MicroAnat_CardiovascularSystem_BloodVessels

8/2/2019 MicroAnat_CardiovascularSystem_BloodVessels

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CMG


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Cardiovascular System


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TUNICA INTIMA Simple squamous epithelium (endothelium)

Loose CT

Internal elastic lamina may be present

TUNICA MEDIA Concentrically arranged smooth muscle cells

Varying amounts of CT (elastin, collagen) secreted by andlocated b/w muscle cells

TUNICA ADVENTITIA Longitudinally arranged connective tissue (mostly collagen)

Large veins contain longitudinally arranged smooth muscle

Large arteries contain nervi vascularis

Large arteries & veins contain vasa vasorum

Muscular arteries contain circumferential external elasticlamina


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ELASTIC ARTERYFunction Conduction of blood from heart

Diameter >1cm

Tunica

Intima

Endothelial cells

Subendothelial connective tissue with smooth muscle cells

Elastica Interna NOT obvious

Tunica

Media

Thickest layer; Smooth Muscle (synthesizes all extracellular matrix in T. Media); NO Fibroblasts

Fenestrated Elastic Lamellae

40-70 layers of fenestrated circumferential elastin sheets allows systole distention and diastole recoil [subsidiary pump]

Fenestrae facilitate the diffusion of nutrients across the T. Media

Tunica

Adventitia

Relatively Thin

Vasa Vasorum (small BVs that supply O2 to outer half of vessel wall)

Nervi Vascularis (autonomic nerves to control smooth muscle contraction)

Collagen, Fibroblasts, Macrophages

Examples Aorta, Pulmonary Artery, Subclavian, Common Carotid, and Common Iliac


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LARGE VEINS

Function Return blood to heart

Diameter >1cm

Tunica Intima Endothelial cells, CT, and Smooth Muscle

Tunica Media Poorly Developed Concentric Smooth Muscle (few)

Tunica Adventitia Thick Elastic & Collagen Fibers

Longitudinal Smooth Muscle

Vasa Vasorum & Lymphatics

Examples Vena Cava, Subclavian, Portal Splenic,

Superior Mesenteric, External Iliac, Renal,and Azygous


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MUSCULAR ARTERIESFunction Distribution of blood to muscles, organs

Diameter 2-10mm

Tunica

Intima

Endothelial cells

Elastica Interna (prominent)

Tunica

Media

Smooth Muscle (4-40 layers connected via gap junctions)

Collagen fibers and elastic laminae

NO Fibroblasts

Tunica

Adventitia

Elastica Externa

Sympathetic, unmyelinated nerve fibers reach the elastica externa (contraction of smooth muscle in T. Media)

Longitudinal orientation of CT (allows continual changes in vessel diameter)

Examples Brachial, Femoral, Popliteal


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MEDIUM VEINSFunction Return blood to heart; reduce backflow w/ valves

Diameter 110mm

Tunica Intima Endothelial cells, CT, and smooth muscle

Tunica Media 2 or more layers of concentric smooth muscle Collagen and elastic fibers

Tunica Adventitia Thickest layer

Longitudinally arranged collagen

Fenestrated elastic lamellae (veins are capacitance vessels can store a lot of blood b/c of their great

distensibility)

Vasa Vasorum

Examples Veins of Extremities Distal to the Popliteal and Brachial; Veins of the Viscera and Head


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Longitudinal section of a

vein showing valves

Derived from the T. Intima

endothelial lining

In the middle, thin plate of

connective tissue

Free margins are directed

toward the heart

Prevent retrograde flow

Valve leaflets


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SMALL ARTERIES AND ARTERIOLES

Function Distribution of blood; Regulate blood pressure (peripheral resistance to flow);

Arterioles control blood flow to capillary beds

Diameter S. Artery = 0.12mm

Arteriole = 10100mTunica Intima Endothelial cells

Elastica Interna (thin)

Tunica Media S. Artery = 3-8 layers smooth muscle

Arteriole = 1-2 layers smooth muscle

Tunica Adventitia Loose Connective Tissue (ill-defined)

Arteriolar tone is controlled by

endothelial factors (nitric oxide,

prostacyclin) and autonomic NS

(sympathetic norepinephrine)


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VENULES AND SMALL VEINS

Function Return blood to heart; Participate in exchange of blood-borne materials; Important in inflammation

(site offluid extravasation and emigration ofWBCs)

