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Hormones

Hormones

(a) define the terms:

(b) explain the meaning of the terms first messenger and second messenger, with reference to adrenaline and cyclic AMP (cAMP)

First messenger – the hormone that transmits a signal around the body.

Second messenger – molecules called cAMP that transmits a signal inside the cell.

Adrenaline:

The adrenaline receptor on the outside of the cell surface membrane has a shape complementary to the shape of the adrenaline molecule. The receptor is associated with an enzyme on the inner surface of the cell surface membrane. The enzyme is called adenyl cyclase.

 

  1. Adrenaline in the blood binds to its specific and complementary receptor on the cell surface membrane. The adrenaline molecule is the first messenger.
  2. When it binds to the receptor is activates the enzyme adenyl cyclase, which converts ATP to cyclic AMP (cAMP – a second messenger).
  3. The cAMP can then cause an effect inside the cell by activating enzyme action.

 

(c) describe the functions of the adrenal glands

The adrenal glands are found lying just above the kidneys – one of each side of the body. Each gland can be divided into a medulla region and a cortex region.

 (d) describe, with the aid of diagrams and photographs, the histology of the pancreas, and outline its role as an endocrine and exocrine gland

The pancreas is a small organ lying below and behind the stomach. It is an unusual organ in that it has both exocrine and endocrine functions.

Pancreatic duct – a tube that collects all the secretions from the exocrine cells in the pancreas and carries the fluid to the small intestine.

α cells – found in the islets of Langerhans and secrete the hormone glucagon.

β cells – found in the islets of Langerhans and secrete the hormone insulin.

Glucagon – the hormone that causes blood glucose levels to rise.

Insulin – the hormone that causes blood glucose levels to fall.

(e) explain how blood glucose concentration is regulated, with reference to insulin, glucagon and the liver

The cells in the islets of Langerhans monitor the concentration of glucose in the blood. The normal concentration of glucose is 80-120mg per 100cm3 of blood, or 4-6 mmol dm-3.

(f) outline how insulin secretion  is controlled, with reference to potassium channels and calcium channels in beta cells

When glucose levels are too high:

(g) compare and contrast the causes of Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes mellitus

Diabetes mellitus – a disease in which blood glucose concentrations cannot be controlled effectively, by the body.

Hyperglycaemia – the state in which the blood glucose concentration is too high (hyper = above, glyc = gucose, aenmia = blood).

Hypoglycaemia – the state in which the blood glucose concentration is too low (hypo = under).

(h) discuss the use of insulin produced by genetically modified bacteria, and the potential use of stem cells, to treat diabetes mellitus

 

Producing Insulin from Genetically Modified Bacteria:

Insulin used to be extracted from the pancreas of animals – usually from pigs as this matches human insulin most closely. However, more recently insulin can be produced by bacteria that have been genetically engineered to manufacture human insulin. Advantages of using genetically engineered insulin include:

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

Treatment of Diabetes:

Type I diabetes is treated using insulin injections. The blood glucose concentration must be monitored and the correct dose of insulin must be administered to ensure that the glucose concentration remains fairly stable.

Scientists have recently found precursor cells in the pancreas of adult mice. These cells are capable of developing into a variety of cell types and may be true stem cells, which can be used to treat type I diabetes.

Type II diabetes is treated by careful monitoring and control of the diet. Care is taken to match carbohydrate intake and use. This may eventually be supplemented by insulin injection or use of other drugs which slow down the absorption of glucose from the digestive system.

(i) outline the hormonal and nervous mechanisms involved in the control of heart rate in humans

The heart pumps blood around the circulatory system. Blood supplies the tissues with oxygen and nutrients such as glucose, fatty acids and amino acids. It also removes waste products, such as carbon dioxide and urea, from the tissues so that they do not accumulate and inhibit cell metabolism.

How does the heart adapt to supply the body with more oxygen and glucose?

  • Increase heart rate – increase in the number of beats per minute.
  • Increase the strength of contraction.
  • Increase the stroke volume – increase the volume of blood pumped per beat.

Control of Heart Rate:

The cardiac muscle is myogenic – the heart will contract and relax by itself. The heart contains its own pacemaker called the sinoatrial node (SAN). The SAN is a region of tissue that can initiate an action potential, which travels as a wave of excitation over the atrial walls, through the atrioventricular node (AVN) and down the Purkyne fibres to the ventricles, causing them to contract.

The heart is supplied by nerves from the medulla oblongata of the brain, which connect to the SAN. These do not initiate a contraction, but they can affect the frequency of the contractions.

  • Action potentials sent down the sympathetic nerve increases the heart rate.
  • Action potentials sent down the vagus nerve decreases the heart rate.

Adrenaline made in the medulla of the adrenal glands can also increase the heart rate.

Under resting conditions the heart rate is controlled by the SAN. This has a set frequency at which is initiates a wave of excitation. The frequency of excitation waves can be controlled by the cardiovascular centre in the medulla oblongata. There are many factors that affect the heart rate:

  • Movement of limbs is detected by stretch receptors in the muscles. These send impulses to the cardiovascular centre informing it that extra oxygen may soon be needed – increases heart rate.
  • The carbon dioxide produced when exercising reacts with water in the blood plasma and reduces the pH. The change in pH is detected by chemoreceptors in the carotid arteries, the aorta and the brain. The chemoreceptors send impulses to the cardiovascular centre – increases heart rate.
  • Adrenaline is secreted in response to stress, shock, anticipation or excitement to help prepare the body for activity – increases heart rate.
  • When we stop exercising the concentration of carbon dioxide in the blood falls, reducing the activity of the sympathetic pathway – decreases heart rate.
  • Blood pressure is monitored by stretch receptors in the walls of the carotid sinus. If blood pressure is too high, the stretch receptors send signals to the cardiovascular centre – decreases heart rate.