1. © SSER Ltd.

2. heart receives oxygenated blood from the lungs via the
Mammalian Heart Structure
The left side of the
heart receives oxygenated
blood from the lungs via the
pulmonary veins
The heart is the major
organ of the circulatory system
Superior
Vena
Cava
Inferior
AORTA
It is a fist-sized muscular
pump consisting of
four chambers
The left side of the
heart pumps oxygenated
blood out into
the body’s arteries via
the aorta
The human heart
recirculates the entire
blood volume (5 dm3)
every minute when
the body is at rest
Pulmonary
Artery
Deoxygenated blood
returns to the right side
of the heart via the
vena cava
The ability of the
heart to perform such
work is due to the
presence of specialised
cardiac muscle in
its walls
Coronary
Arteries
Deoxygenated blood
is pumped to the
lungs via the
pulmonary artery
Heart muscle receives
its own supply of blood from the coronary arteries
The job of the heart is to
pump blood around two separate circuits

3. Mammalian Heart Structure
Aorta
Pulmonary artery
Venae cavae
Pulmonary veins
Semilunar valves
Left atrium
Right atrium
Bicuspid valve
Tricuspid valve
Right ventricle
Left ventricle
Septum
(dividing wall)
Cardiac muscle

4. Cardiac Muscle
Cardiac muscle tissue consists of branched, faintly striated fibres (cells), each of
which contains a centrally placed nucleus
Thickenings of
the plasma
membrane
between
individual
cardiac muscle
cells form
intercalated
discs
Cardiac muscle tissue forms networks due to its branching structure
When one muscle fibre is electrically excited, an impulse is quickly
transmitted to neighbouring fibres such that impulses spread in all directions when cardiac muscle is stimulated

5. of the fibres, the intercalated discs and the nuclei
This photomicrograph of cardiac muscle tissue shows the branching nature
of the fibres, the intercalated discs and the nuclei
Nuclei
Intercalated
disc

6. Mammalian Heart Structure
The mammalian heart is
a muscular pump that consists
of four chambers
Two upper chambers, called the
atria, are thin walled cavities that
receive blood from veins
Two lower chambers, called the
ventricles, are thick walled cavities
that receive blood from the atria and
pump blood away from the heart
Right
atrium
Left
The cavity of the heart is
divided completely by a
partition called the septum
The muscular walls of the
heart are referred to as the
myometrium and consist of
specialised cardiac muscle cells
Right
ventricle
Left
Septum
The thicker walled structure of the left
ventricle is a consequence of the distance
over which it is required to pump blood

7. The direction of blood flow through the heart is maintained be valves
Between the right atrium and the right ventricle is the tricuspid valve
Right
atrium
Left
ventricle
Aorta
This valve prevents the backflow
of blood from the right ventricle
to the right atrium
Pulmonary
Artery
Between the left atrium and the left ventricle is the bicuspid valve or
mitral valve
This valve prevents the backflow of blood from the left ventricle to the left atrium
Semilunar
valves
Bicuspid
or Mitral
valve
Tricuspid
valve
The bicuspid and tricuspid
valves are collectively
known as the atrio-ventricular
valves or AV valves
Pocket-shapes valves known as semilunar valves are
located at the base of the arteries responsible for transporting blood away from the heart

8. Pulmonary semilunar valve
Heart Valves
Pulmonary semilunar valve
Aortic semilunar valve
Bicuspid or mitral valve
Tricuspid valve
Thicker-walled left ventricle
Thinner-walled right ventricle
HEART VALVES VIEWED FROM ABOVE

9. The Cardiac Cycle
The average human heart rate at rest is 72 beats a minute
Each heart beat lasts for approximately 0.8 seconds at rest
The sequence of events taking place during one complete heartbeat is called the cardiac cycle
A single heartbeat is divided into two major phases known as systole and diastole
Systole describes periods when the heart is contracting and Diastole describes periods when the heart is relaxing

10. The Cardiac Cycle
The average human heart rate at rest is 72 beats a minute
Each heart beat lasts for approximately 0.8 seconds at rest
The sequence of events taking place during one complete heartbeat is called the cardiac cycle
A single heartbeat is divided into two major phases known as systole and diastole
Systole describes periods when the heart is contracting and Diastole describes periods when the heart is relaxing

11. The Cardiac Cycle
Since the heartbeat is a cycle of events, there is no absolute first or last phase
This account begins with the phase of late diastole when
both the atria and the ventricles of the heart are relaxed
Passive filling of the ventricles
continues until the ventricles
have filled to about 70% of their capacity to hold blood
The increasing volume of
blood in the ventricles
presses against the AV
valves and they begin to
drift towards a closed position
During late diastole, all chambers of the heart are relaxed with the atrio-ventricular valves
(AV valves) open and the semi-lunar valves closed
At this point both of the
atria contract, rapidly
propelling blood into the
ventricles which stretch
to accommodate their
full capacity for blood
Blood flows passively
from the atria, through
the open AV valves, into
the ventricles that stretch
to accommodate the
extra volume of blood
This phase of the heartbeat
is known as
atrial systole
This phase of the heartbeat is known as
passive filling of the ventricles

12. The Cardiac Cycle At the end of atrial systole, the volume of
blood in the ventricles
is such that the AV
valves are forced closed
There is now a situation
where the AV and the
semilunar valves are
both closed, the atria
are relaxed and the
ventricles enter a
phase of contraction
or systole
AV valves
shut
When the rising pressure
exceeds that in the aorta
and pulmonary arteries,
the semilunar valves are
forced open and blood is
ejected from the heart

13. The Cardiac Cycle
As the ventricles relax, closure of the semilunar valves occurs due to a
brief backflow of blood from the aorta and pulmonary arteries
This phase of the heartbeat
is known as
ventricular
relaxation
(Early Diastole)
The pressures in the
ventricles continue to fall
and reach very low values
When the pressures
in the ventricles fall
below those of the
atria, the AV valves open

14. The Cardiac Cycle
As the ventricles relax, closure of the semilunar valves occurs due to a
brief backflow of blood from the aorta and pulmonary arteries
This phase of the heartbeat
is known as
ventricular
relaxation
(Early Diastole)
The pressures in the
ventricles continue to fall
and reach very low values
When the pressures
in the ventricles fall
below those of the
atria, the AV valves open
Passive filling of the ventricles (late diastole) occurs
as the cycle begins again

15. close as the ventricles
Late Diastole &
Atrial Systole
Ventricular Systole
(Isometric Phase)
AV valves open,
semi-lunar valves
closed
AV valves close
at the end of
atrial systole
All valves closed
as the ventricle
muscles contract
without shortening
(Isometric Contraction)
Passive filling
of the ventricles
followed by
atrial systole
Pressure builds
up in the
ventricles
Ventricular
Relaxation
Ventricular Systole
(Ejection)
Semi-lunar valves
close as the ventricles
begin to relax
Semi-lunar valves
open and blood
is ejected into
the aorta and
pulmonary artery
Pressure in the
ventricles falls
to a very low
value and the
AV valves open
Muscles shorten
as they contract