Circulatory System Dr. Maria Zahiri

Cardiovascular System Consists of:  Blood vessels  Lymphatic vessels  Heart

Blood vessels  Arteries: transport blood away from heart  Veins: drain microvascular beds, returnining blood to heart  Microvascular bed: Arterioles Capillaries postcapillary venules

 Arterioles regulate volume of blood flow  Capillaries have small diameter, thin walled, and are where gas/nutrient exchange take place  Postcapillary venules are the site of passage of blood cells to connective tissue

Tunics of Vessels Walls of blood vessels are composed of 3layers:  Tunica intima  Tunica media  Tunica adventitia

 Tunica intima is composed of: a simple squamous epithelium(endothelium) the subendothelial (loose connective tissue)

 Tunica media usually is the thickest layer of the vessel wall is composed of: helically disposed layers of smooth muscle cells occasionally elastic and reticular fibers (collagen III)

 Tunica adventitia is the outermost layer that blends into surrounding connective tissue  Collagen type I

Arteries There is 3 types of arteries in human body:  large(elastic)  medium(muscular)  small arteries  arterioles

Aorta)) Elastic Artery Special characteristics of elastic arteries are:  Internal elastic lamina  External elastic lamina  Several elastic membranes known as fenestrated membranes alternating with smooth muscle cells located in tunica media

Tunica intima  simple squamous endothelial cells (resting on a basal lamina )  The cells are joined by tight junctions and gap junctions

Tunica intima  subendothelial connective tissue collagen elastin fibrils smooth muscle cells  dense internal elastic lamina

Tunica Media  It is the thickest layer  is composed of many fenestrated elastic lamellae, collagen and smooth muscle cells  The wavy sheets of elastic membranes are located between the smooth muscle fibers of the tunica media (stretching )

Tunica Media  The extracellular matrix of tunica media, is composed of : chondroitin sulfate collagen reticular elastic fibers ( is synthesized and secreted by the smooth muscle cells)  Few fibroblasts also exist in tunica media

Tunica adventitia  is the outermost layer of the vessel wall which merges with the connective tissue of the body wall It consists of : Fibroblasts Collagen thin elastic fibers small blood vessels the vasa vasorum  This layer is thinner than tunica media  Prevents over-stretch of the arterial wall  It also contains nervi vascularis

vasa vasorum  ("the vessels of the vessels") is a network of small blood vessels that supply the walls of large blood vessels, such as elastic arteries (aorta) and large veins (vena cava).

Vascular nerves  are nerves which innervate arteries and veins.  control vasodilation and vasoconstriction, which in turn lead to the control and regulation of temperature and homeostasis

Muscular arteries distribute blood to the organs and tissues They have less elastic lamina and more smooth muscle cells than elastic arteries

Muscular arteries The muscle is arranged so that its contraction narrows the lumen of the vessel Internal and external elastic lamina are present Have smaller diameter than large elastic arteries

Tunica Intima Endothelial lining with basal lamina Little subendothelial connective tissue Internal elastic lamina which is a fenestrated sheet of elastic fibers

Consists of: smooth muscles(are arranged in spiral pattern) collagen type III few elastic fibers There is No fibroblasts External elastic lamina is also present Tunica media

 is continuous with the connective tissue of the organ which is supplied by this vessel  Thick connective tissue layer about equal to tunica media in thickness  High collagen content with fibroblasts  Elastic fibers concentrated in external elastic lamina Tunica adventitia

Small Arteries and Arterioles  Arteriole has a diameter less than 0.1 mm and has 1-3 layers of smooth muscle in tunica media  Arterioles are key control points for blood flow

 Small artery has up to 8 layers of smooth muscle cells in tunica media

Small Arteries and Arterioles  Small arteries and large arterioles have fenestrated internal elastic lamina, but in smaller arterioles it is absent  Tunica adventitia is sparse and poorly developed

Veins  Veins are classified as large, medium and small size  Large and medium veins usually accompany with large and medium arteries  Large and medium veins have tunica intima, tunica media and tunica adventitia

Veins  Tunica media of veins are thinner than arteries of the same size  Wall of a vein is much thinner than artery with the same size  Some veins may have valves to prevent backflow of blood

Large Veins  Vena cava is a good example of a large vein  Tunica intima Endothelium basal lamina thin subendothelial connective tissue internal elastic lamina

Large Veins  Tunica media consists of 4-5 layers of smooth muscle with no distinct border, collagen and fibroblasts  Tunica adventitia is thick with some smooth muscle; many collagen fibers, fibroblasts and some elastic fibers

Medium veins  Tunica intima: endothelium, basal lamina, subendothelial connective tissue and internal elastic lamina  Tunica media: very thin, smooth muscle and some fibroblasts, reticular and elastic fibers  Tunica adventitia: thicker than media, is composed of collagen bundles and a few scattered smooth muscle

Venules  Their wall consists of endothelium, basal lamina and pericytes (contractile) in postcapillary venules  In larger venules, pericytes are replaced by smooth muscle cells  Venules are sensitive to histamine and serotonin, increased permeability to fluid and WBC during allergic and inflammatory reactions