Diameter Small Vein = 0.11mm

Venule = 10100m

Tunica Intima Endothelial cells

Tunica Media Small Vein = Smooth Muscle (2-3 layers continuous with T. Intima)

Venule = Smooth Muscle (1-2 layers)

Postcapillary Venule = None

Tunica Adventitia CT w/ some Elastic Fibers

Postcapillary Venule = None


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CAPILLARIES

Function Exchange of nutrients, metabolites, oxygen and carbon dioxide between the blood

and the tissues

Diameter 79m

Tunica Intima Endothelium (single layer w/ occluding [tight] junctions) Pericytes (enclosed in basal lamina; partially surround the capillaries)

Contain contractile proteins surrounded by basal lamina

Important in blood-brain barrier stability as well as angiogenesis

Tunica Media None

Tunica Adventitia None


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Continuous Capillaries

Function: exchange via pinocytotic vesicles Morphology: endothelium forms a thin, uninterrupted layeraround the

entire circumference of the capillary

Locations: Muscle, Lung, Exocrine Glands, Nervous Tissue (blood-brainand blood-nerve barriers) and Connective Tissue

Fenestrated Capillaries

Function: rapid exchange offluids and metabolites Morphology: endothelium varies in thickness, with some areas exhibiting

pores (fenestrae) 80 - 100 nm in diameter covered by a thin diaphragm(glycoproteins)

Locations: Endocrine glands, Gallbladder, Intestine, Kidney, Pancreas,Choroid plexus In renal glomerulus, pores are NOT covered by diaphragms

Sinusoids (a.k.a. Discontinuous Capillaries) Function: rapid exchange oflarge molecules and cells

Morphology: larger diameter(30 - 40m), irregular cross-sectionaloutlines, a discontinuous endothelial lining with large fenestrations ofvarying size and shape (no diaphragms), and a discontinuous basallamina

Locations: Bone Marrow, Liver, Spleen


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Metarterioles

Arise from arterioles

The proximal segments of thoroughfare channels

Walls contain smooth muscle fibers in declining numbers from proximal to distal

Thoroughfare Channels

Allow some blood to pass more directly from arterioles to venules (bypassing the capillary bed)

Precapillary Sphincters

Smooth muscle cells that encircle capillaries as they arise from a metarteriole

Regulate the entrance of blood into the capillary bed

If they are constricted, blood flows mostly through the thoroughfare channel (not the capillary bed)

Arteriovenous Anastomoses (AVAs; AV shunts)

Direct routes from arteries to veins that divert blood from capillaries

Are coiled arterioles that have a thick, richly innervated smooth muscle layer

Constriction of the smooth muscle sends blood to the capillary bed

Relaxation reduces blood flow to the capillaries Mostly present in the dermis of fingertips, lips, nose (thermoregulation), and in erectile tissue


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1. Venous walls are thinner relative to their diameter than arterial walls

2. Lumens of veins are often collapsed, with irregular shapes

3. Indistinct layers in veins; adventitia is thickest layer

4. Veins may have valves


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Atherosclerosis

Thickening & hardening of Tunica Intima inmedium & large arteries by an atheroma(lipid/cell/CT plaque)

Possible causes of endothelium damage: Free-radical reactions

oxidized serum cholesterol, triglycerides,fibrinogen, homocysteine, insulin

BP

Obesity, chronic inflammation, lifestylefactors (physical inactivity and tobaccosmoking)

Diabetes

The most important complication isthrombosis Can lead to myocardial infarction if in

coronary arteries, stroke if in cerebralarteries.

Endothelium damageddue to serum LDL,

BP, smoking, etc.

Platelets stick to CTand smooth muscle of

T. Intima

Platelets and

damaged endotheliumrelease cytokines

Cytokines encourage

proliferation of smoothmuscle in T. Intima

T. Intima smoothmuscle produces

ECM

Endothelium releasesfree radicals whichoxidize LDL et al

Oxidized LDL et al(lipids) deposit on

endothelium

Intimal macrophagesendocytose lipids

which become foamcells

Lipid is held in T.Intima by impermeable

IEL

Plaque forms in T.Intima

Plaque grows

protrudes into lumen &breaks through IEL

Plaque becomes

fibrotic and eventuallycalcifies


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Varicose Veins Malfunctioning valves orweakness in the wall

