The Cardiovascular System

 Cardio means HEART and Vascular means Blood vessels

 Also called The Circulatory System
 Consists of the HEART, BLOOD VESSELS and LYMPHATICS.
 Divided for descriptive purposes in 2 main parts:
 Heart-pumping action ensures constant circulation of the blood
 Blood Vessels-form a lengthy network through which the blood flows.
 The lymphatic system is closely connected, both structurally and functionally, with the
cardiovascular system.
 Functions:
 Transporting Oxygen and Removing Carbon Dioxide

-most important function of the circulatory system is to supply oxygen to all the
cells in the body.
-Every cell in the body requires a constant supply of oxygen to stay alive.
-most of the cells are not in contact with air, the circulatory system must supply
them with oxygen. 
 Transporting Nutrients and Removing Wastes

-A second critical function of the circulatory system is to supply all the cells in
the body with nutrients and energy.

- After food is digested in the stomach, it migrates through the intestines, where
nutrients from food are absorbed into the bloodstream.

-The blood also absorbs glucose, an energy source, from the liver, which is the
body's glucose distribution center.

-These nutrients and energy are then transported to all the cells of the body, in
a manner similar to the transport of oxygen.

-Blood also absorbs the waste products made by cells, and transports them to
the excretory organs for removal from the body.

 Fighting Disease

- the blood also carries around important disease-fighting cells.

- The organs of the immune system, such as the spleen, create many types of
specialized cells that can kill foreign cells trying to invade the body.

-The circulatory system is responsible for transporting these cells from the
immune system to all other parts of the body.
  Transporting Hormones

-Hormones are crucial chemical signals that the body uses to communicate with
itself.

-Hormones control many things such as growth, the reproductive cycle and
glucose metabolism.

-Hormones are created in one part of the body, such as the brain or the liver,
and then must be transported to another part of the body by the cardiovascular
system in order to deliver their message.

 Regulating Body Temperature

-If body temperature rises too high, blood vessels close to the skin dilate,
increasing in size.

-The larger surface area of blood vessels close to the skin means more heat is
conducted across the skin into the air.

- Conversely, if body temperature drops, the blood vessels constrict, decreasing

in size.

-The smaller surface area of blood vessels next to the skin causes less heat to be
lost across the skin and retains more heat in the body.

HEART
 The heart is a muscular organ about the size of a fist and is composed of special muscle tissue
(cardiac muscle).
 its weight is about 250-300 g
 Situated in the middle of the mediastinum behind the breastbone in the chest, at the level
of thoracic vertebrae T5-T8.( locatedin the chest between the lungs behind the sternum and
above the diaphragm.)
 In the average lifetime the heart beats 250 million times and pumps 340 million litres of blood.
 The heart is a sophisticated pump that is controlled by an electrical current that is initiated in
the brain.
 The largest part of the heart is usually slightly offset to the left side of the chest

***Because the heart is between thelungs, the left lung is smaller than the right lung and has a
cardiac notch in its border to accommodate the heart.

 The Blood Vessels: The heart wall consists of three layers

 the pericardium (tunica adventitia)is made up of two sacs the outer sac consist of
fibrous tissue
  the myocardium (tunica media) is the muscle layer and responsible for heart
contractility
 the endocardium(tunica intima)this lines the chamber and valves of the heart. It is a
thin smooth glistening membrane that permits smooth flow of the blood inside the
heart.

 The heart pumps blood into two anatomically separate systems of blood vessels.
 The pulmonary circulation.
 The systemic circulation.
 The right side of the heart pumps blood to the lungs(the pulmonary circulation) where
gas exchange occurs.
 The left side of the heart supplies the blood intothe systemic circulation, which
supplies blood tothe rest of the body.

 Control of blood vessel diameter

 When nervous activity is increased the smooth muscle of tunica media contracts and
thickens; this process is called vasoconstriction.
 Decreasednerves stimulation relaxes the smooth muscle thinning the vessel wall and
enlarging the lumen . This process is called vasodilatation.
 The heart is supplied with arterial blood by the right and left coronary arteries, the arteries
receive about 5% of blood pumped from heart.

