Homeostasis, Body Temperature Regulation, Fever, and Hyperthermia

Definitions of homeostasis

A condition or variable fluctuates in a predictable and often narrow range. But when disturbed, it goes back to normal

Steady state

A condition that does not change with time; requires energy to maintain a constant condition

Equilibrium

A condition in which opposing forces are balanced; no energy is required

Steady State or Equilibrium?

• Body temperature regulation

• Na+ concentration inside and outside a cell

• Osmotic concentration inside and outside a cell

• Body temperature regulation - Steady State

• Na+ concentration inside and outside a cell - Steady State

• Osmotic concentration inside and outside a cell - Equilibrium

Osmolarity in Equilibrium (4)

• Water goes freely in and out through a water channel

• Osmolarity is the same

• Amount going in = amount going out

• No energy

Na+ concentration in steady state NOT in equilibrium (6)

• Keeps it fairly constant

• Enters via a channel down its concentration gradient

• Pumped out using ATP

• Concentration differs

• Amount going in = amount going out

• NEEDS energy

Set point definition

• The steady state value for any variable that the body attempts to maintain. NEGATIVE FEEDBACK

A few examples of homeostatic variables (i.e. have a set point) (6)

• Body temperature

• Na+ concentration inside and outside the cell

• Blood glucose concentration

• Total body water

• Blood pressure

• ATP concentration in a cell

Lable

What does negative feedback accomplish?

If a variable goes out of the acceptable range, the negative feedback response brings it back to the set point

Sensor or Receptor Definition

Detect a change

Integrating Center Definition

Receive information from one or multiple sensors, coordinate the information, and tell the effector what to do

Effector Definition

Produce a response

Homeostatic regulation of Body Temperature

1. Variable

2. Sensor

3. Afferent

4. Integrating Center

5. Efferent

6. Effector

7. Result

1. Variable - High BT

2. Sensor - Thermoreceptors on internal organs

3. Afferent - Neurons sends signals to the brain

4. Integrating Center - Brain (compare to set point)

5. Efferent - Neurons send signal to the skin

6. Effector - Skin

7. Result - Increase heat loss

After eating an ice cream cone, glucose is absorbed causing an increase in blood glucose levels. This stimulates the pancreatic beta cells to secrete insulin. The insulin acts on muscle and adipose tissue to increase their uptake of glucose, which causes a reduction in blood glucose levels. Which is the integrating center in this scenario?

A. Muscle and adipose tissue

B. Pancreatic beta cells

C. GI tract

D. Blood

B. Pancreatic beta cells

Homeostatic regulation of Blood Glucose

1. Variable

2. Sensor

3. Integrating Center

4. Efferent

5. Effector

6. Result

1. Variable - High BG

2. Sensor - Pancreatic beta cells (compare to set point)

3. Integrating Center - Pancreatic beta cells (compare to set point)

4. Efferent - Insulin

5. Effector - Skeletal muscle and adipose tissue

6. Result - Takes up BG

Typical signals in a homeostatic response (1)(2)

A neuron or hormone that sends information

• From the receptor to the integrating center

• From the integrating center to the effector

There are also positive feedback responses What do they accomplish?

Accelerates a process

What are examples of a positive feedback loop? (select all that are correct)

A. An increase in respiratory rate during exercise

B. Blood clotting when you have a cut

C. Dilation of the pupils when you enter a dark room

D. Milk let down when an infant is nursing

E. Parturition or birth of a baby

B. Blood clotting when you have a cut

D. Milk let down when an infant is nursing

E. Parturition or birth of a baby

Body temperature regulation Why is it necessary? (2)

• Biochemical reactions are temperature dependent

• If body temperature is too high, then neurons malfunction and proteins denature

Environmental temperature

Peripheral or central thermoreceptors?

A more specific location?

Peripheral

Skin

Core body temperature

Peripheral or central thermoreceptors?

A more specific location? (3)

Central
Hypothalamus

Deep body organs

Spinal cord

Homeostatic response for core body temperature regulation
Variable

1. Variable

2. Sensor

3. Afferent

4. Integrating Center

5. Efferent

6. Effector

7. Result

1. Variable - Core temp is too hot or too cold

2. Sensor - Central thermoreceptors In hypothalamus, spinal cord, viscera

3. Afferent - Sensory Neurons are signal

4. Integrating Center - Hypothalamus (compare to set point)

5. Efferent - signal depends on the effector (Typically neuron)

6. Effector - Multiple

7. Result - Necessary response

Feed forward response to changes in skin (ambient) temperature

1. Variable

2. Sensor

3. Afferent

4. Integrating Center

5. Efferent

6. Effector

7. Result

1. Variable - Skin temp is too hot or too cold

2. Sensor - Peripheral thermoreceptors on skin

3. Afferent - Sensory Neurons

4. Integrating Center - Hypothalamus (compare to set point)

5. Efferent - Signal depends on the effector but same as core temp regulation

6. Effector - Multiple

7. Result - Necessary response

What happens to you when you get cold? Decrease circulation to the skin (skin gets pale)

The efferent signal?

The effectors (or how does this happen?)

Why does this happen?

The efferent signal? - Nervous system (SNS)

The effectors (or how does this happen?) - Blood vessels (arterioles) to the skin constrict

Why does this happen? - Reduce heat loss

What happens to you when you get cold? Shiver

The efferent signal?

The effectors (or how does this happen?)

Why does this happen?

