Mrs. Ofelia Solano SaludarDepartment of Natural Sciences

University of St. La Salle

EPITHELIUM: specializED TYPES

STUDY GUIDE1. Describe the CT components of a typical gland.2. Compare and contrast:

a. 4 types of specialized epithelia based on: histological characteristics, location, function

b. Exocrine and endocrine glands: product release, histology, regulation of secretion, examples

c. Unicellular and multicellular glands: histology, example /location

d. Nature of secretion: composition, locatione. Secretory membranes: types, example/locationf. Release mechanisms: types, example/locationg. Endocrine secretions: types, example/locationh. Hormone action: types, example/locationi. Modes of secretion: types, example/ locationj. DNES: types, example/location

1.Neuro-epithelium- tastebuds of tongue, organ of Corti in inner ear, retina of eyeball, olfactory epithelium of nasal cavity. Differs in appearance but are all composed of:

• Chief sensory cell- a true nerve cell or a modified epithelial cell for reception of stimulus

• Supporting or sustantecular cells - maybe tall columnar cells lying side by side with the chief cells, or basal cells with irregular processes found beneath the chief and columnar cells above the basal membrane

SPECIALIZED EPITHELIUM

2.Pigment epithelium- retina, pars ciliaris, pars iridica retinae of eye

3.Myoepithelial cells- contractile epithelial cells located between the basal lamina and the bases of secretory acini and their ducts

• Surround a single duct, and their contraction helps expel the products of exocrine glands

• Found in lacrimal, salivary, mammary, and sweat glands, seminiferous tubules

4.Pyramidal or glandular epithelium – specialized to produce secretion (exocytotic release of products, not metabolic wastes).

Name derived from its secretory or glandular function (found lining secretory portions of the acini of glands) and pyramidal shape of cells.

• Cells are arranged in a single row around a circular lumen of varying size.

• The proximal portion is broader and attached to the basement membrane while the distal end borders the lumen of the cavity

• Molecules to be secreted may be stored in membrane bound secretory granules (vesicles)

• Carcinoma is a malignant neoplasm of the epithelium; adenocarcinoma is derived from glandular epithelium

1.EXOCRINE- system of ducts opening into surface

2.ENDOCRINE- release products into blood or lymph for transport to target tissues

• Highly vascularized.• Neural or hormonal regulation, or both;

e.g. suckling infant generates afferent pathway impulses carried to the brain, stimulating release of oxytocin from pituitary, which in turn cause contraction of myoepithelial cells around acini of mammary gland to eject milk

TYPES OF GLANDS

Formation of glands from

covering epithelia.

Epithelial cells proliferate and

penetrate connective tissue. They may or may

not maintain contact with the surface. When

contact is maintained,

exocrine glands are formed;

without contact, endocrine glands are

formed. The cells of endocrine

glands can be arranged in cords

or in follicles.

• The CT components of a typical exocrine gland (e.g. pancreas) are the stroma; epithelial portion is the parenchyma.

• Gland is enclosed in a condensation of CT forming its capsule.

• Septa of CT extend inward into subdivisions called lobes, continue into smaller units called lobules, & end in microscopic subunits called acini or alveoli

• Groups of acini are drained by intercalary ducts, converge on intralobular ducts, and join larger interlobular ducts in the septa between lobules. Several of the latter form lobar ducts which join to form the main duct.

• Merocrine/ eccrine- release of product with the cell membrane remaining intact (pancreas, pituitary)

• Apocrine- involve constriction and pinching off of a portion of the apical cytoplasm containing secretory granules (mammary glands)

• Holocrine- bulk release of whole cells or discharge of their cytoplasm into the glandular excretory duct (sebaceous glands, spermatozoa)

MECHANISMS OF PRODUCT RELEASE

1. UNICELLULAR GLANDS– mucous or goblet cells • Found among simple columnar cells of the

intestines and pseudo-stratified columnar epithelium of the respiratory system

• Cup-shaped rim of cytoplasm called the theca is filled with secretory droplets, mucinogen, that takes a clear blue basophilic stain and is PAS positive.

