The cardiovascular system consists of the heart, blood vessels, and blood. The heart pumps blood through arteries, veins, and capillaries. Arteries carry oxygenated blood away from the heart while veins carry deoxygenated blood back to the heart. Capillaries allow for gas and nutrient exchange between blood and tissues. The heart has four chambers and uses electrical signals to coordinate contractions that pump blood. Multiple control mechanisms regulate cardiac function, including the renin-angiotensin-aldosterone system which helps control blood pressure.

1. CARDIOVASCULAR SYSTEM (CVS)
Introduction:
Cardiovascular system is made up of
1. Arteries
2. Veins
3. Capillaries
4. Heart
 The heart, blood, and blood vessels are the three structural elements that
make up the circulatory system.
 The heart is the engine of the circulatory system. It is divided into four
chambers: the right atrium, the right ventricle, the left atrium, and the left
ventricle.
 The walls of these chambers are made of a special muscle called
myocardium, which contracts continuously and rhythmically to pump blood.
 The pumping action of the heart occurs in two stages for each heart beat:
diastole, when the heart is at rest; and systole, when the heart contracts to pump
deoxygenated blood toward the lungs and oxygenated blood to the body.
 During each heartbeat, typically about 60 to 90 ml (about 2 to 3 oz) of
blood is pumped out of the heart.
What are the functions of cardiovascular system?
The following are the functions of cardiovascular system:
1. Circulates blood throughout body
2. Transports energy substances like glucose, fatty acids, electrolytes,
hormones etc.
3. Removes waste products like lactate, CO2 etc.
4. Regulates body temperature
What are the features of arteries?
 These are thick walled vessels
 Carry blood from heart to peripheral organ/tissue.
 Carry oxygenated blood only (except pulmonary artery which carries de-
oxygenated blood).
 They gradually narrow in diameter.
 They are high pressure vessels.
 Made up of three layers, they are from inside outward called tunica intima,
media and externa.
 Most of the arteries contain smooth muscles in their wall.
 Contraction of these muscles leads to narrowing of diameter and
relaxation causes increase in diameter

2. What are the features of veins?
 These are thin wall vessels
 They carry blood from tissue/organ to heart.
 Carry de-oxygenated blood only (except pulmonary veins which carry
oxygenated blood).
 Gradually increase in diameter.
 Contain valve within them to allow uni-directional blood flow towards
heart.
 Contraction of leg muscles cause squeezing of veins and pushing the blood
up.
 They contain very small amount of muscle fibres.
What are the features of capillaries?
 Tiny minute vessels connecting terminal arteries with small initial veins.
 Made up of single layer of endothelial cells.
 Allows oxygen transfer at tissue level
Describe the human heart.
 The heart is a hollow muscular organ and lies within the pericardium in
the mediastinum.
 The heart is usually felt to be on the left side because the left ventricle is
stronger (it pumps to all body parts).
 The heart is enclosed by a sac known as the pericardium and is
surrounded by the lungs.
 The pericardium is a double membrane structure containing a serous
fluid to reduce friction during heart contractions.
 The mediastinum, a subdivision of the thoracic cavity, is the name of the
heart cavity.
 The heart is about the size of clenched fist of its owner

3.  It is connected at its base to the great blood vessels but otherwise lies free
within the pericardium.
 It is made up of four chambers, namely left & right atrium and left & right
ventricle.
Layers of heart:
 The heart consists of several layers of a strong muscle called the myocardium.
 Myocardium is covered externally by another thin layer called the
pericardium.
 Pericardium is also known as epicardium.
 On the inner side, there is another thin layer, which is known as endocardium.
How does circulation of blood take place?
 Veins of lower part of the body collectively drain blood into inferior vena cava.
 Veins of upper part of the body drain blood into superior vena cava.
 Both vena cava open into right atrium.
 Blood from right atrium enter into right ventricle from right atrium through
tricuspid valve.
 Pulmonary artery carries blood from right ventricle into lungs.
 Purified blood from lungs is carried by pulmonary veins into left atrium
 From left atrium blood enters into left ventricle through mitral valve.
 Blood is ejected from left ventricle into aorta and then it is circulated to every
part of body through branches of aorta.

