Question

1) Please define the term closed circulatory system. Which animals have it, and what are its’ evolutionary advantages over open systems (why might a closed system be more efficient)?

(10 points)

2) Describe all the events (steps) that occur during a cardiac cycle for mammals (organisms with a

double circulation), as well as the opening and

closing of all heart valves, and the signals arising from the SA and AV nodes. How does this cycle contribute to metabolic homeostasis for our cells, and what is the purpose of the valves?

3) Using information discussed during our lectures thus far, propose 2 physical ways that a human may develop hypertension

(abnormally elevated blood pressure). [One of these mechanisms should

stem from the blood vessels, and the other at the level of the nervous system]. What are the long-

term consequences of elevated hypertension?

Answer 1

Ans 1.

In a closed circulatory system, the blood stays within blood vessels. In this way, blood is kept separate from body tissues. This system has a heart that pumps blood through a continuous circulation pattern. As such, the blood tends to be pumped at a higher pressure.

In organisms with a closed circulatory system, the blood does not fill body cavities. Many vertebrates, such as humans, have a circulatory system known as the cardiovascular system and a secondary system known as the lymphatic system.

Animals with a closed circulatory system tend to be larger than those with an open circulatory system—consider, for example, an elephant versus a grasshopper. This type of system can transport blood to extremities while maintaining a higher blood pressure than the open circulatory system.

There are several different heart configurations for an animal with a closed circulatory system. Most mammals have a four-chambered heart, which separates the oxygenated blood from the deoxygenated blood. A fish has a two-chambered heart, which pumps blood directly to the gills to become oxygenated and then throughout the body. Amphibians have three-chambered hearts, where oxygenated and deoxygenated blood mix within the heart before being pumped to the body. The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squids, octopuses and relatives) are closed, just as in humans. Still, the systems of fish, amphibians, reptiles, and birds show various stages of the evolution of the circulatory system.

The closed circulatory system has more advantages over the open circulatory system.

1. The blood transfers faster in the closed system, thus oxygen, nutritients, and wastes transport fast also.

2. Specialized cells help carry nutrients.

3. The blood and the tissue fluid are distinguished easily.

Ans 2.

The cardiac cycle is the performance of the human heart from the ending of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, followed by a period of robust contraction and pumping of blood, dubbed systole. After emptying, the heart immediately relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting to pump blood to the lungs and those systems. A normally performing heart must be fully expanded before it can efficiently pump again. Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 seconds to complete the cycle. There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously. At the start of the cycle, during ventricular diastole–early, the heart relaxes and expands while receiving blood into both ventricles through both atria; then, near the end of ventricular diastole–late, the two atria begin to contract (atrial systole), and each atrium pumps blood into the ventricle 'below' it. During ventricular systole the ventricles are contracting and vigorously pulsing (or ejecting) two separated blood supplies from the heart—one to the lungs and one to all other body organs and systems—while the two atria are relaxed (atrial diastole). This precise coordination ensures that blood is efficiently collected and circulated throughout the body.The mitral and tricuspid valves, also known as the atrioventricular, or AV valves, open during ventricular diastole to permit filling. Late in the filling period the atria begin to contract (atrial systole) forcing a final crop of blood into the ventricles under pressure. Then, prompted by electrical signals from the sinoatrial node, the ventricles start contracting (ventricular systole), and as back-pressure against them increases the AV valves are forced to close, which stops the blood volumes in the ventricles from flowing in or out; this is known as the isovolumic contraction stage.Due to the contractions of the systole, pressures in the ventricles rise quickly, exceeding the pressures in the trunks of the aorta and the pulmonary arteries and causing the requisite valves (the aortic and pulmonary valves) to open—which results in separated blood volumes being ejected from the two ventricles. This is the ejection stage of the cardiac cycle; (as the ventricular systole–first phase followed by the ventricular systole–second phase).Now follows the isovolumic relaxation, during which pressure within the ventricles begin to fall significantly, and thereafter the atria begin refilling as blood returns to flow into the right atrium (from the vena cavae) and into the left atrium (from the pulmonary veins). As the ventricles begin to relax, the mitral and tricuspid valves open again, and the completed cycle returns to ventricular diastole and a new "Start" of the cardiac cycle.Throughout the cardiac cycle, blood pressure increases and decreases. The movements of cardiac muscle are coordinated by a series of electrical impulses produced by specialised pacemaker cells found within the sinoatrial node and the atrioventricular node. Cardiac muscle is composed of myocytes which initiate their internal contractions without applying to external nerves—with the exception of changes in the heart rate due to metabolic demand.

Diastole and Systole in cardiac cycle: Cardiac diastole is the period of the cardiac cycle when, after contraction, the heart relaxes and expands while refilling with blood returning from the circulatory system. Both atrioventricular (AV) valves open to facilitate the 'unpressurized' flow of blood directly through the atria into both ventricles, where it is collected for the next contraction.

Atrial Systole: Atrial systole is the contracting of cardiac muscle cells of both atria following electrical stimulation and conduction of electrical currents across the atrial chambers . While nominally a component of the heart's sequence of systolic contraction and ejection, atrial systole actually performs the vital role of completing the diastole, which is to finalize the filling of both ventricles with blood while they are relaxed and expanded for that purpose. Atrial systole overlaps the end of the diastole, occurring in the sub-period known as ventricular diastole–late . At this point, the atrial systole applies contraction pressure to 'topping-off' the blood volumes sent to both ventricles; this atrial kick closes the diastole immediately before the heart again begins contracting and ejecting blood from the ventricles (ventricular systole) to the aorta and arteries.

Ventricular Systole: Ventricular systole is the contractions, following electrical stimulations, of the ventricular syncytium of cardiac muscle cells in the left and right ventricles. Contractions in the right ventricle provides pulmonary circulation by pulsing oxygen-depleted blood through the pulmonary valve then through the pulmonary arteries to the lungs. Simultaneously, contractions of the left ventricular systole provide systemic circulation of oxygenated blood to all body systems by pumping blood through the aortic valve, the aorta, and all the arteries. (Blood pressure is routinely measured in the larger arteries off the left ventricle during the left ventricular systole).

Ans 3.The exact causes of high blood pressure are not known, but several things may play a role, including:

• Smoking.
• Being overweight or obese.
• Lack of physical activity.
• Too much salt in the diet.
• Too much alcohol consumption (more than 1 to 2 drinks per day)
• Stress.
• Older age.
• Genetics.

Long term consequences: Damage caused by high blood pressure starts small and builds over time. The longer it goes undiagnosed or uncontrolled, the more serious your risks.Your blood vessels and major arteries carry blood throughout the body and supply it to vital organs and tissue. When the pressure at which blood travels gets increased, it begins to damage artery walls. High blood pressure may play a role in dementia and cognitive decline over time. Reduced blood flow to the brain causes memory and thinking problems. You might have trouble remembering or understanding things, or lose focus during conversations. High blood pressure can cause bone loss, known as osteoporosis, by increasing the amount of calcium your body gets rid of when you urinate. Women who have already gone through menopause are especially at risk. Like the brain and heart, arteries in the lungs can be damaged and blocked. When the artery that carries blood to your lungs gets blocked, it’s called a pulmonary embolism. This is very serious and requires immediate medical attention. An aneurysm can also happen in the lung.