27 - Vascular biology III

Question 1

What is adaptive vascular remodeling?

Answer 1

Adaptive vascular remodeling

• Changes in the stress on a wall of a blood vessel can allow for transformational changes in the wall of the blood vessel in order to normalize the stress exherted on the wall
  
  • Elevation in blood pressure or increased flow lead to an increase in vascular wall stress
  • Drop in blood pressure or decreased flow lead to a decrease in vascular wall stress
• Response to pressure depends on position of vessel in arterial hierarchy

Question 2

What specific changes will you see when the vasculature is exposed to a high blood flow?

Answer 2

High blood flow

• Blood vessel will increase in diameter from the outside
• The luminal diameter will also increase
• The thickness of the wall will remain the same

Pretty much, the vessel gets wider, but not thicker

Question 3

What specific changes will you see when the vasculature is exposed to low blood flow?

Answer 3

Low blood flow

• Low blood flow means decreased stress
• Both the outside diameter and the diameter of the lumen will get smaller
• The wall thickness will also remain the same here

Pretty much, the vessel gets smaller, but not thiner

Question 4

What specific changes will you see when the vasculature is exposed to an increase in pressure?

Answer 4

Pressure increase

• Increase in pressure of a large artery will increase the wall thickness
• The external diameter gets larger because it is building its wall externally, but the lumen diameter will not change

Question 5

What specific changes will you see when small arteries are exposed to increased pressure?

Answer 5

In a small artery, there is an exception - the wall thickness increases in an inward motion, thus decreasing the lumen diameter

Question 6

What three specific changes will you see when arterioles are exposed to an increase in pressure?

Answer 6

Arterioles - increased pressure

1. Inward hypertrophy – wall gets thicker at the expense of lumen diameter
2. Inward remodeling – wall thickness and lumen diameter get smaller
3. Rarefaction – vessels can’t stand the pressure anymore so they are lost

Question 7

What are thre three layers of the heart?

Answer 7

1. Endocardium
   
   • Corresponds to the tunica intima of vessels
2. Myocardium
   
   • There are three types of myocardium, all corresponding to the tunica media of vessels
     
     • Contractile (working muscle cells)
     • Myoendocrine
     • Specialized conductive
3. Epicardium
   
   • Corresponds to the tunica adventitia of vessels

Question 8

What are the four layers of the endocarium?

Answer 8

The endocardium corresponds to the tunica intima

1. Endothelium and its basal lamina
2. Subendothelial layer
3. Myoelastic layer
   
   • Contains elastic and collagen fibers
   • Contains smooth muscle cells
4. Subendocardium
   
   • Contains loose connective tissue
   • Contains small blood vessels and nerve fibers
   • Contains Purkinje fibers in the ventricles, but NOT in the atria

Question 9

What is the thickest layer of the endocardium?

Answer 9

Subendocardium

Question 10

What is the myoendocrine function?

Answer 10

Myoendocrine function

• Myoendocrine cells are one type of cardiomyocytes
  
  • Function as natriuretic factors or B-type natriuretic factors in the ventricles
  • Function in diuresis and vasodilation
• Note that in congestive heart failure, there will be an elevation of B-type natriuretic factors
  
  • This is because they are trying to compensate for the increased blood volume

Question 11

What is the cardiac skeleton? What is its function?

Answer 11

The cardiac skeleton

• Allows for the anchoring of the cardiac valves
• Forms ring-like structures (annuli) in order to hold the valves in place
• Also provides a layer of insulation that separates conduction system of the atrium and ventricles

Question 12

How is the importance of the cardiac skeleton highlighted in the case of a valve replacement surgery?

Answer 12

In valve replacement surgery, new valves will be sutured into the cardiac skeleton so they are tightly secured

• The natural cardiac skeleton is very tough and secure
• There was a case over 20 years ago where a middle school student had a valve replacement surgery and the valves were not sutured as tightly as needed
• A classmate pounded him hard on the chest and they were knocked loose and he died :(

Question 13

What are the physical characteristics of the cardiac skeleton?

Answer 13

Cardiac skeleton

• Cardiac skeleton is fibrous in nature – not skeletal or osseus in nature
• Is possible that it can calcify but typically do not want that to happen
• The fibrous skeleton forms a ring for the mitral valve
• Note that the circumflex artery is a branch of the coronary sinus

Question 14

Describe the AV valve

Answer 14

AV valve

• AV valves have similar features to the semilunar valve, but there are some differences
• The valve has a layer of epithelium on the atrial side, which rests on the basal lamina
• There is also a layer of epithelium on the ventricular side

Question 15

What are the three layers of AV valves?

