# data[].attributes.body
The body systems that are involved and interact in childbirth include the endocrine system, muscular system, circulatory system, and reproductive system.

# data[].attributes.body
This is a positive feedback loop because it allows for the body to release the hormone oxytocin in large amounts to help the uterus contract. The contractions get worse which means the body is further from the homeostasis point. In other words, it uses the sensor information from the cervix and allows the body to increase the average bodily means (hormone release) when necessary.

# data[].attributes.body
Dilation of cervix ...The cycle continues in larger amounts until the baby is delivered.

# data[].attributes.body
The hormone oxytocin is sent to the pituitary gland. It is then secreted into the bloodstream and carried to the uterus. Then, the uterus starts contracting, which helps the target.

# data[].attributes.body
Hypothalamus in the brain which receives message from cervix

# data[].attributes.body
Nerve endings are stimulated from pushing

# data[].attributes.body
Homeostasis Point: Non-dilated cervix + Lower levels of hormone Oxytocin

# data[].attributes.attachment_link.readable_text
Cold Stress and the Cold Pressor Test

Karri Haen Whitmer

Maintaining homeostasis requires that the body continuously monitors its internal conditions. From body temperature to blood pressure to levels of certain nutrients, each physiological condition has a particular set point. A set point is the physiological value around which the normal range fluctuates. A normal range is the restricted set of values that is optimally healthful and stable. For example, the set point for normal human body temperature is approximately 37°C (98.6°F). Physiological parameters, such as body temperature and blood pressure, tend to fluctuate within a normal range a few degrees above and below that point. Control centers in the brain and other parts of the body monitor and react to deviations from homeostasis using negative feedback. Negative feedback is a mechanism that reverses a deviation from the set point. Therefore, negative feedback maintains body parameters within their normal range. The maintenance of homeostasis by negative feedback goes on throughout the body at all times.

The human body regulates body temperature through a process called thermoregulation, in which the body can maintain its temperature within certain boundaries, even when the surrounding temperature is very different. The core temperature of the body remains steady at around 36.5-37.5 °C (or 97.7-99.5 °F). In the process of ATP production by cells throughout the body, approximately 60 percent of the energy produced is in the form of heat used to maintain body temperature. Thermoregulation is an example of negative feedback.

The hypothalamus in the brain is the master switch that works as a thermostat to regulate the body's core temperature (Figure 1). If the temperature is too high, the hypothalamus can initiate several processes to lower it. These include increasing the circulation of the blood to the surface of the body to allow for the dissipation of heat through the skin and initiation of sweating to allow evaporation of water on the skin to cool its surface. Conversely, if the temperature falls below the set core temperature, the hypothalamus can initiate shivering to generate heat. The body uses more energy and generates more heat. In addition, thyroid hormone will stimulate more energy use and heat production by cells throughout the body. An environment is said to be thermoneutral when the body does not expend or release energy to maintain its core temperature. For a naked human, this is an ambient air temperature of around 84 °F. If the temperature is higher, for example, when wearing clothes, the body compensates with cooling mechanisms. The body loses heat through the mechanisms of heat exchange.

Mechanisms of Heat Exchange

When the environment is not thermoneutral, the body uses four mechanisms of heat exchange to maintain homeostasis: conduction, convection, radiation, and evaporation. Each of these mechanisms relies on the property of heat to flow from a higher concentration to a lower concentration; therefore, each of the mechanisms of heat exchange varies in rate according to the temperature and conditions of the environment.

Conduction is the transfer of heat by two objects that are in direct contact with one another. It occurs when the skin comes in contact with a cold or warm object. For example, when holding a glass of ice water, the heat from your skin will warm the glass and in turn melt the ice. Alternatively, on a cold day, you might warm up by wrapping your cold hands around a hot mug of coffee. Only about 3 percent of the body's heat is lost through conduction.

Convection is the transfer of heat to the air surrounding the skin. The warmed air rises away from the body and is replaced by cooler air that is subsequently heated. Convection can also occur in water. When the water temperature is lower than the body's temperature, the body loses heat by warming the water closest to the skin, which moves away to be replaced by cooler water. The convection currents created by the temperature changes continue to draw heat away from the body more quickly than the body can replace it, resulting in hypothermia. About 15 percent of the body's heat is lost through convection.

Radiation is the transfer of heat via infrared waves. This occurs between any two objects when their temperatures differ. A radiator can warm a room via radiant heat. On a sunny day, the radiation from the sun warms the skin. The same principle works from the body to the environment. About 60 percent of the heat lost by the body is lost through radiation.

