How Stress Affects Body Temperature – Maintaining homeostasis requires the body to constantly monitor internal conditions. From body temperature to blood pressure to levels of certain nutrients, every physiological state has a set point. A certain point is the physiological value around which the normal range varies. The normal range is a limited set of values that is optimally stable and stable. For example, the set point for normal human body temperature is about 37°C (98.6°F). Physiological parameters, such as body temperature and blood pressure, vary within a normal range of 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 shift from a set point. Therefore, negative feedback maintains body parameters within their normal range. Maintaining homeostasis through negative feedback is always ongoing throughout the body.
The human body regulates body temperature through a process called thermoregulation, in which the body can maintain its temperature within certain limits, even when the surrounding temperature varies greatly. The body’s core temperature remains constant at around 36.5-37.5 °C (or 97.7-99.5 °F). In the process of producing ATP by cells throughout the body, 60 percent of the energy produced is in the form of heat that is used to maintain body temperature. Thermoregulation is an example of negative feedback.
How Stress Affects Body Temperature
The hypothalamus is the main switch in the brain that acts 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 reduce it. These include increased blood circulation to the body surface to allow heat to dissipate through the skin and initiation of sweating to allow evaporation of water on the skin to cool the surface. Conversely, if the temperature drops below the set core temperature, the hypothalamus can start shivering to generate heat. The body uses more energy and produces more heat. Additionally, thyroid hormone will stimulate more energy use and heat production by cells throughout the body. When the body does not expend or release energy to maintain its core temperature, it is called a thermoneutral environment. For a naked person, this air temperature is around 84°F. If the temperature is higher, for example, when wearing clothes, the body compensates with cooling mechanisms. The body loses heat through heat exchange mechanisms.
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When the environment is not thermoneutral, the body uses four mechanisms of heat exchange to maintain homeostasis: conduction, conduction, radiation and evaporation. Each of these mechanisms relies on the temperature characteristic of moving from a higher concentration to a lower concentration; Therefore, each of the heat exchange mechanisms varies in rate depending on the temperature and environmental conditions.
Heat transfer is the transfer of heat by two objects that are not in direct contact with each other. When the skin comes into contact with something cold or hot. For example, when you hold a glass of frozen water, the temperature of your skin will warm the glass and in turn melt the ice. Alternatively, on a cold day, you might warm your cold hands around a cup of hot coffee. Only 3 percent of body heat is lost through respiration.
Convection is the transfer of heat from the air around the skin. The heated air moves away from the body and is replaced by cooler air. Convection can also occur in water. When the water temperature is lower than the body temperature, the body loses heat by heating the water closest to the skin, which moves away and is replaced by cooler water. Convection currents caused by temperature changes continue to remove heat from the body faster than the body, resulting in hypothermia. About 15 percent of body heat is lost through convection.
Radiation is the transfer of heat through infrared waves. This occurs between two objects when their temperatures differ. A radiator can heat a room with radiant heat. On a sunny day, the sun’s rays warm 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.
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Evaporation is the transfer of heat by rising water. Because it takes a lot of energy for a water molecule to turn from a liquid to a gas, the evaporation of water (in the form of sweat) takes a lot of energy from the skin. However, the rate at which evaporation occurs is dependent on relative humidity – more perspiration occurs in environments with lower humidity. During exercise, sweat is the body’s primary means of cooling, but at rest, 20 percent of the body’s heat loss occurs through evaporation.
Humans have a thermoregulatory feedback system that works by promoting heat loss or heat gain. When the brain’s temperature regulation center receives data from sensors indicating that the body’s temperature is exceeding its normal range, it stimulates a group of brain cells referred to as the “heat loss center.” This stimulation has three main effects:
Figure 1. Hypothalamus Controls Thermoregulation. The hypothalamus controls thermoregulatory networks that lead to increases or decreases in core body temperature. Original image OpenStax Anatomy and Physiology CC-by-4.0. Photo edited by Aric Warner.
Conversely, activation of the brain’s heat gain center by cooling reduces blood flow to the skin, and blood returning from the legs is returned to the deep vascular network (Figure 2). This arrangement keeps heat close to the core of the body, limits heat loss, and increases blood pressure. If the heat loss is severe, the brain sends abnormal signals to the skeletal muscles, causing them to contract and shiver. Muscle contractions release heat when they use 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.
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Figure 2. Physiological response to acute cold. During acute cold, the sympathetic nervous system releases norepinephrine, which results in vasoconstriction, increased blood pressure, and increased heart rate.
Acute cold stress causes activation of the sympathetic nervous system and release of catecholamines (neurotransmitters). Neurotransmitter release affects the cardiovascular system in several ways, including arterial constriction, transient tachycardia, and increased cardiac contractility. Together, these homeostatic changes result in what is called a pressure response, or an increase in blood pressure. The cold pressor test is commonly used in the clinical setting to assess sympathetic nervous system function. In the cold pressor test, subjects immerse their hand or forearm in ice water, and their cardiovascular response is measured.
In this lab, we will use the cold pressor test to assess changes in heart rate, pulse amplitude, and arterial oxygen saturation using a pulse oximeter.
Indirect pulse oximeters estimate arterial oxygen saturation and report it as the oxygen saturation (SpO2) of the subject’s arterial blood. SpO2 is reported as the percentage of oxygenated hemoglobin. Normal pulse oximetry values are usually between 97-100%.
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Figure 3. Pulse oximeter. Fingertip pulse oximeters are used in the physiology laboratory. A light emitting diode rests on the finger, and a photodetector is located under the finger. Figure created by Cameron Miller CC-by-ND.
There are many hypotheses that can be tested in this lab. For example, we might test whether males and females have a different cold breast response, or we could test whether the breast response is the same in the submerged hand versus the non-submerged hand. After collecting the data, you will import it into an excel file in TA for a grade-wide or course-wide statistical analysis.
In preparation for the lab, can you write an IF/THEN hypothesis to test the cold response in men and women?
In this lab you will conduct an experiment to test how exposure to acute cold affects pulse size, heart rate, and hemoglobin-oxygen binding in men and women. You will use a finger sensor called a pulse oximeter, which will measure your pulse as well as peripheral arterial blood oxygenation (SpO2) in your finger.
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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 the lab table, assign a condition to each student before starting the experiment.
This data analysis applies to both baseline and condition 1 or 2 recordings. For basic data, start from the beginning of the recording and find the correct data by browsing and using the clock on the main window.
For test data (condition 1 or 2), start the data analysis at the 1.00 mark and move to 1.05 (five seconds), 1.10 (ten seconds), 1.20 (twenty seconds) and 1.30 (thirty seconds).
An Interdisciplinary Course Research-Based Approach to Human Physiology by Karri Haen Whitmer is licensed under a Creative Commons Attribution-ShareAlike 4.0 International license, except where otherwise noted. A warm welcome
Pdf) Stress Induced Hyperthermia And Hypothermia
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