BASAL LAMINA Extra-cellular material separating

epithelial cells from connective tissue

Visible w/ EM, 20-100 nm Lamina densa Lamina rara or Lamina lucida

BASAL LAMINA

BASAL LAMINA Found not only in epithelial tissues

but also where other cells come in contact w/ connective tissue:

Muscle Adipose Schwann cells of nervous tissue

MAIN COMPONENTS:

Type IV collagenProteoglycans [ perlecan ]Glycoproteins:

LamininEntactin

PROTEOGLYCAN

GLYCOPROTEIN

BASAL LAMINA

Attached to underlying tissue by anchoring fibrils from by Type VII collagen

Components are secreted by: Epithelial cells Muscle cells Adipose cells Schwann cells

RETICULAR LAMINA

Reticular fibers closely associated w/ basal lamina

Reticular lamina Connective tissue cells produce reticular

fibers Fibroblast Mesenchymal cell Adipocyte

FUNCTIONS of Basal Lamina: Support for cells Barrier limiting/regulating exchange of

macromolecules between connective tissue and cells of other tissues

Influence of Cell Polarity Regulation of Cell Proliferation &

differentiation

FUNCTIONS of Basal Lamina: Influence of Cell Metabolism Provision of pathway for Cell Migration Information necessary for Cell-to-Cell

Interactions Reinnervation of deinverated cells

Establishment of new neuromuscular junction

BASEMENT MEMBRANE: Periodic acid-Schiff (PAS)-positive layer Visible with LM Found beneath some epithelia Formed by association of:

2 basal laminae A basal & reticular lamina

BASEMENT MEMBRANE

CELL POLARITY:

Differential and stable organization of cell components

Different parts of the cell may have different functions

CELL POLARITY: Basolateral portion:

Diffusion of nutrients & precursors from lamina propria

Location for receptors of chemical messengers• Hormones• Neurotransmitters

CELL POLARITY: Apical portion:

Enzymes, as integral membrane proteins• Disaccharidase• Peptidase

Prevention of integral membrane protein transfer by Tight junctions

CELL RENEWAL: Epithelial tissues are:

Labile [adaptability to modification] Renewed continuously through mitosis

Every week with intestinal epithelia Slow, as in liver and pancreas Mitosis takes place in stem cells of

germinal layer

METAPLASIA:

Reversible transformation of one type of epithelium to another

Heavy cigarette smokers:PSEUDO-STRATIFIED EPITHELIUM

(lining of Bronchi)STRATIFIED SQUAMOUS EPITHELIA

METAPLASIA:

Chronic Vitamin A defiency:TRANSITIONAL EPITHELIA

(Urinary bladder)STRATIFIED SQUAMOUS EPITHELIA

Also occurs in connective tissue