Human Physiology

Physiology

The study of the functions and operational mechanisms of body structures (how body parts work).

Anatomy

The study of the internal and external physical structure and form of body parts (what parts look like and where they are located).

Principle of Complementarity

The concept that structure and function are inextricably linked; anatomical shape determines physiological function.

6 Properties of Living Things

1. Organization, 2. Metabolism, 3. Responsiveness, 4. Movement, 5. Growth & Development, 6. Reproduction.

Levels of Structural Organization

1. Chemical, 2. Cellular, 3. Tissue, 4. Organ, 5. Organ System, 6. Organismal.

Emergence of Life Level

The Cellular level is the lowest level of structural organization where life emerges.

Integumentary System Function

Protects underlying tissues, regulates body temperature, synthesizes vitamin D, and senses the external environment.

Skeletal System Function

Provides structural support, protects organs, stores minerals (calcium), and produces blood cells (hematopoiesis).

Muscular System Function

Enables body movement, maintains posture, and produces body heat.

Nervous System Function

Detects stimuli, processes information, and rapidly coordinates body activities via electrical impulses.

Endocrine System Function

Regulates long-term body functions via hormones secreted directly into the bloodstream.

Cardiovascular System Function

Pumps and transports blood containing oxygen, nutrients, wastes, and hormones throughout the body.

Lymphatic / Immune System Function

Returns leaked tissue fluid to the blood, filters pathogens, and mounts immune responses.

Respiratory System Function

Exchanges gases (oxygen in, carbon dioxide out) between the air and the bloodstream.

Digestive System Function

Breaks down food, absorbs nutrients into the blood, and eliminates indigestible waste.

Urinary System Function

Filters blood to produce urine, regulating water, electrolyte, and acid-base balance.

Reproductive System Function

Produces gametes (sperm/eggs) and sex hormones to produce offspring.

Organ System Interdependence

Organ systems work dependently on each other; no system operates in complete isolation.

Interstitial Fluid

Extracellular fluid that surrounds and bathes cells, allowing exchange of nutrients, gases, and wastes with blood plasma.

Homeostasis

The body's dynamic ability to maintain a stable, balanced internal environment within narrow limits despite changes.

Two Homeostatic Systems

1. Nervous System (fast-acting via nerve signals), 2. Endocrine System (slower-acting via blood-borne hormones).

Receptor (Sensor)

Homeostatic component that detects changes (stimuli) in the internal environment and sends input to the control center.

Control Center (Integrator)

Homeostatic component that analyzes incoming data against a set point and determines the response (e.g., hypothalamus).

Effector

Homeostatic component that receives output from the control center and carries out the response to alter the stimulus.

Negative Feedback Mechanism

A feedback loop that reverses or negates a deviation from the set point to restore normal internal conditions.

Negative Feedback Example (Temp)

Stimulus: Heat rise -> Receptor: Thermoreceptors -> Control Center: Hypothalamus -> Effector: Sweat glands & vasodilation -> Temperature drops back to set point.

Positive Feedback Mechanism

A feedback loop that amplifies or reinforces a change, driving conditions further away from the set point until an event stops it.

Positive Feedback Example (Labor)

Stimulus: Fetus presses cervix -> Oxytocin release -> Effect: Stronger contractions push fetus harder -> Loop stops upon delivery.

Pathophysiology

The study of functional or physiological changes in the body associated with disease or injury.

Main Cause of Pathophysiology

Uncorrected homeostatic imbalance (failure of homeostatic control loops).

Cytology

The microscopic study of cellular structure, composition, and function.

Cell Theory Premises

1. All organisms consist of 1+ cells; 2. Cell is the basic unit of life; 3. All cells come from pre-existing cells.

Three Basic Parts of a Cell

1. Plasma Membrane, 2. Cytoplasm, 3. Nucleus.

Components of Cytoplasm

1. Cytosol (viscous liquid), 2. Organelles (metabolic structures), 3. Inclusions (stored nutrients/chemicals).

Tight Junctions

Impermeable membrane junctions formed by protein fusion that prevent molecules from passing between adjacent cells.

Desmosomes

Anchoring membrane junctions that join cells with protein plaques and filaments to resist tearing from mechanical stress.

Gap Junctions

Communicating membrane junctions made of hollow protein tubes (connexons) that allow direct passage of small ions/molecules.

Rough Endoplasmic Reticulum (RER)

Membranous network studded with ribosomes; synthesizes, folds, and modifies proteins for membranes or secretion.

Smooth Endoplasmic Reticulum (SER)

Membranous tubular network lacking ribosomes; synthesizes lipids/steroids, metabolizes carbs, and detoxifies toxins.

Golgi Apparatus

Stack of flattened membranous sacs (cisternae); modifies, sorts, packages, and ships proteins from the RER.

Lysosomes

Spherical vesicles filled with digestive enzymes (acid hydrolases); degrades worn-out organelles, debris, and pathogens.

Peroxisomes

Spherical vesicles with oxidative enzymes (oxidases/catalases); neutralizes toxins/free radicals and breaks down fatty acids.

Vacuoles

Fluid-filled storage sacs within cells used for storing water, nutrients, or waste materials.

Mitochondria

Double-membrane, capsule-shaped organelle with cristae; powerhouse that produces ATP through aerobic cellular respiration.

Ribosomes

Non-membrane-bound complexes of rRNA and proteins; the physical sites of protein synthesis (translation).

Centrosomes

Non-membranous region containing a pair of centrioles; acts as microtubule center and forms mitotic spindle in division.

Cytoskeleton

Network of protein filaments throughout cytosol maintaining cell shape, anchoring organelles, and facilitating motility.

Microfilaments

Thinnest cytoskeletal filaments made of actin; responsible for cell movement, muscle contraction, and cytokinesis.

Intermediate Filaments

Tough ribbon-like protein fibers (e.g., keratin); provides mechanical strength and resists pulling forces on cells.

Microtubules

Hollow tubes made of tubulin protein; guides organelle transport, maintains shape, and forms cilia, flagella, and spindles.

Cilia

Hair-like cell surface projections that beat synchronously to move substances across the outer cell surface.

Flagella

Long whip-like cell surface projection that propels an entire cell forward (e.g., tail of a sperm cell).

Microvilli

Tiny non-motile finger-like membrane extensions that increase surface area for cellular absorption.

Nucleus

Large double-membrane organelle that acts as the cell's control center, containing DNA and genetic instructions.

Nuclear Envelope

Double-membrane barrier surrounding the nucleus that regulates entry and exit of molecules via nuclear pores.

Nuclear Pores

Large protein complexes spanning the nuclear envelope that selectively transport macromolecules and RNA.

Nucleoplasm

The fluid, gel-like matrix contained inside the nuclear envelope.

Nucleolus

Dense dark-staining region inside the nucleus where ribosomal RNA (rRNA) is produced and ribosome subunits assemble.