 Interior of the heart

 The heart is divided into right and left side by the septum.

THE CHAMBERS
 Heart contains four (4) hollow chambers:
o Each side is divided by an atrioventricular valve into an upper chamber
called The atrium and a lower chamber called The ventricle.
 The valves between the atria and ventricles open and close passively according
to changes in pressure in chambers.
 The opening of the pulmonary artery is guarded by the pulmonary valve and
the opening of aorta is guarded by the aortic valve.

THE VALVES

 Function:
o the valves allow forward flow of blood through the heart and prevent
backflow.
o Valves open and close in response to pressure changes caused by
ventricular contraction and blood ejection
 The Heart contains four (4) valves.
 Two (2) Atrioventricularvalves (AV)
 The right atrioventricular valve is TRICUSPID
VALVE
- Preventsbackflow from the right
ventricle into the right atrium.
- Has (3) three triangular cusps or
leaflets.
 The left atrioventricular valve is MITRAL VALVE
(BICUSPID)
- Prevents backflow from the left
ventricles into the left atrium.
- Has (2) two cusps, a large anterior and
a smaller posterior

***Chordae tendineae attach the cusps of the AV valves to

papillary muscles in the ventricles.
 Two (2) semilunar valves
 PULMONIC VALVE
- Prevents backflow from the pulmonary
artery into the right ventricle
  AORTIC VALVE
- Prevents backflow from the aorta
into the left ventricle.

***Both semilunar valves have (3) three cusps that are shaped like half-moons

 Conducting system of the heart

 Small group of specialized neuromuscular cells in the myocardium initiate and conduct
impulses, causing coordinated and synchronized contraction of the heart muscle.
 The conduction system of the heart contains pacemaker cells, which have (3) three
unique characteristics:
 Automaticity. The ability to generate an electrical impulse automatically
 Conductivity. The ability to pass impulse to the next cell
 Contractility. The ability to shorten fibers in the heart when receiving impulse.
 Impulse conduction
 Sinoatrial node (SA node)
 Mass of specialized cells
 Lies in the wall of right atrium
 Is the pacemaker of heart
 Firing of SA node causes atrial contraction.
 Atrioventricular node (AV node)
 situated in the wall of atrial septum near the atrioventricularvalve
 conducts the impulse that arrive from SA node, passes it through AV
bundle(Bundle of His) and purkinjefibres which in turn convey the
impulse to the ventricle.

 Cardiac Cycle
 Period from the beginning of one heartbeat to the beginning of the next.
 Electrical and mechanical events must occur in the proper sequence and to the proper
degree to provide adequate blood flow to all the body parts.
 Has (2) two phases:
 Systole-the phase of the heartbeat when the heart muscle contracts and pumps
blood from the chambers into the arteries.
 Diastole-the phase of the heartbeat when the heart muscle relaxes and allows the
chambers to fill with blood.

At the beginning of SYSTOLE Ventricles contract bp in the ventriclesforces AV valves (mitral &
tricuspid) to close and semilunar valves (pulmonic and aortic) to open eject blood in the aorta and
pulmonary artery.

When the ventricles relaxes ventricular pressure falls below the pressure in the pulmonary artery and
the aorta.

At the beginning of DIASTOLE semilunar valves close to prevent the backflow of the blood into the
ventricles mitral & tricuspid valves open allowing blood flow into the ventricles from the atria
Ventricles full ofthe atria contract t send remaining blood to the ventriclesThen a new cardiac cycle
begins as the heart enters systole again.

 Cardiac Output
 Refers to the amount of blood the heart pumps in 1 minute.
 It’s equal to heart rate multiply by stroke volume the amount of blood ejected with each
heartbeat.
 Stroke volume depends on (3) three major factors:
 Preload- stretching of muscle fibers in the ventricles
 Contractility- inherent ability of the myocardium to contract normally.
This is influenced by preload. The greater the stretch the more forceful the
contraction.
  Afterload-refers to the pressure that the ventricular muscles must generate to
overcome the higher pressure in the aorta to get the blood out of the heart.

BLOOD FLOW

As blood makes its way through the vascular system, it travels through (5) five distinct types of
blood vessels involving (3) methods of circulation.

