Endocrine system consists of endocrine glands, that secret chemical substance (hormone) regulating physiological responses. The endocrine system and nervous system are two major communication systems that control homeostasis of the body.

Hormone derived from Greek hormaein meaning "to excite" and was coined by Bayliss and Starling to denote the concept of a diffusible physiological regulator. They discovered secretin, a 29 amino acid peptide, which is released by secretory S cells of the duodenum of the gastrointestinal system in response to H+.

Properties of hormones secreted by specialised glands carried by blood stream (ductless) acting in remote target trace amount causes tremendous effects binding to specific receptors usually has short half life and tightly regulated

Chemical classification of hormones: Amine hormones:derivatives of tyrosine; epinephrine, norepinepherine, thyroid hormone, dopamine Polypeptides and glycoproteins: transcribed from truncated genes; GnRH, GH, insulin, etc..(the largest group)

Steroids metabolites of cholesterol  glucocorticoid (cortisol): mineralcorticoid (aldosterone):  progestin (progestone):  androgens (testosterone):  estrogens (17b-estradiol):  cholecalciferol (1, 25-dihydroxyvitamin D3).

Adrenal Cortex Five hormones are secreted by adrenal gland: Aldosterone, cortisol, corticosterone, dehydroepiandrosterone (DHEA), and androstenedione DHEA and androstenedione are known as androgens, action similar to male hormone, testosterone, but weaker

Gonadal hormones

Fatty acid derivatives Prostaglandins, leukotrienes, hydroxyeicosatetranenoic acid (HETE). Known in 1930s, Euler and Goldblatt identified substance that causes blood vessel and smooth muscle contraction from semen. (prostaglandin)

Physiological effects of prostaglandins: inflammation: Reproduction: Respiration: renal function: blood vessel: gastrointestine

Mode of hormone secretion Hormone release into the blood is infrequently monotone but rather is a complex phenomenon as reflected in rapid changes of plasma concentration at more or less regular intervals named pulsatile release Pulse: Frequency: Amplitude

Hormone transport and metabolism steroid and thyroid hormones Binding to specific proteins Nuclear or cytosolic receptor Slow (hours to days) metabolism Other hormones Free in blood stream Membrane receptor Fast (minutes to hour) metabolism

Fate and actions of a hormone

Mechanisms of hormone action Receptor concept: Only cells express specific “receptor” can response to a particular hormone Nuclear receptor: steroid and thyroid hormones Plasma membrane receptor: other hormones Effect of hormone-receptor binding (Table 11-2)

Actions of hormones with membrane receptor Hormonal signal transduction pathways: cAMP/PKA Phospholipase C (PLC) Receptor tyrosine kinase JAK-STAT: Ion channel

Permissive effect A hormone increases another hormone’s effectiveness: mainly by upregulating the receptor of the second hormone

Inputs that control hormone secretion Can be regulated by more than one input. Change in the plasma concentrations of mineral ions or organic ions Neurotransmitters released from neuron Another hormone or neurohormone

Control by plasma mineral ions or organic nutrients Examples: Insulin: controlled by plasma glucose concentration Parathyroid hormone (PTH): controlled by plasma [Ca+2]

Control by Neurons Adrenal medulla: by autonomic nervous system Hypothalamus: by other neurons

Types of Endocrine Disorders Hyposecretion: too little hormone Primary hyposecretion: adrenalectomy; Lack of dietary iodine leading to low thyroid hormone Secondary hyposecretion: lack of tropic hormone Hypersecretion: too much hormone Primary Secondary Hypo- and Hyper responsiveness: abnormal of receptors, abnormal of signal transduction pathway, abnormal in metabolic activation

Synthesis of Peptide Hormones

Steroids

Synthesis of Steroid Hormones

Typical profile of hormones