Blood, Part 1 - True Blood: Crash Course Anatomy & Physiology #29 — Transcript

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1. 0:00Don’t take this the wrong way, but you’re pretty replaceable.
2. 0:02When it comes to your body, science has figured out how to hack, synthesize, or replace a
3. 0:06surprising amount of its parts and processes.
4. 0:09We have implants to keep heart beats steady, and steel rods to mimic bones.
5. 0:12We’ve got drugs that can replace hormones, and antibiotics to cover for your immune system,
6. 0:17and pretty soon you’ll be able to just 3D print a new ear if you need one. Really!
7. 0:21But one thing we absolutely cannot manufacture -- despite what True Blood would have you believe --
8. 0:25is blood. And yet blood is a thing that we all need.
9. 0:28And sometimes, because of injury or illness, we need extra blood.
10. 0:32In fact, every two seconds, someone in the U.S. needs a blood transfusion. This could
11. 0:36be a victim of a car accident, someone undergoing surgery, or a cancer patient who needs new
12. 0:40blood to maintain their health during chemotherapy.
13. 0:43And because we can’t grow it on trees, or make it in a lab, or even it store it for
14. 0:46all that long, the blood that people need -- nearly 16 million pints a year in the U.S.
15. 0:50-- has to come from people who have donated it.
16. 0:53So let’s talk blood, shall we?
17. 0:54The meal of choice for vampires and female mosquitoes, blood is red, sticky, salty, and
18. 0:59kind of metallic tasting.
19. 1:00It is indeed thicker than water, and super viscous -- which is why Hitchcock used chocolate
20. 1:04syrup as a stand-in in a certain classic shower scene.
21. 1:07For most purposes, blood comes in eight different types, and it accounts for about 8% of your body weight.
22. 1:12You might remember from our episodes on tissues that blood is a type of connective tissue,
23. 1:16which means it’s made of living cells suspended in a nonliving matrix, which in this case
24. 1:20is the fluid ground substance called plasma.
25. 1:23And of course one of blood’s main missions is to transport and distribute oxygen, nutrients,
26. 1:27waste products, and hormones around the body.
27. 1:29But it also helps regulate and maintain body temperature, pH levels, and the volume of
28. 1:34fluids in your body. Plus it protects you from infection and from the loss of blood itself.
29. 1:39Perhaps second only to your brain, your blood is the one component of your body that we
30. 1:43haven’t figured out how to reproduce, synthesize, or imitate.
31. 1:47It’s a part of you that is literally irreplaceable.
32. 2:01It’s Saturday and you feel like doing a good deed, so you head over to your local
33. 2:04Red Cross for a blood drive.
34. 2:06You get your finger pricked and then somebody directs you toward a lounge chair, swabs your
35. 2:09inner elbow with alcohol, and then comes at you with a hollow needle.
36. 2:13Once the bag is full -- they usually take about a pint -- you get unhooked and grab
37. 2:16a cookie and a juice to replace the blood sugar you lost. And the whole process takes around 20 minutes.
38. 2:21But for your blood, the day is just beginning. Soon it will be taken to a lab, where it’ll
39. 2:25be tested for infectious diseases and separated into different parts before heading out to hospitals.
40. 2:30So, hold up: What exactly do I mean by different parts?
41. 2:33Well, the blood that flows from your arm into that bag is whole blood, a mixture of cells
42. 2:38and cell fragments called formed elements, along with water, and lots of dissolved molecules.
43. 2:43A patient who needs a transfusion may only need some of those things and not others,
44. 2:47so the parts are separated.
45. 2:48Once your blood makes it to a lab, technicians put it in a centrifuge, which spins it around
46. 2:52fast enough to send the heavier components to the bottom of the tubes, and bring the
47. 2:55less dense elements to the top.
48. 2:57In the centrifuge, three distinct layers emerge.
49. 2:59Down at the bottom you’ve got a heavy red layer of erythrocytes, or red blood cells
50. 3:04that carry oxygen and carbon dioxide. They make up about 45 percent of your total blood volume.
