Hormonal Communication

Question 1

Define the term “endocrine gland”.

Answer 1

A group of specialised cells which produce hormones and secrete them into the blood.

Question 2

Define the term “exocrine gland”.

Answer 2

A group of specialised cells which produce enzymes and release them via a duct into the duodenum.

Question 3

Define the term “hormone”.

Answer 3

Chemical messengers which travel around the body in the blood stream.

Question 4

Define the term “target tissue”.

Answer 4

Specific cells which hormones act on to stimulate a response.

Question 5

List 7 endocrine glands, the hormone they secrete and the general role of each hormone.

Answer 5

1) Pituitary gland - brain - produces growth hormone, adh and gonadotrophins which control growth of ovaries and testes.
2) Thyroid - throat - produces thyroxine, controls metabolism by controlling the rate glucose is used up in respiration, and promotes growth.
3) Adrenal gland - top of the kidneys - produces adrenaline, raises blood-glucose conc.
4) Testis - testicles - testosterone, controls sperm production and secondary sexual characteristics.
5) Pineal - brain - produces melatonin which affects reproductive development and daily cycles.
5) Thymus - chest - produces thymosin, promotes production and maturation of WBC.
6) Pancreas - Midriff - produces insulin, converts excess glucose to glycogen, lowering blood-glucose conc.
7) Ovary - produces oestrogen, controls ovulation and secondary sexual characteristics; progesterone prepares uterus lining for receiving an embryo.

Question 6

Describe how hormonal communication occurs.

Answer 6

• Hormones are secreted directly into the blood when a gland is stimulated.
• Once secreted, hormones travels around the body in the blood plasma.
• Hormones diffuse out of the blood and bind to receptors specific to that hormone, found on the target cells.
• Once bound to their receptors, the hormones stimulate the target cells to produce a response.

Question 7

State the location of the adrenal glands in the body and describe their structure.

Answer 7

• Located on top of the kidneys.
• Two distinct parts; adrenal cortex and adrenal medulla.
• Adrenal cortex: the outer region of the glands. Produces hormones that are vital to life e.g. cortisol and aldosterone.
• Adrenal medulla: the inner region of the glands, produces non-essential hormones such as adrenaline which helps the body react to stress.

Question 8

Describe the role of the adrenal cortex and the functions of the hormones produced.
(Glucocorticoids)

Answer 8

Production of hormones from adrenal cortex is controlled by hormones released from the pituitary gland.

Glucocorticoids:
- includes cortisol, which helps regulate metabolism by controlling conversion of fats, proteins and carbs to energy. Regulates blood pressure in response to stress.

• Also includes corticosterone, regulates immune response and inflammatory reactions.

Question 9

Describe the role of the adrenal cortex and the functions of the hormones produced.
(Mineralocorticoids)

Answer 9

• Aldosterone, controls blood pressure by maintaining balance of salt/water concentrations. Triggered by signals from the kidney.

Question 10

Describe the role of the adrenal cortex and the functions of the hormones produced.
(Androgens)

Answer 10

• Small amounts of male and female sex hormones. Important for women after the menopause.

Question 11

Describe the role of the adrenal medulla and the functions of the hormones produced.

Answer 11

Hormones of the adrenal medulla are released when the sympathetic nervous system is stimulated - occurs when under stress.

• Adrenaline, increases heart rate sending blood quickly to the muscles and brain. Rapidly raises blood glucose concentration levels by converting glycogen to glucose.
• Noradrenaline, works with adrenaline in response to stress, increases heart rate, widening pupils, widening of air passages in the lungs, narrowing blood vessels in non-essential organs to raise the blood pressure.

Question 12

Define the term “histology”.

Answer 12

Histology is the microscopic study of the structure of biological tissues.

Question 13

Describe the roles of the pancreas.

Answer 13

Functions as exocrine gland and exocrine gland:

• Exocrine, produces enzymes and releases via a duct into the duodenum.
• Endocrine, produces hormones and released them into the blood.

Question 14

What is the pancreas’s function as an exocrine gland?

Answer 14

• Most of the pancreas is exocrine glandular tissue.
• Responsible for producing digestive enzymes and pancreatic juice (an alkaline fluid).
• Enzymes and juice are secreted into ducts which lead to the pancreatic duct, from here they are released into the duodenum (the top part of the small intestine).
• Amylase, protease and lipase are produced.

Question 15

What is the pancreas’s function as an endocrine gland?

Answer 15

• There are islets of langerhans in the exocrine tissue which contain alpha and beta cells.
• Alpha cells produce glucagon, beta cells produce insulin.

Question 16

Draw a diagram of a pancreas section, label it and annotate with the functions of the structures labeled.

