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Homeostasis & Requirements of Life
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Introductory Lecture for Bio 260
• Adapted from Chapter 1, Marieb’s Human
Anatomy and Physiology
• What should you emphasize?
• Principle of complimentarity
• Levels of structural organization
• Necessary life functions & survival needs
• Homeostasis
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Overview of Anatomy and Physiology
Anatomy – the study of the structure of body
parts and their relationships to one another

Physiology – the study of the function of the
body structural systems

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Physiology
The study of functions of specific organ systems
Examples:
• Renal – kidney functions in filtering the blood
and osmoregulation
• Neurophysiology – workings of the brain,
neurons, and receptors
• Cardiovascular – operation of the heart and
blood vessels
Functions of the body often best understood at
the cellular or molecular level
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Physiology

Essential tools for the study of physiology:
 Ability to focus at many levels (from systemic
to cellular and molecular)
 Basic physical principles (e.g., electrical
currents, pressure, and movement)
 Basic chemical principles
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Principle of Complementarity
 Anatomy and physiology are inseparable.
• Function always reflects structure
• What a structure can do depends on its
specific form
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Levels of Structural Organization
• Chemical – atoms and molecules (Chapter 2)
• Cellular – cells and their organelles (Chapter 3)
• Tissue – groups of similar cells (Chapter 4)
• Organ – contains two or more types of tissues
• Organ system – organs that work closely together
• Organismal – all organ systems
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Atoms
Organelle
Smooth muscle cell
Molecule
1 Chemical level
Atoms combine to form molecules.
Cardiovascular
system
Heart
Blood
vessels
2 Cellular level
Cells are made up of
molecules.
Smooth muscle tissue
3 Tissue level
Tissues consist of similar
types of cells.
Blood vessel (organ)
Smooth muscle tissue
Connective tissue
Epithelial
tissue
4 Organ level
Organs are made up of different types
of tissues.
6 Organismal level
The human organism is made up
of many organ systems.
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5 Organ system level
Organ systems consist of different
organs that work together closely.
Figure 1.1
Overview of Organ Systems
• Note major organs and functions of the 11
organ systems (Fig. 1.3)
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Hair
Skin
Nails
(a) Integumentary System
Forms the external body covering, and
protects deeper tissues from injury.
Synthesizes vitamin D, and houses
cutaneous (pain, pressure, etc.)
receptors and sweat and oil glands.
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Figure 1.3a
Bones
Joint
(b) Skeletal System
Protects and supports body organs,
and provides a framework the muscles
use to cause movement. Blood cells
are formed within bones. Bones store
minerals.
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Figure 1.3b
Skeletal
muscles
(c) Muscular System
Allows manipulation of the environment,
locomotion, and facial expression. Maintains posture, and produces heat.
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Figure 1.3c
Brain
Spinal
cord
Nerves
(d) Nervous System
As the fast-acting control system of
the body, it responds to internal and
external changes by activating
appropriate muscles and glands.
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Figure 1.3d
Pineal gland
Pituitary
gland
Thyroid
gland
Thymus
Adrenal
gland
Pancreas
Testis
Ovary
(e) Endocrine System
Glands secrete hormones that regulate
processes such as growth, reproduction,
and nutrient use (metabolism) by body
cells.
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Figure 1.3e
Heart
Blood
vessels
(f) Cardiovascular System
Blood vessels transport blood,
which carries oxygen, carbon
dioxide, nutrients, wastes, etc.
The heart pumps blood.
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Figure 1.3f
Red bone
marrow
Thymus
Lymphatic
vessels
Thoracic
duct
Spleen
Lymph
nodes
(g) Lymphatic System/Immunity
Picks up fluid leaked from blood vessels
and returns it to blood. Disposes of debris
in the lymphatic stream. Houses white
blood cells (lymphocytes) involved in
immunity. The immune response mounts
the attack against foreign substances
within the body.
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Figure 1.3g
Nasal
cavity
Pharynx
Larynx
Trachea
Bronchus
Lung
(h) Respiratory System
Keeps blood constantly supplied with
oxygen and removes carbon dioxide.
The gaseous exchanges occur through
the walls of the air sacs of the lungs.
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Figure 1.3h
Oral cavity
Esophagus
Liver
Stomach
Small
intestine
Large
intestine
Rectum
Anus
(i) Digestive System
Breaks down food into absorbable
units that enter the blood for
distribution to body cells. Indigestible
foodstuffs are eliminated as feces.
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Figure 1.3i
Kidney
Ureter
Urinary
bladder
Urethra
(j) Urinary System
Eliminates nitrogenous wastes from the
body. Regulates water, electrolyte and
acid-base balance of the blood.
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Figure 1.3j
Mammary
glands (in
breasts)
Prostate
gland
Ovary
Penis
Testis
Scrotum
Ductus
deferens
Uterus
Vagina
Uterine
tube
(l) Female Reproductive System
(k) Male Reproductive System
Overall function is production of offspring. Testes produce sperm and male sex
hormone, and male ducts and glands aid in delivery of sperm to the female
reproductive tract. Ovaries produce eggs and female sex hormones. The remaining
female structures serve as sites for fertilization and development of the fetus.
Mammary glands of female breasts produce milk to nourish the newborn.
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Figure 1.3k-l
Organ Systems Interrelationships
All cells depend on organ systems to meet their
survival needs

