Foundations - Histology Cells and Tissues

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Foundations - Intro to Histology (virtual slides)
Histology terminology cartoon

Background and Self-directed Learning for Medicine Foundations.

Practical - Histology Cells and Tissues Virtual Slides by Patrick de Permentier.

This current page content is not part of the Foundations practical class.

A tissue is a functional aggregation of similar cells and their intercellular materials that combine to perform common functions.

An organ is an anatomically discrete structure (e.g. heart, skin) with 1 or more functions.

Four tissues are considered basic or primary: epithelial, connective, muscular and nervous. Many organs contain all 4 types of tissues e.g. skin (covering, packing, muscles, nerves).

Note - As this is a general introduction to the 4 basic tissues, you are not at this stage expected to know the detailed histology of the virtual slides shown in this class. You will be covering these tissues again in detail later in this and future courses.

Links: Moodle Slides page | Histology Introduction | Histology Epithelia and Skin | Histology Stains | Histology Drawings | Expert Tutorial Support

Specific Objectives

  1. Obtain an understanding of the histological appearance of the basic tissues namely epithelium, connective tissue, muscle and nervous tissue.
  2. To examine unique cellular characteristics of each of the basic tissues.


Epithelium forms continuous layers of cells that cover surfaces and line cavities of the body. These cavities include the closed peritoneal, pleural, and pericardial cavities, where the epithelium is called mesothelium, and open organ cavities, i.e. digestive, respiratory, and urogenital organs, which connect with the outside. In addition, epithelium lines the cardiovascular and lymph passageways as endothelium.

The parenchymal (secretory) cells of glands (e.g. sweat, salivary) are also epithelium. Epithelial cells are always in close apposition to each other, with a space between membranes of only about 20nm. A small amount of intercellular material, called cement substance (glycosaminoglycan) allows cells to glide over each other and offers only minimal resistance to the migration of leukocytes and other connective tissue cells through the epithelial layers. Epithelial attachment points (junctional complexes) occur between neighboring epithelial cells to hold adjacent cell membranes in close apposition. They also serve as anchoring sites for the fine filaments of the cytoskeleton, which assists in stabilizing the cell shape.

Epithelial cells rest on a basal lamina separating them from underlying connective tissue (CT). Epithelium is avascular and for its nutrition depends on diffusion of substances across the basement membrane.

Epithelium Nomenclature

(or how to identify the histological naming)

  1. How Many Layers - simple, stratified, pseudostratified.
  2. Shape of Upper Cell Layer - columnar, cuboidal, squamous (flattened)
  3. Specialisations - keratinised, non-keratinised
Epithelium histology cartoon 01.jpg Epithelium histology cartoon 02.jpg
Epithelia cell shape Epithelia sectioning appearance
Epithelia Terms  
  • basal lamina - only visible by electron microscopy.
  • basement membrane - visible in histology by light microscopy. The basal lamina forms part of the basement membrane.
  • columnar - cells are higher than they are wide.
  • cuboidal - cells are as high as they are wide.
  • pseudostratified - looks as if it is stratified, but it is not.
  • simple - consisting of one (cell) layer.
  • squamous (Latin squama = "scale") - flattened cells.
  • stratified - consisting of more than one (cell) layer.

Simple Epithelium

VIRTUAL SLIDE: Gallbladder eg simple epithelium

Gall bladder histology 001.jpg Gall bladder histology 002.jpg

Stratified Epithelium

Stratified epithelia cartoon

VIRTUAL SLIDE: Oesophagus eg stratified epithelium

  • The lumen is lined by an epithelium (stratified epithelium)
    • epithelium rests on a vascular connective tissue, the lamina propria.
  • The lamina propria is in turn surrounded by a narrow band of smooth muscle (muscularis mucosae).
  • These three tissues are collectively referred to as the mucosa of the alimentary canal.
Oesophagus histology 03.jpg

Oesophagus stratified epithelium


Skin Cartoon showing glands

Glands are invaginations of epithelial surfaces that are formed during embryonic development by proliferation of epithelium into the underlying connective tissues to form secretory units. The secretory units, along with their ducts, are the parenchyma of the gland; the stroma of the gland represents the elements of the connective tissue that support the parenchyma. Some glands (endocrine) loose the duct and secrete directly into the blood (e.g. hormones).