4. What are the features of valves in the chambers of heart?
 There are total four valves in the chambers of heart.
 Between right atrium and right ventricle, tricuspid valve is present.
 Between right ventricle and pulmonary artery, pulmonary valve is
present.
 Between left atrium and left ventricle, mitral valve is present, whereas
between left ventricle and opening of aorta, aortic valve is present
 Valves permit uni-directional blood flow.
 Aortic valve regulates flow from left ventricle to aorta.
 Mitral valve - regulates flow from left atrium to left ventricle.
 Tricuspid valve regulates flow from right atrium to right ventricle.
 Pulmonary valve - regulates flow from right ventricle to pulmonary artery

5. How does the heart get arterial blood supply?
 The arterial supply of the heart is provided by the right and left coronary
arteries.
 They arise from the aorta immediately above the aortic valve.
 They and their major branches are distributed over the surface of the heart
lying within sub-epicardial connective tissue.
 The left coronary artery arises from the ascending aorta (left posterior aortic
sinus). In the atrioventricular groove it divides into an anterior interventricular
branch (Left anterior descending, LAD) and a circumflex branch.
 The right coronary artery arises from the ascending aorta (anterior aortic
sinus).

6. How does conduction system of heart work?
 The conducting system of heart is responsible for systole (contraction) and
diastole (relaxation) of chambers of heart.
 The conducting system of the heart consists of specialized cardiac muscle
present in the sino-atrial node, the atrioventricular bundle and its right and left
terminal branches (Right and left bundle branches) and the subendocardial
plexus of Purkinje fibers.
 The sino-atrial node is the site where the electrical cycle begins and it is
often called the pacemaker.
 It is situated just to the right of the opening of the superior vena cava into
the right atrium.
 The conducting system of the heart generates rhythmical cardiac impulses
and conducts these impulses rapidly throughout the myocardium, so that the
different chambers contract in a coordinated and efficient manner.
 The parasympathetic nerves slow the rhythm and diminish the rate of
conduction of the impulse.
 The sympathetic nerves increase the heart rate and conduction velocity.
 Contraction of a chamber is called systole and relaxation is diastole.
 Two atria contract and relax simultaneously.
 Two ventricles also work in same way.
 Atrial and ventricular contraction alternate with each other so that during
atrial systole there is ventricular diastole and vice versa.
How is cardiac function controlled?
 There are multiple control mechanisms for cardiac function.

7.  Two important are adrenergic receptors and RAAS ((Renin Angiotensin
Aldosterone System) of kidneys.
 Adrenergic receptors of two types, α and .  receptors are again
subdivided in to -1 and -2.
 α1 receptors are situated in smooth muscles. In blood vessels, on
stimulation , it leads to vasoconstriction
 α2 receptors located on pre and postsynaptic nerve terminals. Mediates
synaptic transmission.
 -1 receptors are situated in heart and kidney. When stimulated in heart
they increase force (positive inotropic) and rate (positive chronotropic) of
contraction. When stimulated in kidney, they enhance the secretion of renin. So
stimulate the RAAS pathway.
 -2 receptors are located in arteries of skeletal muscles and bronchus
when stimulated causes dilatation of bronchus and artery of skeletal muscles.
 Catecholamine stimulates alpha and beta receptors.
 Kidneys perform important functions like maintenance of blood volume,
excretion of waste products, regulation of electrolytes etc.
 By maintaining sodium, potassium and water kidneys help to maintain
blood volume and subsequently blood pressure.

