5.4 - C - Hormonal Communication

Question 1

What is the endocrine system?

Answer 1

A communication system using hormones as signalling molecule

Question 2

Hormones

Answer 2

Molecules (proteins or steroids) that are released by endocrine glands directly into the blood. They act as messengers, carrying a signal from the endocrine gland to a specific target organ or tissue.

Question 3

What are target cells?

Answer 3

Cells that possess a specific receptor on their plasma membrane for non-steroid hormones. The shape of the receptor is complementary to the shape of the hormone molecule. Many similar cells together form a target tissue.

Question 4

What hormones are produced by each of the following glands?
Adrenal gland
Ovaries
Testes
Pancreas
Pituitary gland
Thyroid

Answer 4

Adrenaline
Oestrogen
Testosterone
Insulin and glucagon
FSH and LH
Thyroxine

Question 5

What are hormones produced by?

Answer 5

Endocrine glands

Question 6

What is the difference between exocrine and endocrine glands?

Answer 6

Endocrine glands produce and secrete hormones directly into the blood ‐ they have no ducts.
Exocrine glands do not produce hormones ‐ they secrete molecules into a duct which carries them to where they are needed such as digestive enzymes and salivary and sweat glands. They are all mammary glands.

Question 7

What are the 2 parts of the adrenal gland?

Answer 7

Adrenal medulla

Adrenal cortex

Question 8

Define the adrenal medulla

Answer 8

In the centre of gland ‐ makes and secretes adrenaline and noradrenaline.

Question 9

What does adrenaline cause?

Answer 9

Relax smooth muscle in bronchioles
Increase stroke volume of heart
Increase heart rate
Vasoconstriction 
Glycogen ‐‐> glucose
Dilates pupils
Increase mental awareness
Inhibits action of gut
Body hair erects

Question 10

Explain adrenaline

Answer 10

A non-steroid hormone (protein/amino acid based hormones) ‐ these can’t dissolve in the cell surface membranes of target cells and get inside and must instead bind to a receptor cell.
It stimulates the body to prepare for fight or flight.

Question 11

Explain what non-steroid hormones are

Answer 11

Non‐steroid hormones are known as first messengers because they transmit the signal around the body and cause an effect on the body when they bind to a receptor.The binding causes a G‐protein to activate adenyl cyclase which converts ATP into cyclic AMP (cAMP) which is the second messenger because it transmits the signal inside the cell and intimates a change inside the cell.

Question 12

What does the adrenal cortex do?

Answer 12

Uses cholesterol to produce steroid hormones

Question 13

Explain the 3 layers of the adrenal cortex

Answer 13

Zona Glomerulosa (nearest outside) secretes mineralocorticoids ‐ help to control sodium and potassium levels in blood and blood pressure.
Zona Fasciculata secretes glucocorticoids e.g. cortisol ‐ helps to control metabolism of carbs, fats and protein in liver.
Zona Reticularis (nearest medulla) secretes precursors to the sex hormones.

Question 14

Explain the difference between steroid and non-steroid hormones

Answer 14

Steroid hormones have a chemical structure similar to cholesterol, since most are derived from it. They are soluble in lipids and diffuse rather easily through plasma membranes and enter the cell and the nucleus to have a direct effect on the DNA in the nucleus. These are secreted from the adrenal cortex, ovaries, testes and the placenta.
Non-steroid hormones are not soluble in lipids, so they cannot easily cross plasma membranes. This group can be subdivided into 2 groups: protein/peptide hormones and amino acid derived hormones. They need to bind to the cell surface membrane and release a second messenger inside the cell.

Question 15

Explain how steroid hormones work

Answer 15

Steroid hormones enter cells by dissolving in the cell surface membrane. They then bind with a receptor in the cytoplasm, the receptor‐hormone complex enters the nucleus and binds to another receptor on the chromosome. This causes mRNA to be made which then produces proteins.

Question 16

How can hormones travel all around the body in the blood yet
still have such specific effects?

Answer 16

Endocrine glands make and secrete hormones and release them directly into the blood.
Hormones bind to specific complementary receptors on the cell surface
membranes of their target cells.
The hormones will not affect cells without these receptors.
Target cells are grouped into target tissues.

Question 17

Using the example of the adrenal glands, describe how different types of hormones are released and take affect on their target cells

Answer 17

Endocrine glands release hormones that travel in blood to target cells. The adrenal medulla releases non‐steroid hormones.
Adrenaline acts as the first messenger.
G‐protein activates adenyl cyclase which converts ATP into cyclic AMP (cAMP), which is the second messenger. This causes an effect in the cell.
The adrenal cortex releases steroid hormones which dissolve in cell surface membrane (of target cells) and bind with a receptor in the cytoplasm. The receptor‐hormone complex binds to receptor on the chromosome/DNA causes mRNA/proteins to be made.

Question 18

What is the adrenal gland

Answer 18

One of a pair of glands lying above the kidneys, which release adrenaline and a number of other hormones known as corticoids (or corticosteroids) such as aldosterone.

