Homeostasis – negative and positive feedback (thermoreg… — Transcript

Overview of homeostasis focusing on negative and positive feedback using thermoregulation and lactation examples.

Key Takeaways

Negative feedback maintains internal stability by reversing changes.
Positive feedback amplifies responses and is less common in homeostasis.
Thermoregulation involves vasodilation, sweating, vasoconstriction, and shivering controlled by the hypothalamus.
Lactation is a positive feedback loop involving prolactin and oxytocin triggered by baby suckling.
Homeostasis is a dynamic equilibrium, not a fixed state.

Summary

Homeostasis is the maintenance of stable internal conditions despite external environmental changes.
Negative feedback is the primary mechanism for homeostasis, reversing changes to maintain stability.
Thermoregulation example: the hypothalamus controls body temperature via vasodilation, sweating, vasoconstriction, and shivering.
Negative feedback stops heat loss or heat production once normal body temperature is restored.
Positive feedback amplifies physiological changes rather than negating them.
Lactation is an example of positive feedback where suckling stimulates prolactin and oxytocin release to produce and eject milk.
Positive feedback loops can be risky as they drive changes away from homeostatic setpoints.
Walter Cannon coined the term homeostasis to describe internal stability.
Homeostasis involves dynamic equilibrium within a limited range, not absolute constancy.
The video explains the difference between negative and positive feedback with clear physiological examples.

Full Transcript — Download SRT & Markdown

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In this video, we're gonna talk about homeostasis. This is an overview. Although the environment around an organism changes, the organism maintains relatively stable internal conditions. This ability to maintain internal stability is called homeostasis. For example, if a person stands in a cold

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wintry night or hot Sub-Saharan Africa, the person is able to maintain a normal internal body temperature between 36 to 37 degrees or 97 to 99° Fahrenheit through homeostasis. The main mechanism to maintain a homeostatic environment is through negative feedback. Negative

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feedback is where the body senses change and activates mechanisms that negate or reverse it. The term homeostasis was coined by an American physiologist, Walter Cannon, to explain this tendency to maintain internal stability of the body. However, the internal stability that is

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maintained is not absolute. Rather, the internal state is maintained between a limited range, and it is useful to use the term dynamic equilibrium. A good example of this is the internal body temperature, which is usually maintained between 36 degrees and 37 degrees. For

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example, again, the main mechanism to maintain a homeostatic environment is through negative feedback. So let's look at how the body maintains normal body temperatures using negative feedback. The stimulus is, for example here, an increase in body temperature because perhaps the

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person is exercising or it's super hot outside. This increase in body temperature will be detected by the brain, which is the control center, and will activate mechanisms to lose heat to keep your body cool. This is done via

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the hypothalamus. The hypothalamus will send signals out that will cause vasodilation, which is widening of the vessels. When blood vessels of the skin dilate, warm blood flows closer to the body surface and loses heat to the surrounding air. If this is not enough to

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return your temperature to normal, sweating occurs through activation of sweat glands. Sweating is the evaporation of water from the skin and has a powerful cooling effect. Now you can imagine when it is hot outside, you are sweating and appear

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flushed from the dilation of the superficial blood vessels in the skin. All these mechanisms are causing the body to reduce the body's internal temperature. When the body's internal temperature returns to normal, the brain's hypothalamus heat loss center shuts off, and this is done through

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negative feedback. The negative feedback essentially stops the hypothalamus heat loss center because the body does not need to lose any more heat. Conversely, if the stimulus causes a decrease in body temperature, such as the cold weather outside, let us just say

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your body temperature drops much below 36 degrees Celsius, the brain, which is the control center, activates heat-conserving mechanisms. The first to be activated is vasoconstriction, a narrowing of the blood vessels in the skin, which serves to retain warm blood deeper in your body

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and minimize heat loss from the skin. If this is not enough, the brain activates shivering, muscle contractions, tremors that will generate heat. These mechanisms increase body temperature, and when the body temperature is back to normal, there will be a negative feedback to the brain

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telling it to shut off the heat-promoting centers so body temperature will increase, and the hypothalamus heat-promoting center will shut off. So that was an example of how negative feedback works to maintain internal stability, and we used temperature

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internal body temperatures as an example. While negative feedback is the main driver of homeostasis, there is also something called positive feedback, which is a self-amplifying cycle in which a physiological change leads to an even greater change in the same direction. In

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a way, positive feedback tries to maintain homeostasis but often with a price. Let's take a look at a positive feedback example, which is a woman breastfeeding. Lactation: a baby suckling on the mother's nipple will activate mechanoreceptors in the nipple. The

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receptors will send signals to the brain via neurons, which are the brain cells, telling the brain's pituitary gland to release two important hormones, prolactin and oxytocin. Prolactin is a hormone which stimulates milk production in the breast tissue, while oxytocin is a hormone which

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stimulates muscle contraction, smooth muscle contraction of the breast, allowing the milk produced to be ejected out of the nipple. The milk ejected is taken by the baby, and the whole process continues. The baby suckling will activate mechanoreceptors, which will

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stimulate the brain. This is a positive feedback loop because nothing is being suppressed here; it is amplifying a response. As you can see, positive feedback is amplifying a response in the same direction, whereas negative feedback negates the response to maintain

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internal stability. Positive feedback can be dangerous because of this self-amplifying capability, which can quickly change the internal state of the body to something far from its homeostatic setpoint. So I hope you enjoyed this video on homeostasis. We looked at the

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two main mechanisms. So I hope you enjoyed this video on homeostasis. The main mechanism of homeostasis is through negative feedback, but also there's something called positive feedback, which is important to know. Thank you for watching.

Topics:homeostasisnegative feedbackpositive feedbackthermoregulationlactationhypothalamusbody temperatureprolactinoxytocinphysiology

Frequently Asked Questions

What is homeostasis and why is it important?

Homeostasis is the process by which organisms maintain stable internal conditions despite changes in the external environment. It is important because it allows the body to function optimally within a narrow range of conditions.

How does negative feedback regulate body temperature?

Negative feedback regulates body temperature by detecting changes via the hypothalamus and activating mechanisms like vasodilation and sweating to cool down or vasoconstriction and shivering to warm up, restoring normal temperature.

What role does positive feedback play in lactation?

In lactation, positive feedback occurs when a baby suckles, activating mechanoreceptors that signal the brain to release prolactin and oxytocin, which stimulate milk production and ejection, amplifying the response until feeding stops.

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