adrenaline
insulin
glucagon
oestrogen
testosterone
Glands & Hormones
Syllabus reference:
• This symbol in the corner of a slide indicates a picture, diagram or table taken from your text book
Glands
Covering and lining most surfaces in the body are epithelial cells.Glands are structures formed from epithelial cells
simple stratified
columnar cuboidal squamous
Types of 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 exocrineexocrine or endocrineendocrine 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 GlandsExocrine glands can also be classified by their secretion mechanismsecretion mechanism.
1. Merocrine glandsMerocrine 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.
Section through a sweat gland of the skin; a coiled tube exocrine gland
Example of a merocrine gland: sweat glands
Example of a merocrine gland: salivary glands
Exocrine GlandsExocrine glands can also be classified by their secretion mechanismsecretion mechanism.
2. Apocrine glandsApocrine 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.
Normal alveoli in lactating mammary gland look like bunches of grapes.
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.
Exocrine GlandsExocrine glands can also be classified by their secretion mechanismsecretion mechanism.
3. Holocrine glandsHolocrine glands: Glands that secrete by shedding entire cells from the lining of a duct.
Examples include the sebaceous glands associated with hair follicles.
disintegrating cell and its released
contents
mitotic divisions to replace lost cells
Sebaceous gland associated with a hair follicle; a branched exocrine gland
Example of a holocrine gland: Sebaceous glands
Endocrine Glands
NOTE: the pancreas has both exocrine and endocrine gland cells
Endocrine Glands • Endocrine glands are the hormone producing structureshormone 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 tissuetarget tissue do they exert an effect.
Secretory cell in endocrine gland
Hormone diffuses into the blood
Only cells in the target tissue or target organ have the correct membrane receptors for this hormone
Cells without the appropriate membrane receptors remain unaffected by this hormone
Endocrine Glands
Key terms:
• Exocrine glandExocrine gland: a gland that secretes externally through a duct
• Endocrine glandEndocrine gland: a gland that secretes hormones
internally directly into the bloodstream • HormoneHormone: the secretion of an endocrine gland that is
transmitted by the blood to the tissue(s) on which it has a specific effect
• Target tissueTarget 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
Aldosterone: hormone produced in the adrenal gland, regulating salt and water balance in the kidney
testosterone
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
ADH – anti diuretic hormoneFSH – follicle stimulation hormoneLH – luteinizing hormone
adrenaline
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 messengerfirst messenger by binding to receptors in the plasma membrane.
• This causes an enzyme to be activated. • This enzyme causes the formation of cyclic AMPcyclic AMP from
ATP.
• Cyclic AMP acts as a second messengersecond messenger to activate a particular reaction pathway in the cytoplasm.
hormone
hormone receptor in plasma membrane
ATP
cyclic AMP
an enzyme activated
another enzyme activated or direct effect on a biochemical reaction in the cytoplasm
How protein-based hormones work – outline of mechanism:
first messenger
second messenger
adenosine
cyclic adenosine monophosphate[cAMP]
adenosine monophosphate[AMP]
What is cyclic AMP?
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:
adrenalineFIRST MESSENGER
receptor protein
G protein
adenylyl cyclase
ATP
cAMP
inactive enzyme
activeenzyme
inactive enzyme
activeenzyme
inactive glycogen phosphorylase
activeglycogen phosphorylase
glycogen glucose phosphate
SECOND MESSENGER
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.