Epithelial Tissue/Glands
I. Cells form 4 basic tissue type
A. Epithelium
§ Outer covering and inner lining cell layer, parenchyma of glands
§ Layers and gland can secrete
B. Connective tissue
§ Connect other tissue types
§ Support and nourishment
§ Produce and maintain intercellular sustances
C. Muscle
§ Irritability, impulse conduction, and contraction
D. Nerves
§ Irritability, transduces energy into nerve impulse, which is transmitted
II. Characteristics of epithelium
§ Cells close association
§ Cells form junctions
§ Little extracellular material b/t cells
§ Lines surfaces and cavities
§ Forms parenchyma of cells (connective tissue forms stroma)
§ Demonstrate polarity- apical, lateral, basal surfaces
§ Basal surface separated and bound to connective tissue by basement membrane (collagen, glycoprotein laminin, proteoglycans)
§ Function in secretion, absorption, transport, protection, diffusion,sensation
§ No blood vessels, nourished by diffusion from underlying capillaries
§ Miotically active
III. Classification of epithelial tissues
A. First name
§ Simple (single layer) Stratified (more than one layer)
B. Second name
§ Squamous (flat) Cuboidal (square) Columnar (retangular)
§ Ciliated, with goblet cells, keratinized or nonkeratinized, microvillus border
C. Additional information
D. Exceptions
§ Pseudostratified columnar- simple epithelium, all cells touch basal lamina, not all cells reach luminal surface
§ Transitional (stratified)-undergoes change in appearance dep on organ distention
§ Myoepithelial cells and Neuroepithelial cells-on exterior side of basal lamina
IV. Types of epithelial
A. Simple squamous epithelium
§ Gaseous diffusion
§ Cardiovascular sys; alveoli in lungs, lining of body cavity, coat of organs, kidney (loop of Henle, Bowman’s capsule)
B. Simple cuboidal epithelium
§ Secretion and absorption
§ Collecting duts, proximal and distal tubes of kidney, thyroid follicles
C. Simple columnar epithelium
§ Absorption
§ Intestines, stomach, gall bladder, uterus
D. Stratified sqamous epithelium
§ Provides protection
§ Epidermis (keratinized) and esophagus (nonkeratinized)
E. Stratified cuboidal epithelium
§ Mid-sized ducts
§ Ducts of sweat gland
F. Stratified columnar epithelium
§ Large ducts
§ Ducts of salivary glands, urethra, conjuctiva
G. Pseudostratified columnar epithelium
§ Secretion and movement along luminal surfaces
§ Upper respiratory tract
§ Male reproductive system
H. Transitional epithelium
§ Accommodate increase in luminal area by changes in cell shape
§ Bladder and Ureter (only in urinary system)
V. Organization of glandular epithelium
A. Exocrine glands
§ From epithelia surfaces during embryogenesis: stalk of cells grows into underlying connective tissue, forming gland
§ Ducted- connection cord remains attached to gland, spaces develop within (straight or branching)
§ Secrete product onto free body surface
§ Secretions to epithelial surface via ducts (some alter nature of secretion by active transport mech)
§ Secretions: enzymes, lubricants, waste products, aqueous fluid for evaporation, oils
B. Endocrine glands
§ Arise from epithelial surfaces- down growths of ectoderm/endoderm into underlying connective tissueàgland primordial
§ Ductless- connecting cord disappears during differentiationà “island” of cells embedded in connective tissue
§ Associated with capillaries (interspersed between cells, permits secretions to enter the blood system
§ Secrete hormones- act on target organs
C. Relationship of secretory epithelial cells, the basal lamina, and underlying connective tissue
§ Stroma- supporting cellular frame work of connective tissue, containing blood vessels and nerves & gives structure to gland
