Chapter 12: The Cardiovascular System

CHAPTER 12:THE CARDIOVASCULAR SYSTEM

Roberto ArceJordan BlakeDaniel RodriguezDean Shoua

Cardiovascular System

The Cardiovascular system consists of two components.1. The Heart

Pumps blood so that it flows to tissue capillaries and lung capillaries.

2. The Blood Vessels through which the blood flows The Cardiovascular system is divided into two

functional systems.1. Pulmonary Circuit

Consists of the right side of the heart and its blood vessels.2. Systemic Circuit

Consists of the left side of the heart and its vessels. Supplies blood to the entire body.

Section 1:

Anatomy of the Heart

The Heart is located in the Thoracic Cavity Between the lungs within the mediastinum

Hollow, cone-shaped, muscular organ As the heart pumps blood through the pulmonary

and systemic vessels, it performs these functions:1. Keeps O2-poor blood separate from O2-rich blood2. Keeps the blood flowing in one direction-blood flows

away from and then back to the heart in each circuit3. Creates blood pressure, which moves the blood

through the circuits4. Regulates the blood supply based on the current

needs of the body

Anatomy of the Heart: The Wall and Coverings of the Heart The heart is enclosed by a two-layered serous

membrane called the pericardium The Visceral Pericardium is considered part of

the heart wall. Forms the epicardium, the outer surface of the heart. The myocardium is the thickest part of the heart.

Made up of cardiac muscle. When cardiac muscle fibers contract, the heart beats.

The inner epicardium is composed of single squamous epithelium. Endothelium not only lines the heart but it also continues

into and lines the blood vessels; preventing blood from clotting unnecessarily.

Anatomy of the Heart: The Wall and Coverings of the Heart The pericardial cavity develops

when the visceral pericardium doubles back to become the parietal pericardium, the other serous layer.

The two serous membranes (epicardium and parietal pericardium) secrete pericardial fluid. The Pericardial fluid reduces friction as

the heart beats.

Anatomy of the Heart: The Wall and Coverings of the Heart The Parietal Pericardium is fused

to the outermost fibrous pericardium.

The fibrous pericardium is a layer of fibrous connective tissue that adheres to the great blood vessels at the heart’s base and anchors the heart to the wall of the mediastinum.

The coverings of the heart protect the heart, confine it to its location, and prevent it from overfilling, while allowing the heart to contract and carry out its function of pumping the blood.

A layer of the heart can become inflamed due to infection, cancer, or a complication of surgery.

Anatomy of the Heart: The Wall and Coverings of the Heart

Anatomy of the Heart: Chambers of the Heart

The Heart has four hollow chambers Two superior atria (sing., atrium) Two inferior ventricles

The atria are separated by the interatrial septum, and the ventricles are separated by the interventricular septum. The heart’s pulmonary circuit (its right side)

is completely separated from its systemic circuit (its left side) by the septum.


The thickness of each chamber’s myocardium is suited to its function. Atria have thin walls and each pumps blood

into the ventricle below. The thinner myocardium of the right

ventricle is suited for pumping blood to the lungs.

The left ventricle has a thicker wall than the right ventricle. Thicker myocardium enables the left ventricle

to pump its blood to all other parts of the body.


Right Atrium Receives O2-poor blood from three veins.

1. The superior vena cava2. The coronary sinus3. The inferior vena cava

Venous blood passes from the right atrium into the right ventricle through an atrioventricular (AV) valve. This valve directs the flow of blood and prevents

any backflow. The AV valve on the right side of the heart is

specifically called the tricuspid valve, due its three cusps, or flaps.


Right Ventricle The cusps of the tricuspid valve are

connected to fibrous cords, called the chordae tendineae (“heart strings”). The chordae tendineae are connected to the

papillary muscles. Blood from the right ventricle passes through

a semilunar valve into the pulmonary trunk. This particular semilunar valve, called the

pulmonary semilunar valve, prevents blood from flowing back into the right ventricle.


