Endocrine Physiology Part 1 of 4 Dr. Meg-angela Christi M. Amores

Coordination of body functions Chemical messenger systems: – Neurotransmitters released by axon terminals of neurons into the synaptic junctions; act locally to control nerve cell functions – Endocrine hormones released by glands or specialized cells into the circulating blood ; influence the function of cells at another location in the body – Neuroendoctrine hormones secreted by neurons into the circulating blood influence the function of cells at another location

Coordination of body functions Chemical messenger systems – Paracrines secreted by cells into the extracellular fluid ; affect neighboring cells of a different type – Autocrines secreted by cells into the extracellular fluid ; affect the function of the same cells that produced them – Cytokines peptides secreted by cells into the extracellular fluid can function as autocrines, paracrines, or endocrine hormones

Endocrine hormones carried by the circulatory system to cells throughout the body they bind with receptors and initiate many reactions Some affect many different cell types Others affect a specific target tissue multiple hormone systems play a key role in regulating almost all body functions

Hormones 3 general classes 1.Proteins and polypeptides Are Stored in Secretory Vesicles Until Needed 2.Steroids Usually Synthesized from Cholesterol and Are Not Stored 3.Derivatives of AA Tyrosine Thyroid hormones Adrenal medullary hormones: epinephrine, norE

Hormone Secretion, Transport, Clearance from body each of the different hormones has its own characteristic onset and duration of action – norepinephrine and epinephrine, are secreted within seconds after the gland is stimulatedepinephrine – thyroxine or growth hormone, may require months for full effect

Control Negative Feedback Prevents Overactivity of Hormone Systems ensure a proper level of hormone activity at the target tissue to prevent oversecretion of the hormone or overactivity at the target tissue Positive Feedback occurs when the biological action of the hormone causes additional secretion of the hormone surge of luteinizing hormone (LH) that occurs as a result of the stimulatory effect of estrogen on the anterior pituitary before ovulation

Cyclical Variations Occur in Hormone Release periodic variations in hormone release that are influenced by seasonal changes, various stages of development and aging, the diurnal (daily) cycle, and sleep – Example: secretion of growth hormone is markedly increased during the early period of sleep due to changes in activity of neural pathways involved in controlling hormone release

Pituitary Hormones Pituitary Gland – Anterior Lobe (adenohypophysis) Growth hormone Adrenocorticotropin Thyroid-stimulating hormone Prolactin FSH and LH – Posterior Lobe (neurohypophysis) Antidiuretic hormone Oxytocin

Anterior Pituitary Hormones CellHormoneFunction SomatotropesGrowth Hormone Stimulates body growth; stimulates secretion of IGF-1; stimulates lipolysis; inhibits actions of insulin on carbohydrate and lipid metabolism CorticotropesACTHStimulates production of glucocorticoids and androgens by the adrenal cortex; maintains size of zona fasciculata and zona reticularis of cortex ThyrotropesThyroid stimulatin g hormone Stimulates production of thyroid hormones by thyroid follicular cells; maintains size of follicular cells GonadotropesFSHStimulates development of ovarian follicles; regulates spermatogenesis in the testis LHCauses ovulation and formation of the corpus luteum in the ovary; stimulates production of estrogen and progesterone progesterone LactotropesProlactinStimulates milk secretion and production

Hypothalamus and Pituitary Almost all secretion by the pituitary is controlled by either hormonal or nervous signals from the hypothalamus hypothalamic releasing and hypothalamic inhibitory hormones Regulates secretion from anterior pituitary

Hypothalamus and Pituitary HormonePrimary action on the Pituitary Thyrotropin-releasing hormone (TRH) Stimulates secretion of TSH by thyrotropes Gonadotropin-releasing hormone (GnRH) Stimulates secretion of FSH and LH by gonadotropes Corticotropin-releasing hormone (CRH) Stimulates secretion of ACTH by corticotropes Growth hormone- releasing hormone (GHRH) Stimulates secretion of growth hormone by somatotropes Growth hormone inhibitory hormone (somatostatin) Inhibits secretion of growth hormone by somatotropes Prolactin-inhibiting hormone (PIH) Inhibits secretion of prolactin by lactotropes

Abnormalities in Growth Hormone Secretion Panhypopituitarism – decreased secretion of all the anterior pituitary hormones Dwarfism – generalized deficiency of anterior pituitary secretion – all the physical parts of the body develop in appropriate proportion to one another – Age 10 years – looks like 4-5 years

Abnormalities in Growth Hormone Secretion Gigantism growth hormone-producing cells of the anterior pituitary gland become excessively active All body tissues grow rapidly, including the bones person becomes a giant-up to 8 feet tall Acromegaly after the epiphyses of the long bones have fused bones can become thicker and the soft tissues can continue to grow bones of the hands and feet and in the membranous bones, including the cranium, nose, bosses on the forehead, supraorbital ridges, lower jawbone, and portions of the vertebrae

Posterior Pituitary do not secrete hormones a supporting structure for large numbers of terminal nerve fibers and terminal nerve endings nerve endings are bulbous knobs that contain many secretory granules Granules secrete the hormones

Posterior pituitary gland HormoneFunctions Antidiuretic hormone (ADH) permeability of the collecting ducts and tubules to water increases greatly and allows most of the water to be reabsorbed -increased water conservation by the kidneys -potent effect of constricting the arterioles throughout the body and therefore increasing the arterial pressure Oxytocin-Causes Contraction of the Pregnant Uterus -Aids in Milk Ejection by the Breasts