Question 19

Explain the exocrine function of the pancreas

Answer 19

The majority of cells produce digestive enzymes ‐ ‘pancreatic juice’. These cells form groups (called acini) secrete enzymes into tubules which lead to the pancreatic duct which takes them to the small intestine.

Question 20

What is in the fluid from the pancreatic duct?

Answer 20

Pancreatic amylase - a carbohydrate which digests amylose to maltose.
Trypsinogen - an inactive protease which will be converted to the active form trypsin when it enters the duodenum.
Lipase - digests lipid molecules.
Sodium hydrogencarbonate (alkali) - helps neutralise the contents of the digestive system that have just left the acid environment of the stomach.

Question 21

Explain the endocrine function of the pancreas

Answer 21

The islets of Langerhans contain alpha and beta cells
The cells detect changes in blood glucose levels (normal = 90mg per 100cm^3)
Alpha cells ‐ produce and secrete glucagon (hormone)
Beta cells ‐ produce and secrete insulin (hormone)
They secrete the hormones directly into closely associated capillaries

Question 22

What do alpha and beta cells secrete?

Where are they both found?

Answer 22

Alpha - glucagon
Beta - insulin
The islets of Langerhans

Question 23

What is glucagon?

Answer 23

A hormone that causes an increase in blood glucose concentration.

Question 24

What is insulin?

Answer 24

The hormone that causes blood glucose levels to decrease. It’s released from the pancreas.

Question 25

What are the 2 main secretions of the pancreas?

Answer 25

Pancreatic juices containing enzymes which are secreted into the small intestine.
Hormones which are secreted from the islets of Langerhans into the blood.

Question 26

Explain the steps in the mechanism of insulin secretion

Answer 26

The cell membrane has K+ and Cl- ion channels.
The K+ ion channels are normally open - so K+ ions flow out.
When blood glucose conc. is high, the glucose moves into the cell. Glucose is metabolised to produce ATP.
The ATP closes the K+ ion channels.
The accumulation of K+ ions alters the P.D. across the cell membrane - the inside becomes less negative.
The change in P.D. opens the calcium ion channels.
Calcium ions cause the vesicles of insulin to fuse with the cell membrane, releasing insulin by exocytosis.

Question 27

Explain how a pancreas looks on a micrograph

Answer 27

Most cells are exocrine.
Groups of cells surrounding smallest hollow tubes ‐ acini.
Slightly larger circular(ish) hollow tubes ‐ tubules leading to pancreatic
duct.
Patches (circularish) with different staining ‐ islets of Langerhans.

Question 28

What is the normal blood concentration of glucose?

Answer 28

Between 4 and 6 mmol dm^-3

Question 29

Define hypoglycaemia.
What is the main cause of it?
What can it cause?

Answer 29

When a person’s blood glucose levels are too low for long periods of time.
An inadequate delivery of glucose to the body tissues and, in particular, the brain.
Mild hypoglycaemia may simply cause tiredness and irritability, however in severe cases there may be impairment of brain function and confusion, which may lead on to seizures, unconsciousness and even death.

Question 30

Define hyperglycaemia.

What can this lead to?

Answer 30

When a person’s blood glucose levels are too high for long periods of time.
Significant organ damage.

Question 31

What constantly monitors the concentration of glucose in the blood?
What hormone is released if blood glucose is too high?
What hormone is release if blood glucose is too low?

Answer 31

Alpha and beta cells in the islets of Langerhans.
Insulin.
Glucagon.

Question 32

What are insulin’s target cells?

Answer 32

Liver cells, muscle cells and some other body cells including those in the brain.

Question 33

What happens when insulin binds to an insulin receptor on a target cell?

Answer 33

The enzyme tyrosine kinase, associated with the receptor on the inside of the membrane, is activated. It cause phosphorylation of inactive enzymes in the cell. This activates the enzymes leading to a cascade of enzyme-controlled reactions inside the cell.

Question 34

List the effects insulin has on the cell

Answer 34

More transporter proteins specific to glucose are placed into the cell surface membrane. This is achieved by causing vesicles containing these transporter proteins to fuse with the membrane.
More glucose enters the cell.
Glucose in the cell is converted to glycogen for storage (glycogenesis).
More glucose is converted to fats.
More glucose is used in respiration.

Question 35

What is glucagon’s target cells?

Answer 35

Hepatocytes

Question 36

What happens when glucagon binds to a glucagon receptor on a target cell?

Answer 36

It stimulates a G protein inside the membrane, which activates the adenyl cyclise inside each cell. The adenyl cyclase converts ATP to cAMP, which activates a series of enzyme-controlled reactions in the cell.

Question 37

List the effects glucagon has on the cell

Answer 37

Glycogen is converted to glucose (glycogenolysis) by phosphorylase A, which is one of the enzymes activated in the cascade.
More fatty acids are used in respiration.
Amino acids and fats are converted into additional glucose, by glucogeonosis.