Evaporation is the transfer of heat by the evaporation of water. Because it takes a great deal of energy for a water molecule to change from a liquid to a gas, evaporating water (in the form of sweat) takes with it a great deal of energy from the skin. However, the rate at which evaporation occurs depends on relative humidity-more sweat evaporates in lower humidity environments. Sweating is the primary means of cooling the body during exercise, whereas at rest, about 20 percent of the heat lost by the body occurs through evaporation.

Homeostatic Response to Environmental Temperatures

Humans have a temperature regulation feedback system that works by promoting either heat loss or heat gain. When the brain's temperature regulation center receives data from the sensors indicating that the body's temperature exceeds its normal range, it stimulates a cluster of brain cells referred to as the "heat-loss center." This stimulation has three major effects:

Blood vessels in the skin begin to dilate allowing more blood from the body core to flow to the surface of the skin allowing the heat to radiate into the environment.

As blood flow to the skin increases, sweat glands are activated to increase their output. As the sweat evaporates from the skin surface into the surrounding air, it takes heat with it.

The depth of respiration increases, and a person may breathe through an open mouth instead of through the nasal passageways. This increases heat loss from the lungs.

During acute exposure to cold conditions in the body:
In contrast, activation of the brain's heat-gain center by exposure to cold reduces blood flow to the skin, and blood returning from the limbs is diverted into a network of deep veins (Figure 2). This arrangement traps heat closer to the body core, restricts heat loss, and increases blood pressure. If heat loss is severe, the brain triggers an increase in random signals to skeletal muscles, causing them to contract and producing shivering. The muscle contractions of shivering release heat while using ATP. The brain also triggers the thyroid gland in the endocrine system to release thyroid hormone, which increases metabolic activity and heat production in cells throughout the body.

Activation of the sympathetic nervous system results in system-wide discharge of catecholamine (norepinephrine).

Catecholamine causes systemic arteriolar constriction, increased heart rate and heart contractility. The heart works harder to push blood through the narrowed blood vessels.

Constricted blood vessels in the extremities divert superficial blood flow to the body's core, thus, reducing the radiation or conduction of heat into the environment.

Vasoconstriction increases the resistance to blood flow, and thus, increases blood pressure.

Vasoconstriction leads to a weaker pulse (lower pulse amplitude) in the arteries of the skin, fingers and hand.

In this laboratory, we will use the cold pressor test to evaluate changes in heart rate, pulse amplitude, and arterial oxygen saturation using a pulse oximeter.
Acute cold stress results in activation of the sympathetic nervous system and release of catecholamines (neurotransmitters). The release of neurotransmitter effects the cardiovascular system in a number of ways, including arterial constriction, transient tachycardia, and increased contractility of the heart. Together, these homeostatic changes result in what is called a pressor response, or an increase in blood pressure. The cold pressor test is commonly used in the clinical setting to evaluate the function of the sympathetic nervous system. In the cold pressor test, subjects immerse their hand or forearm in ice water, and their cardiovascular response is measured.

Pulse oximeters indirectly estimate the arterial oxygen saturation and report it as the oxygen saturation (SpO2) of the subject's arterial blood. SpO2 is reported as a percentage of oxygenated hemoglobin. Normal pulse oximetry values typically range from 97-100%.

Cold pressor response experiment:
In preparation for lab, can you write an IF/THEN hypothesis for testing the cold pressor response in men and women?
There are several hypotheses that could be testing In this laboratory. For example, we may test whether males and females have a different cold pressor response, or we may test whether the pressor response is the same in the submerged versus the non-submerged hand. After collecting the data, you will enter it into an excel file at the TA's bench for a class-wide or course-wide statistical analysis.

Lab activity highlights

We will use iWorx with LabScribe to interpret pulse amplitude, heart rate and SpO2.

Subjects should not wear nail polish, artificial nail coverings, hand or wrist jewelry during the experiment.

Subjects must wear short sleeves or sleeves that can be rolled up above the elbow.

All subjects will participate in either "Baseline/Condition 1" or "Baseline/Condition 2" but not both.

All subjects will submerge their LEFT forearm in the experiments.

Because the pulse oximeter works by detecting pulsation of blood vessels, subjects should sit quietly and motionless during the experiment. Other movements or vibrations could confound the pulse oximeter readings.