51. 3:08Then you’ve got this thin little whitish layer in the middle. Those are your warriors,
52. 3:13the leukocytes or white blood cells, that defend your body from toxins and foreign microbes.
53. 3:17And there are also the cell fragments, called platelets, which help with blood clotting
54. 3:21and make up less than one percent of your blood.
55. 3:23Finally, up at the top you see the yellowish plasma, which accounts for about 55%of your blood volume.
56. 3:29Plasma is actually 90 percent water, but the other 10 percent is chock full of 100 different
57. 3:34solutes, including proteins, electrolytes, gases, hormones, and waste products.
58. 3:37The most of abundant of these solutes are electrolytes -- which you may have heard of
59. 3:41as the secret ingredient in sports drinks. But they’re really just positively-charged cations -- like calcium,
60. 3:46sodium, and potassium -- and negatively-charged anions, like phosphate, sulfate, and bicarbonate.
61. 3:51Together these ions help regulate your blood’s chemistry, maintaining its pH levels and proper osmotic
62. 3:57pressure, and allowing other tissues to do their jobs, like making muscles contract and sending action potentials.
63. 4:03But when measured by weight, the bulk of the solutes in your blood are really the plasma proteins.
64. 4:08Most of these proteins -- like albumin, and alpha and beta globulins -- are made by the
65. 4:12liver, and do things like balance the osmotic pressure between the blood and surrounding
66. 4:16tissues, and transport lipids and ions.
67. 4:19Others run defense for you, like the gamma globulin antibodies that are released by plasma cells during
68. 4:24an immune response, or fibrinogen proteins, which are vital to forming blood clots and stopping bleeding.
69. 4:30All right, bleeding. I want to talk about that.
70. 4:32Because, for the very reason that I mentioned at the beginning -- that we can’t replace
71. 4:36your blood with some synthetic wonder-fluid -- the LAST THING that your circulatory system
72. 4:40wants is for you to fritter away your blood, in some sidewalk scrape or kitchen accident.
73. 4:45So, it has a whole system in place to prevent you from losing too much of it, through a
74. 4:49process known as hemostasis.
75. 4:51So imagine you’re slicing a nice garlic-cheese bagel one morning, and you lacerate the distal
76. 4:56phalanx of your pollex -- in other words, you cut the tip of your thumb.
77. 4:59And now you’re bleeding all over your breakfast.
78. 5:01At the very first sign of a rupture, the blood vessel actually constricts itself, to slow
79. 5:05the flow of blood through it.
80. 5:07Then little cell fragments called platelets gather at the site of the injury, creating
81. 5:10a plug that dams the breech and keeps the blood from leaking further.
82. 5:13Now these free-floating platelets don’t clump together during regular circulation -- that
83. 5:17would be terrible -- but when the endothelial cells lining a blood vessel wall tear, the
84. 5:21underlying collagen fibers are suddenly exposed. And they chemically react with the platelets,
85. 5:26turning them all sticky and glue-like at the scene of the injury.
86. 5:29But that platelet plug still isn’t as strong as it could be -- it needs reinforcement to
87. 5:33complete the clotting process.
88. 5:35This reinforcement comes in the form of fibrin threads, protein strands that join together
89. 5:40to make a sort of mesh that traps the platelets and blood cells.
90. 5:43Eventually, the threads actually pull the opposite sides of the wound together, to close
91. 5:47the vessel wall, so the endothelial cells can be replaced.
92. 5:50Over a few days, the blood vessel heals, and the blood clot dissolves.
93. 5:53Or at least, that’s how it is supposed to happen.
94. 5:55People who suffer from disorders related to hemostasis may have trouble with unwanted
95. 5:59clotting, or the inability to form clots.
96. 6:02In the family of disorders known as hemophilia, a patient can usually complete the first two
97. 6:06steps of hemostasis just fine, but they can’t make an effective fibrin clot. So it’s not that they
98. 6:11bleed more than anyone else, it’s just that they bleed longer. Which, I guess means that they bleed more.
99. 6:15As a result, they may need frequent blood transfusions throughout their lifetime.
100. 6:19Which brings me right back around to that Saturday morning blood drive.
