Physiology
Book - Human Physiology: An
integrated approach
Chapter 1: Introduction to physiology
Physiology = the study of the normal functioning of a living organism and its component parts,
including all its chemical and physical processes.
Genome = collective term for all the genetic information contained in the DNA of a species.
1.1 Physiology is an integrative science
Emergent properties = properties that cannot be predicted to exist based only on knowledge of
the system’s individual components.
An emergent property is not a property of any single component of the system, and it is greater
than the simple sum of the system’s individual parts. Result from complex, nonlinear interactions
of the different components. The most complex emergent properties in humans are emotion,
intelligence and other aspects of brain function.
The integration of function across many levels of organization is a special focus of
physiology.
Collections of molecules in living organisms form cells, the smallest unit of structure capable of
carrying out all life processes. A lipid and protein barrier called the cell membrane separates
cells from their external environment. Collections of cells that carry out related functions are
called tissue. Tissues form structural and functional units known as organs, and groups of
organs integrate their functions to create organ systems.
Integumentary system = composed of the skin, forms a protective boundary that separates the
body’s internal environment from the external environment.
Musculoskeletal system = provides support and body movement.
Four systems exchange material between the internal and external environment:
1. Respiratory (pulmonary) system = exchanges gases.
2. Digestive (gastrointestinal) system = takes up nutrients and water and eliminates
wastes.
3. Urinary (renal) system = removes excess water and waste material.
4. Reproductive system = produces eggs or sperm.
The nervous and endocrine systems coordinate body functions.
Circulatory (cardiovascular) system = distributes materials by pumping blood through the
vessels.
,Immune system = specialized cells of the immune system are scattered throughout the body.
They protect the internal environment from foreign substances by intercepting material that
enter through the intestines and lungs or through a break in the skin.
1.4 Homeostasis
Cannon divided his variables into what he described as environmental factors that affect cells
(osmolarity, temperature, and pH) and “materials for cell needs” (nutrients, water, sodium,
calcium, other inorganic ions, oxygen, as well as “internal secretions” having general and
continuous effects).
Internal secretions = hormones and other chemicals that our cells use to communicate with
one another.
Homeostasis = the regulation of the body’s internal environment, the body monitors its internal
state and takes action to correct disruptions that threaten its normal function.
Pathological condition = if the body fails to maintain homeostasis of the critical variables, then
normal function is disrupted and a disease state.
Two general groups of diseases due to their origin:
1. those in which the problem arises from internal failure of some normal physiological
process.
2. Those that originated from some outside source.
Pathophysiology = the study of body functions in a disease state.
Homeostasis depends on mass balance
The human body is an open system that exchanges heat and materials with the outside
environment. To maintain homeostasis, the body must maintain mass balance.
Law of mass balance = if the amount of a substance in the body is to remain constant, any
gain must be offset by an equal loss.
To maintain mass balance, the body has two options for output.
1. Excretion = the elimination of material from the body, usually through
the urine, feces, lungs, or skin.
2. Convert the substance to a different substance through metabolism.
Total amount of substance x in the body = intake + production - excretion -
metabolism.
Mass flow (amount x/min) = concentration of x x volume flow or (amount x/vol)
x (vol/min).
Control systems and homeostasis
The regulated variables are kept within their acceptable (normal) range by
physiological control mechanisms that kick in if the variable ever strays too far
from its setpoint, or optimum value.
Alle control systems have three components:
1. An input signal.
2. A controller, or integrating center that integrates incoming information and initiates an
appropriate response.
, 3. An output signal that creates a response.
Local control is restricted to a tissue
Local control = restricted to the tissue or cell involved.
Reflex control uses long-distance signaling
Reflex control = any long-distance pathway that uses the nervous system, endocrine system,
or both.
A response loop has three primary components:
1. An input signal
2. An integrating center to integrate the signal.
3. Output signal.
Stimulus → sensor → input signal → integrating center → output signal → target → response.
The input side of the response loop starts with a stimulus – the change that occurs when the
regulated variable moves out of its desirable range. A specialized sensor monitors the variable.
Response loops begin with a stimulus
Antagonistic control = when to different stimulus work on the same thing, to control the
setpoint.
Feedback loops modulate the response loop
Feedback loop = the response “feeds back” to influence the input portion of the pathway.
Negative feedback loops are homeostatic
For most reflexes, feedback loop are homeostatic – that is, designed to keep the
system at or near a setpoint so that the regulated variable is relatively stable. How
well an integrating center succeeds in maintaining stability depends on the sensitivity
of the system.
