Transcript m5zn_dc4109a43372373

Chapter
01
*
Homeostasis:
A Framework for Human
Physiology
Dr. Niveen M. Daoud
Ass. Prof. clinical pathology
1
Section I What is Physiology?
• Physiology: biological sciences
• dealing with the normal life phenomena
exhibited by all living organisms.
• Human physiology: basic sciences
• dealing with normal life phenomena of
the human body.
• Goal of physiology:
• explain the physical and chemical factors
that are responsible for the origin,
development and progression of life.
2
Physiology—The Study of Function
• Sub disciplines
– Neurophysiology (physiology of nervous system)
– Endocrinology (physiology of hormones)
– Pathophysiology (mechanisms of disease)
1-3
The Birth of Modern Medicine
• Christian culture of Europe in Middle Ages
– Science severely repressed
– Taught medicine primarily as dogmatic commentary on Galen and
Aristotle
– Crude medical illustrations
• In Jewish and Muslim cultures free inquiry was less
inhibited
• Jewish physician Maimonides (Moses ben Maimon)
– Wrote 10 influential medical texts
– Was physician to Egyptian sultan, Saladin
• Avicenna (Ibn Sina) from Muslim world
– “The Galen of Islam”
– Combined Galen and Aristotle findings with original discoveries
– Wrote The Canon of Medicine, used in medical schools for 500 years
1-4
Homeostasis
A framework for human
physiology
• homeo = same; stasis = standing
• Homeostasis is the term we use to describe
the constant state of the internal
environment.
• Homeostasis is a state of
balance in the body.
• The processes and activities
that help to maintain homeostasis are
referred to as homeostatic mechanisms.
Homeostasis & Controls
•Successful
compensation
•Homeostasis
reestablished
•Failure to
compensate
•Pathophysiology
•Illness
•Death
6
Organization of the human body
Cells
Tissues
Organisms
Organ
(Human body)
Organs systems
7
Figure 1-1
8
The Hierarchy of Complexity
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Organism is composed of organ
systems
Organism
• Organ systems composed of
organs
• Organs composed of tissues
• Tissues composed of cells
Organ system
Tissue
Organ
• Cells composed of organelles
Cell
• Organelles composed of
molecules
• Molecules composed of atoms
Macromolecule
Organelle
Atom
Molecule
1-9
Section II Internal Environment
and Homeostasis
1. Cells, the fundamental units of life, exchange nutrients
and wastes with their surroundings:
The intracellular fluid is “conditioned by”…
the interstitial fluid, which is “conditioned by” …
the plasma, which is “conditioned by” …
the organ systems it passes through.
10
Body Fluids and Compartments
• The term “body fluids,” is used to refer to the watery solution of
dissolved substances (oxygen, nutrients, etc.) present in the body.
• The fluid in the blood and surrounding cells is called
extracellular fluid (i.e., outside the cell).
• About 20–25 percent is in the fluid portion of blood (plasma) and
the remaining 75–80 percent of the extracellular fluid lies around
cells and in special compartments is known as the interstitial
fluid.
• The total volume of extracellular fluid is the sum of the plasma
and interstitial volumes.
11
Total body water = 60 % BW
Extracellular fluid
Blood Plasma
1/3
2/3
Interstitial fluid
1/5
4/5
Intracellular fluid
= 40 % BW
12
Extracellular fluids
Intracellular
fluid
2. Plasma
1. Interstitial fluid
3. Fluid of special compartments: pericardial fluid, pleural fluid,
cerebrospinal fluid
13
Body Fluids and Compartments
• Intracellular fluid is the fluid located inside the cells.
• The composition of the extracellular fluid is very different from
that of the intracellular fluid. WHY
and HOW????
• Maintaining differences in fluid composition across the cell
membrane is an important way in which cells regulate their own
activity.
14
Differences Between Extracellular and
Intracellular Fluids.
*The extracellular fluid contains large amounts of sodium,
chloride, and bicarbonate ions plus nutrients …..
*The intracellular fluid differs significantly from
the extracellular fluid; specifically, it contains large
amounts of potassium, magnesium, …………
Homeostasis
• Homeostasis is a dynamic, not a static, process.
• Physiological variables can change dramatically
over a 24-hr. period, but the system is still in
overall balance. explain ???
• When homeostasis is maintained, we refer to
physiology; when it is not, we refer to
pathophysiology.
