The cardiovascular system;heart

Lecture Objectives
By the end of this lecture, students are expected to:
1. List and describe the layers of the hart.
2. Outline the histological features of the pericardium.
3. Outline the different types of epithelium simple squamous cells found in heart.
4. nSummarize the functional and histological structure of Purkinje fibres.
The circulatory system: introduction
The circulatory system pumps and directs blood cells and substances carried in blood to all tissues of the body. It includes both the blood and lymphatic vascular systems, and in an adult the total length of its vessels is estimated at between 100,000 and 150,000 kilometers. The blood vascular system , or cardiovascular system, consists of the following structures:
? The heart propels blood through the system.
? Arteries , a series of vessels efferent from the heart that become smaller as they branch into the various organs, carry blood to the tissues.
? Capillaries , the smallest vessels, are the sites of O 2 , CO 2 ,n nutrient, and waste product exchange between blood and tissues. Together with the smallest arterial and venous branches carrying blood to and from them, capillaries in almost every organ form a complex network of thin, anastomosing tubules called the microvasculature or microvascular bed.
? Veins result from the convergence of venules into a system of larger channels that continue enlarging as they approach the heart, toward which they carry the blood to be pumped again. two major divisions of arteries, microvasculature, and veins make up the pulmonary circulation , where blood is oxygenated in the lungs, and the systemic circulation , where blood brings nutrients and removes wastes in tissues throughout the body.
The lymphatic vascular system , begins with the lymphatic capillaries , which are thin-walled, closed-ended tubules carrying lymph, that merge to form vessels of steadily increasing size. The largest lymph vessels connect with the blood vascular system and empty into the large veins near the heart. This returns fluid from tissue spaces all over the body to the blood.
The internal surface of all components of the blood and lymphatic systems is lined by a single layer of a squamous epithelium, called endothelium . As the interface between blood and the organs, cardiovascular endothelial cells have crucial physiologic and medical importance. Not only must endothelial cells maintain a selectively permeable, antithrombogenic (inhibitory to clot formation) barrier, they also determine when and where white blood cells leave the circulation for the interstitial space of tissues and secrete a variety of paracrine factors for vessel dilation, constriction, and growth of adjacent cells.
Dr.Hameda abdulmahdi College of Medicine /Dep. of anatomy & histology 2nd
stage Date:21/11/2016
2
Heart
Cardiac muscle in the four chambers of the heart wall contracts rhythmically, pumping the blood through the circulatory system . The right and left ventricles propel blood to the pulmonary and systemic circulation, respectively; right and left atria receive blood from the body and the pulmonary veins, respectively. The walls of all four heart chambers consist of three major layers: the internal endocardium; the middle myocardium; and the external epicardium.
The simple squamous epithelium of the tunica adventitia layer of the heart (mesothelium) is also the visceral layer of the serous pericardium, the pericardium is a two-layered connective tissue sac that encloses the heart. The fibrous pericardium is the outer layer, and the serous pericardium is the inner layer. The space between the two layers is the pericardial cavity, that contains serous fluid. This facilitates the pumping action of the heart.
The layers of haert
? The endocardium consists of a very thin inner layer of endothelium and supporting connective tissue, a middle myoelastic layer of smooth muscle fibers and connective tissue, and a deep layer of connective tissue called the subendocardial layer that merges with the myocardium Branches of the heart’s impulse-conducting system, consisting of modified cardiac muscle fibers, are also located in the subendocardial layer. The thickest layer, the myocardium, consists mainly of cardiac muscle with its fibers arranged spirally around each heart chamber. Because strong force is required to pump blood through the systemic and pulmonary circulations, the myocardium is much thicker in the walls of the ventricles, particularly the left, than in the atrial walls .
? The epicardium is a simple squamous mesothelium supported by a layer of loose connective tissue containing blood vessels and nerves . The epicardium corresponds to the visceral layer of the pericardium, the membrane surrounding the heart. Where the large vessels enter and leave the heart, the epicardium is reflected back as the parietal layer lining the pericardium.