Getting Started

Turn on the iWorx unit at the switch on the back of the box

Log into your account and click the Folder icon in the lower left task bar

Click "This PC" in the left side task bar

Double click Biol 256L Course Materials P-Drive under "Network Locations"

Double click the "Week4_ColdPressor" settings file

Place the pulse oximeter on the middle finger of the left (condition 1) or right (condition 2) hand as shown in the figure below.

You are now ready to start the experiment.

EXPERIMENT: Effects of Cold Pressor Test on Cardiovascular Functioning

IMPORTANT: This experiment requires half of the subjects to participate in Baseline/Condition 1 and half of the subjects to participate in Baseline/Condition 2. At your lab table, assign each student a condition before starting the experiment.

CONTROL/CONDITION 1: Outfit the middle finger of the left hand with the pulse oximeter. Be prepared to submerge the left forearm in ice water at the one-minute mark.

CONTROL/CONDITION 2: Outfit the middle finger of the right hand with the pulse oximeter. Be prepared to submerge the left forearm in ice water at the one-minute mark.

PART I. Procedure

Check the sensor: click on the red Record

Click on the AutoScale button at the upper task bar. Your recording should look like the traces seen below in Figure 5. If the data does not appear as shown, slightly adjust the oximeter on the finger.

Note the location of the Time in the upper right corner of the window (Fig. 5b). In the figure, the time reads "one minute and twenty-two seconds." You will keep track of the time of the data recording with this timer on the Labscribe window.

When the signals being recorded are suitably displayed, stop the recording and open a new file.

As the subject sits quietly (without moving) record baseline data for one minute.

At exactly the one-minute mark, submerge the left forearm in the ice water. DO NOT put the hand with instrumentation in the water. Remain as still as possible!

Record the data for at least an additional 35 seconds (you may record more).

Stop recording.

You may dry your arm off and warm it on a heating pad. You are done serving as subject after a single exposure to the ice bath.

Save the data file to the computer. Put the subject's name and Week 4 in the title.

This data analysis applies to both the baseline recording and to Condition 1 or 2. For baseline data, start at the very beginning of the recording and find the correct data by scrolling and using the timer on the main window.
PART II. Data Analysis

For the experimental data (condition 1 or 2), start data analysis at the 1.00 mark and scroll to 1.05 (five seconds), 1.10 (ten seconds), 1.20 (twenty seconds) and 1.30 (thirty seconds).

To begin the data analysis:

Calibrate the pulse channel.

Set the time in the Display time window to 120 seconds and then click the Autoscale button in the channel window.

Click on the P. Rate (Pulse) on the Heart Rate channel and select Setup Function

When the window opens drag the blue lines so that the top line is just below the peaks of the ALL the pulse waves and the bottom line is slightly below the blue line (see figure below). It is very important that you see ALL of your data so that you can properly align the blue lines. Click OK.

Analysis

Use the Display Time icon to adjust the Display Time of the Main window to show approximately ten complete Pulse cycles on the Main window.

Scroll through the recording to view exemplary pulse waves at these intervals during data recording: 5 seconds, 10 seconds, 20 seconds and 30 seconds

Start at a pulse wave at around 5 seconds of data recording and click the double cursor icon and place the cursors as follows:

To measure the pulse wave amplitude, place one cursor on the baseline that precedes the pulse wave and the second cursor on the peak of the pulse wave. The value for V2-V1 on the Pulse channel is this amplitude. Determine the pulse amplitude V2-V1 for the four pulse waves at the designated times and record the results in your lab report.

To find the heart rate, select the one cursor icon and place the single cursor at the plateau of the of a heart rate trace on the Heart Rate channel. See the orange cursor in the picture below. Record the value in BPM on your lab report for heart rate data collected at approximately 5s, 10s, 20s and 30s.

To find the SpO2, place cursor on the data at the 30 second mark of recording. Usually this line is completely flat.

Record the SpO2 percent, shown on the O2 Saturation channel, in your lab report.

After recording the data in your lab report, open a new file for the next student.

Students may be asked to submit these data for statistical analysis:

Note: please submit your sex (M or F) and age with your data.

