General and Sports Anatomy - L.V. Kapilevich, K.V. Davletyarova 2008
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Endocrine system
Synonyms: hormonal system, humoral system. Endocrinology is The Study of the Endocrine glands. The Organs of this system lack excretory ducts and secrete Hormones directly into the Blood AND Lymph (Figure 30).
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Figure 30. Organs of the Endocrine System.
Located in the neck anterior to the Larynx; weight 20–30 g. It consists of two lobes (right and left) connected by an isthmus; a pyramidal lobe (pointing upward) is sometimes present. It lies adjacent to the Trachea, larynx, and Esophagus. The gland is composed of follicles lined with thyrocytes and is enclosed in a Connective Tissue capsule. Hormones: thyroxine and triiodothyronine (metabolic stimulators), and thyrocalcitonin (Calcium and phosphorus Homeostasis hormone). Deficiency leads to delayed physical and mental development. Hyperfunction results in Graves' disease. Since these hormones contain iodine, an adequate Dietary intake of iodine is essential for their synthesis.
Four small glands measuring 2*8 mm, located on the posterior surface of The Thyroid Gland. They are enclosed in a connective tissue capsule and consist of chief Cells (parathyroidocytes). They secrete parathyroid hormone, which induces bone demineralization (releasing calcium into the bloodstream). A lack of this hormone leads to hypocalcemic tetany—increased excitability of The Nervous system and Muscles, spasms, and death.
Pineal Gland (Epiphysis).
A part of the epithalamus (located on the corpora quadrigemina). It resembles a pinecone in shape and is covered by a connective tissue capsule. Measuring 1*6 mm, it is well-developed in children, but in adults, it is gradually replaced by connective tissue and calcifications. It secretes melatonin at night and serotonin during the day. It regulates the function of other glands as well as Puberty, acting as the body's biological clock.
Secretes releasing factors that act upon the Pituitary Gland.
Pituitary Gland (Hypophysis).
An oval-shaped body weighing 0.5 g, located in the Sphenoid bone and enclosed externally by a connective tissue capsule. The anterior lobe is the adenohypophysis, consisting of epithelial cords and cells known as adenocytes. It produces ACTH, Growth Hormone (somatotropin), gonadotropins, prolactin, melanocyte-stimulating hormone (MSH), and thyroid-stimulating hormone (TSH).
The posterior lobe (neurohypophysis) contains pituicytes (where nerve fibers from the hypothalamus terminate). Hormones: vasopressin (antidiuretic hormone) and oxytocin (stimulates smooth Muscle contraction).
Paired organs located directly above the Kidneys, weighing 10–15 g and enclosed in a capsule. The right gland is triangular in shape, while the left is semilunar.
The adrenal cortex consists of three zones: the outer zona glomerulosa (containing small adrenocortical cells that produce mineralocorticoids to regulate renal function); the middle zona fasciculata (producing glucocorticoids and corticosteroids, which regulate carbohydrate and Protein METABOLISM and provide anti-inflammatory effects); and the inner zona ret Ecularis (a loose network producing Sex Hormones: androgens, estrogens, and progesterone).
Adrenal medulla: large granular cells producing adrenaline and noradrenaline.
Contains the Islets of Langerhans, measuring 0.1–0.3 mm in diameter. They produce Insulin (facilitates cellular glucose uptake, stimulates Glycogen and fat synthesis, and enhances Carbohydrate Metabolism in muscles), Glucagon (promotes glucose and glycogen breakdown), and Somatostatin (inhibits the secretion of growth hormone, insulin, and glucagon).
Dysfunction leads to Diabetes Mellitus.
Testis (male gonad): interstitial endocrinocytes (Leydig cells) secrete androgens (testosterone), which influence The Development of external genitalia, secondary sex characteristics, and The Musculoskeletal System, along with small amounts of estrogens.
Ovary (female gonad): follicular epithelial cells produce estrogens (influencing the development of external genitalia, secondary sex characteristics, and the musculoskeletal system), while luteal cells produce progesterone (which affects the uterine lining, fetal GROWTH AND DEVELOPMENT, placental maturation, and mammary gland development).
Islands of chromatoblast cells in the nervous system near the aorta (carotid body) synthesize adrenaline and share the same origin as The adrenal medulla.
Last update: 08/08/2026
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