Pooling of blood in vessels enlarged, swollen veins

Saphenous veins of the legs

Veins of the ano-rectal region: Hemorrhoids

Veins of the lower esophagus: Esophageal varices

Veins of the spermatic cord: Varicocele


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Lymphatic vessels collect fluid (lymph) from the tissue spaces and return it to the blood

Lymph circulates only in one direction, toward the heart

Movement of lymph is slow and driven mostly by compression of adjacent skeletal muscle

Similar in structure to veins except they have thinner walls in relation to their diameter

Layers of the wall are indistinct

Lymph nodes

Interposed along lymphatic vessels

Filter the lymph as it percolates toward the blood vascular system

Lymphatic capillaries

Originate in the tissues as blind-ended vessels which consist of a single layer of epithelium (an endothelium) with an

incomplete basal lamina, making them more permeable than capillaries

Anchoring filaments connect them (via the basal lamina) to surrounding collagen fibers and keep them patent (open) during

increased tissue pressure, i.e. edema

Better at removing protein- or lipid-rich fluid from tissue spaces than the blood capillaries (important in small intestine) Lymphatic capillaries converge on increasingly larger lymphatic vessels that ultimately unite to form the thoracic duct and right

lymphatic trunk, which dump the lymph into the venous system in the neck

Larger lymphatic vessels

Media contains both longitudinally and circularly arranged smooth muscle

Relatively undeveloped adventitia

Valves are present


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Cardiovascular System: Blood Vessels


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Tunica intima (ti)

Endothelium

Tunica media (tm)

Thickest part of this vessel Consists of multiple layers offenestrated elastic laminae (dark pink, refractile bands)

layered with lighter pink areas consisting ofsmooth muscle fibers and many collagen fibers

Concentrically arranged tubes of elastic fibers with large holes (fenestrations) in the wall of the tubes

In cross section, the laminae appear discontinuous due to the holes

Elasticity helps propel blood along the aorta away from the heart

When the left ventricle contracts, the wall of the aorta bulges out, storing some of the energy ofsystole (ventricularcontraction) by dilating the fenestrated elastic laminae

When systole ceases, the fenestrated elastic laminae spring back to their original shape

Tunica adventitia (ta)

Nerve fibers

Vasa vasorum

CT fibers

Adipocytes

Patients with Marfan syndrome, a congenital defect in fibrillin structure, frequently die from sudden aortic

aneurysms at a young age. Why?

A: In Marfan syndrome, fibrillin microfibrils are absent and thus elastic fibers are abnormal. Elastic lamellae

of the aorta are therefore not well attached to smooth muscle cells by fibrillin and undergo degeneration,which can eventually result in aortic aneurism with subsequent dissection.


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Tunica Intima

Tunica Media

Fenestrated

Elastic Laminae

Smooth Muscle and

Collagen Fibers

Endothelium


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Tunica Adventitia

Vasa vasorum(supply oxygenated blood

to Tunica Media)

Tunica Media


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Tunica Adventitia

Tunica Media

Tunica Intima

Fenestrated

Elastic Laminae

Fenestrated

Elastic Laminae


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Top of the left ventricle (lv)

Part of the wall of the aorta (a)

One of the three cusps of the aortic

valve (av)

Fibrous CT in the valve merges into

the CT (part of the cardiac skeleton)

between the ventricle and the aorta

Avascular

Covered by an endothelium

More elastin on the ventricular side


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Endocardium(from L ventricle)

Tunic Intima(from Aorta)

Endocardium(from L ventricle)

Tunic Intima(from Aorta)


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This is a transverse section througha large vein in the abdomen -- Startat the lumen (L) and work your wayoutward into the wall of the vessel

Tunica intima

Thin with endothelial cells Tunica media (TM)

Pinkish, smaller, tightly packedsmooth muscle cells Arranged circumferentially with

respect to the lumen

Tunica adventitia (TA) Lighter, larger bundles of smooth

muscle Surrounded with pink borders of

collagen fibers

Arranged longitudinally


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Tunica Adventitia Tunica Media Tunica Intima


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This is a cross section of an artery (A), vein (V)

and nerve (N)

Large muscular artery

~1/5: wall thickness/diameter ratio

Smooth outline Large vein

~1/15: wall thickness/diameter ratio

Irregular outline

More blood in the lumen

Study the walls of both large vessels and identify

the three tunics

See if you can find arterioles, venules, and

capillaries


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Large Vein

Nerve


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Large VeinMuscular Artery


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Muscular Artery Large Vein


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Small muscular arteries and arterioles, located in the connective tissue surrounding the elasticcartilage (EC) in the middle of the epiglottis

