Section 2, Chapter 13
Pituitary Gland (Hypophysis) Location: Lies at the base of the brain in the sella turcica, connected to hypothalamus by a pituitary stalk (infundibulum)
2 Lobes: Anterior pituitary (adenohypophysis)
Posterior pituitary(neurohypophysis)
Control of Pituitary Gland Anterior Pituitary Gland Releasing hormones secreted from hypothalamus regulates the anterior lobe.
Posterior Pituitary Gland Nerve impulses from hypothalamus regulate the posterior lobe.
Anterior Pituitary Gland Hypophyseal Portal System – • Releasing hormones secreted by the hypothalamus are conveyed to the anterior gland through Hypophyseal portal veins. • Releasing hormones act on specific target cells within the anterior pituitary gland • In response, the pituitary gland secretes tropic hormones that travel throughout the body acting on distant target cells. Tropic hormone = hormones that have other endocrine glands as their target
Example of hypophyseal pathway Releasing Hormone: Thyroid releasing Hormone (TRH) secreted from hypothalamus
Tropic Hormone: Thyroid Stimulating Hormone (TSH) is secreted from the anterior pituitary
Target Cells: Thyroid Hormone (Thyroxine) is secreted from thyroid glands
Anterior Pituitary Hormones 1. Growth Hormone (somatotropin) Hypothalamic Control of GH: • Growth Hormone Releasing Hormone (GHRH): promotes GH secretions • Somatostatin: inhibits GH secretion Target Cells: • Epithelial and Connective Tissue • Adipose Tissue • Liver Actions of GH: • Promotes cell growth and division, especially in skeletal muscles and chondrocytes • Promotes breakdown and use of fat for energy • Liver: promotes breakdown of glycogen for energy
Growth Hormone Disorders Gigantism • Results from oversecretion of GH in childhood • Usually caused by a tumor of the pituitary gland
Hypopituitary Dwarfism • Insufficient GH during development • GH therapy may treat condition if administered before the epiphyseal plates ossify
Anterior Pituitary Hormones 2. Thyroid Stimulating Hormone (thyrotropin)
Hypothalamic Control of TSH: Thyroid Releasing Hormone Target Cells: Thyroid Gland Actions: TSH promotes secretions of thyroid hormones (T3 & T4)
Thyroid Hormones and Negative Feedback Under normal conditions, T3 and T4 inhibit further secretions of TRH and TSH
Iodine obtained from the diet is essential for thyroid hormone (T3 & T4) synthesis
An Iodine deficiency prevents the formation of Thyroid Hormones. TRH & TSH continually stimulate the thyroid gland without inhibition.
Goiter = enlarged thyroid gland
Anterior Pituitary Hormones 3. Prolactin (mammotropin) Hypothalamic Control of PRL: • Prolactin Releasing Factor: promotes secretion of prolactin • Prolacting Release Inhibiting Hormone: inhibits PRL secretion
Target Cells: Mammary Glands
Actions: Prolactin promotes milk production
Anterior Pituitary Hormones 3. Adrenocorticotropic Hormone (ACTH) Hypothalamic Control of ACTH: Corticotropin Releasing Hormone
Target Cells: Adrenal Cortex
Actions: ACTH promotes secretions of hormones from the adrenal cortex (e.g. cortisol)
Anterior Pituitary Hormones 4. Follicle Stimulating Hormone (FSH) 4 & 5 = gonadotropes
5. Luteinizing Hormone (LH)
Hypothalamic Control: Gonadotropin Releasing Hormone (GRH) Target Cells: Gonads Male: testes Female: Ovaries Actions of gonadotropes: Follicle Stimulating Hormone: Female = promotes development of ovarian follicles Male = promotes development of sperm Luteinizing Hormone: Female = promotes the secretion of estrogens and progesterone Male = promotes the production of testosterone
Figure 13.15 Hormones released from the hypothalamus, the corresponding hormones released from the anterior lobe of the pituitary gland, and their target organs.
Posterior Pituitary Gland Structurally consists of neurosecretory cells
Hormones are produced by the hypothalamus, then released from the posterior pituitary gland.
Posterior Pituitary Hormones 1. Antidiuretic Hormone (ADH) (also called vasopressin) Target Cells: Kidneys & Blood Vessels Actions of ADH depend the receptors to which it binds V1 receptors • Located within blood vessels • ADH, in high concentrations promotes vasoconstriction • May prevent a drop in blood pressure with profuse bleeding
V2 receptors • Located within tubules of kidneys • ADH promotes water reabsorption at the kidneys, and thus decreases water loss. • Alcohol inhibits ADH secretion, which explains its role as a diuretic.
Posterior Pituitary Hormones 2. Oxytocin Actions of Oxytocin Females: • stimulates smooth muscle contractions in the uterus during delivery • Promotes ejection of milk from mammary glands Males: Function is unknown
End of Section 2, Chapter 13.