Cardiovascular system, POOJA GODIYAL

CARDIOVASCULAR SYSTEM
MRS. POOJAGODIYAL

Introduction
• Cardio – Heart
• Vascular – Blood vessels
• For descriptive purposes it is divided into two
main parts
• The heart, whose pumping action ensures
constant circulation of the blood
• The blood vessels, which forms a lengthy
network through which the blood flows
18/4/2020 MRS. POOJA GODIYAL 2

BLOOD VESSELS
• are the components of the circulatory system
• transport blood throughout the human body
• transport blood cells, nutrients, and oxygen to
the tissues of the body
• take waste and carbon dioxide away from the
tissues

• Blood vessels vary in structure, size and
function, and there are several types
Arteries
Arterioles
Capillaries
Venules
Veins

Arteries and Arterioles
• An artery is an elastic blood vessel that
transports blood away from the heart
• An arteriole is a small-diameter blood vessel in
the microcirculation that extends and branches out
from an artery and leads to capillaries
• Pulmonary arteries transport blood that has a
low oxygen content from the right ventricle to the
lungs
• Systemic arteries transport oxygenated blood
from the left ventricle to the body tissues

• Arteries transport blood away from the heart
and branch into smaller vessels,
forming arterioles
• Arterioles distribute blood to capillary beds,
the sites of exchange with the body tissues
• Capillaries lead back to small vessels known
as venules that flow into the larger veins and
eventually back to the heart

Artery Structure
The artery wall consists of three layers:
• Tunica Adventitia (Externa)- the strong outer
covering of arteries and veins
• It is composed of connective tissue as well as
collagen and elastic fibers
• These fibers allow the arteries and veins to
stretch to prevent over expansion due to the
pressure that is exerted on the walls
by blood flow

• Tunica Media - the middle layer of the walls
of arteries and veins
• It is composed of smooth muscle and elastic
fibers
• This layer is thicker in arteries than in veins

Tunica Intima
• the inner layer of arteries and veins
• In arteries, this layer is composed of an elastic
membrane lining and smooth endothelium (a
special type of epithelial tissue) that is covered
by elastic tissues

• The artery wall expands and contracts due to
pressure exerted by blood as it is pumped by
the heart through the arteries
• Arterial expansion and contraction or
pulse coincides with the heart as it beats
• The heartbeat is generated by cardiac
conduction to force blood out of the heart and
to the rest of the body

Anastomoses
• Defined as communication between the
neighboring blood vessels
• The branches of an artery are connected to the
branches of another neighboring artery
• If one artery supplying the area is occluded,
anastomotic arteries provide a collateral
circulation (the alternate circulation around a
blocked artery or vein via another path, such as
nearby minor vessels)

Anastomoses
• For e.g.
• Arterial anastomosis around scapula
• Arterial anastomosis around elbow joint
• Anastomoses around knee joint

Collateral Circulation
• Occurs when an area or tissue or an organ has a
number of different pathways for blood to reach it
• This happens as a result of anastomosis present
between adjacent arteries

True/Anatomic End Artery
• Those arteries that do not have precapillary
anastomoses with their neighboring arteries
• In case of blockage of an artery due to a thrombus,
the part supplied by it undergoes ischemia and later
avascular necrosis
• E.g. Arteries supplying
kidney, brain and retina

True/Anatomic End Artery

Functional End Artery
• Those arteries whose terminal branches do
anastomose, but the anastomoses is not sufficient to
maintain the blood supply to the part they supply in
case of any blockage in the artery
• E.g. Coronary arteries

Capillaries and Sinusoids
• The capillaries form a vast network of tiny vessels
that link the smallest arterioles to smallest venules
• Capillary walls consist of a single layer of endothelial
cells sitting on a very thin basement membrane
• Their diameter is approx. 7µm
• The capillary bed is the site of exchange of
substances between the blood and the tissue fluid

Capillaries and Sinusoids
• In certain places, including the liver and bone marrow, the
capillaries are significantly wider and leakier than normal
• These capillaries are called sinusoids
• Their walls are incomplete
• Their lumen is much larger than usual, blood flows through
them more slowly under less pressure and can come directly
into contact with cells outside the sinusoid wall

