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 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