THE CIRCULATORY SYSTEM

Introduction

The circulatory system is comprised of the heart,
veins, capillaries, arteries, lymph vessels, and lymph glands, which
work together to supply the body tissues with nourishment and collect
waste materials.

1. Distribute nutrients,
   
2. Transport and exchange oxygen and carbon dioxide,
   
3. Remove waste materials,
   
4. Distribute secretions of endocrine glands,
   
5. Prevent excessive bleeding,
   
6. Prevent infection, and Regulate body temperature.
   

Anatomy and Physiology of the Heart

[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]

The heart is a funnel-shaped, hollow, muscular organ that is responsible for pumping blood to all parts of the body.
The heart is located near the center of the thoracic cavity between the lungs and is contained in the pericardial sac.
The pericardial sac supports the heart and contains some fluid for lubrication.
The broad end, or base, of the heart is also supported by large

arteries and veins.

The pointed end, or apex, of the heart is directed toward the abdomen.
The heart wall is made up of three layers.

Epicardium

– outer layer of heart wall, which is also the inner layer of epicardial
Endocardium

inner layer that consists of endothelial cells, which line the heart, covers the heart valves, and lines the blood vessels.

Myocardium

middle layer composed of cardiac muscle.
The
cardiac muscle is an involuntary, striated muscle with fibers that
intertwine. In mammals and birds, the heart is divided into a right and
left side and each side is divided into an atrium and ventricle.
Therefore, the heart is said to have four chambers (right atrium, right
ventricle, left atrium, and left ventricle)


The
atrioventricular valves (AV valve) separate the atrium and ventricle
on each side of the heart. The AV valves have flaps of tissues, called
leaflets or cusps, which open and close to ensure that the blood flows
only in one direction and does not backflow into the atriums.
The AV valve on the right side of the heart is called the tricuspid valve because it has three leaflets (cusps).
The AV valve on the left side of the heart is called the bicuspid valve (or mitral valve) because it has two leaflets.
The pulmonary valve and the aortic valve prevent blood from back-flowing into their respective ventricles.
The pulmonary valve is located between the right ventricle and the pulmonary artery.
The aortic valve is located between the left ventricle and the aortic artery.
Following the path that the blood takes as it flows through the heart
and lungs is the best way to understand the heart’s operation.
(This process will be discussed later in the topic of pulmonary circulation.)
A group of cells called the sinoatrial node (SA node) control the beat
of the heart by sending out electrical signals to make the heart pump.