Download Evaporation

Topic for Tuesday:
Introduction to Endocrines
Topics for today:
• Physiology of perspiration
• Neural control of temperature
• Temperature control pathologies
• Types of hormones & actions
• Pituitary endocrine physiology
• Discussion of Test #3
Evaporation
Heat source, Kcal/hr
200
160
120
80
40
0
evaporation
40
mode of heat loss above
33oC ambient temp.
Heat loss, Kcal/hr
Evaporation is principal
80
120
160
200
Body cooling
Metabolism
240
280
6
10
14
18
22
Vasomotor
Regulation
26
30
Sweating
34
38
42
46
50
Ambient temperature, °C
1
Evaporative Heat Loss
Each liter of sweat that evaporates removes 580 Kcal
of heat from the skin. During intense exercise*
perspiration can occur at a rate of about 1.5 liters/hour
resulting in removal of heat at a rate of ~870 Kcal/hr,
or about 12 x basal heat production.
*Intense is 12-18 kcal/min (10-15 times basal rate)
Perspiration and Dehydration
Loss of a liter of fluid via perspiration
causes an immediate reduction (~10%)
in blood volume which in turn lowers
cardiac output (~10%).
Obviously, exercise performance during
heavy perspiration requires intake of
fluid to maintain hydration to avoid the
drop in cardiac output.
Mechanisms
of heat gain
& heat loss
Heat gain (all sources) must
equal heat lost (all modes). of
At air temperature >34 o C,
radiation and metabolism are
main sources of gain and
evaporation is main heat loss.
At air temperature <20 o C,
metabolism is main heat gain
and radiation is main heat
loss.
2
Neural control of temperature
hypothalamus - temperature control center
Hypothalamus receives information from peripheral
receptors and, as needed, activates vascular responses,
shivering, and perspiration.
Peripheral Temperature Receptors
cold receptors
warmth receptors
Impulse
frequency
20
30
40
50
°C
Temperature pathology
• fever - change in setpoint
• heat stroke - failure to initiate sweating
• hypothermia - vascular failure
3
Endocrine terminology
• Hormone - a chemical released from an
endocrine organ and transported via the blood to
ellicit effects on target organs.
• Endocrine organs - ductless organs that secrete
chemical effectors (hormones) into the plasma for
transport to target organs
• Target Organ – possesses receptors for hormone
and can therefore respond to the hormone
Endocrine and
exocrine glands
Endocrine glands , such
as the thyroid gland, are
ductless and release
products into capillaries
Exocrine glands , such as
the sweat glands possess
ducts for transporting
secretions
Types of endocrine secretions
there are three major types of hormones*
I. peptide hormones (e.g., adrenocorticotropin)
II. amino acid derivatives
(e.g., norepinephrine)
III. steroids
(e.g., testosterone)
* See Table 18-2, p640
4
Hydrophobic hormone action mechanism
Extracellular
fluid
cytoplasm
nuclear
receptor
hormone
Gene transcription
Multiple effects
Hydrophilic hormone action mechanism
cytoplasm
Extracellular
fluid
second messenger
hormone
Multiple effects
in the cell
membrane
receptor
Example: Action of Epinephrine
5
Major endocrine glands of the body
pineal gland
pituitary gland
parathyroid glands
adrenal glands
thyroid gland
thymus gland
pancreas
testes (male)
ovaries (female)
Pituitary/hypothalamus axis
...interaction of nervous system & endocrine system
Pituitary secretions
anterior pituitary
- TSH
- ACTH
- growth hormone
- FSH
- luteining hormone
- prolactin
neurosecretory cells
in hypothalamus
posterior pituitary
- oxytocin
- antidiuretic hormone
6
Topic for Friday:
Pituitary and Thyroid Hormones
Item for Wednesday:
Test #3
• Blood and coagulation
• Defense systems (immunity)
• Ventilation & O 2 transport
• Kidney mechanisms
• Regulation of pH
• Digestion and Absorption
Questions?
7