Circulatory System - Histology Lecture Notes PDF

General Histolog Dr.hussein ali Al Nisour University Department of pharmacy Lecture one Circulatory System The circulatory system is an organ system that permits blood and lymph circulation to transport...

General Histolog Dr.hussein ali Al Nisour University Department of pharmacy Lecture one Circulatory System The circulatory system is an organ system that permits blood and lymph circulation to transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, blood cells, etc. to and from cells in the body to nourish it and help to fight diseases, stabilize body temperature and pH, and to maintain homeostasis. The vascular system is a continuous network of tubes or vessels that distributes blood throughout the body and returns it the heart. There are three Kinds of Circulation: Systemic circulation.: The movement of blood from the heart through the body to provide oxygen and nutrient to the tissues of the body while bringing deoxygenated blood back to the heart. Coronary circulation: The circulation of blood in the artries and veins that supply the heart muscle  eneral Histolog Pulmonary circulation: Take place from the heart to the lungs and then back to the heart. The circulatory system divided into of two systems:- A. The cardiovascular system The blood vascular system is composed of the following: 1. Heart 2. Arteries 3-Arterioles 4.Veins 5-Venules 6-Capillaries. B. The lymph vascular system The lymphatic system includes the lymph nodes, lymph vessels (thin tubes that carry lymph and white blood cells), bone marrow, spleen, thymus, tonsils and adenoids, and lymph tissue in the small intestine and other parts of the body. The lymphatic system is an important part of the body's immune system. Lymph vessels are lined by endothelial cells and have a thin layer of smooth muscles and adventitia that bind the lymph vessels to the surrounding tissue General Structure of Blood Vessels Blood vessels of various sizes and should be aware that the histological appearances of vessels of different sizes (arterioles, arteries) and different types (arteries ,veins) are different from each other. The division of the walls of the blood vessels into three layers or tunics. These are arranged into three concentric layers: intima, media and adventitia. 1- The intima is the thinnest layer. It is composed of a single layer of endothelial cells and a small amount of sub endothelial connective tissue. The intima is separated from the media by a dense elastic membrane called the internal elastic lamina. General Histolog 2- The media is the thickest layer and provides structural support, vasoreactivity and elasticity. It is composed of smooth muscle cells, elastic fibers and connective tissue, which vary in amount depending on the type of vessel. Smooth muscle cells contract (vasoconstriction) or relax (vasodilatation), which is controlled by autonomic nerves (nervivasorum) and local metabolic factors. 3- The adventitia is composed of connective tissue, nutrient vessels (vasa vasorum) and autonomic nerves (nervivasorum). The intima and inner part of the media are nourished by diffusion of oxygen and nutrients from blood in the lumen, and the adventitia and outer part of the media are nourished by vasa vasorum. General Histolog Arteries Arteries carry blood away from the heart to the rest of the body. The walls of arteries are thicker than that of veins to withstand pulsatile flow and higher blood pressures. As arteries become smaller, wall thickness gradually decreases. Arteries are divided into three types according to size and function. 1- Large elastic arteries (aorta, large aortic branchesand pulmonary arteries) the media is abundant in elastic fibers that allow it to expand with systole and recoil during diastole, thereby propelling blood forward. 2- Medium-sized muscular arteries (other aortic branches, coronary and renal arteries) the media is abundant in smooth muscle cells that vasoconstriction or vasodilation, thereby controlling lumen diameter and regional blood flow. 3- Small arteries and arterioles (in the substance of organs and tissues) the media is abundant in smooth muscle cells that vasoconstriction or vasodilation. In vessels of this size, smooth muscle contraction causes dramatic changes in lumen diameter, thereby controlling systemic blood pressure as well as regional blood flow. The walls of these large arteries are so thick that their peripheral parts cannot derive enough oxygen and nutrients from the blood of the vessel that they form. Larger vessels are therefore accompanied by smaller blood vessels which supply the tunica adventitia The vessels are called vasa vasorum. The vasa vasorum are found in large vein and arteries such as the aorta and its branches. vasa vasorum from the adventitia grow into the media of large arteries and veins and actively regulate blood flow to the wall of these vessels. General Histolog Arterioles Arterioles distribute blood to capillary beds, the sites of exchange with the body tissues. Capillaries lead back to small vessels known as venules that flow into the larger veins and eventually back to the heart. In arterioles, the tunica media contains only one or two layers of smooth muscle cells. Contraction of the smooth muscle cells constricts the lumen of the arteriole, increasing vascular resistance and reducing the flow of blood into capillary beds. Veins Veins are an important part of the cardiovascular system. Their main function is to bring deoxygenated blood back to the heart. The circulatory system is named as such because it is a circle.  