Chapter 12

Cardiovascular System

All but the simplest animals have circulatory systems with 3 main components:

1. A central pump

2. A vascular system

3. The circulating fluid

In the human cardiovascular system,

– The central pump is the heart.

– The vascular system is the blood vessels.

– The circulating fluid is the blood.

1. Blood Vessels

1. Blood Vessels

3 types:• ARTERIES carry blood away from the

heart.

• VEINS carry blood toward the heart.

• CAPILLARIES allow for exchange between the bloodstream and tissue cells.

All blood vessels are lined by a thin layer of tightly packed epithelial cells.

Structural differences in the walls of the different kinds of blood vessels correlate with their different functions.

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arteriole venule

b. Capillary

valve

a. Artery

outer layermiddle layerinner layer

c. Vein

3 layers to an arterial wall

– Endothelium

• Inner layer

• simple squamous

epithelium

– Middle layer

• smooth muscle

– Outer layer

• connective tissue

Veins contain 3

layers but less

smooth muscle

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d.

outer layermiddle layerinner layer

outer layermiddle layerinner layer

artery

vein

20 µm© Ed Reschke

THE CAPILLARIES

• Join arterioles to venules

• Extremely narrow and only a single layer of

endothelium thick

• Form vast networks in all regions of the body

• Very important role in homeostasis –

exchange of substances

– Oxygen and nutrients

– Wastes and carbon dioxide

– Excess fluid picked up by lymphatic system

Anatomy of a Capillary Bed

bloodflow

arteriole

capillaries

arteriovenousshunt

venule

bloodflow

vein

precapillarysphincters

arteryCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Blood Flow Through Capillary Beds

Notice how small the capillaries are, just wide enough for one red cell

The walls of capillaries are thin and leaky.

•As blood enters a capillary at the arterial end, blood pressure pushes fluid rich in oxygen, nutrients, and other substances into the interstitial fluid.

•At the venous end of the capillary, CO2 and other wastes diffuse from tissue cells and into the capillary bloodstream.

THE VEINS

• Walls are structured similarly to the walls of arteries (3 layers)– Less smooth muscle and connective tissue in

veins

• Often have valves to prevent the backflow of blood– Varicose veins, hemorrhoids

• Great capacity to expand– Serve as blood reservoir

VaricosesWeak valves may be due to weak vein walls. Weak walls not so elasticlonger and wider wallsvalves flaps separate blood can flow backward through the valvesThe backflow of blood fills the veins and stretches the walls even moreBigger, swollen veins, often twisted as they try to squeeze into their normal space.

2. the Heart

Pericardium:Sac around the heart

Myocardium:•Major portion of the heart•Consists mainly of cardiac muscle

Endocardium:•Lines the inner surface of the heart•Membrane consisting of connective tissue and endothelium

The human heart is a muscular organ about the size of a fist.

• It is located under the breastbone.

• It has 4 chambers:

1.Right atrium

2.Left atrium

3.Right ventricule

4.Left ventricule

5.Four Valves between chambers separate them, they are like “doors”.

6.The septum separates the left from the right side.

septum

semilunar valve

left atriumright atrium

atrio ventricular(bicuspid) valve

atrio ventricular(tricuspid) vave

chordae tendineaetendons

right ventricle

left ventricle

Blood arrives first in the atrium then goes to the ventricule.

The valves prevent the blood to go back to the previous chamber

Path of Blood Through the Heart

Vena cava right atrium tricuspid valve right ventricle pulmonary semilunar valvepulmonary trunk pulmonary arteries lungs pulmonary veins left atrium bicuspid valveleft ventricle aortic semilunar valve aortabody

http://www.youtube.com/watch?v=rguztY8aqpk

1.The pulmonary circuit

carries blood between the heart and the lungs.

2. The systemic circuit

carries blood between the heart and the rest of the body.

Blood rich in CO2, vessels are blue

Blood rich in O2, vessels are red

The Heartbeat (Cardiac Cycle)

– Each time the heart beats:– The 2 atria contract simultaneously– Then the 2 ventricles contract simultaneously– All the chambers then relax

– Systole: Contraction of the heart muscle

– Diastole: Relaxation of the heart muscle

The Cardiac Cycle

The heart relaxes and contracts regularly:

– Diastole is the relaxation phase of the heart cycle.

