Hormone Secretion and Pituitary Gland PDF

Hormone secretion is [mainly controlled] by **negative feedback**. - Stimulus triggers production of hormone that reduces intensity of the stimulus. - May only involve one hormone. - Can be triggered by... - **[Humoral stimuli]** (change in extracellular fluid) - *...

Hormone secretion is [mainly controlled] by **negative feedback**. - Stimulus triggers production of hormone that reduces intensity of the stimulus. - May only involve one hormone. - Can be triggered by... - **[Humoral stimuli]** (change in extracellular fluid) - **[Hormonal stimuli]** (arrival or removal of hormone) - **[Neural stimuli]** (neurotransmitters) **[Humoral stimuli:]** control hormone secretion by heart, pancreas, parathyroid gland, and digestive tract. **[Hormonal stimuli:]** may involve one or more intermediary steps. - Two or more hormones involved. **[Neural stimuli:]** hypothalamus provides highest level of control. 18-3 The anterior lobe of the pituitary gland produces and releases hormones under hypothalamic control, while the posterior lobe releases hypothalamic hormones. **[PITUITARY GLAND (Hypophysis)]** - Lies within sella turcica. - Sellar diaphragm isolates pituitary gland from cranial cavity. - Hangs inferior to **[hypothalamus]**. - Connected by infundibulum. - Releases nine important peptide hormones. - Bind to extracellular receptors. - Use cAMP as second messenger. **[HYPOTHALAMUS]** - Regulates functions of the pituitary gland. - Synthesizes ADH and OXT and transports them to posterior pituitary gland for release. - Secretes **[regulatory hormones]** that control secretory activity of anterior pituitary gland. - Contains autonomic centers that exert direct control over adrenal medulla. The hypothalamus divides into two lobes: **[the anterior lobe (*adenohypophysis*)]** and the **[posterior lobe (*neurohypophysis*)]**. **The Anterior Lobe of the Pituitary Gland** - Also called **[adenohypophysis] because it is made from epithelial glandular tissue** - Hormones "turn on" endocrine glands or support functions of other organs. **Portal Vessels** - Blood vessels that link two capillary networks that are not primarily for delivery of oxygen and removing wastes. - Entire complex is called a portal system. **[Hypothalamic-Hypophyseal portal system:]** ensures that regulatory hormones from the hypothalamus reach cells in anterior pituitary before entering general circulation. **Hypothalamic Control of Anterior Lobe** Two classes of hypothalamic regulatory hormones: releasing hormones and inhibiting hormones. **[Releasing hormones (RH):]** stimulate synthesis and secretion of one or more hormones at anterior lobe. **[Inhibiting hormones (IH):]** prevent synthesis and secretion of hormones from anterior lobe. Rate of secretion is controlled by negative feedback. **Hormones of Anterior Pituitary Lobe** - **[Thyroid-stimulating hormone (TSH)]** - **[Adrenocorticotropic hormone (ACTH)]** - Released due to **[corticotropin-releasing hormone (CRH)]** - **[Prolactin (PRL)]** - Release inhibited by **[prolactin-inhibiting hormone (PIH)]** - Release stimulated by **[prolactin-releasing hormone (PRH)]** - **[Growth hormone (GH)]**, or somatotropin - Gonadotropins - **[Follicle-stimulating hormone (FSH)]** - **[Luteinizing hormone (LH)]** - In females, it induces ovulation and stimulates secretion of estrogens and progesterone. - In males, it stimulates production of androgens. - Production of FSH and LH is stimulated by **[gonadotropin-releasing hormone (GnRH)]** - **[Hypogonadism:]** caused by low production of gonadotropins. **[Growth hormone (GH)]** stimulates... - Liver cells to release **[somatomedins]** that stimulate tissue growth. - Somatomedins cause skeletal muscle fibers and other cells to increase uptake of amino acids. - Stem cells in epithelia and connective tissues to divide. - Breakdown of triglycerides in adipocytes, which leads to **[glucose-sparing effect]**. - Breakdown of glycogen by liver cells causing **[diabetogenic effect]**. Production of growth hormone is regulated by... - **[Growth hormone--releasing hormone (GH--RH)]** - **[Growth hormone--inhibiting hormone (GH--IH)]** **Pars Intermedia** - Secretes **[melanocyte-stimulating hormone (MSH)]** - Stimulates melanin production. Virtually nonfunctional in adults except in... - Pregnant women - Those with certain diseases **Posterior Lobe of the Pituitary Gland** - Also called **[neurohypophysis] because it is made of neural tissue** - Contains unmyelinated axons/terminals of hypothalamic neurons storing neurohormones in vesicles. - Hypothalamus manufactures two neurohormones: - **[Antidiuretic hormone (ADH)]** - **Helps regulate fluid balance by acting on the kidney and by initiating thirst** - **[Oxytocin (OXT)]** - Stimulates contraction of uterus during labor. - Promotes ejection of milk after delivery.