Endocrine System

Endocrine system Components endocrine glands: thyroid gland,parathyroid gland,adrenal gland,pituitary gland,pineal body,etc. Scattered endocrine cells: islet cells of pancreas,etc. Function: secreting hormones which regulate the functions of the body and maintenance of a steady internal environment state.

general characteristics of the endocrine system 1.Glandular cells arranged in cords,clumps, network or follicles; 2. Without ducts ； 3. Abundant in capillaries 。

thyroid gland thyroid follicles full of homogeneous materials called colloid

1. principal cell (follicular cell) （ 1 ） LM: its shape varies with functional state （ 2 ） EM: numerous microvilli on free surface; RER,Golgi complex ， mitochondria in cytoplasm; secreting granules and colloid vesicles in the top of cytoplasm. （ 3 ） function: synthesize and secret thyroid hormone.

Synthesis of thyroid hormone I+ absorbed from blood

Glycoprotein synthesized by follicular cells

Monoiodotyrosyls or diiodotyrosyls

Iodinated thyroglobulin (colloid in the follicles)

Taken back into the follicular cells to further modify

Thyroid hormones ( T3 and T4)

3. Function of T3 and T4 Stimulates metabolism; Increase nerve excitability; Promote the growth and development 。

Hypothyroidism during development---cretinism

in the adult----myxedema

Hyperthyroidism--eyes that seem to be popping out of their sockets, trembling hands,etc.

Myxedema and hyperthyroidism

cretins

parafollicular cell (C cell) 1.distribution: between follicles or between follicular cells. 2. profile ： larger and stain more lightly. 3.function: secreting hormone calcitonin which decreases the [Ca2+] in the blood.

C cells

C cells

parathyroid gland 1.Chief cell (principal cell): secreting parathormone which increases the level of serum calcium—[Ca2+] 2. Oxyphil (eosinophil cell) ： the function is unclear.

parathyroid gland

adrenal gland

Zona glomerulosa

cortex

Zona fasciculasa Zona reticularis

Adrena l gland medulla

1. Zona glomerulosa (ZG) Cells arranged in groups Cells: smaller ， cuboidal or low columnar, stained densely.

Producing mineralocorticoid hormones to influence the electrolyte and water balance

zona glomerulosa

2. zona fasciculasa (ZF) Cells arranged in cords ； Cells:larger,polyhe dral, stained lightly

Producing glucocorticoids (cortisone and cortisol) Also producing DHA(an androgen).

zona fasciculasa

3. zona reticularis (ZR) Cell cords form networks Cells: smaller ， cuboidal or low columnar, stained densely.

Producing some glucocorticoid and sex hormones:androge

zona reticularis

Medulla of adrenal gland Chromaffin cells

Adrenaline cells secret adrenalin Nordrenaline cells secret noradrenalin

ZG--mineralocorticoid hormones

cortex

Adren al gland

ZF—glucocorticoid hormones and androgen. ZR--

glucocorticoid and sex hormones (androgen and estrogen)

Medulla—adrenaline and noradrenaline

pituitary gland (hypophysis cerebri)

Subdivision of the hypophysis Neurohypophysis pars posterior (pars nervosa) infundibulum Adenohypophysis pars anterior (pars distalis) pars tuberalis pars intermedia

adenohypophysis 1.Pars anterior: several types of cells are responsible for production hormones .It is rich in fenestrated capillaries.

Chromophil cells

Pars anterior

acidophil somatotropic cell (somatotroph) — somatotropin(STH) or GH mammotroph — prolactin (PRL)

basophil Corticotroph — adreno-corticotropin (ACTH) Thyrotroph — thyrotropin (TSH) Gadotroph — follicle stimulating hormone(FSH) and luteinizing hormone(LH) in female; interstitial cell stimulating hormone(ICSH) in male

Pars anterior

Pars anterior

2. Pars tuberalis Mainly consisting of undifferentiated cells. Some acidophil and basophil cells are also present.

3. Pars intermedia Poorly developed in human hypophysis Some cells can produce melanocyte stimulating horone(MSH), Other cells can produce ACTH.

Pars intermedia

4. Blood supply of hypophysis Superior hypophyseal artery

Capillary plexuses in median eminence and infundibular stalk Hÿypothalamo

Portal vessels in infundibulum

-hypophyseal portal system

Sinusoids in pars anterior Veins ending in venous sinuses

5. The relationship between hypothalamus and pars anterior Hypothalamus secrets releasing hormones

Capillary plexuses in median eminence and infundibular stalk Hypothalamo

Nerve impulse or other stimuli

target gland

Portal vessels in infundibulum

Sinusoids in pars anterior

-hypophyseal portal system

Pars posterior It mainly composed of unmyelinated axons of the neurons in hypothalamus and pituicytes. Pars posterior and hypothalamus are structural and functional unity. Supraoptic nucleus: producing antididuretic hormone (ADH)

Paraventricular nucleus: producing oxytocin

Pars posterior

hypophysis

Key points 1. Structure of thyroid gland and the function of two type of cells in thyroid gland. 2. The function of chief cell in parathyroid gland. 3. Structure of adrenal gland( cortex and medulla) ， the secretions of medulla and 3 zona of cortex . 4. The structure of pituitary;cell types in pars anterior and their secretions;the relationship between hypothalamus and pituitary (pars anterior and pars posterior); Hypothalamo-hypophyseal portal system