Left Atrium Receives O2-rich blood from four

pulmonary veins. Two pulmonary veins come from each

lung. Blood passes from the left atrium into the

left ventricle through an AV valve. The AV valve is specifically called the

bicuspid valve because it has two cusps


Left Ventricle The left ventricle forms the apex of the heart. The papillary muscles in the left ventricle are quite

large, and the chordae tendineae attached to the AV valve are thicker and stronger than those in the right ventricle.

Blood passes from the left ventricle through a semilunar valve, called the aortic semilunar valve, into the aorta. The semilunar cusps of this valve are larger and thicker

than those of the pulmonary semilunar valve. The first branches from the aorta are the coronary

arteries, blood vessels that lie on and nourish the heart itself.

Anatomy of the Heart: Coronary Circulation

Cardiac muscle fibers and the other types of cells in the heart wall receive nutrients and rid themselves of wastes at capillaries embedded in the heart wall. Diffusion of oxygen and nutrients from blood in the chambers to all the

cells that make up the heart would be too slow. Right and Left coronary arteries branch from the aorta just beyond

the aortic semilunar valve Each of these arteries branches and then rebranch until the heart is

encircled by small arterial blood vessels. Some of these join so that there are several routes to reach any particular

capillary bed in the heart. Alternate routes are helpful if an obstruction should occur along the path of blood reaching cardiac muscle cells.

After blood has passed through cardiac capillaries, it is taken up by vessels that join to form veins. The coronary veins are specifically called cardiac veins. The cardiac veins enter a coronary sinus, which is essentially a thin-

walled vein. The coronary sinus enters the right ventricle.

Physiology of the Heart

The physiology of the heart pertains to its pumping action, which is the heartbeat.

It is estimated that the heart beats two and a half billion times in a lifetime, continuously recycling 5 liters (L) of blood to keep us alive.

Physiology of the Heart:Conduction System of the Heart

The conduction system of the heart is a route of specialized cardiac muscle fibers that initiate and stimulate contraction of the atria and ventricles. Conduction system is intrinsic, meaning that

the heart beats automatically without the need for external nervous stimulation.

Conduction system coordinates the contraction of the atria and ventricles so that the heart is an effective pump. Without this conduction system, the atria and ventricles would contract at different rates.


Nodal Tissue: The heartbeat is controlled by nodal tissue, which has both

muscular and nervous characteristics. This unique type of cardiac muscle is located in two regions of the heart:

1. The SA (sinoatrial) node: located in the upper posterior wall of the right atrium.

Intiates heartbeat and automatically sends out an excitation impluse every 0.85 seconds. Impluses spread out over the atria, causing them to contract.

The SA node normally functions as the pacemaker for the entire heart because its intrinsic rate is the fastest in the system.

2. The AV (atrioventricular) node: located in the base of the right atrium very near the interatrial septum.

The AV Bundle, its branches, and the Purkinje fibers consist of specialized cardiac muscle fibers that efficiently spread an electrical signal throughout the ventricles.

Cardiac muscle cells are connected to each other by specialized gap junctions called intercalated discs.


Nodal Tissue:3. The SA node pacemaker usually keeps the

heartbeat regular. If the SA node fails to properly, the ventricles still beat

due to impulses generated by the AV node, but the beat is slower (40 to 60 beats per minute).

To correct this condition, it is possible to implant an artificial pacemaker, which automatically gives an electrical stimulus to the heart every 0.85 second.

Should the AV node be damaged, the ventricles still beat because all cardiac muscle cells can contract on their own, however, the beat is so slow that the condition is called a heart block.

Physiology of the Heart: Stages in Cardiac Cycle


Electrocardiogram With the contraction of any muscle, including

the myocardium, electrolyte changes occur that can be detected by electrical recording devices. These changes occur as a muscle action

potential sweeps over the cardiac muscle fibers. The result is called an electrocardiogram, which

helps a physician detect and possibly diagnose the cause of an irregular heartbeat There are many types of irregular heartbeats, called

arrhythmias.

