Physiology Essay: Questions.

Immunology

QUESTION 1

Which type of immunity is expressed in the following scenarios? Choose between:

• Non-specific (first line defence)
• Specific (antibody-mediated)
• Specific (cell-mediated immunity)

(0.5 mark each – total 2 marks)

Scenario	Type of immunity
Bacterial septicaemia (bacterial contamination in systemic circulation)
The pH of hydrochloric acid in the stomach acts to destroy ingested bacteria
A liver cell mutates and becomes cancerous
A virus multiplies inside the epithelial cells in your throat.

 qUESTION 2

Describe how bone cells respond to the hormones involved in the homeostasis of blood calcium ion concentration.  (3 marks) 

QUESTION 3

Choose ONE of the below scenarios and highlight this row bold.  State which general property of adaptive immunity the scenario illustrates in the second column. Select ONE phrase (from the list below) that BEST describes what is happening at a cellular level to result in this property of adaptive immunity. Write the letter corresponding to this phrase in the third column.  An example is included in italics.  (1 mark)

Scenario	General property of immunity	Explanation
Even though your body contains a relatively small number of lymphocytes, your immune system is capable of mounting a response against almost any antigen it encounters.	Versatility	A
Generally, after an initial infection, subsequent immune responses to that antigen are faster, stronger and more sustained.
You can suffer from ‘the flu’ multiple times throughout your lifetime.
Your immune system is capable of distinguishing between antigens on your own cells, and those of an invading pathogen.

Possible phrases are listed below. Not all phrases will need to be used and only ONE phrase is required per row. If you record more than one, you will not be awarded any marks for your explanation. 

A	There are millions of different lymphocyte populations, each of which is sensitive to a different antigen. Lymphocytes proliferate when activated by their specific antigen.
B	The immune response ignores self-antigens and targets non-self antigens.
C	B cells differentiate into T cells to create a long-lived immune response.
D	Each T and B cell can recognise many antigens and respond to a wide variety of possible threats.
E	Each T or B cell has receptors that respond to only one antigen and ignores all others.
F	Phagocytes have a reduced ability to destroy pathogens during subsequent infections.
G	T cells are versatile because they produce copious quantities of antibodies that can respond to a wide variety of threats.
H	Activated lymphocytes produce two groups of cells: one group that attacks the invader immediately, and another that remains inactive unless it is exposed to the same antigen at a later date

QUESTION 4

1. Using the patellar reflex as an example, explain the purpose of a neural reflex. (2 marks)

1. What happens to the patellar reflex when someone clasps their hands and squeezes them strongly? Why does this occur? (2 marks) 

QUESTION 5

Using the diagram provided as a prompt, outline the four steps involved in the transmission of an electrical impulse from the presynaptic neurone to the post synaptic neurone.  (4 marks)

 

Step	Outline
1
2
3
4

QUESTION 6

Describe the series of events occurring at a neuromuscular junction required for muscular contraction. (3 marks) 

QUESTION 7

Think about how the renin-angiotensin-aldosterone system acts to maintain normal blood pressure. Susan has sustained damage to her adrenal glands.  Consequently, her circulating levels of aldosterone are abnormally low. 

1. Where are the target cells for aldosterone located in the body? (1 mark)

1. What do you expect the lack of aldosterone to do to Susan’s blood pressure? Explain your answer. (3 marks) 

QUESTION 8

Explain the term ‘normal sinus rhythm’.  (1 mark) 

QUESTION 9

For each of the scenarios below, indicate whether you would you expect resting heart rate to be greater or less than that associated with normal sinus rhythm.  Explain the cardiac physiology underlying the identified change.  (4 marks)

Heart rate	Situation	Explanation
	A person of average fitness running a 5km fun run.
	An endurance athlete at rest.

QUESTION 10

Explain how baroreceptors contribute to control blood pressure during a short period of widespread vasodilation.  (3 marks)

QUESTION 11

Parents, a father who is heterozygous for blood group A and a mother who is heterozygous for blood group B, are wondering what, if any, are their chances of producing a child with blood group O.

