nat sci ii lecture #5: homeostasis
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NAT SCI II LECTURE #5:HOMEOSTASISJosephine 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
Lower Limit
Set Point
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
Homeostasis at the cellular level
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
Simple Diffusion
Simple Diffusion
Facilitated Diffusion
Osmosis
Osmosis in RBCs
Turgor Pressure in Plant Cells
Active Transport
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
Homeostasis at the Organismic Level
Osmoregulation in Unicellular Organisms
Osmoregulation in Multicellular Organisms
Human Excretory System
The Nephron
Processes: Filtration Absorption Secretion
Product: Urine composed of
water, electrolytes, urea (nitrogenous waste)
Nervous Control
Human Nervous System
Components
CNS Brain Spinal cord
PNS – cranial and spinal nerves exiting the CNS SNS – Somatic Nervous System ANS – Autonomic Nervous System
Functions
Parts of the Brain
Parts of the Cerebrum
Sagittal Section of the Brain
Cranial Nerves
Spinal Cord
Reflexes
Simplest neural circuit
Automatic, rapid, predictable, involuntary responses to stimuli
Autonomic System
Endocrine System
Glands
Autocrine
Paracrine
Endocrine
Hypothalamic-Pituitary Axis
Hormones, Targets and Functions
Hormones, Targets and Functions
Hormones, Targets and Functions
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
Specific Mechanisms for Maintaining Homeostasis
Blood Glucose Control
Blood Clot Formation
Fibrinolysis
Thermoregulation (Homeotherms)
Thermoregulation (Poikilotherms)
Control of Breathing
THANK YOU
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