By: Andrea MelendezClarisa Melendez

Sashank Polavarapu

Cardiovascular System

The cardiovascular system has two components:

1. The heart , which 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. The right side of the heart and its blood vessels form the pulmonary circuit

2. The left side of the heart and its vessels form the systemic circuit, which supplies blood to the entire body.

Function of circulation: connect the body’s trillions of cells to organs of exchange: lungs, small intestine and kidney.

-lungs: oxygen enters and carbon dioxide exits the blood.

-Small intestine: absorbs nutrient molecules into the blood

-Kidney: allow metabolic wastes to exit the blood. The heart is located in the thoracic cavity between the lungs within the mediastinum. The heart pumps the blood through the pulmonary and systemic vessels, it performs these

functions:

1. Keeps O2 –poor blood separate from O2-rich blood

2. Keeps the blood flowing in one direction

3. Creates blood pressure, which moves the blood through the circuits

4. Regulates the blood supply based on the current needs of the body.

12.1 Anatomy of the Heart The wall and Coverings of the Heart- The heart is enclosed by a two-layered serous membrane called the pericardium

- Visceral (meaning “organ”) Pericardium: Considered part of the heart wall

-Forms the epicardium : Outer surface of the heart

- The myocardium : Thickest part of the heart wall

- The inner endocardium is composed of simple squamous epithelium.

- Chambers of the Heart- it has four hollow chambers:

- two superior atria - Each atrium has a wrinkled anterior pouch called an auricle.- Internally, the atria are separated by the interatrial septum- Have thin walls and each pumps blood into the ventricle below

- two inferior ventricles.- They are separated by the interventricular septum- Are thicker and pump blood into blood vessels that travel to other parts of the body

- Right Atrium- at its posterior wall, it receives O2-poor blood from 3 veins: Superior vena cava, coronary sinus, inferior

vena cava- Venousu blood passes from the right t atrium into the right ventricle through an atrioventricular valve.- The AV valve on the right side of the heart is called the tricuspid valve because it ahs 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 papillary muscles, which are conical extensions of the myocardium

-blood from the right ventricle passes through the semilunar valve into the pulmonary trunk

-Pulmonary semilunar valve, prevents blood from flowing back into the right ventricle- Left Atrium

-at is posterior wall, it receives O2 rich blood from four pulmonary veins.

-blood passes from the left atrium into the left ventricle through an AV valve.

-The AV valve on the left side is specifically called the bicuspid valve because it has two cusps.

-(In the U.S., the bicuspid valve is referred to as mitral valve because the valve is similar to a bishop’s hat.)

- Left Ventricle

-Forms the apex of the heart.

-Blood passes from the left ventricle through a semilunar valve into the aorta.

- this semilunar valve is appropriately called the aortic semilunar valve

-Beyond the aortic semilunar valve lie the coronary arteries: blood vessels that lie on and nourish the heart itself.

Operation of the Heart Valves and Heart Sounds

-The AV valves are open

-When a ventricle contracts, the increasing pressure of the blood inside the ventricle forces the cusps of the AV valve to slam shut

-when a ventricle contracts, the papillary muscles also contract, causing the chordae tendinae to tighten and pull on the valve.

-The Semilunar valves are normally closed

-However, the contraction of the ventricles pushes blood at high pressure against the valve cusps, forcing the valves open.

-When the ventricle relaxes, the blood in the artery pushes backward, closing the valve again.

-A heartbeat produces sounds as the chambers contracts and the valves close.

-The first heart sound is heard when the ventricles begin to contract and the atrioventricular valves close. This sound lasts the longest and has a lower pitch

-the second heart sound is heard when the relaxation for the ventricles allows the semilunar valves to close.

Coronary Circulation The right and left coronary arteries branch from the aorta just beyond the aortic semilunar valve.

Some arteries join so that there are several routes to reach any particular capillary bed in the heart.

the coronary veins are specifically called cardiac veins. The cardiac veins enter a coronary sinus, which is essentially a thing-walled vein. The coronary sinus enters the right ventricle.

