Homeostasis

negative feedback loop

*Most processes in the body are controlled by* *the resulting action will always be the opposite direction of the stimulus.*

positive feedback loop

A stimulus reinforced to continue in the same direction until a climatic event occurs. Result is to increase the activity (rather than stopping it) -Occurs less frequently than

Hypothalamus

According to Model 2, what portion of the brain contains sensors that monitor body temperature?

A **Positive feedback** mechanism would be best for amplifying a condition that is advantageous because in **Positive feedback** the **response** **increases** the **stimulus**

Applying feedback Mechanisms in Model 1 to the human body, which would be most useful for amplifying a condition that is advantageous?

When the body is too warm the **stimulus** is the rising temperature and the **response** is sweating and diverting blood to the surface of the body.

Consider the feedback loop that cools the body when it is too warm. Identify the "stimulus" and the "response" in that feedback loop.

set point

The variable is maintained within a normal level.

Negative feedback, Positive Feedback

What are the names of the two types of feedback mechanism illustrated in Model 1?

Oxytocin

What hormone, released from the hypothalamus in the brain, increases the intensity of contractions?

The **response** will continue to **increase** the stimulus (and vice versa) until the baby is pushed so hard against the cervix that it exits the body. At that point, there is no more response (release of oxytocin and ensuing contractions).

What will eventually stop the stimulus and thus stop the childbirth feedback loop?

As the intensity of contractions increases, the push of the baby's head against the cervix (stimulus) **increases.**

When the intensity of contractions increases, will the stimulus increase or decrease?

Stimulus

a change in the variable (physical or chemical) such as a change in light, temperature, chemicals, or stretch in muscle.

**Thermoregulation**

how the body regulates it's internal temperature.

To cool itself, the body increases sweat production and it dilates the blood vessels to the skin so that blood moves towards the skin and loses heat to outside the body.

According to Model 2, What are two mechanisms the body uses to cool itself?

To Heat itself, the body shivers (which generates heat through muscle contraction) and it also diverts blood away from the skin and holds it deeper in the body so that less heat is radiated from the surface of the body.

According to Model 2, what are 2 mechanisms the body uses to heat itself?

The **stimulus** is the baby's head against the cervix, which stretches the cervix. The **response** is release of oxytocin (leading to uterine contractions)

According to Model 3, what is the **stimulus** and what is the **response** during childbirth?

Because positive feedback loops do not negate the stimulus (**they amplify it**) they would not be able to keep internal conditions in the body the same over time. As an example, if positive feedback regulated the body temperature, an increase in body temperature would lead to further increase in body temperature (until you started on fire or something). It wouldn't lead to a decrease in body temperature. Conversely, a decrease in body temperature would lead to further decreases in body temperature would lead to further decreases in body temperature until you died of hypothermia. **Positive feedback** (because it amplifies the stimulus rather than negating it) does not help you maintain a stable environment in your body.

Consider a state of homeostasis-maintaining conditions in the body within certain limits. Would a positive feedback loop ever be helpful in maintaining homeostasis? Justify your reasoning.

In the feedback loop that heats the body when it is too cool the **stimulus ** is **decreasing** temperature and the **response** is shivering and blood diversion away from the skin.

Consider the feedback loop that heats the body when it is too cold. Identify the "stimulus" and the "response" in that feedback loop.

**Stimulus**a thing that rouses activity or energy in someone or something; a spur or incentive. **Signal**a gesture, action, or sound that is used to convey information or instructions **Response** A reaction to something

Define words below as they are used in everyday language: Stimulus, signal, response

The puppy chasing the ball is the **stimulus** and you rubbing the head and saying "good job" is the **response**

Fill in the blank: In the scenario given in the previous question, the puppy chasing the ball is the (stimulus/response), and you rubbing the head and saying good job is the (stimulus/response)

In the scenario given in the previous question, the puppy urinating on the couch is the **stimulus**, and you saying "No, bad dog!" is the **response**

Fill in the blank: In the scenario given in the previous question, the puppy urinating on the couch is the (stimulus/response) and you saying "No, bad dog!" is the (stimulus/response)

a) they both work through stimulus , signal response b) they both are cyclical c) they both are feedback mechanisms

Identify at least 3 similarities in the two types of feedback mechanisms in Model 1