Capillary refill time
• The capillary nail refill test is a quick test done
on the nail beds
• It can be measured by holding a hand higher than
heart-level and pressing the soft pad of a finger or
fingernail until it turns white, then taking note of
the time needed for the color to return once
pressure is released
• Normal capillary refill time is usually less than 2
seconds
• It is used to monitor dehydration and the amount
of blood flow to tissue

Veins and Venules
• Veins return blood at low pressure
to the heart
• Walls of the veins are thinner than
arteries but have the same three
layers of tissue
• Some veins possess valves, which
prevent backflow of blood
• The cusps are semilunar in shape
with concavity towards the heart
• The smallest veins are called
venules

Control of blood vessel diameter

GAS EXCHANGE
• Gas exchange occurs at two sites in the body:
in the lungs, where oxygen is picked up and
carbon dioxide is released at the respiratory
membrane, and at the tissues, where oxygen is
released and carbon dioxide is picked up
• The actual exchange of gases occurs due to
simple diffusion

EXTERNAL RESPIRATION
• External respiration occurs as a function of
partial pressure differences in oxygen and
carbon dioxide between the alveoli and the
blood in the pulmonary capillaries

INTERNAL RESPIRATION
• Internal respiration is the exchange of gases
between capillary blood and local body cells
• Oxygen is carried from the lungs to the tissues
in chemical composition with haemoglobin as
oxyhaemoglobin
• The exchange in the tissues takes place
between blood at the arterial end of the
capillaries and the tissue fluid and then
between the tissue fluid and the cells

HEART
• Roughly cone shaped hollow muscular organ
• About 10cm long
• About the size of the owner’s fist
• Weighs about 225gm in women
• Heavier in men (about 310gm)

Position
• Lies in the thoracic cavity in the mediastinum
between the lungs
• It lies obliquely, a little more to the left than the
right
• It presents a base above, and an apex below
• The apex is about 9cm to the left of the midline at
the level of the 5th intercostal space, i.e. a little
below the nipple and slightly nearer the midline
• The base extends to the level of the 2nd rib

Structure
• Heart is composed of three layers of tissue
Pericardium
Myocardium
Endocardium

Pericardium
• Made up of two sacs
• The outer sac consists of fibrous tissue and the
inner of a continuous double layer of serous
membrane
• The outer fibrous sac is continuous with the
tunica adventitia of the great blood vessels
above and is adherent to the diaphragm below

Pericardium
• The outer layer of the serous membrane, the
parietal pericardium, lines the fibrous sac
• The inner layer, the visceral pericardium, or
epicardium, which is continuous with the
parietal pericardium, is adherent to the heart
muscle
• A similar arrangement of a double membrane
forming a closed space is seen also with the
pleura, the membrane enclosing the lungs

Myocardium
• Composed of specialized cardiac muscle found
only in the heart
• Thickest at the apex and thins out towards the
base

Endocardium
• Forms the lining of the myocardium and the
heart valves
• It is a smooth, glistening membrane which
permits smooth flow of blood inside the heart
• It consists of flattened epithelial cells,
continuous with the endothelium that lines the
blood vessels

Interior of the heart
• Heart is divided into a right and left side by the
septum, a partition consisting of myocardium
covered by endocardium
• After birth blood cannot cross the septum from
one side to the other
• Each side is divided, by atrioventricular valve
into an upper chamber, the atrium, and a lower
chamber, the ventricle

• The atrioventricular valves are formed by
double folds of endocardium strengthened by a
little fibrous tissue
• The right atrioventricular valve (tricuspid
valve) has three flaps or cusps and the left
atrioventricular valve (mitral valve) has two
cusps

• The valves between the atria and ventricles
open and close passively according to the
changes in pressure in the chambers
• They open when the pressure in the atria is
greater than that in the ventricles

• During ventricular systole (contraction) the
pressure in the ventricles rises above that in the
atria and the valves snap shut preventing
backward flow of the blood
• The valves are prevented from opening upwards
into the atria by tendious cords, called chordae
tendineae
• Chordae tendineae extends from the inferior
surface of the cusps to little projections of
myocardium covered with endothelium, called
papillary muscles