12.2 Physiology of the Heart Conduction system of the Heart

-It’s a route of specialized cardiac muscle fibers that initiate and stimulate contraction of the atria and ventricles.

-Its intrinsic meaning that the heart beats automatically without the need for external nervous stimulation.

-It coordinates the contraction of the atria and ventricles so that the heart is an effective pump.

Nodal Tissue:

- The heartbeat is controlled by nodal tissue, which has both muscular and nervous characteristics.

-This type of cardiac muscle is located in two regions:

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

-Initiates the heartbeat and automatically sends out an excitation impulse every 0.85s.

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

-when the impulses reach the AV node, there is a slight delay that allows the atria to finish their contraction before the ventricles begin their contraction .

-The signal for the ventricles to contract travels form the AV node through the two branches of the atrioventricular bundle (AV bundle) before reaching the numerous and smaller Purkinje fibers

-They consist of cardiac muscle fibers that spread an electrical signal throughout the ventricles.

-The cardiac muscle cells are connected to each other by specialized gap junctions called intercalated discs.

-It allows electrical current to flow from cell to cell.

- The SA node pacemaker keeps the heartbeat regular.

- If the AV node is damaged, the ventricles still beat because all cardiac muscle cells contract on their own.

- when a rate of contraction is faster than the SA node a site called ectopic pacemaker can cause an extra beat. (Caffeine can stimulate this.)

Electrocardiogram

-with the contraction of any muscle, electrolyte changes occur that can be detected by electrical recording devices. The resulting record, called an electrocardiogram, helps a physician detect and possibly diagnose the cause of an irregular heartbeat.

-Arrhythmias: an irregular heartbeat

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 from 60 to 100 beats per minute.

-Systole: Contraction of heart muscle

-Diastole: Relaxation of heart muscle.

- During the cardiac cycle, atrial systole is followed by ventricular systole.

Phase 1: Atrial Systole:

-Time= 0.15 sec. During this phase, 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.

-Closure of the AV valves causes the first heart sound.

Phase 2: Ventricular Systole

-Time-0.30s. During this phase, both ventricles are in systole (contracted), while the atria are in diastole (relaxed).

-Rising blood pressure in the ventricles forces the semilunar valves to open.

-Closure of the semilunar valves causes the second heart sound.

Phase 3: Atrial and Ventricular Diastole.

-Time= 0.40s. During this period , both atria and both ventricles are in diastole (relaxed)

Cardiac Output

-Is the volume of blood pumped out of a ventricle in one minute.

-Cardiac output is dependent on two factors:

- heart rate (HR)=beats per minute

-stroke volume(SV)=amount of blood pumped by a ventricle each time it contracts.

-Cardiac output= HR x SV

-The CO of an average human is 5,250 ml per minute = total volume of blood in the human body.

Heart Rate- A cardioregulatory center in the medulla oblongata of the brain can alter the heart rate by way of the autonomic nervous

system.

-Its under the influence of the cerebrum and hypothalamus. When we feel anxious, the sympathetic motor nerves are activated.

- Stroke Volume

-is the amount of blood that leaves a ventricle, depends on the strength of contraction.

-The degree of contraction depends on the blood electrolyte concentration and the activity of the autonomic system.

- Venous Return- Amount of blood entering the heart by way of the venae cavae (right side of heart) or pulmonary veins (left side of heart).

- -the heart adjusts the strength of its own contraction beat by beat, based upon venous return. This principle is called the Frank-Starling law.

- Difference in Blood Pressure

-The strength of ventricular contraction has to be strong enough to oppose the blood pressure with the attached arteries.

-If a person has hypertension or atherosclerosis, the opposing arterial pressure may reduce the effectiveness of contraction and the stroke volume.

Types of Blood Vessels (3):Arteries, Capillaries, Veins

Functions of Blood Vessels: Transport blood & its contentsCarry out exchange of gases plus nutrients for

waste at the systemic capillariesRegulate blood pressureDirect blood flow to those systemic tissues

that most require it at the moment

12.3 Anatomy of Blood Vessels

ARTERIES & ARTERIOLES

Arteries: transport blood away from the heart.

