cardiovascular

15.1: Introduction

The heart pumps 7,000 liters of blood through the body each day.
The heart contracts 2.5 billion times in an average lifetime.
The heart, along with all blood vessels, constitutes the cardiovascular system.
The blood vessels are organized into two circuits:
- Pulmonary circuit
- Systemic circuit

The heart is described as a hollow, cone-shaped, muscular pump.
It consists of four chambers:
- Two atria: These serve for blood storage.
- Two ventricles: Comprising one low pressure pump and one high pressure pump.

Diaphragm: The muscular structure below the heart.
Sternum: The breastbone located anteriorly to the heart.
Apex of heart: The pointed end of the heart, directed inferiorly and laterally.

Layer	Composition	Function
Epicardium	Serous membrane of connective tissue, covered with epithelium, containing blood capillaries, lymph capillaries, and nerve fibers.	Forms a protective outer covering; secretes serous fluid.
Myocardium	Cardiac muscle tissue, separated by connective tissue, including blood capillaries, lymph capillaries, and nerve fibers.	Contracts to pump blood from the heart chambers.
Endocardium	Membrane composed of epithelium and underlying connective tissue, including blood vessels and specialized muscle fibers.	Forms a protective inner lining of the chambers and valves.

Valve	Location	Function
Tricuspid valve	Entrance to right ventricle	Prevents blood from moving from right ventricle into right atrium during ventricular contraction.
Pulmonary valve	Entrance to pulmonary trunk	Prevents blood from moving from pulmonary trunk into right ventricle during ventricular relaxation.
Mitral valve	Entrance to left atrium	Prevents blood from moving from left ventricle into left atrium during ventricular contraction.
Aortic valve	Entrance to aorta	Prevents blood from moving from aorta into left ventricle during ventricular relaxation.

Blood from systemic circuit enters the heart via:
- Venae cavae
- Coronary sinus
- It then flows into the:
- Right atrium
- Through the Tricuspid valve to the Right ventricle
- Pulmonary valve leads to Pulmonary trunk
- Travels through Pulmonary arteries to Alveolar capillaries in the lungs
- Oxygenated blood returns via Pulmonary veins to the Left atrium
- Through Mitral valve into the Left ventricle
- Ejected through the Aortic valve into the Aorta
- Blood is delivered back to the systemic circuit.

The left and right coronary arteries supply blood to the tissues of the heart.
The Aorta: Key arterial structure with connections to the coronary arteries.

A heartbeat auscultated through a stethoscope produces a “lubb-dupp” sound.
The “lubb” sound:
- The first heart sound occurring during ventricular systole when the A-V valves close.
The “dupp” sound:
- The second heart sound occurring during ventricular diastole when the pulmonary and aortic semilunar valves close.
A murmur: An abnormal sound resulting from valve cusps not completely closing.

An electrocardiogram (ECG) is a recording of electrical changes in the myocardium during the cardiac cycle, used to assess the heart's ability to conduct impulses.
The deflection waves of the normal ECG include:
- P wave: Represents atrial depolarization, impulse sent from Left atrium to Right atrium.
- QRS complex (three waves): Represents ventricular depolarization.
- T wave: Represents ventricular repolarization.

Blood pressure: The force exerted by blood against the inner walls of blood vessels; most commonly refers to pressure in systemic arteries.

Arterial blood pressure varies:
- Rises when the ventricles contract (ventricular systole).
- Falls when the ventricles relax (ventricular diastole).
- Systolic pressure: The maximum pressure during ventricular contraction.
- Diastolic pressure: The minimum pressure observed when the ventricles relax.

Blood vessels can be classified into two major pathways:
- The pulmonary circuit.
- The systemic circuit (includes coronary circulation).

The Systemic Circuit consists of vessels that lead from the heart to all body parts (except the lungs) and then return to the heart.
Key components include:
- Aorta and its branches.
- A comprehensive network of veins returning blood to the right atrium.

Portion of Aorta	Branch	General Regions or Organs Supplied
Ascending aorta	Right and left coronary arteries	Supplies the heart.
Arch of aorta	Brachiocephalic artery	Supplies right upper limb and right side of the head.
	Left common carotid artery	Supplies the left side of the head.
	Left subclavian artery	Supplies the left upper limb.
Abdominal aorta	Celiac artery	Supplies organs of the upper digestive tract.
	Renal artery	Supplies the kidneys.
	Gonadal artery	Supplies ovaries or testes.

Various veins apply to the different parts of the body, including those from the brain, head, neck, upper limbs, and abdominal and thoracic walls, forming complex networks that return blood to the heart.