Superior Vena Cava Aorta

Superior Vena Cava  Aorta
Pulmonary Trunk and Thymus

Question 1. Describe the superior vena cava in brief under the following headings:

1. Superior vena cava Introduction
2. Superior vena cava Relations
3. Superior vena cava Tributaries and
4. Superior vena cava Applied Anatomy.

Answer:

Superior vena cava:

1. Superior vena cava Introduction:

• Superior vena cava is the large venous channel, which collects blood from the upper half of the body and drains it into the right atrium.
• Superior vena cava is formed by the union of right and left brachiocephalic veins behind the right first costal cartilage.
• Superior vena cava terminates by opening into the upper part of the right atrium behind the right third costal cartilage.

Read And Learn More: Anatomy Question And Answers

2. Superior vena cava Relations:

• Anterior
• Chest wall
• The right margin of the right lung and pleura
• Right internal thoracic vessels

Superior vena cava Posterior:

• The trachea and right vagus
• Root of the right lung

Superior vena cava Medial

• Ascending aorta
• Brachiocephalic artery

Superior vena cava Lateral

• Right phrenic nerve and pericardiacophrenic vessels
• Right lung and pleura

3. Superior vena cava Tributaries:

• Azygos vein
• Several small mediastinal and pericardial veins

4. Superior vena cava Applied anatomy

Obstruction of superior vena cava (SVC):

superior vena cava may occur either above or below the opening of the azygos vein.

1. In the obstruction of SVC above the opening of Azygos vein, the venous blood from the upper half of the body is returned through the Azygos vein.

Superior vena cava Clinical presentation:  Superficial veins on the chest wall are dilated up to the costal margin.

2. In the obstruction of SVC below the opening of the azygos vein, the venous blood from the lower half of the body is returned through the inferior vena cava via the femoral vein.

Superior vena cava Clinical presentation:

• Superficial veins are dilated on both the chest and abdomen.
• The superficial vein connecting the lateral thoracic vein and the superficial epigastric vein is termed the thoracoepigastric vein.

 

Question 5. Write a short note on the thymus.
Answer:

Thymus:

• The thymus is a central lymphoid organ present in the superior and anterior mediastinum behind the sternum. It is an unequal bilobed gland.
• It is well-developed in the fetus and early childhood. It attains peak development at puberty, and thereafter, it starts convoluting.
• Finally, it is replaced by fibrofatty tissue in old age.

The following figures giving weight to thymus in different age groups rightly justify this fact.

• At birth = 12 – 15 g.
• At puberty = 30 – 40 g.
• In old age (viz. 60 years and above) = 10 – 15 g.

Thymus Development:

• Thymus Development is an epitheliolymphoid organ that develops from two sources:
• Epithelial reticular cells from the endodermal lining of the 3rd pharyngeal pouch
• Lymphocytes from mesoderm

Thymus Functions:

• Production of mature T-lymphocytes which are essential for cell-mediated immunity
• Production of chymosin, a hormone that stimulates the production of T lymphocytes which helps in the maturation of other lymphoid organs

Question 6. Give the histological features of the thymus gland.
Answer:

Thymus gland:

These are as follows:

• Septa arising from connective tissue capsule divides each lobe into incomplete lobules (Note: Septa does not reach into the medulla).
• The Medulla of lobules are continuous with each other.
• The cortex is darkly stained due to densely packed lymphocytes
• The medulla is lightly stained due to less densely packed lymphocytes
• Presence of thy mic or Hassall’s corpuscles in the medulla.
• They consist of central homogeneous hyaline material surrounded by concentric layers of flattened epithelioreticular cells
• Presence of the cellular reticulum formed by the epithelioreticular cells