Circulatory system Heart part 1

Circulation of Blood in the Body

Pulmonary Circulation: Blood flows from the heart to the lungs for purification and returns to the heart. This process involves the right side of the heart, specifically the right ventricle, which pumps deoxygenated blood to the lungs via the pulmonary artery. In the lungs, carbon dioxide is exchanged for oxygen through the alveolar sacs. The newly oxygenated blood then returns to the heart via the pulmonary veins, entering the left atrium.
Systemic Circulation: Purified blood from the lungs is pumped from the left ventricle to various parts of the body through the aorta. This oxygen-rich blood supplies oxygen and nutrients to tissues and organs. After delivering oxygen, the blood returns to the heart as deoxygenated blood through veins, primarily into the right atrium via the superior and inferior vena cavas.
Cardiac Circulation (also known as coronary circulation): This refers specifically to the blood flow that nourishes the heart muscle (myocardium) itself. The coronary arteries branch from the aorta and provide blood to the heart tissue. Hospitals often refer to this circulation when discussing cardiac health and diseases.

Chambers: The heart comprises four chambers:
- Upper Chambers (Atria): Left atrium and right atrium. The atria receive blood coming into the heart.
- Lower Chambers (Ventricles): Left ventricle and right ventricle. Ventricles pump blood out of the heart.
Left Side of the Heart: Responsible for pulmonary circulation, it receives oxygenated blood from the lungs and pumps it into the systemic circulation through the aorta.
Right Side of the Heart: Receives deoxygenated blood from the body through the superior and inferior vena cavas and pumps it to the lungs for purification.

Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs. It is unique because it is one of the few arteries that carry deoxygenated blood.
Pulmonary Vein: Carries oxygenated blood from the lungs to the left atrium of the heart. This is also unique, as most veins carry deoxygenated blood.

Deoxygenated blood enters the right atrium through the superior and inferior vena cavas.
Blood flows from the right atrium to the right ventricle through the tricuspid valve.
The right ventricle contracts, pushing blood through the pulmonary semilunar valve into the pulmonary trunk, directing it to the lungs for oxygenation.
Oxygenated blood returns to the left atrium via the pulmonary veins.
Blood enters the left ventricle through the mitral (bicuspid) valve.
The left ventricle contracts and blood exits the heart to the body through the aorta via the aortic semilunar valve.

The major functions of blood include distributing oxygen and nutrients to body cells, as well as removing carbon dioxide and waste products. This exchange primarily occurs at the capillary level, where blood vessels are only one cell thick, allowing efficient gas and nutrient exchange.

The heart walls consist of three layers:
- Epicardium: The outermost layer, which provides smooth protection and houses blood vessels that supply the heart.
- Myocardium: The thick, muscular layer responsible for the heart's contraction, made up of cardiac muscle tissue.
- Endocardium: The innermost layer that lines the chambers of the heart and is continuous with the blood vessels.
Pericardium: A double-walled membrane enclosing the heart; reduces friction and protects the heart from infections. It contains pericardial fluid, which facilitates movement during heartbeats and aids in heat dissipation.

Atrioventricular Valves: Includes the tricuspid and mitral (bicuspid) valves. They regulate blood flow from the atria to the ventricles, preventing backflow during contraction.
Semilunar Valves: Consist of the pulmonary and aortic valves. These valves prevent blood from flowing back into the ventricles after contraction.

Automaticity: Cardiac cells can initiate impulses that trigger heart contractions independently of external nerves.
Conductivity: These cells can transmit impulses throughout the heart, enabling coordinated contractions.
Contractility: Refers to the effectiveness of the heart muscle to contract and pump blood efficiently.
Excitability: Cardiac cells have the ability to respond to electrical stimuli, allowing for rapid activation and contraction.

Lubb: The first heart sound (S1) marks the closure of the atrioventricular valves during ventricular contraction, signaling the beginning of systole.
Dubb: The second heart sound (S2) marks the closure of the semilunar valves at the end of ventricular contraction, signaling the beginning of diastole.

Blood pressure indicates the force exerted by circulating blood on the walls of blood vessels, measured in millimeters of mercury (mmHg).
Norms: Systolic pressure is approximately 120 mmHg, while diastolic pressure is around 80 mmHg, representing the pressure when the heart is contracting and at rest, respectively.

Sinoatrial Node (SA Node): The heart's primary pacemaker, responsible for initiating the heartbeat at a rate of 60-100 beats per minute.
Atrioventricular Node (AV Node): Acts as a secondary pacemaker with a backup rhythm of 40-60 beats per minute, delaying impulses to ensure efficient chamber filling.
Bundle of His and Purkinje Fibers: Conduct electrical impulses to the ventricles, facilitating their contraction in a coordinated manner.

Deoxygenated blood enters the right atrium.
It passes through the tricuspid valve to the right ventricle.
Blood is pushed through the pulmonary semilunar valve into the pulmonary arteries and into the lungs.
Oxygenated blood returns to the left atrium via pulmonary veins.
It passes through the mitral valve to the left ventricle.
Finally, blood exits through the aortic valve into the aorta to systemic circulation.

Understanding the diagram of the heart is crucial for visualizing blood flow and cardiac function.
Regular monitoring of blood pressure and heart rate is essential for maintaining cardiovascular health and preventing diseases.