The Vascular System PDF

The Vascular system Prof. Dr. Marwa G.A. Hegazy Dr. Heba Afifi  Learning Outcomes: Identify the major components of the vascular system, including arteries, veins, and capillaries, and describe their unique characteristics and functions. Understand the structure and fun...

The Vascular system Prof. Dr. Marwa G.A. Hegazy Dr. Heba Afifi  Learning Outcomes: Identify the major components of the vascular system, including arteries, veins, and capillaries, and describe their unique characteristics and functions. Understand the structure and function of the three layers of blood vessels (tunica intima, tunica media, and tunica adventitia) and their roles in maintaining vascular integrity and blood flow.  Blood Vessels They include: Arteries: Large arteries, medium sized arteries & arterioles. Veins: Large veins, medium sized veins & venules. Arterio-Venous Connections: Blood capillaries.  Arteries 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 but the ratio of wall thickness to lumen diameter increases (i.e. relative lumen size decreases). Arteries are divided into three types according to size and function. 1. large elastic arteries (aorta and pulmonary arteries): the media is abundant in elastic fibers that allow it to expand with systole and recoil during diastole, thereby propelling blood forward  medium-sized muscular arteries (other aortic branches, e.g. coronary and renal arteries): the media is abundant in smooth muscle cells that vasoconstrict or vasodilate, thereby controlling lumen diameter and regional blood flow.  small arteries and arterioles (in the substance of organs and tissues): the media is abundant in smooth muscle cells that vasoconstrict or vasodilate; 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.  Medium-Sized Artery &Vein Simple squamous endotheliu Tunica m intima Internal Elastic lamina Smooth muscle Tunica media Tunica Elastic adventitia fibres  Medium-sized Artery Medium-sized Vein 1-Thick wall and narrow lumen 1-Thin wall and wide lumen 2. The lumen is rounded, doesn't collapse 2-The lumen collapses after death after death 3. It has no valves 3-It has valves 4. The lumen contains no blood after 4-The lumen contains blood after death death 5. T. Intima is thick, folded, rich in elastic 5-T. Intima is thin, not folded, poor in fibers, has a clear internal elastic elastic fibers, has no internal elastic lamina lamina 6-T. Media is thick, made of smooth 6. T. media is thin, made of smooth muscles and elastic fibers muscles, poor in elastic fibers 7. External elastic lamina may be present 7. It has no external elastic lamina in between the media & adventitia 8-T. Adventitia is thin, rich in elastic fiber 8. T. Adventitia is thick, rich in collagen fibers  Blood capillaries are vascular networks inside human body. Formed of a single layer of simple squamous epith. Resting on a basal lamina and rolls up forming a tube. Types of capillaries: 1. Continuous 2. Fenestrated 3. sinusoidal  Continous Fenestrated Sinusoidal capill. capill. capill. Large ,irregular Small ,regular Small ,regular Has pores without diaphragm Continuous Has pores covered epith.& basal by diaphragm Site: lamina Site: liver, bone Site: all over the marrow & spleen intestine, body. endocrine glands.  General structure of blood vessels: It is formed of 3 layers from inside outwards: 1- Tunica Intima: Site: the innermost layer. Function: It is in contact with blood stream. It provides a smooth surface for blood flow It is formed of: 1. Endothelium: simple squamous epith. 2. Subendothelium: loose C.T. to support the endothelium. 3. Internal elastic lamina: a layer of elastic fibers.  2-Tunica Media: Site: the middle layer. Function: It regulates blood flow by muscle contraction. It is formed of: 1. Circularly arranged smooth muscle fibers. 2. Variable amounts of elastic fibers. 3. Its outer layer is limited with external elastic lamina. 3-Tunica Adventitia: Site: The outermost layer. Function: 1. connects the blood vessels to the surrounding tissues 2. prevents over-distension of the vessel. formed of: loose C.T. 1. ( ++++ collagen fibers , some elastic fibers and some C.T. cells). 2. Contains nerves, lymphatics & vasa vasorum  Vasa Vasorum: They are small arteries (blood vessel of the blood vessel) Site: present mainly in the adventitia of large blood vessels e.g. aorta and large veins). Funct: nourish the outer part of the vessel wall.