Chapter 1: Homeostasis: A Framework for Human Physiology Flashcards
1.1 The Scope of Human Physiology
Physiology: the study of how living organisms function on both the molecular and systemic level
Pathophysiology: the study of abnormal changes in body functions that result in a diseased state of the body
Anatomy provides basic knowledge of the structures of the body while physiology provides deeper context into how those structures function.
1.2 How is the Body Organized
How the Body is Organized
- CELLS: the simplest structural unit into which a complex multicellular organism can be divided and still retain functions characteristic of life
H uman life begins as cells that divide into two, four, and so on.
- CELL DIFFERENTIATION: the process of transforming an unspecialized cell
During the development of cells, cells become specialized for a specific function, like movement or sending electrical signals.
- There are four general categories of cells, according to the broad types of functions they perform:
a. muscle cells
b. neurons
c. epithelial cells
d. connective-tissue cells
These cells have variations of specialized function (ex: smooth, cardiac, and skeletal muscle cells).
TISSUES: differentiated cells with similar properties that aggregate; an aggregate of a single type of specialized cell
The four general types of tissue are:
a. connective tissue
b. nervous tissue
c. epithelial tissue
d. muscle tissue
These tissues combine to form the structural fabric of organs and organ systems.
Muscle Cells and Tissues
- generate the mechanical activities that produce force and movement; 3 types include skeletal, cardiac, and smooth muscle cells
a. skeletal- voluntary control; attached through other structures to bones and produces movements of the limbs and trunk, involved in movement of facial expression
b. cardiac- involuntary control; found only in the heart, generates muscle contractions
c. smooth- involuntary control; makeup walls and tubes of the body and have contractions that perform specific functions
Neurons and Nervous Tissue
- initiate and conduct electrical signals, sometimes over long distances
- a collection of neurons forms nervous tissue
- in some parts of the body, cellular extensions from many neurons are packaged together along with connective tissue, making nerves
Epithelial Cells and Epithelial Tissue
- form barriers and selectively secrete and absorb ions and organic molecules; basolateral surface rests on a basement membrane
- epithelia rest on extracellular proteins layers called basement proteins
- identified by their specific shapes, including cuboidal, columnar, squamous, and ciliated
- epithelial tissue, or epithelium, may form from any type of epithelial tissues
- the type of epithelial formed in a particular part of the body reflects the epithelium’s function
Connective-Tissue Cells and Connective Tissue
- CONNECTIVE TISSUES: connect anchor and support the structures of the body
- connective tissues have many different forms like loose or dense connective tissue; blood is also considered a connective tissue
- connective tissue forms the extracellular matrix (ECM) that aids cellular attachment and messaging; this includes collagen fibers and elastin fibers
Organs and Organ Systems
- ORGANS: composed of two or more of the four kinds of tissues
- ORGAN SYSTEMS: groups of organs that perform an overall function
- many organs are composed of small, similar subunits called functional units
Basement membrane & apical
tight junctions
extracellular matrix
collagen
The layer of proteins and polysaccharides that anchors epithelial cell membranes to underlying connective tissue is called the basement membrane.
The side of an epithelial cell’s membrane that faces and is anchored to the basement membrane is referred to as the basolateral side.
Epithelial cells are held together along their lateral surfaces between the apical and basolateral membranes by extracellular barriers called
tight gap.
1.3 Body Fluid Compartments
The Body Fluid Compartments
When we refer to body fluid, we refer to a watery solution of dissolved substances such as oxygen, nutrients, and wastes. Solution is present within and around all cells of the body, and within blood vessels, and is known as the internal environment.
INTRACELLULAR EXTRACELLULAR–> MAJOR COMPARTMENTS
3 compartments of body
1. INTRACELLULAR FLUID: the fluid contained within all cells of the body and accounts for about 67% of all the water in the body
2. PLASMA: the fluid portion of the blood in which blood cells are suspended, and accounts for about 7% of total-body water
3. INTERSTITIAL FLUID: the fluid that lies around and between cells (in the space known as the interstitium) and makes up about 26% of total-body water
- EXTRACELLULAR FLUID: composed of the interstitial fluid (the fluid between the cells [within the place called the interstitium]) and the plasma (noncellular portion of the blood)
a. INTERSTITIAL FLUID
~75-80% of the extracellular fluid
b. PLASMA
~20-25% of the extracellular fluid
Intracellular and extracellular fluid are very different. Different compositions of the body’s compartments reflect the activities of the barriers separating them.
Blood (extracellular fluid) flows through the smallest blood vessels throughout the entire body, and the plasma exchanges oxygen, nutrients, wastes, and other substances of the interstitial fluid. It is considered homogenous.
Intracellular fluids contain proteins important for regulating cellular events such as growth and metabolism, and these proteins must be retained within the intracellular fluid.
