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