BODY FOUNDATIONS · CHAPTER
Small structures. Remarkable work.
A cell separates, builds, exchanges and responds. Tissues give that work an organised setting, connecting microscopic structures to the living body.
Start with the compartments. Follow a protein, examine a boundary, then see how cells and their surroundings form tissues.
Explore inside →Original cellular atlas artwork · representative nucleated cell, not a universal human cell or acquired micrograph.
30-SECOND ORIENTATION · CELL ARCHITECTURE · FB009
One boundary. Different compartments. Cooperating jobs.
See the boundary, then the different spaces inside it. These are cooperating jobs, not a single assembly line used by every human cell.
The same cell contains regions with different chemistry and tasks. Boundaries make that separation possible while controlled exchange keeps the regions connected.
This representative nucleated cell shows boundaries and organelles at a useful teaching scale. Their number, position and proportions vary with cell type and activity.
Evidence: Cell compartments and organelles · NLM: compartmentalisation
Cells build tissues; several tissues cooperate within an organ. Structure and function can be followed across these scales without treating an organ as one uniform material.
A living working unit
Internal components and specialised surfaces support local work.
Cells plus their environment
Organisation includes extracellular material, connections and supporting cells.
Multiple tissues and linked organs
Local units cooperate in circulation, exchange, movement and regulation.
Liver: organ to functional tissue → · Muscle: fibre to body action →
Evidence: Four tissue families · NIH/NIGMS cellular vocabulary
FORM SERVES FUNCTION
The three models below compare specialisations, not actual relative sizes. Losing organelles, extending processes or reorganising contractile machinery can support very different jobs.
A long neuron, a contractile muscle fibre and an absorptive epithelial cell have different structures. A mature human red blood cell lacks a nucleus and mitochondria; it is not a miniature version of the cutaway below.
Reception and long-distance output
Processes connect sites that may be far apart.
Force production
Contractile units occupy much of a specialised cell.
Boundary and exchange
Different surfaces face different environments.
Neural cells and glia → · Muscle hierarchy →
Evidence: Mature human erythrocytes · Four tissue families
INFORMATION & ASSEMBLY
The nuclear envelope protects a separate nuclear environment. Selected RNA messages leave through pores; ribosomes assemble proteins in the cytoplasm, sometimes at ER membranes.
The nuclear envelope has two membranes and regulated pores. The outer membrane continues into the ER. A nucleolus is a nuclear organisation involved in making ribosomal components, not another membrane-enclosed organelle.
Evidence: NLM: endoplasmic reticulum · NIH/NIGMS cellular vocabulary
Nuclear genes can be transcribed into RNA. Selected processed messenger RNAs reach cytoplasmic ribosomes, where protein assembly occurs. Not all RNA codes for protein.
An RNA message is not a strand of DNA travelling through a vesicle to become a protein. Detailed gene expression and chromatin packaging belong to the next foundation module.
Gene-expression principles are introduced here; the molecular detail is developed in the linked independent foundation reading.
Evidence: NIH/NIGMS cellular vocabulary · NLM: compartmentalisation
Ribosomes can be free in cytosol or associated with the ER. Selected signals direct proteins toward particular compartments; many proteins do not travel through a Golgi-to-surface export route.
Evidence: NLM: endoplasmic reticulum · NLM: protein sorting and transport
ER-associated ribosomes work on the outside of the membrane. Selected newly made proteins enter the ER lumen or its membrane, where further processing can begin.
Outside ER lumen
Ribosomes attach here during selected protein assembly.
Selected cargo destinations
Different proteins enter different parts of this system.
Evidence: NLM: endoplasmic reticulum
Transcription produces RNA from a DNA template. Processed messenger RNA can then guide protein assembly at a ribosome. Before division, DNA replication instead copies the genetic material. These processes have different purposes and locations; a ribosome does not turn a DNA strand into protein.
Further reading: transcription and translation →PROCESSING & DESTINATIONS · FB010
Read left to right: rough ER, transport intermediates, Golgi and a surface-fusion example. The membrane-bounded cargo remains separated from cytosol during this selected route.
