Histology

Question 1

What are the 3 layers that compose the wall of the heart?

Answer 1

Epicardium (outermost)
Myocardium (cardiac muscle)
Endocardium (endothelium and connective tissue between cardiac muscle)

Question 2

What tissue are valves made of?

Answer 2

Some cardiac muscle is sometimes found in the valves, but they’re mostly just connective tissue

Question 3

What are the three layers of blood vessels?

Answer 3

Tunica adventitia (outermost)
 tunica media
 tunica intima (innermost)

*Tunica intima includes the internal elastic membrane

Question 4

Which of the layers of blood is modified between vessels? (i.e difference between aorta and arteriole)

Answer 4

Tunica media - variable levels of smooth muscle

*Exception is large veins (i.e. Vena Cava)
- smooth muscle in the t. media is sparse
muscle is actually found in the t. adventitia

Question 5

What is the histological definition that determines if a vessel is a artery or arteriole?

Answer 5

1-2 layers of smooth muscle in t. media constitutes an arteriole

Question 6

How can you compare arteries and veins and determine which is which?

Answer 6

• Often found adjacent to each other
• both lined with endothelial cells, but cells can have different characteristics (responses to serotonin, histamine, acetylcholine, etc)
• Tunica media is more robust in artery comparted to equivalent vein; artery will have more smooth muscle
• Tunica adventitia may contain smooth muscle bundles in larger veins (i.e. vena cava)
• in a non-perfused preparation, veins will artifactually be mishapen (arteries have more smooth muscle to keep their structure)

Question 7

How can you determine an elastic arterie from a musclular artery?

Answer 7

Elastic arteries have a tunica media with many layers of elastic lamella (sheets)

Question 8

What are vaso vasorum?

Answer 8

a network of small blood vessels that supply blood to the larger blood vessels

Question 9

Where is the control of resistance in vasculature?

Answer 9

Arterioles

• contraction of the smooth muscle in the wall of an arteriole increases the vascular resistance and reduces or shuts off the blood going into the capillaries

Question 10

What is the precapillary sphincter?
(what does it do?)

Answer 10

The slight thickening of the smooth muscle of an arteriole at the origin of a capillary bed

• helps control flow through the capillary bed

Question 11

How is the smooth muscle of blood vessels activated into contraction?

Answer 11

• Depolarization or hormonal stimulation opens Ca²⁺ channels and Ca²⁺ flows into the cell
• Intracellular Ca²⁺ binds to calmodulin to form the Ca²⁺-calmodulin complex
• The complex binds to myosin light chain kinase to phosphorylate one of the two regulatory light chains of the myosin molecule
• When phosphorylated, myosin changes conformation and the actin-binding head is alllowed to attach to actin
• If ATP is available, the cell contracts

Question 12

How does diabetes inhibit vasodilation and vasoconstriction?

Answer 12

Glycolation (hyperglycemia and diabetes) inhibits contraction of smooth muscle cells

Question 13

What are the three types of capillaries?
Where are they found?

Answer 13

Continuous (found in muscle, lung, CNS)

Fenestrated (found in endocrine glands and sites of fluid and metabolite absorption - gallbladder, kidney, intestinal tract)

Discontinuous (found in liver, spleen, and bone marrow)

Question 14

What are pericytes

Answer 14

specialized cell type found on capillary and venules

• give rise to muscle and endothelium during injury
• can be involved in disease processes