COMPARTMENTALIZATION is an important part of physiology because barriers between the compartments help determine many functional characteristics.
The fluid matrix of blood is
intracellular and extracellular fluid is most different in composition
The concentration of dissolved proteins in plasma is less than the concentration of dissolved proteins in interstitial fluid.
1.4 Homeostasis
Homeostasis
Homeostasis is the physiological variable in a state of dynamic constancy. Not a static process.
Physiology is when homeostasis is maintained, whereas pathophysiology is when there is a loss of homeostasis.
Common physiological variables- like oxygen, glucose, sodium ions- are maintained within a predictable range, despite varying environmental conditions.
EXAMPLE: blood glucose levels spike after eating, body incites physiological processes to return the blood glucose to its resting point of 90 mg/dL. Stable point is rarely missed because of wide range of control systems activated to regulate the body.
HOMEOSTASIS: the process of maintaining a stable internal environment
- when homeostasis is disturbed for one variable, other variables will compensate
- it fluctuates within a predictable and often narrow range
INTERNAL ENVIRONMENT: the extracellular fluid
DYNAMIC CONSTANCY: a given variable may fluctuate in the body in the short term, but is stable and predictable in the long term
1.5 General Characteristics of Homeostatic Systems
The activity of cells, tissues, and organs must be regulated and integrated with each other so that any change in the internal environment initiates a reaction to correct the change.
HOMEOSTATIC CONTROL SYSTEMS minimize changes but cannot maintain complete constancy of a regulated variable. They maintain these responses.
Feedback loops or systems are a common mechanism to control physiological processes.
Homeostatic systems are held in a STEADY STATE which is a system in which a particular variable is not changing but in which energy must be continuously added to maintain a stable, homeostatic condition. Steady states are not equilibrium and can also be referred to as a set point.
EXAMPLE: The internal human body temperature maintains a general steady state by using energy to stay 37°C. 37°C is the set point for the system.
HOMEOSTASIS results from the operation of compensatory control systems
- a steady state in which a variable is unchanging as long as energy is provided (equilibrium does not require input of energy).
NEGATIVE FEEDBACK CONTROL SYSTEM: minimizes changes from the SET POINT of a system, leading to stability
- a change in a regulated variable brings about responses that move the variable in the direction opposite to the original change
- can occur on organ, cellular, or molecular basis
POSITIVE FEEDBACK CONTROL SYSTEM: accelerates a process by moving a variable further from a set point
- “explosive” system
- much less common
- pushed a conclusion forward
Resetting of Set Points
Set points can be reset to a new value. For example, with a fever, the body maintains homeostatic conditions but at a higher temperature to fight infection. This is an adaptive process and reflects the battling of regulatory systems. Clashing demands result in the adaptation of the set point.
FEEDFORWARD REGULATION:
- anticipates changes in a regulated variable
- fine-tunes homeostatic response
- minimizes fluctuations in the regulated variable
- external or internal environmental detectors stimulate an anticipated response
1.6 Components of Homeostatic Control Systems
REFLEX:
specific, involuntary, unpremeditated response to a stimulus
- some innate but some can be learned or acquired
- example: pulling hand away from hot object
- a pathway mediating a reflex is known as a reflex arc
REFLEXES ARE:
- stimulus –> receptor –> afferent pathway –> integrating center –> efferent pathway –> effector –> response
- a stimulus, or a detectable change in the internal or external environment happens–> a receptor detects the environmental change; a stimulus acts upon a receptor to produce a signal that is relayed to an –> integrating center –> the signal travels between the receptor and the integrating center along the –> afferent (to carry) pathway –> an effector is then produced by the integrating center–> the efferent pathway (meaning to carry away from) carries the response away from the center
- all cells can act as effectors in homeostatic reflexes, but muscles and gland especially
- the glands release hormones- a type of chemical messenger secreted into blood by cells of the endocrine system
LOCAL HOMEOSTATIC RESPONSES:
- involve stimulus-response sequences
- occur only in the area of the stimulus
A stimulus induces an alteration in cell activity to counteract the stimulus.
1.7 The Role of Intercellular Chemical Messengers in Homeostasis
INTERCELLULAR COMMUNICATION: cell-to-cell communication facilitates homeostasis
- essential to reflexes and local responses
- response to a particular stimulus on a local level
- regulate homeostatic mechanisms between cells
- achieved by neurotransmitters, hormones (many of
which are secreted from endocrine glands), paracrine
substances, or autocrine substances
- also occurs to a lesser extent through gap junctions
or cell-bound messengers
neurons, glands, and other cells types sometimes secrete the same chemical messenger.
Homeostatic responses are reliant on the ability of cells to communicate with one another. Intercellular communication is performed by chemical messengers. Four categories:
1. hormones
hormone-secreting gland cells secretes hormone, it travels through blood vessel, and target cells in one or more distant places in the body
Hormones are produced by endocrine glands (gonads, pancreas, thyroid) and distributed to organs. They can affect growth, metabolism, etc.