Different compartments cooperateFollow selected secretory cargo from ER-associated synthesis through Golgi processing to surface fusion. Return traffic, membrane recycling and other destinations are also part of cellular organisation.
Mechanism source · OpenStax cellular organelles · checked 17 October 2026. Original explanation using retained atlas artwork. Compare crossing a membrane with vesicle fusion →
ER-directed cargo can reach the Golgi through transport intermediates. Golgi organisation helps modify and distribute selected products toward the cell surface or other internal destinations.
This selected secretory pathway is not a complete map of every trafficking step or a universal conveyor belt.
Evidence: NLM: protein sorting and transport · NLM: compartmentalisation
Smooth ER lacks the ribosome-studded appearance of rough ER. Its roles include selected lipid metabolism and calcium handling, with different emphases in different cells.
Muscle calcium storage and release → · Steroid-producing tissue context →
Evidence: Cell compartments and organelles · NLM: peroxisomal roles
Lysosomes participate in breakdown and recycling within an acidic environment. Peroxisomes support selected oxidative and lipid reactions. These are different roles, not interchangeable waste bags.
Internal degradation / recycling
Enzymes work on selected delivered material.
Selected lipid / oxidative reactions
Specialised enzymes act within another compartment.
The generic vesicles in the overview are not assigned exact organelle identities from their colour.
Evidence: NLM: peroxisomal roles · NLM: protein sorting and transport
Selected material can be taken into membrane-bounded compartments, sorted and recycled or delivered for further processing. Other vesicles can fuse with the surface to release cargo.
The secretory atlas shows outward fusion. Endocytosed material can be sorted, recycled or processed; a complete inward sequence is not pictured here.
Evidence: NLM: protein sorting and transport · NLM: compartmentalisation
ENERGY & INTERNAL ORGANISATION
A mitochondrion has two membranes. Its internal folds provide a working surface for energy-related machinery, while the matrix is a different compartment from the narrow space between membranes.
See where reactions happen, then follow what is transferred. Electrons, protons and ATP are different participants. They do not form one material stream through a mitochondrion.
Pyruvate oxidation and much of the citric acid cycle occur in the matrix. They generate reduced carriers that feed respiration; they are not simply a mechanism that turns every carbon directly into ATP.
Read the image: The matrix lies on the inner side of the folded membrane. Its enzymes and the membrane machinery perform different, connected jobs.
Mechanism evidence: OpenStax · Pyruvate oxidation and citric acid cycle
A mechanism summary, not a molecular map drawn on the anatomical surface. Energy is transformed; it is not a material added to the ATP chemical formula.
Glycolysis invests ATP before later reactions produce it. Its net ATP gain comes from substrate-level phosphorylation: an enzyme transfers phosphate from a reaction intermediate to ADP. The pathway also produces pyruvate and NADH.
Continuing glycolysis requires NAD+ to be regenerated. Conversion of pyruvate to lactate can do this; the lactate-forming reaction itself does not add another ATP-producing step. Lactate formation is not restricted to cells with absolutely no oxygen.
Mechanism evidence: OpenStax · Cytosolic glycolysis · OpenStax · NAD+ regeneration
After mitochondrial entry, pyruvate can be converted to acetyl-CoA. The citric acid cycle transfers electrons to carriers and releases carbon dioxide; a small amount of nucleotide triphosphate is also formed directly. Much of this chemistry is in matrix, but succinate dehydrogenase belongs to the inner membrane.
Different fuels can enter connected pathways at different points. Carbon dioxide released during oxidation is not the same product as the water formed when oxygen accepts electrons at the respiratory chain. The cycle does not directly consume molecular oxygen at every reaction.
Mechanism evidence: OpenStax · Pyruvate oxidation and citric acid cycle · OpenStax · Oxidative phosphorylation
Electron carriers pass electrons through oxidation-reduction reactions. Some of the released free energy drives proton movement across the inner membrane. Electrons are not ATP molecules, and protons do not ride the electron chain as a single stream.
