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1 DR. JITENDRA PATEL (MBBS, MD) Medical Educator & Researcher Assistant Professor, Department of Physiology Email: [email protected] Web: www.esphys.weebly.com 2 OUTLINE A Role of hypothalamus Post. Pituitary Hormones Physiological Action Regulation of main Hormones Applied Aspect 3 4 5 6 7 8 9 Posterior Pituitary Hormones Antidiuretic hormone (ADH) / Vasopressin Oxytocin (OTC) 11 The ADH Antidiuretic hormone, as the name indicates, prevents diuresis and is chiefly concerned with the conservation of body water. Since it also causes vasoconstriction, it is also called vasopressin or more precisely arginine vasopressin. Synthesis ADH as well as OTC are synthesized in the cell bodies of magnocellular neurons of both paraventricular and supraoptic nuclei of the hypothalamus. However, contains supraoptic ADH nucleus forming predominately neurons while paraventricular nucleus contains mainly the OTC synthesizing neurons. Storage The axons of ADH and OTC synthesizing neurons end in the posterior pituitary gland as terminal swelling. The secretory granules containing hormone precursors, known as Herring bodies, are transported down the axons by axoplasmic flow to the nerve endings in the posterior pituitary. Receptors V1–A receptors: These are involved in the vasoconstrictor effect of ADH. V1–B receptors: These are involved in the action of ADH on the anterior pituitary. V2 receptors: These are involved in the action of ADH on kidney. Actions of ADH Action on kidney: The main role of ADH is regulation of water balance in the body by acting on the kidney (DCT, CD), where it decreases the excretion of free water i.e. antidiuretic and concentrating effect on kidney (Through Aquaporins channel). Actions of ADH… Vasoconstrictor effect: Antidiuretic hormone in large doses cause vasoconstriction and leads to rise in blood pressure. Haemorrhage is a potent stimulus to ADH secretion. Actions of ADH… Action on anterior pituitary: Antidiuretic hormone travels to the anterior pituitary via the portal veins and combines with the V1–B receptors (also called V3 receptors) and causes increased ACTH secretion from the corticotrophs. Actions of ADH… Action on the liver: ADH causes glycogenolysis by combining with the V1–A receptor. Action on the brain: V1–A receptors are also found in brain, where ADH acts as a neurotransmitter and is involved in memory, regulation of temperature, regulation of blood pressure, circadian rhythms and brain development. Regulation of Secretion A. Effective osmotic pressure of plasma or plasma osmolality B. Changes in blood volume 21 22 Regulation of Secretion… Other factors affecting ADH secretion: Stress of pain, chronic emotional stress and surgical procedures cause increase in ADH secretion, Cortisol and thyroid hormones release ADH. Some other factors that increase ADH secretion include nausea, vomiting, standing posture and cytokines. Elderly individuals secrete more ADH than do younger individuals. Adrenaline decreases the ADH, Alcohol reduces ADH secretion. 24 25 Synthesis ADH as well as OTC are synthesized in the cell bodies of magnocellular neurons of both paraventricular and supraoptic nuclei of the hypothalamus. However, contains supraoptic ADH nucleus forming predominately neurons while paraventricular nucleus contains mainly the OTC synthesizing neurons. Storage The axons of ADH and OTC synthesizing neurons end in the posterior pituitary gland as terminal swelling. The secretory granules containing hormone precursors, known as Herring bodies, are transported down the axons by axoplasmic flow to the nerve endings in the posterior pituitary. Actions of Oxytocin Action on breast: Oxytocin causes contraction of myoepithelial cells, thus plays an important role in milk ejection. 29 Actions of Oxytocin… Action on uterus: Oxytocin causes contraction of uterine smooth muscles, thus plays an important role during parturition (labour). Oxytocin also acts on non-pregnant uterus and facilitates the transport of sperm in the female genital tract. 31 Actions of Oxytocin… In males: The circulating levels of oxytocin increases during ejaculation, which causes increased contraction of smooth muscles of vas deferens and helps in propelling the sperms towards urethra. Regulation of Secretion Stimuli which increase oxytocin release are: Oxytocin secretion increases on cholinergic stimulation Suckling stimulates oxytocin release (suckling reflex). Genital tract simulation during coitus and labour increases oxytocin release. Regulation of Secretion… Factors which decrease oxytocin release are: Emotional stress, Sympathetic stimulation, and Drugs such as ethanol and enkephaline 35 “Either be selected or be elected” 36