16
Blood glucose levels
increase after eating.
Levels return to their set
point via homeostasis.
This is an example of
dynamic constancy.
Levels change over short
periods of time, but
remain relatively
constant over long
periods of time.
17
18
Contribution of Organ Systems to the
Maintenance of Homeostasis
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Nervous system
Regulates muscular activity and glandular secretion; responsible for all activities
associated with the mind
Endocrine system
Regulates metabolic processes through secretion of hormones
Muscular system
Allows for body movement; contributes to thermoregulation
Circulatory system
Transports nutrients, O2, waste, CO2, electrolytes, and hormones throughout the body
Respiratory system
Obtains oxygen and eliminates carbon dioxide; regulates acid-base balance (pH)
Gastrointestinal tract
Digests food to provide nutrients to the body
Renal system
Eliminates waste products from the body; regulates blood volume and blood pressure;
regulates acid-base balance
19
20
Regulation of the Body Functions
Regulation- the ability of an organism to maintain a
stable internal conditions in a constantly changing
environment
-Three types:
1. Chemical (hormonal) Regulation- a regulatory process
performed by hormone or active chemical substance in blood
or tissue.
-It response slowly, acts extensively and lasts for a long
time.
2. Nervous Regulation- a process in which body functions
are controlled by nerve system
- Pathway: nerve reflex
21
3. Autoregulation – a tissue or an organ can directly
respond to environmental changes that are independent of
nervous and hormonal control
Characteristics：
Amplitude of the regulation is smaller than other two types.
Extension of the effects is smaller than other two types.
In the human body these three regulations have
coordinated and acts as one system, “feedback control
system”.
22
The nervous system
• The nervous system is composed of excitable
cells called neurones (also neurons)
• Neurones, characteristically, have long thin
extensions which carry electrical nerve
impulses
• This electrical signal of the nerve impulse needs
to be converted into a chemical signal (a
neurotransmitter) so that it can pass from
nerve cell to nerve cell
© 2008 Paul Billiet ODWS
Reflexes
• A reflex is a specific involuntary, unlearned
“built-in” response to a particular stimulus.
• Example: pulling your hand away from a hot
object or shutting your eyes as an object rapidly
approaches your face.
24
Reflexes
• The pathway mediating a reflex is known as the reflex arc.
• An arc has several components: stimulus, receptor, afferent
(incoming) pathway, integration center, efferent (outgoing)
pathway, and effector.
• A stimulus is defined as a detectable change in the internal
or external environment.
• A receptor detects the change.
• The pathway the signal travels between the receptor and
the integrating center is known as the afferent pathway.
The pathway along which information travels away from
the integration center to the effector is known as the
efferent pathway
• .
25
Figure 1-7
Afferent and efferent pathways in temperature homeostasis.
26
Postural Change in Blood Pressure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or
display.
Person rises
from bed
Blood pressure rises
to normal; homeostasis
is restored
Cardiac center
accelerates heartbeat
Blood drains from
upper body, creating
homeostatic imbalance
Baroreceptors above
heart respond to drop
in blood pressure
Figure
1.11
Baroreceptors send signals
to cardiac center of brainstem
Non-nerve Reflexes
• Almost all body cells can act as effectors in
homeostatic reflexes.
• There are, however, two specialized classes of tissues—muscle
and gland—that are the major effectors of biological control
systems.
• In the case of glands, the effector may be a hormone secreted
into the blood.
• A hormone is a type of chemical messenger secreted into the
blood by cells of the endocrine system .
• Hormones may act on many different cells simultaneously
because they circulate throughout the body.
28
Figure 1-9
A given signal can
fit into all 3 categories:
(e.g., the steroid
hormone cortisol
affects the very cells in
which it is made,
the nearby cells that
produce other hormones,
and many distant targets,
including muscles and
liver.)
Multi-factorial control of
signal release adds
more complexity.
29
Example:
Regulation of Blood Glucose
Fig 2.7
III- System Controls
• Feedback loops or systems are a common
mechanism to control physiological processes.
• A positive feedback system (also called a feed
forward) enhances the production of the
product.
• A negative feedback system shuts the system
off once the set point? has been reached.
31
Figure 1-6
Negative
Feedback
“Active product” controls the sequence of chemical reactions
by inhibiting the sequence’s rate-limiting enzyme, “Enzyme A.” 32
Negative Feedback: Inhibitory mechanism .
