Lecture 27: The Cardiovascular System

Question 1

List the three layers (tunics) of the heart wall.

Answer 1

Endocardium:
Myocardium
Epicardium

Question 2

Describe the endocardium

Answer 2

• Innermost layer, lining the atria and the ventricles
• Components:
• Endothelium
• Subendothelial connective tissue
• Continuous with the tunica intima of the blood vessels entering and leaving the heart
• Subendocardiumis a layer located between the endocardium and the myocardium:
• Contains nerves and Purkinje fibers (subendocardial fibers)

Question 3

Describe the myocardium

Answer 3

Consists of cardiac muscle cells. That’s about it.

Question 4

Describe the epicardium

Answer 4

• External surface is covered by simple squamous epithelium (mesothelium).
• Mesothelium overlies fibroelastic connective tissue containing adipose cells, nerves, and coronary vessels.

Question 5

What are Purkinje Fibers?

Answer 5

• Large, specialized cardiac muscle cells
• Carry impulses to ordinary cardiomyocytes
• See Slide 8-9

Question 6

Describe Cardiac Skeleton

Answer 6

• Dense collagenous connective tissue

- Myocardial fibers originate and insert into the cardiac skeleton.

Question 7

The Walls of all blood vessels except capillaries are characterized by three vascular layers (tunics).
Describe the tunica intima?

Answer 7

• Components:
• Endothelium and its basal lamina
• • Found in all arteries and arterioles
• • Endothelial cells produce von Willebrand’s factor VIII.
• Subendothelial connective tissue:
• • Found in all elastic and muscular arteries and some arterioles
• Internal elastic membrane:
• • Incomplete in elastic arteries but thick and complete in muscular arteries.

Question 8

The Walls of all blood vessels except capillaries are characterized by three vascular layers (tunics).
Describe the two layers that “aren’t” the tunica intima.

Answer 8

• Tunica media:
• Made up of circular smooth muscle tissue and fibroblasts
• Contains collagen and elastic fibers
• Tunica adventitia:
• Outermost layer: Lacking in arterioles
• Consists of loose areolar tissue
• Contains irregular fibroelastic tissue with adipocytes
• Has small vessels (vasa vasorum) and nerves (nervi vasorum)

Question 9

Describe the relationship between vascular anatomy (size and shape) vs. blood pressure.

Answer 9

• Note the drop in pressure as arteries leave the heart and become progressively smaller.
• The structure of the tunic, especially the tunica media changes from that of an elastic tunic to that of a muscular tunic.
• The more elastic arteries are conducting arteries.
• The more muscular arteries are distributing arteries.
• See Slide 13-14

Question 10

Describe the elastic artery

Answer 10

• Conducting arteries
• Stretch during systole and recoil during diastole
• Tunica media consists of layers of elastic fibers organized into elastic laminae:
• 40 layers in newborn to 70 layers in older adult
• Connective tissue is interspersed between the elastic laminae.
• Include:
• Aorta
• Pulmonary trunk
• Large branches of aorta

Question 11

Describe the muscular artery

Answer 11

• Distributing arteries
• Tunica media consists of smooth muscle that responds to autonomic stimulation and hormones:
• Thickness of smooth muscle layer decreases as diameter becomes smaller.
• Gradual transition from elastic artery to muscular artery
• Include: All named arteries of body except elastic arteries
• See Slide 18

Question 12

Describe arterioles

Answer 12

• Small arteries
• Tunica media consists of one to three layers of smooth muscle cells.
• Mean arterial pressure depends on proper tone of smooth muscles in arterioles (peripheral resistance arterioles).
• Thickness of smooth muscle layer decreases as diameter becomes smaller.
• Give rise to metarterioles which have a discontinuous layer of smooth muscle tissue.
• Microcirculation: Components and function:
• Pericytes:
• • Undifferentiated mesenchymal cells
• • May be contractile
• • May serve as stem cellsto differentiate into fibroblasts, etc.
• See Slide 21-24. And notice what he said on that last one.

Question 13

Compare veins to arteries.

What are the characteristics of lymphatics?

Answer 13

• Comparison with arteries:
• Larger lumen
• Thinner wall
• Valves are present in many veins.
• Larger veins have a layer of longitudinal smooth muscle in the inner aspect of the tunica adventitia.
• Lymphatic Characteristics:
• Single layer of endothelial cells
• Basal lamina may be absent
• Anchoring filaments
• Valves in larger lymphatics
• See Slide 26-32