Epithelium

• Cells are the functional and building units of all living organisms.
• Tissues are collections of specialized cells with that perform specific functions.
• There are four basic types of tissues :

  1. Epithelial tissue – protection
  2. Connective tissue – support
  3. Muscular tissue – contraction
  4. Nervous tissue – conduction
• Epithelial tissue

  • forms a continuous layer or sheet over the entire body surface and most of the body’s inner cavities.
  • composed of layer or layers of cells with very little or no inter-cellular substance.
• Epithelial tissue

  • On the external surface, it protects the body from drying out, injury, and bacterial invasion.
  • On internal surface, it is specialized for other functions, in addition to protection
• General characteristics of Epithelial tissue

  • It lies on a basement membrane.

  • It has a good regeneration power.

  • The nucleus conforms to the shape of its particular cell.

  1. free or apical surface → exposed to air or fluid
  2. attached surfaces → on basement membrane
• Specialized features of Epithelial tissue

  • the apical surface may have cilia, flagella or microvilli, or keratin depending on the particular function of the cell.
• Fill in the blank

  A) Skin

  B) lung

  C) Kidney

  D) Pleura cavity

  E) Tongue

  F) Sweat glands

  
• Fill in the blank

  A) Protection

  B) Absorption

  C) Secretion

  D) Sensation

  E) Contraction

  
• Types of surface epithelium

  1. Simple epithelium
  2. Stratified epithelium
  3. Pseudo-stratified epithelium
  4. Transitional epithelium
• Fill in the blank

  A) Squamous

  B) Columnar

  C) Nonkeratinized

  D) Keratinized

  E) Columnar

  
• Simple epithelium

  • It consists of only one layer of cells → the cells occur in a single layer (all the cells touch the basement membrane.)
  • According to the shape of cells, it is divided into 3 sub-types:

  1. Simple squamous epithelium
  2. Simple cuboidal epithelium
  3. Simple columnar epithelium
• Simple squamous epithelium

  • composed of one layer of flat or squamous cells, resting on the basement membrane (like a tiled floor).
  • The nucleus is single, flat & central in position.
  • Site: Bowman’s capsule of kidney, lining of body cavities (mesothelium), alveolar walls of lung, lining of blood & lymph vessels (endothelium).
  • Function : diffusion of gases, filtration & dialyzing function
• Simple cuboidal epithelium

  • is composed of a single layer of cubic or square shaped cells resting on the basement membrane.
  • Nucleus is single, round & central in position.
  • Site: Lining of thyroid follicles, germinal epithelium of ovary, collecting tubules of the kidney
  • Function : Secretion and absorption
• Fill in the blank

  A) Simple cuboidal

  
• Simple columnar epithelium

  • It is composed of a single layer of tall cells resting on a basement membrane.
  • Nucleus is single, oval and basal in position. The free surface of the cell may have cilia or microvilli.
  • Site: Lining of GIT from stomach to upper part of the anal canal,lining of uterine tube & uterus.
  • Function : secretion & absorption
• Fill in the blank

  A) Simple columnar

  
• Fill in the blank

  A) Simple striated comlumnar

  
• Stratified epithelium

  • These cover the more exposed surfaces and carry a reserve of cells to assist rapid replacement.
  • The cells are arranged in more than one layer.
  • They are classified according to the cell form on its superficial layer.
  • It is subdivided into:

  1. Stratified squamous epithelium - keratinized or non-keratinized
  2. Stratified cuboidal epithelium
  3. Stratified columnar epithelium
• Stratified squamous epithelium

  • There are 3 types of cells in this epithelium .

  1. Basal layer – single layer of columnar cells
  2. Middle layer – polyhedral cells. Nucleus is single, round & central.
  3. Superficial layer – few layers of flat squamous cells. Nucleus is single, flat & central.
• Stratified squamous epithelium

  • Site: The keratinized type is found in skin and the non-keratinized type lines the esophagus, vagina, outer parts of anal canal & urethra.
  • Function: to withstand wear & tear, protection.
• Fill in the blank (Hint: subdivided of Stratified epithelium)

  A) Stratified squamous non-keratinized epithelium

  B) Stratified squamous keratinized epithelium

  
• Pseudo-stratified epithelium

  • The epithelium has single layer of cells of different heights, and therefore the nuclei are at different levels.
  • Although the nuclei are seen in various layers, all the component cells touch the basement membrane but not all the cells reach the surface.
• Pseudo-stratified epithelium

  • There are 3 types:

  1. Pseudo-stratified columnar ciliated epithelium – seen in trachea & bronchi (unique of the respiratory system)
  2. Pseudo-stratified columnar epithelium with stereo-cilia– epididymis.
  3. Pseudo-stratified columnar non-ciliated epithelium – vas deferens
• Transitional epithelium

  • It lines the hollow organs that are subjected to tension.
  • Its appearance varies with the degree of distension.
  • There is no visible basement membrane (can be seen under electron microscope
  • The component cells have few connections thus facilitating slippage.
  • Site: Lining of urinary passages from calyces to urethra.
  • Function:

  1. To prevent penetration of urinary constituents (urine proof )
  2. To allow distension without the cells breaking apart from one another
• Transitional epithelium

  • There are 3 groups of cells.

  [1] Superficial group of cells – are large round cells or umbrella-shaped cells. Nucleus is single, round & central.

  [2] Middle group of cells – pear or club shaped cells with the broad ends toward the surface & apex pointing downward.

  [3] Basal group of cells – polygonal cells with single, round & centrally placed nuclei.
• The function of glandular epithelium is secretion, which is accomplished by glandular cells. All glands of the body are classified either as exocrine or endocrine.
• • Exocrine glands secrete their products into ducts that empty at the surface of covering or lining epithelium. The secretions of exocrine glands include mucous, sweat, oil, earwax, milk, saliva and digestive enzymes.
  • The secretions of endocrine glands enter the interstitial fluid and then diffuse into the bloodstream or lymph without flowing through a duct. These secretions, called hormones
• Glandular epithelium

  • are composed of cells specialized in producing a fluid secretion that differs in composition in blood or intercellular fluid.
  • They are aggregations of cells specialized for secretion or excretion
• Glandular epithelium

  • The glands are formed from down-growths of the surface epithelium.
  • They remain in contact with the mother surface by means of a duct → exocrine glands.
  • if the surface connection is lost, the secretions are directly drained into the blood or lymph → endocrine glands.
• Exocrine glands are of 2 main types

  (1)Serous gland – secretes a watery, albuminous discharge usually containing enzymes.

  E.g. pancreas, parotid salivary gland.

  (2) Mucous gland – secretes a slimy, chemically inert mucous secretion.

  E.g. sublingual salivary glands

  (3) Sero-mucous glands – secretes a mixed discharge.

  E.g. sub-mandibular salivary gland
• Fill in the blank

  A) Large

  B) Triangular

  C) cuboidal

  D) columnar

  E) Large

  F) Small

  G) flat

  H) Round

  I) mucinogen

  J) zymogen

  
• Fill in the blank

  A) Not clear

  B) Sharply

  C) pale

  
• Classification of Exocrine glands

  • According to cell number

  1. Unicellular gland – single secreting cell within epithelial sheets; acts as a complete glandular unit. E.g. goblet cell
  2. Multi-cellular gland – are composed of clusters of cells opening onto the parent epithelial surface. E.g. sweat gland
• Endocrine glands are ductless and their secretions are released directly into the blood or lymph stream. Each cell lies against a sinusoid or capillary.

  E.g. Islets of Langerhan in pancreas
• Endocrine glands :

  A) epithelial sacs

  B) follicles