chapter 14 p4

Question 1

Potential use of stem cells in diabetes treatment:
p1

Answer 1

• For decades, diabetes researchers have been searching for ways to replace the faulty B cells in the pancreatic islets of diabetic sufferers.
• Each year, over 1000 people with type 1 diabetes receive a pancreas transplant.
• After a year, over 80% of these patients have no symptoms of diabetes and do not have to take insulin.
• However, the demand for transplantable pancreases far outweighs their availability.
• The risk of having a transplant can also be a greater health risk 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 2

Potential use of stem cells in diabetes treatment:
p2

Answer 2

• Doctors have attempted to cure diabetes by injecting patients with pancreatic B islet cells, but fewer than 8% of cell transplants performed have been successful.
• The immunosuppressant drugs used to prevent rejection of these cells increases the metabolic demand on insulin-producing cells.
• Eventually this exhausts their capacity to produce insulin.
• As type 1 diabetes results from the loss of a single cell type, and there is evidence that a relatively small number of islet cells can restore insulin production, the disease is a perfect candidate for stem cell therapy.
• Totipotent stem cells have the potential to grow into any of the body’s cell types.
• Scientists have been researching the best type of stem cells and the signals required to promote their differentiation into B cells, either directly in the patient or in the laboratory before being transplanted.

Question 3

Potential use of stem cells in diabetes treatment:
p3

Answer 3

• It is likely that the stem cells used in diabetes treatment would be taken from embryos.
• To obtain the stem cells, the early embryo has to be destroyed.
• This means destroying a potential human life.
• However, the embryos used as a source for these stem cells would usually be destroyed anyway - they are ‘spare’ embryos from infertility treatments or from terminated pregnancies.
• Stem cells lines formed from a small number of embryos can be used to treat many patients - each treatment does not require a separate embryo.
• An alternative to using embryonic matter is that of using preserved umbilical stem cells.

Question 4

Stem cells offer many advantages over current therapies:

Answer 4

• donor availability would not be an issue - stem cells could produce an unlimited source of new B cells
• reduced likelihood of rejection problems as embryonic stem cells are generally not rejected by the body (although some evidence contradicts this).
• Stem cells can also be made by somatic cell nuclear transfer (SCNT)
• people no longer have to inject themselves with insulin.

Question 5

however… stem cells have disadvantages over current therapies:

Answer 5

because our ability to control growth and differentiation in stem cells is still limited, a major consideration is whether any precursor or stem-like cells transplanted into the body might induce the formation of tumours as a result of unlimited cell growth.

Question 6

• Coordinated responses

Answer 6

On many occasions the body responds to changes in its internal and external environment through a coordinated response.
The nervous and endocrine systems work together to detect and respond appropriately to stimuli.
One example of coordination between these two systems is the mammalian ‘fight or flight’ response.

Question 7

Fight or flight response: p1

Answer 7

• The fight or flight response is an instinct that all mammals possess.
• When a potentially dangerous situation is detected, the body automatically triggers a series of physical responses.
• These are intended to help mammals survive by preparing the body to either run or fight for life, hence the name of the response.
• Once a threat is detected by the autonomic nervous system, the hypothalamus communicates with the sympathetic nervous system and the adrenal-cortical system.
• The sympathetic nervous system uses neuronal pathways to initiate body reactions whereas the adrenal-cortical system uses hormones in the bloodstream.
• The combined effects of these two systems results in the fight or flight response.

Question 8

coordination of the fight or flight response diagram

Answer 8

Question 9

Fight or flight response: p2

Answer 9

• The sympathetic nervous system sends out impulses to glands and smooth muscles and tells the adrenal medulla to release adrenaline and noradrenaline into the bloodstream.
• These ‘stress hormones’ cause several changes in the body, including an increased heart rate.
• The release of other stress hormones which have a longer-term action from the adrenal cortex is controlled by hormones produced by the pituitary gland in the brain.
• The hypothalamus stimulates the pituitary gland to secrete adrenocorticotropic hormone (ACTH).
• This travels in the bloodstream to the adrenal cortex, where it activates the release of many hormones that prepare the body to deal with a threat.

Question 10

The physiological responses which occur as part of the fight or flight response:

Answer 10

Question 11

Action of adrenaline:

Answer 11

One of adrenaline’s main functions during the fight and flight response is to trigger the liver cells to undergo glycogenolysis so that glucose is released into the bloodstream.
This allows respiration to increase so more energy is available for muscle contraction.
Adrenaline is a hormone.
It is hydrophilic therefore cannot pass through cell membranes.
Adrenaline binds with receptors on the surface of a liver cell membrane and triggers a chain reaction inside the cell

Question 12

When adrenaline binds to its receptor:

Answer 12

the enzyme adenylyl cyclase (which is also present in the cell membrane) is activated.

