𝐒𝐭𝐫𝐮𝐜𝐭𝐮𝐫𝐞 𝐚𝐧𝐝 𝐟𝐮𝐧𝐜𝐭𝐢𝐨𝐧 𝐨𝐟 𝐭𝐡𝐞 𝐇𝐞𝐚𝐫𝐭

𝙎𝙩𝙧𝙪𝙘𝙩𝙪𝙧𝙚 𝙤𝙛 𝙩𝙝𝙚 𝙃𝙚𝙖𝙧𝙩

The heart is divided into the left and right side by partitions called septa (singular septum).

The interatrial septum separates the two upper chambers, called atria (from atri/o, meaning "upper chambers").

The interventricular septum separates the two lower chambers, called ventricles (from ventricul/o, meaning "lower chamber).

𝙏𝙝𝙚 𝙃𝙚𝙖𝙧𝙩 𝘾𝙤𝙣𝙨𝙞𝙨𝙩𝙨 𝙤𝙛 𝙁𝙤𝙪𝙧 𝘾𝙚𝙡𝙡 𝙇𝙖𝙮𝙚𝙧𝙨:

The endocardium (from endo- + cardi/o +ium, meaning "inner layer of the heart") is formed by endothelial cells, and it lines the interior of the heart chambers and valves.

 The myocardium (from my/o + cardi/o + -ium, meaning "heart muscle") is the muscular middle layer of the heart that consists ofheart muscle cells. 

The epicardium (from epi- + cardi/o + -ium, meaning "outer layer of the heart") is formed by epithelial cells, and forms the outer cell layer of the heart.

The pericardium (from peri- + cardi/o +-ium, meaning "surrounding the heart") is a membranous sac that surrounds the heart. It consist of two layers called the visceral pericardium (adheres to the epicardium) and parietal pericardium (the outer coat). The space between these two layers is called pericardial cavity and it contains pericardial fluid.

𝙃𝙚𝙖𝙧𝙩 𝘾𝙝𝙖𝙢𝙗𝙚𝙧𝙨 𝙖𝙣𝙙 𝙑𝙖𝙡𝙫𝙚𝙨

The human heart has four chambers, which are responsible for pumping blood and maintaining blood circulation throughout the body. 

The four chambers are named:

The right atrium

The left atrium

The right ventricle

The left ventricle

Blood is only pumped to one direction. Four heart valves ensure that blood does not flow backward within the heart.

𝙏𝙝𝙚 𝙁𝙤𝙪𝙧 𝙃𝙚𝙖𝙧𝙩 𝙑𝙖𝙡𝙫𝙚𝙨 𝙖𝙧𝙚 𝙉𝙖𝙢𝙚𝙙:

*• The tricuspid valve (from tri- + cuspid, meaning "having threepoints") located between right atrium and ventricle.

* The pulmonary valve (from pulmon/o, meaning "lungs") located between right ventricle and pulmonary artery. Also called semilunarvalve.

*• The mitral valve, also called bicuspid valve ( from bi-+ cuspid, meaning "having two points") located between left atrium and ventricle.

*• The aortic valve located between left ventricle and aorta. The tricuspid and bicuspid valves are also called atrioventricular valves (meaning "located between the atrium and ventricle").

The pulmonary artery will deliver the deoxygenated blood to the lungs, where gas exchange occurs.

Oxygen is taken from the air into the blood (now called oxygenated blood), while carbon dioxide is expelled from the blood into the air. The oxygenated blood returns to the left side of the heart via the pulmonary veins.

The oxygenated blood enters the left atrium.

The left atrium pumps blood into the left ventricle. The mitral valve prevents blood from flowing backward into the left atrium.

The left ventricle pumps the blood into the aorta and systemic circulation. The oxygenated blood is delivered everywhere in the body (besides the lungs).

𝗙𝘂𝗻𝗰𝘁𝗶𝗼𝗻 𝗼𝗳 𝘁𝗵𝗲 𝗛𝗲𝗮𝗿𝘁

The heart functions to circulate blood around the body. The right and left side of the heart pump blood into two different circulations.

The right side pumps deoxygenated (from de- + oxygenated, meaning

"without oxygen") blood into the pulmonary circulation, while the

left side pumps oxygenated blood into the systemic circulation. The right atrium receives deoxygenated blood from the body tissues via the superior (from super- meaning "above") and inferior (meaning below) vena cava (from ven/o meaning "vein").

The blood enters the right atrium, which pumps the blood into the right ventricle. The tricuspid valve prevents blood from flowing backward into the right atrium. The right ventricle pumps the blood into the pulmonary artery via the pulmonary valve.

𝘽𝙡𝙤𝙤𝙙 𝘾𝙞𝙧𝙘𝙪𝙡𝙖𝙩𝙞𝙤𝙣

Blood circulates around the body via two distinct pathways; the pulmonary circulation and the systemic circulation.

Together they create a closed pathways that keep the deoxygenated and oxygenated blood separated.

𝙋𝙪𝙡𝙢𝙤𝙣𝙖𝙧𝙮 𝘾𝙞𝙧𝙘𝙪𝙡𝙖𝙩𝙞𝙤𝙣

Pulmonary circulation begins at the right ventricle, where the deoxygenated blood from the body tissues is pumped into the pulmonary arteries and to the lungs.

