Endocrine System OverviewEndocrine System Overview

Chemical classification of hormonesChemical classification of hormones Gland may be entire organ or interspersed Gland may be entire organ or interspersed

bits of tissuebits of tissue Ductless glands produce hormonesDuctless glands produce hormones Target tissues are identified by receptorsTarget tissues are identified by receptors

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HypothalamusHypothalamus

Control Center for Control Center for internal environmentinternal environment

Regulates nervous and endocrine systems via 3 mechanisms:

1. ANS centers exert nervous control on adrenal medulla

2. ADH and Oxytocin production

3. Regulatory hormone production (RH and IH) controls pituitary gland directly and all other endocrine glands indirectly

Fig 19-3www.freelivedoctor.comwww.freelivedoctor.com

Pituitary Gland (= Pituitary Gland (= Hypophysis)Hypophysis)

Structure:Structure: Infundibulum - connection to hypothalamus Infundibulum - connection to hypothalamus In the sella turcica In the sella turcica Two parts with an embryonic double originTwo parts with an embryonic double origin

Posterior Pituitary = neurohypophysisPosterior Pituitary = neurohypophysis Storage Storage shed for ADH and Oxytocin (produced in ?)shed for ADH and Oxytocin (produced in ?)

Anterior Pituitary = adenohypophysisAnterior Pituitary = adenohypophysis production production of 7 peptide hormones, of 7 peptide hormones, see fig 19.5see fig 19.5

Histology

Fig 19-4www.freelivedoctor.comwww.freelivedoctor.com

Hypophyseal Portal System Hypophyseal Portal System

Portal systems:Portal systems: two capillary networks two capillary networks in serial arrangement in serial arrangement Advantage?Advantage?

Named after their Named after their destination: . . . destination: . . .

Portal veins:Portal veins: blood blood vessels that link two vessels that link two capillary networkscapillary networks

Fig 19-6www.freelivedoctor.comwww.freelivedoctor.com

Thyroid GlandThyroid Gland Anterior surface of trachea Anterior surface of trachea

just inferior of thyroid just inferior of thyroid cartilage (or Adam’s apple)cartilage (or Adam’s apple)

Two lobes connected by Two lobes connected by isthmusisthmus

MicroscopicMicroscopic thyroid follicles thyroid follicles produce thyroid hormoneproduce thyroid hormone

C Cells - produce calcitonin C Cells - produce calcitonin ((CaCa2+2+))

Fig 19-7

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Thyroid Gland FunctionThyroid Gland Function

Thyroxin (T4) and triiodothyronine (T3) speed up metabolic rate

Calcitonin lowers blood Ca2+ levels

Thyroid pathologies: Hyper- and Hypothyroidism

Goiter

Exophthalmus

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Hyperthyroidism Hypothyroidism

Slowing of mind and body

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Four Parathyroid Four Parathyroid GlandsGlands

Parathyroid Parathyroid hormone (PTH; hormone (PTH; sometimes also sometimes also called called parathormone)parathormone)

Function: Function: antagonist to antagonist to CalcitoninCalcitonin

Fig 19-9

4 tiny glands embedded in the back of the 4 tiny glands embedded in the back of the thyroid (superior and inferior)thyroid (superior and inferior)

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Thymus GlandThymus Gland Inside thoracic cavity

immediately posterior to sternum above the heart

Most active in infancy and childhood - Largest just before puberty

Thymosin - enhances lymphocyte production and competence. (important for immune system)

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Adrenal or Suprarenal Adrenal or Suprarenal GlandGland

Cortex:Cortex: corticosteroid production aldosterone, cortisol, sexhormonealdosterone, cortisol, sexhormone

Medulla: modified sympathetic Medulla: modified sympathetic ganglion produces adrenaline and ganglion produces adrenaline and noradrenaline (noradrenaline (parallels sympathetic parallels sympathetic division of ANS)division of ANS)

HistologyHistology

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Pancreas Part of endocrine and Part of endocrine and

digestive systems. digestive systems. (99% exocrine)(99% exocrine)

Pancreatic islets or islets of LangerhansPancreatic islets or islets of Langerhans cells: glucagon cells: glucagon ( blood sugar levels by

stimulating liver to convert glycogen to glucose)

cells: insulin cells: insulin ( blood sugar levels by causing the cells to take up glucose for use by the mitochondria)

cells: somatostatincells: somatostatin

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