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Nat Sci ii Lecture #5: Homeostasis. Josephine B. Guerrero, MD Asst. Professor, DB, CAS, UPM. Homeostasis. A state of balance and order achieved by an open system relative to set points Set points or Norms May be internal or external Often occurs in a range
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Nat Sci ii Lecture #5:Homeostasis Josephine B. Guerrero, MD Asst. Professor, DB, CAS, UPM
Homeostasis • A state of balance and order achieved by an open system relative to set points • Set points or Norms • May be internal or external • Often occurs in a range • May be viewed in the level of the: • Cell • Organism • Population
Regulation of Homeostasis • Requires: • Input • Processing • Response • Feedback Loops: • Negative Feedback • Positive Feedback
Negative Feedback • Any deviation from the set point or norm is negated or opposed to bring back the condition to the previous • The result is that the set point is re-established and the system regains homeostasis
Negative Feedback Loop Upper Limit Set Point Lower Limit
Positive Feedback • Any deviation from the set point or norm is duplicated or continued • The result is a condition that is farther from the set point and often a “vicious cycle” that is detrimental to the re-establishment of homeostasis
Illustration of a positive feedback loop Upper Limit Set Point Lower Limit
The Cell Membrane • Selectively permeable • Primarily responsible for the regulation of fluid and solute concentration in cells to maintain the integrity of the cell in terms of form and function
Transport Processes Across the Cell Membrane • Passive Transport • Diffusion • Simple Diffusion • Facilitated Diffusion • Osmosis • Active Transport
Driving Forces • Concentration gradient • Hydrostatic Pressure • Osmotic or Oncotic Pressure • Pumps
Endocytosis • Phagocytosis • “cell-eating” • Solid particulate matter are taken into the cell • Pinocytosis • “cell-drinking” • Liquid droplets are taken into the cell
Exocytosis • Exit of substances from cell • Membrane of secretory vesicle becomes part of the cell membrane
The Nephron • Processes: • Filtration • Absorption • Secretion • Product: • Urine composed of water, electrolytes, urea (nitrogenous waste)
Components • CNS • Brain • Spinal cord • PNS – cranial and spinal nerves exiting the CNS • SNS – Somatic Nervous System • ANS – Autonomic Nervous System
Reflexes • Simplest neural circuit • Automatic, rapid, predictable, involuntary responses to stimuli
Glands • Autocrine • Paracrine
Hormones in Plants • Auxins – for cell elongation, differentiation, root growth, fruit development • Cytokinin – stimulates cell division, delays aging of leaves • Giberellins – cell and stem elongation, seed germination, flowering, fruit formation • Abscissic Acid – slows growth, induces seed dormancy, stress hormone • Ethylene – ripening of fruits, senescence • Brassinosteroids – act like auxins