1. Baseline avg. heart rate

2. Baseline avg. pulse wave amplitude

3. Condition 1 avg. cold pressor heart rate

4. Condition 1 avg. cold pressor pulse wave amplitude

5. Condition 2 avg. cold pressor heart rate

6. Condition 2 avg. cold pressor pulse wave amplitude

Please cite:
Citations

Haen Whitmer, K.M. (2021). A Mixed Course-Based Research Approach to Human Physiology. Ames, IA: Iowa State University Digital Press. https://iastate.pressbooks.pub/curehumanphysiology/

# data[].attributes.attachment_link.title
A Mixed Course-Based Research Approach to Human Physiology

# data[].attributes.attachment_link.description
Cold Stress and the Cold Pressor Test Karri Haen Whitmer Maintaining homeostasis requires that the body continuously monitors its internal conditions. From body temperature to blood pressure to levels of certain nutrients, each physiological condition has a particular set point. A set point is the physiological value around which the normal range fluctuates.

# data[].attributes.body
This is a negative feedback loop because temperature regulation prevents the body from going above or below the average temperature and is necessary for homeostasis.

# data[].attributes.body
Signals are sent to blood cells for it to flow differently, and to the skin for pores to open or close

# data[].attributes.attachment_link.readable_text
Page ID

17075

1. What is Homeostasis?

1. Set Point and Normal Range

2. Maintaining Homeostasis

2. Negative Feedback

1. Body Temperature

2. Cooling Down

3. Heating Up

4. Blood Glucose

3. Positive Feedback

1. Blood Clotting

2. Childbirth

4. When Homeostasis Fails

5. Summary

6. Review

7. Explore More

Steady as She Goes

This device looks simple, but it controls a complex system that keeps a home at a steady temperature. The device is an old-fashioned thermostat. The dial shows the current temperature in the room and also allows the occupant to set the thermostat to the desired temperature. A thermostat is a commonly cited model of how living systems, including the human body, maintain a steady state called homeostasis.

Figure \(\PageIndex{1}\): Thermostat for a building. (CC BY-SA4.0; Vincent de Groot via Wikimedia.org).

What is Homeostasis?

Homeostasis is the condition in which a system such as the human body is maintained in a more-or-less steady state. It is the job of cells, tissues, organs, and organ systems throughout the body to maintain many different variables within narrow ranges that are compatible with life. Keeping a stable internal environment requires continuous monitoring of the internal environment and constantly making adjustments to keep things in balance.

Set Point and Normal Range

For any given variable, such as body temperature or blood glucose level, there is a particular set point that is the physiological optimum value. For example, the set point for human body temperature is about 37 ºC (98.6 ºF). As the body works to maintain homeostasis for temperature or any other internal variable, the value typically fluctuates around the set point. Such fluctuations are normal as long as they do not become too extreme. The spread of values within which such fluctuations are considered insignificant is called the normal range. In the case of body temperature, for example, the normal range for an adult is about 36.5 to 37.5 ºC (97.7 to 99.5 ºF).

Maintaining Homeostasis

Homeostasis is normally maintained in the human body by an extremely complex balancing act. Regardless of the variable being kept within its normal range, maintaining homeostasis requires at least four interacting components: stimulus, sensor, control center, and effector.

1. The stimulus is provided by the variable that is being regulated. Generally, the stimulus indicates that the value of the variable has moved away from the set point or has left the normal range.

2. The sensor monitors the values of the variable and sends data on it to the control center.

3. The control center matches the data with normal values. If the value is not at the set point or is outside the normal range, the control center sends a signal to the effector.

4. The effector is an organ, gland, muscle, or other structure that acts on the signal from the control center to move the variable back toward the set point.

Each of these components is illustrated in Figure \(\PageIndex{2}\). The diagram on the left is a general model showing how the components interact to maintain homeostasis. The diagram on the right shows the example of body temperature. From the diagrams, you can see that maintaining homeostasis involves feedback, which is data that feeds back to control a response. Feedback may be negative, as in the example below, or positive. All the feedback mechanisms that maintain homeostasis use negative feedback. Biological examples of positive feedback are much less common.

Figure \(\PageIndex{2}\): Maintaining homeostasis through feedback requires a stimulus, sensor, control center, and effector. (CC BY-NC 3.0 via CK-12 foundation).

Negative Feedback

In a negative feedback loop, feedback serves to reduce an excessive response and keep a variable within the normal range. Examples of processes controlled by negative feedback include body temperature regulation and control of blood glucose.

Body Temperature

Body temperature regulation involves negative feedback whether it lowers the temperature or raises it (Figure \(\PageIndex{3}\)).

Cooling Down

The human body's temperature regulatory center is the hypothalamus in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the set point, it sets into motion the following responses:

Blood vessels in the skin dilate (vasodilation) to allow more blood from the warm body core to flow close to the surface of the body, so heat can be radiated into the environment.

