hypothalamus and pituitary glands

hypothalamus

provides highest level of endocrine function by integrating nervous and endocrine systems

hypothalamic neurons synthesize two hormones

ADH and OXT, transports them along axons w/i infundibulum to the posterior lobe of pituitary gland

hypothalamus secretes regulatory hormones

control secretory activities of endocrine cells in anterior lobe of pituitary gland

hypothalamus contains autonomic centers

exert direct neural control over endocrine cells of adrenal medulla

hypophyseal portal system is made of

capillary networks and interconnecting vessels between hypothalamus and pituitary gland

regulatory hormones released into hypophyseal portal system

from hypothalamus at median eminence of infundibulum

once inside hypophyseal portal system, regulatory hormones

move from interstitial fluid into fenestrated capillaries, carried to anterior pituitary in portal vessels. form second capillary network w/i anterior pituitary

fenestrated capillaries

vessels that allow relatively large molecules to enter or leave bloodstream

portal vessels

blood vessels that link two capillary networks

hypophyseal portal system allows

hypothalamic hormones to reach target cells in anterior pituitary

hypothalamic hormones

regulate release of hormones from pituitary gland

releasing hormones

stimulate synthesis and secretion of one or more hormones at anterior lobe

inhibiting hormones

prevent synthesis and secretion of one or more hormones at anterior lobe

pituitary gland

small, oval gland nestled w/i sella turcica of sphenoid bone. releases nine peptide hormones

seven hormones from pituitary gland

from anterior lobe, called tropic hormones

tropic hormones

they “turn on” other endocrine glands

two hormones from pituitary gland

from posterior pituitary

all pituitary hormones

bind to membrane receptors and use cAMP as a second messenger

thyroid stimulating hormone

targets thyroid gland, stimulates release of thyroid hormones. released in response to TRH from hypothalamus. release is decreased when thyroid hormone levels rise

adrenocorticotropic (ACTH)

stimulates release of steroid hormones from adrenal cortex (affects glucose metabolism). released in response to CRH from hypothalamus

gonadotropins

regulate activities of gonads. released in response to GnRH from hypothalamus

follicle stimulating hormone (FSH) in females

promotes ovarian follicle development (in combo w/ LH) stimulates secretion of estrogens

follicle stimulating hormone (FSH) in males

promotes maturation of developing sperm

follicle stimulating hormone (FSH)

inhibited by inhibin

luteinizing hormone (LH) in females

induces ovulation, promotes secretion of estrogen and progesterone (prepares body for pregnancy)

luteinizing hormone (LH) in males

stimulates interstitial cells of testes produce sperm hormones (androgens), primarily testerone

growth hormone (GH)

stimulates cell growth and reproduction by accelerating rate of protein synthesis. skeletal muscle and chondrocytes particularly expensive. actions of growth hormone can be direct and indirect

growth hormone regulated by

growth hormone releasing hormone (GH-RH) and growth hormone inhibiting hormone (GH-IH)

indirect action of growth hormone

liver cells synthesize/release somatomedins (stimulate tissue growth) or insulin like growth factors (IGFs). receptors on cells in skeletal muscle/cartilage. results in uptake of amino acids and incorporation into new proteins

direct actions of growth hormones in epithelial and connective tissue

stimulates stem cell division and differentiation

direct actions of growth hormones in adipose tissue

stimulates breakdown of stored triglycerides, releasing fatty acids into blood. tissues use fatty acids instead of glucose to generate ATP

direct actions of growth hormones in liver

stimulates breakdown of glycogen reserves, release glucose into bloodstream

prolactin

works w/ other hormones to stimulate mammary gland development. stimulates milk production. inhibited by PIH stimulated by PRH

melanocyte stimulating hormone (MSH)

released from pars intermedia of anterior lobe. stimulates melanocytes of skin to increase melanin production. (nonfunctional in adults)

antidiuretic hormone (ADH) stimulus

an increase in solute concentration of blood or a decrease in blood pressure or volume.

primary function of ADH

act on kidneys to retain water and decrease urination (vasoconstriction), increase blood pressure

oxytocin

released in response to sensory input. stimulates smooth muscle contraction in uterus and contraction of myoepithelial cells to eject milk