Notes

[Endocrine and Neuroendocrine Physiology]

Endocrine/Neuroendorine system: slow, broadcasting system that use hormones (chemical agents) which are secreted into the bloodstream by secretory cells that may be organized into discrete endocrine glands.

Hormones --> bind to target cells --> which respond based on presence and concentration of receptor molecules for that hormone

Target cells --> modify their metabolism in response to binding the hormone && may release their own hormones.

Hormone concentrations in the blood:
1.) determine the degree of the effect
2.) are controlled by RATE of secretion and RATE of removal/degradation

Types of Signaling
- Neural Transmission: fast addressed signals (neuron to neuron)
- Endocrine Transmission: slow, broadcast signals (Nonneural endocrine cell to blood to other cells' receptor molecules)
- Neurosecretory Transmission: neurotransmitters broadcasted (neurosecretory cell to blood to other cells' receptor molecules)
- Paracrine Transmission: local diffusion (cell to cell)
- Autocrine Transmission: local diffusion (self-cell)

Control Signals over many Distances
Cytoplasmic contact (gap junctions )--> recognition molecules on adjacent cells (cell adhesion)--> local diffusion (neurotransmitters, paracrines/autocrines) --> transport in blood (hormones and neurohormones)--> outside environment (pheromones and kairomones)

Hormones: metabolically produced chemical that exerts regulatory influences on the functions of distant cells -- effective at very low concentrations -- secreted into the blood or extracellular fluid

Types of Hormones:
1.) Steroid hormones - made from cholesterol, lipid soluble
2.) Peptide and protein hormones - few to several hundred amino acids, water soluble
3.) Amine hormones - modified amino acids, water or lipid-soluble
*Hormones are transported bound to carrier proteins and are broadcasted to bind to receptors in target cells to execute specific actions.

1.) Steroid hormones (Ex. cholesterol to pregnenolone makes either A. aldosterone or cortisol or B. Testerone -->Estradiol)
- Carrier --> LDL and HDL
- Receptors --> intracellular
- Not stored
- Synthesized on demand
- Secreted by diffusion

2.) Peptide and protein hormones (Ex. Gonadotropin-releasing hormone (GnRH) and insulin)
- Carrier --> ?
- Receptors --> extracellular (typically GPCRs)
- Stored in vesicles
- Secreted on demand

3.) Amine hormones (Ex. Tyrosine to either A. catecholamines/extracellular<<dopamine, norepinephrine, epinephrine>> or B. Thyroid hormones/intracellular <<thyroxine, triiodothyronine>>; tryptophan --> melatonin)
- Carrier --> ?
- Receptors --> Both -- hydrophilic catecholamines use extracellular and lipophilic iodothyronines use intracellular
- Stored in vesicles
- Secreted on demand
Types of Amine Hormones:
A.) Catecholamines
- extracellular receptors
- water soluble
B.) Thyroid hormones
- intracellular receptors
- lipid soluble

Peptide hormones
- secreted from appendix K except adrenal cortex and medulla, thyroid and pineal glands, and skin VIA exocytosis
- c hains of amino acids
- water-soluble
- synthesized at rough ER; processed in Golgi; stored in vesicles

Steroid hormones
- secreted from adrenal cortex, gonads, skin, and placenta of pregnant mammals VIA simple diffusion through cell membrane
- derived from cholesterol - lipid-soluble
- synthesized on demand in intracellular compartments; not stored

Catecholamines
- secreted from adrenal medulla VIA exocytosis
- derived from tyrosine
- water-soluble
- synthesized in cytoplasm;stored in vesicles (chromaffin granules)

Thyroid hormones
- secreted from the thyroid gland VIA simple diffusion through cell menbrane
- derived from tyrosine and iodine
- lipid-soluble
- made prior to use; stored in a colloid island within the gland

Melatonin
- secreted from the pineal gland VIA exocytosis
- derived from the tryptophan
- water-soluble
- synthesized in the cytoplasm; stored in vesicles

Hormone Effects:
- all metabolic changes in target cells (upregulation and downregulation of enzymes and DNA transcription)
- may bind to G protein-coupled receptors, intracellular receptors, or enzyme-linked membrane receptors
- may activate second-messenger systems via G proteins
- many cells may have receptors which leads to whole-organism effects (ex. insulin)
- hormone tropins influence endocrine gland activity

How and where are hormones made?
- synthesized, stored, and released by endocrine glands which are made up of secretory cells in exocrine or endocrine glands
- discrete glands (testes/pituitary)
- diffuse glands (adrenal glands of amphi./gastrin secreting G cells of stomach lining)

Glands Types:
1.) Exocrine - secretion into ducts
2.) Endocrine - ductless glands - directly into bloodstream

Secretory Cell Types:
1.) Epithelial (nonneural) cells secrete hormones in response to other hormones, but can also respond to neural input [adrenal cortex]
2.) Neurosecretory (neural)- neurosecretory cells secrete neurohormones by synaptic input from neurons/neural input [adrenal medulla]