Thermoregulation Lecture (Dr. Karius) TEST 2 Flashcards
Normal Body Temperature
- In the MORNING: 36.7 Degrees Celsius
- The NORMAL RANGE: 36.3 to 37.1
Control Systems
1) Controlled Variable
2) Is measured by
- —>
3) Sensory
- —->
4) Controller (SET POINT)
- —->
5) Effector
- —->
This is a FEEDBACK System, Information is FED BACK to the CONTROLLER to Report CHANGES in the Controlled Variable*
Variable Maintained around a Set Point
- Any change in the Controlled Variable causes a Reaction that brings it back to the SET POINT!!!
Feed- Forward Systems
- In Feed- Forward System, information is used to PREVENT Changes in the Controlled Variable
Negative Feedback Systems
- The Vast Majority of Feedback Systems in the Human Body are NEGATIVE FEEDBACK
- Thermoregulation is one of these, although there are FEED-FORWARD Aspects
Thermoreceptors
Definition
DEFINITION: Thermoreceptors are Neurons which Change their FIRING RATE in Response to Changes in LOCAL TEMPERATURE
Thermoreceptors
Description
- Presumed to be BARE NERVE EDINGS (Neuritis Complex)
- May be WARM or COLD Sensitive
- Found in:
1) The SKIN!!!!!!!
2) The VISCERA!!!!!!
3) The BRAIN!!!!!! - Different Locations tell the Brian about DIFFERENT TEMPS
WARM SENSITIVE:
- 4 Channels Id’d so far
- TRP-V1 through 4!!!!!!!!!!!!!
- Sensitive Over Different Ranges
- V = VANILLOID = CAPSAICIN (Hot Peppers)!!!!!!!!!!
- Allows Na+ or Ca++ INFLUX
COLD SENSITIVE:
- Two Receptors
a) TRPM8 (= CMR-1)
b) TRPA2? - Also ACTIVATED by MENTHOL!!!!
- Activation:
a) Opens as Temp DECR
b) Allows Na+ or Ca++ INFLUX
Hypothalamus
- The Hypothalamus has the Connections to Control the HORMONAL, AUTONOMIC, and BEHAVIORAL Changes that are part of Thermoregulation
Thermoregulatory System
Respons to Hear and Cold
1) ANTERIOR HYPOTHALAMUS:
- Response to HEAT!!!!
* ** HEAT LOSS Behavior!!!
2) POSTERIOR HYPOTHALAMUS:
- Response to COOLING!!!!
* * HEAT PRODUCTION Behavior!!!!1
Core Temperature
- Core Temp: 36
- Oral Temp: 34
- “Average Skin”: 32
- Hands: 30
- Feet 26
Body Temp Changes with Activity
1) With SLEEP:
* ** TEMP DECREASES!!!!***
- Circadian Influence!
- Set Point Decrease?
2) With EXERCISE:
* ** TEMP INCREASES (As HIGH as 40C)!!!**
- INCR Heat Production
- Set Point Increase
Body Temp is Influenced by the Circadian Rhythm
- Varies about 1 to 2 Degrees over 24 Hour Period
*** LOW at 6:00 am!!!!!
The Hypothalamus- Core Temp
- The Hypothalamus has a “SET POINT” for Core Temperature!!!!
SET POINT: the Desired Value
Current Body Temp and the Temp around the Body
What my Current Body Temp is:
- Temp affects ENZYME ACTIVITY (Q10)
- Will Change CELLULAR FUNCTION
- For better or Worse (Usually Worse)
What is the Temp around Me:
- Environmental Temperature is a Threat to MY TEMP
Thermoreceptors in the Core and Cutaneous
1) Thermoreceptors in “CORE”:
- Brain
- Viscera
2) Cutaneous Thermoreceptors:
- Axons located IN SKIN
Peripheral Thermoreceptors
- Often BIMODAL (Temp and Touch Sensitive)
- May be Warm or Cold Sensitive
- ** 10x as many COLD SENSITIVE!!!!!****
- These tell us about ENVIRONMENTAL CONDITIONS!!!!!
Visceral Thermoreceptors
Why would I put Thermoreceptors in the Gut?
- Not just sending Core Temp
- Threats to Maintenance:
a) Food Ingested may Change Body Temp
b) Tell Hypothalamus about these Threats
Central Thermoreceptors
LOCATION:
1) PREOPTIC Region of Hypothalamus
2) SUPEROPTIC Region of Hypothalamus
WHAT:
- Neuron cell Bodies Sensitive to CHANGE Sin Temp
a) 3x as many WARM SENSITIVE RECEPTORS
b) They relay their Information to Other areas of the Hypothalamus
****These Regions detect CORE TEMPERATURE!!!!!!
The Hypothalamus and Thermoregulation
- Integration of AFFERENT
1) Determination of “Set Point”
2) Compare CORE TEMP to “Set Point”
3) If Different: Generate RESPONSE
4) RESPOND to Environment
Effectors of the Hypothalamus
1) Heat Production
2) Heat Loss
Heat Production
MECHANISM:
1) ANS: SYMPATHETIC System!!!!!
