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.