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Anatomy First class L
The circulatory system
The circulatory system is divided into: (1) cardiovascular system, which consists of the heart, blood vessels, and blood. (2) lymphatic system, which consists of lymphatic vessels and lymphoid tissues within the spleen, thymus, tonsils, and lymph nodes.
Cardiovascular system (CVS)
The cardiovascular system which is closed system consists of : (1) the heart , which
pumps blood so that it flows to body tissue capillaries, (2) the series of blood
vessels through which the blood flows, there are certain blood vessels are a part of
the pulmonary circuit, and others are a part of the systemic circuit and (3) blood.
Heart
The heart is located in the thoracic cavity between the lungs within the mediastinum
(anatomical region that extends from the sternum to the vertebral column) rests on
the diaphragm. It is a hollow, cone-shaped, relatively small roughly the same size as
a closed fist. Its mass averages 250 g in adult females and 300 g in adult males. The
base of the heart is superior to its apex which rests inferiorly on the diaphragm.
The heart is on a slant. About two-thirds of the mass of the heart lies to the left of
the body’s midline.
As the heart pumps the blood through the pulmonary and systemic vessels, it
performs these functions:
1. Keeps O2-poor blood separate from O2-rich blood. 2. Keeps the blood flowing in one direction—blood flows away from and then back
to the heart in each circuit.
3. creates blood pressure, which moves the blood through the circuits. 4. Regulates the blood supply based on the current needs of the body.
Pericardium
The membrane that surrounds and protects the heart is the pericardium fused with
base of great vessels. The Function of the Pericardium: (1) Protects and anchors the
heart (2) Prevents overfilling of the heart with blood (3) allows for the heart to work
in a relatively friction-free environment.
Layers of the Heart Wall
The wall of the heart consists of three layers: the epicardium (external layer), the myocardium (middle layer) composed of cardiac muscle, It’s the thickest of the three layers and the endocardium (inner layer).
Chambers of the Heart
The heart has four hollow chambers: two superior atria (single atrium) and two
inferior ventricles. Each atrium has a wrinkled anterior pouch called an auricle.
Internally, the atria are separated by the interatrial septum , and the ventricles are
separated by the interventricular septum****. Therefore, the heart has a left and a right
side. The thickness of a chamber’s myocardium is suited to its function. The atria
have thin walls, and they send blood into the adjacent ventricles. The ventricles are
thicker, and they pump blood into blood vessels that travel to parts of the body. The
left ventricle has a thicker wall than the right ventricle; the right ventricle pumps
blood to the lungs, which are nearby. The left ventricle pumps blood to all the other
parts of the body.
Right Atrium The right atrium forms the right border of the heart. It receives blood from three veins: superior vena cava, inferior vena cava, and coronary sinus. Veins always carry blood toward the heart. Venous blood passes from the right atrium into the right ventricle through an atrioventricular ( AV ) valve. This valve, like the other heart valves, directs the flow of blood and prevents any backflow. The AV valve also called the tricuspid valve because it has three cusps, or flaps.
Right Ventricle In the right ventricle , the cusps of the tricuspid valve are connected to fibrous cords, called the chordae tendineae. The chordae tendineae in turn are connected
Conduction System of the Heart
The conduction system of the heart is a route of specialized cardiac muscle fibers that initiate and stimulate contraction of the atria and ventricles. The conduction system is said to be intrinsic , meaning that the heart beats automatically without the need for external nervous stimulation. The conduction system coordinates the contraction of the atria and ventricles so that the heart is an effective pump. Without this conduction system, the atria and ventricles would contract at different rates. Conduction system of the heart. (1) The sinoatrial node (SA) cardiac pacemaker sends out a stimulus, which causes the atria to contract. (2) When this stimulus reaches the atrioventricular node (AV) , it signals the ventricles to contract. (3) Impulses pass down the two branches of the atrioventricular bundle (4) and then to the Purkinje fibers , and thereafter, the ventricles contract.
Anatomy of Blood Vessels Blood vessels are of three types: arteries, capillaries, and veins. These vessels function to transport blood and its contents; Carry out exchange of gases in the pulmonary capillaries and exchange of gases plus nutrients for waste at the systemic capillaries; Regulate blood pressure; Direct blood flow to those systemic tissues that most require it at the moment.
Arteries transport blood away from the heart. Blood vessels belong to either the pulmonary circuit or the systemic circuit. The path of blood through the pulmonary circuit can be traced as follows: deoxygenated blood from all regions of the body first collects by veins in the right atrium and then passes into the right ventricle, which pumps it into the pulmonary trunk. The pulmonary trunk divides into the pulmonary arteries, which in turn divide into the arterioles of the lungs. The arterioles then take blood to the pulmonary capillaries, where carbon dioxide and oxygen are exchanged. The blood then enters the pulmonary venules and flows through the pulmonary veins back to the left atrium. The systemic circuit includes all of the other arteries and veins of the body. The largest artery in the systemic circuit is the aorta , and the largest veins are the superior vena cava and inferior vena cava. The superior vena cava collects blood from the head, chest, and arms, and the inferior vena cava collects blood from the lower body regions. Both venae cavae enter the right atrium. The aorta and venae cavae are the major pathways for blood in the systemic system.
The Major Systemic Arteries After the aorta leaves the heart, it divides into the ascending aorta , the aortic arch , and the descending aorta. The left and right coronary arteries, which supply blood to the heart, branch off the ascending aorta. Three major arteries branch off the aortic arch: the brachiocephalic artery, the left common carotid artery, and the left subclavian artery. The brachiocephalic artery divides into the right common carotid and the right subclavian arteries. These blood vessels serve the head (right and left common carotids) and arms (right and left subclavians). The descending aorta is divided into the thoracic aorta , which branches off to the organs within the
Special Systemic Circulations Hepatic Portal System The hepatic portal system receives all of the blood draining from the abdominal digestive tract, as well as from the pancreas , gallbladder, and spleen. It is called a portal system because it connects capillaries of the intestines and other digestive organs to modified capillaries ( hepatic sinusoids ) of the liver ; thus, the blood passes through two capillary beds in series before it returns to the heart.
Fetal circulation The lungs are not functional in the fetus. The blood passes directly from the right atrium to the left atrium via the foramen ovale or from the right ventricle to the aorta via the pulmonary trunk through ductus venosus to aorta. The two umbilical arteries take fetal blood to the placenta where exchange of molecules between fetal and maternal blood takes place. Oxygen and nutrient molecules diffuse into the fetal blood, and carbon dioxide and urea diffuse from the fetal blood. The umbilical vein returns blood from the placenta to the fetus.
