List the basic components of the human circulatory system.
Trace the routes of blood flow in the human cardiovascular system.
Explain the factors that cause blood to exist under different pressures.
Describe the major cardiovascular disorders and their causes.
Impacts/Issues
The Breath of Life
The Breath of Life
During sudden cardiac arrest the heart stops its regular beating.
CPR (cardiopulmonary resuscitation) is an immediate life-saving technique.
As soon as possible a defibrillator should be used to shock the heart back to its usual rhythm; AEDs (automated external defibrillators) are now available in many public places.
The heart, and its associated blood vessels, is a complicated life-sustaining system.
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Section 1
The Cardiovascular System – Moving Blood Through the Body
The Cardiovascular System – Moving Blood Through the Body
The heart and blood vessels make up the cardiovascular system.
The cardiovascular system has two major elements:
The heart is the muscular pump that generates the pressure required to move the blood through the body.
Blood vessels are the distribution tubes of varying diameters.
The route of circulation: heart >>> arteries >>> arterioles >>> capillaries >>> venules >>> veins and finally back to the heart.
The Cardiovascular System – Moving Blood Through the Body
Circulating blood is vital to maintain homeostasis.
The cardiovascular system is the body’s internal rapid-transport system for oxygen, nutrients, secretions, and wastes via the blood.
Homeostasis depends on the reliable supply of blood to all of the body.
The Cardiovascular System – Moving Blood Through the Body
The cardiovascular system is linked to the lymphatic system.
Because of the pressure in the cardiovascular system, water and proteins leak out to become part of the interstitial fluid.
The lymphatic system vessels pick up the fluid and return it to the general circulation.
The cardiac cycle is a sequence of contraction (systole) and relaxation (diastole).
As the atria fill, the ventricles are relaxed.
Pressure of the blood in the atria forces the AV valves open; the ventricles fill as the atria contract.
When the ventricles contract, the AV valves close, and blood flows out through the semilunar valves.
The Heart: A Double Pump
The cardiac output is the amount of blood each ventricle can pump in a minute; on average the output from each ventricle is about 5 liters.
The heart sound “lub” is made by the closing of the AV valves; the “dup” sound is the closure of the semilunar valves.
Section 3
The Two Circuits of Blood Flow
The Two Circuits of Blood Flow
The pulmonary circuit: Blood picks up oxygen in the lungs.
The pulmonary circuit receives blood from the tissues, taking it through the lungs for gas exchange.
The path of blood flow: blood from tissues enters the right atrium >>> tricuspid valve >>> right ventricle >>>right semilunar valve >>> pulmonary arteries >>> lungs >>> pulmonary veins >>> left atrium.
The Two Circuits of Blood Flow
Blood returning from the body tissues is high in carbon dioxide and low in oxygen; these concentrations are reversed after passage through the lung capillaries.
The Two Circuits of Blood Flow
In the systemic circuit, blood travels to and from tissues.
In the systemic circuit, oxygenated blood is pumped through the body.
Blood moves from the left atrium >>> bicuspid valve >>> left ventricle >>>left semilunar valve >>> aorta >>> body tissues.
Blood from the upper body travels through the superior vena cava; blood from the lower body travels through the inferior vena cava.
The Two Circuits of Blood Flow
Blood from the digestive tract is shunted through the liver for processing.
After a meal, blood laden with nutrients is carried from the digestive tract in the hepatic portal vein to the liver capillaries.
There it passes through the liver capillary beds before leaving via the hepatic vein to return to the general circulation; oxygenated blood reaches the liver through the hepatic artery.
Electrical signals from “pacemaker” cells drive the heart’s contractions.
Cardiac muscle cells are linked by intercalated discs, which rapidly pass signals to contract throughout the heart.
The cardiac conduction system consists of noncontractile cells that are self-excitatory (pacemaker cells).
Excitation for a heartbeat is initiated in the sinoatrial (SA) node; it then passes to the atrioventricular (AV) node and on to the Purkinje fibers, which make contact with the muscle cells that result in ventricular contraction.
How Cardiac Muscles Contract
It is the action of the cardiac pacemaker (SA node) that produces our normal heartbeat.
The nervous system adjusts heart activity.
The nervous system can adjust the rate and strength of cardiac muscle contraction; stimulation by one set of nerves increases the rate and strength while stimulation by other nerves decreases heart rate.
Centers for nervous control of the heart lie in the spinal cord and the brain.
Section 5
Blood Pressure
Blood Pressure
Blood exerts pressure against the walls of blood vessels.
The force of blood against
the vessel walls can be
measured as blood pressure.
Normal systolic pressure
(peak pressure in the aorta)
is 120 mm of Hg; normal diastolic pressure (lowest pressure in the aorta) is 80 mm.
Blood Pressure
Blood pressure values give important clues as to the condition of the vessels and the flow of blood through them.
In hypertension, the blood pressure is too high, which can lead to stroke or heart attack.
Because of their large diameters, arteries present little resistance to flow; blood pressure does not decrease very much in them.
Structure and Functions of Blood Vessels
Arterioles are control points for blood flow.
