Circulatory System

Question 1

Objectives

Answer 1

• Heart
  
  • Identify the heart layers
  • Review the Purkinje fibers in the hert
• Blood and lymph vessels
  
  • Descibe the layer of a typical blood or lymph vessl
  • Descibe and recognize the differences bewteen elastic arteries, muscular arteries, arterioles, capillaries, veins, and lymph vesselts
  • Identify the vasa vasorum and nervi vasorum (blood vessels and verve vessels in the tunica adventitia or large vessels)
  • Recognize and descibe arteries, arterioles, capillaries, veins and lymph vessels
• Define:
  
  • Endothelium, tunica intima, tunica media, tunica adventitia, inernal elastic lamina, basement membrane, sinusoid, pericyte, fenestrated, interstitial, endocardium, myocardium, epicardium, visceral pericrdium, vasoconstriction, hypovolemia, edema

Question 2

Heart Layers

Answer 2

• Endocardium:
  
  • Has endothelium
  • small amount of supporting connective tissue (delicate collagenous layer and deeper fibroelastic layer
  • Adipose tissue deposits in places
  • Simple squamous epithelium
• Myocardium:
  
  • Contains cardiac myocytes and purkinje fibers
  • Muscle layer, with vessels
• Epicardium: (Visceral pericardium)
  
  • Contains mesothelium that secretes serous fluid
  • some supporting connective tissue similar to that of endocardium
  • broad layer of adipose tissue
  • Essentially the same as endocardium, but with thick layer of fat

Question 3

Purkinje fibers

Answer 3

• Part of the myocardium
• modified cardiac myocytes

Question 4

Cardiac skeleton

Answer 4

• Serves as an anchor for the valves at level of the valves of the heart
• Annulus - surround valves
• Trigone - Triangular area between the 2 AV canals
• Septum - between the ventricles

Question 5

Heart Valves

Answer 5

• Folds of endocardium
• supported by the cardiac skeleton
• Edges of cusps of valves are anchored by the chordae tendinae

Question 6

Blood and Lymph systems General Introduction

Answer 6

• Blood and Lymph vascular systems are similar in some respects, and different in others
  
  • Blood passes through a circuit
  • Lymph is a one-way drainage from the tissues back to the vascular system
  • They are often found together with nerves
  • Blood vessels have a stronger wall with more components of the layers than lymph vessels
    
    • In small lymph vessels only the endothelium is visible

Question 7

Vessels General Introduction

Answer 7

• An Arteriole is a small artery; a venule is a small vein
  
  • Arterioles -have an objective way to idetify them, based on the number of smooth muscle cell layers
  • Venules - Not so much, but they accompany arterioles (veins accompany arteries)
• When comparing arteries and veins:
  
  • Arteries/arterioles have a uniform thickness of the wall
  • Veins/venules have a very thin wall relative to the size of the vessel, and it may not be uniformly thick
• Arteries do NOT have valves
  
  • Exception is Aorta
• Veins and lymph vessels usually have valves
  
  • Valves in the simplest form are double- layered folds of endothelium

Question 8

Layers of Vessels Walls

Answer 8

• Tunica Intima - Epithelium and some connective tissue, and an elastic layers
  
  • Endothelium
  • Connective tissue
  • Internal elastic lamina
• Tunica Media - smooth muscle cells and variable amounts of fibers (mainly elastin)
  
  • Elastic arteries have smooth muscle with large sheets of elastin
  • Layers of smooth muscle with elastic fibers
  • Elastic fibers are very prominent in elastic arteries
  • External elastic lamina, but not always obvious
• Tunica Adventitia - Connective tissue covering of the vessel
  
  • May contain vessels and nerves if the blood vessel is very large
  • Elastic arteries have a more collagenous outer covering, while muscular artreies have a more elastic outer covering
  • Outer layer of connective tissue
  • Mixed collagen and elastic fibers
    
    • More collagen in the elastic arteries
    • More elastin in the musculr arteries
    • May contain vascular and nerve plexus

Question 9

Tunica Intima

Answer 9

• 3 layers
  
  • Endothelium
  • Connective tissue
  • Internal elastic lamina

Question 10

Tunica Media

Answer 10

• smooth muscle cells and variable amounts of fibers (mainly elastin)
  
  • Elastic arteries have smooth muscle with large sheets of elastin
• Layers of smooth muscle with elastic fibers
• Elastic fibers are very prominent in elastic arteries
• External elastic lamina, but not always obvious

Question 11

Tunica Adventitia

Answer 11

• Connective tissue covering of the vessel
• May contain vessels and nerves if the blood vessel is very large
• Elastic arteries have a more collagenous outer covering, while muscular artreies have a more elastic outer covering
• Outer layer of connective tissue
• Mixed collagen and elastic fibers
  
  • More collagen in the elastic arteries
  • More elastin in the musculr arteries
  • May contain vascular and nerve plexus

Question 12

Elastic Arteries

Answer 12

• Tunica Intima contains all 3 layers
• Tunica Media is the thickest layer
  
  • Many concentric layers of elastin, with smooth muscle cels between the layers
  • External elastic lamina is not readily apparent because of the thick elastic laminae
• Tunica Adventitia is thin comparitively

Question 13

Muscular Arteries

Answer 13

• Tunica Intima - contains endothelium, connctive tissue, and internal elastic lamina
  
  • Connective tissue hard to see with light microscope unless thickened by atherosclerosis
• Tunica Media - thick layer of smooth muscle
  