  • duct - (excretory duct) the epithelial "pipe" through which secretions from the gland are transmitted to the surface of an epithelium. Most are formed by simple cuboidal epithelium, but there are also other types of duct cellular structures.
  • serous - "watery" secretion, appears darkly stained in HE stain.
  • mucus - "slimy" secretion, appears lightly stained in HE stain.
  • mucoserous gland - (mixed) gland has both a mucus and serous secreting component and has a mixed staining appearance.


Integumentary histology 01.jpg Integumentary histology 03.jpg

Connective Tissue

Respiratory histology 05.jpg Bone-femur.jpg
Cartilage (trachea) Bone (femur)

Connective tissues (CT) are the supporting framework for all tissues and organs of the body. In addition, they provide the means of anchoring and binding organs together as well as providing the packing tissue between them. CT varies in structure and character from loose (subcutaneous areas), to dense irregular (dermis of skin), to dense regular (ligaments and tendons), to firm and flexible (cartilage in the trachea, intervertebral discs, external ear, to rigid (calcified bone), to circulating (blood and lymph).

Despite this wide range, all CT have an intercellular matrix composed of an amorphous ground substance in which are embedded cells and one or more types of extracellular fibres, (elastic, collagen, or reticular). In blood and lymph, the fibres are strands of fibrin, seen only during clotting. The predominant cell type of CT is the fibroblast which makes fibres. Other types are wandering cells such as mast cells, plasma cells, various leukocytes, and macrophages.

Liver Structure Liver - reticular fibre Liver - Kupffer cells and reticular fibres
Liver histology 001.jpg Liver histology 007.jpg Liver- Kupffer cell and reticular fibre.jpg

VIRTUAL SLIDES: Liver H&E Liver - Reticular fibres

VIRTUAL SLIDE: Trachea - Hyaline cartilage

VIRTUAL SLIDE: Rib (decalcified) - Bone

  • -blast - a suffix used to describe an immature or developmental form of a cell type (fibroblast, chondroblast, osteoblast).
  • CT - Connective Tissue
  • -cyte - a suffix used to describe the mature form of a cell type (fibrocyte, chondrocyte, osteocyte).
  • extracellular matrix - within connective tissues, the secreted material lying outside and separating the cells that form that tissue. It can be formed by the many different cell types (chondrocytes, osteocytes, epithelial, fibroblast, adipocyte, endothelial) and can be specific to specific tissues (bone, cartilage). The components include water, proteins and polysaccharides, with the major glycoprotein component being the many different forms of collagen.
  • intercellular matrix - the extracellular matrix between 2 cells.
  • reticular fibre - (reticular fiber (US spelling), reticulin) secreted by fibroblasts and reticular cells in connective tissue and is composed of type III collagen. Found in loose CT, around adipocytes, blood vessels, muscles and nerves. Seen also in haemopoietic and lymphatic tissues. Histologically not seen in HE staining, but visible in PAS and silver staining.


Muscle cells (fibers; the cell is longer than wide) produce force which can be used for movements such as locomotion, contraction of organs (e.g. bladder) and pumping movements of the body. This is achieved by the muscle cells contractility state by changing their length and developing tension.

The contractile elements of muscle cells are (myofibrils) composed of specific arrays of myofilaments, the proteins (actin and myosin) responsible for the contractile capability of the cell.

  • intercalated disc - a specialised feature seen in cardiac muscle, joining 2 cardiac muscle cells (cardiomyocytes) and also acting as a site of communication between these cells. Visible at light and electron microscope levels.
  • involuntary muscle - cardiac and smooth muscle, you cannot control this muscle contraction.
  • striated muscle - cardiac (contracts heart) and skeletal (moves skeleton) muscle. Presence of highly organised contractile filaments into sarcomeres in series gives the striated appearance.
  • voluntary muscle - skeletal muscle, you can control this muscle contraction.

