Physiology: Study of the function and relationship of the various organ systems

1
Introduction

• Physiology Study of the function and
  relationship of the various organ systems

2
The body

• Made of 40 solid particles and 60 H2O
• The percentage of H2O varies with age, sex
• Babies up to 80 H2O
• Older, slim person 60

3
Figure 1.4
4
Fluid compartments

• 2/3 cell fluid (intracellular fluidICF)
• 1/3 fluid outside the cell ? extracellular fluid
  (ECF)
• - 80 interstitial fluid (IF)
• - 20 circulating fluid
• mostly plasma CSF
• eye and ear fluid

5
Figure 1.5
6
Homeostasis

• The process of maintaining a constant internal
  environment despite changing external environment
• Components
• - Sensors
• - Integrating center
• - Effectors

7
Regulatory mechanisms

• Negative feedback the most common
• Positive feedback rare (exblood coagulation,
  parturition)
• Most parameters controlling body function (heart
  rate, breathing rate, blood pressure, blood
  glucose..) are maintained within a narrow range

8
Negative feedback

• If a parameter value increases, body mechanisms
  works to bring the value down, within normal
  range
• The most common mechanism

9
Positive feedback

• As a value increases, the body reacts to increase
  the value further
• Example parturition (labor and delivery) and
  blood clotting

10
Regulation of body temperature

• Body heat is a by-product of muscle contraction
• Heat losses or gains are due to
• - convection transfer of energy through moving
  gases or liquids
• - conduction transfer of heat energy between
  objects in direct contact
• - radiation transfer of energy through
  electromagnetic waves
• - evaporation loss of heat when water is
  evaporating

11
Body temperature regulation Normal body
temperature 37oC 98.6oF

• If external temperature is high? body reacts to
  cool down
• skin flush appearance due to blood vessel
  dilation, sweating
• Heart rate increases
• Respiratory rate increases

• If external temperature is low ? body reacts to
  warm up
• skin pale appearance due to blood vessel
  constriction, goose bumps
• Heart rate decreases
• Respiratory rate decreases
• Muscle shivering

12
Figure 1-4
13
Mechanism of regulation

• Temperature receptors in the skin and deep within
  the body send temperature information to the
  temperature integrating center in the
  hypothalamus
• The integrating center makes a decision about the
  adjustments to be made
• Effectors in charge of adjusting the temperature
  are activated

14
If body temperature is too cold
15
Body temperature regulation Normal body
temperature 37oC 98.6oF

• If external temperature is high? body reacts to
  cool down
• skin flush appearance due to blood vessel
  dilation, sweating
• Heart rate increases
• Respiratory rate increases

16
Pathology of temperature regulation heat
exhaustion

• A person is working in the sun, is hot, sweat and
  drinks large amount of water
• The electrolytes (salts) lost through sweating
  are not replaced ? risk of seizures, loss of
  consciousness and death
• Treatment give fluids and electrolytes (ex
  gatorade)

17
Pathology of temperature regulation heat stroke

• A person is working in the sun, is hot. The sun
  increases body and especially brain temperature
• If the brain temperature reaches too high level,
  the brain becomes unable to react ? sweating
  stops
• Body temperature reach very high levels ? the
  person dies

18
So what is fever?

• Body temperature can be as high as 35-36oC
  (105-106oF), despite external temperatures being
  much cooler.
• Pathogens invade the body ? macrophages fight
  against the infection and in the process secrete
  a special compound, a pyrogen.
• A pyrogen has the ability to reset the bodys
  internal temperature to a higher level
• When it does, the body reacts to increase its
  temperature ? shivering, ? fever
• When the body has won its battle against the
  pathogen, the macrophages no longer secrete
  pyrogen.
• However, the body temperature is high ? the
  temperature center in the hypothalamus direct the
  body to cool down ? sweating .

19
Readings

• Chp. 1 p2-20. Book pages corresponding to notes.
• Clinical connections p 10