Question 38

Explain the steps in how the body carries out negative feedback when there’s a fall in blood glucose concentration

Answer 38

Detected by alpha cells in the islets of Langerhans.
Alpha cells secrete glucagon into the blood.
Glucagon detected by receptors on liver cells.
Liver cells convert glycogen to glucose and release glucose into the blood.

Question 39

Explain the steps in how the body carries out negative feedback when there’s a rise in blood glucose concentration

Answer 39

Detected by beta cells in the islets of Langerhans.
Beta cells secrete insulin into the blood.
Insulin detected by receptors on liver and muscle cells.
Liver and muscle cells remove glucose from the blood and convert glucose into glycogen.

Question 40

Define diabetes mellitus.

What can this lead to?

Answer 40

A condition in which the body is no longer able to control its blood glucose concentration effectively.
This can lead to hyperglycaemia after a meal rich in sugars and other carbohydrates, or hypoglycaemia after exercise or fasting.

Question 41

What are stem cells?

Answer 41

Unspecialised cells that have the potential to develop into any type of cell

Question 42

Explain Type 1 diabetes

Answer 42

A.K.A. insulin-dependent diabetes. It usually starts in childhood, it is thought to be the result of an autoimmune response in which the body’s immune system attacks and destroys the beta cells. They may also result from a viral attack.
A person with it is no longer able to synthesise sufficient insulin and cannot store excess glucose as glycogen. Excess glucose in the blood is not removed quickly, leaving a prolonged period of high concentration. However, when the blood glucose falls, there’s no store of glycogen that can be used to release glucose. They suffer a ‘hypo’ - a period of hypoglycaemia.

Question 43

Explain Type 2 diabetes

Answer 43

A.K.A. non-insulin-dependent diabetes. They can produce insulin, but not enough. As people age, their responsiveness to insulin declines. This is probably because the specific receptors on the surface of the liver and muscle cells become less responsive and the cells lose their ability to respond to the insulin in the blood. The blood glucose concentration is almost permanently raised, which can damage major organs and circulation.

Question 44

What factors seem to bring an earlier onset of Type 2 diabetes?

Answer 44

Obesity, lack of regular exercise, high diet in sugars, particularly refined sugars, Asian or Afro-Caribbean origin, family history.

Question 45

Explain treatment for Type 1 diabetes

Answer 45

Usually treated using insulin injections. The blood glucose concentration must be monitored and the correct dose of insulin administered to keep the glucose concentration fairly stable.
Alternatives:
Insulin pump therapy - small device that constantly pumps insulin at a controlled rate into the bloodstream through a needle that is permanently inserted under the skin.
Islet cell transplantation - healthy beta cells from the pancreas of a dead guy are implanted into the Type 1 pancreas guy.
A complete pancreas transplant.
Recent research shows possible stem cells.

Question 46

Explain treatment for Type 2 diabetes

Answer 46

Usually treated by changes in lifestyle. They’ll be advised to lose weight, exercise regularly and carefully monitor their diet, taking care to match carbohydrate intake and use. This may be supplemented by medication that reduces the amount of glucose the liver releases to the bloodstream or that boosts the amount of insulin released from the pancreas. Further treatment may include insulin injections or other drugs that slow down the absorption of glucose from the digestive system.

Question 47

Where was insulin originally sourced from?

What about now?

Answer 47

Used to be extracted from the pancreas or animals - usually pigs as this matches human insulin the closest.
However, more recently, insulin has been produced by E. coli that have undergone genetic modification to manufacture human insulin.

Question 48

List the advantages of using insulin from genetically modified bacteria

Answer 48

It’s an exact copy of human insulin, therefore it’s faster acting and more effective.
Less chance of developing insulin tolerance.
Less chance of rejection due to an immune response.
Lower risk of infection.
Cheaper to manufacture than extract from animals.
The manufacturing process is more adaptable to demand.
Some people are less likely to have moral objections to manufacturing than extracting from animals.

Question 49

Explain what happens when blood glucose is too high

Answer 49

Beta cells detect rise in blood glucose level. This stimulates insulin production by beta cells in the pancreas. Glucagon production by alpha cells in inhibited. Insulin is secreted into the blood and binds to receptors on target cells (hepatocytes and muscle cells). More glucose channels inserts into plasma membrane and more glucose enters cells. Glucose is converted to glycogen and fats. This increases the rate of glucose used in respiration. This results in less glucose in the blood.

Question 50

Explain what happens when blood glucose is too low

Answer 50

Alpha cells detect fall in blood glucose level. This stimulates glucagon production by alpha cells. Insulin production is inhibited by beta cells. Glucagon is secreted into the blood and binds to receptors on target cells (hepatocytes). This causes hydrolysis of glycogen to glucose, the conversion of fats and amino acids to glucose and the use of more fatty acids in respiration. The glucose is released into the blood = more glucose in the blood.

Question 51

Define glycogenesis

Answer 51

The conversion of glucose to glycogen

Question 52

Define glycogenolysis

Answer 52

Hydrolysis of glycogen to glucose

Question 53

Define gluconeogenesis

Answer 53

The conversion of fats and amino acids to glucose