Cardiac Histo

Question 1

Layers of vascular wall (innermost to outer)

Answer 1

Tunica intima
Tunica media
Tunica adventitia

Question 2

Tunica intima

Answer 2

Single layer of endothelial cells (simple squamous epithelium)
Subendothelial layer of loose CT - containing fibroblasts and myointimal cells (which accumulate lipids w/ age)

Question 3

Tunica media

Answer 3

Circularly oriented smooth muscles
Collagen type III (reticular fibers)
Elastic fibers in large arteries

Question 4

Tunica adventitia

Answer 4

Collagen type I fibers
Longitudinally oriented smooth muscles in large veins
Vasa vasorum: system of vessels that supplies blood to the vascular walls of large arteries and veins
Nervi vasorum: network of autonomic nerves that control contraction of the smooth muscle in the vessel walls

Question 5

Elastic lamina of arteries and large arterioles

Answer 5

Internal elastic lamina b/w intima and media

External elastic lamina b/w media and adventitia

Question 6

Large elastic arteries

Answer 6

Aorta, Pulmonary trunk (artery), and their direct branches
*Tunica media most prominent
Concentric sheets of elastic membranes (fenestrated membranes) - in tunica media
These elastic laminae are sheets of fenestrated elastic material produced by smooth muscle cells in the tunica media
These help to minimize changes in BP w/ ventricular systole and diastole; highly pulsatile blood flow
W/ advancing age the arterial system becomes less elastic thereby increasing peripheral resistance and thus arterial BP

Question 7

Medium muscular arteries

Answer 7

(Most named arteries)
*Tunica media most prominent
Main function: regulate blood flow to individual organs/parts of the body (by contracting or relaxing the smooth muscles)
Tunica media may contain up to 40 layers of smooth muscle cells
Prominent internal elastic lamina

Question 8

Arterioles

Answer 8

Internal elastic lamina usually absent
Tunica media: 1-2 layers of smooth muscles
No external elastic lamina
*Arteriole has thicker wall and smaller diameter lumen than venules
The endothelium of arterioles is able to sense changes in BP, blood flow, and O2 tension and to respond to these changes by releasing signals - ex: endothelin (vasoconstrictor) and NO (vasodilator)

Question 9

Metarterioles

Answer 9

Arise from arterioles and give rise to capillaries
Possess precapillary sphincters (bands of smooth muscle) - regulate blood flow into true capillaries
*These vessels are responsible for maximum peripheral resistance
Thoroughfare channel: distal portion of metarteriole, lacks smooth muscle cells and merges w/ the postcapillary venule
True capillaries: the smallest vessels, branch from the metartiole and thoroughfare channel - lack smooth muscle cells (although may have pericytes)

Question 10

Pericytes

Answer 10

Only along capillaries and post-capillary venules
Cells w/ long cytoplasmic processes
Contractile functio - contain actin, myosin, tropomyosin, desmin
Controlled by NO
If tissue injury: pericytes and proliferate and differentiate to form new blood vessels

Question 11

Capillary

Answer 11

Single layer of endothelial cells rolled up in form of a tube
All true capillaries branch off of metarterioles and thoroughfare
Endothelial cells joined by fasciae occludentes (tight junctions) and characteristically contain pinocytic vesicles
Endothelium surrounded by a basal lamina and occasional pericytes
Lumen just large enough to allow the passage of RBCs one at a time
3 types: continuous, fenestrated, discontinuous

Question 12

Continuous/Somatic capillaries

Answer 12

No fenestrae in its wall
Continuous basal lamina
Pinocytic vesicles +++ (except CNS)
Tight junctions - tightly regulate materials
Cell junctions are frequently marked by cytoplasmic (marginal) folds that protrude into the lumen
*Muscle, CT, lungs, CNS, exocrine glands

Question 13

Fenestrated/Visceral capillaries

Answer 13

Large fenestra in wall - bridged by a diaphragm (glycocalyx) - except in renal glomerulus
Continuous basal lamina
Fewer pinocytic vesicles
*SI, gallbladder, endocrine glands

