PITUITARY GLAND HYPOTHALAMUS Anatomical Relations Pituitary Sella Turcica

PITUITARY GLAND HYPOTHALAMUS

Anatomical Relations • • • Pituitary Sella Turcica Optic Chiasm Median Eminence Mamillary Body Cavernous Sinus (not visible)

Subdivisions of the Pituitary (Hypophysis) • Adenohypophysis (Anterior Pituitary) – Pars Distalis – Pars Intermedia – Pars Tuberalis • Neurohypophysis (Posterior Pituitary) – Pars Nervosa – Infundibular Stalk

Adenohypophysis

Pars Distalis

Cells: • Acidophils – Somatotroph – Lactotroph • Basophils – Gonadotrophs – Thyrotrophs • Corticotrophs (can’t distinguish) • Chromophobes

Hormones • Prolactin/Growth Hormone Family – Prolactin – Growth Hormone • Glycoprotein Family – Thyroid Stimulating Hormone (TSH) – Gonadotropins: • Follicle Stimulating Hormone (FSH) • Luteinizing Hormone (LH) • Pro-opiomelanocortin Family – ACTH

Prohormones • Many small hormones, especially peptide hormones, are synthesized as part of a larger peptide. • The large peptide is called a prohormone • The active hormone is cut of the larger prohormone by an enzyme. • The prohormone generally is not active.

POMC

Pars Intermedia • MSH – Pro-opiomelanocortin Family – Alpha – Beta • Also in Hypothalamus – Involved in regulating metabolism and appetite

Pars Tuberalis

Hypothalamus

Hypothalamo-hypophyseal Portal System • Superior hypophyseal artery • Portal Vessels • Capillary Bed of Pars Distalis

Hypothalamic Releasing Hormones • • • Thyrotropin Releasing Hormone (TRH) Corticotropin Releasing Hormone (CRH) Gonadotropin Releasing Hormone (Gn. RH) Growth Hormone Releasing Hormone (GRH) Somatostatin (GIH) Prolactin Inhibiting Hormone (PIH)

Feedback Control of Anterior Pituitary • Long Loop • Short Loop • Ultrashort Loop • Amplitude • Frequency

Pathologies • Hypersecretion • Hyposecretion • Classification – Primary (Pituitary’s Target Gland) – Secondary (Pituitary) – Tertiary (Hypothalamus) • Pituitary adenomas

Growth Hormone (GH)

Chemistry • • Single chain protein, 191 amino acids MW 21, 500 2 -disulfide bridges Synthesized as part of a larger protein, pre. GH (MW 28, 000)

Function • Stimulate Secretion of Insulin-like Growth Factor 1 (IGF-1) • Increase linear growth • Increase protein synthesis • Decrease protein catabolism • Increase lipid catabolism • Decrease carbohydrate uptake and utilization

GHRH Control of Secretion: Somatostatin (GHIH) Stimulates • GRH Inhibits the Secretion of GH – Neural regulation • • Diurnal Rhythms Deep Sleep Stress Exercise – Metabolic control • Blood Glucose • Blood Fatty Acids • Blood Amino Acids • Somatostatin Secretion of GH

Feedback • GH--Short Loop • IGFs--Long Loop • Metabolic control – Blood Glucose – Blood Fatty Acids – Blood Amino Acids • Neural regulation – – Diurnal Rhythms Deep Sleep Stress Exercise

Long-Loop Diurnal Feedback Rhythms Exercise Sleep Regulation Stress GH Short-Loop Somatostatin Feedback Hypothalamus Serum: Glucose Lipids Amino Acids GRH Ant. Pituitary IGF 1 Liver IGF 1 GH Serum: Glu. Lipids Amino Acids Other Target Tissues

Pathologies

Hypersecretion

Gigantism

Acromegaly

Glucose Intolerance • A form of Diabetes • Caused by Hyperglycemia • Leads to Type II Diabetes

Hyposecretion

Dwarfism

Prolactin (PRL) • Chemistry • Function: • Control of Secretion

Control of PRL Baby Suckles Nipple Baby Weaned Sensory Impulses to Hypothalamus Milk Production Dopamine Secretion Prolactin

Adrenocorticotropic Hormone (ACTH) • • Chemistry Biosynthesis Function Control of Secretion

Control of ACTH Stress Sleep Hypothalamus CRH Ant. Pituitary ACTH Adrenal Cortex Glucocorticoids

Thyroid Stimulating Hormone (TSH) • Chemistry – Glycoprotein – 2 Chains • Function – Stimulate production of thyroid hormone (T 4 & T 3)

Control of TSH Hypothalamus TRH Anterior Pituitary TSH Thyroid T 4 & T 3 T 4

Gonadotropins • Follicle Stimulating Hormone (FSH) • Luteinizing Hormone (LH) • Chemistry – Glycoprotein • Function – Stimulate function of the reproductive tract

Gonadotropin Control Hypothalamus Gn. RH (FSH Only) Ant. Pituitary FSH LH Gonad Inhibin E 2 & P or T

Posterior Pituitary Pars Nervosa

Anatomical Structure • An extension of the hypothalamus • Pituicytes • Axons • Supraoptic n. – ADH • Paraventricular n. – Oxytocin

Hormones

Antidiuretic Hormone (ADH, Vasopressin) • Supraoptic nucleus • Chemistry • Receptors – V 1 – V 2

Function: • Vasoconstriction – Increase Blood Pressure • Increase permeability of collecting tubule to H 2 O

Blood Pressure Control of ADH Blood Pressure Vasoconstriction Blood Vessels Supraoptic Nucleus Blood Osmolality Posterior Pituitary ADH H 2 O Absorption Kidney, Collecting Duct

Diabetes insipidis

Oxytocin (Pitocin) • Paraventricular nucleus • Chemistry • Receptors – Phosphatidylinositol pathway • Function – Increases frequency and duration of uterine smooth muscle contraction – Stimulates milk “let down. ”

Positive Feedback Delivery Shuts Control of Oxytocin Loop Shut-Off Suckling On Nipple Off Positive When Child. Loop is Full Feedback Unknown? Hypothalamus Labor Contractions Milk Let-Down Post. Pituitary Mammary Myoepithelial Cells Oxytocin Uterine Smooth Muscle