Hypothalamic and Pituitary hormones Dr. Howaida Nounou 1
Functional Types of Hormones Trophic(tropic) Originate from anterior pituitary gland Specific for another endocrine gland.( regulate growth and function of other endocrine glands) Direct effector Secreted by non-pituitary endocrine glands Act directly on peripheral tissue Exert a feedback effect on the hypothalamus or anterior pituitary gland Negative feedback-an increase in the product causes a decreased in the system Positive feedback-an increase in the product causes an increase in the activity of the system 2
Regulation of Hormones Occurs by controlling the rate of synthesis rather than the rate of degradation Primary control= Hypothalamus Small gland next to pituitary gland Connected to the pituitary by the pituitary stalk Stores and releases antidiuretic hormone (ADH) ( vasopressin) and oxytocinfrom the posterior pituitary gland Pituitary Gland Releases both tropic and effector hormones 3
Hypothalamus and Pituitary The hypothalamus-pituitary unit is the most dominant portion of the entire endocrine system. The output of the hypothalamus-pituitary unit regulates the function of the thyroid, adrenal and reproductive glands and also controls somatic growth, lactation, milk secretion and water metabolism. 4
Hypothalamus and pituitary gland 5
Hypothalamus and pituitary gland 6
Hypothalamus and Pituitary Pituitary function depends on the hypothalamus. The pituitary gland lies in a pocket of bone at the base of the brain, just below the hypothalamus to which it is connected by a stalk containing nerve fibers and blood vessels. The pituitary is composed to two lobes-- anterior and posterior Two distinct portions Anterior pituitary (adenohypophysis) Posterior pituitary (neurohypophysis) 7
Pituitary Gland Control Hypothalamic releasing hormones stimulate cells of anterior pituitary to release hormones Nerve impulses from hypothalamus stimulate nerve endings in the posterior pituitary gland to release hormones 8
Posterior Pituitary: neurohypophysis Posterior pituitary: an outgrowth of the hypothalamus composed of neural tissue Hypothalamic neurons pass through the neural stalk and end in the posterior pituitary. The upper portion of the neural stalk extends into the hypothalamus and is called the median eminence. 9
Neurosecretory cells of Posterior Pituitary Posterior pituitary gland does NOT have cells that produce hormones Neurosecretory cells of hypothalamus release hormones Directly into Posterior pituitary Which is released into systemic blood stream Rapid response 10
Hypothalamus and posterior pituitary magnocellular neurons paraventricular and supraoptic nuclei secrete oxytocin and vasopressin directly into capillaries in the posterior lobe 11
Hypothalamo-hypophyseal portal system Carries hypothalamic hormones specifically to the anterior pituitary withoutdilution in the systemic blood. 1. Allows rapid response 2. Little dilution of peptide hormones 3. Peptides have short 1/2 life 12
Hypothalamus-pituitary Hypothalamus Pituitary Stalk Hypophyseal Portal Vessels Posterior Pituitary (Neurohypophysis) Anterior Pituitary (Adenohypohysis) 13
Hypothalamic Hormones Corticotropin releasing hormone (CRH) Gonadotropin Releasing Hormone (GnRH) Thyrotropin Releasing Hormone (TRH) Growth Hormone Releasing Hormone (GHRH) Growth hormone release inhibiting hormone ( GHIH) ( Somatostatin, SS) Prolactin release factor (PRF) Prolactin release inhibiting hormone ( PIH) Oxytocin Vasopressin (VAP) or antidiuretic hormone (ADH) 14
Hypothalamus Releasing Hormones: Secretion Is influenced by emotions Can be influenced by the metabolic state of the individual Delivered to the anterior pituitary via the hypothalamic-hypophyseal portal system 15
Hypothalamic Hormones 13-16 16
Hypophysiotrophic Hormones Products produced by the hypothalamus, effecting pituitary function Hormone Thyrotropin releasing hormone (TRH) Action Stimulates release of TSH and prolactin Gonadotropin releasing hormone (GnRH) Stimulates release of LH and FSH Corticotropin releasing hormone( CRH) Growth hormone releasing hormone (GHRH) Growth hormone-inhibiting hormone (GHIH), Somatostatin Prolactin-inhibiting hormone (PIH), dopamine Prolactin release factor (PRF) Stimulates release of ACTH Stimulates release of GH Inhibits GH and TSH release Inhibits prolactin release Stimulates prolactin release
Control of Hormonal Secretions primarily controlled by negative feedback mechanism 13-11 18
Feedback Control of Hormone Production Feedback loops are used extensively to regulate secretion of hormones in the hypothalamic-pituitary axis. An important example of a negative feedback loop is seen in control of thyroid hormone secretion 19
Stress Circadian rhythm (-) 1-Hypothalamic-pituitary adrenal (HPA) axis Immune system: altered Anterior Pituitary Gland Kidney Adrenals ACTH Hypothalamus CRH Posterior Pituitary Gland Glucocorticoids, Catecholamines, etc.. Muscle: Net loss of amino Acids (glucose) Liver: Deamination of proteins into amino acids, gluconeogenesis (glucose) Fat Cells: Free fatty acid mobilization Heart rate: Increased 20
Hypothalamic-Pituitary-Adrenal Axis Hypothalamus CRH stimulates the production of ACTH by anterior pituitary. ACTH stimulates the production of cortisol (glucocorticoids) by the adrenal cortex. Coritsol inhibits hypothalamus and anterior pituitary to secret CRH and ACTH respectively ( negative feed back inhibition) 21
Physiologic stress, surgery, hypoglycemia, fever increases ACTH production ACTH acts on adrenal gland through CAMP mechanism resulting in synthesis and secretion of Cortisol, Aldosterone and Androgens Cortisol feeds back negatively to inhibit both CRH and ACTH 22
- Testosterone GnRH Anterior Pituitary Hypothalamus 2-Hypothalamic-Pituitary- Gonadal Axis (HPG): Males LH FSH + - Testosterone 23
Hypothalamic-Pituitary- Gonadal Axis (HPG): Females GnRH - - - - 24
Hypothalamic-Pituitary Gonadal Axis GnRH (LHRH) is secreted by hypothalamus then stimulates synthesis & secretion of LH & FSH by anterior pituitary. LH & FSH stimulate the production of testosterone & estrogen and progesterone from the gonads( Testis & ovaries) High levels of estrogens suppress the release of GnRH providing a negative-feedback control of hormone levels. Elevated levels of progesterone control themselves by the same negative feedback loop used by estrogen (and testosterone). 25
3-Hypothalamicpituitary thyroid axis (HPT) - Hypothalamus secrets thyrotropin releasing hormone (TRH) that stimulates the production of thyroid stimulating hormone ( TSH) by anterior pituitary. - TSH stimulates the production of thyroid hormones ( T3 & T4) by the thyroid gland. - Thyroid hormones feed back negatively on hypothalamus and anterior pituitary to inhibit secretion of TRH and TSH. ( negative feed back inhibition) 26