Basic organization of CV components
<strong>ALL components of the CV system have 3 layers
</strong>1. Tunica intima (inner, endocardium)
2. Tunica media (middle, myocardium)
3. Tunica adventitia (outer, epicardium)

Tunica Intima
<strong>Lumenal (inner) layer</strong>
Endothelium (simple squam.) contacts blood
Subendothelium (loose CT / some smooth m. cells)

How is the tunica intima oriented?
<answer>
<strong>Longitudinally</strong>!

endothelium / subendothelial elements arranged on the axis of blood flow
</answer>

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

Tunica Media
<strong>Most prominent layer in arteries
</strong>- Smooth muscle / Elastic membranes (concentric / relative)
- Reticular fibers (type III collagen)
- Proteoglycans

How are elements of the tunica media oriented
Elements of media are oriented <strong><span style="text-decoration:underline;">concentrically</span></strong> (spiral)
(smooth muscle / elastic membranes)

What synthesizes all the ECM in the tunica media?
ECM made by <strong><span style="text-decoration:underline;">smooth muscle cells</span></strong>

<question>
Predominant feature of elastic arteries?
Where is it found? 
What does it do?
</question>
<answer>
Elastic lamellae (type III reticular fibers / proteoglycans)

Found in the tunica media

Elastin rebound maintains BP in diastole (relaxation)
</answer>

What separates the t. intima and t. media?
Internal elastic lamina 
(both; prominent in muscular arteries)

What separates the t. media and t. adventitia?
External elastic lamina 
(muscular arteries)

Tunica Adventitia
<answer>
<strong>Most prominent layers in veins</strong>
<span style="text-decoration:underline;">Connective tissue sheath 
</span>  - mainly type I collagen
  - elastic fibers
  - smooth muscle
<span style="text-decoration:underline;">Vasomotor nervi vascularis
</span>  - innervated smooth m. of <strong>media 

</strong>large vessels may have vasa vasorum
</answer>

Where are vasa vasorum found? Be specific
Vasa vasorum found in t. adventitia of large blood vessels

How are elements of the tunica adventitia oriented
t. adventitia is oriented <strong><span style="text-decoration:underline;">longitudinally</span></strong>

Basic organization of heart tissue
1. Endocardium
2. Myocardium
3. Epicardium
4. Conducting system of specialized cardiac m. cells

Endocardium
<strong>Innermost heart layer (analog = t. intima)</strong>
Endothelial lining
Subendocardium

Subendocardium
<answer>
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
</answer>

Purkinje cells
<strong>Specialized cardiac muscle cells (subendocardium)</strong>
- larger than reg. cardiac m. cells
- fewer myofibrils (stains lighter)
- central nucleus (often binucleated) surrounded by glycogen (light area)

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.

Myocardium
<strong>Middle heart layer (analog = t. media)
</strong>- Thicker in ventricles (inner circular / outer spiral layers)
- Cardiac m. is anchored to cardiac skeleton (dense fibrous CT) 
- Cardiac m is postmitotic

Histological changes in myocardial infarcted tissue
<answer>
- Lots of inflammatory cells
- Necrotic tissue

With time, inflammatory cells increase in number / lots of scar tissue
</answer>

Epicardium
<strong>Outermost heart layer (analog = T. Adventitia)</strong>
- Thick layer of loose CT / adipose
- Contains neurovasculature
- Outermost layer = mesothelium (simple. squam)
     - forms visceral serous pericardium

Heart valves
1. Right AV (tricuspid)
2. Left AV (mitral)
3. Pulmonic
4. Aortic

<question>
Elastic Arteries
(conducting arteries)
</question>
<span style="text-decoration:underline;"><strong>Tunica Intima</strong></span>
   - endothelial cells rest on thick subendothelium
   - longitudinal oriented CT
   - internal elastic lamina not clearly defined
<span style="text-decoration:underline;"><strong>Tunica Media</strong></span>
   - concentric lamellae of elastin (40-70)
   - some smooth muscle
<span style="text-decoration:underline;"><strong>Tunica Adventitia</strong></span> 
- thin, compared to vessel
- vasa vasorum, extend into t. media

<question>
Muscular Arteries
(distributing arteries)
</question>
<span style="text-decoration:underline;"><strong>Tunica Intima</strong></span>
   - endothelial cells rest on subendothelium (some smooth m.)
- longitudinal orientation
- internal elastic lamina, prominent identifying feature
<span style="text-decoration:underline;"><strong>Tunica Media</strong></span>
- concentric smooth muscle (3-40)
- some elastin (special stain required)
<span style="text-decoration:underline;"><strong>Tunica Adventitia</strong></span>
- external elastic lamina
- longitudinal oriented fibroblasts / collagen / elastic fibers
- vasa vasorum / lymphatics

Arterioles
<span style="text-decoration:underline;"><strong>Tunica Intima</strong></span>
- endothelial cells rest on <span style="text-decoration:underline;">thin</span> subendothelium
- internal elastic lamina not usually visible
<span style="text-decoration:underline;"><strong>Tunica Media</strong></span>
- concentric smooth muscle (&lt; 3)
<span style="text-decoration:underline;"><strong>Tunica Adventitia</strong></span>
- very thin

<question>
Continuous Capillaries
(somatic capillaries)
</question>
- Continuous endothelium resting on basal lamina
- Cells joined by tight junctions (zonula occludens)
- Found in CNS / PNS, muscle, CT, exocine glands

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

<question>
Fenestrated Capillaries 
(visceral capillaries)
</question>
- Continuous endothelium interrupted by pores (fenestrae)
- Pores may have thin diaphragm over them (except renal glomeruli)

Endocrine vs. Exocrine capillaries
Endocrine = fenestrated
Exocrine = continuous

<question>
Sinusoidal Capillaries
(discontinuous capillaries)
</question>
<answer>
- Specialized w/ relatively large lumens
- Many open fenestrations
- Absence of continuous basal lamina
- Macrophages present along walls

Found in liver / lymphoid / hematopoietic organs
</answer>

Venules
- small, postcapillary vessels
- paired w/ arterioles 
- very thin walls
- functional characteristics of capillaries (exchange vessels)

Veins
<answer>
<span style="text-decoration:underline;"><strong>Tunica Intima </strong></span>
- very thin
- valves formed by subendothelial CT (not in large veins)
- valves have covering of endothelium

<strong><span style="text-decoration:underline;">Tunica Media</span></strong> = poorly developed 
<strong><span style="text-decoration:underline;">Tunica Adventitia</span></strong> = very well developed
</answer>

What are the prominent layers in arteries vs. veins?
Artery = prominent media
Vein = prominent adventitia

Large arteries vs. Large veins
<answer>
<span style="text-decoration:underline;"><strong>Large Artery</strong></span>
- thick intima 
- thick media
- underdeveloped adventitia

<span style="text-decoration:underline;"><strong>Large Vein</strong></span>
- thick intima
- thin media
- well developed adventitia w/ longitudinal bundles of smooth m.
</answer>

Lymphatic vessels
<answer>
- 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
</answer>