– Systole is the contraction phase.

The HeartbeatHeart Sounds described as

a “lub-dup” sound• “Lub” sound:

atrioventricular valves closing• “Dup” sound:

semilunar valves closing

A heart murmur (swishing sound) may be due to a leaky valve

http://www.wilkes.med.ucla.edu/Physiology.htm

The Pacemaker and the Control of Heart Rate

The pacemaker sets the tempo of the heartbeat. It is composed of specialized muscle tissue in the wall of the right atrium.

The impulses sent by the pacemaker produce electrical currents that can be detected by electrodes placed on the skin. These are recorded in an electrocardiogram (ECG or EKG).

An artificial pacemaker:

is a medical device which uses electrical impulses, delivered by electrodes contracting the heart muscles, to regulate the beating of the heart.

Electrocardiogram (ECG)http://www.youtube.com/watch?v=nK0_28q6WoM&feature=related

A recording of the electrical changes occurring in the heart

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b.

R

PT

Q

S

• P Wave occurs just prior to atrial contraction

• QRS complex occurs just prior to ventricular

contraction

• T wave occurs after ventricular contraction

Blood pressure• Systolic Pressure results from the

contraction of the ventricule

• Diastolic Pressure is the pressure in the arteries when the heart relaxes

• As blood flows from the aorta into the arteries and arterioles, blood pressure falls

• Also, the difference between systolic and diastolic pressure gradually diminishes

• In the capillaries, blood flow is slow and fairly even

Blood pressure is expressed in millimeters of mercury (mmHg)

Optimal blood pressure for adults is <120 systolic and < 80 diastolic.

High blood pressure or hypertension is:

• persistent systolic blood pressure 140

• and/or diastolic blood pressure 90.

Blood Return Through VeinsAfter chemicals are exchanged between the blood and body cells, blood returns to the heart via the veins.By the time blood enters the veins, the pressure from the heart has dropped to near zero but blood still moves through the veins against the force of gravity.•As skeletal muscles contract, they help squeeze the blood along.•Valves prevent backflow

4. BLOOD

4. Blood

Contains:

1. Plasma (1/2 of this volume) liquid

2. Different types of cellular components:

– Red blood cells

– White blood cells

– Platelets

BLOOD FUNCTIONS

– Transport functions

– Regulatory functions

– Protective functions

c.

neutrophils

platelets

monocyte

eosinophil

lymphocyte

basophil

250

red bloodcell

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© EdReschke

A. Red Blood Cells and Oxygen Transport

• most numerous type of blood cell.

• also called erythrocytes.

• Manufactured in red bone marrow

• When mature lack a nucleus

Hemoglobin:• Large amount are contained in each red blood cell.• contains iron and transports oxygen throughout

the body.

capillary

a. Blood capillary 400 b. Red blood cells SEM 4,175

helical shapeof the polypeptidemolecule

hemegroup

iron

c. Hemoglobin molecule

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a: © Ed Reschke/Peter Arnold; b: © Andrew Syred/Photo Researchers, Inc.

Contain hemoglobin• Red iron-containing pigment• Heme portion binds oxygen• Carbon monoxide can also bind at heme sites

-Combines more readily than oxygen-Can be lethal

Red Blood Cells

– Last around 120 days

– Destroyed in the liver and spleen• Iron is mostly recycled• Heme portion degraded – bile pigments

– Carbohydrates at the surface will determine blood type

BLOOD TYPE

Anemia

• Too few red blood cells

• Not enough hemoglobin in red blood cells

• 3 causes1. Decreased production of red blood cells

• Iron-deficiency anemia

2. Loss of red blood cells

3. Destruction of red blood cells

B. White Blood Cells and Defense

• fight infections and cancer.

• also called leukocytes.

• Larger than red blood cells

• Nucleated

White Blood Cells• Granular leukocytes have visible granules in

cytoplasm (enzymes and proteins)– Neutrophils: most abundant leukocyte, phagocytic– Basophils: granules stain deep blue and release

histamine– Eosinophils: stain deep red, fight parasitic worms

• Agranular leukocytes lack visible granules– Lymphocytes-T and B cells, roles in immunity– Monocytes-largest WBC’s, phagocytic dendritic

cells and macrophages

C. Platelets and Blood Clotting

Blood contains 2 components that aid in clotting:

– Platelets (thrombocytes) are bits of cytoplasm pinched off from larger cells in the bone marrow.