1. State the genotype of each parent, and complete the Punnett square below. (2 marks)

Parent	Genotype
Father
Mother

1. 
   What is the chance of these parents producing a blood group O child? Explain your reasoning. (1 mark) 

QUESTION 12

Describe TWO differences between the intrinsic and extrinsic pathways in blood clotting.  (2 marks)

QUESTION 13

The Wigger’s diagram (below) represents pressure and volume relationships in the left side of the heart during one cardiac cycle.  To answer this question, you should focus on the changes in pressure in different chambers of, or vessels leading from, the left side of the heart.

For ONE of the labelled points, state which valve is open/closed at that time.  Highlight your chosen point in bold.  You must also explain WHY that valve opened/closed and where the blood is flowing immediately after this point in time, due to the change in position of the valve.  An example is provided in italics.  (2 marks)

Label	Valve (name and open/closed)	Explanation
A
B
C
D	Left AV/bicuspid valve opens	The pressure in the left ventricle becomes lower than that in the left atrium.  Blood flows from the left atrium to the left ventricle.

 QUESTION 14

Consider the events occurring after you have eaten a high carbohydrate meal.  For each of the organs listed in the table below, describe ONE mechanical and ONE chemical digestion event that will contribute to the digestion of carbohydrates.  (2 marks per location - 6 marks total)

Location	Mechanical digestion event	Chemical digestion event
Mouth
Stomach
Small intestine

QUESTION 15

Continue to consider the events occurring after you have eaten a high carbohydrate meal.  In the table below explain how the listed organs are involved in the absorption and metabolism events (specific to carbohydrates) that occur after this meal. (1 mark per location - 2 marks total)

Location	Absorption and metabolism events
Small intestine
Liver

QUESTION 16

The figure below illustrates inspiration and expiration.  Refer to this figure to answer the following questions.  (0.5 marks each - 3 marks total) 

Question	Answer
Contraction of which muscle/s produces the movement labelled "1"?
Contraction of which muscle/s produces the movement labelled “2”?
At label “3”, is pressure outside greater than or less than pressure inside the lungs?
Is the pressure in the space labelled "4", higher or lower compared to the atmospheric pressure?
At label “8”, is pressure outside greater than or less than pressure inside the lungs?
Name any ONE muscle that contracts to cause the extra movement required when you need to expire forcefully (indicated by the arrows labelled "6" and "7").

 QUESTION 17

1. Complete the below table of partial pressures in internal respiration. (1 mark)

	pO2 (mmHg)	pCO2 (mmHg)
Capillary
Tissue

Describe how the differences in partial pressures drives the direction of gas movement between the blood and tissues (2 marks) 

QUESTION 18

1. Describe the epithelium lining in the trachea? (1 mark)

1. How does the structure of this epithelium relate to its function in the trachea? (1 mark)

QUESTION 19

What personal protective equipment should be worn when handling someone else’s urine?  Explain.  (1 mark) 

QUESTION 20

The results of dipstick urinalysis of two urine samples are listed below.

Sample 1 belongs to a 16-year-old male ‘gamer’ who has locked himself in his room all weekend to play computer games (he didn’t really even come out to eat or drink).  

Sample 2 belongs to a 22-year-old female triathlete who is careful with her diet, hydration, and almost exercises to excess.

For each parameter, fill in the normal values. (Hint: Refer to the Week 10 laboratory activity to get you started).

Parameter	Normal values	Sample 1	Sample 2
Colour		Dark yellow	Reddish tinge
Glucose		-	-
Bilirubin		-	-
Ketones		++	-
Specific gravity		1.039	1.010
Blood		-	++
pH		5.5	6.0
Protein		-	++
Nitrite		-	-
Leukocytes		-	-

 Choose ONE of the samples described above and answer the following questions in the space provided.

1. Compare the normal and sample values. List any abnormalities you observe in the section below. Are they higher or lower than normal? (1 mark)
2. Give a situation in which you might expect to see these changes in an otherwise healthy (1 mark)
3. What might have been happening in the nephron to cause these abnormal results? Explain your observed abnormalities by linking them with the part of the nephron involved and the process involved (ie filtration, secretion or reabsorption). Ensure that any relationships between the abnormal readings are made clear in your response.  (2 marks)

Chosen sample:
A
B
C

QUESTION 21

In regards to the nervous endocrine system, explain the appearance of urine with a higher than normal specific gravity.  (3 marks)

Immunology

QUESTION 1

Which type of immunity is expressed in the following scenarios? Choose between:

• Non-specific (first line defence)
• Specific (antibody-mediated)
• Specific (cell-mediated immunity)