• Basophilia is due to abundant free and attached ribosomes

• Secretion is continuous within their 4 day lifespan, but maybe accelerated by parasympathetic nerves

TYPES OF EXOCRINE GLANDS

2.MULTICELLULAR GLANDS- secretory portion is connected to a surface by an unbranched duct (SIMPLE); branched ducts (COMPOUND)

intestinal mucosa

sweat glands

duodenum

salivary glands

pancreasmammary glands

prostate

MUCOUS- lubricating, viscous fluid rich in

mucopolysaccharides (goblet cells, sublingual

salivary glands)

NATURE OF SECRETIONS

SEROUS- watery secretion rich in

enzymes (pancreas, parotid glands)

MIXED GLANDS- mucous cells make up bulk of gland, with serous cells forming caps called serous demilunes over the ends of the acini (e.g. submandibular glands)

Ultrastructure of a hypothetical

STEROID-secreting cell. Note the

abundance of the smooth endoplasmic reticulum (SER), lipid

droplets, Golgi complex, and

lysosomes. The numerous

mitochondria have mainly tubular cristae. They not only produce the energy necessary for the activity of the

cell but are also involved in steroid hormone synthesis. Rough endoplasmic

reticulum (RER) is also shown.

PANCREAS

SECRETORY MEMBRANES

• Form organs (peritoneal, gut tube lining, etc.)• Names based upon type of secretions:1.Serous Membrane - thin, flat layer of squamous

epithelial cells moistened by exudates from underlying blood vessels.

2.Mucous Membrane - moist epithelial surface, usually columnar, but may be cuboidal or squamous, that is moistened by secretions produced by glands formed by the epithelium itself.

1.Polypeptide secretions (insulin, glucagon, gowth hormone, TSH, GTH, ACTH, thyroglobulin)- rER of cells is less extensive due to low volume of secretory output; secretory granules are membrane-bound (except thyroglobulin which is stored extracellularly)

2.Steroid secretions (ovary, testis, adrenals)- steroidogenic cells accumulate cholesterol for synthesis of steroid hormones via sER; little or no storage of hormones is observable.

ENDOCRINE SECRETIONS

1.Protein hormones- bind to receptors which are integral protein molecules of cell membrane

• Binding of hormone (1st messenger) to a receptor results to: conformational change in receptor and G-protein, activating adenylate cyclase and catalyzing the formation of cAMP (2nd messenger).

• This sets in motion reactions leading to specific physiological response of target cell to hormone.

MECHANISM OF HORMONE ACTION

2.Steroid hormones- diffuse through membrane & bind to receptors located in the nucleus

• Hormone-receptor complex binds to DNA and activate transcription needed for cellular response

• Receptor anomalies result to testicular feminization, and familial male pseudo- hermaphroditism

• Antibodies that bind to receptors results to Grave’s disease (excess thyroid hormone production), diabetes (IgG blocks insulin binding)

1.Short-range diffusion of chemical signals (cytokines, paracrine, autocrine)

2.Distribution of chemical signals in the blood (hormones, endocrine)

3.Conduction of action potentials along nerve axons (neurotransmitters)

TYPES OF RELEASE MECHANISMS

1.Constitutive- product is rapidly transported directly to cell surface in small vesicles

2.Regulated- cells concentrate and store their products in membrane-bounded granules until a neural or hormonal signal for its release is received

MODES OF SECRETION

• Secretory proteins mRNAs have codons for a signal peptide that binds to SRP; forms ribosome receptor proteins in the ER membrane.

• These line the transmembrane channel through which the elongating polypeptide chain extends into the ER lumen.

• After synthesis, it is incorporated into transport vesicles, move to the C-face of the Golgi complex, where condensing vacuoles form, & finally moving up to the apical cytoplasm to form secretory granules.

• Endocrine cells that occur individually or in small groups in the brain and in epithelia of intestinal and respiratory tracts

• Also called APUD (amine precursor uptake and decarboxylation) cells since they concentrate bioactive amines such as epinephrine, norepinephrine and serotonin in their cytoplasm

DIFFUSE NEURO-ENDOCRINE SYSTEM (DNES)

Secretions of DNES:1.Enteroendocrine

hormones- influence secretory activity of GI tract and gut motility

2.Interleukins or lymphokines of lymphocytes- signal molecules that affect differentiation and behavior of other cells in the immune system

3.Colony-stimulating factors (CSF) of bone marrow- specific factors that affect development of stem cells in bone marrow

EM micrograph of a cell of the DNES. Note the accumulation of secretory granules in the basal region of the cell. The Golgi complex seen in the upper part of the micrograph shows some secretory granules; it is here

that these granules first appear. The arrow indicates the basal lamina.

QUESTIONS?