VIRTUAL SLIDES: Skeletal Smooth and Cardiac muscle

Skeletal Muscle

Sarcomere animation.gif

These skeletal muscle images listed below are in more detail than you require for this practical. Though you can have a look through and see if there are common features you recognise.

Muscle Histology: Muscle Development | Human HE x4 longitudinal and transverse | Human HE x40 transverse | Human HE x40 longitudinal | Human HE x40 longitudinal | Human HE x4 longitudinal and transverse | Muscle Spindle HE x40 | Human HE x40 | Human HE x40 | Human HE x40 | Human HE x100 | Human HE x100 | Fetal human muscle | Myotendinous junction label | Myotendinous junction HE x40 | Whipf 1 | Whipf 2 | Whipf 3 | Tongue HE x10 transverse | Tongue x100 | Muscle spindle HE x20 | Muscle spindle HE x40

Smooth muscle

  • Smooth muscle makes up the visceral or involuntary muscle.
    • You will see smooth muscle in the walls of arteries in all the slides today.
  • consists of spindle shaped cells of variable size.
    • largest smooth muscle cells occur in the uterus during pregnancy (12x600 µm).
    • smallest smooth muscle cells are found around small arterioles (1x10 µm).
  • form layers surrounding the gastrointestinal tract.
  • smooth muscle cells contain one centrally placed nucleus.
  • innervation of smooth muscle is provided by the autonomic nervous system.
Jejunum histology 01.jpg

Gastrointestinal tract (jejunum) smooth muscle.

Cardiac Muscle

Cardiac muscle histology.jpg Heart histology 004.jpg

These cardiac muscle images listed below are in more detail than you require for this practical. Though you can have a look through and see if there are common features you recognise.

Links: Heart Histology | Cardiac AZB Labeled | Cardiac AZB | Cardiac label LS | Cardiac LS | Cardiac label TS | Cardiac TS | Purkinje fibres | Purkinje fibres detail | Histology

Nervous Tissue

Peripheral Nerve (osmium)

The brain and spinal cord comprise the central nervous system (CNS). The nerves that emerge from the spinal cord and brain to pass to parts of the body are the peripheral nervous tissue (PNS). Nervous tissue, with many interconnections, forms a complex system of neuronal communication within the body and is specialized for detecting stimuli, integrating functions, controlling effectors and higher functions. Nervous tissue consists of cell bodies, cell processes (nerves), and neuroglia (supporting cells).

  • myelin - the wrapping around neural axons formed by glial cell (neuroglia) membrane. The peripheral nerve glia are Schwann cells.
  • neurovascular bundle - the nerves, arteries and veins (and often lymphatics) running together within connective tissue. This is also given the acronym/mnemonic NAVL.
  • Schwann cells - the peripheral nerve glial cells that form the myelin sheathes around each nerve.

VIRTUAL SLIDE: Peripheral Nerve

Self-Directed Learning

This is intended as a self-directed learning exercise and will not be covered in the practical lab time. Note also that the questions in your practical notes are for you and not the tutor to answer.

  • You have seen the basic tissues of the body from various locations and using a variety of histology stains.
  • It should be obvious that histological sections from any body region will include components from these basic tissues.
  • Now study the VIRTUAL SLIDE: Tongue-circumvallate papillae, linked from todays practical.
    • Note this tongue images shown on this current page are not the VIRTUAL SLIDE, but a similar region from the sheep tongue.
    • There are deliberately no labels on this image.
  • See if you can identify the basic tissues located in this section of the tongue.
    • epithelia
    • connective tissue
    • glands
    • muscle
    • nervous

