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Basic organization of CV components
- ALL components of the CV system have 3 layers1. Tunica intima (inner, endocardium)
- 2. Tunica media (middle, myocardium)
- 3. Tunica adventitia (outer, epicardium)
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Tunica Intima
- Lumenal (inner) layer
- Endothelium (simple squam.) contacts blood
- Subendothelium (loose CT / some smooth m. cells)
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How is the tunica intima oriented?
Longitudinally!
endothelium / subendothelial elements arranged on the axis of blood flow
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Functions of endothelium
- 1. Maintains selective permeability barrier.
- 2. Maintains non-thrombogenic barrier.
- 3. Modulates blood flow and vascular resistance.
- 4. Regulates cell growth.
- 5. Regulates immune response.
- 6. Maintains ECM.
- 7. Involved in lipoprotein metabolism
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Tunica Media
- Most prominent layer in arteries- Smooth muscle / Elastic membranes (concentric / relative)
- - Reticular fibers (type III collagen)
- - Proteoglycans
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How are elements of the tunica media oriented
- Elements of media are oriented concentrically (spiral)
- (smooth muscle / elastic membranes)
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What synthesizes all the ECM in the tunica media?
ECM made by smooth muscle cells
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Predominant feature of elastic arteries?
Where is it found?
What does it do?
Elastic lamellae (type III reticular fibers / proteoglycans)
Found in the tunica media
Elastin rebound maintains BP in diastole (relaxation)
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What separates the t. intima and t. media?
- Internal elastic lamina
- (both; prominent in muscular arteries)
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What separates the t. media and t. adventitia?
- External elastic lamina
- (muscular arteries)
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Tunica Adventitia
- Most prominent layers in veins
- Connective tissue sheath - mainly type I collagen
- - elastic fibers
- - smooth muscle
- Vasomotor nervi vascularis - innervated smooth m. of media
large vessels may have vasa vasorum
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Where are vasa vasorum found? Be specific
Vasa vasorum found in t. adventitia of large blood vessels
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How are elements of the tunica adventitia oriented
t. adventitia is oriented longitudinally
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Basic organization of heart tissue
- 1. Endocardium
- 2. Myocardium
- 3. Epicardium
- 4. Conducting system of specialized cardiac m. cells
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Endocardium
- Innermost heart layer (analog = t. intima)
- Endothelial lining
- Subendocardium
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Subendocardium
Underlying layer of the endocardium
- Composed of loose CT / elastic fibers / some smooth m. cells
- Contains small veins / nerves
In some locations, also contains Purkinje fibers
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Purkinje cells
- Specialized cardiac muscle cells (subendocardium)
- - larger than reg. cardiac m. cells
- - fewer myofibrils (stains lighter)
- - central nucleus (often binucleated) surrounded by glycogen (light area)
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Conduction system of the heart
- - Impulse initiated at SA node (pacemaker)
- - Travels to AV node
- - AV bundle (of His) sends impulse to L/R bundle branches to apex of heart.
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Myocardium
- Middle heart layer (analog = t. media)- Thicker in ventricles (inner circular / outer spiral layers)
- - Cardiac m. is anchored to cardiac skeleton (dense fibrous CT)
- - Cardiac m is postmitotic
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Histological changes in myocardial infarcted tissue
- - Lots of inflammatory cells
- - Necrotic tissue
With time, inflammatory cells increase in number / lots of scar tissue
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Epicardium
- Outermost heart layer (analog = T. Adventitia)
- - Thick layer of loose CT / adipose
- - Contains neurovasculature
- - Outermost layer = mesothelium (simple. squam)
- - forms visceral serous pericardium
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Heart valves
- 1. Right AV (tricuspid)
- 2. Left AV (mitral)
- 3. Pulmonic
- 4. Aortic
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Elastic Arteries
(conducting arteries)
- Tunica Intima
- - endothelial cells rest on thick subendothelium
- - longitudinal oriented CT
- - internal elastic lamina not clearly defined
- Tunica Media
- - concentric lamellae of elastin (40-70)
- - some smooth muscle
- Tunica Adventitia
- - thin, compared to vessel
- - vasa vasorum, extend into t. media
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Muscular Arteries
(distributing arteries)
- Tunica Intima
- - endothelial cells rest on subendothelium (some smooth m.)
- - longitudinal orientation
- - internal elastic lamina, prominent identifying feature
- Tunica Media
- - concentric smooth muscle (3-40)
- - some elastin (special stain required)
- Tunica Adventitia
- - external elastic lamina
- - longitudinal oriented fibroblasts / collagen / elastic fibers
- - vasa vasorum / lymphatics
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Arterioles
- Tunica Intima
- - endothelial cells rest on thin subendothelium
- - internal elastic lamina not usually visible
- Tunica Media
- - concentric smooth muscle (< 3)
- Tunica Adventitia
- - very thin
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Continuous Capillaries
(somatic capillaries)
- - Continuous endothelium resting on basal lamina
- - Cells joined by tight junctions (zonula occludens)
- - Found in CNS / PNS, muscle, CT, exocine glands
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What is special about CNS capillaries?
- Surrounding basal lamina of continuous capillaries is layer of astrocytic endfeet. Endfeet induce formation of blood-brain barrier
- - endothelial tight junctions
- - paucity of pinocytotic vesicles
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Fenestrated Capillaries
(visceral capillaries)
- - Continuous endothelium interrupted by pores (fenestrae)
- - Pores may have thin diaphragm over them (except renal glomeruli)
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Endocrine vs. Exocrine capillaries
- Endocrine = fenestrated
- Exocrine = continuous
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Sinusoidal Capillaries
(discontinuous capillaries)
- - Specialized w/ relatively large lumens
- - Many open fenestrations
- - Absence of continuous basal lamina
- - Macrophages present along walls
Found in liver / lymphoid / hematopoietic organs
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Venules
- - small, postcapillary vessels
- - paired w/ arterioles
- - very thin walls
- - functional characteristics of capillaries (exchange vessels)
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Veins
- Tunica Intima
- - very thin
- - valves formed by subendothelial CT (not in large veins)
- - valves have covering of endothelium
- Tunica Media = poorly developed
- Tunica Adventitia = very well developed
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What are the prominent layers in arteries vs. veins?
- Artery = prominent media
- Vein = prominent adventitia
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Large arteries vs. Large veins
- Large Artery
- - thick intima
- - thick media
- - underdeveloped adventitia
- Large Vein
- - thick intima
- - thin media
- - well developed adventitia w/ longitudinal bundles of smooth m.
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Lymphatic vessels
- - very thin-walled vessels
- - large irregular lumens (some valves)
- - larger lymphatics similar to veins w/o well defined tunics
Should not see RBC's in lymphatics
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