Endocrine System

Endocrine system

communicating and regulating system

Endrocrine signalling

Hormones released into interstitial fluid travel via bloodstream to distant targets

Paracrine signalling

Signals only travel to nearby cells

Autocrine signalling

Target cell is the same as the one sending the signal

Synapic signalling

Uses the nervous system: signal molecules are neurotransmitters (not hormones)

Neuroendocrine signalling

Uses the nervous system working together with the endocrine system

Water soluble hormones

actively secreted from the cell, but then freely diffuses into blood.

• To enter target cell, it needs a receptor protein

Lipid soluble hormones

diffuses freely in and out of secretory and target

cell.

• To enter blood vessel, it needs a transport protein

Signal transduction for water-soluble hormones

When a hormone binds to a receptor protein at the membrane, it triggers a cellular response

• This could be:

  • enzyme activation

  • change in uptake of a specific molecule

  • rearrangement of the cytoskeleton

  • proteins moving into nucleus and altering gene transcription

Signal transduction for lipid-soluble hormones

When a hormone binds to a receptor protein in the cytoplasm, it triggers a cellular response.

• This is usually a change in gene expression

Epinephrine

• Increasing blood glucose → Energy for escape

• Increase blood flow to skeletal muscles → brings more oxygen to those muscles about to get moving

• Decrease blood flow to intestinal muscles walls → suspend digestion

Simple endocrine pathways

Cells respond directly to an internal (e.g., changing pH) or external (e.g., scary predator) stimulus by secreting a hormone

• Stimulus is received by a sensory neuron, which stimulates a neurosecretory cell.

• The neurosecretory cell then by secretes a hormone

• The hormone travels in the bloodstream to the target cell.

• Target cell brings a physiological response

hypothalamus

plays a central role in regulating the endocrine and nervous systems

• signals to the pituitary

pineal gland

helps regulate biorhythm

• produces the hormone melatonin.

Posterior pituitary

is an extension of the hypothalamus. The axons from the brain secrete neurohormones

• ADH – regulates kidney function

• Oxytocin – mammary glands (lactation, uterine contractions in childbirth,

  also brain function)

anterior pituitary

is a gland the synthesis and secretes hormones in response to signals from the hypothalamus.

tropic hormones

regulate other endocrine cells/glands

Hypothyroidism

too little thyroid hormone produced

Hyperthyroidism

too much thyroid hormone produced

Parathyroid hormones

• Regulate blood Calcium levels

• Ca2+ ions are essential for normal function of cells

• PTH raises blood Ca2+ directly and indirectly

Adrenal hormones

Like the pituitary; this is a fused endocrine and neuroendocrine gland. The cortex consists of true endocrine cells; the medulla derives from neural tissue