Answer 16

Two main structures:
- Islets of Langerhans; large spherical structure, endocrine tissue, produce and secrete hormones (contains alpha and beta cells).

• Pancreatic acini; small berry-like clusters, exocrine tissue, produce and secrete digestive enzymes.

Question 17

Identify the components of the pancreas in a photomicrograph of a stained section.

Answer 17

Dark pink surroundings are the pancreatic acini (the exocrine tissue) and the spherical, white-blue blobs are the islets of Langerhans (endocrine tissue).
(see pp.387)

Question 18

Define the term “α-cell”.

Answer 18

Alpha cell - present in the islets of Langerhans (endocrine tissue), they produce and secrete glucagon, which stimulates the conversion of glycogen to to glucose, thus raising blood-glucose concentration.

Question 19

Define the term “β-cell”.

Answer 19

Beta cell - present in the islets of langerhans (endocrine tissue), they produce and secrete insulin, which stimulates the conversion of glucose to glycogen, thus lowering blood-glucose concentration.

Question 20

Define the term “Islet of Langerhans”.

Answer 20

Specialised cells within the pancreas responsible for producing insulin and glucagon. Endocrine tissue.

Question 21

Define the term “acinus”.

Answer 21

Exocrine tissue in the pancreas. A small sac-like cavity surrounded by secretary cells. Produces digestive enzymes.

Question 22

Define the term “tubule/ central duct”.

Answer 22

Central duct - exit way for enzymes produced by acini tissue into the small intestine (duodenum).

Question 23

Define the term “pancreatic duct”.

Answer 23

Same as central duct - a tube leading from the pancreas to the duodenum.

Question 24

Define the term “insulin”.

Answer 24

A globular protein hormone involved in the regulation of blood-glucose concentration (responsible for the conversion of glucose to glycogen).

Question 25

Define the term “glucagon”.

Answer 25

A hormone found in the pancreas which promotes the break down of glycogen to glucose.

Question 26

State which cells monitor blood glucose levels.

Answer 26

Alpha and beta cells.

Question 27

State which cells monitor blood glucose levels.

Answer 27

Alpha and beta cells.

Question 28

State the normal blood glucose concentration.

Answer 28

90mg cm-3 of blood.

Question 29

Define the term “hepatocyte”.

Answer 29

Liver cells, take up 70 - 85% of liver’s mass.

Question 30

Name the two hormones involved in regulating blood glucose concentration.

Answer 30

Insulin, glucagon.

Question 31

State the condition in which insulin is released and from which cells, and describe how insulin has its effect on cells.

Answer 31

• Insulin is secreted into the bloodstream by beta cells which blood-glucose concentration goes above the norm.
• Most cells in the body have insulin receptors (glycoproteins) and when insulin binds to the glycoprotein, 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 enzymes within the cell which convert glucose to glycogen and fat. Rate of glycogeneis increased.

Question 32

State the effects insulin has on cells.

Answer 32

• increases rate of glucose absorption by cells
• increases respiratory rate of cells
• increases rate of glycogeneis (liver converting glucose to glycogen for storage)
• increases rate of glucose to fat conversion
• inhibits release of glucagon from alpha cells

Question 33

Define the term “glycogenesis”.

Answer 33

• conversion of glucose to glycogen.

Question 34

Define the term “glycogenolysis”.

Answer 34

• conversion of glycogen to glucose.

Question 35

Describe three factors that effect blood-glucose concentration.

Answer 35

• Diet, specifically carbohydrate-rich food.
• Level of stress (increased stress levels raises blood-glucose concentration).
• Level of exercise i.e. rate of respiration.

Question 36

Explain why insulin must be constantly secreted in order to maintain its effect.

Answer 36

Because it is broken down by enzymes in the cells of the liver.

Question 37

Explain why it is important that insulin is constantly being broken down by enzymes.

Answer 37

As your blood-glucose concentration returns to the norm, you do not want to maintain a higher level of glycogeneis (glucose to glycogen) so it must be constantly broken down to make sure you don’t have too low a glood-glucose concentration.

Question 38

State the condition in which glucagon is released and from which cells, and describe how glucagon has its effect on cells.

Answer 38

• Secreted by alpha cells of islets of langerhans when blood-glucose concentration drops below the norm.
• Liver and fat cells are the only ones that have glucagon receptors so they are the only ones that respond.
• 0

Question 39

State the effect glucagon has on cells.

Answer 39

• glycogeneis, the liver breaks down its glycogen store into glucose and releases it back into the bloodstream. Increases glycogenolysis.
• reducing the amount of glucose reabsorbed by the liver cells.
• increasing gluconeogenesis, increasing the conversion of amino acids and glycerol into glucose in the liver.

