Comparison between tract and nerve

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  Comparison between tract and nerve Nerve Nerve contain bundle of axons (nerve fibers) in the peripheral nervous system (PNS) that transmits signals between the central nervous system (CNS) and other parts of the body. It is the most important part of peripheral nervous system Location: Peripheral nervous system. Structure: Made of axons, connective tissue layers (endoneurium: axon is surrounded by it , perineurium: bundle of axons are surrounded by it, epineurium: whole nerve trunk is surrounded by it), and blood vessels. It gets myelination by Schwann cell   Function: Carries sensory signals to the CNS (afferent) from peripheral part of body or motor signals carry from from the CNS (efferent) to target organs like skeletal muscle, cardiac muscle, smooth muscle or glands Example: Sciatic nerve, median nerve, except optic nerve (though optic nerve is technically part of CNS in develop...
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Difference between azygos vein, hemiazygos vein & accessory hemiazygos vein

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Difference between azygos vein and hemiazygos vein

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topics

Azygos vein

Hemiazygos vein

Accessory hemiazygos vein

Location

It is present only on the right side in the upper abdominal wall

It is also known as inferior hemiazygos vein . it lies on the left side only and corresconds to the lower part of the azygos vein

It is also known as superior hemiazygos vein . it lies on the left side only and corresponds to the upper part of azygos vein

Tributaries

1.    Right ascending lumbar vein

2.    Right subcostal vein

3.    Right superior intercostals vein (created by 2-4th right posterior intercostals veins

4.    Hemiazygos vein

5.    Accessory hemiazygos vein

6.    Right brochial veins

7.    Esophageal veins

8.    Mediastinal veins

9.    Pericardial veins  

1.    Lower 3 (9-11th ) left posterior intercostals veins

2.    Left subcostal vein

3.    Left ascending lumbar vein

4.    Small esophageal and mediastinal veins

1.    5th to 8th left posterior intercostals vein

2.    Left bronchial veins (occationally )

Formation

Its formation is variable:

1.    It is formed by the union of the ascending lumbar veins with the right subcostal veins at the level of the 12th thoracic vertebra, 

2.    Arises from the posterior aspect of the inferior vena cava near the renal veins

3.    As a continuation of right subcostal vein

4.    Occationally it may arise from the right renal or right first lumbar vein

It is formed on the left side similar to the azygos vein by the union of left ascending lumbar vein and left subcostal vein

It may arise from the posterior surface of the left renal vein

The accessory hemiazygos vein is formed by the confluence of the middle left posterior intercostal veins. 

Course

 It enters the thorax via the aortic hiatus in the diaphragm and ascends posteriorly alongside the vertebral bodies,

The hemiazygos vein enters the thorax either through the aortic hiatus or directly through the diaphragmatic crura.

It descends to the left of midline, adjacent to the thoracic vertebrae and crosses posteriorly to the aorta at the level of T7-8 to drain into the azygos vein.

Variant anatomy

The azygos vein may rarely drain into the right brachiocephalic vein, right subclavian vein, intrapericardial SVC or directly into the right atrium

·         hemiazygos continuation of the IVC: often occurs with duplicated IVCs

·         interazygos vein: occurs when forming a common trunk with the accessory hemiazygos vein anterior to the aorta

·         drains via a common trunk with the hemiazygos vein into the azygos vein

·         forms a common trunk with the hemiazygos vein that passes anterior to the aorta called the interazygos vein 2

·         drains directly into the left brachiocephalic vein (rare) 

Drainage area

Thoracic wall and upper lumbar region

·         It drains the left inferior hemithorax

·         It drains the left superior hemithorax. 



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