 Blood Vessels
 Arteries-is a vessel that carries blood away from the heart and toward other tissues and
organs.
 While most arteries carry oxygenated blood, there are two exceptions to this,
the pulmonary and the umbilical arteries
Functions:
 Carry blood that is oxygenated after it has been pumped from the heart
 Arteries also aid the heart in pumping blood
 Arteries carry oxygenated blood away from the heart to the tissues, except for
pulmonary arteries, which carry blood to the lungs for oxygenation. 
 Arterioles-is a small diameter blood vessel in the microcirculation that extends and
branches out from an artery and leads to capillaries.
 have muscular walls (usually only one to two layers of smooth muscle) and are
the primary site of vascular resistance.
 receive autonomic nervous system innervation and respond to various
circulatinghormones in order to regulate their diameter.
 Capillaries-are the smallest of a body's blood vessels 
 These microvessels, measuring around 5 to 10 micrometres (µm) in diameter,
connect arterioles and venules, and they help to enable the exchange of
water, oxygen, carbon dioxide, and many other nutrients and waste substances
between the blood and the tissues.
Functions:
 performs an important function by allowing nutrients and waste
substances to pass across it. Molecules larger than 3 nm such
as albumin and other large proteins pass through transcellular
transport carried inside vesicles, a process which requires them to go
through the cells that form the wall.
 Venules-is a very small blood vessel in the microcirculation that allows blood to return
from the capillary beds to drain into the larger blood vessels, theveins.
 Venules range from 7 to 50μm in diameter.
 Veins contain approximately 70% of total blood volume, 25% of which is
contained in the venules.
 Many Venules unite to form a vein.

 Veins-are blood vessels that carry blood toward the heart.

 Most veins carry deoxygenated blood from the tissues back to the heart;
exceptions are the pulmonary and umbilical veins, both of which carry
oxygenated blood to the heart.
  Veins are less muscular than arteries and are often closer to the skin.
 There are valves in most veins to prevent backflow.

CIRCULATION

3 methods of circulation:

 Pulmonary Circulation
Blood travels to the lungs to pick up oxygen and release carbon dioxide
(CO2).
Route:
As the blood moves to the heart, to the lungs, and back again, it
proceeds as follows:
o Unoxygenated blood travels from the right ventricle through
the pulmonic valve into the pulmonary arteries
o Blood passes through progressively smaller arteries and
arterioles into the capillaries of the lungs.
o Blood reaches the alveoli and exchanges carbon dioxide for
oxygen.
o Oxygenated blood then returns via venules and veins to the
pulmonary veins, which carry it back to the heart’s left atrium.

 Systemic Circulation
Blood pumped from the left ventricle carries oxygen and other
nutrients to body cells and transports waste products for excretion.
Route:
The major artery, THE AORTA, braches into vessels that supply specific
organs and areas of the body. As it arches out of the top of the heart
and down to the abdomen, (3) three arteries branch off the top of the
arch to supply the upper body with blood:
o The left common carotid artery supplies blood to the brain.
o The left subclavian artery supplies the arms.
o The innominate artery supplies the upper chest.

As the AORTA descends through the thorax and abdomen, its

branches supply the organs of the GI and genitourinary systems,
spinal column, and lower chest and abdominal muscles. Then the
aorta divides into the iliac arteries, which further divided the femoral
arteries.

Cardiovascular changes in aging

 As a normal part of aging, the heart usually becomes slightly smaller. Contractile strength also
declines, making the heart less efficient.

 In most people resting cardiac output diminishes 30% to 35% by the age of 70. Veins dilate and
stress with age, and coronary artery blood flow drops 35% between ages 20 and 60.

 The aorta becomes more rigid, causing systolic blood pressure to rise disproportionately higher
than the diastolic, resulting in a winded pulse pressure.

 Between ages 30 and 80, the left ventricular walls grows 25% thicker from increased efforts to
pump blood.

 Heart valves also become thicker from fibrotic and sclerotic changes. This can prevent the valves
from closing completely, causing systolic murmurs.

smdv//dlsl.con//2023