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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 classes1. 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 stimulated– 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 HormonesCell Hormone Function
Somatotropes Growth Hormone
Stimulates body growth; stimulates secretion of IGF-1; stimulates lipolysis; inhibits actions of insulin on carbohydrate and lipid metabolism
Corticotropes ACTH Stimulates production of glucocorticoids and androgens by the adrenal cortex; maintains size of zona fasciculata and zona reticularis of cortex
Thyrotropes Thyroid stimulating hormone
Stimulates production of thyroid hormones by thyroid follicular cells; maintains size of follicular cells
Gonadotropes FSH Stimulates development of ovarian follicles; regulates spermatogenesis in the testis
LH Causes ovulation and formation of the corpus luteum in the ovary; stimulates production of estrogen and progesterone
Lactotropes Prolactin Stimulates 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 PituitaryHormone Primary 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 glandHormone Functions
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