epithelial cells

epithelia

line body surfaces, cavities and tubes

what are epithelia supported by

basement membrane and connective tissues

3 characteristics of epithelia

number of cell layers , shape of cells and surface specialisations

number of cell layers

simple, pseudostratified, stratified

shape of cells

squamous (flattened) cuboidal, columnar

surface specialisations

cilia (oviduct), microvilli (gi tract) and keratin (epidermis)

oviduct

simple, columnar and ciliated

epidermis

stratified, squamous and keratinised

bladder

transitional

exocrine glands

intestinal gland and sebaceous gland

intestinal gland

simple tubular

sebaceous gland

simple branched acinar

endocrine glands

pituitary gland

functions of epithelial tissues

secretion , absorption, protection, sensory perception

basement membrane

not penetrated by blood vessels, contains laminin and collaged iv, synthesised by epithelial cells

laminin

3 chains - alpha beta gamma arranged in an asymmetric cross , can bind to collagen and other cells, helps epithelia to attach to bm

ecm

extracellular matrix (extracellular part of any organism or tissue)

ecm in animals

basement membrane and interstitial matrix which is filled with collagen and gels of polysaccharides

types of connective tissue

dense , loose , bone or cartilage

cells embedded in ecm

fibroblasts, adipocytes, mast cells / macrophages

ecm in dense and loose connective tissue

consist of collagen and elastin

proteoglycans

a glycoprotein consisting of a core protein with many carbohydrate chains attached form gels and resist compressive forces in ecm

collagen

3 alpha chains wound around each other to form a triple helical structure which then form fibrils which then become larger cable like fibres.

what does collagen resist

stretching forces

elastin

tropoelastin in soluble and secreted form which is then cross linked

elastic fibres

inner core of elastin surrounded by microfibrils

fibroblasts

In connective tissue cells that secrete the proteins of the fibers.

structure of the skin

epidermis, dermis, hypodermis

epidermis

stratified squamous epithelium

dermis

dense connective tissue

hypodermis

loose connective tissue

epidermis contains

hair follicles , sebaceous glands and sweat glands

layers of epidermis

keratinocytes, melanocytes, langerhans cells

terminal differentiation

final stage of a cell in which it is highly specialized, can no longer divide and make more cells

cornified envelope

insoluble sack made of cross linked proteins formed beneath plasma membrane of differentiating keratinocytes in terminal differentiation

stratum corneum

outermost layer of epidermis

structure of stratum corneum

flat anuclear keratinocytes embedded in a lipid matrix

importance of stratum corneum

prevents water loss and protects against microbes

percutaneous drug delivery

topical therapy: skin target , transdermal therapy: general circulation target, drug must penetrate stratum corneum

transappendageal

via sweat glands or hair follicles

transepidermal

via paracellular or transcellular

topical therapy

penetrating stratum corneum as a cream, ointment or lotion

examples of topical therapy

lidocaine for eczema , tetracycline for acne, hydrocortisone for psoriasis

transdermal therapy

must penetrate stratum corneum, epidermal cells and basement membrane , drug administered via patch

features of drugs applied to skin

low molecular mass , lipophilic , low daily dose

examples of transdermal therapy

estrogen + progestin contraceptive , nicotine smoking cessation , nitroglycerin angina