As blood flow to the skin increases, sweat glands in the skin are activated to increase their output of sweat (diaphoresis). When the sweat evaporates from the skin surface into the surrounding air, it takes the heat with it.

Breathing becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases heat loss from the lungs.

Figure \(\PageIndex{3}\): The hypothalamus plays a major role in temperature regulation. (CC0; ChancroVet via Wikimedia.org).

Heating Up

When the brain's temperature regulatory center receives data that body temperature is lower than the set point, it sets into motion the following responses:

Blood vessels in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body. This reduces heat loss from the surface.

As the temperature falls lower, random signals to skeletal muscles are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.

The thyroid gland may be stimulated by the brain (via the pituitary gland) to secrete more thyroid hormone. This hormone increases metabolic activity and heat production in cells throughout the body.

The adrenal glands may also be stimulated to secrete the hormone adrenaline. This hormone causes the breakdown of glycogen (the carbohydrate used for energy storage in animals) to glucose, which can be used as an energy source. This catabolic chemical process is exothermic, or heat producing.

Blood Glucose

In the control of the blood glucose level, certain endocrine cells in the pancreas called alpha and beta cells, detect the level of glucose in the blood. Then they respond appropriately to keep the level of blood glucose within the normal range.

If the blood glucose level rises above the normal range, pancreatic beta cells release the hormone insulin into the bloodstream. Insulin signals cells to take up the excess glucose from the blood until the level of blood glucose decreases to the normal range.

If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone glucagon into the bloodstream. Glucagon signals cells to break down stored glycogen to glucose and release the glucose into the blood until the level of blood glucose increases to the normal range.

Positive Feedback

In a positive feedback loop, feedback serves to intensify a response until an endpoint is reached. Examples of processes controlled by positive feedback in the human body include blood clotting and childbirth.

Blood Clotting

When a wound causes bleeding, the body responds with a positive feedback loop to clot the blood and stop blood loss. Substances released by the injured blood vessel wall begin the process of blood clotting. Platelets in the blood start to cling to the injured site and release chemicals that attract additional platelets. As the platelets continue to amass, more of the chemicals are released and more platelets are attracted to the site of the clot. The positive feedback accelerates the process of clotting until the clot is large enough to stop the bleeding.

Figure \(\PageIndex{4}\): Normal childbirth is driven by a positive feedback loop. Positive feedback causes an increasing deviation from the normal state to a fixed endpoint rather than a return to a normal set point as in homeostasis. (CC BY 4.0; OpenStax via Wikimedia.org).

Childbirth

Figure \(\PageIndex{4}\) shows the positive feedback loop that controls childbirth. The process normally begins when the head of the infant pushes against the cervix. This stimulates nerve impulses, which travel from the cervix to the hypothalamus in the brain. In response, the hypothalamus sends the hormone oxytocin to the pituitary gland, which secretes it into the bloodstream so it can be carried to the uterus. Oxytocin stimulates uterine contractions, which push the baby harder against the cervix. In response, the cervix starts to dilate in preparation for the passage of the baby. This cycle of positive feedback continues, with increasing levels of oxytocin, stronger uterine contractions, and wider dilation of the cervix until the baby is pushed through the birth canal and out of the body. At that point, the cervix is no longer stimulated to send nerve impulses to the brain, and the entire process stops.

When Homeostasis Fails

Homeostatic mechanisms work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail. When they do, homeostatic imbalance may result, in which cells may not get everything they need or toxic wastes may accumulate in the body. If homeostasis is not restored, the imbalance may lead to disease or even death. Diabetes is an example of a disease caused by homeostatic imbalance. In the case of diabetes, blood glucose levels are no longer regulated and may be dangerously high. Medical intervention can help restore homeostasis and possibly prevent permanent damage to the organism.

Normal aging may bring about a reduction in the efficiency of the body's control systems. This makes the body more susceptible to disease. For example, older people may have a harder time regulating their body temperature. This is one reason they are more likely than younger people to develop serious heat-induced illnesses such as heat stroke.

Feature: My Human Body

Diabetes is diagnosed in people who have abnormally high levels of blood glucose after fasting for at least 12 hours. A fasting level of blood glucose below 100 is normal. A level between 100 and 125 places you in the pre-diabetes category, and a level higher than 125 results in a diagnosis of diabetes.

