Cardiac/Vascular Histology

Question 1

Myocardium

Answer 1

Thickest layer of heart
Contains: cardiocytes (contractile), nodal cardiocytes (in AV/SA nodes), myoendocrine cardiocytes
Characterized by: striations, intercalated discs, lipofuscin granules

Question 2

Intercalated discs

Answer 2

Interdigitating junctions b/w cardiocytes
At sites were cells meet end to end, coincide with Z lines
Bind cells, transmit forces of contraction, allow spread of excitation

Question 3

Transverse region (perpendicular) of intercalated disc junction

Answer 3

Fascia adherens: actin filaments at ends of terminal sarcomeres insert into junction
-transmit contractile forces b/w cells
-most predominant
Desmosomes: provide anchorage for the intermediate filaments of the cytoskeleton

Question 4

Longitudinal region (parallel) of intercalated disc junction

Answer 4

Gap (nexus) junctions: sites of low electrical resistance

- allows excitation to pass b/w cells

Question 5

Diad T-tubules

Answer 5

In heart, T-tubules form diad with 1 t-tubule and 1-SR cisterna
Found at Z-lines
Permits uniform contraction of myofibrils within a single cardiocyte

Question 6

Nodal cardiocytes

Answer 6

Modified cells w/in SA/AV nodes that initiate/relay electrical signals
Parasympathetic and sympathetic fibers terminate in the nodes
Only MODIFY rate of intrinsic cardiac muscle contraction

Question 7

Purkinje fibers

Answer 7

Specialized cardiac muscle cells
Conduct electrical impulses that allow coordinated contraction
Fewer myofibrils, but increased glycogen
Larger and typically seen at periphery of myocardium
Mostly lack T-tubules

Question 8

Atrial granules

Answer 8

Myoendocrine cardiocytes: atrial cells that contain membrane bound granules. Smaller quantities are found in the left atrium and the ventricles
Contain precursor of atrial natriuretic factor ANF- which targets kidneys to decrease Na and H2O retention

Question 9

Cardiac skeleton

Answer 9

Contributes to interventricular and interatrial septa
Extends into the valve cusps and chorea tendinae
Dense irregular CT located in the endocardium
Anchors valves and surrounds AV canals to maintain shape

Question 10

Heart valves

Answer 10

Core of fibroelastic CT (lamina fibrosa) covered by endothelium
Continuous with the cardiac skeleton
Fibroelastic layer of endocardium condenses to forma a valve ring
-creates a central portion of the valve

Question 11

Tunica intima layers

Answer 11

Endothelium- single layer of squamous epithelium
Basal lamina- thin EC layer of collagen/glycoproteins
Subendothelial layer- loose CT - consists of internal elastic membrane in arteries/arterioles

Question 12

Tunica media

Answer 12

Circumferentially arranged layers of smooth muscle
Thickest in arteries
Extends from internal to external elastic membrane

Question 13

Tunica adventitia

Answer 13

Longitudinally arranged collagenous tissue
Will merge with loose CT surrounding vessels
Thin in arterial system, thick in veins
Vasa vasorum- vessels of TA that supply blood to the tunics- found in large arteries and veins
Nervi vasorum- ANS input that controls contraction of vascular smooth muscle

Question 14

Large (elastic) arteries

Answer 14

Elastin forms concentric sheets b/w muscle cell layers
No fibroblasts, smooth muscle synthesizes collagen, elastin
No internal elastic membrane

Question 15

Medium arteries

Answer 15

Prominent internal elastic membrane becomes apparent
Recognizable external elastic membrane
Thick tunica adventitia, about same size as tunica media

Question 16

Pericytes

Answer 16

Perivascular contractile cells
Controlled by NO
Promote stability of capillaries and postcapillary venules

Question 17

Discontinuous/sinusoidal capillaries

Answer 17

Located where exchange of b/w blood and tissue must openly occur
Larger fenestrations than fenestrated capillaries
Large cell movements allowed through membrane
Discontinuous basement membrane
Found in bone marrow, liver, spleen

Question 18

Fenestrated capillaries

Answer 18

Have tight junctions among endothelial cells
Greater exchange than continuous capillaries, but limited to size of molecule
Continuous basement membrane
Found in endocrine glands like kidney

Question 19

Continuous capillaries

Answer 19

Tight, occluding junctions sealing off clefts
All molecular exchange via diffusion or transcytosis
Continuous basement membrane
Located throughout body

Question 20

Precapillary sphincters, metarterioles, true capillaries

Answer 20

Metarterioles are first branch off arteriole supplying tissues
True capillaries branch from metarteriole, LACK smooth muscle, must have pericytes
Precapillary sphincters regulate blood flow through capillaries

Question 21

Thoroughfare channel

Answer 21

Distal end of metarteriole, lacks smooth muscle

Connects to postcapillary venule

Question 22

Arteriole

Answer 22

Tunica media only has one-two layers of smooth muscle

Thin tunica adventita

Question 23

Vein vs artery

Answer 23

Veins have thinner walls, lumen is larger and often collapsed

Question 24

Venules

Answer 24

Receive blood from capillaries, subclassified as postcapillary and muscular venules
Postcapillary–>muscular–>small vein
Postcapillary have no true tunica media
Muscular have 1-2 layers of smooth muscle in tunica media and a thin tunica adventitia

Question 25

Medium veins

Answer 25

Travel with muscular arteries
Thicker tunica media and adventitia
Contain valves

Question 26

Large veins

Answer 26

Tunica adventitia is thickest layer, contains collagen, elastic fibers, fibroblasts and smooth muscle cells
Tunica media is thin w/smooth muscle cells, collagen and fibroblasts
Tunica intima is thin and blends with media