1. Unit 1 Intro/Atlas ppt 2 Homeostasis

2. Characteristics of Life
Cellular composition
Metabolism
anabolism, catabolism and excretion
Responsiveness and movement
stimuli
Homeostasis
Development
differentiation and growth
Reproduction

3. Within all humans there are many Physiological Variations
Sex, age, diet, weight, physical activity
Typical physiological values
reference man
22 years old, 154 lbs, light physical activity
consumes 2800 kcal/day
reference woman
same as man except 128 lbs and 2000 kcal/day

4. Anatomical Variation No two humans are exactly alike
70% most common structure
30% anatomically variant
variable number of organs
missing muscles, extra vertebrae, renal arteries
variation in organ locations
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Normal
Pelvic kidney
Horseshoe kidney
Figure 1.8
Normal
Variations in branches of the aorta

5. All organisms must be able to maintain Homeostasis
Homeostasis – the body’s ability to detect change, activate mechanisms that oppose it, and thereby maintain relatively stable internal conditions
Must maintain constant internal conditions regardless of external conditions
internal body temperature ranges from 97 to 99 degrees despite variations in external temperature
Loss of homeostatic control causes illness or death
The Human body has a tremendous capacity for self-restoration
Homeostasis is maintained using 2 mechanisms.

6. The fundamental mechanism that keeps a variable close to the set point is
1 Negative Feedback!
Internal conditions are not absolutely constant but fluctuate within a range. (set point)
Internal state of the body is at a
Dynamic Equilibrium in which there is a certain SET POINT (average value)

7. Negative Feedback Loop
Process in which the body senses a change and activates mechanisms to reverse it - dynamic equilibrium
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Room temperature
falls to 66°F (19°C) 1
Room cools down
C 10°
15°
20°
25° 6
F 50°
60°
70°
80° 2
Thermostat activates
furnace
C 10°
15°
20°
25°
F 50°
60°
70°
80°
Thermostat shuts
off furnace 5
Room temperature
rises to 70°F (21°C) 4
Figure 1.9a
Heat output
(a) 3

8. Negative Feedback, Set Point
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Furnace turned
off at 70°F 70
Room temperature (°F)
Set point 68°F 65
Furnace turned
on at 66°F 60
Time
Figure 1.9b
(b)
Room temperature does not stay at set point of 68 degrees -- it only averages 68 degrees

9. Negative Feedback in Human Thermoregulation
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Sweating
37.5°C
(99.5°F)
Vasodilation
Core body temperature
37.0°C
(98.6°F)
Set point
Vasoconstriction
36.5°C
(97.7°F)
Time
Figure 1.10
Shivering
Brain senses change in blood temperature
if to warm, vessels dilate (vasodilation) in the skin and sweating begins (heat losing mechanisms)
if too cold, vessels in the skin constrict (vasoconstriction) and shivering begins (heat gaining mechanism)

10. Negative Feedback Control of Blood Pressure
Sitting up in bed causes a drop in blood pressure in the head and upper thorax
Baroreceptors in the arteries near the heart alert the cardiac center in the brainstem
Cardiac center sends nerve signals that increase the heart rate and return the blood pressure to normal
Failure of this to feedback loop may produce dizziness in the elderly

11. Control of Blood Pressure
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Person rises
from bed
Blood pressure rises
to normal; homeostasis
is restored
Blood drains from
upper body, creating homeostatic imbalance
Cardiac center
accelerates heartbeat
Baroreceptors above
heart respond to drop
in blood pressure
Figure 1.11
Baroreceptors send signals
to cardiac center of brainstem

12. Components of a Feedback Loop
1. Receptor - senses change in the body
2. Integrating (Control) Center - control center that processes the sensory information, ‘makes a decision’, and directs the response
3. Effector – carries out the final corrective action to restore homeostasis

13. 2 Positive Feedback Loops (second mechanism)
Self-amplifying cycle
When a physiological change leads to greater change in the same direction
feedback loop is repeated – change produces more change!!
Normal way of producing rapid changes
occurs with childbirth, blood clotting, protein digestion, fever, and generation of nerve signals
These are good effects of positive feedback 3
Figure 1.12

15. Harmful Positive Feedback Loop
Fever > 104 degrees F
metabolic rate increases
body produces heat even faster
body temperature continues to rise
further increasing metabolic rate
Cycle continues to reinforce itself
Becomes fatal at 113 degrees F