatic duct. From here, theyre released into the duodenum, the top part of the small intestine. The pancreas produces three important types of digestive enzymes;
Amylase- break down starch into simple sugars. e.g. pancreatic amylase.
protease- breals down proteins into amino acids, e.g. trypsin
lipases- break down lipids into fatty acids and glycerol e.g pancreatic lipase

Question 17

explain the role of the pancreas as an endocrine gland.

Answer 17

It’s responsible for producing insulin and glucagon. These hormones play an essential role in controlling blood glucose conc. Within the exocrine tissue there are small regions called islets of Langerhans. The cells in the islets of Langerhans are responsible for producing insulin and glucagon, and secreting these hormones directly into the blood stream.

Question 18

What are the different types of cells in the islets of Langerhans?

Answer 18

alpha cells- produce and secrete glucagon
beta cells- produce and secrete insulin
alpha cells are larger and more numerous than beta cells within an islet. Using standard staining techniques it is very difficult to tell the difference. If a differential stain is used, the cell types will be different colours.

Question 19

how does blood glucose concentration increase?

Answer 19

diet- when you eat carbohydrate rich foods such as pasta and rice and sweet foods such as cakes, the carbs they contain are broken down in the digestive system to release glucose. The glucose released is absorbed into the bloodstream and blood glucose conc rises
glycogenolysis- glycogen stored in the liver and muscle cells is broken down into glucose which is released into the bloodstream, increasing blood glucose conc.
gluconeogenesis- the production of glucose from non-carbohydrate sources. e.g. the liver is able to make glucose from glycerol and amino acids. This glucose is released into the bloodstream and causes an increase in blood glucose conc.

Question 20

How is blood glucose conc. decreased

Answer 20

Respiration- some of the glucose in the blood is used by cells to release energy. This is required to perform normal body functions. However, during exercise, more glucose is needed as the body needs to generate more energy in order for muscle cells to contract. The higher the level of physical activity, the higher the demand for glucose and the greater the decrease of blood glucose conc.
glycogenesis - the production of glycogen. When blood glucose conc. is too high, excess glucose taken in through the diet is converted into glycogen which is stored in the liver.

Question 21

What is the role of insulin?

Answer 21

It is produced by the beta cells in the islets of Langerhans in the pancreas. If the blood glucose conc is too high, the beta cells detect this rise in blood glucose conc and respond by secreting insulin. Virtually all body cells have insulin receptors on their cell membrane surface membrane. when insulin binds to its glycoprotein receptor, it causes a change in the tertiary structure of the glucose transport protein channels. This causes the channels to open allowing more glucose to enter the cell. Insulin also activates the enzyme within some cells to convert glucose to glycogen and fat.

Question 22

How does insulin lower blood glucose conc. ?

Answer 22

• Increasing the rate of absorption of glucose by cells, in particular skeletal muscle cells
• Increasing the respiratory rate of cells- this increases their need for glucose and causes a higher uptake of glucose from the blood.
• Increasing the rate of glycogenesis- insulin stimulates the liver to remove glucose from the blood by turning the glucose into glycogen and storing it in the liver and the muscle cells.
• Increasing the rate of glucose to fat conversion
• Inhibiting the release of glucagon from the alpha cells of the islets of Langerhans.

Question 23

What is the role of glucagon?

Answer 23

It is produced by the alpha cells in the islets of langerhans in the pancreas. If the blood glucose conc is too low, the alpha cells detect this, and respond by secreting glucagon directly into the bloodstream. Unlike insulin, the only cells in the body which have glucagon receptors are the liver cells and fat cells- therefore these are the only cells that can respond to glucagon.

Question 24

How does glucagon raise blood glucose levels?

Answer 24

• Glycogenolysis: the liver breaks down its glycogen store into glucose and releases it back into the bloodstream.
• reducing the amount of glucose absorbed by the liver cells
• Increasing gluconeogenesis: increasing the conversion of amino acids and glycerol into glucose in the liver.

Question 25

Explain the steps for control of insulin secretion.

