transports food, hormones, metabolic wastes, and gases (oxygen, carbon dioxide) to and from cells
CARDIOVASCULAR SYSTEM/ CIRCULATORY SYSTEM
Components of the circulatory system include:
blood: consisting of liquid plasma and cells
blood vessels (vascular system)
the "channels" (arteries, veins, capillaries) which carry blood to/from all tissues
Arteries carry blood away from the heart
Veins return blood to the heart
Capillaries are thin-walled blood vessels in which gas/ nutrient/ waste exchange occurs
C. heart: a muscular pump to move the blood
There are two circulatory "circuits":
involving the "right heart," delivers blood to and from the lungs
The pulmonary artery carries oxygen- poor blood from the "right heart" to the lungs, where oxygenation and carbon-dioxide removal occur
Pulmonary veins carry oxygen- rich blood from the lungs back to the "left heart"
B. Systemic circulation
driven by the "left heart," carries blood to the rest of the body
Food products enter the system from the digestive organs into the portal vein
Waste products are removed by the liver and kidneys
All systems ultimately return to the "right heart" via the inferior and superior vena cavae
specialized component of the circulatory system is the lymphatic system, consisting of a moving fluid (lymph/interstitial fluid); vessels (lymphatics); lymph nodes, and organs (bone marrow, liver, spleen, thymus)
Through the flow of blood in and out of arteries, and into the veins, and through the lymph nodes and into the lymph, the body is able to eliminate the products of cellular breakdown and bacterial invasion
Arteries and veins run parallel throughout the body with a web-like network of capillaries connecting them
Arteries use vessel size, controlled by the sympathetic nervous system, to move blood by pressure
veins use one-way valves controlled by muscle contractions
strong, elastic vessels adapted for carrying blood away from the heart at relatively high pumping pressure
Arteries divide into progressively thinner tubes and eventually become fine branches called arterioles
Blood in arteries is oxygen-rich, with the exception of the pulmonary artery, which carries blood to the lungs to be oxygenated
Arteries transport blood away from the heart
With thick walls composed of an inner endothelium layer, an outer connective tissue layer, and also a thick middle layer of elastic fibers and smooth muscle
The aorta is the largest artery in the body, the main artery for systemic circulation
The major branches of the aorta (aortic arch, ascending aorta, descending aorta) supply blood to the head, abdomen, and extremities
the right and left coronary arteries supply blood to the heart
Blood leaving the capillary beds flows into a series of progressively larger vessels, called venules , which in turn unite to form veins
Veins are responsible for returning blood to the heart after the blood and the body cells exchange gases, nutrients, and wastes
Pressure in veins is low, so veins depend on nearby muscular contractions to move blood along
Veins have valves that prevent back-flow of blood
Blood in veins is oxygen-poor, with the exception of the pulmonary veins, which carry oxygenated blood from the lungs back to the heart
The major veins, like their companion arteries, often take the name of the organ served except superior vena cava and the inferior vena cava, which collect blood from all parts of the body (except from the lungs) and channel it back to the heart
At any given time, more than half of the total blood volume is found in veins and venules
If blood is lost due to, for example, hemorrhaging, sympathetic nervous stimulation causes the veins to constrict, providing more blood to the rest of the body. In this way, the veins act as a blood reservoir.
