Applied Anatomy & Physiology: Key Physiological Concepts

Vocabulary practice flashcards covering tissue histology, connective tissue mechanics, load and disuse, mechanotransduction, inflammatory cascade, wound healing dynamics, and the paradigms of homeostasis versus allostasis.

Epithelial Tissue

A primary tissue type that covers body surfaces and organs, forms the inner lining of body cavities, lines hollow organs, and composes glands. It generally lacks blood vessels and divides rapidly.

Simple Squamous Epithelium

A single layer of flattened cells functioning in filtration, diffusion, osmosis, and surface coverage; found in lung air sacs, capillary walls, blood and lymph vessel linings, and serous membranes.

Simple Cuboidal Epithelium

A single layer of cube-shaped cells functioning in secretion and protection; located on ovary surfaces, kidney tubule linings, and the ducts of certain glands.

Simple Columnar Epithelium

A single layer of elongated cells functioning in protection, secretion, and absorption; lines the uterus, stomach, and intestines.

Pseudostratified Columnar Epithelium

A single layer of cells appearing layered due to varied nucleus positions, often possessing cilia and goblet cells; functions in protection, secretion, and mucus transport within respiratory passages.

Stratified Squamous Epithelium

A multi-layered tissue with flattened surface cells that provides protection; located in the superficial layer of the skin and linings of the oral cavity, throat, vagina, and anal canal.

Transitional Epithelium

A specialized stratified epithelium capable of stretching while preventing distension damage; lines the urinary bladder, ureters, and superior part of the urethra.

Fibroblast

The most common fixed cell type in connective tissue, responsible for producing protein fibers (collagen, elastic, and reticular fibers).

Mast Cell

A connective tissue cell located near blood vessels that releases heparin (an anticoagulant) and histamine (promotes inflammation and allergic responses).

Collagen Fibers

Thick, flexible protein threads characterized by great tensile strength that resist pulling forces and hold structures together.

White Adipose Tissue

A form of adipose tissue that stores nutrients and triglycerides for nearby cells, insulates the body, and cushions organs.

Brown Adipose Tissue

A specialized adipose tissue rich in mitochondria that breaks down nutrients to generate heat for thermoregulation.

Dense Connective Tissue

Tissue containing densely packed collagen and elastic fibers with few fibroblasts and a poor blood supply; forms tendons and ligaments to withstand pulling forces.

Hyaline Cartilage

The most common rigid cartilage type featuring very fine collagen fibers; provides support, frameworks, and shock absorption at bone ends, the nose, and respiratory rings.

Fibrocartilage

A highly durable, shock-absorbing cartilage with abundant tough collagen fibers; found between vertebrae (intervertebral discs), in the pelvic girdle, and in the knee menisci.

Ligament

A fibrous connective tissue connecting bone to bone to stabilize joints, composed of interwoven collagen fibers ($\\thickapprox 80\%$ Type I with elevated Type III) suited for multi-directional stresses.

Tendon

A dense connective tissue connecting muscle to bone to transmit force, composed of highly parallel collagen fibers ($\\thickapprox 95\%$ Type I) designed for high uniaxial tensile loads.

Tenocyte

An elongated, specialized fibroblast-like cell embedded within tendon tissue responsible for synthesizing extracellular matrix and maintaining tendon structural integrity.

Enthesis

The specialized anatomical junction where a tendon or ligament attaches into bone.

Skeletal Muscle

Voluntary, striated muscle tissue comprising long, multi-nucleated fibers with peripherally located nuclei, responsible for moving the head, trunk, and limbs.

Cardiac Muscle

Involuntary, striated muscle found exclusively in the heart wall, characterized by branched cells, a single central nucleus, and intercalated discs.

Smooth Muscle

Involuntary, non-striated, spindle-shaped muscle tissue found in the walls of hollow organs such as the stomach, intestines, urinary bladder, uterus, and blood vessels.

Sarcomere

The functional repeating contractile unit of a skeletal or cardiac muscle fiber, extending from one Z disc to the next Z disc.

Triad (Muscle)

A skeletal muscle complex formed by one central transverse tubule (T tubule) flanked on either side by two terminal cisternae of the sarcoplasmic reticulum.

Astrocyte

A star-shaped neuroglial cell that contributes to the blood-brain barrier, regulates extracellular ion and neurotransmitter concentrations, and forms scar tissue following central nervous system injury.

Oligodendrocyte

A neuroglial cell of the central nervous system that produces myelin sheaths around multiple axons.