Answer 25

1. At normal blood glucose conc. levels, potassium channels in the plasma membrane of beta cells are open and potassium ions diffuse out of the cell. Inside the cell is at a potential of -70mV with respect to the outside of the cell.
2. When blood glucose conc. rises, glucose enters the cell by a glucose transporter.
3. the glucose is metabolised inside the mitochondria, resulting in the production of ATP.
4. The ATP binds to potassium channels and causes them to close. They are known as ATP sensitive potassium channels.
5. A potassium can no longer diffuse out of the cell, the potential difference reduces to around -30mV and depolarisation occurs.
6. Depolarisation causes the voltage gated calcium channels to open.
7. Calcium ions enter the cell and cause secretory vesicles to release the insulin they contain via exocytosis.

Question 26

What is type 1 diabetes?

Answer 26

They’re unable to produce insulin. The beta cells is the islets of Langerhans dont produce insulin. The cause isnt known at the moment, the disease cannot be prevented or cured. It is possible, however, to treat the symptoms. Evidence suggests that in many cases the condition arises as a result of an autoimmune response, where the body’s own immune system attacks the beta cells. This condition normally begins in childhood, and people develop symptoms of the disease quickly.

Question 27

What is type 2 diabetes?

Answer 27

Body can’t effectively use insulin and control their blood sugar levels. This is either because the persons beta cells cant produce enough insulin or the persons body doesn’t respond properly to insulin. Often due to the glycoprotein insulin receptor on the cell membrane doesn’t work properly. the cells lose their responsiveness to insulin, and therefore don’t take up enough glucose, leaving it in the bloodstream. It is largely as a result of excess body weight, physical inactivity, and habitual, excessive overeating of carbs. Symptoms develop more slowly and are less severe than that of type 1.

Question 28

How can type 1 diabetes be controlled?

Answer 28

Regular injections of insulin- insulin dependent. Blood sugar levels should be regularly checked. The amount of insulin they need to inject is then calculated. The insulin administered increases the amount of glucose absorbed by cells and causes glycogenesis to occur, resulting in a reduction of blood glucose conc.
If too much insulin is injected, hypoglycaemia may occur. This can result in unconsciousness and death if not treated. Careful monitoring and dose regulation is therefore required.

Question 29

How can type 2 diabetes be treated?

Answer 29

First approach would be to control a person’s carbohydrate intake through their diet and matching this to their exercise levels. This often involves increasing exercise. Overweight people are also encouraged to loose weight.
In some cases blood glucose drugs also have to be used. These can include drugs that stimulate insulin production, drugs that slow the rate at which the body absorbs glucose from the intestine, and ultimately, even insulin injections.

Question 30

What are the advantages of using medically produced insulin vs insulin from cows and pigs?

Answer 30

-Human insulin is produced in a pure form- this means its less likely to cause an allergic - reaction.
- Insulin can be produces in much higher quantities.
- Production costs are cheaper
- People’s concerns over using animal products in humans, which may be religious or ethical, are overcome.

Question 31

Why is it undesirable to use a pancreas transplant as a cure for diabetes?

Answer 31

The demand for transplantable pancreases outweighs the availability. The risks of having a transplant can be greater than the diabetes itself. Immunosuppressant drugs are required to ensure the body accepts the transplanted pancreas, which can leave a person susceptible to infection.

Question 32

How could stem cell treatment possibly cure diabetes?

Answer 32

There is evidence that a relatively small number of islet cells can restore insulin production. Scientists have been researching the best types of stem cells that can differentiate into beta cells, either in the patient or in the laboratory before being transplanted

Question 33

What are the possible issues with stem cell therapy to treat diabetes?

Answer 33

Its likely that the stem cells used in treatment would be embryonic stem cells. To obtain these, an early embryo has to be destroyed. However, the embryos used as a source for these stem cells would usually be destroyed anyway- they were ‘spare’ embryos from infertility treatments or terminated pregnancies.
Stem cells from a small number of embryos can be used to treat many patients- each treatment doesn’t require a separate embryo. An alternative could be using embryonic matter is that of using umbilical stem cells.

Question 34

What advantages do stem cells offer over current therapies?

Answer 34

• Donor availability wouldnt be an issue, stem cells could produce an unlimited source of new beta cells.
• reduced likelyhood of rejection problems as embryonic stem cells are generally not rejected from the body. Stem cells scan also be made by stomatic cell nuclear transfer.
  -people would no longer have to inject themselves with insulin.