Histology: Circulatory System and Heart Flashcards
1
Q
Layers of Heart Wall
A
- Epicardium: outermost; includes visceral layer of serous pericardium
- Myocardium: middle layer
- Endocardium:
2
Q
Epicardium
A
-
Visceral layer of serous pericardium
- CT and adipose tissue deep to mesothelium
- Adheres to outer surface of heart
- Blood vessels and nerves within the adipose tissue
3
Q
Myocardium
A
- Cardiac muscle
- Principle component of heart wall
- Thinner in atria than in ventricles (atria lower pressure)
4
Q
Endocardium
A
3 Sub-Layers
- Endothelium and Subendothelial CT (En)
- Connective Tissue and Smooth Muscle Cells
-
Subendocardial Layer (SEn)
- Continuous with CT of myocardium
- Conducting system (P is purkinje fibers)
5
Q
Fibrous Skeleton of Heart
A
- Dense irregular CT
-
Provides attachments for valve cusps (4 rings) and cardiac muscle
- 2 trigones connect rings
- Insulates conducting system between atria and ventricles
6
Q
Valve Cusps
A
-
Fibrosa: forms core of the valve cusp
- Extensions of fibrous skeleton
-
Songiosa: loose CT (shock absorber) at top of valve cusp
- Arterialis - Semilunar valves
- Auricularis - AV valves
-
Ventricularis: dense CT on bottom
- Covered by endothelium
- Continuous with chordae tendinae
7
Q
Conducting System of Heart
A
- Located in sunendocardial layer
- SA Node
- Pacemaker (70 bpm)
- AV Node
- Bundle of His
- Passes through fibrous skeleton
- R/L Bundle Branches
- Subendocardial fibers (purkinje fibers)
- Stimulates ventricular contraction
8
Q
Purkinje Fibers
A
- Located in subendocardial layer of ventricles
- Larger than cardiac muscle cells
- Large, round nuclei
- Sparce myofibrils
- Contain large amounts of glycogen (resistant to hypoxia)
9
Q
Blood Vessels
A
Tunica Intima
- Simple Squamous Endothelium
- Subendothelial layer (CT)
- Internal elastic lamina (in arteries)
Tunica Media
- Thickest layer (arteries)
- Smooth muscle
- External elastic lamine (in arteries)
Tunica Adventitia (Externa)
- CT
- Thickest layer (veins)
- Vaso vasorum (vessels of the vessels)
- Nervi vasorum (nerves of the vessels
10
Q
Endothelium
A
- Simple squamous (selectively permeable)
- Maintains non-thrombogenic surface (prevents blood clotting)
- Does secrete clotting factors in response to injury
- Regulates vascular tone
- Regulates inflammation and immune responses
11
Q
Large Arteries
A
- “Elastic Arteries”
-
Tunica Intima
- Wavy due to contraction following cell death
-
Tunica Media
- Very thick
- 50 layers of elastic lamellae
-
Tunica Adventitia
- CT
- Maintain uniform blood pressure in response to ventricular contraction/relaxation
12
Q
Medium Arteries
A
- Most named arteries
-
Tunica Intima:
- Folded after vessel death
- Prominant internal elastic lamina
-
Tunica Media:
- 40 layers of smooth muscle
- Few elastic lamellae
-
Tunica Adventitia
- Prominant external elastic lamina
13
Q
Arterioles
A
- Smallest arteries
- Lumen as wide as wall
-
Tunica Intima:
- NO internal elastic lamina
-
Tunica Media:
- 1-2 layers of smooth muscles
-
Tunica Adventitia
- Thin, inconspicuous
-
Major determinant of systemic blood pressue
- Regulate capillary flow
14
Q
Capillaries
A
-
Single layer of endothelial cells surrounded by basal lamina
- Attached to each other by tight junctions
- Site of exchange between blood and tissue fluid
- Supplied by metarterioles (contains precapillary sphinctors to prevent blood flow to capillary beds)
15
Q
Continuous Capillaries
A
- Tight junctions between endothelial cells
-
Continuous basal lamina
- Vesicle-mediated transcytosis
- Muscle, lungs, exocrine glands, nervous tissue
16
Q
Fenestrated Capillaries
A
-
Openings in endothelial cells (fenestrations)
- Rapid exchange between blood and tissues
- Continuous basal lamina
- Kidneys, intestine, endocrine glands
17
Q
Sinusoidal Capillaires
A
- Spaces between cells and large fenestrations
- Discontinuous basal lamina
- Larger diameter
- Spleen (filter old red blood cells out of blood), liver, bone marrow
18
Q
Pericytes
A
- Undifferentiated mesenchymal cells
- Form new blood vessels after an injury
- Located along capillaries and post-capillary venules
- Larger nucleus than endothelial cell
- Long cytoplasmic processes surround endothelial layer
19
Q
Venules
A
Postcapillary Venules
- Covered by pericytes
- Site of action for histamine/serotonin during allergic reactions and inflammation
-
High Endothelial Venules (HEVs)
- Found in lymphoid tissue
- Can recruit lymphocytes
- Cuboidal endothelial cells
Muscular Venules
- Distal to postcapillary venules
- 1-2 layers smooth muscle
- No pericytes
20
Q
Medium Veins
A
- Most of deep veins that accompany arteries
- Contain valves
Tunica Intima:
- Subendothelial layer containing scattered smooth muscle cells
Tunica Media:
- Thinner than arteries
- Circular smooth muscle
Tunica Adventitia:
- Most prominant layer
- Scattered longitudinal smooth muscle
21
Q
Large Veins
A
- SVC, IVC, Brachiocephalic vv.
- Contain valves
Tunica Intima:
- Subendothelial layer with smooth muscle
Tunica Media:
- Circular smooth muscle
Tunica Adventitia:
- Thickest layer
- Lots of longitudinal smooth muscle
22
Q
Arteriovenous Shunts
A
- Anastomoses between arterioles and venules
- Thicker tunica media (innervated by ANS)
- Thermoregulation: bypass capillary bed to conserve heat
23
Q
Venous Portal System
A
- Blood flows through 2 successive capillary beds connected by a portal vein (connects the two capillary beds)
- Allows substances to be absorbed into blood in 1st capillary bed
- Substances delivered to tissues in 2nd capillary bed
- E.g. Hepatic Portal System
24
Q
Lymphatic Capillaries
A
- Blind ended tubes
- Collect excess interstitial fluid (lymph)
- Valves facilitate fluid entry and prevent escape
- More permeable than blood capillaries
- Anchoring filaments maintain patency
25
Q
Lymphatic Vessels
A
- Thin walls with CT and smooth muscle (no discernable tunics)
- Tight junctions prevent lymph from leaking out
- Valves prevent backflow
- Interrupted by lymph nodes
- Converge to form lymphatic trunks/ducts
