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Homeostasis and Temp regulation


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What is Physiology?
The study of the function of the body, how you live, and the study of the regulatory processes by which the body maintains homeostasis.
What is the concept of homeostasis?
the concept that the chemical and physical conditions of the internal fluid environment that bathes the body's cells remains relatively constant.
What constitutes the internal fluid environment that bathes the body's cells?
Body temp
H+ protons
how is the fluid environment bathing body cells kept constant?
by physiological control systems.
What is the term for the internal fluid bathing the body cells?
what are the various compartments in the total body fluid called?
1. ICF = Intracellular fluid
2. ECF = Extracellular fluid
a. Interstitial fluid
b. Plasma
what is interstitial fluid?

interstit fluid is the fluid that surrounds the body's cells in tissue.

plasma is the fluid that surrounds the cells in the blood vessels.
Numerically how is body water distributed in a 70 kg man?
Total body water = 42 L
ICF = 28L
ECF = 14L
Interstitial tissue fluid = 11L
plasma blood vessel fluid = 3 L
By percent how is body fluid distributed?
Total body water = 60% body weight
ICF = 67% of body WATER
ECF = 33% of body water
Interstit. fluid = 80% of ECF
Plasma fluid = 20% of ECF
How do physiological control systems maintain homeostasis?
By performing regulatory responses to stimuli.
What are 3 types of Regulatory Responses performed by physiological control systems?
1. Negative Feedback control
2. Positive Feedback control
3. Feed forward
What is the definition of a negative feedback control system?
Negative feedback is the opposing physiological response that negates a change in a regulated variable.
What is the classic example of a negative feedback response?
Temperature control
What are the components of a negative feedback control system?
1. regulated variable
2. sensor
3. afferent pathway
4. integrating center
5. efferent pathway
6. effectors
what is a regulated variable?

What is being controlled by a physiological system - eg, body temp, blood glucose, etc.
What is a "sensor"?
What senses changes in the regulated variable. e.g., a thermometer, neuron, nerve cell or endocrine cell.
what is an afferent pathway?

2 examples:
the communication pathway between a sensor and integrating center.

usually a nerve or a hormone.
what are the 2 responsibilities of an integrating center?
1. Comparing the actual value of the regulated variable to the desired value of it.

2. Activating effectors to oppose the change.
What is a set point?
the desired value of a controlled variable.
what is the efferent pathway?

2 examples:
the communicating pathway between an integrating center and effector.

Most often a nerve or a hormone.
What are effectors?
organs and cells that change a regulated variable. usually muscles
What is a positive feedback control system?
A reinforcing response by a physiological control system to a change in a regulated variable. Not many examples are found.
What are the two ways a positive feedback system will end?
1. Either self-limiting, the stimulus just stops, or

2. It is pathological and kills you.
What are the components of a Positive feedback control system?
Same as a negative
What is an example of a positive feedback control system?
Partruition (childbirth)
How does partruition exemplify positive feedback?
Oxytocin makes the uterus contract, baby's head pushes on the cervix; oxytocin is released. cervical nerves sense the oxytocin,
how does loss of blood exemplify a negative feedback regulatory mechanism?
-Loss of blood causes decreased b.p.
-Baroreceptors sense changed b.p.
-send signal to medulla to.
-medulla compares b.p. to setpoint. activates sympathetic nerve to heart.
-heart rate inreases, b.p. increases.
one more time, how does partruition exemplify positive feedback?
-oxytocin causes uterine contractions.
-contractions, baby's head push on cervix.
-cervix stretches, stim oxytocin release.
-oxytocin causes uterine contractions.
what is the definition of FEED FORWARD?
what is its purpose?
-a response is evoked in anticipation of a change to a regulated variable.

-this anticipatory response minimizes the change in the regulated variable.
what is an example of a feedforward response?
there are temp receptors on the SKIN surface. when they detect a change in outside temp, they signal the hypothalamus to counteract the change, so the body's internal temp remains constant with minimal fluctuation.
what do the blood vessels do?
-if it's cold outside
-if it's hot outside
Cold: constrict to keep the skin away from body surface.

Hot: dilate to send as much blood as possible to the body surface to cool off.
In Temp Regulation, what is the regulated variable?

What is the set point?
CORE body temp.

Set Point = 37 C
What are the 2 Types of Sensors in thermoregulation?

What is the purpose of each?
-Peripheral thermoreceptors (skin) send feedfoward info to brain to PREVENT temp change.

