Human Anatomy
The Cardiovascular System
Cardiovascular System
This vital system consists of the heart, the blood vessels, and the blood that carries oxygen and defensive cells throughout the body while also removing toxins and waste.
The Circulatory System
This system has two components: systemic circulation and pulmonary circulation. The heart is the pump, and the blood vessels are the delivery channels, while blood is the medium that transports oxygen, nutrients, and the by-products of metabolism.
As with any type of circulatory system-physiological, electrical, or mechanical - the human circulatory system is designed to move something around in what is called a “closed loop,” meaning it returns each time to its point of origin. In this case, the heart, a muscular pumping device, enables circulation and is also the point of origin. The heart pumps in order to send oxygen-rich blood into tubes called arteries. The arteries are divided into tiny capillaries that have walls thin enough to allow a two-way exchange. Oxygen and nutrients in the blood flow into the surrounding tissues and cells into the capillaries. The capillaries join and enlarge to form veins, which take blood back to the heart from where it is routed to the lungs for oxygenation- and carbon dioxide - and to the kidneys for filtration. In addition to the above functions, blood also protects the body: It contains white blood cells, antibodies, and complementary proteins that defend the body against pathogens like bacterial microbes, harmful fungi, and viruses. Blood is also involved in the thermoregulation of the body and regulating pH levels and the water content of cells and tissues. Clotting mechanisms of the blood protect the body from extensive blood loss after injuries. Thus, with its interconnected pathways of veins, arteries, and capillaries, the cardiovascular system keeps blood and life pumping through the body.
The human vascular system: Also known as the circulatory system, it is composed of the vessels that carry blood and lymph throughout the body- the arteries and veins that transport red blood cells, white blood cells, platelets, and plasma.
Jugular vein: carries blood from the brain, face, and neck toward the heart.
Carotid artery: carries blood from the heart to the brain, neck, and face.
Subclavian vein: carries blood from the upper limbs to the heart.
Aorta: the primary artery, which circulates blood from the heart to the rest of the body.
Heart: pumps blood throughout the circulatory system.
Inferior vena cava: carries deoxygenated blood from the lower body into the heart.
Abdominal aorta: carries oxygenated blood to the lower body.
Femoral artery: supplies blood to the legs and lower body.
Femoral vein: carries blood from the thighs to the heart.
Great saphenous vein: the longest vein in the body, it carries blood from the legs and feet to the heart.
Anterior tibial artery: carries blood to the front of the legs and top of the feet.
Blood cells: Blood contains many types of cells, including defensive white blood cells (monocytes, lymphocytes, neutrophils, eosinophils, basophils, macrophages), red blood cells (erythrocytes), which carry oxygen, and platelets, which help blood clot.
The structure of the Heart
The heart is the central pump of the cardiovascular system, maintaining the unidirectional flow of blood. It is enclosed in a double-layered membrane (the pericardium). The outer layer of the pericardium surrounds the roots of the hearts’s major blood vessels and is attached to the spinal column and diaphragm by ligaments.
The human heart is a fist-sized, four-chambered muscular organ located between the lungs in the middle of the chest and behind and slightly to the left of the sternum, (or breastbone).
The four chambers of the heart are the right and left atria (upper chambers) and the right and left ventricles (lower chambers). The left chambers from the arterial part of the heart, and the right chambers form the venous part. The left ventricle is the largest and strongest chamber in the largest and strongest chamber in the heart.
The heart wall has three layers: the epicardium (outer layer) secretes a lubricating fluid, the myocardium (middle layer) is a thick muscular layer formed by cardiac muscles, and the endocardium (inner layer) is an epithelial lining in all the chambers. The heart is surrounded by a closed fibrous sac called the pericardium. It has a fibrous outer layer and a serous inner layer. The serous layer has two laminae- the parietal and visceral laminae with serous fluid in the pericardial cavity in between. The fluid decreases the surface tension and lubricates the organ, allowing free movement of the heart when it contracts.
Blood flow through the heart is regulated by four valves. Flow between the right atrium and right ventricle is regulated by the tricuspid valve. The pulmonary valve controls blood flow from the right ventricle into the pulmonary arteries, which carry blood to the lungs. The mitral valve regulates the flow of the oxygenated blood from the lungs, to pass from the left atrium into the left ventricle. From here the oxygenated blood is pumped into the aorta through the aortic valve.
