Cardiovascular System

Cardiovascular System:-

The cardiovascular system consists of the heart, blood vessels, and the approximately 5 liters of blood that the blood vessels transport. Responsible for transporting oxygen, nutrients, hormones, and cellular waste products throughout the body, the cardiovascular system is powered by the body’s hardest-working organ of the heart, which is only about the size of a closed fist. Even at rest, the average heart easily pumps over 5 liters of blood throughout the body every minute...


                            

The Heart

The heart is a muscular pumping organ located medial to the lungs along the body’s midline in the thoracic region. The bottom tip of the heart, known as its apex, is turned to the left, so that about 2/3 of the heart is located on the body’s left side with the other 1/3 on right. The top of the heart, known as the heart’s base, connects to the great blood vessels of the body: the aorta, vena cava, pulmonary trunk, and pulmonary veins. 

Cardiac Cycle:-

One heartbeat makes up one cardiac cycle.The top chamber of the heart is called atria.The bottom chamber of the heart called ventricles.Here are the actions that occur:

• Right atrium contracts < tricuspid valve opens < blood flows into the right ventricle.
• Left atrium contracts < bicuspid valve opens < blood flows into the left ventricle.
• Right ventricle contracts < tricuspid valve closes, pulmonary semilunar valve opens < blood is pushed into the trunk of the pulmonary artery.
• Left ventricle contracts < bicuspid valve closes, aortic semilunar valve opens < blood is pushed into the aorta.

Circulatory Loops

There are 2 primary circulatory loops in the human body: the pulmonary circulation loop and the systemic circulation loop.

Pulmonary circulation transports deoxygenated blood from the right side of the heart to the lungs, where the blood picks up oxygen and returns to the left side of the heart. The pumping chambers of the heart that support the pulmonary circulation loop are the right atrium and right ventricle.

Systemic circulation carries highly oxygenated blood from the left side of the heart to all of the tissues of the body (with the exception of the heart and lungs). Systemic circulation removes wastes from body tissues and returns deoxygenated blood to the right side of the heart. The left atrium and left ventricle of the heart are the pumping chambers for the systemic circulation loop.

Blood vessels 

Blood vessels are the body’s highways that allow blood to flow quickly and efficiently from the heart to every region of the body and back again. The size of blood vessels corresponds with the amount of blood that passes through the vessel. All blood vessels contain a hollow area called the lumen through which blood is able to flow. Around the lumen is the wall of the vessel, which may be thin in the case of capillaries or very thick in the case of arteries.

There are three major types of blood vessels: arteries, capillaries and veins

Arteries and Arterioles: 

Arteries are blood vessels that carry blood away from the heart. Blood carried by arteries is usually highly oxygenated, having just left the lungs on its way to the body’s tissues. The pulmonary trunk and arteries of the pulmonary circulation loop provide an exception to this rule – these arteries carry deoxygenated blood from the heart to the lungs to be oxygenated.small branches of arteries are called arterioles.

Capillaries: 

Capillaries are the smallest and thinnest of the blood vessels in the body and also the most common. They can be found running throughout almost every tissue of the body and border the edges of the body’s avascular tissues. Capillaries connect to arterioles on one end and venules on the other.

Veins and Venules: 

Veins are the large return vessels of the body and act as the blood return counterparts of arteries. Because the arteries, arterioles, and capillaries absorb most of the force of the heart’s contractions, veins and venules are subjected to very low blood pressures. This lack of pressure allows the walls of veins to be much thinner, less elastic, and less muscular than the walls of arteries.

Blood
The average human body contains about 4 to 5 liters of blood. As a liquid connective tissue, it transports many substances through the body and helps to maintain homeostasis of nutrients, wastes, and gases. Blood is made up of red blood cells, white blood cells, platelets, and liquid plasma.

                            
• Red Blood Cells: Red blood cells, also known as erythrocytes, are by far the most common type of blood cell and make up about 45% of blood volume. 

• White Blood Cells: White blood cells, also known as leukocytes, make up a very small percentage of the total number of cells in the bloodstream, but have important functions in the body’s immune system. 

• Platelets : Also known as thrombocytes, platelets are small cell fragments responsible for the clotting of blood and the formation of scabs. Platelets form in the red bone marrow from large megakaryocytic cells that periodically rupture and release thousands of pieces of membrane that become the platelets. Platelets do not contain a nucleus and only survive in the body for up to a week before macrophages capture and digest them.

• Plasma: Plasma is the non-cellular or liquid portion of the blood that makes up about 55% of the blood’s volume. Plasma is a mixture of water, proteins, and dissolved substances. Around 90% of plasma is made of water, although the exact percentage varies depending upon the hydration levels of the individual. 

Functions of the Cardiovascular System:-

The cardiovascular system has three major functions: transportation of materials, protection from pathogens, and regulation of the body’s homeostasis.