-Central thermoreceptors send negative feedback info to brain to NEGATE a change in core body temp.
where are the core thermoreceptors located?
in the GI tract, spinal cord, and brain.
what are the afferent pathways and integrating centers in thermoregulation?
-sensory nerves from skin and core thermoreceptors to the brain.
-interneurons within the brain

integrating center:
brain - pre-optic anterior hypothalamus
What is the Integrating Center in thermoregulation, what does it do?
the Pre-optic anterior hypothalamus.

it compares the sensed temperature to the optimal temp, setpoint
what are the 2 (3 in animals/newborns) efferent pathways in thermoregulation?
1. autonomic nerves to skin blood vessels and sweat glands
2. motor nerves to skeletal muscles

3. thyroid hormones/epinephrine circulate to brown fat
what is brown fat, and what is its purpose?
fat in newborns and hibernating animals that has a lot of blood vessels and mitochondria in it.

when hormones and epinephrine activate it, it generates a lot of heat.
What are the 4 Effectors in Thermoregulation?
1. Skeletal muscles
2. Arterioles
3. Sweat glands
4. Brown fat
What must be controlled to change body temp?
1. Control heat production
2. Control heat loss
What's the difference between Warm and Coldblooded animals?
warm: generate heat, are homeothermic/endothermic.

cold: don't generate heat. depend on an external source for heat - poikilothermic, ectothermic.
What 4 things does Skeletal muscle do to effect body temp?
1. Voluntary movement - contract to generate heat.
2. Involuntary mvment - shivering increases heat generation 2-5x.
3. Control behavior - put on a jacket
4. Changes posture - curl up to conserve heat, stretch out to cool off.
How do arterioles effect Body temp?
By controlling how much blood flows to any region by using smooth muscle to constrict or dilate.
how do sweat glands effect body temp?
by controlling how much heat evaporates. To cool the body, plasma exudes from the blood and heat generated causes the plasma to evaporate.
If the external temp is higher than the body's internal, what is the only way to cool off?
by sweating.
what is brown fat used for?

how does it work?
non-shivering thermogenesis in infants and animals.

More heat is produced in metabolism because ATP production is made ineffecient by uncoupling oxidative phosphorylation.
what controls nonshivering thermogenesis?
Thyroid hormones, Epinephrine, & Sympathetic Nervous system.
What is the most efficient way to regulate body temp?
by changing the arteriole size.
the zone where your skin vasomotor can control body temp, and most efficiently, because vasocontrol is most efficient.

It is: 70-85 F
how do you control body temp within the thermoneutral zone?
by vasoconstricting or dilating.
once again, how does vasocontrol regulate body temp?
by incr/decr blood flow to the skin
what 2 factors affect a person's thermoneutral zone?
-Body surface area:mass ratio. the higher it is, the colder you'll be.

-How fat you are
As body temp decreases from 80 to 70, how does the body react?
blood vessels constrict while still in the zone.
at 70, vasoconstriction is MAX.
at 69, the body temp will start to decrease, so the body starts to shiver and you jump around and put more clothes on and curl up.
What are 4 alterations to normal temp regulation?
1. heat exhaustion
2. heat stroke
3. hypothermia
4. fever
what is heat exhaustion?
fainting due to decreased blood pressure as a result of loss of plasma (sweat) and decreased blood pressure (from vasodilation).
is heat exhaustion really a thermoregulatory problem?
no it's a cardiovascular problem - b.p. too low - bp should be regulated at the expense of temp, not vice versa.

if B.P. were being regulated correctly, the body would have corrected the problem before bp got too low.
what is heat stroke, and 4 things it can cause?
a breakdown in temp regulation that can cause delirium, seizures, prolonged unconciousness, and death.
what is heat stroke caused by?
exposure to hot and humid environments where you can't sweat to cool off. or overexertion in it. Hypothalamus fails and you keep getting hotter till you die.
what is unique about heat stroke?
it becomes a positive feedback response because as internal body temp continues to increase, the failing hypothalamus says DONT sweat, GO UP MORE!
what is hypothermia?
the result of body temp decreasing so much that thermoproduction and conservation response mechanisms can't counteract it.
how does falling body temp alter: -metabolism
Metabol: slows down; heat production slows

Brain: stops working; you make stupid decisions like turning down the wrong path in a blizzard.
what is FEVER?
an increased body temp because the body is trying to maintain a new, increased setpoint.
What is the time course of a fever?
1. you're at normal setpoint
2. something changes the setpoint
3. now your sensors tell the brain you're too cold.
4. effectors cause vasoconstriction, shivering, curling up, to warm up.
5. reach your new setpoint. then the setpoint is returned to normal.
6. Now you're too hot, so you sweat and try to cool back down.
how does the setpoint get changed - what is the FEBRILE MECHANISM?
-macrophages ingest an infectious organism
-macrophages induce endogenous pyrogens to travel to the brain, and the vagus nerve sends input to the hypothalamus in the brain to produce Prostaglandins.
-Prostaglandins change the set point
ultimately what changes body temp setpoint?
how are prostaglandins inhibited?
by Tylenol and Aspirin - they inhibit synthesis and reduce fever.
Is fever beneficial?
What evidence supports your response?
Lizards get fevers. When given bacterial injections, if prevented from getting fevers, they die. If htey get fevers, the lizards live. Fever reduces Fe levels so bacteria die.

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