Human Physiology: Homeostasis and Control Systems

Homeostasis

• Homeostasis is the body's ability to maintain a stable internal environment, despite external changes.
• Extracellular fluid (ECF) is easier to regulate than intracellular fluid (ICF).
• Oxygen and blood CO2 levels are examples of regulated variables.
• The control system uses receptors, a control center (nervous system/glands), and effectors (muscles/glands) to respond to stimuli and maintain set points.

Control Systems

• Local controls act proximal (close to) the source of a disturbance, while reflex controls act distally (further away).
• The control center interprets stimulus information received from receptors and signals effectors to respond. This response may decrease or increase the stimulus variable.

Human Physiology Objectives

• Anatomy is the structure of the body; physiology is its function.
• The levels of organization are chemical, cellular, tissue, organ, and bodily systems (e.g., digestive).
• Major organ systems have specific functions and are composed of various organs. (e.g. Circulatory System = Heart/Blood Vessels/Blood)

Regulation Variables

• Regulated variables (e.g., pH, temperature) fluctuate around set points within a normal range.

Control System Components

• Receptors detect a change (stimulus).
• The control center determines the response.
• Effectors perform the response.

Feedback Loops

• Feedback loops allow systems to maintain homeostasis.
• Negative feedback loops reduce/stop change.
• Positive feedback loops amplify change.

Control Systems Examples

• Local control is proximal control and occurs in response to immediate changes in local tissue (e.g., blood vessel diameter).
• Reflex control is distal control and involves the central nervous system.

Protein Interactions

• Passive transport does not require energy. Secondary transport relies on primary transport to occur. Active transport is dependent on energy.
• Simple diffusion happens at the kidneys but not at the lungs. Hydrophobic molecules move freely across cellular membranes, while hydrophilic molecules require transport proteins.

Membrane Transport

• Membranes are semi-permeable (some substances can pass, others cannot).
• Passive transport includes simple diffusion, facilitated diffusion, osmosis, and filtration. Active transport requires energy.

Osmosis

• Osmosis is the movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.
• Isotonic solutions have the same solute concentration as the cell.
• Hypertonic solutions have a higher solute concentration than the cell.
• Hypotonic solutions have a lower solute concentration than the cell.

Cell Communication

• Intercellular communication allows cells to communicate and work together.
• The six main types are gap junctions, contact-dependent signals, autocrine/paracrine signals, hormones, neurotransmitters, and neurohormones.

Signal Transduction

• Signal transduction is the process of converting an external signal into a cellular response. This often involves a cascade of events, with the initial "first messenger" triggering a series of intracellular "second messengers" to amplify and carry out the response.

Action Potentials

• Action potentials are rapid, large changes in membrane potential that are propagated (conducted) along axons to transmit signals over long distances.
• Action potentials involve voltage-gated ion channels.
• Three important states of VG-gated channels are resting (closed), activation (open), and inactivation (closed).
• A refractory period prevents overlapping action potentials.
• Ion channels (Sodium, Potassium) create action potentials.

Synaptic Transmission

• Synapses are junctions between neurons or between a neuron and a target cell (muscle/gland).
• Neurotransmitters are chemical messengers that transmit signals across synapses.
• Neurotransmitter removal terminates signals.
• Temporal summation determines whether or not EPSPs and IPSPs bring a postsynaptic neuron to threshold.

Nervous System

• The brain and spinal cord are central components.
• Sensory areas receive and process input.
• Motor areas control output.

Voluntary Movement

• The association areas of the brain integrate information to direct voluntary movements.
• The right and left hemispheres have specialized functions in the brain.

Sleep and Biological Rhythms

• Sleep is a state of rest characterised by altered brain activity and decreased responsiveness to stimuli.
• REM and slow-wave sleep are two important stages of sleep.

Learning and Memory

• Learning involves acquiring new information or skills.
• Memory is the ability to store and recall that information.
• Short-term and long-term memory are different storage types for information, with the process of consolidation transferring short-term to long-term memory.

Language

• Broca's and Wernicke's areas are important in speech.