Glandular Epithelium A gland is a single cell or a mass of
epithelial cells adapted for secretion. Classification of Glands By
destination By structure By nature of the secretion By the method
of discharge There are two types depending on how the cells release
the substances they produce: Exocrine glands and endocrine glands
Slide 2 Classification by Structure Secretory part: unicellular /
multicellular acinar (alveolar) / tubular coiled / branched Duct
system: Simple gland (single duct) Complex gland (branched ducts)
Branching ducts: Main > interlobular > Intralobular >
Intercalary (ducts define structure of complex glands) Slide 3
1)Exocrine glands secrete into ducts or directly onto a free
surface. Their secretions include mucus, sweat, oil, ear wax and
digestive enzymes. EXO = out side and crine = secret Structural
classification of exocrine glands multicellular glands - most
glands, have a distinctive appearance. Communicates with the
surface Slide 4 Examples include :- pancreas, stomach, sweat
glands, salivary glands, mammary glands, sebaceous glands, etc.
unicellular glands - single cell. goblet cells. No ducts. Slide 5
Slide 6 Slide 7 Slide 8 Endocrine glands - called ductless glands
discharge their secretions into the intracellular fluid, where it
diffuses into the blood stream. These secretions are hormones, or
chemical messengers, which regulate many body functions. Slide 9
Formation of glands from covering epithelia. During fetal
development epithelial cells proliferate and penetrate the
underlying connective tissue. They may-or may not- maintain a
connection with the surface epithelium. When the connection is
maintained, exocrine glands are formed; with the connection lost,
endocrine glands are formed. Exocrine glands secrete to the body
surface or gut via duct systems formed from the epithelial
connection. Slide 10 The cells of endocrine glands, which secrete
hormone) can be arranged in cords or in follicles with lumens for
storing the secretory product. From either the cords or follicles
of endocrine cells, the secretory product is released outside the
cells and picked up by the blood vessels for distribution
throughout the body. Slide 11 Slide 12 General structure of
exocrine glands. Exocrine glands by definition have ducts that lead
to an organ or body surface. Inside the gland the duct runs through
connecting septa and branches repeatedly, until its smallest
branches end in the secretory portions of the gland. Slide 13 Slide
14 exocrine glands have a secretory portion, which contains the
cells specialized for secretion, and ducts, which transport the
secretion out of the gland. the morphology of these components
allows the glands to be classified as follows :- Slide 15 1-Ducts
can be simple ( un branched ) or compound ( with two or more
branches) 2-Secretory portions can be tubular ( either short or
long and coiled ) or acinar ( round or globular) 3-Either type of
secretory portion may be branched. 4-Compound glands can have
tubular, acinar, or tubuloacinar secretory portions Slide 16 Slide
17 Slide 18 Slide 19 Classification by nature of secretion The
three major salivary glands: parotid, sub mandibular and
sublingual. Slide 20 Glands containing mucous acini (e.g. the
sublingual glands) are called mucous glands. Glands containing
serous acini (e.g. the parotid glands) are called serous glands. If
both types of acini are present the gland is muco-serous or mixed
gland. Slide 21 1- Mucous glands ( glands containing cells produce
a viscous secretion that lubricates and or protects the inner
lining of organs ). Morphology : the cell is pyramidal in shape,
flatten nuclei are displaced basally, their cytoplasm is completely
filled with a light staining, secretory product called mucus. Slide
22 Slide 23 Slide 24 Serous glands ( glands with cell that produce
watery secretions, which are often rich in enzymes ). Morphology :
are similar in shape to mucous cells also pyramidal in shape,
spherical or round nuclei are displaced basally by secretory
granules that accumulate in the apical regions. Slide 25 Slide 26
Slide 27 Mixed glands ( glands that contain a mixture of both
mucous and serous secretory cells). Morphology : mucous cells
predominant, serous cells form a crescent or moon-shaped cap over
the mucous cells, called serous demilune Slide 28 Slide 29 Slide 30
Classification by method of secretion Merocrine Apocrine Holocrine
Slide 31 Merocrine secretion is exocytosis Membrane bounded
component approaches cell surface It fuses with plasma membrane Its
contents are in continuity with the extracellular space Plasma
membrane transiently larger Membrane retrieved, stabilizing cell
surface area Slide 32 Slide 33 Apocrine secretion Non-membrane
bounded structure (e.g. lipid) approaches cell surface Makes
contact and pushes up apical membrane Thin layer of apical
cytoplasm drapes around droplet Membrane surrounding drop[let
pinches off from cell Plasma membrane transiently smaller Membrane
added to regain original area Slide 34 Slide 35 Slide 36 Holocrine
secretion Disintegration of the cell Release of contents Discharge
of whole cell Slide 37 Slide 38 Slide 39 Slide 40 Endocytosis
Engulfing material initially outside the cell Opposite of
exocytosis (merocrine secretion) Endo- & Exo-cytosis are
coupled in transepithelial transport Transepithelial Transport
material endocytosed at one surface transport vesicle shuttles
across cytoplasm material exocytosed at opposite surface Slide 41
Slide 42 Golgi Apparatus: Structure Stack of disc-shaped cisternae
One side of discs are flattened; other concave Discs have swellings
at their edges Distal swellings pinch off as migratory Golgi
Vacuoles Slide 43 Golgi Apparatus: Function Packaging through
condensation of contents Transport Adding sugars to proteins and
lipids (Glycosylation) Golgi Product Destinations Majority extruded
in secretory vesicles Some retained for use in the cells (e.g.
lysosomes) Some enters the plasma membrane (Glycocalyx) Slide 44
Glycosylation & Specificity Branching sugars offer complex
shapes for specific interactions in the glycocalyx Destruction of
this layer by enzymes alters many specificity based properties of
cells: - adhesion to substrates & neighboring cells - mobility
of cells - communication with neighboring cells - contact
inhibition of movement and division Slide 45 Control of Secretion
Nervous Endocrine control Neuro-endocrine control Negative feedback
chemical mechanism Slide 46 The Pancreas, an exocrine and endocrine
gland. Slide 47 An islet of Langerhans surrounded by exocrine
pancreatic acini (high power). Slide 48 The thyroid gland Slide 49
Simple cuboidal epithelium of the thyroid gland surrounding
homogeneous colloid in each follicle. Slide 50 Parathyroid glands
Slide 51 Adrenal gland Slide 52 Slide 53 Slide 54 Slide 55 Slide 56
Summary 1 Epithelial cells form glands: the organs of secretion
Glands are: tubular / acinar / coiled / branched simple / complex
endocrine / exocrine serous / mucous Slide 57 Summary 2 Secretion
is Merocrine, Apocrine or Holocrine Nascent proteins & lipids
are processed in the Golgi Golgi products are retained, exported or
added to membrane Glycosylation confers additional specificity
Control: chemical, neural, endocrine or neuro- endocrine