Is the mechanisms prevent small changes from becoming
too large.
33
Non-Biological Control System
 in room
Temperature
below 200 C
Room
temperature
Returns to 200 C
Room Temperature
Signals thermostat
To turn off heat
Heating System
Thermostat set
at 200 C
A Review
• Example: thermostatic heating system in a home
Components of an automatic control system
• Variable: the changeable (internal temp in this
example).
• Sensor (receptor) detects changes in variable and
feeds that information back to the integrator (control
center) (thermometer in this example).
Example Continued
• Integrator (control center) integrates (thermostat in
this example).
• Set point is the "ideal" or "normal" value of the
variable.
• Effector is the mechanism that has an "effect" on the
variable (internal temperature in this example).
Figure 1-8
Communication systems use signals that bind to receptors.
37
http://fig.cox.miami.edu/~cmallery/150/physiol/c44x10thermo-
39
A strategy for exploring homeostasis
• Identify the internal environmental variable.
example: concentration of glucose in the blood
• Establish the “set point” value for that variable.
example: 70 to 110 mg glucose/dL of blood
• Identify the inputs and outputs affecting the variable.
example: diet and energy metabolism
40
A strategy for exploring homeostasis
• Examine the balance between the inputs and outputs.
example: resting versus exercising
• Determine how the body monitors/senses the variable.
example: certain endocrine cells in the pancreas
“sense” changes in glucose levels
• Identify effectors that restore the variable to its set point.
example: a hormone that increases glucose
synthesis by the liver
Many homeostatic mechanisms utilize neural
communication.
41
Positive feedback
The
feedback signal or output from the
controlled system increases the action of
the control system
42
• A-Sometimes Be Useful.
•
Hemostasis??
• Blood clotting is an example of a valuable use of positive
feedback. When a blood vessel is ruptured and a clot begins to
form, multiple enzymes called clotting factors are activated
within the clot itself. Some of these enzymes act on other
unactivated enzymes of the immediately adjacent blood, thus
causing more blood clotting. This process continues until the
hole in the vessel is plugged and bleeding no longer occurs.
43
Positive Feedback: Stimulatory.
Stimulus trigger mechanisms that amplify the
response and reinforces the stimulus.
45
• B-Sometimes Cause Vicious Cycles and
Death:
• Hypovolemic shock
• If the person is suddenly bled 2 liters, the amount of
blood in the body is decreased to such a low level that
not enough blood is available for the heart to pump
effectively. As a result, the arterial pressure falls, and
the flow of blood to the heart muscle through the
coronary vessels diminishes. This results in
weakening of the heart, further diminished pumping,
a further decrease
46
• in coronary blood flow, and still more
weakness of the heart; the cycle repeats
itself again and again until death occurs.
47
Positive Feedback and Rapid Change
• Septic shock
• Fever > 104°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°F
1-48
Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 8 April 2005 01:55 PM)
© 2005 Elsevier
Adaptation and Acclimatization
• The term adaptation denotes a characteristic that
favors survival in specific environments.
• Acclimatization refers to the improved
functioning of an already existing homeostatic
system based on an environmental stress.
• In an individual, acclimatizations are reversible;
adaptations are not.
50
Balance in the Homeostasis of
Chemical Substances in the Body
• Many homeostatic systems regulate the balance
between addition and removal of a chemical substance
from the body.
• Two important generalizations concerning the balance
concept: (1) During any period of time, total-body
balance depends upon the relative rates of net gain and
net loss to the body; and (2) the pool concentration
depends not only upon the total amount of the substance
in the body, but also upon exchanges of the substance
within the body.
51
Some of the potential inputs and outputs that can
affect the “pool” of a material (like glucose) that is a
dynamically regulated physiological variable.
52
Figure 1-12
Sodium homeostasis: Consuming greater amounts of dietary
sodium initiates a set of dynamic responses that include greater
excretion of sodium in the urine. Though not shown here, the
amount excreted would likely exceed the amount ingested until
the “set point” is restored.
53
Check your understanding
• What are the main topics of our lecture?
• Why homeostasis is frame work of
physiology?
• Body deal with hypocalemia by stimulating
parathyroid gland this mechanism is known
as………… . Discuss this strategy , control
system, feed back mechanism .
54
The End.
55