Flow of Blood through the heart
• Superior and Inferior venae cavae (two largest
veins of the body)
empty their contents
Right atrium
Blood passes via
Right atrioventricular valve (tricuspid valve)
Right ventricle

• Pumped into the pulmonary artery or trunk (the only artery
that carry deoxygenated blood)
Opening of the pulmonary artery is guarded by pulmonary
valve, formed by three semilunar cusps
after leaving the heart
Pulmonary artery divides into right and left pulmonary artery
Carries venous blood into the lungs where exchange of gases
take place
CO2 is excreted and O2 is absorbed

• Two pulmonary veins from each lung carry
oxygenated blood back to the left atrium
Blood than passes through
Left atrioventricle valve into the left ventricle
From there
Blood is pumped into the aorta (first artery of
general circulation)
The opening of the aorta is guarded by three
semilunar cusps

Blood supply to the heart
• Arterial supply: Right and Left Coronary
artery
• Venous drainage: Most of the venous blood is
collected into several small veins that join to
form the coronary sinus which opens into the
right atrium.
• The remainder passes into directly into the
heart chambers through little venous channels

Conducting System of the heart
• Heart has an intrinsic system whereby the
cardiac muscle is automatically stimulated to
contract without the need for a nerve supply
from the brain
• Small groups of specialised neuromuscular
cells in the myocardium which initiate and
conduct impulses causing coordinated and
synchronised contraction of the heart muscle

Sinoatrial node (SA node)
• The small mass of specialised cells is in the
wall of the right atrium near the opening of the
superior vena cava
• SA node is the pacemaker of the heart (because
it normally initiates impulses more rapidly
than other groups of neuromuscular cells)

Atrioventricular node (AV node)
• This small mass of neuromuscular tissue is
situated in the wall of the atrial septum near
the atrioventricular valves
• AV node is stimulated by impulses that sweep
over the atrial myocardium
• Also capable of initiating impulses but at a
slower rate than SA node

Atrioventricular bundle (AV bundle
or bundle of His)
• This is a mass of specialised cells that
originate from the AV node
• At the upper end of the ventrcular septum, it
divided into right and left bundle branches
• Within the ventricular myocardium the
branches break up into fine fibres, called the
Purkinje fibres

Atrioventricular bundle (AV bundle
or bundle of His)
• The AV bundle, bundle branches and Purkinje
fibres convey electrical impulses from the AV
node to the apex of the myocardium where the
wave of the ventricular contraction begins
• Than sweeps upwards and outwards, pumping
blood into the pulmonary artery and the aorta

Factors affecting heart rate
• Autonomic nervous system: The rate at which
the heart beats is a balance of sympathetic and
parasympathetic activity
• Circulating chemicals: Hormones adrenaline
and noradrenaline, secreted by adrenal
medulla, increases the heart rate
Other hormones including thyroxine increases
heart rate by their metabolic effect

Factors affecting heart rate
• Position: When the person is upright, the heart rate is
usually faster than when lying down
• Exercise: Active muscles need more blood than resting
muscles and this is achieved by an increased heart rate
and vasodilation
• Emotional states: During excitement, fear or anxiety the
heart rate is increased
• Gender: the heart rate is faster in women than men
• Age: In babies and small children the heart rate is more
rapid than in older children and adults
• Temperature: The heart rate rises and falls with body
temperature

The Cardiac Cycle
• The heart act as a pump and its action consists
of a series of events known as the cardiac
cycle
• During each heart beat, or cardiac cycle, the
heart contracts and then relaxes
• The period of contraction is called systole
• The period of relaxation is called diastole

Stages of the Cardiac Cycle
• The normal number of cardiac cycle per
minute ranges from 60 to 80
• Taking 74 as an example each cycle lasts about
0.8 of a second and consists of:
• Atrial systole: contraction of the aorta (0.1sec)
• Ventricular systole: contraction of the
ventricles (0.3sec)
• Complete cardiac diastole: relaxation of the
atria and ventricles (0.4sec)

