PowerLecture: Chapter 9 Circulation The Heart and Blood Vessels



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PowerLecture: Chapter 9


Learning Objectives

  • 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.



How Would You Vote?

  • To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu.

  • Would you favor mandatory CPR training in high schools?

    • a. Yes, it would save countless lives.
    • b. No, it’s just another graduation requirement.


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.


Section 2

  • The Heart: A Double Pump



The Heart: A Double Pump

  • The heart is a durable pump made mostly of cardiac muscle (myocardium).

    • The heart is surrounded by a tough, fibrous sac
    • (pericardium).
    • The inner lining of the heart is the endocardium; it is composed of connective tissue and epithelial cells (endothelium).




The Heart: A Double Pump

  • The heart has two halves and four chambers.

    • The septum divides the heart into two halves, right and left.
      • Each half consists of an atrium (receiving chamber) and a ventricle (pumping chamber) separated by an atrioventricular valve (AV valve).
      • The AV valve on the right is a tricuspid valve; the one on the left is the bicuspid, or mitral valve.
      • Chordae tendineae (“heartstrings”) connect the AV valve flaps to the ventricle wall.
    • Blood exits each ventricle through a semilunar valve.




The Heart: A Double Pump

    • Heart muscle cells are serviced by the coronary circulation; coronary arteries branch off the aorta, forming a capillary bed around the heart.






The Heart: A Double Pump

  • In a “heartbeat,” the heart’s chambers contract, then relax.

    • 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.








Section 4

  • How Cardiac Muscle Contracts



How Cardiac Muscles Contract

  • 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.
    • In hypotension, the blood pressure is too low; loss of water or blood volume can lead to circulatory shock.






Section 6



Structure and Functions of Blood Vessels

  • Arteries are large blood pipelines.

    • Because of their elastic walls,
    • arteries tend to “smooth out” the
    • pressure changes associated with
    • the discontinuous pumping cycle of
    • the heart (felt as a pulse).
    • 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.
    • Billions of capillaries ensure that all cells are
    • 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; bradycardia is 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.





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