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  1. 1. THE ENDOCRINE SYSTEM • Lecture 2; Holes, Chapter 13 1 THE PITUITARY GLAND Secretes 9 hormones Divided into 2 parts: Anterior lobe Posterior lobe Anterior: glandular tissue. (adenohypophysis) Posterior: nervous tissue (neurohypophysis) Pituicytes (type of glial cell). Secretes neurohormones from hypothalamus 2 The Pituitary Gland 3
  2. 2. PITUITARY GLAND Anterior lobe (adenohypophysis) Posterior lobe (neurohypophysis) Glandular tissue. Pituicytes & Nerve cells. Derived from epithelial tissue of oral muscosa. Actually part of the brain. Makes its own hormones. Receives hormones from hypothalamus. Growth hormone Thyroid-stimulating hormone Oxytocin Adrenocorticotrophic hormone (ACTH) Antidiuretic hormone (ADH) Follicle-stimulating hormone (FSH) Luteinizing hormone Prolactin (all use cAMP 2°messenger system) 4 POSTERIOR PITUITARY GLAND & THE HYPOTHALAMUS Hypothalamus: Supraoptic nucleus (ADH) Paraventricular nuclei (Oxytocin) Hypothalamic-hypophyseal tract (hormones travel down neurons) Posterior Pituitary (hormones released into capillary beds when neurons fire) 5 ANTERIOR PITUITARY GLAND & THE HYPOTHALAMUS Hypothalamus sends chemical instructions to the Anterior Pit. Gland Primary capillary plexus Hypophyseal Portal system Secondary capillary plexus Anterior Pituitary Epithelial tissue 5 types of secretory cells 6
  3. 3. HYPOTHALAMUS: CONDUCTOR OF THE HORMONE ORCHESTRA Hypothalamus Hormone releasing chemicals Posterior Pit. Gland Oxytocin ADH Anterior Pit. Gland Growth Hormone TARGET ORGAN Prolactin (pro-opiomelanocortin) (melanocyte stimulating hormone) TSH ACTH “Trophins” Other hormones FSH LH 7 GROWTH HORMONE (GH; SOMATOTROPIN) Made and secreted by somatotropic cells in Anterior Pit. Gland Protein hormone Promotes growth/division of most cell types: Major targets: Bone & Muscle (stimulates epiphyseal plate, muscle mass increase) Promotes Anabolic activity Increases Protein Synthesis (amino acid movement) Increases Fat mobilization (alternative fuel to CHO) Conserves carbohydrates Acts either directly or via Insulin-like growth factor (IGF) IGF produced by liver, muscle, bone & other tissues. 8 GROWTH HORMONE FUNCTION Release of IGF (liver, muscle, bone) Increase Increase sulfur Decrease Amino Acid uptake glucose use Uptake Stimulation of bone growth Increase Increase Increased Fat protein cartilage release and synthesis production utilization 9
  4. 4. CONTROL OF GROWTH HORMONE RELEASE HYPOTHALAMUS Growth hormone releasing hormone Growth hormone inhibiting hormone (GHRH) (somatostatin) ANTERIOR PIT. GLAND Growth hormone released GH release decreased Other factors: Age Sleep GH blood Nutritional status levels rise IGF increase 10 GROWTH HORMONE RELEASE Hypersecretion: Gigantism & Acromegaly 11 GROWTH HORMONE RELEASE Hyposecretion: Pituitary dwarfism Synthetic GH now produced and cases of pituitary dwarfism are reduced 12
  5. 5. THYROID STIMULATING HORMONE Released by thyrotrophin-releasing hormone (hypothalamus) Stimulates secretions from Thyroid gland Rising blood levels of TSH inhibit further release of TRH at ant.pit.gland. Also inhibited at hypothalamus. Also released during pregnancy, emotional stress, cold temperature 13 THYROID STIMULATING HORMONE Hypersecretion: Grave’s disease: overactive thyroid Hyposecretion: Cretinism (children): retardation of mental and physical growth Myxedema (adults): lowered mental awareness, fatigue, weakness. 14 ADRENOCORTICOTROPHIC HORMONE (ACTH) ACTH: Secreted by anterior Pit. Gland Controlled by hypothalamic corticotrophin releasing hormone. (daily rhythm: highest in morning). ACTH acts on adrenal cortex Adrenal cortex stimulated to release corticosteriods Glucocorticoids feedback and inhibit ACTH release 15
  6. 6. ADRENOCORTICOTROPHIC HORMONE (ACTH) Hypersecretion: Cushing’s disease. Prolonged exposure to elevated corticosteroids: upper body obesity rounded face increased fat around the neck thinning arms and legs Children tend to be obese with slowed growth rates. 16 GONADOTROPHINS Follicle-stimulating hormone & Luteinizing hormone (FSH) Gamete production: eggs, sperm (LH) Controls gonad hormones FSH & LH cause maturation of egg follicle; LH causes egg release LH stimulates testes to produce testosterone (male) FSH & LH - maturation of gonads during puberty Both released by gonadotrophin-releasing hormone (GnRH) from the hypothalamus 17 PROLACTIN Stimulates milk production by the breasts. (increases testosterone in males) Release controlled by hypothalamus - Prolactin-releasing hormone (serotonin) & Prolactin-inhibiting hormone (dopamine) PIH and PRH affected by estrogen; increased estrogen causes increase in prolactin. Prolactin levels rise toward end of pregnancy. Sustained rise results in milk production by breast tissue 18