Atrial systole (0.1sec)
SVC and IVC transports deoxygenated blood into the
right atrium
At the same time 4 pulmonary veins convey oxygenated
blood into the left atrium
The SA node triggers a wave of contraction that spreads
over the myocardium of both atria
Emptying the atria and completing ventricular filling
Atrial systole

Ventricular systole (0.3sec)
When the wave of contraction reaches the AV node it is
stimulated to emit an impulse
Which quickly spreads to the ventricular muscle via the
AV bundle, the bundle branches and Purkinje fibres
This results in a wave of contraction
Which sweeps upwards from the apex of the heart and
across the wall of the both ventricles
Pumping the blood into the pulmonary artery and the
aorta
Ventricular systole (0.3 sec)

Complete Cardiac Diastole (0.4sec)
After contraction of the ventricles there is complete
diastole
When atria and ventricles are relaxed
During this time the myocardium recovers and
the atria refill in preparation for the next cycle
Cardiac diastole (0.4 sec)

Cardiac output
The amount of blood ejected from the heart. Expressed in liters
/minute
Calculated by
Cardiac output = Stroke volume X Heart rate
Stroke volume
The amount expelled by each contraction of the ventricle is stroke
volume
The stroke volume is determined by the volume of blood in the
ventricles immediately before they contract i.e., the ventricular
end diastolic volume (VEDV), sometimes called pre-load
In a healthy adult at rest, the stroke volume is approx. 70ml and if
the hear rate is 72/min, the cardiac output is 5lit/min

Blood pressure
Blood pressure is the force or pressure which the blood
exerts on the walls of the blood vessels
Systolic Blood Pressure
When the left ventricle contracts and pushes blood into
the aorta the pressure produced within the arterial
system is called the systolic blood pressure
Diastolic blood pressure
When complete cardiac diastole occurs and the heart is
resting following the ejection of blood, the pressure
within the arteries is called diastolic blood pressure

Control of Blood Pressure
Blood pressure is controlled in two ways
• Short term control: which involves the
baroreceptor reflex, chemoreceptors and
circulating hormones
• Long term control: which involves regulation
of blood volume by the kidneys and the renin
angiotensin aldosterone system

The cardiovascular centre (CVC) is a collection
of interconnected neurons in the brain and is
situated within the medulla and pons
The CVC receives, integrates and coordinates
inputs from:
Baroreceptors (pressure receptors)
Chemoreceptors
Higher centres in the brain

• The CVC sends autonomic nerves (both
sympathetic and parasympathetic) to the heart
and blood vessels
• It controls BP by slowing down and speeding
up the heart rate and by dilating or constricting
blood vessels

The sympathetic and
parasympathetic nervous systems
Sympathetic
stimulation
Parasympathetic
stimulation
Heart ↑ Rate
↑ Strength of
contraction
↓ Rate
↓ Strength of contraction
Blood
vessels
Most constrict There is little
parasympathetic innervation
to most blood vessels

Baroreceptors
• These are nerve endings sensitive to pressure
changes (stretch) within the vessel, situated in the
arch of the aorta and in the carotid sinuses
• A rise in BP in these arteries stimulates the
baroreceptors, increasing their input to the CVC
• CVC respond by increasing parasympathetic
nerve activity to the heart; this slows the heart
down
• At the same time, sympathetic stimulation to the
blood vessels is inhibited, causing vasodilation
• The net result in fall in systemic BP

Baroreceptors
• Conversely, if pressure within the aortic arch
and carotid sinuses falls, the rate of
baroreceptor discharge also falls
• CVC respond by increasing sympathetic drive
to the heart to speed it up
• Sympathetic activity in blood vessels is also
increased, leading to vasoconstriction
• Baroreceptor control of BP is also called the
baroreceptor reflex

Chemoreceptors
• These are nerve endings situated in the carotid
and aortic bodies
• They are primarily involved in control of
respiration
• They are sensitive to changes in the levels of
CO2, O2 and the acidity of the blood (pH)

Chemoreceptors
↑[H +

Higher centres in the brain
• Input to the CVC from the higher centres is
influenced by emotional states such as fear,
anxiety, pain and anger that may stimulate
change in BP