**Stimulus** chemical signal; **response** platelets adhere to form a plug; **Positive feedback**

Identify the stimulus/response and state whether it is positive or negative feedback: When human tissue, such as the skin or a blood vessel, is torn or cut, the cells near the damage send out a chemical signal that activates platelets in the vicinity. As the platelets begin to form a plug, they release more chemical signals to attract more platelets and other clotting chemicals to the area, until bleeding is stopped

**Stimulus** decrease in pH; **Response** increased respiration/heart rate; **Negative Feedback**

Identify the stimulus/response and state whether it is positive or negative feedback: When a human increases physical activity, the amount of fuel burned in its cells also increases, which in turn increases the concentration of carbon dioxide dissolved in the blood. The carbon dioxide reacts with water in the blood to make a weak acid, which lowers the pH of the blood. Sensory cells in an area of the brain known as the medulla detect this drop in pH and send signals to the muscles used for breathing to increase respiration, and to the heart ot increase the rate at which it is beating. This will clear the carbon dioxide from the bloodstream.

**Stimulus** decrease pH; **Response** releases of ADH and **decrease** in urine production; **Negative feedback**

Identify the stimulus/response and state whether it is positive or negative feedback: When a person has not taken in sufficient water, they become dehydrated. This may cause a loss of blood pressure, which will trigger the release of antidiuretic hormone (ADH) from the hypothalamus and pituitary glands in the brain. This hormone signals the kidney to decrease the amount of urine produced, so that more water stays in the blood, helping to bring the blood pressure back to normal levels.

When the **Stimulus** amplifies the **response** and the **response** amplifies the stimulus and this repeats until everything is super intense outside of normal ranges, this is**positive feedback**. "Vicious cycles" are based on positive feedback. Here's an example: Let's suppose you have 2 friends that don't get along. Friend 1 insults friend 2, and so friend 2 insults back. This angers friend 1, who further insults friend 2. Each becoming angrier and angrier insulting more and more until things spiral out of control and we've got a vicious cycle that is amplifying itself. In a negative feedback cycle, friend 2 would simply walk away or turn the other cheek after receiving an insult from friend 2 and this negative feedback would prevent the vicious cycle from even beginning. It would negate the situation instead of amplifyig it.

Identify the stimulus/response and state whether it is positive or negative feedback: You've probably hear the saying "a vicious cycle" used before. Do you think this relates more to positive or negative feedback loops? Explain your answer.

The puppy would likely chase the ball again because he enjoyed being praised and having his head rubbed.

Imagine that you have just gotten a puppy. In the course of playing with the puppy you throw the ball and the puppy chases after it. You then say, "Good job!" and rub the puppy's head to show him he did what you wanted him to do. Is the puppy likely to chase the ball the next time you throw it? Justify your reasoning

childbirth is a **positive feedback** loop because the response amplifies or encourages the stimulus.

Is childbirth an example of a positive or negative feedback system? Justify your answer.

The feedback loop that cools the body when it is too warm is an example of **negative feedback loop**. The reason is the **stimulus** (rising temperature) is negated- stopped by the **response** (sweating, blood diversion to the skin)

Is the feedback loop that cools the body when it is too warm an example of positive or negative feedback? Justify your reasoning

This is an example of **positive feedback** because the response **increases** the **stimulus**

Is this scenario an example of negative or positive feedback? Justify your reasoning. You must use the words "stimulus" and "response" in your answer for credit.

The puppy would not be likely to urinate on the couch again because he didn't enjoy being reprimanded or placed outside.

Later that day, your puppy urinates on the couch. You then say, "No bad dog!" and place the puppy outside. Is the puppy likely to urinate on the couch again? Justify your reasoning

A **Negative feedback** mechanism would be best for either **stopping** or limiting a situation, as the response **decreases** the stimulus.

Which feedback mechanism from Model 1 would be most useful for **stopping** a condition that is either detrimental or needs to be limited to certain levels?

The puppy urinating on the couch scenario is an example of **negative feedback**, because the response **decreased or stopped** the **stimulus*

Would the puppy urinating on the couch scenario be an example of negative or positive feedback? You must justify you reasoning using the words stimulus and response in your answer.

Homeostasis

the ability of an organism to maintain a consistent internal environment, or "steady state", in response to changing internal or external conditions.

Receptor

the body structure that detects changes in a variable in which is a substance or process that is regulated. * typically consists of sensory neurons (nerve cells)*

control center

the structure that both interprets input from the receptor and initiates changes through the effector. **generally the nervous system or endocrine system**

Effector

the structure that brings about the change to alter the stimulus (effector causes the effect).