(0.5 mark each – total 2 marks)

Scenario	Type of immunity
Bacterial septicaemia (bacterial contamination in systemic circulation)	Specific (cell-mediated immunity)
The pH of hydrochloric acid in the stomach acts to destroy ingested bacteria	Non-specific (first line defence)
A liver cell mutates and becomes cancerous	Specific (cell-mediated immunity)
A virus multiplies inside the epithelial cells in your throat.	Specific (antibody-mediated)

QUESTION 2

Describe how bone cells respond to the hormones involved in the homeostasis of blood calcium ion concentration.  (3 marks)

when the blood calcium is low, the parathyroid gland secretes parathyroid hormone which has several effects to various organs like kidneys and bones. In the bones, the parathyroid hormone increases bones breakdown in the bone cells (osteoblasts) to release calcium ions. 

QUESTION 3

Choose ONE of the below scenarios and highlight this row bold.  State which general property of adaptive immunity the scenario illustrates in the second column. Select ONE phrase (from the list below) that BEST describes what is happening at a cellular level to result in this property of adaptive immunity. Write the letter corresponding to this phrase in the third column.  An example is included in italics.  (1 mark)

Scenario	General property of immunity	Explanation
Even though your body contains a relatively small number of lymphocytes, your immune system is capable of mounting a response against almost any antigen it encounters.	Versatility	A
Generally, after an initial infection, subsequent immune responses to that antigen are faster, stronger and more sustained.
You can suffer from ‘the flu’ multiple times throughout your lifetime.	Differentiation	C
Your immune system is capable of distinguishing between antigens on your own cells, and those of an invading pathogen.

Possible phrases are listed below. Not all phrases will need to be used and only ONE phrase is required per row. If you record more than one, you will not be awarded any marks for your explanation. 

A	There are millions of different lymphocyte populations, each of which is sensitive to a different antigen. Lymphocytes proliferate when activated by their specific antigen.
B	The immune response ignores self-antigens and targets non-self antigens.
C	B cells differentiate into T cells to create a long-lived immune response.
D	Each T and B cell can recognise many antigens and respond to a wide variety of possible threats.
E	Each T or B cell has receptors that respond to only one antigen and ignores all others.
F	Phagocytes have a reduced ability to destroy pathogens during subsequent infections.
G	T cells are versatile because they produce copious quantities of antibodies that can respond to a wide variety of threats.
H	Activated lymphocytes produce two groups of cells: one group that attacks the invader immediately, and another that remains inactive unless it is exposed to the same antigen at a later date

QUESTION 4

1. Using the patellar reflex as an example, explain the purpose of a neural reflex. (2 marks)

The patellar reflex is a stretch reflex which tests the l2,3 and 4 regions of the spinal cord. The neuronal reflex therefore involves the alpha motor neuron which conducts efferent impulses back to the quadriceps femoris of the muscles., leading to a muscle contraction (Brussé et al., 2015).  

1. What happens to the patellar reflex when someone clasps their hands and squeezes them strongly? Why does this occur? (2 marks)

During clapping, the patellar reflex is stricken in the patellar tendon using a reflex hammer bellow the patella. Then the muscle fibres on the hands stretches out to form a signal which travels beck to the spinal cord. 

QUESTION 5

Using the diagram provided as a prompt, outline the four steps involved in the transmission of an electrical impulse from the presynaptic neurone to the post synaptic neurone.  (4 marks)

Step	Outline
1	Voltage gated calcium ions are activated (Weingart & Rüdisüli, 2017)
2	Binding of neurotransmitters to postsynaptic end
3	Changes in electrical voltages of sodium and potassium ions
4	Production of the electrical impulse to the postsynaptic end

QUESTION 6

Describe the series of events occurring at a neuromuscular junction required for muscular contraction. (3 marks)

At the neuromuscular junction, a chemical synapse is formed when a contact is made between muscle fibres and motor neuron (Tintignac et al., 2015). This junction begins once an action potential reaches at the presynaptic end of a motor neuron. The voltage dependent calcium ion channels are activated allowing calcium ions to enter into the neuron. These ions bind to the synaptic end causing vesicle fusion on the cell membrane. And a release of the neurotransmitter from neurons into synaptic cleft (Rudolf et al., 2016).

