13.1 Hypothalamus and Pituitary Gland Chapter 13 Endocrine System 13.1 Hypothalamus and Pituitary Gland

Endocrine System Endocrine system releases hormones into the blood Blood delivers hormones throughout the body Endocrine system acts more slowly than the nervous system Endocrine system consists of the Endocrine glands Pituitary, thyroid, parathyroid, adrenal and pineal glands Also consist of other organs and tissues not specifically part of the Endocrine system Hypothalamus, pancreas, ovaries, testes, kidneys, liver

Hormone Functions Regulation of: Control growth and development Chemical composition and volume of interstitial fluid Metabolism and energy balance Contraction of smooth and cardiac muscle Gland secretions Control growth and development Regulate operation of reproductive system Help establish circadian rhythm

Hormone Actions Endocrine hormones are delivered throughout the body via the blood Hormones only affect specific target cells Hormones bind to specific receptors on the target cells Only target cells for a given hormone have receptors that bind and recognize that hormone Hormone secretion is controlled by signals from the nervous system, chemical changes in the blood, other hormones

Hypothalamus and Pituitary Gland Hypothalamus: small region in the brain Synthesizes 9 hormones Pituitary Gland: secretes hormones that control other Endocrine glands Composed of 2 lobes Anterior Pituitary Posterior Pituitary Pituitary hormones are controlled by inhibiting and releasing hormones produced by the hypothalamus

Hypothalamus and Pituitary Gland Anterior Pituitary Hormones Human Growth Hormone (hGH): most abundant anterior pituitary hormone Synthesizes and secretes insulin growth factors (IGF) Stimulate protein synthesis, help maintain muscle and bone mass, promote healing of injuries and tissue repair Control of hGH secretion: Growth hormone-releasing hormone (GHRH): promotes secretion of hGH Growth hormone-inhibiting hormone (GHIH): stops secretion of hGH

Hypothalamus and Pituitary Gland Anterior Pituitary Hormones Control of hGH secretion example: Low blood sugar levels (hypoglycemia) stimulates the hypothalamus to secrete GHRH (Growth hormone-releasing hormone) High blood sugar levels (hyperglycemia) inhibits the release of GHRH and stimulates the release of GHIH (Growth hormone-inhibiting hormone) Thyroid-Stimulating Hormone (TSH): stimulates synthesis and secretion of thyroid hormones Thyrotropin-releasing hormone (TRH) from the hypothalamus controls TSH secretion via negative feedback There is no Thyrotropin-inhibiting hormone

Hypothalamus and Pituitary Gland Anterior Pituitary Hormones Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) Females: FSH initiates development of ovarian follicles LH triggers ovulation Both FSH and LH stimulate follicular cells to secrete estrogen Males: FSH stimulates sperm production in the testes LH stimulates testes to secrete testosterone Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates release of FSH and LH Release of FSH, LH, GnRH is suppressed by estrogen in females and testosterone in males via negative feedback loops

Hypothalamus and Pituitary Gland Anterior Pituitary Hormones Prolactin (PRL) Helps stimulate milk production Prolactin-inhibiting hormone (PIH) suppresses release of prolactin Prolactin-releasing hormone (PRH) stimulates a rise in prolactin level during pregnancy Adrenocorticotropic Hormone (ACTH) Produces and secretes glucocorticoid hormone Corticotrophin-releasing hormone (CRH) from the hypothalamus stimulates secretion of ACTH Release is caused by low-blood glucose or physical trauma

Hypothalamus and Pituitary Gland Posterior Pituitary Hormones Doesn’t synthesize hormones but it stores and releases 2 hormones Oxytocin Stimulates contraction of the uterus and ejection of milk from the breast Secretion is stimulated by uterine stretching Function in males and in non-pregnant females is unknown Partly responsible for feelings of sexual pleasure during and after intercourse

Hypothalamus and Pituitary Gland Posterior Pituitary Hormones Antidiuretic Hormone (ADH) Acts to retain body water and increase blood pressure Causes the kidneys to retain more water = decreasing urine volume Without ADH urine output increase from 1-2 liters to 20 liters a day Amount of ADH secreted depends on blood osmotic pressure and blood volume As blood volume FALLS --> blood osmotic pressure RISES As blood volume RISES --> blood osmotic pressure FALLS

Hypothalamus and Pituitary Gland Posterior Pituitary Hormones Regulation of Secretion and actions of ADH High osmotic pressure (drop in blood volume) due to dehydration stimulates osmoreceptors Neurosecretory cells receive excitatory input from the osomoreceptors Generate nerve impulses that cause the release of ADH in the posterior pituitary

Hypothalamus and Pituitary Gland Posterior Pituitary Hormones Blood carries ADH to 3 target tissues: Kidneys: respond by retaining more water  decreasing urine output Sweat glands: lowers rate of water loss by perspiration from the skin Smooth muscle walls in the arteries: artery walls to constrict  increasing blood pressure Low blood osmotic pressure or highblood volume inhibits osmoreceptors Inhibition of osmoreceptors reduces or stops ADH secretion Causing the opposite effect on the target organs

Check for Understanding 1 4 functions of hormones Explain how target cells and receptors affect hormone actions Most abundant anterior pituitary hormone If your blood pressure drops what hormone is secreted in order to raise it again In order for our body to release hGH what must be released first Initiates follicle development in females and sperm production in males

Check for Understanding 1 Regulation, Control of growth and development, regulate reproductive system, establish circadian rhythm Endocrine glands secrete a hormone, that hormone will only be able to affect a target cell with a receptor for that hormone Human Growth Hormone (hGH) Antidiuretic Hormone (ADH) Human Growth Hormone releasing Hormone (GHRH) Follicle Stimulating Hormone (FSH)