Endocrine System

Greek- to excite Chemicals released in minute amount

that can elicit specific response

• Not all hormones are released by glands (e.g. Hypothalamus)

Nerves communicate faster due to impulses and structure of neurons

The endocrine system is responsible for slower biological processes (e.g. Growth)

The endocrine system and nervous system are structurally, chemically and functionally related

Presence of neurosecretory cells- specialized neurons

Chemicals that function as both hormones and neurotransmitters

Positive feedback• Nervous- opening of sodium ion gates

during the threshold potential• Endocrine- release of milk

Negative feedback

Hydra- hormone for growth and budding; prevents sexual reproduction

More complex- both are integrated in the control of reproduction and development

Aplysia- hormone for egg-laying counters feeding and locomotion

Arthropods- presence of ecdysone• Insects- secreted by prothoracic glands

Responsible for molting Favors metamorphosis Some insects- presence of brain

hormone (BH)• Promotes development by stimulating the

prothoracic glands Juvenile hormone (JH)- balances BH

and ecdysone• From corpora allata

Occurs when corpora allata stops producing JH• Regulation of production is not known

Could be nervous or neurohormonal Adult: inhibition via nervous

connection in the brain

Larvae: corpora allata is activated by neurohumoral factor from the brain during development

Inactivated by nervous inhibition before metamorphosis

Endocrine glands- ductless glands that release hormones (via the bloodstream)

Paracrine glands- like endocrine but target adjacent cells

Exocrine glands- release secretions through ducts

Holocrine- releases secretions through rupture of the plasma membrane (oil gland)

Apocrine – releases secretions through membrane-bound vesicles (mammary gland)

Merocrine- releases their secretion through exocytosis of their secretory vesicles

hormones- via the bloodstream Local regulators- targets nearby cells Pheromones- carry messages to

different individuals• Mate attraction

Secreted by cells to nearby/adjacent target cells• E.g. Interleukin, growth factor

Peptides and proteins that stimulate cell proliferation

a given growth factor can have different effects depending on the target cell• Nerve growth factor (NGF)

Speeds up development of embryonic nerve cells

Also affects developing white blood cell and other kinds of cell

A form of a non-surgical operation in treating injuries

Use of blood plasma where some growth factors are present

Highly reactive and toxic Action is rapid When secreted by neurons:

neurotransmitter WBC: kills bacteria and cancer cells Endothelial cells: dilate BVs; relax

smooth muscles

Modified fatty acid from lipids of plasma membrane

First found in semen In semen: stimulates uterine

contraction In placenta: induce labor Induce fever, inflammation and

intensify sensation of pain PGE: muscle relaxation in the lungs PGF: muscle contraction in the lungs

Signal molecule: has specific shape Reception: binding of signal to

receptor• Located at the plasma membrane or inside

the cell Signal transduction- series of events

signalled by the reception of signal mol on the plasma membrane

Response- change in a cell’s behavior

Occurs if there is a correct signal molecule

Specific receptor is present Depends on the location of the

binding site of a signal molecule

Signal transduction• Receptor is on the surface• Composed of series of events that can lead to

a response• E.g. Response is in the form of enzyme

activation Change in gene expression

• Signal molecule penetrates the cell and binds to a receptor inside

• Receptor acts as transcription factor• Change in gene expression

Darkness of skin depends on arrangement of melanocytes in the skin

Light skin: melanosome at the nuclei Dark skin: melanosome in the

cytoplasm Arrangement of melanosome is

controlled by MSH

Secreted by the pituitary gland MSH present: melanosomes disperse MSH absent: at the nuclei Direct injection does not lead to

dispersion• Why?

Signal receptor at the plasma membrane

Converts extracellular signal to intracellular response

Can amplify a signal to substantial response