• Transportation: The cardiovascular system transports blood to almost all of the body’s tissues. The blood delivers essential nutrients and oxygen and removes wastes and carbon dioxide to be processed or removed from the body. Hormones are transported throughout the body via the blood’s liquid plasma.

• Protection: The cardiovascular system protects the body through its white blood cells. White blood cells clean up cellular debris and fight pathogens that have entered the body. Platelets and red blood cells form scabs to seal wounds and prevent pathogens from entering the body and liquids from leaking out. Blood also carries antibodies that provide specific immunity to pathogens that the body has previously been exposed to or has been vaccinated against.

• Regulation: The cardiovascular system is instrumental in the body’s ability to maintain homeostatic control of several internal conditions. Blood vessels help maintain a stable body temperature by controlling the blood flow to the surface of the skin. Blood vessels near the skin’s surface open during times of overheating to allow hot blood to dump its heat into the body’s surroundings. 

The Circulatory Pump 

The heart is a four-chambered “double pump,” where each side (left and right) operates as a separate pump. The left and right sides of the heart are separated by a muscular wall of tissue known as the septum of the heart. 

The right side of the heart receives deoxygenated blood from the systemic veins and pumps it to the lungs for oxygenation. 

The left side of the heart receives oxygenated blood from the lungs and pumps it through the systemic arteries to the tissues of the body. Each heartbeat results in the simultaneous pumping of both sides of the heart, making the heart a very efficient pump.

Blood Pressure 

Several functions of the cardiovascular system can control blood pressure. Certain hormones along with autonomic nerve signals from the brain affect the rate and strength of heart contractions. Greater contractile force and heart rate lead to an increase in blood pressure. Blood vessels can also affect blood pressure. 

Vasoconstriction decreases the diameter of an artery by contracting the smooth muscle in the arterial wall. The sympathetic (fight or flight) division of the autonomic nervous system causes vasoconstriction, which leads to increases in blood pressure and decreases in blood flow in the constricted region. 

Vasodilation is the expansion of an artery as the smooth muscle in the arterial wall relaxes after the fight-or-flight response wears off or under the effect of certain hormones or chemicals in the blood. The volume of blood in the body also affects blood pressure. A higher volume of blood in the body raises blood pressure by increasing the amount of blood pumped by each heartbeat. Thicker, more viscous blood from clotting disorders can also raise blood pressure.

Heart Sounds:-

During one cardiac cycle, you can hear two heart sounds. The sounds are called Lubb and Dubb. 

                                   
Lubb:-  This is the first heart sound and occurs when the ventricles contract and the tricuspid and bicuspid valves snap shut.

Dubb:- This is the second heart sound and occurs when the atria contract and the pulmonary and aortic semilunar valves snap shut.

Cardiac Conduction System

The cardiac conduction system consists of a group of structures that send electrical impulses through the heart. when cardiac muscle receive an electrical impulse , it contracts.

Components of the cardiac conduction system:-

• Sinoatrial Node (SA node)
• Atrioventricular Node (AV node)
• Bundle of His
• Purkinje Fibers

                                             

Electrocardiogram (ECG or EKG)

This is the test used by physician to know if the cardiac conduction system is working properly. The first wave P indicates that an electrical impulse was sent through the atria, causing them to contract (Depolarization).

                                      

The O, R, and S waves occurs together and make up the ORS complex. This complex indicates that an electrical impulse was sent through the ventricles, causing them to contract(Depolarization).

Finally, T wave indicates electrical changes that occurs in the ventricles as they relax (Repolarization).

Why I Choose This System?

•  It takes 20 seconds for blood to circulate the entire body. Oxygenated blood leaves the aorta about about 1 mile an hour.

• The power output of the heart ranges from 1-5 watts per minute. Which is the equivalent to the usage of a 60 watt bulb. It has been said that enough energy is produced a day to drive a truck 20 miles. 

• “Ventricle” means “little belly” in Latin where as “Atrium” is Latin for “entrance hall”.

• Red blood cells live for upto 4 months and make approximately 250,000 round trips around the body before returning to the bone marrow, where they were born, to die. Between 2.5 and 3 million red blood cells (erythrocytes) are lost and replaced every second.

• Human blood is colorless, it is the hemoglobin that makes it red. 

• Due to the heart having its own electrical impulse, it will continue to beat even when removed from the body as long as it has an adequate supply of oxygen.

• Though weighing only 11 ounces on average, a healthy heart pumps 2,000 gallons of blood through 60,000 miles of blood vessels each day.

• The fetal heart rate is approximately twice as fast as an adult’s, at about 150 beats per minute. By the time a fetus is 12 weeks old, its heart pumps an amazing 60 pints of blood a day.

• Five percent of blood supplies the heart, 15-20% goes to the brain and central nervous system, and 22% goes to the kidneys.

• A woman’s heart typically beats faster than a man’s. The heart of an average man beats approximately 70 times a minute, whereas the average woman has a heart rate of 78 beats per minute.