Cardiovascular System Flashcards
3 Layers of Vessels (Tunics)
- Tunica intima
- Tunica media
- Tunica adventitia
Tunica Intima
- Endothelial cells
- Basal lamina
- Subendothelial connective tissue
-Internal elastic lamina composed of elastin (most prominent in muscular arteries)
Tunica Media
- Circularly arranged smooth muscle
- Contraction narrows the lumen
- Elastic fibers, reticular fibers, proteoglycans produced by smooth muscle cells (not fibroblasts)
- Replaced by pericytes in capillaries and postcapillary venules
-External elastic lamina seperates media from adventitia (most prominent in muscular arteries)
Pericytes
- Contractile cells that wrap around endothelial cells
- Undifferentiated mesenchymal cells that can become smooth muscle or endothelium
Tunica Adventitia
- Longitudinally oriented collagen (Type I) and elastic fibers
- Blends into surrounding connective tissue
- Contains automatic nerves that enter tunica media
-Thick vessels: contains vasa vasorum
Vasa Vasorum
- Found in adventitia
- Nourishes the adventitia and media of vessels with walls too thick for diffusion of nutrients
- Found in veins because of low nutrient content of blood passing through
Innervation
- Smooth muscle in tunica media by parasympathetic/sympathetic fibers
- SNS Norepinephrine (vasculature) causes vasoconstriction
- SNS Acetylcholine causes (skeletal muscle) causes vasodilation
- PNS causes vasodilation
- More prevalent in arteries (more muscle)
Endothelial Cells
- Permeability barrier
- Secretes collagen Type IV/laminin into basement membrane
Endothelial Cell Secretions
- Thrombus Formation: VWF for platelet adhesion
- Vasoactive factors to regulate blood flow (vasodilate/constrict) (endothelin, NO)
- Minimize thrombus formation: PIG2
- Growth factors (FGF, PDGF)
- Cell adhesion molecules (selectins/integrins)
- Contain membrane-bound organelles called Weibel-Palade bodies
Weibel-Palade bodies
- Stores products of endothelial cells such as VWF
- Derived from Golgi
Arteries
- Tunica media is dominant layer
- Narrower lumen than vein
- Thick wall relative to lumen
Elastic Arteries
Aorta, Pulmonary trunk
-Elastic recoil helps with steadier flow
Intima: -internal elastic lamina Media: -reticular fibers + ground substance -no external elastic lamina Adventitia -Loose network of collagen/elastic fibers -Vasa vasorum -Fibroblasts+macrophages -Loosely defined outer boundary
Muscular Arteries
Most of body
-Distribute blood to specific organs as needed
Intima:
-Internal elastic lamina prominent and wavy during contraction
Media:
-Many layers (up to 40) of smooth muscle
-Few elastic fibers
-Fragmented external elastic lamina that extend into adventitia
Adventitia:
-Collagen and adipose
-Larger vessels have vasa vasorum
-Blends into surrounding connective tissue
Arterioles
-Regulates blood pressure and distribution of blood to capillary beds
Intima: -May or may not have internal elastic lamina Media: -5 layers of smooth muscle or less -External elastic lamina absent Adventitia:
Metarterioles
- Smallest arterioles
- Discontinuous layer of smooth muscle
- Preferential channels through capillary beds (bypasses)
- Precapillary sphincters control flow into capillaries
Capillaries
- Single endothelium layer + basal lamina
- Discontinuous layer of pericytes surround
- No media, adventitia, internal/external laminae
Continuous capillaries
- Found in most tissues
- Tight junctions between endothelial cells forms barrier
- No fenestrations
Fenestrated Capillaries
- Found in GI, kidney, endocrine
- Fenestrations/pores allow for greater permeability
- Diaphragms in most organs (except glomerular capillaries)
Discontinuous Capillaries (sinusoids)
- Found in liver, bone marrow, spleen, adrenal cortex
- Leakiest type of capillary
- Wide diameter and irregular shape
- Large gaps between endothelial cells
- Discontinuous or absent basal lamina
Veins
- Large lumens, thin walls, low hydrostatic pressure
- Valves to prevent backflow of blood (folds of tunica intima)
- Valves most common in large veins below heart
- Classified on basis of size (venules, small, medium, large)
Postcapillary Venules
- Wide diameter distinguishes from capillaries
- Mainly endothelium, basal lamina, discontinuous layer of pericytes
- Main site of diapedesis of leukocytes
Muscular venules
Media:
-1-2 layers smooth muscle
Adventitia
-Very thin
Medium/Large Veins
Intima:
-Thin subendothelial connective tissue layer
-Some smooth muscle cells
-Thin internal elastic lamina
-Valves are paired folds of intima
Media:
-Thinner than media of a similar sized artery
Adventitia
-Thickest layer of the vessel wall
-Collagen, elastic fibers, fibroblasts
-Large veins also have bundles of longitudinal smooth muscle
In artery-vein companion pairs, vein is usually larger and appears collapsed or irregular in shape
Lymphatic Capillaries
- Single layer of endothelial cells
- Discontinuous/absent basal lamina
- More irregular shape than regular capillaries
Large Lymphatic Vessels
- Similar to small veins
- Larger lumens, thinner walls, have valves
- Large lymphatic vessels with up to three layers of media
Cardiac Wall
- Endocardium continuous with tunica intima and contains impulse conduction system
- Myocardium continuous with tunica media
- Epicardium continuous with tunica adventitia
Endocardium
- Endothelium
- Subendothelial connective tissues (Collagen, Elastic fibers)
Ventricular Endocardium
- Contains Purkinje fibers
- Middle layer of connective tissue
- Smooth muscle cells
- Subendocardial layer of collagenous/elastic fibers
Myocardium
- Mostly cardiac muscle (involuntary striated)
- Ventricular myocytes are larger
- Thicker in ventricle than atria and left than right
Epicardium
- Outermost layer is visceral pericardium
- Subserosal connective tissue contains abundant adipocytes, large blood vessels, large nerve bundles
Visceral Pericardium
-Mesothelium plus fibrous connective tissue
Atrioventricular Valves
- Folds of endocardium covering fibrous core
- Do not include myocardium
- Base of each leaflet attached to annulus fibrosus of cardiac skeleton
- Free edges of leaflets anchored to papillary muscles via chordae tendineae
- Chordae Tendineae have connective tissue cores re-covered by endocardium
Semilunar Valves
- Pulmonary and atrial/aortic
- Not associated with chordae tendineae or papillary muscles
Cardiac Skeleton
- Dense collagenous tissue (not cartilage or bone)
- Anchoring point of myocytes
- Annuli FIbrosi, 2 Fibrous Trigones (left/right), Septum Membranaceum
Annuli Fibrosi
- Surround openings of aorta, pulmonary artery, atrioventricular orifices
- Attachment sites for leaflets of heart valves
Fibrous Trigones
- Unite annuli fibrosi together
- AV bundle pierces right fibrous trigone to reach interventricular septum
Septum membranaceum
- Extend downward from right fibrous trigone
- Upper non-muscular part of interventricular septum