Physiology of the Heart:Cardiac Cycle

A cardiac cycle includes all the events that occur during one heartbeat. On average, the heart beats about 70

times a minute, although a normal adult heart rate can vary between 60 to 100 beats per minute.

Systole – contraction of heart muscle Diastole – relaxation of heart muscle


Phase 1: Atrial Systole. Time: 0.15 second. Both atria are in systole (contracted),

while the ventricles are in diastole (relaxed). Rising blood pressure in the atria forces the blood to enter the two ventricles through the AV valves.

Atrial Systole ends when the atrioventricular valves slam shut. Close of the AV valves is caused by the rising pressure of blood filling the ventricle.


Phase 2: Ventricular Systole. Time: 0.30 second Both ventricles are in systole (contracted),

while the atria are in diastole (relaxed). Rising blood pressure in the ventricles forces the semilunar valves (aortic and pulmonary) to open. Blood in the right ventricle exits through the pulmonary artery trunk to the right and left pulmonary arteries. Simultaneously, blood in the left ventricle exits into the aorta.

Both semilunar valves are open, and the atrioventricular are valves closed.


Phase 3: Atrial and Ventricular Diastole Time: 0.40 second Both atria and ventricles are in diastole

(relaxed). Pressure in all the heart chambers is low. Blood returning to the heart from the

superior and inferior venae cavae and the pulmonary veins fills the right and left atria and flows passively into the ventricles.

Both atrioventricular valves are open and the semilunar valves are closed.

Physiology of the Heart:Cardiac Output

Cardiac output (CO) is the volume of blood pumped out of a ventricle in a minute. Cardiac output is dependent on two factors:

1. Heart rate (HR) = beats per minute.2. stroke volume (SV) = amount of blood pumped

by a ventricle each time it contracts3. Cardiac output = HR X SV The CO of an average human is 5.250 ml per

minute. Cardiac output can vary because stroke volume and

heart rate can vary. Heart regulates the blood supply, dependent on the body’s needs.


Heart Rate A cardioregulatory center in the medulla

oblongata of the brain can alter the heart rate by way of the autonomic nervous system. Receives sensory input from receptors within the

cardiovascular system. Cardioregulatory center is under the influence of the

cerebrum and the hypothalamus, causing an anxious feeling upon sympathetic motor nerve activation.

Parasympathetic motor impulses conducted by the vagus nerve cause the heart rate to slow, and sympathetic motor impulses conducted by sympathetic motor fibers cause the heart rate to increase.


Stroke Volume Stroke volume, which is the amount of blood that leaves

a ventricle, depends on the strength of contraction. Degree of contraction depends on the blood electrolyte

concentration and activity of the autonomic system. Two additional factors also influence the strength of contraction: Venous Return: the amount of blood entering the heart by

way of the venae cavae (right side of the heart) or pulmonary veins (left side of the heart).

Difference in Blood Pressure: the strength of ventricular contraction has to be enough to oppose the blood pressure within the attached arteries. If a person has hypertension or atherosclerosis, the opposing arterial pressure may reduce the effectiveness of contraction and the stroke volume.

Anatomy of Blood Vessels

Three types of blood vessels Arteries, capillaries, and veins.

Function Transport blood and its contents Carry out exchange of gases in the

pulmonary capillaries and exchange of gases plus nutrients for waste at the systemic capillaries

Regulate blood pressure Direct blood flow to those systemic tissues

that most require it at the moment.

Anatomy of Blood Vessels

Arteries

Arteries functions transport blood away form the heart The arteries are composed of three layers

the (tunica interna , tunica media, and tunica externa)

Tunica interna is an endothelium layer with a basement membrane

Tunica media is the middle layers of smooth muscle and elastic fibers

Tunica externa is an outer connective tissue layer made up of elastic and collagen fibers.

