Endocrine system uses Hormones communicate.

Glands can be classified as :

Endocrine
Paracrine
Autocrine
Neuroendocrine( dopamine,Epinephren,norepi.)

Hormones are made from:

Peptides/Proteins
Amines(T3,T4,Norepi.,Epi)
Steriod
Glycoproteins

Hormones are classified to 2 Types depending on their Lipid solubility:

Lipid soluble(Lipophillic)---> (Dissolve through the plasma membrane and bind to the receptor inside the cell or bind to the nucleus for DNA transcription for protein synthesis
Lipid insoluble(Lipophobic)---> Bind to receptors at the cell membrane Cause they cant dissolve through the Plasma membrane. It mostly works through second messengers

Hormonal release Is controlled by Negative feedback mostly (sometimes through positive feedback )

Hormones are released due to 3 different types of stimuli which are :

Humoral Stimuli (Humoral=Body fluids) ---> change in ECF cause secretion of some hormones or levels of electrolyte in blood can be a stimuli (like Calcium (Calcitonin or PTH), Glucose (Glucagon or Insulin)
Neural Stimuli --->(Nerve Fibers stimulating Hormonal release,Like the Preganglionic Fibers stimulate Adrenal medulla to secrete Epi,norep.)
Hormonal stimuli ---> (one hormone stimulates the release of another hormone) like how hypothalamus secretes hormones that stimulate the pituitary gland to secrete other hormones that effect different glands in our body )

Hyposecretion can be caused by Heredity ,Dietary Deficiency,immunological factors, disease processes

It can be primary or secondary (by primary being for example Adrenal gland and secondary being Anterior Pituitary ,Somtimes we have tertiary which is in this example its The hypothalamus) ,get it,.

Hypersecretion can be caused by a Tumor(Adenohypophysis;Adenoma) Or Immunological factors(it could be a stimulation of an antibody).

Endocrine Dysfunction can be caused by unresponsiveness of target cells Receptors.

Physiology of systems