Of the two types of diabetes, type 2 diabetes is the most common, accounting for about 90 percent of all cases of diabetes in the United States. Type 2 diabetes typically starts after the age of 40. However, because of the dramatic increase in recent decades in obesity in younger people, the age at which type 2 diabetes is diagnosed has fallen. Even children are now being diagnosed with type 2 diabetes. Today, about 30 million Americans have type 2 diabetes, and another 90 million have pre-diabetes.

You are likely to have your blood glucose level tested during a routine medical exam. If your blood glucose level indicates that you have diabetes, it may come as a shock to you because you may not have any symptoms of the disease. You are not alone, because as many as one in four diabetics do not know they have the disease. Once the diagnosis of diabetes sinks in, you may be devastated by the news. Diabetes can lead to heart attacks, strokes, blindness, kidney failure, and loss of toes or feet. The risk of death in adults with diabetes is 50 percent greater than it is in adults without diabetes, and diabetes is the seventh leading cause of death of adults. In addition, controlling diabetes usually requires frequent blood glucose testing, watching what and when you eat, and taking medications or even insulin injections. All of this may seem overwhelming.

The good news is that changing your lifestyle may stop the progression of type 2 diabetes or even reverse it. By adopting healthier habits, you may be able to keep your blood glucose level within the normal range without medications or insulin. Here's how:

Lose weight. Any weight loss is beneficial. Losing as little as seven percent of your weight may be all that is needed to stop diabetes in its tracks. It is especially important to eliminate excess weight around your waist.

Exercise regularly. You should try to exercise five days a week for at least 30 minutes. This will not only lower your blood sugar and help your insulin work better; it will also lower your blood pressure and improve your heart health. Another bonus of exercise is that it will help you lose weight by increasing your basal metabolic rate.

Adopt a healthy diet. Decrease your consumption of refined carbohydrates such as sweets and sugary drinks. Increase your intake of fiber-rich foods such as fruits, vegetables, and whole grains. About a quarter of each meal should consist of high-protein foods, such as fish, chicken, dairy products, legumes, or nuts.

Control stress. Stress can increase your blood glucose and also raise your blood pressure and risk of heart disease. When you feel stressed out, do breathing exercises or take a brisk walk or jog. Also, try to replace stressful thoughts with more calming ones.

Establish a support system. Enlist the help and support of loved ones as well as medical professionals such as a nutritionist and diabetes educator. Having a support system will help ensure that you are on the path to wellness and that you can stick to your plan.

Summary

Homeostasis is the condition in which a system such as the human body is maintained in a more-or-less steady state. It is the job of cells, tissues, organs, and organ systems throughout the body to maintain homeostasis.

For any given variable, such as body temperature, there is a particular set point that is the physiological optimum value. The spread of values around the set point that is considered insignificant is called the normal range.

Homeostasis is generally maintained by a negative feedback loop that includes a stimulus, sensor, control center, and effector. Negative feedback serves to reduce an excessive response and to keep a variable within the normal range. Negative feedback loops control body temperature and the blood glucose level.

Positive feedback loops are not common in biological systems. Positive feedback serves to intensify a response until an endpoint is reached. Positive feedback loops control blood clotting and childbirth.

Sometimes homeostatic mechanisms fail, resulting in homeostatic imbalance. Diabetes is an example of a disease caused by homeostatic imbalance. Aging can bring about a reduction in the efficiency of the body's control system, making the elderly more susceptible to disease.

Review

1. What is homeostasis?

2. Define the set point and normal range for physiological measures.

3. Identify and define the four interacting components that maintain homeostasis in feedback loops.

4. Compare and contrast negative and positive feedback loops.

5. Explain how negative feedback controls body temperature.

6. Give two examples of physiological processes that are controlled by positive feedback loops.

7. A negative feedback loop:
A. brings a variable's level back to a normal range

B. can lower, but not raise, body temperature

C. is the type of feedback involved in blood clotting

D. A and B

8. a. During breastfeeding, the stimulus of the baby sucking on the nipple increases the amount of milk produced by the mother. The more sucking, the more milk is usually produced. Is this an example of negative or positive feedback? Explain your answer.

b. What do you think might be the evolutionary benefit of the milk production regulation mechanism described in part a?