The walls of veins are thinner than the walls of arteries, while their diameter is larger.  The tunica intima is very thin.  Only the largest veins contain an appreciable amount of sub endothelial connective tissue.  Internal and external elastic laminae are absent or very thin.  The tunica media appears thinner than the tunica adventitia  The appearance of the wall of veins also depends on their location. The walls of veins in the lower parts of the body are typically thicker than those of the upper parts of the body. Difference between artery and veins General Histolog Venules: Veins begin as tiny vessels called venules and get gradually larger as they near the heart.They are larger than capillaries.. Small venules are usually surrounded by pericytes, and larger venules are surrounded by smooth muscle. Venules collect blood from the capillary beds and play a critical role in immune responses to infection as they are the sites where immune cells cross from the blood into the surrounding tissue. VenaCava A large vein that carries blood to the heart from other area of the body. The vena cava has two parts: the superior vena cava and the inferior vena cava. The inferior vena cava is the largest vein in the human body. It collects blood from veins serving the tissues inferior to the heart and returns this blood to the right atrium of the heart. There are two in humans, the inferior vena cava (carrying blood from the lower body) and the superior vena cava (carrying blood from the head, arms, and upper body). Capillaries Capillaries: any of the fine branching blood vessels that form a network between the arterioles and venules. Capillaries: a tube that has an internal diameter of hairlike thinness. General Histolog  Small, normally around 3-4µm, but some capillaries can be 30-40 µm in diameter. The largest capillaries are found in the liver. Capillaries connect arterioles to venules. They allow the exchange of nutrients and wastes between the blood and the tissue cells, Types of capillaries 1- Fenestrated cappillaries: Have the same structure of non fenestrated but several circular opening in their endothelium cell are closed by diaphragm. This type capillary found in kidney and endocrine gland. 2- Sinusoid or discontinuous capillary A large capillaries with diameter of (30-40)pm or more. It consists of cells which are irregular in shape and discontinuous basal membrane. The endothelium is not connected by desmosome and associated with macrophagocytic or (Kupffer cells). This type is found in spleen, bone marrow, and liver. 3- Non fenestrated (Continuous capillaries) Are most common in body consist the wall endothelial cell resting on basal membrane and contain pericyte and pinocytotic vessel. This type capillary found in skin and muscle. Are formed by "continuous" endothelial cells and basal lamina. The endothelial cell and the basal lamina do not form openings, which would allow substances to pass the capillary wall Both endothelial cells and the basal lamina can act as selective filters in continuous capillaries. Heart The heart is a muscular organ in humans and other animals, which pumps blood through the blood vessels of the circulatory system. Blood provides the body with oxygen and nutrients, and also assists in the removal of metabolic wastes. The heart is located in the middle compartment of the mediastinum in the chest, the heart is a pump with four chambers and valves that maintain a one-way flow of blood. Tunica Intima: ( Endocardium) The Endocardium is composed of a continuous endothelial lining, with attendant basement membrane, that lies on top of a layer of collagen. The endothelium of the heart is continuous with that of the aorta, vena cava, pulmonary artery, and pulmonary veins, Purkinje Fibers ( impulse conducting fibers ,it is large modified of muscle cell). There are three recognized layers in the endocardium, which includes the endothelium with its basal lamina, the subendothelial layer, and the elastic layer.  Tunica Media: ( Myocardium) The myocardium is a variably-sized layer of cardiomyocytes that lies between the endocardium and epicardium and makes up the bulk of the heart's mass, and contains cardiac muscle fibres, and loose endomysial connective tissue that contains lots of capillaries.The Cardiac muscle cells (also called cardiomyocytes).The cells are surrounded by an extracellular matrix produced by supporting fibroblast cells. cardiomyocytes are arranged end to end, in a branching network of fibers and are attached to one another by specialized sections of membrane known as intercalated discs. The membrane at intercalated discs possess a large number of gap junctions which allow nearly free passage of ions between cardiomyocytes which is critical for cardiac action potential propagation. Tunica Adventitia: (Epicardium) The epicardium of the heart is lined by a layer of flat mesothelial cells that lie on top of a layer of collagenous tissue. The epicardium is composed of mesothelium, a cell type that covers and protects most of the internal organs of the as well as fat and connective tissue. The epicardium predominantly surrounds the heart and the roots of the emerging from it, including the aorta, the superior vena cava, and the cava. The heart also has four valves composed of connective tissue layered with endothelium on each side. Valves consist of three layers: Spongiosa (loose collagen) between fibrosa and ventricles, fibrosa (dense connective tissue in the aortic side). Ventricularis in the ventricles side. Each layer contributes to ensuring an optimal hemodynamic and mechanical environment without any abnormal disturbance.