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Presentation on theme: "© SSER Ltd.."— Presentation transcript:

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


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