Download The Foundation of Physiology

11/2/11
Dr Áine Kelly
Dept of Physiology, School of Medicine
Email: [email protected]
http://medicine.tcd.ie/physiology/student/
Diagrams: Sherwood, Human Physiology (7th Ed.)
Textbooks:
Fox, Human Physiology
Sherwood, Human Physiology, from Cells to Systems
Germann and Stanfield, Principles of Human Physiology
Vertebrate Form and Function
Form (structure): Anatomy
Function: Physiology
This lecture: Organisation of the body and Homeostasis
Homeostasis: The Foundation of Physiology
Claude Bernard (1813-1878)
"La fixité du milieu intérieur est la condition
d'une vie libre et indépendante"
("The constancy of the internal environment is
the condition for a free and independent life").
Defined as maintenance of a relatively stable
internal environment
Does not mean that composition,
temperature, and other characteristics are
absolutely unchanging
Essential for survival and function of all cells
Each cell contributes to maintenance of a
relatively stable internal environment
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Homeostasis: What is the internal environment?
Extracellular fluid (ECF)
Fluid environment in which the cells live
Plasma; interstitial fluid
Intracellular fluid (ICF)
Fluid contained within all body cells
Also termed cytosol
Homeostasis: normal living
Factors homeostatically regulated include:
Concentration of nutrient molecules
Concentration of O2 and CO2
Concentration of waste products
pH
Concentration of water, salt, and other electrolytes
Volume and pressure
Temperature
Homeostasis: What is the external environment?
Dublin
Height above sea level:0m
Atmospheric pressure:760mmHg
PO2 :160mmHg
PaO2: 100mmHg
Record temperature: -12 to 30oC.
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Homeostasis: What is the external environment?
Everest: 29,029ft (8,848m) above sea level
PaO2: 25mmHg
Dallol, Ethiopia (now a ghost town)
1960’s: average annual temp: 34oC
La Rinconada, Peru: 16,732ft (5,100m)
Oykmayon, Russia. January 1926: -71.2oC
Recorded annual temp difference of 100oC
Homeostasis: What is the external environment?
Drought
Lack of water: 3-5 day survival
Famine
Lack of food: weeks/months,
depending on fat stores
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Free diving record: 122m
Underwater breath-holding record: 11m35s
Hossein Rezazedeh: 263.5kg at Athens Olympics
Functional Organization of the Body
Organism
Body system
Organ
Tissue
Cell: basic unit of life
Subcellular
Molecular
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Cells
Exchange materials (eg. nutrients, oxygen, carbon dioxide, wastes) with surrounding
environment
Perform chemical reactions that provide energy for the cell
Synthesize needed cellular components
Sense and respond to changes in surrounding environment (receptors)
Reproduce (divide)
Cell physiology, biochemistry and molecular biology allows us to further assess
function of subcellular organelles, proteins etc.
Cells are structurally specialised for function
Humans are very different from single-celled or simple
multicellular organisms!
Neuron
Cardiac muscle cell
Gamete
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Stem Cells
Undifferentiated cells that can give rise to specialised cells
Can we use these cells to treat disease?
Spinal cord injury, parkinson’s disease, diabetes mellitis, cancer
Engineer replacement body parts?
Hip replacement, burns, bladder
Embryonic stem cells: pluripotent (can give rise to many different cell types)
Ethical considerations - embryos are destroyed during this process
Adult stem cells. Tissue-specific
Bone marrow, brain, muscle
Tissues
Groups of cells with similar structure and specialized function
Four primary types
Muscle tissue (excitable)
Nervous tissue (excitable)
Epithelial tissue (exchange)
Connective tissue (connection and support): includes blood, bone
Organs
Consist of two or more types of primary tissues working together to perform
particular function(s) eg. Stomach:
Inside lined with epithelial tissue
Wall contains smooth muscle
Nervous tissue controls muscle contraction & gland secretion
Connective tissue binds all the above tissues together
Body Systems
Groups of organs that perform related functions and interact to accomplish a common
activity essential to survival of the whole body
Do not act in isolation from one another
Human body has 11 systems
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Role of Body Systems in Homeostasis
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Homeostatic Control Systems
In order to maintain homeostasis, control system must be able to
Detect deviations from normal in the internal environment
(receptors)
Integrate this information with other relevant information (CNS)
Make appropriate adjustments in order to restore factor to its
desired value
Intrinsic controls
Extrinsic controls
Local controls that are
inherent in an organ
Regulatory mechanisms
initiated outside an organ
Accomplished by nervous
and endocrine systems (note
special role of hypothalamus)
Homeostatic Control Systems: Feedforward
Term used for responses made in anticipation of a change eg. during digestion
(before absorption occurs) presence of food causes insulin release - insulin
promotes uptake of nutrients into cells after their absorption from gut into
bloodstream.
Homeostatic Control Systems: Feedback
Responses made after change has been detected
Positive feedback
Amplifies an initial change
Does not occur as often as negative
feedback
Example
Uterine contractions become
increasingly stronger until the birth
of the baby
Propagation of an action potential
(Na+ channels)
Negative feedback
Primary type of homeostatic control
Opposes initial change
Components
Sensor (receptor of some type)
monitors magnitude of a controlled
variable
Control center compares sensor’s
input with a set point
Effector makes a response to
produce a desired effect
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Homeostatic Control Systems: Feedback
Positive feedback
Negative feedback
Opening of sodium channels at threshold
Control of body temperature
Disruptions in Homeostasis: pathophysiology
Abnormal functioning of the body associated with disease or injury
Haemorrhage - blood loss
Body compensates to maintain blood pressure and circulation. If wound is not
closed, death will occur (circulatory shock)
Cholera - caused by toxins of bacterium vibrio cholera
Fluid loss through diarrhoea, disturbance of pH of body fluids
If oral rehydration therapy is not administered, death will occur
Alzheimer’s Disease irreversible, incurable, terminal
brain disease
Amyloidβ plaques outside cells
and neurofibrillary tangles inside
cells compromise cell function
Cell death
Memory loss
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