Control of heart rate

Figure 2 shows a drawing of a myelinated motor neurone.

Name the parts labelled A to D.

Osmotic demyelination syndrome (ODS) results in destruction of the myelin sheath of neurones in the brain.

ODS can increase reflex response times.

Explain why.

The parasympathetic nervous system (PNS) uses acetylcholine as its neurotransmitter. Atropine is an anticholinergic drug that attaches to postsynaptic receptors.

Atropine can be used to increase the heart rate in patients with bradycardia (a slower than normal heart rate).

Use the information provided to explain how atropine causes an increase in the heart rate.

One study has suggested that the atropine dosage for severely obese male patients should be 0.01 mg kg^–1 of lean body weight (LBW).

LBW is determined by using this equation.

where TBW = total body weight BMI = body mass index

Calculate the suggested dosage of atropine, in mg, for a severely obese male patient whose:

• TBW = 115.2 kg

• BMI = 41

Give your answer to 3 significant figures.

Show your working.

Describe the myogenic stimulation of the heart and how the regular contraction of the atria and ventricles is coordinated.

Do not include the autonomic nervous system in your answer.

Atrial fibrillation (AF) is a condition that causes an irregular heart rate. Scientists used a statistical test to investigate the association between different factors and the risk of developing AF.

Table 2 shows some of the scientists’ results, including the probability (P) values obtained using the statistical test.

What can you conclude from Table 2 ?

Describe and explain how three features of the cells in the proximal convoluted tubule allow the rapid reabsorption of glucose into the blood.

Antidiuretic hormone (ADH) binds to V receptors found in cell-surface membranes in two parts of a nephron.

Name the two parts of a nephron where V receptors are found.

V receptors only bind with ADH.

Suggest and explain why.

A decrease in blood pressure stimulates the release of ADH.

Give the location of the receptors that detect a decrease in blood pressure and explain how the release of ADH will affect blood pressure.

ATP is essential for muscle contraction (line 1).

Describe the roles of ATP in muscle contraction.

Calculate how long maximum exercise would last if ATP was not resynthesised (lines 3–4).

Describe and explain how taking creatine supplements (lines 5–6) and ‘carbohydrate loading’ (lines 6–7) can improve performance of different types of muscle fibres during different types of exercise.

Suggest and explain how GLUT4 and CD36 transport proteins (lines 10–11) are beneficial during exercise.

An increase in muscle activity causes an increase in heart rate (lines 12–14).

Describe and explain how.

Following a body injury, bone marrow stem cells move to the site of damage and undergo cell differentiation.

Figure 5 shows how this differentiation occurs.

Suggest how SCFR is destroyed by a lysosome.

After a heart attack, cardiomyocytes (cardiac muscle cells) die, and become infarcted tissue. Infarcted tissue cannot contract.

Stem cells in bone marrow cannot move to the infarcted tissue and differentiate into cardiomyocytes. Scientists used laboratory rats to investigate if bone marrow stem cell transplants could be used to repair infarcted tissue resulting from a heart attack.

They split the rats into three groups.

• Control group did not get a transplant of bone marrow stem cells.

• c-KIT+ group got a transplant of bone marrow stem cells with a functioning c-KIT gene.

• c-KIT– group got a transplant of bone marrow stem cells with no functioning c-KIT gene.

After 9 days, the scientists measured the mean ventricular blood pressure of each of the three groups.

Figure 6 shows their results.

The differences between the groups were all statistically significant.

Using all of the information, suggest explanations for the results for the Control group and the c-KIT– group shown in Figure 6.

Nine days after transplantation, the c-KIT+ group showed that 68% of infarcted tissue was made up of new cardiomyocytes. The control group had no new cardiomyocytes.

Assuming that mean ventricular blood pressure is directly proportional to the number of cardiomyocytes, calculate the percentage of infarcted tissue that was made up of new cardiomyocytes in the c-KIT– group.

All new cardiomyocytes produced:

• Connexin-43, a channel protein that allows electrical impulses to pass between cardiomyocytes

• GATA-4, a transcriptional factor that stimulates the expression of genes for actin and myosin.

