Human Structure and Function: Cells, Tissues, and Homeostasis

Vocabulary practice flashcards covering cell biology, organelle functions, membrane transport, tissue types, and homeostatic control mechanisms.

Anatomy

The study of the structure of what is inside the body (such as bones, muscles, organs, nerves, blood vessels, tissues, and cells), describing what the body looks like and what it is made of.

Physiology

The study of how the body works and how it functions, including how it responds to changes and challenges.

Mechanism

The process explaining how bodily structures and physiological functions work together to produce a response or behaviour.

Molecules

A chemical level of organisation consisting of atoms joined together, such as water, oxygen, glucose, DNA, proteins, and lipids.

Biological Molecules

Molecules involved in living organisms and their functions, specifically proteins, DNA, carbohydrates, and lipids.

Molecular Structure

The specific manner in which atoms are arranged and chemically bonded together to form a molecule.

Cell

The fundamental building block of the body containing organelles and genetic material; capable of producing energy from fuel molecules, dividing to make new cells, and specialising for distinct functions.

Mitochondrion

The site of aerobic respiration that produces energy in the form of $ATP$ for the cell.

Ribosomes

Organelles responsible for synthesising proteins.

Rough endoplasmic reticulum

An organelle covered with ribosomes that synthesises and transports proteins.

Smooth endoplasmic reticulum

An organelle that synthesises lipids, assists with detoxification, and stores calcium.

Lysosome

An organelle containing digestive enzymes that break down waste materials.

Cell membrane

The outer boundary of a cell that regulates and controls what enters and leaves the cell.

Nucleus

The cellular organelle that contains genetic material ($DNA$) and directs the cell's activities.

Nucleolus

A dense structure situated within the nucleus that produces ribosomes.

Centriole

A cellular structure that assists with cell division by forming spindle fibres.

Golgi apparatus

An organelle that modifies, sorts, and packages proteins and lipids for transport or secretion.

Cytoplasm

A jelly-like intracellular fluid where organelles are suspended and where most cellular activities take place.

Phospholipid bilayer

The primary structural foundation of the plasma membrane, arranged according to the fluid mosaic model with hydrophilic heads and hydrophobic tails.

Hydrophilic heads

The water-loving portions of phospholipid molecules that orient toward the aqueous external and internal environments.

Hydrophobic tails

The water-fearing fatty acid portions of phospholipid molecules that face inward, away from water.

Channel proteins

Membrane transport proteins that create passageways allowing specific substances to pass through without energy consumption.

Integral protein

A membrane protein that spans across the phospholipid bilayer.

Peripheral protein

A membrane protein situated on the outer or inner surface of the phospholipid bilayer.

Glycoprotein

A membrane molecule composed of a protein joined with a carbohydrate chain.

Carbohydrate chain

Molecules attached to the exterior of the plasma membrane that assist in cell recognition and cellular communication.

Cholesterol (plasma membrane)

A lipid embedded within the plasma membrane that maintains its fluidity and structural stability.

Apical surface

The side of an epithelial cell that faces the lumen (e.g., gut or airway), involved in absorption or secretion, and often possessing microvilli.

Basolateral surface

The side of an epithelial cell facing surrounding tissue and blood vessels, involved in nutrient and waste exchange, and possessing specialized receptors and proteins.

Simple / Passive diffusion

The net movement of substances directly across the plasma membrane down their concentration gradient without the expenditure of energy.

Facilitated diffusion

The passive transport of substances across the plasma membrane with the assistance of transport proteins, requiring no energy.

Active transport

The movement of substances across the plasma membrane against a concentration gradient requiring cellular energy in the form of $ATP$.

Exocytosis

A cellular transport mechanism where an intracellular vesicle fuses with the plasma membrane to release its contents into the extracellular space.

Endocytosis

A cellular transport process in which the plasma membrane surrounds extracellular substances to engulf and take them inside the cell.

Tissue

A group of similar cells working together to perform a specific function.

Cilia

Tiny hair-like projections extending from cell surfaces that beat rhythmically to move substances across the cell.

Epithelial tissue

A primary tissue type that covers and protects body surfaces, lines hollow organs and cavities, forms glands, and carries out absorption and secretion.

Simple squamous epithelium

A single layer of thin, flat cells that allows rapid diffusion and filtration, found in lung alveoli, capillaries, and kidneys.

Simple cuboidal epithelium

A single layer of cube-shaped cells involved in absorption and secretion, found in kidney tubules, sweat glands, and the thyroid gland.

Simple columnar epithelium

A single layer of tall, column-shaped cells specialised for absorption and secretion, located in the small intestine, large intestine, and stomach.

Pseudostratified columnar epithelium

Epithelium that appears stratified because nuclei lie at different heights, but where every cell contacts the basement membrane; frequently ciliated and found in the trachea and respiratory tract.

Stratified squamous epithelium

An epithelial tissue composed of multiple layers of cells that protects underlying tissues against wear and tear, found in the skin epidermis, mouth lining, and oesophagus.

Connective tissue

A primary tissue that supports, connects, and protects body structures, provides strength, stores energy, and assists in transport (e.g., bone, cartilage, blood, and adipose).

Connective tissue proper

A major group of connective tissue comprising loose tissue that fills spaces and surrounds organs, as well as dense strong tissue located in tendons and ligaments.