The efferent signal? - Nervous system

The effectors (or how does this happen?) - Skeletal muscle contracts

Why does this happen? - To generate heat

Radiation definition

Heat emission in the form or electromagnetic energy or waves

Conduction definition

Transfer of heat via thermal energy (collision of 2 adjacent molecules)

Convection definition

Conduction of heat aided by movement of air or water next to the body

Babies can’t shiver so they

So they exhibit nonshivering thermogenesis to generate heat and stay warm

Nonshivering thermogenesis pathway (4)

1. Cold exposure →

2. Epinephrine, SNS, thyroid hormone →

3. Brown adipose tissue (thermogenic tissue) →

4. Uncoupling of oxidative phosphorylation

What does uncoupling of oxidative phosphorylation mean?

Using glucose to make ATP

Uncoupling of oxidative phosphorylation pathway (3)

1. Oxidation (metabolism and release of energy) →

2. Uncoupling proteins inhibit Phosphorylation (production of ATP) →

3. Produce heat instead of ATP

What are your behavioral responses when you get cold? Advantages? (3)

1. Fold your arms - Reduces surface area for heat loss

2. Put on more clothes - Insulation to prevent heat loss

3. Move to a warmer environment - Self explanatory

What happens when you get hot? Increase circulation to the skin (skin gets red)

The efferent signal?

The effectors (or how does this happen?)

Why does this happen?

The efferent signal? - Nervous system SNS

The effectors (or how does this happen?) - Blood vessels (arterioles) to the skin dialate

Why does this happen? - To increase heat loss by RCC

What happens when you get hot? Sweat

The efferent signal?

The effectors (or how does this happen?)

Why does this happen?

The efferent signal? - Nervous system SNS

The effectors (or how does this happen?) - Sweat glands produce More sweat

Why does this happen? - To lose heat by evaporation

Any skeletal muscle and behavioral changes when you get hot?

Cooler place, fan yourself

Two ways to lose heat by evaporation (2)(2)(1)

1. Insensible water loss (600 ml/day)

   1. Diffusion of water through the skin

   2. Exhaling

2. Sweating

   1. Involved in homeostasis

You are taking a bath and the temperature of the water is 80oF. You get out of the tub and very quickly dry off, and the room temperature is 75oF. How does your body maintain its core temperature?

A. Cutaneous vasoconstriction

B. Shivering

C. This is a small change, so no reflex response is necessary

A. Cutaneous vasoconstriction

What is the thermoneutral zone (for a nude individual), what happens at the thermoneutral zone, and what happens above and below?

1. Environmental temperature (75-86 degrees)

   1. Blood flow to the skin can regulate core temperature

2. If below - Add heat generation (eg shiver)

3. If above - Add sweating

You are in Death Valley National Park, CA where the temperature is 105oF, and the relative humidity is 13% (average relative humidity in WI in the afternoon is 64%). How does your body keep cool?

A. Sweating

B. Cutaneous vasodilation

C. Decreasing it’s basal metabolic rate

D. Both cutaneous vasodilation and decreasing basal metabolic rate

E. Both cutaneous vasodilation and sweating

A. Sweating

If temperature higher than body temp, vasodilation does not happen

In a hot and humid environment, is sweating more efficient, less efficient, or have the same efficiency in reducing core body temperature as in a hot and dry environment?

A. More efficient

B. Less efficient

C. Same efficiency

B. Less efficient

Fever pathway (7)

1. Infection or other fever producing stimulus →

2. Macrophages

3. Release endogenous pyrogens (EP)

   1. Interleukin 1B (IL-1B)

   2. Interleukin 6 (IL-6)

   3. Tumor necrosis factor-a (TNF-a)

4. Brain →

5. Cells release prostaglandin E2 (PGE2) →

6. Raises the set point of the hypothalamus →

7. Body responds by activating reflexes that will raise core or body temperature

Will you shiver or sweat during a rapid onset of a fever? What else might happen?

Shiver

Vasoconstriction

Hyperthermia is often caused by

exercise

With hyperthermia, what do you think happens to the set point and core body temperature?

A. Core body temperature does not change

B. Core body temperature decreases

C. Core body temperature increases

D. The set point does not change

E. The set point decreases

F. The set point increases

C. Core body temperature increases

D. The set point does not change

What happens if a person develops hyperthermia, but things get worse?

They can develop heat exhaustion and then eventually heat stroke!

What will most likely happen to core body temperature with heat exhaustion? Are the cooling mechanisms still working?

1. Higher

2. Yes, Since they are working, core body temperature will usually be less than 104oF

Why does heat stroke develop? (3)

1. The body’s ability to regulate it’s temperature totally breaks down

2. Cooling system is ineffective

3. Core temperature continues to rise

Key Consequences of heat stroke (2)(2)

1. Excessive hyperthermia

   1. Core temperature > 104oF

2. Neurological problems

   1. Seizures, altered consciousness, persistent delirium

Other consiquences of Heat stroke (2)(1)

1. Not sweating – skin hot and dry

   1. Note: sometimes sweating!

2. Skin can also become pale instead of red

An individual with heat stroke may be dry (not sweating) and pale (cutaneous vasoconstriction). Why? (1)(2)(3)

1. Dehydrated

   1. Decreased BP

      1. Reflex vasoconstriction of cutaneous arterioles (help maintain BP to perfuse the brain)

      2. Reduced blood flow to he skin

      3. No extracellular fluid to make sweat

   2. No extracellular fluid to make sweat

Hypothermia is most often caused by

exposure to cold weather or immersion in a cold body of water.

Why does immersion in cold water rapidly cause hypothermia? (2)

1. Heat transfer in water is about 100 times better than in air →

2. Body loses heat faster than it can produce heat

What is the body’s response to hypothermia? (2)

Shivering

Vasoconstriction