Superior Vena Cava (Azygos, Hemiazygos, Brachiocephalic) | Anatomy — Transcript

Full transcript

1. 0:03Let's now talk about the superior vena cava and its associated veins.
2. 0:07So in this video, we're first going to talk briefly about the superior vena cava,
3. 0:12We'll talk a little bit about the azygos vein Then we'll cover the hemiazygos vein and the
4. 0:17accessory hemiazygos vein After that, we'll talk about the right and
5. 0:21the left brachiocephalic veins.
6. 0:23We'll go through their characteristics, their tributaries and what structures they all generally
7. 0:28drain.
8. 0:29Awesome So, the easiest way to understand the veins
9. 0:33of the systemic circulation is to divide them into their own systems.
10. 0:37So the veins of the heart form their own system We have the Veins of the Inferior Vena Cava,
11. 0:43which is responsible for supplying the lower half of the body
12. 0:46Veins of the superior vena cava for the upper half of the body
13. 0:50And the portal system, which drains nutrients from the intestines
14. 0:53and waste products from the spleen and dumps them into the liver to be processed,
15. 0:58which then lead the blood into the inferior vena cava again.
16. 1:01So these are the 4 main systems of veins we have in our bodies.
17. 1:05Let's now talk briefly about the superior vena cava and it's associated veins.
18. 1:10The superior vena cava is a short vein as you see here,
19. 1:14And it has a quite large diameter.
20. 1:16Approximately 2-3 cm wide It carries deoxygenated blood from the upper
21. 1:21half of the body, so the head, neck, upper limbs, thorax, and upper part of the back.
22. 1:27Then it descends vertically to empty into the right atrium at the level of the third
23. 1:32sternocostal joint.
24. 1:34So that was mainly everything for the superior vena cava.
25. 1:38Now let's talk about the azygos vein, which is a vein that drains into the superior vena
26. 1:43cava.
27. 1:44The Azygos vein is located very close to the vertebra, behind the inferior vena cava.
28. 1:50So if we cut through the inferior vena cava, We'll be able to see the azygos vein here
29. 1:55very clearly.
30. 1:56Ok, so where does it get its blood from?
31. 1:59Well, here you see the common iliac vein.
32. 2:03The common iliac vein has a tributary called the right ascending lumbar vein,
33. 2:08And this vein becomes the Azygos vein at around the 12th thoracic vertebra.
34. 2:14And as the azygos vein ascends along the right side of the vertebral column.
35. 2:19It arches anteriorly at the level of T4, to then empty into the Superior Vena Cava.
36. 2:25Ok, so here are some fun facts about the azygos vein.
37. 2:28The Greek root zyg refers to a pair.
38. 2:32'A-' means not.
39. 2:34That means a-zygos means unpaired.
40. 2:37That's why you'll find this vein only on the right side of the vertebral column, while
41. 2:42on the left side you'll find the hemiazygos and its accessory on the left side of the
42. 2:46body.
43. 2:47Kinda makes sense doesn't it?
44. 2:49Another thing that's good to know is that the azygos vein and the hemiazygos vein are
45. 2:53valveless.
46. 2:54Usually when you study veins, you'll see that veins have valves to prevent backflow of blood.
47. 3:00These two doesn't have any of these.
48. 3:02They therefore may function as portocaval and cavo-caval anastomoses.
49. 3:07Meaning if there's a liver disease that causes narrowing of the portal vein.
50. 3:11The blood starts shunting over to other places since it can't get through the liver.
51. 3:17So it can go through the esophageal branches of the azygos vein causing esophageal varices
52. 3:23. But that's pathology, we'll cover this in
53. 3:24the future.
54. 3:25Alright.
55. 3:26That was a little fun fact about the ayzygos vein
56. 3:27So it do have tributaries, or side branches if you may.
57. 3:31It has visceral tributaries And parietal tributaries.
58. 3:35Visceral going to organs, parietal going to muscle and bone
59. 3:40And so I wanna start with this vein right here, called the hemiazygos vein.
60. 3:46Similar to the azygos vein, the hemiazygos vein also starts from the ascending lumbar
61. 3:51vein, but the left one this time, at around T12.
62. 3:54And it empties into the azygos vein at around T8 to T9.
63. 3:59We have the accessory hemiazygos vein a little higher up, which receives blood from the left
64. 4:044-7th intercostal veins.
65. 4:07These veins vary a lot between people.
66. 4:09It can either anastomose with the left superior intercostal veins of the left brachiocephalic
67. 4:14vein, or not.
68. 4:16It can just start from the 4-7th left intercostal veins as well.
69. 4:20And in the lower direction; It can either anastomose with the hemiazygos
70. 4:25vein, or Anastomose with the azygos vein, as you see
71. 4:29here.
72. 4:30That's why I feel like It can be pretty daunting studying veins.