Cardiac Blood Vessels: Blood is supplied to the heart by its own vascular system-coronary circulation. The right and left coronary arteries branch from the aorta as it leaves the heart. Metabolic waste from the heart tissue is removed by the coronary veins, particularly the coronary sinus.
Under stress, such as exercise or sudden loud noises, men’s vascular systems respond by increasing blood pressure, while women’s systems increase heart rate resulting in higher cardiac output.
Valve Placement: The heart’s four valves are positioned between its chambers and within its various entry points. If valves become narrowed, it takes more pressure to pump blood through them.
Tricuspid valve: prevents regurgitation (or back flow) of blood from the right ventricle into the right atrium.
Right ventricle: responsible for pumping oxygen-depleted blood to the lungs.
Left atrium: acts as a holding chamber for blood returning from the lungs.
Crural septum: the dividing wall between the heart’s two main chambers.
Aorta: the largest artery in the body.
Heart: a hollow, muscular organ of cardiac muscle and connective tissue that pumps blood throughout the body’s tissues.
Abdominal aorta: the largest artery in the abdominal cavity.
Men’s hearts tend to be larger than women’s by about one-third, but in some cases they can be 80 percent bigger.
How heart valves work: The heart had four valves- the mitral (or bicuspid), tricuspid, pulmonary, and aortic-that keep blood flowing in the correct direction via flaps that open and close once during each heartbeat.
Mitral valve: helps prevent blood from being regurgitated as it moves through the heart.
Pulmonary valve: this one-way valve allows blood to leave the heart via arteries.
Tricuspid valve: the boundary between the right ventricle and right atrium.
Heart Function and Cycle
The heart produces a two-part pumping action with every heartbeat that takes about a second to complete. The cardiac cycle encompasses the different phases of contraction and relaxation of the heart muscle that drive blood throughout the body. Systole is the phase of the heartbeat when it contracts and pumps blood from the chambers into the arteries. Diastole is the short resting phase.
The cardiac cycle is the way in which the human heart functions from the end of one heartbeat to the beginning of the next. It is made up of two periods: when the heart muscle relaxes and refills with blood, which is called diastole, and when the muscle contracts and pumps blood, which is called systole.
The first step of this cycle is atrial depolarization and contraction, which ends when the mitral valve closes. During this phase, only 20 percent of the ventricle is filled, as the remaining capacity is filled passively, prior to the heart muscle’s contraction.
Ventricular is-volumetric contraction, the next phase, occurs when both the left and right atrioventricular valves are closed and ends when the aortic valve opens. This is the early phase of ventricular systole. The contraction is isovolumtric, meaning the ventricle is contracting as a closed chamber without any change in its volume.
Rapid ventricular ejection is the third phase of the cardiac cycle. At this stage the aortic valve opens, and blood is quickly ejected into the aorta while the left atrium receives oxygenated blood from the lungs. This is considered the peak phase of ventricular systole.
The ventricles contract during the slow ventricular ejection phase, and intraventricular pressure starts falling as blood is ejected. This is the early phase of ventricular diastole. The aortic valve remains open at this point, so blood is slowly ejected into the aorta. This phase ends when the aortic valve closes.
Ventricular isovulumetric relaxation occurs when both valves are closed. The ventricles start relaxing and intraventricular pressure begins to fall. This phase ends when the mitral valve opens.
During the rapid passive ventricular filling phase, once the mitral valve has opened, blood that was previously accumulated in the atrium rushes into the ventricle. This rapid filling is done passively, without atrial contraction.
During the slow passive ventricular filling phase, the atrioventricular valve opens and blood coming from the atrium rushed directly into the ventricle. With a normal resting heart rate, the ventricle is about 90 percent filled by the end of this phase.
Cardiac Conduction: The cardiac conduction system is a group of specialized cells in the myocardium that send electrical signals to the heart, causing it to contract. When electrical impulse is released from the sinoatrial (SA) node, it triggers atrial contraction. The signal then passes to the atrioventricular (AV) node, where the impulse is slowed down. The impulse then travels down the conduction pathway through the bundle of His (also called the atrioventricular bundle), down its branches, and through the Purkinje fibers, contracting the ventricles. Each contraction of the ventricles represents a single heartbeat.
Sinus node: known as the heart’s natural pacemaker.
Purkinje fiber: essential for maintaining a consistent heartbeat.
Atrioventricular node: electrically connects the ratio and ventricles.
Carotid sinus baroreceptor: sensitive to pressure changes in arterial blood.
