Circulatory System

Dr. Maria Zahiri

Cardiovascular System

Consists of: Blood vesselsLymphatic vesselsHeart

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

ArteriesThere 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 laminaExternal elastic laminaSeveral elastic

membranes known as fenestrated membranes alternating with smooth muscle cells located in tunica media

Tunica intimasimple squamous endothelial cells (resting on a basal lamina )

The cells are joined by tight junctions and gap junctions

Tunica intimasubendothelial connective tissue • collagen • elastin fibrils • smooth muscle cells

dense internal elastic lamina

Tunica MediaIt is the thickest layeris 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 MediaThe 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 vasorumThis layer is thinner than tunica mediaPrevents over-stretch of the arterial wallIt 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 vasoconstrict

ion, 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 80-100 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 60- 80 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 bedIntermediate segment has a thickened tunica media, Its subendothelial layer is composed of plump modified polygonal smooth muscle cellsAre 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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