Bone Cells and Homeostasis

QUESTION 7

Think about how the renin-angiotensin-aldosterone system acts to maintain normal blood pressure. Susan has sustained damage to her adrenal glands.  Consequently, her circulating levels of aldosterone are abnormally low. 

1. Where are the target cells for aldosterone located in the body? (1 mark)

Kidneys

1. What do you expect the lack of aldosterone to do to Susan’s blood pressure? Explain your answer. (3 marks)

Low blood pressure.

This is due to lack of reabsorption of sodium, and the excretion of potassium from and into the renal tubes of the kidneys leading to loss blood pressure.

QUESTION 8

Explain the term ‘normal sinus rhythm’.  (1 mark)

This indicates a normal heart beat in terms of both the rhythms as well as the heart rate. Under normal cases, the heart rate is between 60 to 100 beats per minute. Thus in a normal sinus rhythm’, the P waves or the sinus is normal in terms of morphology and the ECG measurements are normal too (Carrara et al., 2015).

QUESTION 9

For each of the scenarios below, indicate whether you would you expect resting heart rate to be greater or less than that associated with normal sinus rhythm.  Explain the cardiac physiology underlying the identified change.  (4 marks)

Heart rate	Situation	Explanation
High	A person of average fitness running a 5km fun run.	The body cells will need a lot of oxygen supply for the respiring tissues to metabolize glucose to make energy for the activity.
low	An endurance athlete at rest.	At rest no much energy needed so need for aerobic metabolism (Allen et al., 2015).

QUESTION 1

Explain how baroreceptors contribute to control blood pressure during a short period of widespread vasodilation.  (3 marks)

The baroreceptors are unique sensors that detect any changes in blood pressure. These baroreceptors are common at the aorta and carotid (Victor, 2015). In case of vasodilation, the blood pressure becomes low causing action potentials to be sent into the cardiac regulation centre in the medulla. This is through the sensing of low blood pressure inside the arteries. To raise blood pressure, there is sympathetic nerve activity in the Sino atrial nodes so that they fire very fast thus raising the heart rate (Salman et al., 2017)

QUESTION 11

Parents, a father who is heterozygous for blood group A and a mother who is heterozygous for blood group B, are wondering what, if any, are their chances of producing a child with blood group O.

1. State the genotype of each parent, and complete the Punnett square below. (2 marks)

Parent	Genotype
Father	AO, AA
Mother	BO, BB

1. 
   What is the chance of these parents producing a blood group O child? Explain your reasoning. (1 mark)

The chance of these getting a blood group O child is 25%. This is because since they are heterozygous for their blood groups, upon cross overs of these genotypes, the F1 generations will have children containing the blood groups in the following rations: 1AB: 1A: 1B: 1O.

QUESTION 12

Describe TWO differences between the intrinsic and extrinsic pathways in blood clotting.  (2 marks)

intrinsic blood clotting- this clotting pathway id activated by trauma that occurs inside the blood vessels. This pathway is activated by the blood clotting cells known as the platelets which are exposed by some chemicals and collagen (Doolittle et al., 2016). However, this clotting pathway is slower than the extrinsic pathway and is facilitated by the blood clotting factors namely; factors XII, VIII, XI and IX.

Blood Pressure Regulation

extrinsic blood clotting- this blood clotting pathway is activated by external traumatic events which make the blood to move away from the blood vessels. This pathway is faster than the intrinsic blood clotting pathway because it involves the activity of blood clotting factor VII.

QUESTION 13

The Wigger’s diagram (below) represents pressure and volume relationships in the left side of the heart during one cardiac cycle.  To answer this question, you should focus on the changes in pressure in different chambers of, or vessels leading from, the left side of the heart.

For ONE of the labelled points, state which valve is open/closed at that time.  Highlight your chosen point in bold.  You must also explain WHY that valve opened/closed and where the blood is flowing immediately after this point in time, due to the change in position of the valve.  An example is provided in italics.  (2 marks)

Label	Valve (name and open/closed)	Explanation
A	Tricuspid valve open	Prevent backflow of blood from the right ventricle
B	Mitral valve closed	Blood from the aorta to body tissues at high pressure
C	Aortic valve open	Allow flow of blood from left atrium
D	Left AV/bicuspid valve opens	The pressure in the left ventricle becomes lower than that in the left atrium.  Blood flows from the left atrium to the left ventricle.