Fluid connective tissue

A connective tissue category comprising blood, which transports materials throughout the body, and lymph, which maintains fluid balance and supports immunity.

Supporting connective tissue

Connective tissues that provide structure, physical protection, and cushioning, including bone, cartilage, and adipose tissue.

Nervous tissue

Tissue composed of specialised cells that receive, process, and transmit electrical signals to facilitate body communication and coordination.

Neurons

Excitable cells of nervous tissue that transmit electrical signals, consisting of dendrites, a cell body, and an axon.

Dendrites

Branching extensions of a neuron that receive incoming electrical signals from other neurons or sensory receptors.

Cell body (neuron)

The central structural region of a neuron that maintains cell life and processes incoming signals.

Axon

The elongated neuronal projection that conducts electrical impulses away from the cell body toward another neuron, muscle, or gland.

Glial cells

Non-neuronal cells in the nervous system that support, insulate, and protect neurons.

Schwann cells

Glial cells that produce myelin sheaths around neurons in the peripheral nervous system, increasing nerve impulse conduction velocity.

Oligodendrocytes

Glial cells that form myelin sheaths around axonal fibres in the central nervous system (brain and spinal cord).

Microglial cells

Specialised glial cells that protect the central nervous system by phagocytosing damaged cells, pathogens, and cellular waste.

Skeletal muscle

Muscular tissue attached to bones that contracts voluntarily to execute body movements, such as walking or lifting.

Cardiac muscle

Involuntary muscular tissue found exclusively in the heart that contracts automatically to circulate blood throughout the body.

Smooth muscle

Involuntary muscular tissue found in the walls of hollow organs (stomach, intestines, and blood vessels) that contracts automatically to propel substances.

Organ

A discrete structure composed of two or more distinct tissue types working cooperatively to carry out a specific physiological function.

Organ system

An integrated association of organs exhibiting complementary functions that operate together to sustain the life of the organism.

Organism

A complete individual living entity capable of performing all essential biological processes required to remain alive.

Homeostasis

The physiological capacity to maintain a state of dynamic equilibrium within the internal environment, keeping controlled variables within a normal range around a set point despite environmental changes.

Internal environment

The fluid surrounding and bathing all body cells, specifically referred to as extracellular fluid or interstitial fluid.

Dynamic equilibrium

A homeostatic state in which a controlled physiological variable is not rigidly fixed, but fluctuates within an acceptable normal range around a target set point.

Controlled variable

A measurable physiological condition or parameter (e.g., body temperature, ion concentrations, blood glucose) monitored and maintained within set limits by the body.

Set point

The ideal or target reference value established for a physiological controlled variable.

Normal range of Blood Glucose

The normal homeostatic concentration range for glucose in the blood, given as $3.5\text{--}6.0\text{ mM}$.

Normal range of Blood Osmolarity

The normal homeostatic range for blood osmolarity, recorded as $280\text{--}205\text{ mOsM}$.

Normal range of Body Temperature

The homeostatic range of human body temperature, maintained within $36.5\text{--}37.5\text{ Celsius}$.

Normal range of Arterial Blood Pressure

The homeostatic reference value for arterial systemic blood pressure, stated as $120/8-\text{ mmHg}$.

Normal range of Arterial $P_{\text{O}_2}$

The homeostatic partial pressure of oxygen in arterial blood, kept within $80\text{--}100\text{ mmHg}$.

Normal range of Arterial pH

The homeostatic range for arterial blood pH, tightly regulated between $7.35\text{--}7.45$.

Stimulus (homeostasis)

A detectable change or deviation in a controlled physiological variable from its normal range.

Sensor (Receptor)

A homeostatic component that detects changes or disturbances in a controlled variable.

Afferent pathway

The anatomical or physiological communication route along which sensory information travels from sensors to the integration control centre.

Control centre

The integration centre that compares incoming sensory information against the set point and coordinates an appropriate response.

Efferent pathway

The transmission route that conveys regulatory output signals from the control centre to target effectors.

Effector

A target cell, tissue, or organ that executes the physiological response commanded by the control centre.

Negative feedback

A homeostatic control mechanism in which the physiological response counteracts or reverses the initial stimulus, driving the variable back towards its set point.

Feed-forward mechanism

An anticipatory regulation process wherein the body predicts a homeostatic challenge and initiates responses before the variable changes (such as insulin secretion upon seeing or smelling food).

Positive feedback

A physiological mechanism where an initiated response amplifies and reinforces the initial change, moving the variable progressively farther from the set point (such as oxytocin release during labour).

Physiological changes

Normal, expected fluctuations in body function that occur naturally or during activities (such as exercise, rest, or circadian cycles) from which the body can recover and return to its normal range.

Circadian rhythms

Natural, regular variations in bodily functions that follow an approximate $24\text{-hour}$ cycle, including changes in core body temperature, blood pressure, and melatonin secretion.

Hierarchy of homeostasis

The principle that distinct physiological variables are interconnected, requiring the body to manage multiple parameters collaboratively (e.g., coordinating blood osmolarity and blood volume).

Pathological changes

Abnormal homeostatic disturbances caused by disease, trauma, or injury that impair regulatory systems and may prevent variables from returning to normal ranges.

Intrinsic regulation

The process by which an individual cell, tissue, or organ adjusts its own internal activities in direct response to environmental changes without external neural or endocrine commands.