9. Explain why homeostasis is regulated by negative feedback loops, rather than positive feedback loops.

10. A set point is usually:

A. the top of a normal range

B. the bottom of a normal range

C. in the middle of a normal range

D. the point at which changes can no longer occur

11. The level of a sex hormone, testosterone (T), is controlled by negative feedback. Another hormone, gonadotropin-releasing hormone (GnRH), is released by the hypothalamus of the brain, which triggers the pituitary gland to release luteinizing hormone (LH). LH stimulates the gonads to produce T. When there is too much T in the bloodstream, it feeds back on the hypothalamus, causing it to produce less GnRH. While this does not describe all the feedback loops involved in regulating T, answer the following questions about this particular feedback loop.

a. What is the stimulus in this system? Explain your answer.

b. What is the control center in this system? Explain your answer.

c. What is the pituitary considered in this system: stimulus, sensor, control center, or effector? Explain your answer.

Explore More

You can learn how the body maintains homeostasis in its water content by watching this video:

Check out this video on the comparisons between positive and negative feedback:

Back to top

There are no recommended articles.

# data[].attributes.attachment_link.description
Page ID 17075 What is Homeostasis? Set Point and Normal Range Maintaining Homeostasis Negative Feedback Body Temperature Cooling Down Heating Up Blood Glucose Positive Feedback Blood Clotting Childbirth When Homeostasis Fails Summary Review Explore More Steady as She Goes This device looks simple, but it controls a complex system that keeps a home at a steady temperature.

# data[].attributes.body
The hypothalamus located in the brain initiates processes that will raise or lower body temperature

(Pores open to allow sweating, Blood flow goes to surface, pores close and hair strands stand to preserve heat)

# data[].attributes.attachment_link.readable_text
Learning Outcomes

Explain how different organ systems relate to one another to maintain homeostasis

Each organ system performs specific functions for the body, and each organ system is typically studied independently. However, the organ systems also work together to help the body maintain homeostasis.

Water Levels

For example, the cardiovascular, urinary, and lymphatic systems all help the body control water balance. The cardiovascular and lymphatic systems transport fluids throughout the body and help sense both solute and water levels and regulate pressure. If the water level gets too high, the urinary system produces more dilute urine (urine with a higher water content) to help eliminate the excess water. If the water level gets too low, more concentrated urine is produced so that water is conserved.

Internal Temperatures

Similarly, the cardiovascular, integumentary (skin and associated structures), respiratory, and muscular systems work together to help the body maintain a stable internal temperature. If body temperature rises, blood vessels in the skin dilate, allowing more blood to flow near the skin's surface. This allows heat to dissipate through the skin and into the surrounding air. The skin may also produce sweat if the body gets too hot; when the sweat evaporates, it helps to cool the body. Rapid breathing can also help the body eliminate excess heat. Together, these responses to increased body temperature explain why you sweat, pant, and become red in the face when you exercise hard. (Heavy breathing during exercise is also one way the body gets more oxygen to your muscles, and gets rid of the extra carbon dioxide produced by the muscles.)

Conversely, if your body is too cold, blood vessels in the skin contract, and blood flow to the extremities (arms and legs) slows. Muscles contract and relax rapidly, which generates heat to keep you warm. The hair on your skin rises, trapping more air, which is a good insulator, near your skin. These responses to decreased body temperature explain why you shiver, get "goose bumps," and have cold, pale extremities when you are cold.

Case Study: Fevers

So what happens when you have a fever? Does this mean your body is unable to maintain its homeostasis, in the same way your house will get too hot if your air conditioner is broken?

In extreme cases, a fever can be a medical emergency; but fever is an adaptive physiological response of our body to certain infectious agents. Certain chemicals called pyrogens will trigger your hypothalamus to shift the set point to a higher value. This is more like you programming the thermostat in your house to a higher temperature to save energy on a hot day when you are not going to be home during the day. These pyrogens can come from microorganisms that infect you, or they can be produced by your body cells in response to an infection of some sort.

Practice Questions

1. As the level of pyrogens increases in your blood, and the set point resets higher, chemoreceptors now stimulating the hypothalamus are responding to ________ as the variable, rather than thermoreceptors responding to body temperature as the variable.

1. temperature

2. pyrogens

3. heart rate

4. blood pressure

2. The control center is the _________.

1. skeletal muscle

2. sweat glands

3. blood vessels

4. hypothalamus

3. Because the set point has been increased, you now feel cold even though you have what would normally be a body temperature within the healthy range. This produces the "chills" you feel when you get a fever. In response, the hypothalumus will work to increase body temperature. Which response will do this?