Question 40

. Draw a flow chart showing the negative feedback system that controls blood sugar level.

Answer 40

(pp. 391)
- Blood glucose concentration is self-regulating.
- The quantity of insulin and glucagon that is released determines blood-glucose conc.
- blood-glucose conc is not fixed but fluctuates around a set point.
- When blood glucose conc rises above the norm the beta cells detect this and produce insulin, the alpha cells also detect this and reduce their secretion of glucagon.
- When blood-glucose conc returns to normal this is detected by the alpha cells.
- This is an example of negative feedback because corrective measures are turned on and off, returning the system to its original.

Question 41

. Draw a flow chart showing the negative feedback system that controls blood sugar level.

Answer 41

(pp. 391)
- Blood glucose concentration is self-regulating.
- The quantity of insulin and glucagon that is released determines blood-glucose conc.
- blood-glucose conc is not fixed but fluctuates around a set point.
- When blood glucose conc rises above the norm the beta cells detect this and produce insulin, the alpha cells also detect this and reduce their secretion of glucagon.
- When blood-glucose conc returns to normal this is detected by the alpha cells.
- This is an example of negative feedback because corrective measures are turned on and off, returning the system to its original.

Question 42

Describe how insulin is secreted by beta cells in response to a high blood glucose concentration.

Answer 42

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. The inside of the cell is at potential of -70mV with respect to the outside.
2) When blood-gluc 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) ATP binds to the potassium channels and causes them to close.
5) Potassium ions can no longer diffuse out of the cell so the potential difference reduces to -30mV and depolarisation.
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 by exocytosis.

Question 43

Define the term “diabetes mellitus”.

Answer 43

Medical condition which affects a person’s ability to control their blood-glucose concentration.

Question 44

Define the term “Type 1 diabetes”.

Answer 44

Inability to produce insulin due to faulty beta cells. Thought that the condition arises due to an autoimmune response.

Question 45

Define the term “Type 2 diabetes”.

Answer 45

When a person’s beta cells do not produce enough insulin, or their body cells are unable to respond to insulin. This means they cannot control their blood sugar levels. Often due to faulty glycoprotein insulin receptor on the cell membrane. Cells lose their responsiveness to insulin and therefore do not take up enough glucose from the bloodstream.

Common lifestyle cause is obesity.

Question 46

Define the term “hyperglycaemia”.

Answer 46

Excess of glucose in the bloodstream (often associated with either type of diabetes, when untreated).

Question 47

Define the term “hypoglycaemia”.

Answer 47

Deficiency of glucose in the bloodstream.

Question 48

How is type 1 diabetes treated?

Answer 48

• Regular injections of insulin (therefore insulin-dependent).
• Blood-glucose concentration must be regularly tested to determine the volume of insulin injection needed.
• Insulin administered increases the uptake of glucose by cells and so causes glycogenesis to occur, resulting in a decrease of blood-glucose concentration.
• Too much or too little insulin will result in either hypoglycaemia or hyperglycaemia, respectively.

Question 49

How is type 2 diabetes treated?

Answer 49

• Regulating carbohydrate intake in relation to exercise levels.
• Increased exercise levels and weight loss.
• In some cases, drugs are also used which stimulate insulin production.

Question 50

List 4 benefits of using insulin produced from genetically engineered bacteria rather than from pigs to treat diabetes. For each benefit explain why the benefit exists.

Answer 50

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

Question 51

Describe how stem cells could be used to treat diabetes.

Answer 51

• Could be used to replace faulty beta cells in pancreatic islets.
• Problem occurs from loss of a single cell type; evidence that a small amount of islet cells can restore insulin production.
• Totipotent stems cells could be used because they have the potential to grow into any type of cell.
• Stem cells could be extracted from embryos or preserved umbilical stem cells.
• Stem cells can also be made from somatic cell nuclear transfer.

Question 52

Describe the potential benefits of stem cell treatment for Type 1 diabetes over insulin injection or whole pancreas transplantation.

Answer 52

• Donor availability would not be an issue, stem cells could produce an unlimited source of new beta cells.
• Reduced likelihoods of rejection problems as embryonic stem cells are generally not rejected by the body.
• People no longer have to inject themselves with insulin.

Question 53

Describe one risk of using stem cells to treat Type 1 diabetes.

Answer 53

• Slight risk of rejection.

- Risk that stem cells transplanted into the body might induce the formation of tumours due to unlimited cell growth.

Question 54

Explain why stem cell treatment is not likely to be suitable for treating Type 2 diabetes.

Answer 54

All body cells are faulty in type 2 diabetes so they cannot all be replaced by stem cells, however in type 1 diabetes only beta cells are faulty so they are possible to replace.