Module 1B: Histology Of Cardiovascular System

Question 1

How are the cardiac muscle fibers connected?

Answer 1

Number ous layers of cardiac muscles fibers can be found one below the other. Cells of each layer can communicate with other layers through gap junctions. Gap junctions between different layers of myocardial cells acts as ‘electrical synapses’ which efficiently transmits the electrical impulse causing synchronous contraction of many cells at once.

Question 2

Does myocardial cells have abundant mitochondria?

Answer 2

Yes, 40% of cell volume is occupied by mitochondria.

Question 3

Can cardiac cells regenerate like skeletal muscle?

Answer 3

These lack the satellite cells, so upon damage like the one caused due to ischemia (caused by lack of oxygen due to blockage of the coronary artery), the heart muscle has little to no ability to repair.

Question 4

What are the 3-layers of the heart wall?
Inner to Outer

Answer 4

Epicardium
Myocardium
Endocardium

Question 5

Where are the nodes located? How does the electrical impulse flow through the heart?

Answer 5

The Sinoatrial node (SA node) located in the right atrium wall and the atrioventricular node (AV node) located in the floor of the right atrium initiate the electrical impulse for contraction

This impulse spreads through specialized cardiac muscle cells present in the interventricular septum and then branch into left and right Purkinje fibers going towards the left and the right ventricles. Purkinje fibers are also specialized cardiac muscle cells whose function is to efficiently conduct electrical impulses in the heart.

Question 6

Where do the right and left ventricles propel blood to?

Answer 6

the pulmonary and systemic circulation

Question 6

Where do the right and left atria propel blood to?

Answer 6

The blood from the body and the pulmonary veins

Question 7

What does the endocardium consist?

Answer 7

a layer of lining endothelium + some elastic connective tissue + some smooth muscle

• Lines the inner surface of the heart
• Endothelial cell layer on a basal lamina
• Collagen, elastin and thin layer of smooth
muscle

Question 8

What does the epicardium consist of?

Answer 8

A layer of mesothelium with some connective tissue that surrounds the heart on the outer side. With CT also comes the nerve and blood supply here. This layer is also known as the visceral pericardium.

• Mesothelium (squamous type)
• Basal lamina
• Loose connective tissue (with blood vessels and nerves)

Question 9

What does the pericardium consist of?

Answer 9

fibrous tissue that surrounds the heart and the roots of the great blood vessels

Question 10

What does the myocardium consist of? Why is the myocardium the way it is?

Answer 10

• Thickest layer of the heart wall
• Made of cardiac muscle

Because strong force is required to pump blood through the systemic and pulmonary circulations, the myocardium is much thicker in the walls of the ventricles, particularly the left, than in the atrial walls

Question 11

What do the Purkinje fibers consist of?

Answer 11

Purkinje fibers- modified myocytes that are present between the endocardium and the myocardium in the ventricles- transmit action potentials that are generated by the cardiac pacemaker cells of the sinoatrial node

Purkinje myocytes have extensive gap junctions that allows for rapid conduction of action potential for ventricular contractions, these are large cells with lots of glycogen

Question 12

What are the layers of the vascular wall inside to outside?

Answer 12

Common basic structure:
1. T unica intima: Endothelium + a basement membrane and delicate collagenous tissue
2. Tunica media: circularly arranged smooth muscle - if contracted - smaller lumen - increase blood pressure.
3. Tunica adventitia: layers of connective tissue, collagen & elastic fibers. Large and some medium veins may contain bundles of longitudinally arranged smooth muscle. Vasa vasorum and nervi vasorum may be present in large vessels.

Question 13

What are the layers of an artery? Inside to outside

Answer 13

Intima
Endothelium
Subendothelial layer
Internal elastic lamina
Media - thick
External elastic lamina
Adventitia
Vasa vasorum - thin

Question 14

What are the layers of an vein? Inside to outside

Answer 14

Intima
Endothelium
Subendothelial layer
Media - thin
Adventitia
Vasa vasorum - thick

Question 15

What are the function of arteries?

Answer 15

Function: 1) To distribute blood from the heart to capillaries
2) The flow of blood - regulated by changing the diameter of the distributing vessels

•The controlled by the sympathetic nervous system and adrenal medulla hormones

Question 16

What are the structures of arteries?

Answer 16

Structure:
1) Common basic structure- TI, TM, TA 2) Lumen appears round in sections
3) Presence of high amount of elastic fibers
4) Smooth muscles present

Question 17

Where are there large elastic arteries and small elastic arteries? Describe each of the layer of elastic arteries

Answer 17

large elastic arteries like aorta can be identified by their thick wall. Small elastic artery like the renal, brachiocephalic, common iliac, pulmonary artery

Dozens of thin sheets arranged over one another. These sheets are called lamellae
L= lumen
TI= tunica intima (endothelium over a basal lamina, collagen present)
TM= tunica media (lots of elastin present here that stains dark), collagen and smooth muscle in between elastin fibers, elastin allows the vessels to stretched when blood under pressure flows through it

Question 18

What do muscular arteries do?

