Cardiovascular I

Question 1

describe Purkinje fibers

Answer 1

• Purkinje fibers are at the outermost aspect of the subendothelial connective tissue
  
  • conducts electrical impulse through heart
• PF can be recognized by their large size and pale nature due to high content of glycogen and less myofibrils

Question 2

describe valves

Answer 2

• completely lined by endothelium that is filled with CT
  
  • 3 zones:
    
    • spongiosa
      
      • loose CT with elastic fibers in between
    • fibrosa
      
      • dense irregular CT
    • ventricularis
      
      • dense CT

Question 3

name the layers of the pericardium

Answer 3

• fibrous pericardium
• serous pericardium
• parietal layer
• visceral layer (epicardium)
  
  • epicardium contains loose CT with adipocytes, coronary vessels and nerves

Question 4

describe the tunica intima

Answer 4

• endothelium
  
  • simple squamous epithelium
  • joined by tight junctions and communicate via gap junctions
  • oriented in longitudinal fashion
• subendothelial CT
• internal elastic lamina
  
  • fenestrated elastic membrane; diffusion of materials through the layers to reach underlying cells
  • separates t. intima from t. media

Question 5

describe the tunica media

Answer 5

• circumferential layers of smooth muscles that secrete the ECM components of this layer
  
  • elastic fibers, collagen fibers (type III) and proteoglycans

Question 6

describe the tunica adventitia

Answer 6

• mainly collagen type I fibers and a few elastic fibers–loose network
• contains nerves (nervi vascularis), vasa vasorum (vessel of vessels) and lymphatics
• in smaller vessels, merges with surrounding CT

Question 7

what are the functions of endothelial cells

Answer 7

• permeability barrier: controls the composition of interstitial tissue fluid
• movement of inflammatory cells into tissues
• EDGF (endothelium derived GF) provides for angiogenesis in the embryogenesis
  
  • as well as in vascular trauma or tumor
• vasoconstriction vs vasodliation
• anticoagulant signals (thrombomodulin)
• pulmonary endothelial cells produce ACE

Question 8

describe Weibel Palade bodies

Answer 8

• endothelium cells contain rod-shaped inclusions called Weibel Palade bodies
  
  • WP bodies store von Willibrand factor (glycoprotein) that binds clotting factor VIII
    
    • allows in formation of clots and stop bleeding

Question 9

describe the 3 layers shown

Answer 9

• t. intima: endothelial cells, sunendothelial CT
• t. media: 40-70 layers of elastic lamellae, smooth muscle cells type III collagen
• t. adventitia: dense irregular CT, prevents excessive expansion of the vessel

Question 10

describe muscular arteries

Answer 10

• brachial, radial, femoral, tibial, etc.
• most abundant in body
• named muscular bc they contain more smooth muscle cells in the tunica media than elastic fibers
• as they become smaller than elastic arteries, they lose the elastic fibers which now form external elastic laminae (EEL) between t. media and adventitia
  
  • EEL characteristic of muscular arteries

Question 11

Answer 11

• t. intima: distinct IEL (internal elastic lamina)
• t. media: 8 - 40 layers of smooth muscle cells arranged in circular fashion
  
  • Distinct EEL
• t. adventitia: dense CT with collagen and elastic fibers

Question 12

describe the small artery

Answer 12

• t. intima: endothelial cells, minimal subendothelial CT
  
  • IEL present
• t. media: 3-8 layers of smooth muscle cells, arranged in circular fashion
• t. adventitita: CT with type I collagen (decreases)

Question 13

describe arterioles

Answer 13

• smallest arteries
  
  • can be closed to generate high resistance flow
  • major determinant of blood pressure
• t. intima: endothelium
• t. media: 1-2 layers of smooth muscle cells
• t. adventitia: ill-defined, merges with surrounding CT

Question 14

describe the precapillary sphincter

Answer 14

• regulates the flow of blood from the arteriole into the capillary bed per physiologcal demands

Question 15

describe metarterioles

Answer 15

• initial segment of the channel connecting the arteriole to the venule
  
  • capillaries emergy from metarteriole and the channel to make the capillary plexus

Question 16

describe the continous/somatic capillary

Answer 16

• continous basal lamina
• tight junctions present between cells
• significance:
  
  • complete control over diffusion, endocytosis and exocytosis
  • vessels that form barriers in organs such as brain, thymus, lung, testis

Question 17

describe the fenestrated/visceral capillaries

Answer 17

• continous basal lamina
• tight junctions between endothelial cells
• fenestrations of about 80-100nm in diameter
• significance:
  
  • presence of thin, non membranous diaphragm across the fenestrations (except in the glomerular capillaries of kidney)

Question 18

describe the discontinous/sinusoidal capillaries

Answer 18

• discontinous basal lamina
• absence of tight junction between the cells
• presence of large fenestrations
• significance:
  
  • fenestrations: large and variable, reach several microns
  • allow passage of macro molecules
• locations:
  
  • liver
  • spleen
  • bone marrow