In the respiratory chain, complexes I, III and IV contribute to proton pumping; complex II transfers electrons without acting as a proton pump. Oxygen receives electrons at the terminal reaction. These protein identities come from biochemical evidence, not from interpreting bumps on the anatomical render.
Mechanism evidence: OpenStax · Oxidative phosphorylation · Alberts · The mitochondrion
The inner membrane separates matrix from the intermembrane space. Respiratory pumping helps establish a proton electrochemical gradient: a difference in proton concentration together with a voltage across the membrane.
During ATP synthesis, protons pass toward matrix through ATP synthase. Their downhill passage can drive the enzyme in the ATP-forming direction. A fold increases working membrane area; it is not an open pipe carrying ATP between the two compartments.
Mechanism evidence: OpenStax · Oxidative phosphorylation · Alberts · The mitochondrion
A common ATP-use reaction is ATP plus water yielding ADP and inorganic phosphate. Under cellular conditions its overall free-energy change can favour products. Breaking a chemical bond alone requires energy; the outcome depends on the whole reaction and its surroundings, including the products formed.
Enzymes connect an ATP reaction to another process through shared intermediates or coordinated structural changes. Merely placing an ATP-hydrolysis reaction beside an unrelated reaction does not couple them. Regenerating ATP requires an energy input; it is not an automatic reversal without a source.
Mechanism evidence: OpenStax · ATP regeneration and coupling · OpenStax Chemistry · Breaking and forming bonds · Alberts · Catalysis and cellular energy use
The inner membrane controls exchange as well as separating compartments. Phosphate must be available for synthesis, while ADP and ATP exchange through transport machinery. Cytosolic NADH does not freely cross this membrane; shuttle systems transfer reducing equivalents instead.
ATP supply responds to demand and substrate availability within interacting controls. ADP and phosphate availability help connect use to production. A single organelle image cannot establish a cell-wide ATP rate, a fixed yield per food molecule or a timetable for every cell.
Mechanism evidence: Alberts · The mitochondrion · Cooper · Metabolic energy
Chemical work includes enzyme-driven biosynthesis and the activation of building blocks. Transport work includes ATP-dependent pumps that maintain ion differences; some other transporters use those gradients indirectly rather than hydrolysing ATP themselves.
Mechanical work includes molecular motors and muscle cross-bridge cycling. These require ordered protein interactions; a generic cell cutaway is not a sarcomere diagram. ATP also supports cellular maintenance when no whole-body movement is visible. Follow the linked specialised lessons for the detailed mechanisms.
Mechanism evidence: Alberts · Catalysis and cellular energy use · Cooper · Metabolic energy
A mature human erythrocyte has no mitochondria, so it cannot use mitochondrial oxidative phosphorylation. Cytosolic glycolysis supplies its ATP. This is why mitochondria cannot be presented as the only place where human cells make ATP.
Other cell types combine pathways differently with their functions and conditions. Mitochondrial abundance, fuel use, transport costs and coupling differ. Neither a textbook glucose calculation nor the size of a drawn mitochondrion is a universal measure of ATP production in living human tissues.
Mechanism evidence: OpenStax · Mature erythrocytes · OpenStax · Cytosolic glycolysis · Cooper · Metabolic energy
No. Electron transfer helps establish a proton gradient. Proton return through ATP synthase supports a separate chemical reaction that forms ATP from ADP and phosphate.
No. Mature erythrocytes lack mitochondria and depend on glycolysis. Even cells with mitochondria have cytosolic ATP-producing reactions.
No. Bond breaking requires energy. Consider the complete reaction, cellular conditions and the enzyme mechanism that couples it to useful work.
No. They locate existing anatomical compartments. Protein identity and proton direction are supplied by the independently checked explanation, not assigned to unresolved texture.
Normal cell physiology · source checks 21 October 2026. Retained generated compartment illustrations are distinct from acquired microscopy elsewhere in this chapter. No universal ATP yield, oxygen-treatment advice or exercise prescription. AI-assisted source checking is not physician review or fine molecular-structure certification.