-They have thick, strong, walls composed of 3 layers:

1) The tunica interna is an endothelium layer with a basement membrane.

2) The tunica media is a thick middle layer of smooth muscle and elastic fibers.

3) The tunica externa is an outer connective tissue layer composed of elastic & collagen fibers.

Arteriole: Branch from an artery that leads into a capillary.

Arterioles that are constricted or dilated affects blood distribution and blood pressure.

Ex: when a muscle is contracting, the arterioles dilate and more blood flows to the muscle to supply it with oxygen and glucose.

CAPILLARIESArterioles branch into capillaries.Capillaries: Extremely narrow, microscopic

blood vessels with a wall composed of only one layer of endothelial cells.

Importance: Nutrient and waste molecules are exchanged only across their thin walls. Oxygen and glucose diffuse out of capillaries into the tissue fluid that surrounds cells, and Carbon Dioxide with wastes diffuse into the capillaries.

Capillary beds: networks of many capillaries-Most capillary beds allow blood to move

directly from an arteriole to a venule( a small vessel leading to a vein) when the capillary bed is closed.

-Sphincter muscles, called Precapillary sphincters, encircle the entrance to each capillary.

VEINS & VENULES

Vein: Blood vessel that takes blood to the heart

Venule: Type of blood Bessel that takes blood from capillaries to veins.

Valve: Allow blood to flow only toward the heart when they are open and prevent the backward flow of blood when they are closed.

Varicose Veins & PhlebitisVaricose veins: Abnormal & irregular

dilations in superficial veins, especially in lower legs.

Hemorrhoids: Abnormally dilated blood vessels (Varicose veins) of the rectum.

Phlebitis: Inflammation of a veinPulmonary Embolism: Blockage of a

pulmonary artery by a blood clot that commonly originates in a vein of the lower legs.

12.4 PHYSIOLOGY OF CIRCULATION

Circulation: Is the movement of blood through blood vessels, from the heart to the body and then back to the heart.

VELOCITY OF BLOOD FLOWThe velocity of blood flow is slowest in the

capillaries.Explanation: This is because the aorta

branches into the other arteries, & these in turn branch into the arterioles, until blood finally flows into the capillaries. Each time and artery branches, the total cross sectional area of the blood vessels increases, reaching the maximum cross sectional area in the capillaries.(Fig 12.10)

 Adversely, blood flow increases as venules

combine to form veins, and velocity is faster in the venae cavae than in the smaller veins.

BLOOD PRESSURE

Blood Pressure: Is the force of blood against the walls of blood vessels.

-Arterial blood pressure is highest in the aorta because the pumping action of the thick-muscled left ventricle forces blood into the aorta.

-Figure 12.11 : Blood pressure changes throughout the systemic circuit. Blood pressure decreases with distance from the left ventricle. Blood pressure varies in the arterial system between systolic blood pressure & diastolic blood pressure.

-During Systole, the left ventricle is pumping blood out of the heart, & during diastole the left ventricle is resting.

2 factors that affect blood pressure are: 1) Cardiac Output: which equals heart rate x

Stroke Volume 2) Peripheral Resistance: Resistance to flow

between blood & walls of a blood vessel. Blood Pressure & Cardiac Output

The faster the heart rate, the greater the cardiac output is. As cardiac output increases, blood pressure increases as well. The larger the stroke volume, the greater the blood pressure. Stroke volume & Heart Rate increase blood pressure only if the venous return is adequate.

Venous Return Depends on 3 factors:1) A blood pressure difference2) The skeletal muscle pump & the respiratory

pump3) Total blood volume in the cardiovascular systemSkeletal Pump: When skeletal muscles contract,

they compress the weak walls of the veins that causes blood to move past a valve. (Fig.12.12) Once past it, backward pressure of blood closes the valve and prevents its return.

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

Blood pressure & Peripheral Resistance:The nervous & endocrine system both affect peripheral resistance.