Answer 15

Three layers are present between the two ends of the valve (starting from the atrial side)

• Atrialis layer
  
  • Contains elastic fibers that are used to stretch the valves
• Spongiosa layer
  
  • Rich in proteoglycans that absorb the forces of valve closure
• Fibrosa layer
  
  • Contains collagen - it is the deepest layer that gives the valves its structural integrity

Question 16

What happens when there is an increase in the deposition of dermatan sulfate in the spongiosa layer of an AV valve?

Answer 16

Valve becomes “floppy” and there is a disorganization of the various layers

Question 17

Describe the semilunar valves

Answer 17

Semilunar valves

• There are two
  
  • Between the right ventricle and the pulmonary trunk
  • Between the left ventricle and the aorta
• There are three layers
  
  • Fibrosa
  • Spongiosa
  • Ventricularis (the elastic layer)
• The fibrosa layer is much thicker in semilunar valves compared to AV valves due to differences in pressure

Question 18

Describe calcific degeneration of the aortic valve

Answer 18

Calcific degeneration

• Most often occurs in patients with atherosclerotic risk factors
• You will see calcifications of the valve
• The valve does not function properly

Question 19

What makes up the conduction system of the heart?

Question 20

Describe the SA nodes of the conduction system

Answer 20

SA nodes

• SA nodal cells are smaller than atrial cells
• SA nodes contain few myofibers
• SA nodes will not stain as acidophilic as the working or contractile atrial cells

Question 21

What makes up the AV bundle?

Answer 21

Purkinje fibers

Question 22

Describe the purkinje fibers within the AV bundle

Question 23

Under which circumstance will cardiac stem cells (CSCs) and early committed cells (ECCs) be reactivated?

Answer 23

CSCs and ECCs

• These cells will be activated to reconstitute necrotic myocardium (death of heart cells)
• CSCs and ECCs are know to exist in the AV sulcus under normal conditions
• CSCs and ECCs have the ability to migrate from the AV sulcus to the _site of injury _
• Once they reach the site of injury, CSCs and ECCs are able to differentiate into cardiomyocytes, SMCs and endothelial cells
• hCSCs are able to replace the myocyte compartment 11-15 times
• The cardiac cells we are born with ARE replaced over our lifetime… We do NOT die with the cardiac cells we are born with

Question 24

Describe the basics of the lymphatic vascular system

Answer 24

Lymphatic system

• In the microcirculation, there is a net fluid loss and that fluid gets picked up by the lymphatics

Question 25

Describe the characteristics of a lymphatic capillary

Answer 25

Lymphatic capillary

• These capillaries are thin
  
  • The endothelium along the edges of the capillary gets gently pushed in to allow fluid inside
• The basal lamina is absent or discontinuous
  
  • This would be a barrier to flow
• Interstitial fluid exists
• Anchoring fibrils
  
  • Prevent the tube from collapsing
• Pericytes (and RBCs) are absent

Note that the profile of a lymphatic capillary is very delicate

Question 26

What forms lymphatic vessels and valves?

Answer 26

• Lymphatic capillaries join together to form larger lymphatic vessels
• Note that you can always identify a lymphatic vessel because there are no RBCs present in the vessel

Question 27

Describe the characteristics of a medium-sized lymphatic vessel

Answer 27

Medium-sized lymphatic vessel

• Much more muscular in appearance
• The tunica media will contain more smooth muscle
• Lymph and leukocytes can be seen in the lumen
  
  • NO red blood cells

Question 28

What is a specific lymphatic endothelial marker?

Answer 28

LYVE-1

• Lymphatic endothelial cells secrete this marker
• This marker will appear as brown deposits
• This marker helps to identify the malignant spread of a tumor because if there is a high density of this marker in a tumor, the malignant cells have probably gained access to the lymphatic system and spread through it
• When there is an increased lymphatic vasculature in a tumor, malignant cells can easily get into the lymph and metastasize other tissues

Question 29

What are the effects of rheumatic fever on the heart?

Answer 29

Rheumatic fever affects the mitral valve

• Streptococcal pharyngitis is the infection of rheumatic fever
• The immune response to this infection causes vegetation on the mitral valve and Aschoff bodies will form
  
  • This is a signature feature of Rheumatic fever
• These morphologic changes are due to antibodies cross-reacting with self-antigens in the heart and T cell-mediated reactions