The inner membrane encloses the matrix and forms cristae. Its proteins support energy conversion and selective transport; the outer membrane has a different structure and permeability.
Evidence: NLM: mitochondrial membranes
Mitochondrial processes link nutrient oxidation to ATP production. Glycolysis occurs outside mitochondria. Workload, fuels and cellular specialisation affect which routes contribute.
Selected energy-conversion machinery
Membrane organisation helps couple reactions and gradients.
Another ATP contribution
Energy supply is not located only in one organelle.
Energy supply during muscle work → · Liver fuel processing →
Evidence: NLM: mitochondrial membranes · Mature human erythrocytes
Actin filaments, intermediate filaments and microtubules contribute different forms of organisation. Their roles include shape, mechanical resilience and selected intracellular movement.
Surface and contractile organisation
Networks can support changing shape and force.
Mechanical resilience
Their composition depends on cell type.
Organisation and selected transport
Tracks and associated proteins help organise movement.
Muscle contractile units → · Neural cell organisation →
Evidence: Cell compartments and organelles
THE CELL MEMBRANE · FB010
The lipid interior restricts many substances. Membrane proteins provide selected passages and transport mechanisms; gradients and energy determine the direction and conditions of movement.
Choose a route to connect its explanation with the structure. A compact comparison of all five remains below the image.
Example shown: a higher concentration outside supports net entry. Reversing the gradient can reverse net movement.
Mechanism source · OpenStax cell membrane · checked 17 October 2026. Follow selected secretory cargo →
Membrane lipids organise into a bilayer, with polar regions facing water and hydrophobic regions toward the interior. Proteins provide selected transport, attachment and signalling roles.
The enlarged molecular teaching model shows two faces and selected transport context. It is not atomic reconstruction.
Evidence: Membrane structure and transport
Diffusion reflects random molecular movement with a net effect when conditions differ. Channels and carriers can allow selected passive movement; water movement depends on permeability and osmotic conditions.
Gas exchange context → · Renal fluid and epithelial transport →
Evidence: Membrane structure and transport
Primary active transport directly couples to an energy source. Secondary transport couples movement of one substance to a gradient maintained by other processes. These differ from simple diffusion.
A gradient comparison is not a calibrated patient model or a promise about transport rate.
Evidence: Membrane structure and transport
CELLS IN THEIR ENVIRONMENT · FB014
A tissue includes cells, their connections and extracellular material. Most organs combine several families; an organ is not simply a larger version of one cell.
Covering, lining, exchange and secretion.
Connective →Support, integration and a varied extracellular matrix.
Muscle →Skeletal, cardiac and smooth cells produce force.
Nervous →Neurons and glia support communication and regulation.
Epithelial, connective, muscle and nervous tissues describe broad structural and functional patterns. Most organs combine several families rather than belonging to just one.
Covering, lining and secretion
Closely adjoining cells organise boundaries.
Support and integration
Cells work with a substantial extracellular environment.
Force and movement
Contractile cells contribute force in several organ systems.
Information and support
Neurons work with active supporting cells.
Evidence: Four tissue families
Look first for a surface, the material between cells, or a repeated arrangement. Then connect that observation with the retained atlases. A tissue photograph and an explanatory cutaway answer different questions.
RECORDED · LIGHT MICROSCOPY
Mikael Häggström · source photograph · CC0 1.0. Full frame proportionally reduced; no recolouring, cropping, sharpening or AI-generated detail. Independent teaching labels and vector leaders are not part of the acquisition.
Independent normal structure–function reference →
Compare the retained epithelial cutaway →
Compare the existing real blood smear and fluid connective context →
The micrographs have different specimens, preparation and fields of view. Their display sizes do not establish a size comparison. Neither source supplies a calibrated scale for this field; no new scale bar or numerical cell size is invented.
Staining increases contrast. Pink and green are not a universal code for tissue identity, and the photograph does not measure movement, secretion, force or electrical signalling. The general functional account is supported separately, and the retained atlases explain structures that a section may hide.