  7. 7. POSTERIOR PITUITARY (HYPOTHALAMIC) HORMONES Oxytocin and Antidiuretic Hormone. Posterior Pituitary stores the hormones Released by neural stimulation from hypothalamus 19 OXYTOCIN (GR. SWIFT BIRTH) Causes smooth muscle contractions uterus wall - childbirth myoepithelial cells in breast tissue Number of receptors increase near end of pregnancy Contractions cause increased release via stimulation of the hypothalamus. (Positive feedback). Suckling child stimulates ‘letdown’ reflex - release of oxytocin and stimulation of breast to release milk. Synthetic Oxytocin used to induce labor Males: plays a role in sexual arousal and nurturing behavior (‘cuddle hormone’) 20 ANTIDIURETIC HORMONE (ADH) (Diuresis - production of urine) Dehydration: high salt concentration in blood Osmoreceptors in hypothalamus start firing Release of ADH in to bloodstream Target organ: Kidney Osmoreceptors in stop firing Kidney tubules reabsorb more water Blood Salt concentration Blood volume rises, urine decreases production slows 21
  8. 8. ANTIDIURETIC HORMONE (ADH) Alcohol: dehydration Drug: antagonist to ADH to induce diuresis In high concentrations, ADH is powerful vasoconstrictor (vasopressin) Hyposecretion: e.g. Diabetes insipidus - damage to pit.gland or hypothalamus means less ADH, means more urine produced. Hypersecretion: e.g. meningitis, hypothalamic injury - blood retention, head ache, hypotonic blood. 22 THE THYROID GLAND Butterfly shaped gland Largest gland in body Very high blood supply Hollow follicles Squamous/cuboidal epithelium (follicular cells) Inside lumen: Thyroglobulin + iodine = colloid = precursor to Thyroid hormone Parafollicular cells: producing calcitonin 23 THYROID HORMONE (TH) Two forms of the hormone (both amines, both with iodine): Triiodothyronine (T3) - Thyroxine (T4) - secreted by follicle converted from T4 at target cells cells Target cells: everywhere BUT brain, spleen, testes, uterus and thyroid itself. TH stimulates glucose oxidation (increases metabolism) Essential for normal bone and nerve development and reproductive development. 24
  9. 9. TRANSPORT OF THYROID HORMONE (TH) T4 & T3 are bound to transport proteins Both forms can bind to receptors; T3 much more readily Hypothalamus Thyrotropin-releasing Peripheral tissues have enzymes to convert T4 to T3 hormone T4 & T3 both act like steroids and act in the nucleus Regulation: Anterior Pit.Gland Thyroid Stimulating If T4 blood levels fall, thyroid-stimulating hormone (TSH) is Hormone released. T4 is released from gland to increase blood levels Thyroid gland TSH levels fall, T4 release is slowed Thyroid hormone (Can be over-ridden is times of need: cold temperature, pregnancy) TARGET CELLS 25 DISORDERS OF THYROID HORMONE (TH) Hyposecretion: Hypersecretion: Endemic - lack of dietary iodine Grave’s disease Autoimmune disease - constant stimulation of thyroid to release TH. Cretinism, myxedema - low metabolic rate, chills, mental retardation (children) or High metabolic rate, nervousness, weight sluggishness (adults) loss, protusion of eyeballs (Exophthalmos) 26 CALCITONIN Produced by parafollicular cells (or C cells) Released when blood Ca++ is high Lowers blood Calcium. Inhibits ________ activity, stimulates ________ activity Increases Ca++ excretion by the kidney Humoral stimulus (raised Ca++ levels) Fast, but short acting response. 27
  10. 10. PARATHYROID GLAND Four small glands Posterior surface of the thyroid gland Vary in number and position Gland made up of: Chief cells - PTH Oxyphil cells - ? 28 PARATHYROID HORMONE PTH release stimulated by falling blood Ca++ Raises falling Ca++ levels. Stimulates, bone, kidney and intestine. Activates Vitamin D - precursor of calcitrol 29 DISORDERS OF PARATHYROID HORMONE Hypersecretion Hyposecretion Hyperparathyroidism Surgery or trauma (rare, cancer) Bones are broken down Lower Ca++ : Increased excitability of Raised Ca++ : neurons Depression of Nervous Tetany - loss of System sensation, muscle twitches, Muscle weakness convulsions Kidney stones Paralysis Metastatic calcification 30