2) HORMONAL:
a) Thyroxin
b) Epinephrine/ Norepinephrine
2) WAYS to PRODUCE HEAT
a) MUSCULAR ACTIVITY
b) NON-SHIVERING THERMOGENESI (Non-Muscular)
Heat Production
Muscle Activity
MUSCULAR ACTIVITY
1) SHIVERING
a) DORSOMEDIAL POSTERIOR HYPOTHALAMUS!!!!!!!!!!!!!!
b) Incr Motoneuron Excitation
2) INCR Voluntary Activity
a) Via CORTEX
b) Jumping, Running
Heat Production
Non-Shivering Thermogenesis
1) HORMONAL INGLUENCE STRONG:
a) THYROXIN INCR Metabolic Rate (Heat Production)
- Stimulus for TRH Release: COLD
b) EPINPEHRINE
2) INCR Food Intake: INCR Metabolism
3) BROWN ADIPOSE TISSUE
Heat Production
Brown Adipose Tissue
1) LOW EFFICIENCY HYDROLYSIS of ATP
- Low Efficiency = Lots of Heat Production
2) SYMPATHETIC
a) Innervation of Brown Fat
b) Circulating Epinephrine (A Catecholamine)
3) IMPORTANCE IN HUMAN:
a) STRONG in Infants
b) Recent Evidence shows Existence in Adults
Additional Information:
- Distribution APPEARS to differ from that of Other Animals
- Requires EXPOSURE to COLD (Acute)
- Requires SYMPATHETIC ACTIVATION
Heat Loss
ANTERIOR!!!!!!!!!
(Heat Loss Behavior)
***EVAPORATION Heat Loss: Energy (Heat) LOST as WATER EVAPORATES
Two Kinds of Heat Loss:
1) INSENSIBLE (Respiratory)
2) SWEATING (Controlled)
Heat Loss
Convection and Conduction
CONVECTION:
- Movement of MOLECULES AWAY from Contact (Air Heating and Rising)
CONDUCTION:
- Transfer of Heat between Object in PHYSICAL CONTACT with One Another
RADIATION:
- Infrared Radiation transferring HEAT between 2 Objects NOT in PHYSICAL CONTACT
How can we Control These Forms?
- Add layers of Clothing!!!
**In ODER to respond to Chagnes in CORE TEMPERATURE, the HYPOTHALAMUS will ADJUST BOTH HEAT LOSS and HEAT PRODUCTION
Integrative Response: INCREASE Core Temp
( Tb > Tset point)
1) DECREASE Heat Production:
- Apathy/ Inertia
- Anorexia
2) INCREASE Heat Loss:
- Blood to Skin
- EHL (Sweat)
- Insensible Heat Loss (Pant)
Heat Loss
- How much Blood is sent to the Skin determines how much HEAT MOVES from Blood to External Environment
Sweating
SWEAT GLAND:
- Lots of Blood Vessels Nearby
- Coiled Region by Vessels
- DUCT LEADING to the SKIN
INNERVATION:
- ** SYMPATEHTIC CHOLINERGIC!!!!****
- ACh is the Neurotransmitter, biding to MUSCARINIC RECEPTOR!!!
Sweating Cont
Primary Secretion is HIGH in:
- Water
- Sodium
- **Primary Secretion is PLASMA (no proteins)
- ** WATER and SODIUM are REABSORBED (Taken Back to the Blood) in the DUCT of the Sweat Gland!!!!!
- Cl can also be Reabsorbed along the Duct
LOW FLOW RATES of SWEAT:
- CONCENTRATED Sweat*
- LITTLE Water
- HIGH SODIUM
HIGH FLOW RATES of SWEAT:
- * NOT Concentrated*
- LOTS of Water
- LITTLE Sodium
Integrative Response: DECREASED Core Temp
(Tb
Fever
DEFINITION:
- A CONTROLLED INCR in Body Temp
IMPLICATION:
- SET POINT INCR: Body Temp is only doing what Hypothalamus DIRECTS it to do!!!
Making a Fever- STEP ONE
1) Secretions of ENDOTOXINS
2) IMMUNE CELLS activated by “Bugs” release CYTOKINES
Endotoxins and Cytokines lead to the production of PROSTAGLANDIN E2 (Major Player)!!!!!!!!!!!!!!!
- EP3 receptor
** The Production of Prostaglandin E2 leads to an INCREASE HYPOTHALAMIC SET POINT for Temp (Tb
Making a Fever- STEP TWO
Tb
Making a Fever- STEP THREE
Tb = Tset point
“COMFORT” - in a relative Sense
Making a Fever- STEP FOUR
1) The Bud is Vanquished : NO ENDOTOXINS
2) No more Activation of Immune Systems
** These lead to the HYPOTHALAMIC Set Point returning to NORMAL
Tb > Tset point
Making a Fever- STEP FIVE
( Tb > Tset point)
1) DECREASE Heat PRODUCTION
- Apathy/ Inertia
- Anorexia
2) INCREASE Heat LOSS:
a) Conduction/ Convection
b) EHL (Sweat)
c) Insensible Heat Loss (Pant)
Making a Fever- THE END
Tb = Tset point
The REAL COMFORT!!!!!!!
Hyper and Hypothermia
DEFINITION:
- UNCONTROLLED Changes in BODY TEMPERATURE
IMPLICAITONS
- Set Point remains NORMAL
- Environmental Stresses EXCEED Body’s ABILITY to REGULATE TEMP
- At Extremes: Hypothalamic Regulation MAY BE LOST!
Thermoregulation- Case Study about Hypothalamic Tumor
HYPOTHALAMIC TUMOR:
- Abolishes the ABILITY to THERMOREGULATE
- Although a Fever is MORE COMMONLY SEEN with Tumors, this tumor has also DESTROYED her ability to SECRETE TSH, so NO Thyroxin is being Produced.
- Thus, her BASAL METABOLIC RATE is VERY LOW and the HEAT PRODUCTION is LOW!!!