Source and teaching checks: 20 October 2026. Source photograph licences remain attached above; new independent labels and explanations are offered under CC BY-SA 4.0. AI-assisted source checks are not physician or original specimen certification.
AN APICAL FACE & A BASAL FOUNDATION
This representative simple columnar layer faces a lumen above and supporting connective tissue below. A capillary supplies that supporting tissue; nutrients reach the avascular epithelium across the intervening environment.
This representative simple columnar layer meets a lumen above and supporting tissue below. Lateral connections organise neighbouring cells; the basal foundation is separate from the plasma membrane.
Evidence: Epithelial polarity and junctions
Microvilli increase surface area. Motile cilia can move surface material; specialised nonmotile cilia have sensory roles. These structures are not interchangeable long hairs.
Surface area
Short projections support selected exchange surfaces.
Surface movement
Coordinated activity can move a layer of material.
Selected sensing
Specialised ciliary structures support particular inputs.
Intestinal absorptive surface → · Airway protection → · Olfactory sensory surface →
Evidence: Epithelial polarity and junctions
Tight junctions help regulate between-cell passage. Anchoring junctions link cells or connect cells with matrix. Gap junctions permit selected small-molecule and ion exchange between cells.
Supporting symbols show roles, not exact proteins, pore diameters or universal junction locations. They do not let whole proteins freely travel between all cells.
Evidence: Epithelial polarity and junctions
The sperm tail contains a motile flagellar apparatus. Coordinated bending helps propel the cell. Its microtubule-based movement differs from an actin-supported microvillus, whose main role is to increase surface area. The epithelial image above shows microvilli, not a sperm tail or a resolved ciliary motor.
Source · cytoskeleton, cilia and flagella →EXTRACELLULAR MATRIX
Fibres, hydrated ground substance and resident cells create a mechanical and biochemical setting. The loose tissue here is one arrangement, not the structure of tendon, cartilage, bone or blood.
Cells · extracellular fibres · hydrated surrounding material
Both views contain living cells and extracellular material. In the dense view, aligned collagen dominates the selected field; the cell nuclei are sparse and elongated.
The two views teach different organisations. They are not a calibrated magnification pair, a conversion between tissues or a force measurement.
Structure and function: NCBI · Cells and the extracellular matrix · Tendon structure–function relationships · Tendon hierarchical organisation
Follow the visible fibres and living cells, then connect their arrangement to support, exchange and maintenance. Existing tissue and organ lessons supply the specialised examples.
Cytoplasm belongs inside a cell. Extracellular matrix lies outside cells and includes fibrous proteins and hydrated ground substance. Interstitial fluid and dissolved substances occupy this environment; matrix is not the shared cytoplasm of a giant cell.
The retained loose-tissue image places a fibroblast beside collagen and a local vessel. Its generous spaces suit this selected arrangement. They must not be reused as the proportions of a dense tendon.
Structure and function: NCBI · Cells and the extracellular matrix · NCBI · Extracellular matrix organisation
Collagen is organised at several scales. Small fibrils form larger fibrous structures; groups contribute to fascicles, and fascicles contribute to a tendon. Connective material separates and links neighbouring units. Terminology for the intermediate levels varies among descriptions.
The new cutaway contrasts a long-axis view with exposed cross-cut fascicular organisation. The little ends are illustrative texture, not counted collagen molecules or a calibrated fibril-size distribution.
Structure and function: Tendon hierarchical organisation · Tendon structure–function relationships
Collagen-rich fibres contribute tensile support while remaining flexible. Elastin-rich structures contribute recoil. A reticular framework uses fine branching collagenous fibres to support cells in selected organs. One yellow line cannot establish the molecular identity of a fibre.
Many tissues combine these materials. The contrast is a set of structural roles, not a rule that tendon contains only collagen or that every ligament has the same elastic contribution.
Structure and function: NCBI · Cells and the extracellular matrix · NCBI · Extracellular matrix organisation
Ground substance includes molecules that associate with water, including glycosaminoglycans and proteoglycans. This hydrated environment fills spaces around cells and fibres and contributes to how a tissue exchanges material and responds to loading.
