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Chapter 1 Lecture Notes
page 1
I. Homeostasis
A. definition and example
definition: homeostasis is the maintenance of a relatively stable internal
environment
example: Your body temperature stays very close to 98.6ºF (37ºC ) whether the
room temperature is 72ºF (22.2ºC) or 105ºF (40.5ºC)
What are some examples of body conditions that must be kept stable?
B. components of a homeostatic control mechanism
1. receptors - cells or organs that monitor and detect changes in the environment
(internal and external)
2. set point - a normal value or range of values within which the condition has to remain
for the body to work correctly
3. control center - set of cells or organ that
a. compares input from receptors to the set point to see if there is a discrepancy
b. if a discrepancy exists, directs the effectors to make adjustments to the
controlled condition
4. effectors - cells, tissues or organs that can change the controlled condition
5. feedback - information that tells the sensors and control center when the set point
has been reached
changes in output from the effectors are used by the system to determine further
action:
 if the set point has not been reached, then the effectors continue to
produce output
 if the set point has been reached, then the effectors stop producing output
BIOL 2404
Strong/Spring 2007
Chapter 1 Lecture Notes
page 2
C. types of homeostatic regulation
1. negative feedback
a. if a controlled condition deviates from normal, this mechanism returns it to the
set point
b. negative feedback provides stable, long-term control
c. it is the most common type of control mechanism in the body
d. examples: body temperature, blood pressure, blood glucose
2. positive feedback
a. causes rapid and extreme change in the controlled condition
b. important for processes that must be completed rapidly
c. temporary
d. examples: blood clotting, labor
D. how a homeostatic regulation mechanism works:
controlled condition = body temperature
deviation = hypothermia
sensors = thermoreceptors in hypothalamus
set point = ave. 37ºC (98.6ºF); range = 36.7 to 37.2ºC
control center = hypothalamus
effector output:
shivering in skeletal muscle
constriction of blood vessels in skin
increased body temperature
feedback
BIOL 2404
Strong/Spring 2007
Chapter 1 Lecture Notes
page 3
II. Anatomical Concepts
A. anatomical position
1. upright (standing)
2. hands at sides, palms forward
3. left and right always refer to the subject, never to the observer
B. directional terms
front of the body
back of the body
towards upper part of the body
towards lower part of the body
towards midline of the body
away from midline of the body
towards an attached base
away from an attached base
on or nearer to the surface
farther away from the surface
C. planes of section
1. sagittal - splits the body into left and right sections
midsagittal, median - splits body into equal left and right sections along the
longitudinal midline
2. transverse - splits the body into upper and lower sections
3. frontal - splits the body into front and back sections
coronal - a frontal section in the head or brain
BIOL 2404
Strong/Spring 2007
Chapter 1 Lecture Notes
page 4
D. body cavities and membranes
1. dorsal
a. cranial
walls = cranial bones
contents = brain
b. spinal
walls = vertebrae
contents = spinal cord
 there are connective tissue membranes called meninges surrounding the organs in
the dorsal cavity
BIOL 2404
Strong/Spring 2007
Chapter 1 Lecture Notes
page 5
2. ventral
a. thoracic
 the lungs are located in the lateral thoracic cavity
 the space between the lungs is called the mediastinum - it is not a
cavity
 the heart is in the inferior mediastinum
 the thoracic cavity is separated from the abdominopelvic cavity by the
diaphragm
walls = ribs, muscles, vertebrae, diaphragm
contents = lungs, heart, blood vessels, trachea, esophagus
b. abdominopelvic
 abdominal - above the pelvic brim
 pelvic - below the pelvic brim
walls = abdominal muscles, diaphragm, vertebrae
contents = stomach, liver, intestines
BIOL 2404
Strong/Spring 2007
Chapter 1 Lecture Notes
page 6
3. epithelial membranes line the ventral cavities and cover organs in the ventral cavities
a. pleura (noun singl.), pleurae (noun plural), pleural (adjective),
 visceral layer covers surface of lungs
 parietal layer lines part of inside of thoracic cavity
the pleural cavity is between the visceral pleura and parietal pleura
the lungs are not inside the pleural cavity, they are surrounded by it
the pleural cavity contains a thin layer of fluid
b. pericardium (noun singl.), pericardial (adjective)
 visceral layer covers surface of heart
 parietal layer forms a sac surrounding the heart
the pericardial cavity is between the visceral pericardium and the parietal
pericardium
the heart is not inside the pericardial cavity, it is surrounded by the cavity
the pericardial cavity contains a thin layer of fluid
BIOL 2404
Strong/Spring 2007
Chapter 1 Lecture Notes
page 7
c. peritoneum (noun singl.), peritoneal (adjective)
 visceral layer covers surface of many organs
 parietal layer lines part of inside of abdominal wall
 double layers of peritoneum called mesenteries support organs within
the cavity
the peritoneal cavity is between the visceral and parietal peritoneum
the organs are not inside the peritoneal cavity, they are surrounded by it
the peritoneal cavity contains a thin layer of fluid
BIOL 2404
Strong/Spring 2007