 

QUESTION 14

Consider the events occurring after you have eaten a high carbohydrate meal.  For each of the organs listed in the table below, describe ONE mechanical and ONE chemical digestion event that will contribute to the digestion of carbohydrates.  (2 marks per location - 6 marks total)

Location	Mechanical digestion event	Chemical digestion event
Mouth	Physical breakdown of food into smaller pieces when food is chewed.	Digestion of carbohydrate foods when they are mixed with saliva. The saliva contains the enzyme amylase which is the first enzyme in carbohydrate digestion in the mouth (Campbell, 2015).
Stomach	Mechanical breaking of food through churning and mixing	Digestion of proteins mixing with enzymes like pepsin and trypsin, and use of acids like hydrochloric acid in protein digestion.
Small intestine	Mechanical breakdown of food through peristalsis, where the muscles undergo involuntary contractions to facilitate chime movement	The chyme undergoes chemical digestion through mixing with enzymes from the pancreas and bile produced by the liver.

 QUESTION 15

Continue to consider the events occurring after you have eaten a high carbohydrate meal.  In the table below explain how the listed organs are involved in the absorption and metabolism events (specific to carbohydrates) that occur after this meal. (1 mark per location - 2 marks total)

Location	Absorption and metabolism events
Small intestine	The carbohydrates are absorbed in the small intestines at the brush region of the small intestinal known as the villi which requires use of energy in these cells (Donowitz & Petri Jr, 2015). The metabolism of carbohydrates in the small intestines involves the specific activity of glucose -6- phosphate dehydrogenase and 6-phosphogluconate dehydrogenase specifically in the mucosa of small intestines.
Liver	The liver produces hormones in the hepatocytes that are involved in carbohydrate metabolism. In this case, the liver controls the blood sugar concentrations. The liver converts glucose into glycogen and other stores glycogen or transports glucose to blood.

QUESTION 16

The figure below illustrates inspiration and expiration.  Refer to this figure to answer the following questions.  (0.5 marks each - 3 marks total)

Question	Answer
Contraction of which muscle/s produces the movement labelled "1"?	External intercostal muscles
Contraction of which muscle/s produces the movement labelled “2”?	Diaphragm
At label “3”, is pressure outside greater than or less than pressure inside the lungs?	Less
Is the pressure in the space labelled "4", higher or lower compared to the atmospheric pressure?	Greater
At label “8”, is pressure outside greater than or less than pressure inside the lungs?	Greater
Name any ONE muscle that contracts to cause the extra movement required when you need to expire forcefully (indicated by the arrows labelled "6" and "7").	External intercostal muscles

QUESTION 17

1. 
   Complete the below table of partial pressures in internal respiration. (1 mark)

	pO2 (mmHg)	pCO2 (mmHg)
Capillary	40	45
Tissue	100	40

1. 
   Describe how the differences in partial pressures drives the direction of gas movement between the blood and tissues (2 marks)

When the ventilation in the lungs is low, the partial pressure of oxygen drops while that of carbon dioxide remain high. On the other hand, sufficient ventilation means that oxygen can enter into the alveoli at high rates and get delivered to the tissues and this raises the partial pressure of oxygen while that of carbon dioxide remains low.

 QUESTION 18

1. Describe the epithelium lining in the trachea? (1 mark)

It is lined with pseudostratified columnar epithelial tissues and ciliate and contains mucus secreting cells. 

1. How does the structure of this epithelium relate to its function in the trachea? (1 mark)

These cells facilitate the exchange of air; the cilia trap foreign materials from outside to avoid contamination of the airway system. 

QUESTION 19

What personal protective equipment should be worn when handling someone else’s urine?  Explain.  (1 mark)

Gloves

Lab coat

This prevents the contamination with infectious body fluids which could lead to infection of the person handling this sample.

Respiratory System

QUESTION 20

The results of dipstick urinalysis of two urine samples are listed below.

Sample 1 belongs to a 16-year-old male ‘gamer’ who has locked himself in his room all weekend to play computer games (he didn’t really even come out to eat or drink).  

Sample 2 belongs to a 22-year-old female triathlete who is careful with her diet, hydration, and almost exercises to excess.

For each parameter, fill in the normal values. (Hint: Refer to the Week 10 laboratory activity to get you started).