101. 6:21Another thing you’re going to need to know before you give blood is what type you have
102. 6:25-- do you have A, B, AB, or O?
103. 6:28These different types all do the job equally well, they just sort of have a different flavor
104. 6:32related to your immune system.
105. 6:34All the cells in your body have a plasma membrane with specialized glycoprotein markers on them
106. 6:38that act like name tags or labels, sort of like “This cell is Property of Hank.”
107. 6:42These markers are your antigens.
108. 6:44And your body’s immune system is totally fine with your particular antigens, but if
109. 6:48it detects antigens from someone else’s cells -- including viruses or bacteria -- then
110. 6:53it’ll send out antibodies to bind to those markers, often to tag them for destruction by the immune system.
111. 6:58Your red blood cells have specialized antigens on them, called agglutinogens, that activate antibodies
112. 7:03that work by binding invading cells to each other, which causes coagulation, or the clumping of blood.
113. 7:09Which agglutinogens you have on your erythrocytes defines your blood type.
114. 7:12But they’re classified in two different ways.
115. 7:14In the most important blood classification -- the kind people are most familiar with
116. 7:17-- there are only two kind of agglutinogens, simply A and B. And your blood can either have
117. 7:22one, or both, or neither of these molecules.
118. 7:24So the name of your blood type refers to what kind you have or don’t have: A-type has
119. 7:29A antigens, B-type has B, AB has both, and O has neither.
120. 7:34So, why do you need to know what type you are before you give or receive blood?
121. 7:37Well, like I mentioned: If you have either of these antigens, your body will be fine
122. 7:40with it, because it doesn’t produce any antibodies that label it for attack.
123. 7:43So if you don’t have a particular antigen on your blood cells -- say the type B -- then
124. 7:47you do have antibodies that are going to label those B antigens for attack, should they enter your space.
125. 7:52So AB-type folks are called universal recipients, because they have both antigens, and therefore
126. 7:57no antibodies for either. So they can accept A, or B, or AB, or O blood. Meanwhile, O-type
127. 8:04doesn’t have A or B antigens, so those folks have antibodies for both. That means that they
128. 8:09can only accept other O blood.
129. 8:11And yet that lack of antigens means that Type O blood can mix with other types of blood
130. 8:15without getting attacked, which is why it’s known as the universal donor.
131. 8:19But just to complicate things a little bit more, you’ve got a whole other set of antigens
132. 8:22with totally different protocol. These are your Rhesus, or Rh antigens, named after the
133. 8:27species of monkey they were first identified in.
134. 8:30Much like A and B, you either have the Rh antigens, in which case you’re Rh positive,
135. 8:34or your don’t, and are Rh negative.
136. 8:36Most of the population is Rh positive, so they don’t have the anti-Rh antibodies,
137. 8:41which means they can accept either positive or negative blood. But negative types should
138. 8:45stick to just the Rh negative blood.
139. 8:47And since the presence of A-B antigens is controlled by different genes than the Rh
140. 8:51ones, we end up with eight different blood types -- four separate groups, each with two variations.
141. 8:56And now, hopefully, you understand why it’s so hard to replace blood, and why True Blood
142. 9:01is...not true. I’ve not actually ever seen that show.
143. 9:04Along the way, you also learned the basic components of blood -- including erythrocytes,
144. 9:08leukocytes, platelets, and plasma -- as well as the basic process of hemostasis that stops
145. 9:13bleeding, and how antigens are responsible for the blood type that you have.
146. 9:16Thanks to all of our Patreon patrons who make Crash Course possible through their monthly
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148. 9:25everyone in the world, you can go to patreon.com/crashcourse
149. 9:28Also, a big thank you to Bryan Drexler for co-sponsoring this episode.
150. 9:32Crash Course Anatomy and Physiology is filmed in the Doctor Cheryl C. Kinney Crash Course
151. 9:36Studio. This episode was written by Kathleen Yale, the script was edited by Blake de Pastino,
152. 9:40and our consultant, is Dr. Brandon Jackson. It was directed and edited by Nicole Sweeney,
153. 9:45the sound design was by Michael Aranda, and our graphics team is Thought Cafe.