1. Major types of adult tissues
Tissues: collections of similar cells and the substances surrounding them
Tissue classification: based on structure of cells, composition of non cellular extracellular matrix, and cell function
Major types of adult tissues
Epithelial
Connective
Muscle
Nervous

3. 3 major germ layers that form the embryonic disc (source of stem cells)
Endoderm
Inner layer
Forms lining of digestive tract and derivatives
Mesoderm
Middle layer
Forms tissues as such muscle, bone, blood vessels
Ectoderm
Outer layer
Forms skin and neuroectoderm

4. Epithelial tissue

5. Epithelium Cellularity - Consists almost entirely of cells
Covers body surfaces, lines hollow organs, and forms glands
Outside surface of the body
Lining of digestive, respiratory and urogenital systems
Heart and blood vessels
Linings of many body cavities
Polarity - Has apical, basal, and lateral surfaces
Rests on a basement membrane
Specialized cell contacts bind adjacent cells together
Avascular - no blood vessels
Regenerative -Replaces lost cells by cell division

6. Special characteristics

7. Functions of epithelial tissue
Protection: Epithelial cells protect underlying tissue from mechanical injury,
harmful chemicals and pathogens and excessive water loss.
Sensation: Sensory stimuli are detected by specialised epithelial cells. Specialised
epithelial tissue containing sensory nerve endings is found in the skin, eyes, ears and nose and on the tongue.
Secretion: In glands, epithelial tissue is specialised to secrete specific chemical
substances such as enzymes, hormones and lubricating fluids.
Absorption: Certain epithelial cells lining the small intestine absorb nutrients from
the digestion of food.
Excretion: Epithelial tissues in the kidney excrete waste products from the body
and reabsorb needed materials from the urine. Sweat is also excreted from the body by epithelial cells in the sweat glands.
Diffusion: Simple epithelium promotes the diffusion of gases, liquids and
nutrients. Because they form such a thin lining, they are ideal for the diffusion of gases (e.g. walls of capillaries and lungs).

8. Classification of epithelia
Classification of epithelial cells is based on a number of individual components including cell arrangement, cell shape, surface specializations and cell adaptations.
1. Cell arrangement
Simple: single layer of cells. Each extends from basement membrane to the free surface
Stratified: composed of several layers of cells.
Pseudostratified: cells appear to be several layers however all are in contact with underlying matrix.

9. Classification by Cell shape
Squamous: flat, scale-like
Cuboidal: about equal in height and width
Columnar: taller than wide

11. Simple Cuboidal Epithelium

12. Simple Columnar Epithelium

13. Transitional Epithelium

15. Surface specializations
Microvilli
finger-like extensions of plasma membrane
abundant in epithelia of small intestine and kidney
maximize surface area available for absorption of nutrients or across which molecules enter or leave
Cilia
whip-like, highly motile extensions of apical membranes
move fluid or mucous over the surface of the cell
confer cell motility

17. Epithelial cell adaptations
A) SECRETORY
Mucous secreting epithelial cells contain goblet cells which secrete mucous.
The mucous acts:
as a lubricant in the mouth and vagina.
To protect the lining of the stomach from destruction by the acids present.

18. ii) Steroid secreting epithelial cells secrete hormones
ii) Steroid secreting epithelial cells secrete hormones. Examples: adrenal glands, ovary and testis. iii) Ion pumping epithelial cells allow ions to be transported across a membrane. Examples: kidney tubules transport ions and water, stomach transports H+ ions.

19. Two types of glands formed by infolding of epithelium:
Glandular epithelium: A gland is one or more cells that makes and secretes an aqueous fluid
Two types of glands formed by infolding of epithelium:
Endocrine: secrete hormones directly into the bloodstream, no contact with exterior of body; ductless; produce hormones (pituitary, thyroid, adrenals, pancreas)
Exocrine: open to exterior of body via ducts (sweat, oil)
Exocrine glands classified either by structure or by the method of secretion
Classified by structure
Unicellular: goblet cells
Multicellular: sweat, oil, pituitary, adrenal

20. Glandular epithelia

21. Barrier Function
Prevents diffusion of molecules between cells and therefore prevents diffusion of substances from one side of an epithelium to the other.
Specializations which produce barrier functions are tight cell junctions, desmosomes and keratinization.
Cell adhesions are mediated by cell junctions- form seals around cells and allow for contact and communication between cells.

22. Melanin formation
Melanocytes are cells located in the bottom layer (the stratum basale) of the skin's epidermis, that produce melanin which is a pigment for skin& hair

23. Melanin formation

24. Albinism
Albinism is an inherited condition present at birth, characterized by a lack of pigment that normally gives color to the skin, hair, and eyes. Many types of albinism exist, all of which involve lack of pigment in varying degrees. The condition, which is found in all races, may be accompanied by eye problems and may lead to skin cancer later in life.
Albino lack an enzyme called tyrosinase. Tyrosinase is required for melanocytes to produce melanin from the amino acid tyrosine.