Glandular epithelium

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Glandular epithelium
Epithelial tissue is present in 2 forms
covering
glandular
Covering epithelium - as
sheets of contiguous cells
that cover the body on its
external surface and line the
body on its internal surface
Glandular epithelium glands, which originate
from invaginated epithelial
cells
Glands originate from epithelial cells that
leave the surface
CT-stroma
parenchyma
Glandular epithelial cells
penetrate into the underlying
connective tissue,
manufacturing a basal lamina
around them
The secretory units (+ ducts)
are the parenchyma of the
gland, whereas elements of
the connective tissue form
the stroma of the gland
Glandular epithelia manufacture their product
intracellularly by synthesis of macromolecules
Products are packaged and stored in vesicles
called secretory granules
The secretory product may be a polypeptide
hormone (e.g., from the pituitary gland); a waxy
substance (e.g., from the ceruminous glands of
the ear canal); a mucinogen (e.g., from the
goblet cells); or milk, a combination of protein,
lipid, and carbohydrates (e.g., from the
mammary glands)
Gland classification on the basis of the
method of product distribution
Exocrine glands secrete their products via
ducts onto the external or internal epithelial
surface from which they originated.
Endocrine glands secrete their products into
the blood or lymphatic vessels for distribution
Exocrine gland classification
On the basis of the number of cells (unicellular
or multicellular)
On the basis of their mode of secretion
(holocrine, merocrine, apocrine)
On the basis of the nature of their secretion
(mucous, serous, or mixed)
Unicellular exocrine glands – goblet cells
The simplest form of exocrine
gland
Represented by isolated
secretory cells in an epithelium
– e.g. intestinal or respiratory
Have basal stem and apical
theca, filled with membranebound secretory droplets
(mucinogen granules) – their
release is stimulated by chemical
irritation and parasympathetic
innervation
Goblet cell with PAS stain (red)
Simple columnar
epithelium with
goblet cells by
TEM
Mu = mucous granules
BB = brush border
Mv = microvilli
A = absorptive (columnar
epithelial) cell
Simple columnar
epithelium (AC)
with goblet cells
(GC) containing
mucous granules
(MG) by TEM
The 4 main differentiated cell types found in
the epithelial lining of the small intestine
Molecular Biology of the Cell (© Garland Science 2008)
Multicellular exocrine glands
Exist as organized clusters of secretory units,
arranged in varying degrees of organization
Do not act alone and independently but instead
function as secretory organs
Subclassified according to
organization of their secretory and duct components
simple - their ducts do not branch
compound
(branched) - their ducts branch
shape of their secretory units
tubular
acinar (alveolar, resembling a grape)
tubuloalveolar
Multicellular exocrine glands - overview
Simple tubular
mucus secreting
glands - colon
Simple acinar mucus secreting glands – male urethra
Exocrine gland classification on the basis
of their mode of secretion
Holocrine glands (e.g., sebaceous gland) - a
secretory cell matures, it dies and becomes the
secretory product
Apocrine glands (e.g., lactating mammary
gland) - a small portion of the apical cytoplasm
is released along with the secretory product
Merocrine glands (e.g., parotid gland) - via
exocytosis; i.e., neither cell membrane nor
cytoplasm becomes a part of the secretion
Exocrine gland classification on the basis of
their mode of secretion
Holocrine
Merocrine
Apocrine
Larger multicellular glands have additional
components
Collagenous connective tissue
capsule
Capsule sends septae (strands
of connective tissue) into the
gland, subdividing it into
smaller compartments known
as lobes and lobules
Vascular elements, nerves, and
ducts utilize the connective
tissue septa to enter and exit
the gland. In addition, the
connective tissue elements
provide structural support for
the gland.
