Endocrine System

• The other regulating system of the body is the Endocrine System, which consists of Endocrine glands that secrete chemicals called hormones.
• Endocrine glands are ductless; that is, they do not have ducts to take their secretions to specific sites.
• Hypothalamus releases hormones to stimulate pituitary gland to release hormones.
• Hypothalamus is the master regulator or the control center of the endocrine system because it secretes hormones that stimulate or suppress the release of hormones in the pituitary gland
• Anterior : GH, TSH, ACTH, FSH, LH, Prolactin
• Posterior : ADH, Oxytocin
• Pineal gland - Melatonin
• Thyroid gland - Thyroxine and T3 Calcitonin
• Parathyroid gland - PTH
• Thymus gland - Immune hormones
• Adrenal glands(Cortex) : Aldosterone , Cortisol, Sex hormones
• Adrenal glands(Medulla) : Epinephrine, Norepinephrine
• Pancreas - Insulin, Glucagon
• Ovaries - Estrogen, Progesterone, Inhibin
• Testes - Testosterone, Inhibin
• Hormones may be classified into three groups: Amines, Proteins, and Steroids.
• The Pituitary gland (or hypophysis) hangs by a short stalk (infundibulum) from the hypothalamus and is enclosed by the sella turcica of the sphenoid bone.
• what are the two major portions of the pituitary gland: posterior pituitary gland (neurohypophysis), and the anterior pituitary gland (adenohypophysis).
• Oxytocin stimulates contraction of the uterus at the end of pregnancy and stimulates release of milk from the mammary glands.
• The release of posterior pituitary gland hormones are stimulated by nerve impulses from the hypothalamus
• Antidiuretic hormone (also called vasopressin) increases the reabsorption of water by kidney tubules, which decreases the amount of urine formed.
• Growth hormone (GH) is also called somatotropin, and it does indeed promote growth.
• Prolactin, as its name suggests, is responsible for lactation. More precisely, prolactin initiates and maintains milk production by the mammary glands
• Adrenocorticotropic hormone (ACTH) stimulates the secretion of cortisol and other hormones by the adrenal cortex.
• Calcitonin decreases the reabsorption of calcium and phosphate from the bones to the blood, thereby lowering blood levels of these minerals.
• Insulin increases the transport of glucose from the blood into cells by increasing the permeability of cell membranes to glucose
• Estrogen is secreted by the follicle cells of the ovary
• Testosterone is a steroid hormone secreted by the interstitial cells of the testes
• Melatonin is a hormone produced by the pineal gland
• Hormones are secreted when there is a need for their effects. Each hormone has a specific stimulus for secretion.
• The secretion of most hormones is regulated by negative feedback mechanisms: As the hormone exerts its effects, the stimulus for secretion is reversed, and secretion of the hormone decreases.
• Posterior Pituitary — stores hormones produced by the hypothalamus
• Oxytocin — stimulates contraction of myometrium of uterus during labor and release of milk from mammary glands.
• Amines — structural variations of the amino acid tyrosine; thyroxine, epinephrine.
• Proteins — chains of amino acids; peptides are short chains. Insulin, GH, glucagon are proteins; ADH and oxytocin are peptides.
• Steroids — made from cholesterol; cortisol, aldosterone, estrogen, testosterone.
• ADH — increases water reabsorption by the kidneys, decreases sweating, in large amounts causes vasoconstriction.
• Oxytocin — stimulates contraction of myometrium of uterus during labor and release of milk from mammary glands.
• Anterior Pituitary — secretions are regulated by releasing hormones from the hypothalamus
• TSH — increases secretion of thyroxine and T3 by the thyroid. Stimulus: TRH from the hypothalamus.