arterioles branch into the microscopic capillaries, or capillary beds, which lie bathed in interstitial fluid, or lymph, produced by the lymphatic system
Capillaries are the points of exchange between the blood and surrounding tissues
Materials cross in and out of the capillaries by passing through or between the cells that line the capillary
a cone-shaped, muscular organ about the size of a clenched fist
It is located in the thorax between the lungs, anterior to the backbone and posterior to the sternum
Its apex is tilted to the left, and about two-thirds of the heart is located to the left of the body's midline
FUNCTIONS OF THE HEART:
Generating blood pressure
Contractions of the heart generate blood pressure, which is responsible for blood movement through the blood vessels
2. Routing blood
the heart separates the pulmonary and systematic circulations, which ensures the flow of oxygenated blood to the tissues
3. Ensuring one-way blood flow
The valves of the heart ensure a one-way flow of blood through the heart and blood vessels
4. Regulating blood supply
Changes in the rate and force of heart contraction match blood delivery to the changing metabolic needs of the tissues, such as during rest, exercise and changes in body position
The heart lies within a sac formed by the pericardial membranes:
a. fibrous pericardium , a layer of fibrous connective tissue that adheres to the blood vessels at the heart's base and the sternal wall of the thorax and the diaphragm below
b. parietal pericardium , a serous membrane that is separated by a small space, called the pericardial cavity
Epicardium is part of the heart wall which also has two other layers
Myocardium is the thickest part of the heart wall and is made up of cardiac muscle
Inner endocardium includes an endothelium that not only lines the heart but also continues into and lines the blood vessels. The endotheliums' smooth nature helps prevent blood from clotting unnecessarily
Four chambers of the Heart:
the right and left atria and superior to the right and left ventricles
The atria are smaller and have thinner walls than the ventricles
Internally, the atria are separated by the interatrial septum, and the ventricles are separated by the interventricular septum. Thus, the heart has a right and left side
Left Anterior Descending
Superior Vena Cava
Inferior Vena Cava
Passage of Blood Through the Heart
Blood follows this sequence through the heart: superior and inferior vena cava -> right atrium -> tricuspid valve -> right ventricle -> pulmonary semilunar valve -> pulmonary trunk and arteries to the lungs -> pulmonary veins leaving the lungs -> left atrium -> bicuspid valve -> left ventricle -> aortic semilunar valve -> aorta -> to the body .
receives de-oxygenated blood from the body through the superior vena cava (head and upper body) and inferior vena cava (legs and lower torso)
The sinoatrial node sends an impulse that causes the cardiac muscle tissue of the atrium to contract in a coordinated, wave-like manner
The tricuspid valve, which separates the right atrium from the right ventricle, opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle
receives oxygenated blood from the lungs through the pulmonary vein
As the contraction triggered by the sinoatrial node progresses through the atria, the blood passes through the mitral valve into the left ventricle
receives de-oxygenated blood as the right atrium contracts
The pulmonary valve leading into the pulmonary artery is closed, allowing the ventricle to fill with blood
Once the ventricles are full, they contract
As the right ventricle contracts, the tricuspid valve closes and the pulmonary valve opens
The closure of the tricuspid valve prevents blood from backing into the right atrium and the opening of the pulmonary valve allows the blood to flow into the pulmonary artery toward the lungs
receives oxygenated blood as the left atrium contracts
The blood passes through the mitral valve into the right ventricle
The aortic valve leading into the aorta is closed, allowing the ventricle to fill with blood
Once the ventricles are full, they contract
As the left ventricle contracts, the mitral valve closes and the aortic valve opens
The closure of the mitral valve prevents blood from backing into the left atrium and the opening of the aortic valve allows the blood to flow into the aorta and flow throughout the body
Superior Vena Cava The superior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava, which empties into the right atrium of the heart
Inferior Vena Cava The inferior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart
Aorta The aorta is the largest single blood vessel in the body. It is approximately the diameter of your thumb. This vessel carries oxygen-rich blood from the left ventricle to the various parts of the body.
Pulmonary Artery The pulmonary artery is the vessel transporting de-oxygenated blood from the right ventricle to the lungs Pulmonary Vein The pulmonary vein is the vessel transporting oxygen-rich blood from the lungs to the left atrium .