Each organ system does not function
independently, but work cooperatively to perform
necessary life functions

Example:
• Digestive and respiratory systems, in contact with
the external environment, take in nutrients and
oxygen
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Organ Systems
Interrelationships


Nutrients and oxygen
are distributed by the
blood
Metabolic wastes are
eliminated by the
urinary and respiratory
systems
Digestive system
Takes in nutrients, breaks them
down, and eliminates unabsorbed
matter (feces)
Respiratory system
Takes in oxygen and
eliminates carbon dioxide
Food
O2
CO2
Cardiovascular system
Via the blood, distributes oxygen
and nutrients to all body cells and
delivers wastes and carbon
dioxide to disposal organs
Blood
CO2
O2
Heart
Nutrients
Interstitial fluid
Urinary
system
Eliminates
nitrogenous
wastes and
excess ions
Nutrients and wastes pass
between blood and cells
via the interstitial fluid
Integumentary system
Feces Protects the body as a whole Urine
from the external environment
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Figure 1.2
Necessary Life Functions
1. Maintaining boundaries – the internal
environment remains distinct from the
external environment
•
Plasma membranes of cells
•
Skin of an organism
2. Movement (contractility)
•
Of body parts (skeletal muscle)
•
Of substances (cardiac and smooth muscle)
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Necessary Life Functions
3. Responsiveness – ability to sense changes
in the environment (internally & externally)
and respond to them
•
Withdrawal reflex
•
Control of breathing rate
4. Digestion
•
Breakdown of ingested foodstuffs
•
Absorption of simple molecules into blood
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Necessary Life Functions
5. Metabolism – all the chemical reactions
that occur in the body that allow the
organism to function
•
Catabolism and anabolism
6. Excretion – The removal of wastes from
metabolism and digestion
•
Urea, carbon dioxide, feces
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Necessary Life Functions
7. Reproduction – producing the next
generation
•
Cellular – an original cell divides and
produces two identical daughter cells for
growth or repair
•
Organismal – sperm and egg unite to make a
whole new person (production of offspring)
8. Growth – increase in size of a body part or
of the entire organism
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Survival Needs
1. Nutrients
•
Sources of energy to power chemical
reactions and building materials
•
Carbohydrates, fats, proteins, minerals,
vitamins
2. Oxygen
•
Essential for energy release (ATP
production)
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Survival Needs
3. Water
•
Most abundant chemical in the body
•
Provides the environment for chemical
reactions
4. Normal body temperature
•
Affects rate of chemical reactions
5. Appropriate atmospheric pressure
•
For adequate breathing and gas exchange in
the lungs
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Homeostasis
 Homeostasis – ability to maintain a relatively
stable internal environmental conditions in an
ever-changing outside world
 The internal environment of the body is in a
dynamic state of equilibrium
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Homeostatic Control Mechanisms
Involve continuous monitoring and regulation
of many factors (variables)