Answer 18

These arteries control the blood flow to the organs by contracting and relaxing when needed. This contraction is done my the smooth muscles in the arterial walls.

Question 19

What do arterioles do?

Answer 19

Arterioles- fine control of blood flow by dilatation or constriction can contribute significantly to changes in blood pressure

This changes the high-pressure intermittent flow to steady low-pressure blood flow going into the capillary networks
No EEL

Question 20

What is the blood flow sequence when sphincters are open?

Answer 20

Blood flow sequence when sphincters are open: Arteriole- Metarteriole - capillary bed – post-capillary venule

Question 21

What is the blood flow sequence when sphincters are closed?

Answer 21

Blood flow sequence when sphincters are closed: Arteriole- Metarteriole - thoroughfare channel - post capillary venule

Question 22

What are thoroughfare channel?

Answer 22

drains blood into the postcapillary venule-
bypassing the capillary bed

Question 23

What is thermoregulation?

Answer 23

the skin involves arterioles that can bypass capillary networks and connect directly to venules.

Question 24

What do capillaries do?

Answer 24

• Made of endothelial cells on a basal lamina • Associated with pericytes (contractile- type cells) – Pericytes can differentiate into smooth muscle or fibroblasts during wound healing and angiogenesis – Pericytes not found in fenestrated or sinusoidal capillarie

Question 25

What is the most common type of capillaries?

Answer 25

Continuous capillaries

Question 26

Describe continuous capillaries

Answer 26

have tight, occluding junctions sealing the intercellular spaces between all the endothelial cells to produce minimal fluid leakage. All molecules exchanged across the endothelium must cross the cells by diffusion or transcytosis. These are associated with Pericytes. Pericytes are not found with the other 2 types of capillaries.

Question 27

Describe fenestrated capillaries

Answer 27

• Have gaps in the endothelial layer • Found in the gut, renal glomerulus Perforations (fenestrations) through the endothelial cells allow greater exchange across the endothelium. Fenestrated capillaries are found in organs where molecular exchange with the blood is important, such as endocrine organs, intestinal walls, and choroid plexus.

Question 28

Describe Sinusoidal capillaries

Answer 28

Larger diameter capillaries Found in liver, spleen, bone marrow Large gaps in their walls allows transport of whole cells from the blood to the tissue

Question 29

What are the structures of the vein?

Answer 29

Structure: 1) Common basic structure- IMA 2) TA is always the thickest 3) IEL absent 4) Overall walls of veins are thin compared to arteries 5) Irregular lumen (compared to round lumen in arteries) 6) May have valves to prevent retrograde flow

Question 30

What are the function of the vein?

Answer 30

1) To drain blood from organs and tissue back to the heart 2) Fluid and nutrient exchange 3) Transfer of leukocytes 4) Reservoir for blood 5) Involve in inflammatory responses

Question 31

How do veins work?

Answer 31

Blood entering veins is under very low pressure and moves toward the heart by contraction of the smooth muscle fibers in the media and by external compressions from surrounding skeletal muscles and other organs. The tunica intima is usually thin, the media has small bundles of smooth muscle cells mixed with a network of reticular fibers and delicate elastic fibers, and the collagenous adventitial layer is thick and well developed.

Question 32

What are the arrangements in medium veins?

Answer 32

• Well developed TA, thin TM • Lacks IEL and EEL • Here the vein is filled with blood and lumen holds shape • Otherwise, lumen is irregular • Have valves

Question 33

What are the arrangements in large veins? Where are large veins?

Answer 33

• TI-TM-TA arrangement • Irregular but large lumen • Have valves Thicker TA, relatively thin TM. TI has elastic fibers in it. Ex: superior vena cava inferior vena cava large pulmonary veins.

Question 34

How do valves assist in venous function?

Answer 34

• Found in medium and large veins • They are inward extensions of tunica intima • Occur in pairs • Prevent back flow of blood • Malfunction results in a condition called ‘Varicose veins’

Question 35

How does is vasa vasorum help with blood supply?

Answer 35

• Supply nutrients/ oxygen to medium and large arteries and veins • More extensive in veins than in arteries. In arteries- it only penetrates up to TA. In veins- they penetrate up to TI required to provide metabolites to cells in those tunics in larger vessels because the wall is too thick to be nourished solely by diffusion from the blood in the lumen. Luminal blood alone does provide the needs of cells in the intima. Because they carry deoxygenated blood, large veins commonly have more vasa vasorum than arteries.

Question 36

Describe the lymph vascular system

Answer 36

• Vascular system that circulates the fluid present in the interstitial spaces • Made of Lymph capillaries and lymph vessels Contains proteins, lipids, electrolytes and cells (ex: lymphocytes) Gathers lymphocytes from the tissue and supply antibodies from the lymph nodes into the veins

Question 37

What is Edema?

Answer 37

• Obstruction of lymph vessels- accumulation of interstitial fluid • Usually due to inflammation or parasitic infection • Ex: lymphatic filariasis (aka Elephantiasis) Caused when the parasite multiplies and grows inside the blood stream and eventually occludes the lymphatics