The end result of homeostasis is a regulated variable that oscillate around the
setpoint.
Negative feedback = a pathway in which the response opposes or removes the
signal.
Negative feedback loops stabilize the regulated variable and thus aid the
system in maintaining homeostasis.
Negative feedback loops can restore the normal state but cannot prevent
the initial disturbance.
Positive feedback loops are not homeostatic
In a positive feedback loop, the response reinforces the stimulus rather
than decreasing or removing it. The response sends the regulated variable even
farther from its normal value.
Because positive feedback escalates the response, this type of feedback requires
some intervention or event outside the loop to stop the response.
Example: hormonal control of uterine contractions during childbirth.
, Feedforward control allows the body to anticipate change
Feedforward control = anticipatory responses, a few reflexes have evolved that enable the
body to predict that a change is about to occur and start the response loop in anticipation of the
change.
Example: salivation reflex = the sight, smell or even the thought of food is enough to start our
mouths watering in expectation of eating the food.
Biological rhythms result from changes in a setpoint
Factors that influence an individual’s setpoint for a given variable include normal biological
rhythms, inheritance and the conditions to which the person has become accustomed.
Biorhythm = regulated variables that change predictably and create repeating patterns or
cycles of change.
Circadian rhythm = daily biological rhythms.
Example in humans: blood pressure, body temperature and metabolic processes. Body
temperature peaks in the late afternoon and declines dramatically in the early hours of the
morning.
The adaptation of physiological processes to a given set of environmental conditions is known
as acclimatization when it occurs naturally. It the process takes place artificially in a laboratory
setting, it is called acclimation.
Chapter 6: Communication, integration, and
homeostasis
6.1 Cell-to-cell communication
The human body is composed of about 75 trillion cells. Those cells face a daunting task- to
communicate with one another in a manner that is rapid and yet conveys a tremendous amount
of information.
There are two basic types of physiological signals:
1. Electrical signals = changes in a cell’s membrane potential.
2. Chemical signals = molecules secreted by cells into the extracellular fluid, responsible
for most communication within the body. They act as ligands that bind to proteins that
initiate a response.
Target cells = cells that respond to electrical or chemical signals.
There are four basic methods of cell-to-cell communication:
1. Gap junctions = allow direct cytoplasmic transfer of electrical and chemical signals
between adjacent cells. (local communication)
Book - Human Physiology: An
integrated approach
Chapter 1: Introduction to physiology
Physiology = the study of the normal functioning of a living organism and its component parts,
including all its chemical and physical processes.
Genome = collective term for all the genetic information contained in the DNA of a species.
1.1 Physiology is an integrative science
Emergent properties = properties that cannot be predicted to exist based only on knowledge of
the system’s individual components.
An emergent property is not a property of any single component of the system, and it is greater
than the simple sum of the system’s individual parts. Result from complex, nonlinear interactions
of the different components. The most complex emergent properties in humans are emotion,
intelligence and other aspects of brain function.
The integration of function across many levels of organization is a special focus of
physiology.
Collections of molecules in living organisms form cells, the smallest unit of structure capable of
carrying out all life processes. A lipid and protein barrier called the cell membrane separates
cells from their external environment. Collections of cells that carry out related functions are
called tissue. Tissues form structural and functional units known as organs, and groups of
organs integrate their functions to create organ systems.
Integumentary system = composed of the skin, forms a protective boundary that separates the
body’s internal environment from the external environment.
Musculoskeletal system = provides support and body movement.
Four systems exchange material between the internal and external environment:
1. Respiratory (pulmonary) system = exchanges gases.
2. Digestive (gastrointestinal) system = takes up nutrients and water and eliminates
wastes.
3. Urinary (renal) system = removes excess water and waste material.
4. Reproductive system = produces eggs or sperm.
The nervous and endocrine systems coordinate body functions.
Circulatory (cardiovascular) system = distributes materials by pumping blood through the
vessels.
,Immune system = specialized cells of the immune system are scattered throughout the body.
They protect the internal environment from foreign substances by intercepting material that
enter through the intestines and lungs or through a break in the skin.
1.4 Homeostasis
Cannon divided his variables into what he described as environmental factors that affect cells
(osmolarity, temperature, and pH) and “materials for cell needs” (nutrients, water, sodium,
calcium, other inorganic ions, oxygen, as well as “internal secretions” having general and
continuous effects).
Internal secretions = hormones and other chemicals that our cells use to communicate with
one another.
Homeostasis = the regulation of the body’s internal environment, the body monitors its internal
state and takes action to correct disruptions that threaten its normal function.