Microglia

The resident immune defense cells and phagocytes of the central nervous system that clear cellular debris, pathogens, and damaged neurons.

Ependymal Cells

Ciliated neuroglial cells lining the ventricles of the brain and central canal of the spinal cord that produce, monitor, and circulate cerebrospinal fluid.

Disuse Spectrum (Bloomfield 1997)

A conceptual continuum of decreasing musculoskeletal loading, progressing from reduced physical activity to bed rest/microgravity, casting, and spinal cord injury.

Envelope of Function (Dye 2005)

The range of musculoskeletal load and frequency combinations within which a joint or tissue maintains homeostatic equilibrium without undergoing structural failure or injury.

Zone of Supraphysiological Overload

The region beyond a tissue's maximum tolerated dose where load or frequency surpasses tissue repair capacity, causing structural microdamage and inflammation.

Mechanocoupling

The initial step of mechanotransduction wherein physical force applied to the cell membrane is detected by sensors (such as integrin complexes and stretch-activated ion channels), triggering intracellular signals such as $\text{Ca}^{2+}$ influx.

Effector Cell Response (Mechanotransduction)

The third stage of mechanotransduction where gene activation and protein synthesis inside the nucleus lead to targeted extracellular matrix remodeling and tissue adaptation.

Cardinal Signs of Inflammation

The classic localized manifestations of inflammation: redness (rubor), swelling/edema (tumor), heat (calor), pain (dolor), and loss of function (functio laesa).

Chemotaxis

The directional migration of white blood cells (leukocytes) along a chemical concentration gradient toward the site of tissue injury or infection.

C-Reactive Protein (CRP)

An acute-phase plasma protein synthesized by the liver that appears in the bloodstream within $24-48\text{ h}$ following acute inflammation, tissue injury, or necrosis.

Tissue Repair

A healing process involving blood clot formation and excessive connective tissue (collagen) deposition, quickly restoring structural integrity through non-functional scar tissue (fibrosis).

Tissue Regeneration

The complete biological restoration of damaged tissue architecture and specialized function through proliferation of residual uninjured cells and stem cell differentiation, without scarring.

Primary Intention Healing

Wound closure occurring when wound edges are clean and closely approximated (e.g., via sutures), resulting in minimal granulation tissue and minor scarring.

Secondary Intention Healing

Wound healing in large defects with separated margins (e.g., severe burns, extraction sockets), requiring extensive granulation tissue, wound contraction, and significant scar formation.

Tertiary Intention Healing

Delayed primary wound closure where a contaminated or infected wound is intentionally kept open and cleaned until safe to close, preventing abscess formation.

Labile Cells

Constantly dividing cells derived from stem cell populations that exhibit exceptional regenerative capacity (e.g., skin epithelial cells, intestinal mucosa).

Stable Cells

Quiescent, mature differentiated cells that normally possess low turnover but can enter active cell division (hyperplasia) upon injury (e.g., hepatocytes in the liver).

Permanent Cells

Terminally differentiated cells devoid of stem cells that lack regenerative capacity; damaged tissue is irreversibly replaced by scar tissue (e.g., cardiac myocytes, CNS neurons).

Homeostasis

The auto-regulation of physiological variables to preserve internal equilibrium and keep biological parameters stable within a narrow operating range via reactive negative feedback.

Negative Feedback Loop

A continuous regulatory control mechanism where the effector produces a physiological response that counteracts and reverses the original stimulus to restore a set point.

Positive Feedback Loop

A self-amplifying regulatory cycle where the effector enhances or drives the original deviation further until a definitive biological endpoint is reached (e.g., oxytocin-mediated uterine contractions during labor).

Allostasis

A brain-centered, predictive regulatory mode defined as 'stability through change' (Schulkin & Sterling), adjusting physiological set points in anticipation of future internal or external demands.

Cephalic-Phase Response to Food

A predictive parasympathetic (vagal) response triggered by sensory food cues (sight, smell, taste) that stimulates anticipatory salivation, gastric acid secretion, and pancreatic insulin release.

Acute Threat Response

A predictive sympatho-adrenal fight-or-flight response coordinated by the amygdala and hypothalamus that releases epinephrine and norepinephrine to elevate heart rate, redirect blood flow to skeletal muscles, and mobilize glucose.

Allostatic Load

The cumulative physiological wear-and-tear on the body resulting from repeated or chronic exposure to stress and sustained recalibration of regulatory set points.

Allostatic Overload

The point of physiological network exhaustion where the body can no longer sustain adaptive recalibrations, precipitating system breakdown, accelerated aging, disease, and death.