Adenylyl cyclase triggers the conversion of ATP into cyclic adenosine mono-phosphate (cAMP) on the inner surface of the cell membrane in the cytoplasm.

The increase in CAMP levels activates specific enzymes called protein kinases which phosphorylate, and hence activate, other enzymes. In this example, enzymes are activated which trigger the conversion of glycogen into glucose.

Question 13

This model of hormone action is known as

Answer 13

the second messenger model.
The hormone is known as the first messenger (in this example, adrenaline) and CAMP is the second messenger.
One hormone molecule can cause many cAMP molecules to be formed.
At each stage, the number of molecules involved increases so the process is said to have a cascade effect (Figure 3).

Question 14

The human heart beats at

Answer 14

approximately 70 beats per minute at rest.
However, when you exercise, or in times of danger, it is essential that the heart rate increases to provide the extra oxygen required for increased respiration.

Question 15

Controlling heart rate:

Answer 15

Heart rate is involuntary and controlled by the autonomic nervous system.
The medulla oblongata in the brain is responsible for controlling heart rate and making any necessary changes.

two centres within the medulla oblongata, linked to the sinoatrial node (SAN) in the heart by motor neurones:

Question 16

two centres within the medulla oblongata, linked to the sinoatrial node (SAN) in the heart by motor neurones:

Answer 16

one centre increases heart rate by sending impulses through the sympathetic nervous system, these impulses are transmitted by the accelerator nerve

one centre decreases heart rate by sending impulses through the parasympathetic nervous system, these impulses are transmitted by the vagus nerve.

Which centre is stimulated depends on the information received by receptors in the blood vessels.

Question 17

two types of receptors which provide information that affects heart rate:

Answer 17

baroreceptors (pressure receptors) - these receptors detect changes in blood pressure.
For example, if a person’s blood pressure is low, the heart rate needs to increase to prevent fainting.
Baroreceptors are present in the aorta, vena cava, and carotid arteries.

chemoreceptors (chemical receptors)
these receptors detect changes in the level of particular chemicals in the blood such as carbon dioxide.
Chemoreceptors are located in the aorta, the carotid artery a major artery in the neck that supplies the brain with blood), and the medulla.

Question 18

Chemoreceptors: p1

Answer 18

Chemoreceptors are sensitive to changes in the pH level of the blood.
If the carbon dioxide level in the blood increases, the pH of the blood decreases because carbonic acid is formed when the carbon dioxide interacts with water in the blood.
If the chemoreceptors detect a decrease in blood pH, a response is triggered to increase heart rate - blood therefore flows more quickly to the lungs so the carbon dioxide can be exhaled.

Question 19

Chemoreceptors: p2

Answer 19

When the carbon dioxide level in the blood decreases, the pH of the blood rises.
This is detected by the chemoreceptors in the wall of the carotid arteries and the aorta.
This results in a reduction in the frequency of the nerve impulses being sent to the medulla oblongata.
In turn, this reduces the frequency of impulses being sent to the SAN via the sympathetic nervous system, and thus heart rate decreases back to its normal level.

Question 20

diagram of control of heart rate

Answer 20

Question 21

effect of excersize on cardiac output

Answer 21

Question 22

Baroreceptors:
p1

Answer 22

Baroreceptors present in the aorta and carotid artery wall detect changes in pressure.
If blood pressure is too high, impulses are sent to the medulla oblongata centre which decreases heart rate.
The medulla oblongata sends impulses along parasympathetic neurones to the SAN which decreases the rate at which the heart beats.
This reduces blood pressure back to normal.

Question 23

Baroreceptors:
p2

Answer 23

If blood pressure is too low, impulses are sent to the medulla oblongata centre which increases heart rate.
The medulla oblongata sends impulses along sympathetic neurones to the SAN which increases the rate at which the heart beats.
This increases blood pressure back to normal.

Question 24

Hormonal control:

Answer 24

Heart rate is also influenced by the presence of hormones. For example, in times of stress adrenaline and noradrenaline are released.
These hormones affect the pacemaker region of the heart itself - they speed up your heart rate by increasing the frequency of impulses produced by the SAN.

Question 25

Monitoring heart rate

Answer 25

Heart rate can be determined by taking a pulse. Each time the heart beats a surge of blood travels around the body, which can be felt as a pulse in your blood vessels. The most common places to take a pulse are at the wrist (radial artery) or in the neck (carotid artery). The number of pulses felt per minute is equivalent to the number of times your heart beats per minute (bpm). Many people who exercise regularly and have a keen interest in monitoring their fitness levels wear a pulse monitor.