  • contains fibers and proteoglycans (smooth muscle and fibrocytes are developmental “cousins”)
  • External elastic lamina is part of tunica media
• Tunica Adventitia - external connective tissue layer, can be very thick

Question 14

Tunica Intima - Muscular Artery

Answer 14

• Inner lining; can have 3 sublayers;
  
  • Endothelium (always)
  • Subendothelial connective tissue (not visibe in small vessels)
  • Internal elastic lamina

Question 15

EM slide of small muscular artery

Answer 15

• Muscular (or distibuting) artery is a medium-sized artery composed principally of a tunica intima and circularly arranged smooth muscle
• Tunica Intima:
  
  • Endothelium (green) - single layer of flattened endothelial cells
  • Inner Elastic Lamania (tan) - layer of elastic fibers
• Tunica Media (light blue) - thick layer of smooth muscle along with collagen fibers and a few elastic fibers
  
  • Caveolae - large number of small invaginations of the plasma membrane of the smooth muscle cells
• Tunica Adventitia - only a few collagenfibers of this layer are visible in this micrograph
• Part of a red blood cell (dark red) can be seen in the lumen of the artery

Question 16

Tunica Media - Muscular Artery

Answer 16

• Smooth muscle with varying amounts of elastic laminae
  
  • The external elastic lamina is part of this layer but may be difficultto see

Question 17

Tunica Adventitia - Muscular Artery

Answer 17

• The external connective tissue of the vessel wall
• Dense or loose irregular connective tissue
• More elastin in the tunica adventitia of a muscular artery, especially right next to the muscle layer

Question 18

Arterioles

Answer 18

• Smallest branch
• Delivers and regulates flow of blood to the capillary bed
• Regulates systemic blood pressure; generalized constictions increases resistance to peripheral blood flow
• Description of layers:
  
  • Tunica Intima - present, internal elastic lamina disappearing
  • Tunica Media - 1-3 layers of smooth muscle cells
  • Tunica Adventitia - narrow layer of connective tissue

Question 19

Small Muscular Arteries vs Arterioles

Answer 19

• Small Artery
  
  • > 0.3 mm diameter lumen or >3 layers of muscle cells
• Arteriole
  
  • No external elastc lamina
  • Deminishing internal elastic lamina
  • 3 or less layers ofmuscle cells

Question 20

Capillaries

Answer 20

• Only endothelium and basement membrane
• Diameter is approximately the same as that of a RBC (7-9 um)
  
  • Exception: sinusoids (30-40 um) in liver, spleen, lymph nodes, and bone marrow
• Thin endothelial cell allows exhange of water and solutes between blood and tissues (in tissues), and between blood and enironment (in lung)

Question 21

Continuous Capillaries

Answer 21

• Most common type: muscle, brain, thymus, bone, lung, and elsewhere
  
  • Uninterrupted endothelium
  • Continuous basal lamina
  • Numerous pinocytotic vesicles
• Pericyte - cell that share the basement membrane and are associated mainly with capillaries

Question 22

Pericyte

Answer 22

• A residual mesenchymal cell
• Involved in:
  
  • Blood flow
  • blood-brain barrier
  • angiogenesis
  • muscle regeneration

Question 23

Fenestrated Capillaries

Answer 23

• Have pores within endothelial cells
  
  • diaphragm covers the pore
• Found in tissues involved in absorption and fluid transport (small intestine and kidneys) and some endocrine glands
• Picture:
  
  • Capillary (green) - inner (lumenal) surface of the endothelial cells
    
    • Fenestrations (approx. 50 - 100 nm) - endothelial cells contain numerous pores lacking diaphragms
    • Fenestrations allow access of blood to the underlying basement membrane
  • Podocyes (yellos) - remnants surrounded the capillary

Question 24

Sinusoidal Capillaries

Answer 24

• ​Special capillaries found in the liver, spleen and bone marrow
• Have a wide lumen with a discontinuous endothelium (gaps between endthelial cells)

Question 25

Veins

Answer 25

* Thin muscular wall - may be somewhat broken up * The Adventitia usually the thickest part * Internal elastic lamina absent except large veins * Wide lumen compared to wall thickness * More likely to be packed with RBCs

Question 26

Pulmonary Vein

Answer 26

* Large Vein * Wide lumen and thin wall compared to overall size * Thickness of the wall is variable * Internal elastic lamina is absent except in large veins

Question 27

Veins and venules

Answer 27

* Distiction between venules and small veins is somewhat artificial * If next to an artery its a vein * if next to an arteriole its a venule * Both can have valves

Question 28

Venules

Answer 28

* size comparable to an arterioles * Layers: * Tunica Intima - endothelium only * Tunica Media - either abscent or only a very thin layer * Tunica Adventitia - present

Question 29

Lymph Vessels

Answer 29

* Associated with the venous system * valves help assure that fluid continues toward the large veins cranial to the heart * Very low pressure system * easily occluded, obstructed or overwhelmed * **Leads to edema** * One-way system: * Smallest lypmh vessels (lymph capillaries) are blind-ended and begin in the perivascular space in the tissue beds * No perivascular cells * **Function**: transport excess interstitial fluid, proteins, solutes an macromolecules through lymph nodes and back to the venous system * Safety valve between the extravascular and intravascular fluid pools * A filtering system to impede microorganisms and cancer cells * Have NO basement membrane, Endothelium only, look like space in the tissue * Larger lymph vessels have thinner wall than veins of comparable size and have valves (more numerous) * Should NOT find RBC's instead precipitated protein

Question 30

Vasa Vasorum, Nerve vasorum

Answer 30

* In larger vessels, Adventitia carries a blood and nerve supply for that vessel