The elastic stain stains the elastic fibers in this specimen a dark purple/black color

A counter stain conveniently stains RBCs yellow so look for these inside blood vessels

Small muscular arteries

Prominent wrinkled internal elastic lamina

5-10 layers of smooth muscle in the media

Sparse external elastic lamina

Arterioles

~2 layers of smooth muscle in the media

Little or no internal elastic lamina

The distinction between the smallest muscular arteries and the largest arterioles is slight and of no

great significance

The arteries may be accompanied by veins and the arterioles may be accompanied by venules

Capillaries are also present


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This thin plastic sectionfrom the male reproductivesystem

Has a lot of CT (pink)between efferent ductules(purple lumina)

Small muscular arteries

Companion veins

Arterioles Venules

Many capillaries


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Arteriole

Venule


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This is a thin plastic section of the liver -- consists of cords and plates of hepatic parenchymal cells

surrounded by hepatic sinusoids

In any given organ, the parenchymal cells are the organ-specific cells

Many organs have both parenchymal and nonparenchymal cells, e.g., CT, blood vessels, nerves, lymphatics

A sinusoid is a generic term for a capillary

Implies that there is sluggish, meandering blood flow through a network of capillaries with large lumina

Sinusoids are also found in bone marrow, the spleen, endocrine organs, etc

The hepatic sinusoids carry nutrient-laden blood from the GI tract and as they pass by the hepatic

parenchymal cells, the nutrients leave the blood and enter the liver, for processing

Hepatic sinusoids are unusual capillaries -- they are intermingled stretches ofdiscontinuous capillaries

and fenestrated continuous capillaries, although these details are not visible in this slide

Two distinct types ofmarginal cells

Flattened, typical endothelial cells The capillaries here have one additional peculiaritythey have a thin, discontinuous basement membrane

Fatter, phagocytic Kupffer cell

The Kupffer cell nuclei are harder to locate and difficult to differentiate from hepatic parenchymal cells


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Slide 90, Pituitary Gland, H&E

Continuous Fenestrated Capillaries

The pituitary gland is the master endocrine organ of

the body -- It has two main components, a

neurohypophysis (N) (an extension of the CNS,

directly connected to the brains hypothalamus) and

an adenohypophysis (A)

Adenohypophysis -- contains a plethora ofcapillaries (sinusoids) engorged with RBCs

Secretes hormones, synthesized in plates, cords,

and follicles of epithelial cells, into the blood in the

capillaries that surround the epithelial cells

These capillaries are continuous fenestrated

capillaries

At high mag., you can see the flattened nuclei of

capillary endothelial cells

The fenestrations are not visible in the light

microscope


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Continuous

Fenestrated

Capillaries


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Cardiovascular System: Blood Vessels

The three basic types of capillaries,


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differentiated by the continuity

between the endothelial cell and

the basal lamina

A. Continuous capillary X120,000

B. Fenestrated capillary X70,000

C. Discontinuous capillary X30,000

(sinusoid)Continuous capillary

Fenestrated capillary

Discontinuous capillary


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TEM, transverse section of a muscle capillary, continuous type. Note nucleus andjunction between

neighboring cells (N). Pinocytotic vesicles are abundant in the cytoplasm (arrows).

Pinocytotic vesicles

Continuous Capillary


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Light micrograph of a cast of the blood supply to skeletal muscle. The tissue has been

digested away, but the capillaries (Ca) follow a course parallel to the muscle fibers. They

are supplied by arterioles (Ar) and drained by venules (Ve). X350.

Capillaries

Venule

Arteriole


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TEM of an arteriole showing the lining endothelial cells (star) and a subadjacent smooth muscle cell (dot).

A connective tissue cell lies at the periphery.

Lining Endothelial Cells

Subadjacent Smooth

Muscle Cell

Connective

Tissue Cell

Arteriole


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TEM, muscular artery -- detail of the

inner part of the vascular wall. Through

a fenestra of the internal elastic lamina,processes of the endothelial cell

establish a myoendothelial junction (Mej)

with the adjacent smooth muscle cell

belonging to the media. In the latter, the

prevalent muscular tissue is

interspersed with the less frequent anddiscontinuous elastic lamellae X6000

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MicroAnat_CardiovascularSystem_BloodVessels