Circulation of the blood
• Although circulation of blood round the body
is continuous, it is convenient to describe it
into two parts:
• Pulmonary circulation
• Systemic or general circulation

Pulmonary circulation
• This consists of the circulation of blood from
the right ventricle of the heart to the lungs and
back to the left atrium
• In the lungs, carbon dioxide is excreted ad
oxygen is absorbed

The pulmonary artery or trunk, carrying deoxygenated
blood
Leaves the upper part of the right ventricle
It passes upwards and divides into
Right and left pulmonary arteries (at the level of 5th
thoracic vertebrae)
Left pulmonary artery runs to the root of the left lung
where it divides into two branches, one passing into
each lobe

The right pulmonary artery passes to the root of the
right lung and divides into two branches
The larger branch carries blood to the middle and lower
lobes, and the smaller branch to the upper lobe
Within the lung these arteries divide and subdivide into
smaller arteries, arterioles and capillaries
The interchange of gases takes place between capillary
blood and air in the alveoli of the lungs
In each lung the capillaries containing oxygenated blood
join up and eventually form two veins

Two pulmonary veins leave each lung, returning
oxygenated blood to the left atrium of the heart
During atrial systole this blood passes into the left
ventricle and
During ventricular systole it is forced into the aorta (the
first artery of general circulation)

Systemic or general circulation
The blood pumped out from the left ventricle is carried
by the branches of the aorta around the body
and is returned to the right atrium of the heart by the
SVC and IVC

AORTA
• The aorta begins at the upper part of the left ventricle
and, after passing upwards for a short way, it arches
backwards and to the left
• It then descends behind the heart through the thoracic
cavity a little to the left of the thoracic vertebrae
• At the level of 12th thoracic vertebrae it passes behind
the diaphragm then downwards in the abdominal
cavity to the level of the 4th lumbar vertebrae, where
it divided into the right and left common iliac arteries

Thoracic Aorta
• This part of the aorta is above the diaphragm and is
described in three parts:
1. Ascending aorta
2. Arch of the aorta
3. Descending aorta in the thorax

Ascending Aorta
• This is about 5cm long and lies behind the sternum
• Right and left coronary arteries are its branches
Arch of the aorta
• It is the continuation of the ascending aorta
• It begins behind the manubrium of the sternum and
runs upwards, backwards and to the left in front of
the trachea
• It than passes downwards to the left of the trachea
and is continuous with the descending aorta

Arch of the aorta
• Three branches are given off from its upper aspect:
 Brachiocephalic artery or trunk
 Left common carotid artery
 Left subclavian artery

Descending aorta in the thorax
• This part of the aorta is continuous with the arch of
the aorta and begins at the level of the 4th thoracic
vertebrae
• It extends downwards on the anterior surface of the
bodies of the thoracic vertebrae to the level of the
thoracic vertebrae to the level of the 12th thoracic
vertebrae, where it passes behind the diaphragm to
become the abdominal aorta

Portal circulation
• In all the parts of the circulation venous blood passes
from the tissues to the heart by the most direct route
through only one capillary bed
• In the portal circulation, venous blood passes from
the capillary beds of the abdominal part of the
digestive system, the spleen, pancreas to the liver
• It passes through a second capillary bed, the hepatic
sinusoids, in the liver before entering the general
circulation via the inferior vena cava

Portal circulation
• In this way blood with a higher concentration of
nutrients, absorbed from the stomach, intestines, goes
to the liver first
• In the liver certain modifications take place, including
the regulation of nutrient supply to other parts of the
body

Portal circulation
1. Small intestine absorbs products of digestion
2. Nutrient molecules travel in hepatic portal vein to
liver
3. Liver monitors blood content
4. Blood enters general circulation by way of hepatic
vein

Portal vein
S.NO NAME OF VEIN DRAINS BLOOD FROM
1. Splenic vein Spleen, Pancreas, Stomach
2. Inferior mesentric
vein
Descending colon, Rectum
3. Superior
mesentric vein
Small intestine, Ascending colon,
Transverse colon
4. Gastric vein Stomach, Oesophagus
5. Cystic vein Gall bladder

Cardiovascular system, POOJA GODIYAL

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