Venules  They have No real tunica media, just have 1-2 layers of smooth muscle  Some collagen and a few fibroblast  Endothelial cells of venules are cuboidal in certain lymphoid tissue and are called high-endothelial venules

Capillaries  Single layer of endothelial cells with basal lamina  7-9 micrometer  Pericytes are located along the outside of the capillaries and small venules, forming gap junctions with endothelial cells  Site of most nutrient and gas exchange between tissue and blood  Longest: in muscle

Pericytes  are contractile cells  wrap around the endothelial cells of capillaries and venules throughout the body.  Also known as Rouget cells or mural cells

Capillaries  Continuous (nonfenestrated) capillaries  Discontinuous (fenestrated) capillaries have pores are nm in

Capillaries  Continuous (nonfenestrated= somatic) capillaries have no pores in their wall, have tight junctions: CNS, PNS, muscle, connective tissue, exocrine gland Have 70 nm vesicles CNS capillaries have No vesicles

Capillaries Discontinuous (fenestrated= visceral) capillaries nm pores covered by a pore diaphragm, (endocrine glands, intestines, In renal glomerulus that fenestrated capillaries lack diaphragms

Sinusoidal capillaries  Special thin-walled, incomplete capillaries with irregular large diameter  Discontinuous endothelial wall contain many large fenestrae without diaphragms  Found in liver, lymph nodes and hemopoietic tissues such as bone marrow and spleen

Metarteriole  is a short vessel  links arterioles and venules.  Instead of tunica media, they have individual smooth muscle, each forming a precapillary sphincter  that encircles the entrance to that capillary bed.

arteriovenous anastomoses (AVA)  are direct vascular connections between arterioles and venules that bypass the capillary bed  Intermediate segment has a thickened tunica media, Its subendothelial layer is composed of plump modified polygonal smooth muscle cells  Are useful in thermoregulation  are abundant in skin

Glomus  Vascularize nail beds and tips of fingers and toes  This small organ receives an arteriole without elastic lamina and richly innervated smooth muscle cell layer,which surround the lumen, thus directly control blood flow to region before emptying into a venous plexus

the carotid sinus  (or carotid bulb)  is a dilated area at the base of the internal carotid  just superior to the bifurcation of the common carotid  is sensitive to pressure changes in the arterial blood at this level.  It is the major baroreception site in humans and most mammals.

Carotid body  (carotid glomus or glomus caroticum)  is a small cluster of chemoreceptors and supporting cells located near the bifurcation of the carotid artery  It detects changes in the composition of arterial blood flowing through it (pressure of oxygen,carbon dioxide, pH and temperature)

Necrosis  is a form of cell injury which results in the premature death of cells in living tissue by autolysis.  Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma which result in the unregulated digestion of cell components.

apoptosis  is a naturally occurring programmed and targeted cause of cellular death.  While apoptosis often provides beneficial effects to the organism, necrosis is almost always detrimental and can be fatal

Aneurism

Atherosclerosis

Heart Heart wall is composed of 3layers: endocardium, myocardium epicardium

Endocardium  composed of endothelium with subendothelial (fibroelastic connective tissue)  Middle layer is dense connective tissue with smooth muscle and elastic fibers  Outer layer called subendocardium and is continuous with connective tissue of myocardium, containing small blood vessels and purkinje fibers

Myocardium  Thick middle layer of the heart, is composed of cardiac muscle cells

 The outermost layer, composed of mesothelial cells with underlying loose connective tissue contains coronary vessels and nerves and ganglia,and usually has adipose tissue too  Homologue of the tunica adventitia of the vessels Epicardium

Heart Valve  Endothelial lining on surface  Core of dense irregular connective tissue with many elastic fibers

Purkinje Fibers  Large diameter cardiac muscle cells that are pale staining, conduct electrical impulses

Lymphatic Vessels  Lymphatic vessels are thin walled, unidirectional, carry excess interstitial fluid from tissues back to vascular system  Lymphatic capillaries begin as blind tubes and converge into larger vessels  2 main vessels empty into vascular system at base of neck

Lymphatic Vessels  Fluid passes through lymph nodes before returning to vascular system  Lymph capillaries have incomplete basal lamina and are very permeable

Lymphatic Vessels  Bundles of anchoring filaments terminate on the plasma membrane  Lymphatic capillaries are slightly larger in diameter than blood capillaries  The ends of the endothelial cells that make up the wall of a lymphatic capillary overlap

Lymphatic ducts  Lymphatic ducts are similar to large veins  Tunica intima composed of endothelium and several layers of elastic and collagen fibers  In tunica media smooth muscle cells are oriented circularly and longitudinally  Tunica adventitia contains smooth muscle and collagen fibers

Angiosarcoma  is a malignant neoplasm (cancer) of endothelial-type cells that line vessel walls.  This may be in reference to blood (hemangiosarcoma) or lymphatic vessels (lymphangiosarcoma).

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