Neural Regulation of Peripheral Resistance:Vasomotor Center: Neurons in the brain stem that control the diameter of the arteries.

Hormonal Regulation of Peripheral Resistance:-When the blood volume and blood sodium level are low, the kidneys secrete the enzyme rennin. Renin: Secretion from the kidney that activates angiotensingen to angiotensin I.-When the atria of the heart are stretched due to increased blood volume, cardiac cells release a hormone called atrial natriuretic hormone (ANH): which inhibits rennin secretion by the kidneys and aldosterone secretion by the adrenal cortex.

EVALUATING CIRCULATION

Pulse & Blood Pressure are 2 ways to evaluate circulation.

Pulse: Vibration felt in arterial walls due to expansion of the aorta following ventricular contraction.

Blood Pressure: Force of blood against a blood vessel wall.

Blood pressure is measured in the brachial artery with a sphygmomanometer (FIG 12.15)

-20% of Americans suffer from Hypertension, which is high blood pressure. It is present when the systolic blood pressure is 140 or greater, or the diastolic blood pressure is 90 or greater.

Circulatory Routes Blood vessels belong to either the pulmonary circuit or the

systematic circuit. Blood from all regions of body first collects in the right atrium

and then is passed into the right ventricle, and pumps it into the pulmonary trunk.

The pulmonary trunk divides into the pulmonary arteries, which in turn divide into the arterioles of the lungs.

The blood is then exchanged with for oxygen and carbon dioxide in the pulmonary capillaries.

The blood then enters the pulmonary venules and flows through the pulmonary veins back to the left atrium

Congestive heart failure In congestive heart failure a damaged left side of the heart

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

The congested vessels leak fluid into the tissue spaces causing pulmonary edema.

This will result in short breath, constant cough, and fatigue. It is treated with either diuretics, digoxin, or dilators.

Sometimes heart transplants are also done.

The major systematic arteries After the aorta leaves the heart it is divided into the ascending

aorta, the aortic arch, and the descending aorta. The left and right coronary arteries, which supply blood to the

heart, branch off the ascending aorta. The Brachiocephalic artery, the left common carotid artery,

and the left subclavian artery are the 3 major branches. These blood vessels serve the head and arms.

The major systematic veins The external, and internal jugular veins drain blood from the

head and neck. An external jugular vein enters a subclavian vein that, along

with an internal jugular vein enters a brachiocephalic vein. Right and left brachiocephalic veins merge, giving rise to the

superior vena cava. In the abdominal cavity , the hepatic portal vein receives blood

from the abdominal viscera and enters the liver. Emerging from the liver, the hepatic veins enter the inferior

vena cava. In the pelvic region, veins from the various organs enter the

internal iliac.

Effects of aging The heart generally grows larger with age because fat deposits

in epicardium and myocardium. With age, the valves, particularly the aortic semilunar valve,

become thicker and more rigid. As a person ages, the myocardium loses some of its contractile

power and some of its ability to relax. The resting heart rate decreases throughout life, and the maximum possible rate during exercise also decreases.

Effects of agingIn the elderly, arterial walls tend to thicken with

plaque and become inelastic, signaling that atherosclerosis and arteriosclerosis are present.

The chances of coronary thrombosis and heart attack increase with age.

The occurrence of varicose veins increases with age, particularly in people who are required to stand for long periods of time.

Thromboembolism as a result of varicose veins can lead to death if a blood clot settles in a major branch of a pulmonary artery.

HomeostasisHomeostasis is possible only if the cardiovascular system

delivers oxygen and nutrients to and takes metabolic wastes from the tissue fluid surrounding the cells.

Blood’s composition is maintained by other systems of the body.

Growth factors regulate the manufacture of formed elements in the red bone marrow, which is a lymphatic organ.

The digestive system absorbs nutrients into the blood, and the lungs and kidneys filter metabolic wastes from blood. The kidneys are responsible for maintaining a safe pH level within the blood.

The liver produces plasma proteins, stores glucose until it’s needed, and transforms ammonia into urea.