Cardiovascular System

Question 1

Microvascular Bed

Answer 1

• Functional unit of blood vascular system
• Components:
  
  • Arteriole
    
    • Pre-capillary sphincter controls bloodflow into capillaries
  • Capillary network
  • Post-capillary venule
  • Metaarteriole
    
    • Connection between arterioles and venules that allow blood to bypass capillaries
• Function:
  
  • Site of two-directional exchange of fluids and solutes between blood and tissues

Question 2

Continuous Capillaries (Macula adherens type)

Answer 2

• Endothelial cells are continuous and attached by macula adherens junctions (i.e. desmosomes)
  
  • Allows leakage of fluid and solutes
• Covered by continuous basement membrane
• Most common type of capillary

Question 3

Continuous Capillaries (Zonula occludens type)

Answer 3

• Endothelial cells are continuous and attached by zonula occludens junctions (i.e. tight junctions)
  
  • No leakage; fluid and solutes cross endothelial cells via vesicles
  • Component of blood-tissue barriers
• Covered by continuous basement membrane

Question 4

Fenestrated Capillaries

Answer 4

• Endothelial cells perforated by circular holes (fenestrations)
  
  • Allows leakage of fluid and low MW solutes
• Covered by continuous basement membrane
• Found in sites of extensive blood-tissue exchange
  
  • E.g. intestinal villi and kidney glomeruli

Question 5

Discontinuous (Sinusoidal) Capillaries

Answer 5

• Large spaces between endothelial cells, also perforated by large holes
• Covered by discontinuous basement membrane
  
  • Allows free movement of fluid, solutes, and cells between capillary and tissues

Question 6

Tunica intima

Answer 6

• Innermost layer of vessel
• Consists of:
  
  • Endothelium
  • Subendothelial layer
    
    • Loose connective tissue
    • Internal elastic membrane (present only in arteries)

Question 7

Tunica media

Answer 7

• Middle layer of vessel
• Consists of:
  
  • Mainly smooth MM oriented perpendicularly to long axis of vessel
    
    • Contraction/relaxation responsible for vasoconstriction/dilation of vessels
  • May contain bands of elastic fibers between layers of smooth MM in arteries (elastic lamellae)

Question 8

Tunica adventitia

Answer 8

• Outermost layer of vessel
• Consists of:
  
  • Mainly CT
  • May contain elastic fibers in arteries
  • Vessels that supply/drain walls of larger vessels (vaso vasorum)
  • Nerves that innervate tunica media (nervi vascularis)

Question 9

Blood Pressure

Answer 9

• Blood pressure largely controlled by arteries:
  
  • Systolic pressure
    
    • Caused by contraction of heart
      
      • Provides primary push to move blood and causes walls of elastic arteries to expand
  • Diastolic pressure
    
    • Caused by recoil of walls of expanded elastic arteries
      
      • Provides secondary push to move blood while ventricles are relaxed

Question 10

Endocardium

Answer 10

• Innermost layer of heart that lines chambers
• Consists of:
  
  • Endothelial layer
  • Subendothelial layer of CT
  • Middler layer of CT and smooth MM
  • Subendocardial layer of CT
    
    • Site of conducting system
    • Continuous with CT of myocardium

Question 11

Myocardium

Answer 11

• Middle, muscular layer of heart
• Consists of:
  
  • Cardiac MM
  • Connective tissue
  • Blood vessels
  • Purkinje fibers

Question 12

Epicardium

Answer 12

• Outermost layer of heart
• Consists of:
  
  • Connective Tissue
  • Blood vessels
  • Nerves
  • Adipose tissue
    
    • Provides cushioning in pericardial cavity
  • Mesothelial layer (Visceral Epicardium)
    
    • Simple squamous epithelium facing pericardial cavity

Question 13

Conducting System

Answer 13

• System of modified cardiac muscle cells that function to synchronize cardiac muscle contraction
• Pathway:
  
  • Sinoatrial (SA) Node: pacemaker (i.e. initiates electrical impulse), located at junction of SVC and right atrium
  • Internodal Tracts
  • Atrioventricular (AV) Node: located in floor of right atrium
  • Bundle of His: carry impulse across fibrous skeleton, from atria to ventricles
  • R/L Bundle Branches: continuation of Bundle of His that carries impulse down interventricular septum into ventricles
  • Purkinje Fibers: distribute impulse throughout ventricles to cardiac muscle fibers

Question 14

Precapillary Sphincter

Answer 14

• Band of smooth MM encircling a capillary at the point where it originates from an arteriole
  
  • Contraction/relaxation of sphincter can open and close entrance to capillary to control blood flow and blood pressure