– Fibrinogen is a membrane-wrapped protein found in plasma.

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Fibrinogen

Ca2+

1. Blood vessel is punctured.

2. Platelets congregate and form a plug.

3. Platelets and damaged tissue cells release prothrombin activator, which initiates a cascade of enzymatic reactions.

4. Fibrin threads form and trap red blood cells.

Blood-clotting process

Prothrombin activator

Prothrombin Thrombin

Fibrin threadsCa2+

Platelets release molecules that convert fibrinogen into fibrin.

– Fibrin is a threadlike protein.– Fibrin forms a dense network to create a patch.

Hemophilia

• Inherited disorder– Most common type has faulty gene on X

chromosome

• Deficiency in a clotting factor

• Internal bleeding can cause serious damage to cells and tissues

• Hemophilia is treated by blood transfusions and injections of clotting factors

6.The Role of the Cardiovascular System in

Homeostasis

5.The Role of the Cardiovascular System in

HomeostasisThe cardiovascular system performs several homeostatic functions:

1. Controlling chemical balance

2. Controlling the composition of the blood

3. Regulating body temperature

4. Distributing hormones

5. Defending against foreign invaders

What happens when this homeostasis is not maintained?

Cardiovascular Disease

Cardiovascular disease accounts for 40% of all deaths in the United States. The leading cause of death in the United States is heart attack.

chronic cardiovascular disease (lasts for a long time or recurrent).

1.The blood vessels become impaired gradually.

2.Vessels are narrowed by plaques of cholesterol and other substances. This fatty material thickens, hardens, and may eventually block the arteries.

3.The tissue will not be supplied with blood and will die.

A. Atherosclerosis

Cause of strokes, heart attack.

fat

coronary artery ulceration

lumenof vessel

cholesterolcrystals

atheroscleroticplaque

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© Biophoto Associates/Photo Researchers, Inc.

B. Heart Valve Disease– 90,000 people/year have faulty heart valves

repaired or replaced– May be malformed at birth– More commonly degenerate due to age or

disease

– A narrowing of the aorta is the

most common cause, it results in

the bicuspid valve to prolapse or

“fall” into the ventricule.

C. STROKE

• Cerebrovascular accident

• Arteriole in the brain bursts or is blocked by an embolus

• Lack of oxygen to brain can cause paralysis or death

• Warning signs: numbness in hands or face, difficulty speaking, temporary blindness in one eye

D. HEART ATTACK

When blood exits the heart, several coronary arteries immediately branch off to supply the heart muscle.

If 1 or more of these arteries is blocked, the heart muscle cells will quickly die.

Coronary Bypass Operations

• Bypass blocked areas of coronary arteries

• Can graft another vessel to the aorta and then to the blocked coronary artery past the point of blockage

• Gene therapy may be a future treatment

• Angioplasty– Catheter is placed in clogged artery– Balloon attached to catheter is inflated– Increases the lumen of the vessel– Stents can be placed to keep vessel open

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stent

catheter

a. Artery is closed.b. Stent is placed.

c. Balloon is inflated.

arterialwall

Heart Transplants

– Transplants usually successful but shortage of donors

– LVAD-left ventricular assist device• Temporary alternative to heart transplant• Tube passes blood from left ventricle to the LVAD• Blood is pumped to the aorta

TAH-total artificial heart

– Generally only used on very ill patients– Survival rates are not good but may be

because patients are so ill

Hypertension (high blood pressure)http://blood-pressure.emedtv.com/high-blood-pressure-video/introduction-to-high-blood-pressure-video.html

– Affects about 20% of all Americans– Usually caused by a narrowing of the arteries,

which means the blood pressure needs to be higher to get the blood through

– Age, gender, and lifestyle can influence blood pressure

• Obesity• Smoking• High dietary salt intake

– Medications can be used to treat this disease

How can you avoid becoming a heart disease victim?

–Don’t smoke. O2 to the heart and to other tissues

exercise tolerance. HDL (good) cholesterol. blood pressure and heart rate

–Exercise.

–Eat a heart-healthy diet.