A blue tint in the retained image only separates the surrounding material visually. It does not measure water content, pressure, chemical concentration or tissue stiffness. Follow cartilage for a different matrix specialised for regional support.
Structure and function: NCBI · Cells and the extracellular matrix · NCBI · Extracellular matrix organisation
Fibroblasts synthesise and organise extracellular components. Tendon cells occupy a collagen-rich environment and participate in maintaining it. The elongated nuclear profiles in the dense illustration are cellular context, not dark collagen fibres.
Matrix is continually maintained and remodelled, but there is no single turnover clock for every protein, tissue or person. These normal relationships do not supply an injury-healing timetable.
Structure and function: NCBI · Cells and the extracellular matrix · Tendon structure–function relationships
Connections between cell surfaces and extracellular components help link the cellular interior to the surrounding scaffold. The organisation and mechanical setting of matrix influence how cells behave; cells in turn produce and reorganise matrix.
The illustration locates cells and fibres. It does not resolve individual adhesion receptors, prove a specific signalling pathway or simulate a cell sensing a measured force.
Structure and function: NCBI · Extracellular matrix organisation · NCBI · Cells and the extracellular matrix
A dense arrangement contains abundant fibrous material. A regular arrangement has a strong preferred alignment; dense irregular tissue contains substantial bundles oriented in different directions. The dermis provides a familiar regional example of the latter.
This helps explain why aligned tendon is suited to transmitting tension along its principal axis. It does not imply perfect parallelism, identical behaviour across every tendon, or equal strength in all directions in an irregular tissue.
Structure and function: OpenStax · Connective tissue structure and function · Tendon structure–function relationships
Some tendon collagen structures show crimp or waviness. Recruitment, alignment and interactions among structural levels contribute to a tendon’s mechanical response. A simplified description of straightening does not explain every part of that response.
The image includes gentle waviness to convey living fibrous organisation. Neither its amplitude nor an on-screen arrow is a measured strain, a training target or a prediction of failure.
Structure and function: Tendon structure–function relationships · Load transfer in tendons and ligaments
Tendons commonly transmit muscle-generated force to bone. Ligaments connect bones and help guide or constrain joint movement. Their collagen-rich organisation can overlap, while attachments, regional structure and mechanical demands differ.
The tendon itself does not contract like a muscle fibre. Continue the established hand and foot lesson for tendon courses and attachments, rather than reading this generic tissue window as a named regional tendon.
Structure and function: OpenStax · Connective tissue structure and function · Load transfer in tendons and ligaments
The capillary in the loose-tissue image supports local exchange. Dense tendon has its own regional vascular and connective arrangements; absence of a drawn vessel in the new cutaway does not mean a living tendon is universally avascular.
Cartilage and mineralised bone solve supply and support differently again. Their existing lessons explain those arrangements; a capillary should not be added to an avascular cartilage matrix merely to reuse this picture.
Structure and function: Tendon structure–function relationships · OpenStax · Connective tissue structure and function
Adipose is cell-rich; blood has a fluid matrix; cartilage and bone have distinct supporting matrices. These are useful comparisons of cells, extracellular composition and organisation, not stages through which one loose tissue must pass.
Use the established organ and tissue lessons to see the appropriate structure at the right scale. The two images here are selected loose and dense examples, not a complete histological atlas.
Structure and function: OpenStax · Connective tissue structure and function · NCBI · Cells and the extracellular matrix
Section orientation, preparation and staining affect the appearance of a real tissue image. A dark elongated profile may help locate a nucleus, but a routine field does not by itself identify every resident cell or collagen subtype.
The retained acquired tissue observations remain separate from these generated atlas illustrations. Neither an attractive render nor one section measures stiffness, three-dimensional fibre orientation or the full loading history.
Structure and function: Tendon structure–function relationships · NCBI · Extracellular matrix organisation
No. Most of the selected fibrous material is extracellular. Separate tendon-cell nuclei and cytoplasm lie among the collagen structures.