In the lungs, the blood exchanges carbon dioxide (waste product of cellular respiration) to oxygen.

The oxygenated blood them travels back to the heart and the left atrium, via the pulmonary vein.

𝙎𝙮𝙨𝙩𝙚𝙢𝙞𝙘 𝘾𝙞𝙧𝙘𝙪𝙞𝙩

The systemic circulation begins at the left ventricle that pumps oxygenated blood into the aorta.

Aorta branches out into smaller arteries, which carry the oxygenated

blood to the rest of the body (with the exception of lungs).

Oxygen is delivered to the body tissues and exchanged to carbon dioxide. The now deoxygenated blood is carried back to the heart and the right atrium via veins.

𝘼𝙧𝙩𝙚𝙧𝙞𝙚𝙨 𝙫𝙨 𝙑𝙚𝙞𝙣𝙨

The blood vessels that carry blood AWAY from heart are called arteries.

The blood vessels that carry blood TOWARD the heart are called veins.

Only in systemic circulation arteries carry oxygenated blood, while in the pulmonary circulation arteries carry deoxygenated blood.

𝗖𝗼𝗻𝘁𝗿𝗮𝗰𝘁𝗶𝗼𝗻 𝗼𝗳 𝘁𝗵𝗲 𝗛𝗲𝗮𝗿𝘁

The contraction of the muscular wall of the heart chambers, called myocardium generates the force to pump blood.

The heart contraction is divided into two phases: systole (meaning "contraction") and diastole (meaning "relaxation").

Blood is pumped from the chambers during a contraction phase. The heart chambers are filled with blood during a relaxation phase.

𝙊𝙣𝙚 𝙧𝙤𝙪𝙣𝙙 𝙤𝙛 𝙝𝙚𝙖𝙧𝙩 𝙘𝙤𝙣𝙩𝙧𝙖𝙘𝙩𝙞𝙤𝙣𝙨 𝙘𝙖𝙣 𝙗𝙚 𝙙𝙞𝙫𝙞𝙙𝙚𝙙 𝙞𝙣𝙩𝙤 𝙩𝙝𝙚 𝙛𝙤𝙡𝙡𝙤𝙬𝙞𝙣𝙜 𝙥𝙝𝙖𝙨𝙚𝙨:

Relaxation phase → Blood flows from the atria into the ventricles passively via open atrioventricular valves.

The atrial systole → Contraction of atria. Pumps the rest of the blood into the ventricles.

The ventricular systole → Contraction of the ventricles. Forces blood into the pulmonary and systemic circulation. (During the ventricular systole, the atria relax and begin to fill with blood arriving from vena cava or the pulmonary veins.

Ventricular diastole → The ventricles and atria are relaxed.

𝗦𝗶𝗻𝗼𝗮𝘁𝗿𝗶𝗮𝗹 (𝗦𝗔) 𝗡𝗼𝗱𝗲

Myocardium contracts after it receives an electrical impulse generated by a specialized tissue located within the right atrium.

This is called the sinoatrial node (SA node), also called the pacemaker of the

heart. The SA node is a bundle of neurons that triggers the contraction of

the atria during the cardiac cycle.

The electrical currents next reach the ventricles, which contract after the atria. The SA node initiates approximately 75 electrical impulses each minute, with

variation between individuals' age and general health

𝗔𝘁𝗿𝗶𝗼𝘃𝗲𝗻𝘁𝗿𝗶𝗰𝘂𝗹𝗮𝗿 𝗻𝗼𝗱𝗲 (𝗔𝗩 𝗻𝗼𝗱𝗲)

This small mass of neuromuscular tissue is situated in the wall of the atrial septum near the atrioventricular valves. Normally, the AV node merely transmits the electrical signals from the atria into the ventricles. There is a delay here; the electrical signal takes 0.1 of a second to pass through into the ventricles. This allows the atria to finish contracting before the ventricles start.

The AV node also has a secondary pacemaker function and takes over this role if there is a problem with the SA node itself, or with the transmission of impulses from the atria. Its intrinsic firing rate, however, is slower than that set by the SA node (40-60 beats per minute)

𝗧𝗵𝗲 𝗣𝘂𝗿𝗸𝗶𝗻𝗷𝗲 𝗙𝗶𝗯𝗲𝗿𝘀

The Purkinje fibers are cells in the inner ventricle walls, just beneath the endocardium. These fibers run between the ventricles to the apex (bottom) of the heart. The Purkinje fibers play a crucial role in the cardiac cycle.

When an electrical stimulus leaves the AV node, it travels via the bundle of His and branches to the Purkinje fibers. These fibers then carry the impulse through the inner wall of each ventricle. This causes the ventricles to contract after the atria contract.

The ventricle contraction forces blood from the right ventricle to the lungs (pulmonary circulation) and from the left ventricle to the body (systemic circulation).

These three elements generate a healthy heart rhythm known as sinus rhythm. The rhythm, or contraction of the heart pumps blood throughout the body. In roughly a minute's time, blood travels from the heart to the body and back.

By : @ummedsaini_