Tongue histology 05.jpg

VIRTUAL SLIDES: Tongue - circumvallate papilla HE stain


  • adipose - fat cells, "chicken-wire" appearance, lipid has been lost during histology processing. Two main types white adipose in many different body tissues (seen in most of your histology slides) and brown adipose for heat and energy production (seen in newborn or neonatal tissues).
  • artifact - changes and distortions introduced to the normal tissue structure by the histological processing. Common artifacts include: folds (gives the tissue a darker appearance), tears (rips in the tissue can be seen in epithelia) and shrinkage (removal of the water or lipid leaves clear spaces that did not exist in the tissue). Rule of thumb is that if it looks "interesting" then it is an artifact!
  • axon - make up the neural component in peripheral nerve, conduct from cell body away.
  • cardiac muscle - striations, intercalated discs
  • collagen - extracellular fibres consist of the main protein found in the ECM and abundant in connective tissue. One of the most abundant proteins in the body.
  • connective tissue - tissues consist of cells separated by varying amounts of extracellular matrix (ECM). Extracellular substance consists of fibres (collagen fibres, reticular fibres and elastic fibres) embedded in ground substance containing tissue fluid. Cells are fixed (fibroblast and adipose) and wandering (macrophage, monocyte, lymphocyte, plasma cell, eosinophil and mast cell).
  • connective tissue layers - in muscle and nerve 3 different CT layers from individual fibres (endo...), to groups in a bundle or fascicle (peri....) and finally around the whole muscle or nerve (epi....).
  • elastic fibres - coloured light yellow in fresh tissues, special stains required to show in tissue sections. Composed of the protein elastin, can be stretched and return to original length.
  • eosin - histology stain: cytoplasm pink to red; red blood cells are also bright red. Common counterstain to haematoxylin. (Stain - Haematoxylin Eosin)
  • epithelium - covers all free surfaces of the body and lines the large internal body cavities (mesothelium). Avascular tissues with closely apposed cells without intervening intercellular substances. Separated by underlying connective tissue by a basement membrane.
  • fat cell = adipose cell
  • fascicle - bundle, usually enclosed in connective tissue.
  • haematoxylin - (hematoxylin) histology stain: nuclei blue to dark-blue, matrix of hyaline cartilage, myxomatous, and mucoid material pale blue, myelin weakly but is not noticeable if combined with eosin stain. (Stain - Haematoxylin Eosin)
  • histology - anatomical study of the microscopic structure of tissues.
  • marrow - (bone marrow) site of blood cell synthesis.
  • matrix - (extracellular matrix, ECM) material secreted by cells and lying outside cells. Connective tissue has lots of ECM between cells. Epithelia have a very little ECM, and a specialised ECM that the basal cells sit upon.
  • muscle - specialised contractile cells. Three main types (skeletal, cardiac and smooth) and also characterised as striated (skeletal, cardiac) and non-striated (smooth) due to the organisation of the contractile apparatus within the muscle cell.
  • muscle connective tissue layers - ....mysium (small to large) endomysium, perimysium, epimysium.
  • neural connective tissue layers - ....neurium (small to large) endoneurium, perineurium, epineurium.
  • neurovascular bundle - peripheral nerve and associated blood vessels (artery + vein) there is often also a lymphatic vessel as they pass through body tissues. Remember by the acronym NAVL (Nerve, Artery, Vein, Lymph) they usually travel together and in connective tissue.
  • reticular fibres - extracellular fibres consist of delicate and fine networks instead of thick bundles.
  • parenchyma - functional cells of a tissue, compared to stroma support or structural cells.
  • periosteum - connective tissue covering the surface of bone (except articular surfaces).
  • Schwann cell - makes myelin in peripheral nerve.
  • skeletal muscle - striations, fibers (muscle fiber = muscle cell), multinucleated, clustered fascicles.
  • smooth muscle - no striations, sheets, single elongated nuclei, involuntary (you don't control it).
  • stroma - support or structural cells of a tissue, compared to parenchyma functional cells.

Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.

Kierszenbaum, A. L., & Tres, L. L. (2012). Histology and cell biology: An introduction to pathology. Philadelphia, PA: Elsevier Saunders.

Glossary Links

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Cite this page: Hill, M.A. (2024, May 18) Embryology Foundations - Histology Cells and Tissues. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G