Download Glands & Hormones

Glands &
Hormones
oestrogen
glucagon
adrenaline
insulin
testosterone
Syllabus reference:
• This symbol in the corner of a
slide indicates a picture,
diagram or table taken from
your text book
Glands
simple
stratified
Types of epithelial cells
columnar
cuboidal
squamous
Covering and lining most surfaces in the body are epithelial cells.
Glands are structures formed from epithelial cells
Some epithelial cells are specialized by having cilia; others are capable of
secreting complex molecules.
Glands of the body are classified as either exocrine or endocrine types.
Glands; summary so far:
 Glands are multicellular epithelial structures that specialize in
synthesizing and secreting complex molecules including hormones
and enzymes.
 Glands are classified as either exocrine or endocrine glands.
 Exocrine glands have ducts to body surfaces or body cavities.
 Endocrine glands are small isolated blocks of tissues with no
ducts to surfaces. They are therefore referred to as
"ductless" glands.
 The products of exocrine glands collect in the duct of the gland
and flow toward the surface through the duct.
 Since endocrine glands lack ducts, their product is released
across the cell membrane into interstitial spaces around the
cells. They then diffuse into capillaries.
Types of gland
Exocrine Glands
• Most glands of the body are exocrine glands with ducts
connecting to body surfaces or body cavities.
• For example, your salivary glands open into the oral cavity and
sweat glands deposit their product on the skin surface.
Types of exocrine gland structure:
Simple tube
Coiled tube
Branched tube
Exocrine Glands
Exocrine glands can also be classified by their secretion mechanism.
1.
Merocrine glands: these secrete substances by the process of exocytosis.
Vesicles fuse with the plasma membrane resulting in the release of their
contents into the extracellular space.
Examples include most sweat glands, the salivary glands and the goblet
cells lining of the respiratory and digestive tracts.
secretory product
Most exocrine glands release their
products in this way.
Example of a merocrine gland:
sweat glands
Section through a sweat gland of the skin;
a coiled tube exocrine gland
Example of a merocrine gland:
salivary glands
Exocrine Glands
Exocrine glands can also be classified by their secretion mechanism.
2.
Apocrine glands: Glands that secrete by shedding a portion of their
cytoplasm, containing the secretory product, into a duct
pinched off
portion of the cell
Examples include the mammary
glands and sweat glands in the
armpits.
Example of an apocrine gland:
mammary glands
Simplified diagram of a mammary
gland Each one is a functional unit
[alveolus] of epithelial cells that
secretes milk into its centre.
Normal alveoli in lactating mammary gland
look like bunches of grapes.
Exocrine Glands
Exocrine glands can also be classified by their secretion mechanism.
3.
Holocrine glands: Glands that secrete by shedding entire cells from the
lining of a duct.
disintegrating cell
and its released
contents
mitotic divisions
to replace lost cells
Examples include the
sebaceous glands
associated with hair
follicles.
Example of a holocrine gland:
Sebaceous glands
Sebaceous gland associated with a hair follicle;
a branched exocrine gland
Endocrine Glands
NOTE: the pancreas has both exocrine and endocrine gland cells
Endocrine Glands
• Endocrine glands are the hormone producing structures of the body.
• Some, like the thyroid are large and obvious.
• Others, for instance the Islets of Langerhans found in the pancreas,
are small islands of endocrine cells embedded within the larger
exocrine portion of this organ.
• Endocrine cells release their
secretory products into the
interstitial spaces around the cells.
• The hormones then diffuse into
nearby capillaries and are
carried to all parts of the body.
• Only when the hormones encounter
a target tissue do they exert an effect.
Endocrine Glands
Only cells in the target tissue or target organ
have the correct membrane receptors for this
hormone
Secretory cell in
endocrine gland
Hormone
diffuses into
the blood
Cells without the appropriate
membrane receptors remain
unaffected by this hormone
Key terms:
• Exocrine gland: a gland that secretes externally through
a duct
• Endocrine gland: a gland that secretes hormones
internally directly into the bloodstream
• Hormone: the secretion of an endocrine gland that is
transmitted by the blood to the tissue(s) on which it has a
specific effect
• Target tissue: cells of an organ that are affected by
specific hormones
Hormones
There are 2 major types of hormones:
• Lipid-based Hormones
• Protein-based Hormones
Lipid-based hormones
• The commonest type of lipid-based hormones are the
steroids
• Examples include aldosterone and the sex hormones
such as oestrogen and testosterone
testosterone
Aldosterone: hormone produced in the adrenal gland,
regulating salt and water balance in the kidney
Lipid-based hormones
• Lipid based hormones are hydrophobic which means they are
lipid soluble.
• They can diffuse through the cell membrane without the need
for a receptor on the membrane.
• These hormones bind to receptor proteins in the cytoplasm or
nucleus.
• This steroid-protein complex then binds to DNA and either
starts or inhibits transcription of a particular gene.
• This means it coordinates which genes should be transcribed as
mRNA, to make a protein.
How steroid hormones work:
1. Steroid hormone diffuses
across the plasma
membrane
2. Steroid hormone binds
with protein receptor
3. Steroid-protein complex
diffuses into the nucleus
4. Steroid-protein complex
binds to a specific gene
5. Gene is transcribed to
produce a section of
mRNA

6. mRNA is translated by
ribosomes in the
cytoplasm to produce the
required protein
Protein-based hormones
• These include:
– Polypeptides e.g. insulin; ADH
– Glycoproteins e.g. FSH; LH
– Catecholamines e.g. adrenaline; noradrenaline
adrenaline
ADH – anti diuretic hormone
FSH – follicle stimulation hormone
LH – luteinizing hormone
Protein-based hormones
• Protein based hormones are hydrophilic and are not lipid
soluble. That means they cannot diffuse across a membrane.
• The protein hormone acts as a first messenger by binding to
receptors in the plasma membrane.
• This causes an enzyme to be activated.
• This enzyme causes the formation of cyclic AMP from ATP.
• Cyclic AMP acts as a second messenger to activate a particular
reaction pathway in the cytoplasm.
How protein-based hormones work – outline of mechanism:
hormone first messenger
hormone receptor
in plasma membrane
cyclic AMP
ATP
second messenger
an enzyme activated
another enzyme activated or
direct effect on a biochemical
reaction in the cytoplasm
What is cyclic AMP?
adenosine
adenosine monophosphate
[AMP]
cyclic adenosine monophosphate
[cAMP]
How protein-based hormones work – detailed mechanism:
1. Protein hormone binds to
a protein in the plasma
membrane of a target cell
2. G-Protein activated
3. Cyclase enzyme activated.
This catalyses the
conversion of ATP to
cyclic AMP (cAMP)
4. cAMP activates an
enzyme in the cytoplasm.
This enzyme will catalyse
the required reaction in the
target cell.

How adrenaline affects target tissues:
FIRST MESSENGER
adenylyl cyclase
adrenaline
ATP


SECOND
MESSENGER



inactive
enzyme
inactive
enzyme
cAMP
G protein
active
enzyme
inactive
glycogen phosphorylase
active
enzyme
active
glycogen phosphorylase
receptor
protein

glycogen
glucose
phosphate
How adrenaline affects target tissues






The pancreas
• Both endocrine and exocrine functions can
be found in the same organ.
• The pancreas simultaneously produces
exocrine secretions like digestive enzymes
and endocrine secretions like insulin and
glucagon that are released into the blood
to exert their effects throughout the body.