Parameter	Normal values	Sample 1	Sample 2
Colour	yellow	Dark yellow	Reddish tinge
Glucose	-	-	-
Bilirubin	-	-	-
Ketones	-	++	-
Specific gravity	1.00	1.039	1.010
Blood	-	-	++
pH	6-8	5.5	6.0
Protein	-	-	++
Nitrite	-	-	-
Leukocytes	-	-	-

Choose ONE of the samples described above and answer the following questions in the space provided.

1. Compare the normal and sample values. List any abnormalities you observe in the section below. Are they higher or lower than normal? (1 mark)
2. Give a situation in which you might expect to see these changes in an otherwise healthy (1 mark)
3. What might have been happening in the nephron to cause these abnormal results? Explain your observed abnormalities by linking them with the part of the nephron involved and the process involved (ie filtration, secretion or reabsorption). Ensure that any relationships between the abnormal readings are made clear in your response.  (2 marks) 

Chosen sample: 1
A	Ketones were high pH was low
B	During starving and fasting
C	The nephron did not reabsorb the ketones produced during fatty acids oxidation.  The distal convoluted tubule could not reabsorb the ketones and thus they were released in the urine. The high ketones mean that the patient is fasting or starving and thus no proteins and carbohydrate available to the cells (Goffinet et al., 2017). The cells result to use of fatty acids and hence high production of ketones.

 QUESTION 21

In regards to the nervous endocrine system, explain the appearance of urine with a higher than normal specific gravity.  (3 marks)

The presence of high specific gravity in urine determines the nature of kidney functions. This could be due to dehydration of the body due to lack of sufficient amounts of the hormone antidiuretic hormone. Thus the body is unable to eliminate various waste materials from the blood. 

References

Allen, B., Jennings, J. R., Gianaros, P. J., Thayer, J. F., & Manuck, S. B. (2015). Resting high?frequency heart rate variability is related to resting brain perfusion. Psychophysiology, 52(2), 277-287.

Brussé, I. A., Visser, G. H., Marel, I. C., Facey?Vermeiden, S., Steegers, E. A., & Duvekot, J. J. (2015). Electromyographically recorded patellar reflex in normotensive pregnant women and patients with preeclampsia. Acta obstetricia et gynecologica Scandinavica, 94(4), 376-382.

Campbell, I. (2015). The mouth, stomach and intestines. Anaesthesia & Intensive Care Medicine, 16(1), 37-39.

Carrara, M., Carozzi, L., Moss, T. J., De Pasquale, M., Cerutti, S., Ferrario, M., ... & Moorman, J. R. (2015). Heart rate dynamics distinguish among atrial fibrillation, normal sinus rhythm and sinus rhythm with frequent ectopy. Physiological measurement, 36(9), 1873.

Donowitz, J. R., & Petri Jr, W. A. (2015). Pediatric small intestine bacterial overgrowth in low-income countries. Trends in molecular medicine, 21(1), 6-15.

Doolittle, R. F. (2016). Some important milestones in the field of blood clotting. Journal of innate immunity, 8(1), 23-29.

Goffinet, L., Barrea, T., Beauloye, V., & Lysy, P. A. (2017). Blood versus urine ketone monitoring in a pediatric cohort of patients with type 1 diabetes: a crossover study. Therapeutic advances in endocrinology and metabolism, 8(1-2), 3-13.

Rudolf, R., Deschenes, M. R., & Sandri, M. (2016). Neuromuscular junction degeneration in muscle wasting. Current opinion in clinical nutrition and metabolic care, 19(3), 177.

Salman, I. M., Ameer, O. Z., Sridhar, A., Lewis, S. J., & Hsieh, Y. H. (2017). Abstract P110: Low Intensity Stimulation of Aortic Baroreceptors as a Potential Therapeutic Alternative for Hypertension Treatment.

Tintignac, L. A., Brenner, H. R., & Rüegg, M. A. (2015). Mechanisms regulating neuromuscular junction development and function and causes of muscle wasting. Physiological reviews, 95(3), 809-852.

Victor, R. G. (2015). Carotid baroreflex activation therapy for resistant hypertension. Nature Reviews Cardiology, 12(8), 451.

Weingart, R., & Rüdisüli, A. (2017). Gap junctions in adult ventricular muscle. In Biophysics of gap junction channels (pp. 43-56). CRC Press.