- neurotransmitters
neuron sends an electrical signal that travels through a neurotransmitter, and a neuron or effector cell in close proximity to site of neurotransmitter release
chemical messengers released from the soma or the end of the neuron, and it sends an electrical signal
- paracrine substances
local cell secretes paracrine substance, and target cells in close proximity to site of release of paracrine substance
paracrine signals supplement communication between cells. they are synthesized by the cells, and released, once given the appropriate stimulus, into the extracellular fluid. they then diffuse to neighboring cells. they are generally inactivated by locally existing enzymes.
- autocrine substances
the local cell releases autocrine substance, and the autocrine substance acts on the same cell that secreted the substance.
Two types of cell communication that do not require secretion:
1. gap junctions
- proteins connect two cell membrane
- passageway that connects the cytosol
- ions and small molecules can pass
- juxtacrine signaling
- extracellular proteins link
- helps cells “recognize” each other
- important in growth & immunity
1.8 Processes Related to Homeostasis
ADAPTATION: any characteristic that favors survival in a specific environment; many are inheritable, such as homeostatic control systems
- homeostatic control systems are also inherited biological adaptations and allow an individual to adapt to encountered environmental changes
- ex: ability to digest milk
ACCLIMATIZATION: improved functioning of an already existing homeostatic system
- induced by prolonged exposure to a stress with no change in genetic endowment
- typically reversible
CIRCADIAN RHYTHMS: biological functions with a cycle of approximately 24 hours
- feedforward component to homeostatic control systems without detectors
- internally driven by pacemakers; the
SUPRACHIASMATIC NUCLEUS is the principal pacemaker, inputs indicate to the hypothalamus certain entrainments, one output of the pacemaker goes to the pineal gland which then secretes the hormone melatonin (only in dark) which then stimulates sleep
- entrained by light- ENTRAINMENT- or setting the actual hours of the rhythm
- FREE RUN without entrainment; FREE-RUNNING RHYTHM- a disorder in which the intrinsic circadian rhythm is no longer entrained to the 24-h schedule
BALANCE OF CHEMICAL SUBSTANCES IN THE BODY
- homeostatic systems regulate the balance between addition and removal of a chemical substance in the body
- there are net gains from things like food or air and net loss from things like metabolism and waste production
TOTAL-BODY (MASS) BALANCE: matching inputs and outputs of a substance in the body
- can be negative (net loss), positive (net gain), or stable (loss = gain)
- during any period of time, total-body balance depends upon the relative rates of net gain and net loss
- the pool concentration depends on the total amount of substance in the body, but also upon exchanges of substance within the body
- ex: Ca 2+ ions in the body
CALCIUM IN FOOD - IN FECES = IN URINE
1.9 General Principles of Physiology
GENERAL PRINCIPLES OF PHYSIOLOGY: includes homeostasis; information flow; coordination of functions between different organ systems; transfer of matter and energy; structure determines function; physiological process follow the laws of chemistry and physics
- homeostasis is essential for health and survival. ability to maintain physiological variables (like body temp. or glucose levels) is underlying factor of physiology. processes of feedback and feedforward are basis of this. disease and environmental factors can pose challenges to homeostasis.
- functions of organ systems are coordinated with each other. physiological mechanisms operate on levels of cells, tissues, organs, and organ systems. organ systems function together, not independent. ex: urine and circulatory.
- most physiological functions are controlled by multiple regulatory systems, often working in opposition. control systems operate around certain steady variable with both inhibitory and stimulatory variables. ex: heart rate
- information flow between cells, tissues, and organs is essential feature of homeostasis and allows for integration of physiological processes. cells nearby each other can communicate with chemically secreted signals. cells can also communicate long distances using chemical signals and electrical messages called hormones.
- controlled exchange of materials occurs between compartments and across cellular membranes. movement of water and solutes between intracellular and extracellular fluid is critical for cell survival and body survival. this way essential biological molecules are transported and wastes are eliminated and mechanisms are facilitated.
- physiological processes are dictated by laws of chemistry and physics. chemical reactions facilitate processes. processes also have properties of physics like electromagnetism and gravity.
- physiological processes require the transfer and balance of matter and energy. growth and the maintenance of homeostasis require regulation and movement of energy-yielding nutrients and molecular building blocks to all areas of body. ATP and inorganic molecules must be regulated ad often play essential process of physiology. requires coordinated allocation of resources.
- structure is determinant of- and has coevolved with- function. the form and compsoition of cells, tissues, organs, and organ systems determine how they interact with each other in the physical world. different parts of body structure converge to perform similar functions. ex: membrane diffusion and transport in respiratory and circulatory.
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