- Major communication systems in the body

- Integrate stimuli and responses to chanes in external and internal envionrment

- Both are crucial to coordinatead functions of highly differentiated cells, tissues, and organs

- Unlike the nervous system, the endocrine system is anatomically discontinuous. 

- Broacasts its hormonal messages to essentially all cells by secretion into blood and extracellular fluid.

It requires receptors to recieve teh message

- In other words, a cell must bear the receptor for hte hormone being broadcast in order to respond. 

- Most hormones come into contact with nearly every cell.  Howeer, each hormone usually affects only a limited number of cells, called target cells. 

- A target cell responds to a hormone because it bears the receptors for hte hormone 

- Maintenance of the internal environment in the body

- Integration and regulation of growth and development.

- Control, maintenance and instigation of sexual reproduction, including....
    - Gametogenesis
    - Coitus
    - Fertilization
    - Fetal Growth
    - Development
    - Nourishment of the newborn

- In the neuronal cell bodies in the hypothalamus

- These are released via synapses in posterior pituitary

- Examples of these kinds of hormones include Oxytocin and Antidiuretic hormone (ADH) 

- Range from 3 amino acids to hundreds of amino acids in size

- Often produced as larger molecular weight precursors that are proteolytically cleaved to the active form of the hormone

-Water soluble

- Comprise the largest number of hormones - perhaps in thousands 

- Encoded by specific gene, which is translated into mRNA, then translated into a protein precursor called a prehormone.

- Prehormones are post-translationally modified in ER to contained carbohydrates (glycosylation).

- Prehormones contain signal peptides (hydrophobic amino acids) which targets them to the golgi, where the signal sequence si removed to form prohormone.  

- Prohormone is processed into active hormone and packaged into secretory vessicles.  

- Secretory vessicles move into plasma membrane where they await a signal, then they are secreted.

- In some cases the hormone is converted into the active hormone while in the E.F 

- There are two groups of hormones derived from the amino acid tyrosine.

- These are Thyroid hormones and Catecholamines 

- Basically a "double" tyrosine with a critical incorporation of 3 or 4 iodine atoms.

- Thyroid hormone is produced by the thyroid gland and is lipid soluble

- Thyroid hormones are produced by modification of a tyrosine residue contained in thyroglobulin, post-translationally modified to bind iodine, then proteolytically claved and released as T4 and T3.  T3 and T4 then bind to thyroxin binding globulin for transport in the blood.   

- They are both neurohormones and neurotransmitters.

- These include epinephrine, and norepinephrine

- Epinephrine and norepinephrine are produced by the adrenal medulla both are water soluble.  

- Secreted like peptide hormones 

- All are derived from Cholesterol

- All steroids are lipid soluble (Not stored in cells)

- Not packaged, but synthesized and immediately released

-  Enzymes which produce steroids from Cholesterol are located in ER and Mito

- Not water soluble, so have to be carried in blood

- Corticosteroid binding globulin carries cortisol

- Sex steroid globulin carries testosterone and estradiol.

- Steroid sec. by one cell can be activated by target cell (androgen --> estrogen)

- Rate limiting step is free cholesterol from cyto into Mito

- Cholesterol comes from acetate and/or stores in intracellular lipid 

- Derived from cholestrol, like a steroid, and is lipid soluble

- Not really a "Vitamin" as it can be synthesized de novo (over again, anew, fresh)

- Acts as a true hormone 

- Arachadonic acid is the most abundant precursor for these hormones.

- Lipases release the stores of arachadonic acid in the membrane lipds

- Specific Eicosanoids synthesized are dictated by the battery of processing enzymes in that cell

- These hormones are rapidly inactivated by being metabolized, and are typically active for only a few seconds.   

- Large group of molecules derived from polyunsaturated fatty acids

- Principal groups of hormones of this class are prostaglandins, prostacyclins, leukotrines, and thromboxanes 

- Receipt of stimulus

- Synthesis and secretion of hormone

- Dlivery of hormone to target cell

- Evoking target cell response

- Degradation of hormone 

- The physiologic effects of hormones depend largely on their concentration in blood and extracellular fluid.

- Almost inevitably, disease results when hormone concentrations are either too high or too low, and precise control over circulating concentrations of hormones is therefore crucial

- Rate of production

- Rate of delivery

- Rate of degradation and elimination 

- Hormones, like all biomolecules, have characteristic rates of decay, and are metabolized and excreted from the body through several routes. 

- Shutting off secretion of a hormone that has a very short half-life causes circulating hormone concentration to plummet, but if a hormone's biological half-life is long, effective concentrations persist for some time after secretion ceases.   

- Response-stimulus coupling enables the endocrine system to remain responsive to physiological demands

- Secretory episodes occur with diferent periodicity

- Pulses can be as frequent as every 5-10 minutes 

- Demonstrated by GnRH infusion

- If given once hourly, gonadotropin secretion and gonadal function are maintained normally

- A slower frequency won't maintain gonad function

- Faster, or continuous infusion inhibits gonadotropin secretion and blocks gonadal steroid production 

- Negative feedback is most common: for example, LH from pituitary stimulates the testis to produce testosterone which in turn feeds back and inhibits LH secretion.

- Postiive feedback is less common: examples include LH stimulation of sestrogen which stimulates LH surge at ovulation