No. This selected window omits detailed vascular anatomy. Tendon supply varies with region and must not be inferred from an omitted structure.
It can support comparison, but it cannot establish the dense tissue’s proportions or alignment. Use the distinct tendon view.
No. Those questions need appropriate chemical, structural or mechanical evidence. Generated colours and counts are teaching choices.
AI-assisted normal educational explanation and generated atlas. Human medical review and physical-phone acceptance have not been performed. Existing acquired observations retain their own identities and limits.
Extracellular fibres and ground substance support tissue organisation. Cells maintain and interact with this environment; it is not empty space or the cytosol of one enormous cell.
Evidence: NLM: extracellular matrix · NLM: cells and extracellular organisation
The loose context above differs from dense tendon, cartilage, mineralised bone and fluid blood. Fibre organisation, cells and matrix composition influence their roles.
Force transmission
Organised collagen contributes to a tensile structure.
Specialised support
Matrix and embedded cells provide regional mechanical properties.
Mineralised support
Matrix and cells form a living remodelling tissue.
Fluid connective context
Cells and plasma carry materials through vessels.
Bone and joints → · Tendons and muscle attachments → · Lymph and tissue exchange →
Evidence: Connective tissue diversity
Adipose tissue is dominated by lipid-storing cells with relatively little extracellular matrix. This organisation supports energy storage, cushioning and insulation. It differs from the loose collagen-rich setting in the atlas above; not every connective tissue has the same cell-to-matrix balance.
Source · connective-tissue diversity →Ligaments link bones at joints and help constrain movement. Many contain dense collagen-rich tissue, with collagen and elastic contributions varying by ligament. Tendons commonly transmit force from muscle to bone. Both are connective tissues, but their attachments and mechanical jobs differ.
Source · tendon and ligament attachments →MAINTENANCE, DIFFERENTIATION & REGULATION
Repair, renewal and specialisation depend on cell type and local signals. Division alone is not enough: new cells must be organised, connected and supplied within a tissue.
Cells and their surroundings are maintained through different combinations of division, differentiation, remodelling and repair. There is no single turnover clock for every body cell.
Turnover differs between tissues. Detailed lineage and inheritance mechanisms are separate foundation topics; no regenerative-treatment claim.
Skin barrier maintenance → · Neural supporting cells →
Evidence: Four tissue families · NLM: cells and extracellular organisation
Cell-cycle controls coordinate growth, DNA replication and chromosome separation. Mitosis distributes copied chromosomes into new nuclei; cytokinesis divides the cytoplasm. A specialised identity instead involves regulated gene activity and changes in cellular structure and function.
This is a foundation overview, not a complete lineage or molecular cell-cycle model.
Cell growth and division →Some stem-cell populations supply specialised descendants within a restricted lineage. Stem-cell potential and normal tissue renewal differ between tissues; replacing damaged cells is not a universal automatic repair mechanism or a treatment promise.
Differentiation and stem-cell potential →AUTHENTIC SPECIMEN · DISTINCT FROM ATLAS ART
A specimen records cells in a prepared sample. Colour, section or smear preparation, illumination and scale change what can be recognised; they do not reproduce the atlas palette.
Numerous erythrocyte profiles surround fewer darker nucleated cells. The scale bar supplies a size reference. The image is a blood smear, not a section of epithelium or a model of relative organelle size.
Broad cell populations can be compared here; this page does not grade the specimen, identify every leukocyte subtype or infer a diagnosis. The atlas models above provide different kinds of spatial information.
No AI-generated micrograph is presented as a real acquisition.
The existing blood smear shows whole-cell profiles. Here, a real electron micrograph exposes internal folds at a different scale. Compare what was recorded with the retained explanatory cutaway; the two views are not the same specimen.
RECORDED · TRANSMISSION ELECTRON MICROSCOPY
EXPLANATORY · RETAINED MEDICAL ATLAS
Exact source photograph and rights record · Louisa Howard · author’s public-domain dedication. Original grayscale, source strip and scale retained; proportionally resized for the web. The teaching labels are independent of the photograph.