Arteries branch into smaller arterioles, where the greatest pressure drop occurs.
The wall of an arteriole has rings of smooth muscle over a single layer of elastic fibers.
Arterioles serve as control points where
adjustments can be made in blood volume
distribution.
Structure and Functions of Blood Vessels
Capillaries are specialized for diffusion.
A capillary is the smallest and thinnest tube in the path of circulation and is specialized for exchange of substances with interstitial fluid.
Total resistance is less than in arterioles so the drop in blood pressure is not as great.
Venules and veins return blood to the heart.
Capillaries merge into venules.
Venules merge into veins.
Structure and Functions of Blood Vessels
Veins are blood volume reservoirs (50-60% of blood volume) because their walls can distend or contract.
Skeletal muscles adjacent to veins squeeze the walls
to move the blood along on its way back to the heart;
valves prevent backflow.
Varicose veins can form when the veins have become overstretched, and the valves weakened.
Structure and Functions of Blood Vessels
Vessels help control blood pressure.
The brain monitors signals from various arteries to determine the rate of heartbeat and any changes needed in vessel diameters.
If the blood pressure increases, the arterioles are instructed to relax (vasodilation).
If the pressure decreases, the diameter of the arterioles decreases (vasoconstriction).
In the baroreceptor reflex, special receptors in the carotid arteries monitor changes in blood pressure and send the information to the brain for action.
Section 7
Capillaries: Where Blood Exchanges Substances with Tissues
Capillaries: Where Blood Exchanges Substances with Tissues
A vast network of capillaries weaves close to nearly all living body cells.
Capillaries comprise most
of the cardiovascular
system.
The velocity of blood flow
slows as the diameter of the vessels decreases.
It is slowest in the capillaries to provide for
maximum exchange.
Capillaries: Where Blood Exchanges Substances with Tissues
Many substances enter and leave capillaries by diffusion.
Diffusion is a slow process and is not efficient over long distances.
near enough to a capillary to receive nutrients and give up wastes;
blood flow is slow
enough here to allow
diffusion.
Capillaries: Where Blood Exchanges Substances with Tissues
Some substances pass through “pores” in capillary walls.
Water-filled, slitlike areas between the cells of capillary walls allow water-soluble substances to exit the blood due to pressure (bulk flow).
This movement of fluids and solutes is important to homeostasis and maintaining blood pressure.
Capillaries: Where Blood Exchanges Substances with Tissues
Blood in capillaries flows onward to venules.
Precapillary sphincters regulate the flow of blood into capillaries.
Capillaries are the “turnaround points” for the cardiovascular system.
Section 8
Cardiovascular Disorders
Cardiovascular Disorders
Many factors may influence your chance of developing a cardiovascular disorder.
Some risk factors include: family history, hypertension, obesity, smoking, or simply age.
Inflammation, which leads to the production of C-reactive protein by the liver, may also play a role in cardiovascular disease.
Cardiovascular Disorders
Arteries can be clogged or weakened.
Arteriosclerosis is a hardening of the arteries. When cholesterol and other lipids build up in these hardened arteries, atherosclerosis occurs.
Atherosclerotic plaques can impede blood flow.
Coronary arteries are narrow and vulnerable to clogging with these plaques; chest pain (angina pectoris) or heart attack may occur.
Cardiovascular Disorders
High blood levels of cholesterol can lead to atherosclerosis.
Low-density lipoproteins (LDL or “bad” cholesterol) carry cholesterol into the arterial walls; high-density lipoproteins (HDL or “good” cholesterol) remove it.
A total of 200 mg cholesterol per milliliter of blood or less is considered acceptable for most people.
Cardiovascular Disorders
Surgery may be needed to clear blocked arteries.
Coronary bypass involves using a large vessel from elsewhere in the body to bypass a completely blocked artery in the heart.
Cardiovascular Disorders
Laser angioplasty uses a laser to vaporize plaques while balloon angioplasty uses small balloons to flatten the plaques to open room in the artery; a wire “stent” may be inserted to keep the ballooned area open.
Statins are drugs designed to reduce the amount of cholesterol in the blood.
Disease, injury, or defects can weaken artery walls so they bulge outward due to blood pressure, forming an aneurysm; aneurysms can be fatal if the artery wall bursts.
Cardiovascular Disorders
Heart damage can lead to heart attack and heart failure.
A heart attack is damage to or death of heart muscle.
In heart failure, the heart is weak and does not pump blood as efficiently.
Cardiovascular Disorders
Arrhythmias are abnormal heart rhythms.
Electrocardiograms (ECGs) are recordings of the cardiac cycle and can be used to reveal irregular heart rhythms.
Arrhythmias are irregular heart rhythms; bradycardiais a below normal rhythm, while tachycardia is an above normal rhythm.
Ventricular fibrillation occurs when the ventricles contract haphazardly so that blood is not pumped correctly; this can lead to cardiac arrest.
Cardiovascular Disorders
A heart-healthy lifestyle.
Lifestyle changes can greatly reduce the risk
of cardiovascular disease.
Diets low in fat and cholesterol, regular exercise, and not smoking are three key strategies.