Question 14

Discontinuous/Sinusoidal capillaries

Answer 14

Endothelial cells form a discontinuous layer
Multiple fenestrations w/o diaphragm
Discontinuous basal lamina
Lack pinocytic vesicles
*Liver, bone marrow, spleen

Question 15

AV Anastomosis/Shunts

Answer 15

AV shunts serve in thermoregulation at body surface
Closing AV shunt in skin: causes blood to flow through capillary bed, enhancing heat loss
Opening AV shunt in skin: reduces blood flow to skin capillaries, conserving body heat
Erectile tissues (penis) - closing AV shunt directs blood flow into corpora cavernosa

Question 16

Portal Circulation

Answer 16

In venous portal systems: one capillary bed drains into a vein that then branches again into another capillary bed
This allows molecules entering the blood in 1st set of capillaries to be delivered quickly and at high conc to surrounding tissues at 2nd capillary bed - important in anterior pituitary gland and liver

Question 17

Venules, post-capillary (pericytic) venules

Answer 17

Composed of endothelium and very thin subendothelial layer (no smooth muscle)
Loose endothelial junctions
Media in post-capillary venules contain only contractile pericytes
Other venules have at least a few smooth muscle cells in their walls
Post-capillary venules are primary sites involved in inflammatory response; allow leukocytes to migrate into the affected tissues in cases of inflammation

Question 18

Medium veins

Answer 18

(Most named veins)
Thin subendothelial layer, may be absent
IEL usually absent
Tunica media contains small bundles of smooth muscle cells
*Collagenous adventitial layer is well developed, much thicker than media

Question 19

Veins w/ valves

Answer 19

Valve consists of delicate semilunar projections of tunica intima of vein wall; the projections are composed of fibro-elastic tissue lined on both sides by endothelium
Each valve usually consists of 2 leaflets, the free edges of which project in the direction of blood flow
*Valves occur only in veins >2 mm in diameter, particularly those draining the extremities

Question 20

Large veins

Answer 20

*Adventitial layer thickest and best developed - frequently contains longitudinal bundles of smooth muscles
*SVC, IVC, Hepatic portal vein
Very narrow tunica intima
Media contains a thin layer of circularly arranged smooth muscle cells
Tunica adventitia is broad and contains longitudinally arranged smooth muscle bundles

Question 21

Lymphatic capillaries

Answer 21

Thin, close-ended vessels
Single layer of endothelium - no fasciae occludentes (tight junctions), incomplete basal lamina
Fluids enter through flaps - flows to lymphatic vessels

Question 22

Lymphatic vessels

Answer 22

Structure similar to that of veins except:
Thinner walls, larger lumen, more numerous internal valves
(when distinguishing from blood vessels - look for RBCs in lumen)

Question 23

Layers of pericardium

Answer 23

3 intrinsic walls of heart layer: endocardium, myocardium, epicardium
Endocardium: single layer of endothelial cells and subendothelial CT (conducting system) - in contact w/ heart
Epicardium: visceral layer of serous pericardium - single layer of mesothelial cells and CT and adipose tissue (coronary nerves and vessels)
Pericardial cavity
Fibrous pericardial layer (outermost) and parietal pericardium (single layer of mesothelial cells) fused
Lots of epicardial fat and fibrous CT
Conducting cells = in subendothelial layers

Question 24

Cardiac muscle: Intercalated disk

Answer 24

Fascia adherens major constituent - holds the cardiac muscle cells at their ends and serves as attachment site for thin filaments
Maculae adherentes - reinforce the fascia adherens
Gap junctions - found only in the lateral component of the ID

Question 25

Fibrous skeleton of heart

Answer 25

Comprises:
4 fibrous rings
2 fibrous trigones
membranous part of IVS: devoid of cardiac muscle, contains a short length of the AV bundle
Serves as attachment for:
Cardiac muscle, cuspid AV valves and semilunar aortic and pulmonary valves

Question 26

Heart: Conducting System

Answer 26

SAN and AVN: smaller than cardiac myocytes, no ID
Purkinje fibers: larger than cardiac myocytes, Central nucleus larger than cardiac myocyte, variable location and number of ID, glycogen rich