8. Renin - Angiotensin - Aldosterone System (RAAS):
Kidney is an important system for regulation of blood pressure as shown in figure
The renin-angiotensin-aldosterone system (RAAS) plays an important role in
regulating blood volume and systemic vascular resistance, which together
influence cardiac output and arterial pressure. As the name implies, there are
three important components to this system:
1) Renin,
2) Angiotensin, and
3) Aldosterone.
Renin, which is primarily released by the kidneys, stimulates the formation of
angiotensin in blood and tissues, which in turn stimulates the release of
aldosterone from the adrenal cortex.
STIMULATION BLOCKER
α Vasoconstriction
: Raises BP
Vasodilation: Lowers BP
 1 Increase force and rate of
contraction of heart &
stimulates RAAS by
increasing renin secretion.
Vasodilation
Bronchodilation, Vasodilation
Reduces rate & force of heart
contraction, suppresses
RAAS.
Vasoconstriction
BP
 2

9. Renin is a proteolytic enzyme that is released into the circulation primarily by the
kidneys. Its release is stimulated by
1) Sympathetic nerve activation (acting via beta-adrenoceptors)
2) Renal artery hypotension (caused by systemic hypotension or renal artery
stenosis)
3) Decreased sodium delivery to the distal tubules of the kidney.
When renin is released into the blood, it acts upon a circulating substrate,
angiotensinogen, that undergoes proteolytic cleavage to form the decapeptide
angiotensin I. Vascular endothelium, particularly in the lungs, has an enzyme,
angiotensin converting enzyme (ACE), that cleaves off two amino acids to form
the octapeptide, angiotensin II (AII), although many other tissues in the body
(heart, brain, vascular) also can form AII.
All has several very important functions:
 Constricts resistance vessels (via Angiotensin II [AT1] receptors) thereby
increasing systemic vascular resistance and arterial pressure
 Acts on the adrenal cortex to release aldosterone, which in turn acts on the
kidneys to increase sodium and fluid retention
 Stimulates the release of vasopressin (antidiuretic hormone, ADH) from
the posterior pituitary, which increases fluid retention by the kidneys
 Stimulates thirst centers within the brain
 Facilitates norepinephrine release from sympathetic nerve endings and
inhibits norepinephrine re-uptake by nerve endings, thereby enhancing
sympathetic adrenergic function
 Stimulates cardiac hypertrophy and vascular hypertrophy
Terms
 Preload:
It is the degree to which the ventricles are stretched prior to contraction
 Afterload
It is the tension produced by a chamber of the heart in order to contract.
Afterload can also be described as the pressure that the chamber of the heart has
to generate in order to eject blood out of the chamber.
 End diastolic Volume (EDV): The amount of blood in the ventricles just
before systole. Range from 65ml to 240ml. (Avg. value 120ml).
 End Systolic Volume (ESV): The amount of blood in the ventricles just
before diastole. Range from 16ml to 143ml. (Avg. value 50ml).
 Stroke volume (SV) :

10. It is the amount of blood pumped by the left ventricle of the heart in one
contraction. Equation: SV = End Diastolic Volume (EDV) [120ml] – End Systolic
Volume (ESV) [50ml] = 70ml. Therefore, Average normal stroke volume is 70ml.
(Range from 55 to100ml).
 Cardiac output:
It is the volume of blood being pumped by the heart, in particular a ventricle in a
minute. It is equal to the heart rate multiplied by the stroke volume. An average
resting cardiac output (Q) would be 5.6 L/min for a human male and 4.9 L/min
for a female.
 Ejection fraction ( EF)
It is the fraction of blood ejected by the Left Ventricle (LV) during the contraction
phase of the cardiac cycle (known as Systole). It measures the capacity at which
heart is pumping. A normal LV ejection fraction is 55 to 70%.
 Cardiac cycle
It is the term referring to all or any of the events related to the flow of blood that
occurs from the beginning of one heartbeat to the beginning of the next.
 Blood pressure:
The force exerted by circulating blood on the walls of arteries.
BP= Cardiac output (C.O.) x Total peripheral resistance (TPR).