Endocrine system

• Endocrine system is a complex network of glands and organs. It uses hormones to control and coordinate your body's metabolism, energy level, reproduction, growth and development, and response to injury, stress, and mood.
• Hormones serve as chemical messenger in the body to produce biochemical changes, usually to increase the level of activity of a process or series of reactions
• These are the Chemical signals produced by specialized cells secreted into the blood stream and carried to a target tissue: Hormones
• hormones act at tissues sites different from where they are synthesized and released.
• Sometimes hormones are influenced by physiologic factors such as age as in the case of elderly who secrete less triiodothyronine, parathyroid hormone, aldosterone and cortisol.
• The majority of Endocrine functions are regulated through the pituitary gland, which in turn is controlled by secretions from the hypothalamus.
• Positive Feedback mechanism (PFM) is a system in which an increase in the product results to evaluation of the activity of the system and the production rate
• examples of positive feedback mechanisms: gonadal, thyroidal and adrenocortical hormones
• Negative Feedback mechanism (NFM-common feedback mechanisms is a system in which an increase in the product results in decreased activity of the system and the production rate.
• Long FM: Feedback from hormones produced in the pituitary target glands on the hypothalamus.
• Short FM: Feedback of Hormones at the level of the pituitary gland
• ultrashort FM: feedback mechanism between pituitary gland and hypothalamus.
• endocrine: Secreted in one location and released into blood circulation Binds to a specific receptor to elicit physiological response.
• Paracrine: Secreted in the endocrine cells and released into interstitial space. Binds to a specific receptor in adjacent cell and affects its function
• Autocrine: Secreted in endocrine cells and sometimes released into interstitial space. Binds to a specific receptor on cell of origin resulting to self - regulation of its function.
• juxtacrine: Secreted in the endocrine cells and remains in that same cellular space in relation to plasma membrane Acts Immediately adjacent cell by direct cell to cell contact.
• Intracrine: Secreted in endocrine cells and function inside the origin of synthesis.
• Exocrine: Secreted in endocrine cells and released into lumen of gut, and affects their functions.
• Neurocrine: Secreted in neurons and and released into extracellular space. Binds to a receptor in nearby cell and affects its function.
• Neuroendocrine: Secreted in neurons and released into extracellular space Binds with a receptor of cells at distant site.
• Circadian rhythms: biological rhythms (endogeneously generated) with period close to 24 hours.
• Diurnal rhythms: a circadian rhythm that is synchronized with the day and night cycle
• Ultradian rhythms: biological rhythms (ex. Feeding cycles) with much more shorter period (Ex. much higher frequency) compared to a circadian rhythm
• Infradian rhythm: biological rhythm with a cycle that last longer than 24 hours (ex. Human menstrual cycle)
• Hypothalamus hormones: Thyrotropin-releasing hormone , Corticotrophin-releasing hormone.
• anterior pituitary gland: Follicle- Stimulating Hormone (FSH), Lutenizing Hormone (LH), Growth Hormone, Prolactin
• Posterior pituitary: Vasopressin, Oxytocin
• Adrenal Medulla: Epinephrine, Norepinephrine
• Adrenal Cortex: Cortisol, I-deoxycortisol, aldosterone
• Thyroid gland: Triiodothyronine (T3), Thyroxine (T4), Calcitonin
• Parathyroid: Parathyroid hormone (PTH)
• Pancreas: Insulin, Glucagon
• ovaries: estrogen
• Testes: testosterone
• Classification of hormones by structure: Peptide Hormones, Steroid Hormones, Amino Acid Hormones, and Fatty acid Hormones.
• Peptide hormones are polymers of small numbers of amino acids (from fewer than ten to a few hundred); in other words, they are small proteins.
• Peptide hormones are water soluble and not bound to carrier protein.
• Steroid hormones are derived from cholesterol that act as chemical messengers in the body. Ex: Cortisol, Progesterone, Testosterone, Estrone, Estradiol and Aldosterone.
• The steroid hormones regulate many physiologic processes, including the development and function of the reproductive system.
• amino acid-derived hormones are relatively small molecules derived from the amino acids tyrosine and tryptophan. ex: epinephrine and norepinephrine, T3, T4 and melatonin