Exocrine glands with merocrine secretion classification on the basis of the nature of their secretion
Mucous
secrete mucinogens - large glycosylated proteins that, upon
hydration, swell to become a thick, viscous, gel-like protective
lubricant known as mucin, a major component of mucus
examples
Serous
unicellular: goblet cells
multicellular: minor salivary glands of the tongue and palate
secrete an enzyme-rich watery fluid
examples – pancreas, parotid salivary
Mixed – have both mucous and serous components
Mucous gland with a duct (arrow)
Serous gland with ducts (arrows)
Serous secretory unit (high magnification)
Serous acinar cells at TEM – rich in RER
Mixed gland with serous demilunes (SD)
SA – serous acinus
MA – mucous acinus
StD – striated duct
Serous demilunes - a group of cells in
mucous acini that secrete a serous fluid
Organization of a
large multicellular
gland – a salivary
gland
Myoepithelial cells
Stellate or spindle-shaped cells located between the
basal lamina and the basal pole of secretory or duct
cells in several exocrine glands (eg, sweat, lacrimal,
salivary, mammary)
Possess processes which embrace an acinus as an
octopus – connected via gap junctions and
desmosomes
Specialized for contraction (contain myosin and a large
number of actin filaments) - contract around the
secretory or conducting portion of the gland and thus
help propel secretory products into the duct
Myoepithelial cells
Endocrine glands
Cords
Follicles
Ductless, and thus their secretory products are released
directly into the bloodstream or the lymphatic system
Their cells can be arranged in cords or in follicles with
lumens for storing the secretory product
Overview of the endocrine system
System of ductless glands that secrete hormones
Hormones are messenger molecules (“first messenger”)
Circulate in the blood
Act on distant target cells
Target cells respond to the hormones for which they have
receptors
The effects are dependent on the programmed response of
the target cells
Hormones are just molecular triggers
Basic categories of hormones
Amino acid based: modified amino acids (or amines), peptides
(short chains of amino acids), and proteins (long chains of
amino acids)
Steroids: lipid molecules derived from cholesterol
Hormones
Hormones are organic chemical messengers produced
and secreted by endocrine cells into the bloodstream.
Hormones regulate, integrate and control a wide range
of physiologic functions.
Modes of cell communication
autocrine paracrine
juxtacrine
Endocrine organs
Purely endocrine organs
Pituitary gland
Pineal gland
Thyroid gland
Parathyroid glands
Adrenal: 2 glands
Cortex
Medulla
Endocrine cells in other organs
Pancreas
Thymus
Gonads
Hypothalamus
Endocrine glands
The hypothalamic-pituitary axis
The hypothalamic-pituitary axis
Hypothalamic Hormones:
Gondotropin RF
Corticotropin RF
Thyrotropin RF
Growth Hor RF
Prolactin RF
(CRF)
Pituitary Hormones:
Follicle SH &
Adrenocorticoptropin Thyrotropin SH
Growth
Prolactin
Hormone
Lutenizing Hor. Hormone (ACTH)
Target Gland or Structure:
Ovaries & Testes
(androgens, estrogen)
Adrenal Gland
Thyroid Gland
(cortisol)
(thyroxine)
Cells of body
Bones, breasts
& cells of body
Thyroid is composed of spherical follicles
Follicle cells: produce thyroglobulin, the precursor of thryoid
hormone (thyroxin)
Colloid lumen is of thyroglobulin
Parafollicular “C” cells: produce calcitonin
Thyroid gland follicles
F = follicle
CT = connective tissue
BV = blood vessel
Adrenal (suprarenal) glands
(“suprarenal” means on top of the kidney)
Each is really two endocrine glands
Adrenal cortex (outer)
Adrenal medulla (inner)
Unrelated chemicals but all help with extreme situations
Cords of endocrine cells in adrenal cortex
The Pancreas
Exocrine and endocrine cells
Acinar cells (forming most of
the pancreas)
Exocrine function
Secrete digestive enzymes
Islet cells (of Langerhans)
Endocrine function
α-cells – glucagon
β-cells – insulin
The Gonads (testes and ovaries)
main source of the steroid sex hormones
Testes
Interstitial cells (of Leydig) secrete androgens
Primary androgen is testosterone
Maintains secondary sex characteristics
Helps promote sperm formation
Ovaries
Androgens secreted by theca folliculi
Directly converted to estrogens by follicular granulosa cells
Granulose cells also produce progesterone
Corpus luteum also secretes estrogen and progesterone
Non-endocrine gland hormones
Stomach (gastrin)
Small intestine (gastrin, secretin, cholecystokinin)
Heart (atrial natriuretic peptide)
Kidneys (erythropoietin, active vitamin D3)
Adipose tissue (over 100 adipokines)
Skin
Placenta (human chorionic gonadotropin, human
placental lactogen, relaxin)
Functions regulated by the endocrine system
Growth
Healing
Water
balance & blood pressure
Calcium metabolism
Energy metabolism
Stress
Regulation of other endocrine organs
Tumors from epithelial cells
Tumors that arise from epithelial cells may be benign
(nonmalignant) or malignant. Malignant tumors arising
from epithelia are called carcinomas; those arising
from glandular epithelial cells are called
adenocarcinomas. It is interesting to note that cancers
in adults are most often adenocarcinomas and after age
45 about 90% are of epithelial cell origin. However, in
children under 10 years of age, epithelium-derived
cancers are the least prevalent type of cancer.
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