Histology of the Cardiovascular System

Question 1

What are the functions of the cardiovascular system?

Answer 1

• Maintenance of adequate blood flow (cardiac output)
• Delivery of oxygen, nutrients, hormones, electrolytes, and water to peripheral tissues
• Removal of carbon dioxide and other metabolic waste products
• Maintenance of normal thermoregulation and GFR –> urine output

Question 2

Picture of a normal circulatory system

Answer 2

Question 3

Relationship between blood pressure, vascular permeability and structural characteristics of different types of blood vessels (bottom)

Answer 3

Question 4

Describe the normal vascular pattern

Answer 4

Artery –> arteriole –> metarteriole –> capillaries –> venule –> vein

Question 5

Endocardium

Answer 5

Endothelial lining of the heart chambers surface; also covers the surface of the valves; subendocardium contains a thin layer of connective tissue; Purkinje fibers may be found in this area

Question 6

Myocardium

Answer 6

• cardiac muscle mass
• central single nucleus
• intercalated disks
  
  • gap junctions
  • anchoring junctions
• lipofuscin
• sarcoplasmic reticulum
• many mitochondria, up to 20% cell volume –> requires a lot of O₂

Question 7

Epicardium

Answer 7

Formed by a single layer of flattened epithelial cells, the mesothelium (simple squamous epithelium), supported by connective tissue including fat; a similar mesothelial layer lines the opposing parietal surface of the pericardial sac; mesothelial cells secrete a small amount of serous fluid that lubricates the movement of the epicardium on the opposite parietal pericardium; the epicardium represents the visceral layer of the pericardial sac

Question 8

The cardiac skeleton

Answer 8

• consists of 4 dense bands of fibrous connective tissue that encircles the base of the pulmonary trunk, aorta, and the AV valves - provides structural support to the heart
• a triangular mass of fibrous connective tissue - the fibrous trigon - connects the the aortic arterial ring and the left and right atrioventricular ring; this area undergoes osseous differentiation and forms the “Os Cordis” - primarily seen in cattle

Question 9

Tunics of vessels

Answer 9

• tunica intima
  
  • innermost layer
  • endothelium, internal elastic membrane, subendothelial connective tissue
• tunica media
  
  • middle layer
  • smooth muscle and elastic lamellae/fibers
• tunica adventitia/externa
  
  • outermost layer
  • CT, primarily collagen, may contain blood vessels, nerves, capillaries

Question 10

Vascular endothelium

Answer 10

• role in homeostasis
  
  • anti-thrombotic and pro-fibrinolytic in the normal state
  • pro-thrombotic and anti-fibrinolytic during injury
• modulates perfusion
  
  • nitric oxide relaxes and causes vasodilation
  • endothelin casues vasoconstriction
• role in inflammation
  
  • regulates the traffic of inflammatory cells
  • produces pro-inflammatory cytokines
  • control angiogenesis and tissue repair

Question 11

Elastic artery

Answer 11

• best example is aorta
• all 3 tunics exist:
  
  • tunica media - consists largely of repeating elastic lamellae
  • tunica intima - endothelium and loose CT
  • tunica adventitia - contains vasa vasorum to assist in supplying nutritional needs of thick tunica media

Question 12

Muscular arteries

Answer 12

• tunica media is primarily smooth muscle (it’s the thickest tunic)
• generally have a round appearance in XS
• prominent internal elastic membrane

Question 13

Vascular smooth muscle

Answer 13

• smooth muscle cells are circumferentially arranged within the tunica media
• regulates diameter and tone (vasodilation/vasoconstriction)

Question 14

Arterioles

Answer 14

• 1-3 layers of smooth muscle
• greatest effect on blood pressure
• nuclei bulge into lumen
• round appearance of vessel
• no internal elastic membrane in the smallest arterioles with 1 smooth muscle cell
• metarteriole is a terminal vessel, has precapillary sphincters that can regulate flow to the capillary bed

Question 15

Pericytes (Rouget cells)

Answer 15

• mesenchymal-like contractile cells (contain acitn, myosin, tropomyosin) that wrap around capillaries and venules and “communicate” with endothelial cells by physical contact and paracrine signaling
• have own basal lamina
• proliferate after injury; may be repalcement stem cell source; important in angiogenesis

Question 16

What does each letter represent?

Answer 16

• P = pericyte
• T = tight junction, capillary endothelial cell
• M = skeletal muscle
• C = capillary
• Cl = collagen fibers in transverse section

Question 17

Capillaries

Answer 17

• thin walled tubules of mesenchymal origin; in a cross section they are made of only one endothelial cell rolled into the tube
• represent the site of exchange between blood and surrounding tissue
• 3 types:
  
  • continuous
  • fenestrated
  • discontinuous (sinusoidal)

Question 18

Continuous capillary

Answer 18

• most common
• found in muscle, brain, bone, lung, etc.
• nucleus of endothelial cell
• pinocytotic vesicles
• tight junctions
• basement membrane/lamina

Question 19

Glomerular capillary (example of fenestrated)

Answer 19

The renal corpuscle/glomerulus is a tightly coiled network of fenestrated capillaries and is responsible for the filtration of plasma

Question 20

Discontinued/sinusoidal capillaries

Answer 20

• lumen is enlarged and irregular
• lining endothelium is discontinuous and fenestrated
• basal lamina may be absent (hence discontinuous)

Question 21

Venules

Answer 21

• called postcapillary venules
• very ‘leaky’ vessels
• no smooth muscle
• leukocyte diapedesis possible here

Question 22

Veins

Answer 22

• large, wide lumen, thin walls in comparison to same-size arteries
• valves present
• thin tunica media
• the tunica adventitia is the thickest tunic
• large veins may have vasa vasorum

Question 23

Lymphatic vessels

Answer 23

• very thin wall, very low pressure, may contain valves
• no RBCs in lymph, so appear clear