2. HEART
• The heart is a hollow, cone-shaped, muscular pump.
Dimensions of Heart • The heart is a
small Organ, it is about 12 cm (5 in.)
long, 9 cm (3.5 in.) wide at its
broadest point, and 6 cm (2.5 in.)
thick, with an average mass of 250 g
in adult females and 300 g in adult
males.
• The heart rests on the diaphragm,
near the midline of the thoracic
cavity.
• The heart lies in the mediastinum
an anatomical region that extends
from the sternum to the vertebral
column, from the first rib to the
diaphragm, and between the lungs
3. Relations of Heart
Inferiorly – the diaphragm
Superiorly – the aorta, superior vena
cava, P artery and pulmonary vein.
4. Anteriorly – the ribs and intercostal muscles.
Posteriorly – the esophagus, trachea, left and
right bronchus, descending aorta, inferior vena
cava and thoracic vertebrae
laterally
– the lungs
5. Four Chambers of the Heart
• Right Atrium
• Right Ventricle
• Left Atrium
• Left Ventricle
6. Two chambers on the top (atrium, plural atria) and two on the bottom
(ventricles), one on each side of the heart.
•Right atrium: Two large veins deliver oxygen-poor blood to your right
atrium. The superior vena cava carries blood from your upper body. The
inferior vena cava brings blood from the lower body. Then the right atrium
pumps the blood to your right ventricle.
•Right ventricle: The lower right chamber pumps the oxygen-poor blood to
your lungs through the pulmonary artery. The lungs reload blood with
oxygen.
•Left atrium: After the lungs fill blood with oxygen, the pulmonary veins
carry the blood to the left atrium. This upper chamber pumps the blood to
your left ventricle.
•Left ventricle: The left ventricle is slightly larger than the right. It pumps
oxygen-rich blood to the rest of your body.
Heart valves
Four Chambers of the Heart
7. Valves
• 4 Heart Valves
• Tricuspid Valve
• Pulmonary Semilunar Valve
• Mitral (Biscuspid) Valve
• Aortic (Semilunar) Valve
• Purpose: prevent backflow
of blood, keep blood
flowing in one direction
8. The atrioventricular (AV) valves open between your upper and lower heart
chambers. They include:
•Tricuspid valve: Door between your right atrium and right ventricle.
•Mitral valve: Door between your left atrium and left ventricle.
Semilunar (SL) valves open when blood flows out of your ventricles. They
include:
•Aortic valve: Opens when blood flows out of your left ventricle to
your aorta (artery that carries oxygen-rich blood to your body).
•Pulmonary valve: Opens when blood flows from your right ventricle to
your pulmonary arteries (the only arteries that carry oxygen-poor blood to
your lungs).
Valves
14. Electrical System
• AKA the Cardiac Conduction
System
• Consists of three parts:
• 1. Sinoatrial (SA) node
• 2. Atrioventricular (AV) node
• 3. Bundle of His and Purkinje
fibers
16. conduction system contains
specialized cells and nodes
that control your heartbeat.
These are the:
•Sinoatrial node.
•Atrioventricular node.
•Bundle of His
(atrioventricular bundle).
•Purkinje fibers.
17. The sinoatrial (SA) node is a collection of specialised cells (pacemaker cells), and is located in the upper
wall of the right atrium, at the junction where the superior vena cava enters.
These pacemaker cells can spontaneously generate electrical impulses. The wave of excitation created by the
SA node spreads via gap junctions across both atria, resulting in atrial contraction (atrial systole) – with blood
moving from the atria into the ventricles.
Atrioventricular Node
After the electrical impulses spread across the atria, they converge at the atrioventricular node – located
within the atrioventricular septum, near the opening of the coronary sinus.
The AV node acts to delay the impulses by approximately 120ms, to ensure the atria have enough time to
fully eject blood into the ventricles before ventricular systole.
The wave of excitation then passes from the atrioventricular node into the atrioventricular bundle.
Atrioventricular Bundle
The atrioventricular bundle (bundle of His) is a continuation of the specialised tissue of the AV node, and
serves to transmit the electrical impulse from the AV node to the Purkinje fibres of the ventricles.
It descends down the membranous part of the interventricular septum, before dividing into two main bundles:
Right bundle branch – conducts the impulse to the Purkinje fibres of the right ventricle
Left bundle branch – conducts the impulse to the Purkinje fibres of the left ventricle.
Purkinje Fibres
The Purkinje fibres (sub-endocardial plexus of conduction cells) are a network of specialised cells. They are
abundant with glycogen and have extensive gap junctions.
These cells are located in the subendocardial surface of the ventricular walls, and are able to rapidly
transmit cardiac action potentials from the atrioventricular bundle to the myocardium of the ventricles.
This rapid conduction allows coordinated ventricular contraction (ventricular systole) and blood is moved
from the right and left ventricles to the pulmonary artery and aorta respectively.
18.
19. CARDIAC CYCLE PHASES
Following are the different phases that occur in a cardiac cycle:
Atrial Diastole: In this stage, chambers of the heart are calmed. That is when the aortic valve and pulmonary
artery closes and atrioventricular valves open, thus causing chambers of the heart to relax.
Atrial Systole: At this phase, blood cells flow from atrium to ventricle and at this period, atrium contracts.
Isovolumic Contraction: At this stage, ventricles begin to contract. The atrioventricular valves, valve, and
pulmonary artery valves close, but there won’t be any transformation in volume.
Ventricular Ejection: Here ventricles contract and emptying. Pulmonary artery and aortic valve close.
Isovolumic Relaxation: In this phase, no blood enters the ventricles and consequently, pressure decreases,
ventricles stop contracting and begin to relax. Now due to the pressure in the aorta – pulmonary artery and
aortic valve close.
Ventricular Filling Stage: In this stage, blood flows from atria into the ventricles. It is altogether known as
one stage (first and second stage). After that, they are three phases that involve the flow of blood to the
pulmonary artery from ventricles.
Duration of Cardiac Cycle
In a normal person, a heartbeat is 72 beats/minute. So, the duration of one cardiac cycle can be
calculated as:
1/72 beats/minute=.0139 minutes/beat
At a heartbeat 72 beats/minute, duration of each cardiac cycle will be 0.8 seconds.
Duration of different stages of the cardiac cycle is given below:
Atrial systole: continues for about 0.1 seconds
Ventricular systole: continues for about 0.3 seconds
Atrial diastole: continues for about 0.7 seconds
Ventricular diastole: continues for about 0.5 seconds
20. There are two coronary arteries, each containing several branches:
•Right coronary artery (RCA): The RCA supplies blood to your right
and right ventricle (where deoxygenated blood goes before heading to
the lungs). Its branches supply the sinoatrial (SA) and atrioventricular (AV)
nodes. These nodes send electrical signals through your heart, so the
heart muscles know when to contract. Branches of the RCA also deliver
blood to one-third of your interventricular septum, which is the wall
between your heart’s two lower chambers.
•Left main coronary artery (LMCA): The LMCA supplies blood to your
atrium and left ventricle. This is where oxygenated blood arrives from your
lungs before your heart pumps it out to the rest of your body. Its branches
BLOOD SUPPLY TO THE HEART