73. 4:32There are so many variations.
74. 4:33So that's these ones.
75. 4:34Now, let's add some organs.
76. 4:36The first visceral tributary of the azygos vein is the oesophageal veins.
77. 4:41If we go ahead and turn this model to the side,
78. 4:43We'll see that both the azygos and hemiazygos veins have tributary veins that drain the
79. 4:49esophagus.
80. 4:50And if we go ahead and add the bronchi.
81. 4:52You'll see that it also has bronchial veins that drain into the azygos vein
82. 4:57We have pericardial veins as well, And mediastinal veins, draining various structures
83. 5:02in the mediastinum like lymph nodes.
84. 5:05Alright Let's now add the ribs on the right side.
85. 5:09The azygos vein has parietal tributary veins called the right superior intercostal veins,
86. 5:16which drain the 2nd ad 3rd Right intercostal spaces.
87. 5:20Sometimes the 4th as well.
88. 5:22It has the right posterior intercostal veins, which drain the lower 8 right intercostal
89. 5:27spaces.
90. 5:28Now just to give you a complete picture.
91. 5:30On the left side.
92. 5:31Here we have the left posterior intercostal veins, which drain into the accessory and
93. 5:36the hemiazygos vein.
94. 5:39Alright.
95. 5:40Then we have a vein that's associated with the Diaphragm
96. 5:43Called the superior phrenic vein.
97. 5:45Alright!
98. 5:46That was the azygos and the hemiazygos vein!
99. 5:48Now.
100. 5:49As the Superior Vena Cava ascends, it splits into the right and the left brachiocephalic
101. 5:55veins.
102. 5:56And these two veins are formed by a union of the
103. 6:00Subclavian vein, and the Internal Jugular Vein.
104. 6:03Now let's zoom in and focus on these two for a minute.
105. 6:07Even though the right and the left brachiocephalic vein have identical names.
106. 6:12There are quite a few differences between their tributaries and size.
107. 6:17Veins are generally very asymmetrical due to their variations.
108. 6:21The right brachiocephalic vein is about 3 cm long, while the left is about 6 cm long.
109. 6:28Let's now go through their tributaries.
110. 6:30The right Brachiocephalic vein receives blood from the right vertebral vein.
111. 6:35Which goes through the vertebral transverse foramina, as you see here.
112. 6:39So what it does is that it drain the external and internal vertebral venous plexuses and
113. 6:45the deep muscles of the back in the neck region.
114. 6:49It collects all of that blood; then it goes down through the transverse foramina together
115. 6:54with the vertebral artery and then opens into the right brachiocephalic vein.
116. 6:58Next, we have the Right Inferior Thyroid Vein.
117. 7:03This vein originates from a glandular venous plexus at the thyroid gland.
118. 7:08And then it descends and travels superficially to the trachea and inserts into the brachiocephalic
119. 7:15veins.
120. 7:16Next we have the Right Internal Thoracic Vein.
121. 7:19It follows exactly the same path as the internal thoracic artery.
122. 7:24It will Descend along the anterior wall of the thoracic cavity.
123. 7:27On its way, it mainly drains the upper 5-6 intercostal spaces.
124. 7:32And then at the level of the 7th rib, it Receives blood from two veins.
125. 7:37One of them is the Musculophrenic vein Which receives blood from the lower 5-6 intercostal
126. 7:43spaces, as the anterior intercostal branches And the other one is the Superior Epigastric
127. 7:50Vein, which passes the diaphragm at the sternocostal triangle – and communicates with the inferior
128. 7:55epigastric vein.
129. 7:57And all of these anterior intercostal veins communicate with the posterior intercostal
130. 8:03veins we mentioned earlier.
131. 8:06Alright.
132. 8:07Next we have the right supreme intercostal vein.
133. 8:10This one.
134. 8:12Which drains the upper 1 – 2 intercostal spaces.
135. 8:15So that was the most important tributaries of the Right brachiocephalic vein.
136. 8:19Now let's turn this model to the other side and cover the Left brachiocephalic vein!
137. 8:24The left brachiocephalic vein has more or less the same tributaries as the right one.
138. 8:29Which is the Left Vertebral Vein Left Inferior Thyroid Vein
139. 8:34Left Internal Thoracic Vein And the Left Supreme Intercostal Vein.
140. 8:39But it does have some additional tributaries we should mention here as well.
141. 8:42And the first one is the left superior intercostal vein which drains the upper 3 – 4 intercostal
142. 8:49spaces of the left side.
143. 8:51And then another vein that drains the Thymus called the thymic veins.
144. 8:55And then there's the Pericardiophrenic Vein, which drains tributaries from the superior
145. 9:00diaphragm and pericardium So that was all the veins that I wanted to
146. 9:05cover in this video The next video is going to be about the veins
147. 9:08of the upper limb