Pathological condition = if the body fails to maintain homeostasis of the critical variables, then
normal function is disrupted and a disease state.
Two general groups of diseases due to their origin:
1. those in which the problem arises from internal failure of some normal physiological
process.
2. Those that originated from some outside source.
Pathophysiology = the study of body functions in a disease state.
Homeostasis depends on mass balance
The human body is an open system that exchanges heat and materials with the outside
environment. To maintain homeostasis, the body must maintain mass balance.
Law of mass balance = if the amount of a substance in the body is to remain constant, any
gain must be offset by an equal loss.
To maintain mass balance, the body has two options for output.
1. Excretion = the elimination of material from the body, usually through
the urine, feces, lungs, or skin.
2. Convert the substance to a different substance through metabolism.
Total amount of substance x in the body = intake + production - excretion -
metabolism.
Mass flow (amount x/min) = concentration of x x volume flow or (amount x/vol)
x (vol/min).
Control systems and homeostasis
The regulated variables are kept within their acceptable (normal) range by
physiological control mechanisms that kick in if the variable ever strays too far
from its setpoint, or optimum value.
Alle control systems have three components:
1. An input signal.
2. A controller, or integrating center that integrates incoming information and initiates an
appropriate response.
, 3. An output signal that creates a response.
Local control is restricted to a tissue
Local control = restricted to the tissue or cell involved.
Reflex control uses long-distance signaling
Reflex control = any long-distance pathway that uses the nervous system, endocrine system,
or both.
A response loop has three primary components:
1. An input signal
2. An integrating center to integrate the signal.
3. Output signal.
Stimulus → sensor → input signal → integrating center → output signal → target → response.
The input side of the response loop starts with a stimulus – the change that occurs when the
regulated variable moves out of its desirable range. A specialized sensor monitors the variable.
Response loops begin with a stimulus
Antagonistic control = when to different stimulus work on the same thing, to control the
setpoint.
Feedback loops modulate the response loop
Feedback loop = the response “feeds back” to influence the input portion of the pathway.
Negative feedback loops are homeostatic
For most reflexes, feedback loop are homeostatic – that is, designed to keep the
system at or near a setpoint so that the regulated variable is relatively stable. How
well an integrating center succeeds in maintaining stability depends on the sensitivity
of the system.
The end result of homeostasis is a regulated variable that oscillate around the
setpoint.
Negative feedback = a pathway in which the response opposes or removes the
signal.
Negative feedback loops stabilize the regulated variable and thus aid the
system in maintaining homeostasis.
Negative feedback loops can restore the normal state but cannot prevent
the initial disturbance.
Positive feedback loops are not homeostatic
In a positive feedback loop, the response reinforces the stimulus rather
than decreasing or removing it. The response sends the regulated variable even
farther from its normal value.
Because positive feedback escalates the response, this type of feedback requires
some intervention or event outside the loop to stop the response.
Example: hormonal control of uterine contractions during childbirth.
, Feedforward control allows the body to anticipate change
Feedforward control = anticipatory responses, a few reflexes have evolved that enable the
body to predict that a change is about to occur and start the response loop in anticipation of the
change.
Example: salivation reflex = the sight, smell or even the thought of food is enough to start our
mouths watering in expectation of eating the food.
Biological rhythms result from changes in a setpoint
Factors that influence an individual’s setpoint for a given variable include normal biological
rhythms, inheritance and the conditions to which the person has become accustomed.
Biorhythm = regulated variables that change predictably and create repeating patterns or
cycles of change.
Circadian rhythm = daily biological rhythms.
Example in humans: blood pressure, body temperature and metabolic processes. Body
temperature peaks in the late afternoon and declines dramatically in the early hours of the
morning.
The adaptation of physiological processes to a given set of environmental conditions is known
as acclimatization when it occurs naturally. It the process takes place artificially in a laboratory
setting, it is called acclimation.
Chapter 6: Communication, integration, and
homeostasis
6.1 Cell-to-cell communication
The human body is composed of about 75 trillion cells. Those cells face a daunting task- to
communicate with one another in a manner that is rapid and yet conveys a tremendous amount
of information.
There are two basic types of physiological signals:
1. Electrical signals = changes in a cell’s membrane potential.
2. Chemical signals = molecules secreted by cells into the extracellular fluid, responsible
for most communication within the body. They act as ligands that bind to proteins that
initiate a response.
Target cells = cells that respond to electrical or chemical signals.
There are four basic methods of cell-to-cell communication:
1. Gap junctions = allow direct cytoplasmic transfer of electrical and chemical signals
between adjacent cells. (local communication)