Suggest how production of Connexin-43 and GATA-4 could give the result seen in the c-KIT+ group in Figure 6 (on page 13).

Do not include details of transcription or translation in your answer.

Read the following passage.

North American black bears can hibernate for up to 7 months without food or water. The bears survive using the fat stores in their bodies. The bears build up the fat stores during the summer. During hibernation, the heart rate of black bears decreases from a summer mean of 55 beats per minute to 14 beats per minute. Their metabolic rate falls by 75%. 5

In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation. Uncoupling proteins are found in the inner mitochondrial membrane and act as proton channels during chemiosmosis. However, these proton channels do not generate ATP.

In the mountains of North America, when winter changes into spring, the coat 10 colour of snowshoe hares changes from white to brown. Climatic changes have caused the snow to melt earlier. This has reduced the survival rate of snowshoe hares in these habitats. The change in coat colour occurs when new fur replaces old fur. This is called moulting. Recent research has shown that snowshoe hares within a population moult at different times. Moulting at 15 different times could be a major factor in ensuring the survival of snowshoe hare populations.

Use the information in the passage and your own knowledge to answer the following questions.

Black bears can hibernate for up to 7 months without food or water (lines 12).

Suggest and explain how.

During hibernation, the heart rate and the metabolic rate of black bears decrease

Use your knowledge of the nervous control of heart rate to describe how these are linked.

In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation (lines 67).

Suggest and explain how.

Climatic change has reduced the survival rate of snowshoe hares in mountain habitats

Suggest and explain how.

Snowshoe hares within a population moult at different times (line 15).

Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats.

Damage to the myelin sheath of neurones can cause muscular paralysis (lines 2–4).

Explain how.

Sometimes Guillain–Barré syndrome causes heart rate irregularities (lines 4–5).

Suggest and explain why.

The first successful drug trial to reduce concentrations of huntingtin in the brain used single-stranded DNA molecules (lines 13–14).

Suggest and explain how this drug could cause a reduction in the concentration of the protein huntingtin.

Scientists from the first successful drug trial to reduce concentrations of huntingtin (lines 9–11) reported that the drug is not a cure for Huntington’s disease.

Suggest two reasons why the drug should not be considered a cure. Do not include repeats of the drug trial in your answer.

Suggest two reasons why people had the drug injected into the cerebrospinal fluid (lines 12–13) rather than taking a pill containing the drug.

Figure 2 shows a photograph of a dissected heart.

Name valve A and chamber B.

Give two safety precautions that should be followed when dissecting a heart.

Explain how valve A in Figure 2 maintains a unidirectional flow of blood.

A research scientist investigated the effect of caffeine on heart rate in human volunteers.

The scientist divided volunteers into three groups. Each group was given the same volume of fluid.

• Each member of Group I was given a sports drink containing caffeine and sugar.

• Each member of Group J was given a sports drink containing caffeine and no sugar.

• Each member of Group K was given water.

The scientist recorded the volunteers’ heart rate before the drink was given and for 120 minutes after the drink was given.

Her results can be seen in Figure 3.

Caffeine affects the autonomic nervous system.

Suggest how caffeine could account for the results of Group I in Figure 3 at 60 minutes.

Before taking the drink, the mean heart rate of Group J was 68 beats per minute.

Fifteen minutes after taking the drink, the mean volume of blood leaving the hearts of Group J was 4700 cm³ per minute.

Calculate the mean volume of blood leaving the heart at each beat fifteen minutes after taking the drink.

The increase seen in Group I could be due to the combination of caffeine and sugar.

Suggest one drink to be given to an additional group that should be investigated to find out if this is true.

Give a reason for your answer.

Group to be given

Exercise causes an increase in heart rate.

Describe the role of receptors and of the nervous system in this process.

AMP-activated protein kinase (AMPK) is an enzyme that regulates a number of cellular processes. Exercise leads to activation of AMPK.

Figure 1 shows one effect of activation of AMPK during exercise.

CPT1 is a channel protein that transports fatty acids into mitochondria.

Using Figure 1, explain the benefit of activation of AMPK during exercise.