TEM passes electrons through a sufficiently thin sample. This field gives a two-dimensional view of a prepared section, rather than opening every part of an intact cell. The specific section thickness and preparation chemistry of this acquisition are not supplied here.
Serial-section reconstruction instead aligns many adjacent sections. A single field cannot establish how all of its profiles connect through the missing depth.
Method basis: ultrathin section · serial-section TEM.
Outer and inner membranes delimit different compartments. Cristae extend the inner membrane, where machinery involved in oxidative ATP production operates. The matrix has other metabolic roles. The photograph shows structural context; the functional interpretation needs independent biology, not a coloured arrow or a live-energy claim.
Function basis: mitochondrial organisation and function.
A prepared TEM field records electron contrast, not the normal colours of living organelles. Section direction, preparation and image resolution affect the appearance. The atlas deliberately separates spaces and opens a structure, and does not reproduce this specimen.
The source describes mammalian lung tissue, without a species identification. It supports a general cellular comparison, not proof of human-specific morphology, a healthy-versus-diseased diagnosis or the cellular machinery of every tissue.
Source and method checks: 20 October 2026. Original photograph retains the credited public-domain status. The new accompanying labels and explanations are offered under CC BY-SA 4.0. No photographer or instrument-maker endorsement, human medical review or independent calibration is claimed.
An illustration makes selected relationships clear. Identified light microscopy, electron microscopy and molecular measurements provide different kinds of evidence, each with preparation and interpretation limits.
Selected relationships
Can separate compartments and explain function.
Tissue organisation
Can show cells and tissue patterns at its resolution.
Ultrastructural context
Can reveal membrane organisation at finer scale.
Identified blood-smear microscopy and one mammalian mitochondrial TEM comparison are shown above. A broader cell-specific ultrastructure course remains incomplete; no generated image is presented as acquired human histology.
Evidence: NIH/NIGMS cellular vocabulary · Four tissue families
Nuclear work ↗See how compartments connect.A selective boundary ↗Compare ways to cross a membrane.Tissue interfaces ↗Follow the lumen-to-vessel relationship.Beyond the cell ↗Explore the active extracellular setting.FROM FOUNDATIONS TO ORGANS
Neural signals require cellular boundaries and energy. An organ combines tissue arrangements with blood supply, supporting material and regulation.
Follow existing epithelial, neural, contractile and metabolic lessons rather than repeating the same cellular illustration in every organ.
Absorption and epithelial transport → · Filtration and recovery → · Hepatocytes and tissue routes → · Neural communication → · Sensory hair-cell interfaces →
Evidence: Four tissue families
The chapter teaches cell organisation, selected organelle roles, boundaries and transport, tissue interfaces and system links. It does not supply complete molecular biology, clinical histology or diagnostic guidance.
Source-supported broad educational relationships are separate from fine generated texture and topology. Human medical review: not performed. Real physical-phone acceptance: not performed. Educational only.
Text-free original masters, editable concept labels and controlled supporting paths remain separate. No new working-database entity, schema or publication state is created.
Evidence: NIH/NIGMS cellular vocabulary
Brain: cells and signals → · Stroke: tissue supply and injury →
Original source-informed teaching text preserves the existing cell and tissue knowledge and reorganises it across connected learning groups. The private reference book supplies topic/depth guidance (FB009/010/014), not copied prose, images or medical authority. New atlas images are generated illustrations; the human blood smear and mammalian TEM photograph have separate authentic provenance. The TEM source does not identify the species as human.
Human medical review has not been performed. Generated fine molecular topology, dimensions, counts and textures are illustrative; the labels identify selected visible broad relationships. Desktop and simulated narrow-browser evidence is versioned separately; a physical-phone review is not implied. This is education, not diagnostic or treatment advice.
Content version: cells-night-20261013-v1. Original masters, replacement mapping, source-access limits and actual QA evidence are retained in the project editorial record.
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