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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 reg
ulated
Chemical classification of hormones: Amine hormones:derivatives of tyrosine; e
pinephrine, 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 (17-estradiol): cholecalciferol (1, 25-dihydroxyvita
min D3).
Adrenal Cortex
1. Five hormones are secreted by adrenal gland: Aldosterone, cortisol, corticosterone, dehydroepiandrosterone (DHEA), and androstenedione
2. 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 effectA 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 mi
neral ions or organic ions Neurotransmitters released from neuron Another hormone or neurohormone
Control by plasma mineral ions or organic nutrients
Examples:1. Insulin: controlled by
plasma glucose concentration
2. 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