Arterioles

Arterioles are very small just visible by the naked eye for the most part it is composed of smooth muscle but it also contains elastic tissue.

if the muscle contracts the lumen cavity would decrease

if the fibers relax the lumen of the arteriole enlarges.

Whether arterioles are constricted or dilated affects blood distribution and blood pressure

Arterioles branch into capillaries.

Capillaries

Extremely narrow, microscopic blood vessels with a wall composed of only one layer of endothelial cells.

Important to the cardiovascular system because nutrients and waste molecules are exchanged only across their thin walls.

Oxygen and glucose defuse out of capillaries into the tissue fluid that surrounds cells

Carbon dioxide and other wastes defuse into the capillaries.

Capillary beds

Networks of many capillaries. Present in all regions of the body. Not all capillary beds are open or in

use at the same time. Most capillary beds have a small

passage that allows blood to move directly from an arteriole to a venule when the capillary bed is closed. Venule: small vessel leading to a vein.

Precapillary Sphincters

Encircle the entrance to each capillary

When constricted the capillary bed closes preventing blood from entering the capillaries.

When relaxed the capillary beds open

The larger the number of beds open the lower the blood pressure.

Veins and Venules

Veins and smaller vessels called venules return blood from the capillary beds to the heart.

first the venules drain the blood form the capillaries and then join together to form a vein.

Vein walls are a lot thinner than the walls of an artery, because the mid layer of muscle and elastic fiber is thinner.

Within the major veins of the arms and legs valves allow blood to flow only to ward the heart when they are open to prevent to backward flow of blood to reach the heart.

Varicose

Varicose veins are irregular in superficial veins, mainly those in the lower legs.

These types of veins develop when the valves of the veins become weak due to the backward pressure of the blood.

Phlebitis

Phlebitis is the inflammation of a vein, this is a very serious condition because thromboembolism can occur.

Thromboembolism is an obstruction of a blood vessel by a blood clot that has become dislodged from another site in circulation.

This is a condition that can become fatal.

Velocity of Blood Pressure Blood flow has the slowest velocity in the capillaries each time

an artery branches the total cross-sectional area of the blood vessels increase.

The slow rate of the blood flow in the capillaries is beneficial because it allows exchange of gases in pulmonary capillaries and for the exchange of gases and nutrients for wastes in the systemic capillaries.

Conversely blood flow increases as venuels combine to form veins, and velocity is faster in the venae cavae than in the smaller veins .

The cross sectional area of the two venae cavae is more than twice that of the aorta. And the velocity of the blood returning to the heart remains low compared to the blood leaving the heart.

In a resting individual it takes only a minute for a drop of blood to go form the heart to the foot and back again to the heart.

Blood Pressure

Force of blood against the walls of blood vessels.

Arterial blood pressure is higher because the pumping action of the powerful, thick muscled left ventricle forces blood into the aeorta.

Mean Arterial Blood Pressure (MABP)

Pressure in the arterial system averaged over time.

The more blood that leaves the left ventricle the greater the pressure of blood against the wall of an artery.

Skeletal Muscle Pump

When muscles contract they compress the weak walls of the veins they cause the blood to move past the valve.

Once past the valve, backwards pressure of blood closes the valve and prevents its return. Blood in veins always return to the heart.

Gravity can assist the return of venous blood from the head to the heart but not the return of blood from the extremities and trunk to the heart.

Respiratory Pump

When inhalation occurs, thoracic pressure falls and abdominal pressure rises as the chest expands.

This aids in the flow of venous blood back to the heart because blood flows from areas of higher pressure rise as the chest expands.

This aids in blood flow because areas of higher blood pressure flow into areas of lower pressure.

Neural regulation of peripheral resistance

A vasomotor center is the medulla oblongata controls vasoconstriction. This center is under control of the cardio regulatory center.

The vastemotor center then stimulates sympathetic nerve fibers which cause the heart rate to increase and the arterioles to constrict.