Aortic baroreceptor: plays an important role in regulating arterial blood pressure.
Short-term blood pressure regulation is managed by the autonomic nervous system. Changes in blood pressure are detected by baroreceptors located in the aortic arch and carotid sinus.
The four cardiac chambers contract and relax to pump blood through the body.
Circulatory System: Deoxygenated blood is brought to the right atrium by the superior and inferior vena cave. The right atrium pumps this blood to the right ventricle through the tricuspid valve. The right ventricle pumps blood through the pulmonary valve to the pulmonary artery, carrying it to the lungs for oxygenation. Oxygenated blood is then brought to the left atrium through the pulmonary veins. The left atrium pumps the blood to the left ventricle through the mitral valve. Oxygenated blood is then pumped from the left ventricle through the aortic valve into the aorta and then to the rest of the body.
Blood Vessels
The cardiovascular system circulates blood throughout the body. The pulmonary circuit supplies the lungs, while the systemic circuit supplies the rest of the body. Vessels that carry blood away from the heart are called arteries, and vessels that bring blood to the heart are called veins.
Blood vessels are the “plumbing pipes” through which blood is transported throughout the body. Arteries carry blood away from the heart, and veins carry blood to the heart. Blood oxygenation determines whether it is arterial or venous blood. Arterial blood is oxygenated, while venous blood is deoxygenated. The pulmonary artery, for example, supplies blood from the heart to the lungs, but it carries venous blood since it is taking deoxygenated blood to the lungs. Capillaries carry blood from the arteries to the veins and are where gas, nutrient, and metabolite are exchanged. Sinusoids, which are small, irregular, and discontinuous vessels perform the same role as capillaries in the bone marrow, liver, and spleen.
Arteries and veins have three layers: the intimacy (inner), media (middle), and adventitia or tunica externalities (outer). The intimacy is the thinnest layer and is lined by the endothelium.
The media, the thickest arterial layer, is lined with smooth muscles that have adrenergic receptors. Stimulation of these receptors constricts the blood vessels, thereby increasing blood pressure.
High blood pressure can, over time, cause heart disease or stroke. Since it often has no symptoms, it is called the “silent killer.” It is therefore important to have your blood pressure taken regularly, either at a clinic or at home with a blood pressure monitor. Normal blood pressure is less than 120 systolic over 80 diatonic.
Blood vessels: The walls of both veins and arteries are composed of three layers, but these are thicker in arteries because they experience a pressure wave from the heart as they transport freshly oxygenated blood.
Capillaries: These tiny blood vessels are 5 to 10 micrometers in diameter, with walls one endothelial cell thick. They carry blood between the articles and venues.
Blood Components
The adult contains about 6 quarts (5 L) of blood, which is composed of plasma and various cells. These help transport gases (oxygen, carbon dioxide, nitrogen), nutrients, lipids infections and support clotting.
Blood makes up about 8 percent of an average adult’s weight. Blood cells account for 45 percent of the blood volume and the rest is plasma, which contains water, plasma proteins, electrolytes, and other substances. Plasma proteins include albumin, which maintains the blood’s colloid oncotic pressure; fibrinogen, which helps blood clot; and globulins, which transport lipids like cholesterol and protect the body from microbes.
The three types of specialized blood cells all come from bone marrow and begin as stem cells. Red blood cells, called erythrocytes, are round and biconcave cells that transport oxygen. Three kinds of white blood cells (or leukocytes) are part of the body’s immune system and are involved in allergic reactions: lymphocytes, monocytes, and granulocytes. The latter are further divided into neutrophils, eosinophils, and basophils. Platelets (or thrombocytes) are fragments of a cell called megakaryocytic and help blood clot-the process by which blood forms a gel-like texture in order to stanch wounds.
Blood is classified into four types based on markers (or antigens): A has A markers, B has B markers, AB has both A and B markers, and O has neither marker. Blood types must be matched before a transfusion, so that the immune system recognizes the new blood as compatible with its own cells. Blood is further broken down into Rh-positive of Rh-negative, based on the presence of a certain protein on the outside of red blood cells. The Rh factor may create antibodies in an Rh-negative mother if a fetus is Rh-positive. Type O negative, with no antigens, is the universal recipient blood because it has both antigens.
Hemoglobin is the iron-containing protein molecules, found in red blood cells, which transport oxygen from the lungs to the body’s tissues and then carry carbon dioxide from the tissues back to the lungs to be expelled.