Variables (O2 level, body temperature, blood
pressure, etc) alter body functions

Nervous and endocrine systems accomplish
the communication via nerve impulses and
hormones

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Components of a Control Mechanism
1. Receptor (sensor)
•
Monitors the environment
•
Responds to stimuli (changes in controlled variables)
2. Control center
•
Determines the set point at which the variable is
maintained
•
Receives input from receptor
•
Determines appropriate response
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Components of a Control Mechanism
3. Effector
•
Receives output from control center
•
Provides the means to respond to stimuli
•
Response acts to reduce or enhance the
stimulus (feedback)
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Homeostatic Control Mechanisms
3 Input: Information
sent along afferent
pathway to control
center.
2
Receptor
detects
change.
Receptor
4 Output:
Control
Center
Afferent
Efferent
pathway
pathway
1
Stimulus
produces
change in
variable.
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BALANCE
Information sent along
efferent pathway to
effector.
Effector
5
Response
of effector
feeds back
to reduce
the effect of
stimulus
and returns
variable to
homeostatic
level.
Figure 1.4
Negative Feedback
 In negative feedback systems, the response
reduces or shuts off the original stimulus
 Produces an opposite effect to the current state
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Negative Feedback
 Example (non-biological) –
• Regulation of room temperature by a thermostat
 Examples (biological) –
• Regulation of body temperature
(a nervous mechanism)
• Regulation of blood glucose by insulin and glucagon
(an endocrine mechanism)
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Regulation of Room Temperature
by a Thermostat
Set
point
Control center
(thermostat)
Signal
wire turns
heater off
Receptor-sensor
(thermometer in
Thermostat)
Heater
off
Effector
(heater)
Response;
temperature
drops
Stimulus:
rising room
temperature
Balance
Response;
temperature
rises
Stimulus:
dropping room
temperature
Heater
on
Set
point
Effector
(heater)
Receptor-sensor
(thermometer in
Thermostat)
Signal
wire turns
heater on
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Control center
(thermostat)
Figure 1.5
Regulation of Body Temperature
Control Center
(thermoregulatory
center in brain)
Information sent
along the afferent
pathway to control
center
Afferent
pathway
Information sent
along the efferent
pathway to
effectors
Efferent
pathway
Receptors
Temperature-sensitive
cells in skin and brain
Effectors
Sweat glands
Sweat glands activated
Response
Evaporation of sweat
Body temperature falls;
stimulus ends
Stimulus
Body temperature
rises
BALANCE
Stimulus
Response
Body temperature rises;
stimulus ends
Body temperature falls
Receptors
Temperature-sensitive
cells in skin and brain
Effectors
Skeletal muscles
Shivering
begins
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Efferent
pathway
Information sent
along the efferent
pathway to effectors
Afferent
pathway
Control Center
(thermoregulatory
center in brain)
Information sent
along the afferent
pathway to control
center
Figure 1.5
Pancreatic Hormones and Blood Sugar
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Positive Feedback
 The response enhances or exaggerates the
original stimulus
 May exhibit a cascade or amplifying effect
 Usually controls infrequent events –
Examples:
• Enhancement of labor contractions by oxytocin
(Chapter 28)
• Platelet plug formation and blood clotting
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Initiation of Labor
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Platelet Plug Formation and Blood Clotting
1 Break or tear
occurs in blood
vessel wall.
Positive feedback
cycle is initiated.
3 Released
chemicals
attract more
platelets.
2 Platelets
Positive
feedback
loop
adhere to site
and release
chemicals.
Feedback cycle ends
when plug is formed.
4 Platelet plug
forms.
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Figure 1.6
Homeostatic Imbalance
 Disturbance of homeostasis or the body’s
normal equilibrium
• Increases risk of disease
• Contributes to changes associated with aging
• May allow destructive positive feedback
mechanisms to take over (e.g., heart failure)
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