Increasing heart rate increases cardiac output constricting the arterioles which increases peripheral resistance which results in a rise of blood pressure.

Hormonal Regulation of Peripheral Resistance

Certain hormones cause blood pressure to raise epinephrine and norepinephrine, the hormones from adrenal medulla, increase the heart rate.

The cardiac output and blood pressure also increase.

Epinephrine and norepinephrine also constrict arterioles in capillary beds supplying the skin abdominal kidneys.

Evaluating Circulation

Taking blood pressure and pulse are two ways to evaluate circulation.

Pulse

Surge of blood entering the arteries causes their elastic walls to stretch and recoil.

These superficial arteries are called pulse points. Customary locations to check pulse

include: radial artery, side of wrist, and neck.

Pulse is usually 70 times per minute.

Blood Pressure

Usually measured in the brachial artery with a sphygmomanometer.

Sphygmomanometer is wrapped around patients arm, and a stethoscope is placed over brachial artery.

Cuff is inflated until no blood flows through it. Cuff pressure is slowly lowered until blood begins to pump

again. (systolic pressure) While there is pressure the pulse makes a sound only

heard through the stethoscope, these sounds are called Korotkoff sounds.

As the pressure is lowered even more the sounds get weaker and once the sound is completely gone you have reached diastolic pressure.

Hypertension is high blood pressure.

Blood Pressure

http://www.youtube.com/watch?v=qWti317qb_w




Congestive heart failure

Heart failure is caused when there is damage to the left side of the heart.

It fails to pump adequate blood and blood backs up in the pulmonary circuit.

Causing the blood vessels to become congested

Congested vessels leak fluid into tissue spaces causing pulmonary edema

Pulmonary causes shortness of breath, fatigue, and a constant cough.

Circulatory routes

Pulmonary Arteries o Blood from all regions of the body

first collects in the right atrium and then passes into the right ventricle which gets divide throughout the pulmonary arteries.

Pulmonary veins o Oxygen enriched blood flows

through the pulmonary veins to fill the lungs with oxygen

The Major Systemic Arteries Three major arteries branch off the aortic

arch1. Brachiocephalic artery- is a short artery

that arises from the aorta and divide into the carotid and subclavian arteries

2. Left common carotid artery- supply the head and neck with oxygenated blood and divide in the neck to form carotid arteries

3. Left subclavian artery- gets blood from the aortic arch and supply blood to the left arm.

The major systemic veins

major veins 1. External and Internal jugular veins- drain

blood from the head, neck, and brain the external vein enters the brachiocephalic vein

2. Brachiocephalic vein- right and left Brachiocephalic veins merge giving rise to the superior vena cava.

3. Hepatic portal vein- enter the inferior vena cava in the pelvic region, veins from the various organs enter the internal iliac veins..

Effects of Aging

The heart generally grows larger with age mainly because of fat deposition in the epicardium and myocardium.

As a person ages the myocardium loses some of its contractile power and some of its ability to relax.

In the elderly arterial walls tend to thicken with plaque and become inelastic.

Chances of a hear increase with age

Homeostasis

Homeostasis is possible only if the cardiovascular system delivers oxygen and nutrients to and takes metabolic wastes from the tissue fluid surrounding the cells.

Maintaining Blood Composition, pH, and Temperature

Composition of the blood is maintained by the other systems of the body.

Growth factors regulate the manufacture of formed elements in the red bone marrow(lymphatic organ).

Red blood cells assist the respiratory system by carrying oxygen.

Immune system would not be able to function without the ability of white blood cells.

Digestive system absorbs nutrients into blood, and the lungs and the kidneys remove metabolic wastes from blood.

The kidneys maintain pH of the blood. The liver is a key regulator of blood components by producing

plasma proteins, storing glucose until it is needed, transforming ammonia into urea, and changing other poisons into molecules that are also excreted.

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Chapter 12: The Cardiovascular System