§ Parenchyma- secreting cells of the gland which perform the gland’s essential function
VI. Classification of exocrine glands
A. Cell number
§ Unicellular- goblet cell of intestine and respiratory tract
§ Multicellular
Without duct- ductless sheet of secretory epithelial cells ex/ mucous ling of stomach; cervical lining
With duct-most exocrine glands ex/ salivary glands
B. Type of Secretions
Mucous
§ Viscous, slimy
§ Mucigen + water = mucous
§ Mucin- glycoprotein from RER. Carbohydrate moiety added by golgi, packaged in apical mucigen granules for secretion)
§ All mucus is not same since glycoprotein vary in stucture
§ Flattened nuclei, empty apical cytoplasm
§ Ex/ Salivary glands, gld of esophagus, cardiac, pyloric gld of stomach, brunners of duodenum, colonic crypts, vestibular glds, urethral glds of litter
Serous
§ Watery
§ Wide variety of protein components, not always enzymes
§ Enzymes produced by RER packed in apical zymogen granules containing proenzymes, become activated after secretion
§ Round basal nuclei, cytoplasm acidophilic protein containing granules, pyramidyl shaped cells surround small central lumen of acinus
§ Ex/ exocrine prancreas, parotid salivary glds, uterine glds
Mixed (seromucous)
§ Mixture of all mucous and all serous acini or mixed seromucous acini
§ Seromucous acini organized as mucous acini capped by serous “demilunes”
§ Submandibularand sublingual salivary gld, mixed glds of nasal cavitgy, paranasal sinuses, nasopharynx, larynx, traches, bronchi
C. Mode of Secretion
Merocrine (errine)
§ Cell product secreted by exocytosis into lumen
Apocrine
§ Product and small portion of apical cytoplasm secreted by pinching off from cell
Holocrine
§ Entire cell with product released into acinus lumen
§ Sebaceous gland s of skin and nose, ovary and testis
D. Structure of Duct System
§ Unbranched duct- Simple glands ex. Sweat gland
§ Branched duct- Compound gland ex. Exocrine pancreas
E. Shape of Secretory Unit
§ Tubular- cylindrical unit ex/ sweat glands
§ Acinar-saclike unit ex/ sebaceous gland, mammary
§ Tubuloacinar- having tubular and alveolar units ex/ exocrine of pancrease, submandibular salivary gland
VII. Classification of endocrine glands
A. Nature of hormone secreted
§ Steroid hormones- enzymes for hormone synthesis localized in SER ex/ ovary, testes, adrenal cortex, placenta
§ Polypeptide hormones- maybe simple or glycoproteins ex/ hypophysis (pituitary), thyroid (parafollicular cells), parathyroid, pancreatic islet, neuroendocrine system APUD cells, placenta
§ Amino acid derivatives-ex/ thyroid (follicular cells), adrenal medulla, pinea, neuroendocrine system APUD cells
B. Organization of Endocrine Gland
§ Discrete endocrine glands- ex/ hypothesis, thyroid, parathyroid, adrenals, pineal
§ Endocrine component of endocrine/exocrine glands
Pancreas- islets of langerhans
Ovary-follicle, courpus luteum
Testies-leydig cells
Kidney-juxtaglomerular cells
Placenta-sycytiotrophoblast
§ Diffuse neuroendocrine system
Widely distributed in body organs
Located adjacent to and secrete toward basal lamina
Basal secretory granules in EM
Secrete both ply peptide (act at distant site) and amine (act on nearby site) hormone products
In GI system, comprise enteroendocrine cells
C. Site of Action of Hormone
§ Endocrine- acts at distant site
§ Paracrine- acts on nearby site
§ Autocrine-acts on cell producing hormone
Tags: apocrine, basal lamina, branched duct, cuboidal epithelium, epithelial tissue classification, Epithelium, Exocrine glands, holocrine, juxtaglomerular, Mucous, Myoepithelial, ovary, pancreas, Parenchyma, Placenta-sycytiotrophoblast, polypeptide hormones, Pseudostratified, seromucous, Stroma, Submandibularand sublingual, testies