1. The hypothalamus will stimulate sweat glands and dilating blood vessels as effectors to cool off the body.

2. The hypothalamus will stimulate skeletal muscles to shiver and constricting blood vessels.

Although the evidence is only indirect, fever is believed to enhance the body's immune response. The increased temperature may actually impair the replication of infecting bacteria and viruses that are adapted to survive best at your normal homeostatic body temperature range. This can give your immune cells a chance to destroy the microorganisms before they can rapidly multiply and spread in the body. There is also some indirect evidence that increased body temperature slightly modifies several metabolic reactions in ways that also allow the immune system to function more efficiently.

Practice Questions

1. Once the new higher set point is reached, the thermoreceptors stimulate the _________ as the control center.

1. skeletal muscle

2. sweat glands

3. blood vessels

4. hypothalamus

2. In response, the sweat glands and blood vessels (effectors) are stimulated to _________.

1. secrete sweat for evaporation and dilate vessels for increased heat loss from blood near the surface of the skin.

2. shiver to create heat and constrict vessels to conserve heat by keeping blood away from the surface of the skin.

Unfortunately during some infections, pyrogen levels come in "waves." This adjusts your temperature set point up and down. When pyrogen levels dip, you get the other part of the fever experience: "the sweats" and feeling flushed. As long as the pyrogen levels continue to increase and decrease you will feel like you are swinging back and forth.

Practice Question

Once the pyrogen level is reduced because the infection is under control, the ________ (control center) will reset the higher set point to normal.

1. thermoreceptors

2. chemoreceptors

3. hypothalamus

Your body will continue to swing back and forth between the body's normal upper and lower temperature limits, but because it is now within your "normal" temperature range, you probably won't even notice that your body is still at work, maintaining the homoeostasis of this variable.

Practice Question

Patients often get a fever after an operation. Which of the following would not be a reasonable cause of such a response?

1. Tissue trauma from the operation has stimulated body cells to release pyrogens.

2. Despite precautions, some bacteria have infected the person during the operation.

3. The operation has damaged the thermoreceptors

4. Post-operative medications have impacted the immune system, causing the release of pyrogens.

Homeostasis of Ions

Body functions such as regulation of the heartbeat, contraction of muscles, activation of enzymes, and cellular communication require tightly regulated calcium levels. Normally, we get a lot of calcium from our diet. The small intestine absorbs calcium from digested food.

The endocrine system is the control center for regulating blood calcium homeostasis. The parathyroid and thyroid glands contain receptors that respond to levels of calcium in the blood. In this feedback system, blood calcium level is the variable, because it changes in response to the environment. Changes in blood calcium level have the following effects:

When blood calcium is low, the parathyroid gland secretes parathyroid hormone. This hormone causes effector organs (the kidneys and bones) to respond to increase calcium levels. The kidneys prevent calcium from being excreted in the urine. Osteoclasts in bones reabsorb bone tissue and release calcium.

When blood calcium levels are high, the thyroid gland releases calcitonin. Calcitonin causes the kidneys to reabsorb less calcium from the filtrate, allowing excess calcium to be removed from the body in urine. Calcitonin also suppresses the formation of active vitamin D in the kidneys; without vitamin D the small intestines don't absorb as much dietary calcium. Osteoblasts, stimulated by calcitonin, use calcium in the blood to add to bone tissue.

Practice Questions

Based on the above description of calcium homeostasis, try to answer these questions:

Calcium imbalance in the blood can lead to disease or even death. Hypocalcemia refers to low blood calcium levels. Signs of hypocalcemia include muscle spasms and heart malfunctions. Hypercalcemia occurs when blood calcium levels are higher than normal. Hypercalcemia can also cause heart malfunction as well as muscle weakness and kidney stones.

Practice Question

What problem(s) is/are associated with calcium homeostasis dysfunction?

Watch this video for another discussion on homeostasis and organ systems:

Contribute!

Did you have an idea for improving this content? We'd love your input.
Improve this page Learn More

# data[].attributes.attachment_link.description
Explain how different organ systems relate to one another to maintain homeostasis Each organ system performs specific functions for the body, and each organ system is typically studied independently. However, the organ systems also work together to help the body maintain homeostasis. For example, the cardiovascular, urinary, and lymphatic systems all help the body control water balance.

# data[].attributes.body
The body systems that are involved and interact during temperature regulation are the cardiovascular, respiratory, and muscular systems.

# data[].attributes.body
Temperature regulatory center in the brain (Hypothalamus)

# data[].attributes.body
Nerve cells in our skin and brain (Thermoreceptors)

# data[].attributes.body
Homeostasis is how the body maintains proper internal conditions

# data[].attributes.body
Homeostasis Point: 37 ºC (98.6 ºF)