Homeostasis and Negative/Positive Feedback — Transcript

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1. 0:06Did you know, just sitting here right now, you’re doing something absolutely remarkable?
2. 0:10Well you…your cells, tissues, organs, organ systems---yep we just leveled up those biological
3. 0:17levels of organization--- they’re all working towards something called homeostasis.
4. 0:22It’s a state of balance.
5. 0:24Yes, homeostasis means many things in your body: for example, that your blood stays within
6. 0:29a certain pH level range.
7. 0:31It means your blood glucose remains within a certain range.
8. 0:34It means your internal body temperature stays within a certain range.
9. 0:38See, we’ve mentioned the major body systems before, and that they work together---and
10. 0:42today we’re going to talk about HOW they work together---using something called positive
11. 0:46and negative feedback.
12. 0:48And, also, how this relates to homeostasis.
13. 0:52So many years ago, I had a pet bearded dragon.
14. 0:56Her name was Debbie and she was the best lizard ever.
15. 0:58Debbie used to sit on our couch with me when I’d watch TV.
16. 1:02And she loved to have her chin scratched.
17. 1:04I even got her a bearded dragon leash so I could take her outside…yeah, they make those…anyway,
18. 1:09Debbie loved her heat lamp.
19. 1:11She would sit under the heat lamp on her rock.
20. 1:13And when she got too hot, she would get off her rock and out of the heat lamp range and
21. 1:17go somewhere else.
22. 1:19She had a huge enclosure too because, I wanted Debbie to be a happy lizard, so she could
23. 1:23find an ideal temperature.
24. 1:24Well why all this talk about Debbie?
25. 1:26Well, Debbie is an example of an animal that some people refer to as cold-blooded.
26. 1:32Or a fancier term, ectotherm.
27. 1:35We actually like the fancier term a bit better though, because her blood isn’t necessarily
28. 1:39cold.
29. 1:40Her body temperature can fluctuate with the environment
30. 1:44But not you.
31. 1:45You are warm-blooded, or the fancier term, an endotherm.
32. 1:49Your body works hard to keep the internal temperature it keeps.
33. 1:53It’s also a beautiful example of something called negative feedback.
34. 1:57Before we define it---let us show you this example.
35. 2:00Say you are in an environment that is very hot.
36. 2:03Like…being outside in the Texas summer heat.
37. 2:06That’s typically hot.
38. 2:07Thanks to nerves which can act as sensors, the brain notices this.
39. 2:11It will send signals to counteract this variable.
40. 2:15Sweat glands do what they do best: sweat!
41. 2:18Heat is lost as that sweat evaporates off of your skin.
42. 2:21You may have some redness too---that’s because of your blood vessels are getting wider (dilating)---in
43. 2:26order to help get rid of that heat.
44. 2:28The result, whether you realize it or not, helps you lower your body temperature.
45. 2:32But wait!
46. 2:34What if you now go inside and the AC is blasting.
47. 2:37You will stop sweating.
48. 2:38You may even shiver.
49. 2:40The muscle contractions of shivering can generate heat.
50. 2:43And those blood vessels will now decrease in diameter size (constrict) to help you conserve
51. 2:48the heat because that makes it harder for heat to escape.
52. 2:51Your body temperature can increase then.
53. 2:53This is negative feedback.
54. 2:56So a simplified definition: negative feedback is when some variable triggers a counteracting
55. 3:01response---in order to come back to some set point.
56. 3:05If we consider that this whole thing is actually a negative feedback loop, we can see that
57. 3:10the negative feedback brings the body back to the set point, which in this case, is a
58. 3:15stable temperature. Keeping homeostasis.
59. 3:18Negative feedback is also going on in the regulation of your glucose (your blood sugar).
60. 3:23Ok we’re really simplifiying this here, as we often do, but when glucose (blood sugar)
61. 3:28is too high, one hormone that is released is insulin.
62. 3:32I always imagine insulin as this hormone that makes the cells say, “FEED ME!” because
63. 3:37it has the ability to make cells take in glucose.
64. 3:41On the flip side, if glucose is too low in the blood, a hormone called glucagon can be
65. 3:46released.
66. 3:47This hormone can have many effects and one of them is that it can cause the liver to
67. 3:51release glucose into the blood.
68. 3:53There’s more to the regulation of blood sugar than this but you can see how that’s
69. 3:57negative feedback---you have counteracting responses here in order to keep homeostasis.
70. 4:04So what about positive feedback?
71. 4:07Positive feedback is when, instead of getting a counteracting response to some variable,
72. 4:12you instead intensify the variable.
73. 4:14Positive feedback can be like “more more more” instead of “let’s counteract this.”
74. 4:19The example that always stuck with me when I was a student is the example about the human
75. 4:23human baby being born.
76. 4:25In biology classrooms everywhere, it’s a classic example.
77. 4:28When a human baby is ready to be born, there is pressure on the cervix.
78. 4:32And that pressure and the hormones involved cause contractions of the uterus---because
79. 4:35that’s a big part about how the baby is going to be born.
80. 4:39More release of hormones will equal more contractions and pressure which will cause more release
81. 4:45of hormones.
82. 4:46And more release of hormones will mean more contractions and pressure.
83. 4:51Contractions help get the baby out, but it’s also part of a beautiful illustration of what
84. 4:55positive feedback can do.
85. 4:57So why do we care about feedback?
86. 5:00Other then, you know, the importance of negative feedback in maintaining homeostasis and the
87. 5:05role of positive feedback in many body processes?
88. 5:08Well we also need to understand feedback so we can understand
89. 5:11what is happening when there is a problem in the feedback systems.
90. 5:15One example: perhaps you’ve heard of Type 1 diabetes.
91. 5:19It’s a disorder that can mean that your pancreas, which is an organ that is involved
92. 5:24with making some hormones like insulin, is not working correctly.
93. 5:29Insulin is not produced and, because of that, one issue is that you are not going to be able to get
94. 5:33glucose (the blood sugar) into your cells.
95. 5:37Glucose outside of the cells cannot be used in cellular respiration---the cells need to
96. 5:41take the glucose IN to make ATP energy in cellular respiration.
97. 5:46Therefore, your cells need to be able to take IN the glucose to survive.
98. 5:50So, many Type 1 diabetics need to give themselves insulin and monitor their blood sugar because
99. 5:56the negative feedback may not work as it should.
100. 6:00Well, that’s it for the Amoeba Sisters and we remind you to stay curious!