attach to the lower portion of the interior wall of the ventricles
They connect to the chordae tendineae, which attach to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle
The contraction of the papillary muscles opens these valves
When the papillary muscles relax, the valves close
tendons linking the papillary muscles to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle
As the papillary muscles contract and relax, the chordae tendineae transmit the resulting increase and decrease in tension to the respective valves, causing them to open and close
string-like in appearance and are sometimes referred to as "heart strings
separates the right atrium from the right ventricle
It opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle
It closes as the right ventricle contracts, preventing blood from returning to the right atrium; thereby, forcing it to exit through the pulmonary valve into the pulmonary artery
separates the left atrium from the left ventricle
It opens to allow the oxygenated blood collected in the left atrium to flow into the left ventricle
It closes as the left ventricle contracts, preventing blood from returning to the left atrium; thereby, forcing it to exit through the aortic valve into the aorta
separates the right ventricle from the pulmonary artery
As the ventricles contract, it opens to allow the de-oxygenated blood collected in the right ventricle to flow to the lungs
It closes as the ventricles relax, preventing blood from returning to the heart
separates the left ventricle from the aorta
As the ventricles contract, it opens to allow the oxygenated blood collected in the left ventricle to flow throughout the body
It closes as the ventricles relax, preventing blood from returning to the heart
Features of the Circulatory System
The surge of blood entering the arteries causes their elastic walls to swell, but then they almost immediately recoil
This alternate expanding and recoiling of an arterial wall can be felt as a pulse in any artery that runs close to the surface
The pulse rate indicates the heartbeat rate and also gives information about the strength and rhythm of the heartbeat
the force of blood against a blood vessel wall
Two aspects of blood pressure are considered: 1) how blood pressure is maintained in the arteries and arterioles, and 2) how blood pressure varies in other parts of the circulatory system
Blood is forced out of the ventricles with each heartbeat
The stroke volume is the volume of blood pumped by a ventricle with each beat
The cardiac output is the volume of blood pumped by one ventricle per minute
In a resting adult, the cardiac output is usually about five liters--approximately the amount of blood in the body
A heartbeat produces the familiar "lub-dub" sounds
These sounds are due to vibrations caused by pressure changes that occur when the chambers contract and the valves close
The "lub" sounds is heard when the ventricles contract and the atrioventricular valves close
This sound lasts longer and has a lower pitch than the "dub" sound, which is heard when the semilunar valves close and the ventricles relax
Extrinsic Control of Heartbeat
A cardiac control center in the medulla oblongata speeds up or slows down the heart rate by way of the autonomic nervous system branches: parasympathetic system (slows heart rate) and the sympathetic system (increases heart rate).
Hormones epinephrine and norepinephrine from the adrenal medulla also stimulate faster heart rate.
The beating of the heart is necessary to homeostasis because it creates pressure that propels blood in arteries and the arterioles.
Arterioles lead to the capillaries where nutrient and gas exchange with tissue fluid takes place.
Blood Flow in Arteries
Blood pressure due to the pumping of the heart accounts for the flow of blood in the arteries.
Systolic pressure is high when the heart expels the blood.
Diastolic pressure occurs when the heart ventricles are relaxing.
Both pressures decrease with distance from the left ventricle because blood enters more and more arterioles and arteries.
Blood Flow in Capillaries
Blood moves slowly in capillaries because there are more capillaries than arterioles.
This allows time for substances to be exchanged between the blood and tissues.
Blood Flow in Veins
Venous blood flow is dependent upon:
skeletal muscle contraction,
presence of valves in veins, and
Compression of veins causes blood to move forward past a valve that then prevents it from returning backward.
Changes in thoracic and abdominal pressure that occur with breathing also assist in the return of blood.
Varicose veins develop when the valves of veins become weak.
Hemorrhoids (piles) are due to varicose veins in the rectum.
Phlebitis is inflammation of a vein and can lead to a blood clot and possible death if the clot is dislodged and is carried to a pulmonary vessel.
Cardiovascular disease ( CVD ) is the leading cause of death in Western countries.
Modern research efforts have improved diagnosis, treatment, and prevention.
Major cardiovascular disorders include atherosclerosis, stroke, heart attack, aneurysm, and hypertension.
Atherosclerosis is due to a build-up of fatty material ( plaque ), mainly cholesterol, under the inner lining of arteries.
The plaque can cause a thrombus (blood clot) to form.
The thrombus can dislodge as an embolus and lead to thromboembolism .
Stroke, Heart Attack, and Aneurysm
A cerebrovascular accident , or stroke , results when an embolus lodges in a cerebral blood vessel or a cerebral blood vessel bursts; a portion of the brain dies due to lack of oxygen.
A myocardial infarction , or heart attack , occurs when a portion of heart muscle dies due to lack of oxygen.
Partial blockage of a coronary artery causes angina pectoris , or chest pain.
An aneurysm is a ballooning of a blood vessel, usually in the abdominal aorta or arteries leading to the brain.
Death results if the aneurysm is in a large vessel and the vessel bursts.
Atherosclerosis and hypertension weaken blood vessels over time, increasing the risk of aneurysm.
Coronary Bypass Operations
A coronary bypass operation involves removing a segment of another blood vessel and replacing a clogged coronary artery.
It may be possible to replace this surgery with gene therapy that stimulates new blood vessels to grow where the heart needs more blood flow.
Clearing Clogged Arteries
Angioplasty uses a long tube threaded through an arm or leg vessel to the point where the coronary artery is blocked; inflating the tube forces the vessel open.
Small metal stents are expanded inside the artery to keep it open.
Stents are coated with heparin to prevent blood clotting and with chemicals to prevent arterial closing.