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.