Glands – types
according to their
function
Structure 28
Glands
Glands are epithelial cell populations, producing
●
material with a biological function (secreta)
and transporting it to the intercellular space
●
Glands are localised in the connective tissue
beneath covering epithelium
Classification:
●
●
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Exocrine glands (product of secretion is
excreted on the surface)
Endocrine (product of secretion is excreted
into the blood )
Exocrine and endocrine
glands
Exocrine gland
Endocrine gland
direct communication
with surface or in the
form of duct – system
of the ducts
Product of secretion is
transported by the
ducts
communication with the
surface in further
development
disappears
Product of secretion =
hormone is released
into the intercellular
space and to the
blood
Classification of exocrine
glands accordind to
1. mechanism how the product of secretion is released
(eccrine / merocrine /apocrine / holocrine);
2. secretory cells localisation related to surface
epithelium (intra-epithelial / extra-epithelial);
3. structure of secretory portion (tubular/ acinar/
alveolar)
4. gland architecture (simple, compound);
5. content of secreta (serous / mucous).
Glands
Exocrine glands
according to the mechanism of secretion
Merocrine secretion – secretory cells release
protein rich secreta via exocytosis (pancreas)
Eccrine secretion – molecules and ions are
transported in particularly as osmotically
active substances, followed by water (sweat
glands) + merocrine glands need eccrine
secretion as well /water like vehiculum of the
saliva
Exocrine glands
according to the mechanism of secretion
Apocrine secretion - (apocytosis) cells release the apical cytoplasm into the product of
secretion - lactating mammary gland (for lipid
component in the milk). Lipid droplets are released
with cytoplasm and cytoplasmic membrane
-apocrine / axillar sweat glands
Holocrine secretion –the whole cells become the part
of secreta (Greek: holos, whole), esp. fat; the cell
becomes apoptotic after synthesis of lipid droplets
– degraded – secreta - sebaceous glands, skin
Glands
Merocrine glands –
the majority of
glands
Apocrine gland –
mammary gland
during lactation
Holocrine gland –
sebaceous glands in
the skin
Location of glandular cells
Intra-epithelial glands: Goblet
cells are scattered in epithelium
as unicellular glands
In some organs (stomach,uterine
cervix) covering epithelium is
established by mucus secreting
cells
Extra-epithelial glands – are
localised underneath the origin
epithelium.
They consist of
the secretory portion
duct, one or system of branched
ducts
Stomach
Structure of the secretory
portion
Tubular (mucous glands,
eccrine sweat glands
Acinar (pancreas, parotid
gland)
Alveolar (sebaceous
gland)
Tubo-acinar (gl.
submandibularis,
gl.sublingualis)
Tubo-alveolar
(mammary gland
during lactation,
apocrine sweat glands
Glandular architecture
Simple tubular glands - tubes; with well
developed lumen, visible in LM - mucinous
glands, eccrine sweat glands
Simple acinar glands: ball, vesicle (lat. acinus =
berry) – lumen is unvisible in LM
Simple alveolar glands – a ball with visible
lumen
Compound (tubo-acinar, tubo-alveolar)
Ducts
Compound glands have a branching system of
ducts.
Epithelial cells of ducts can change the primary
secreta: (ion composition,water). Primary
product of secretion is changed into secondary
– Ducts:
• Intralobular
– Intercalated
– Striated
• Interlobular
• Main
Glands
Secretion characteristics /
composition
Product of secretion is waterish material (except for
sebaceous secreta – sebum)
• Ion and water transport (sweat glands, lacrimal gland)
• Serous glands
• Mucous glands
• Mixed seromucous (glandula submandibularis, glands
of respiratory mucosa
• „Serous demilune” - the cap formed by serous cells
and present at the end of mucous tubule
●
Serous cell




Round nucleus
RER, GA
Secretory
(zymogenous)
granules
Produces proteins
- enzymes
Mucous cells



Produces mucus
RER and GA
Mucous secretory
granules –
glycoprotein - PAS +
PAS+ - goblet cells in colon
Striated duct



Baso-lateral
labyrinth –
invagination of
plasmalemma
and
mitochondria
Na,K ATP ase
Absorption of
water
Salivary
glands
Mucoustubules
Serous –
acini
Serous demilunes
Ducts:
Intercalates
Striated
Interlobular
Main
Myoepithelial cell
contractile epithelial cells, contribute to the process
of the product release
Present in the secretory portion and the initial
portion of the duct system
sweat gland, mammary, salivary, lacrimal,
oesophageal gl, respiratory mucosa gl, ABSENT in
pancreas
• stellate , basket cells resisting on basal lamina
(share it with secretory or duct system cells)
Myoepithelial cell
Content of
cytokeratins as
epithelial cells and
actin and myosin as
smooth muscle cells
It has the same basal
lamina as epithelial
cells
Regulation of the secretory
activity
secretory activity is regulated by parasympathetic
innervation,
or/and by hormones
• under pathological conditions, mediators of
inflammation can influence ammount and quality
of secreta
Structure of endocrine glands
and liver
Reverse orientation,
secretion is
produced toward to
the basal lamina
Cords of cells
Folicles in thyroid
gland (storage of
iodine within it)
Liver architecture – cords of
hepatocytes