Glands are organs responsible for synthesising and releasing substances such as hormones into the body. There are two main types of gland and they are exocrine and endocrine glands. Exocrine glands secrete substances into cavities or surfaces in the body, while endocrine glands secrete substances straight into the bloodstream.

Types of gland

  • Exocrine glands secrete substances via a duct with examples including the sweat glands, mammary glands, salivary glands and glands located in the digestive system. Categories of exocrine gland include:
    • Serous glands: these glands secrete watery fluids rich in protein
    • Mucous glands: these glands secrete thick fluids rich in carbohydrate
    • Sebaceous glands: these glands secrete lipid substances
    • Endocrine glands secrete substances directly and do not use ducts. Examples of endocrine glands include the thyroid gland, pituitary gland, hypothalamus and the parathyroid gland.

    Endocrine glands and the hormones they secrete

    Hypothalamus gland produces:

    • TRH (thyrotropin-releasing hormone)
    • GNRH (growth hormone releasing hormone)
    • GnRH (gonadotropin-releasing hormone)
    • CRH (corticotropin-releasing hormone)
    • SS (somatostatin)
    • GHIH (growth factor inhibiting hormone)
    • Dopamine

    Pineal gland produces:

    • Melatonin
    • Dimethyltryptamine

    Pituitary gland produces:

    (From the anterior pituitary lobe):

    • LH (luteinizing hormone)
    • GH (growth hormone)
    • PRL (prolactin)
    • TSH (thyroid stimulating hormone)
    • ACTH (adrenocorticotropic hormone)
    • FSH (follicle stimulating hormone)

    (From the posterior pituitary lobe):

    • Oxytocin
    • Lipotropin
    • AVP (arginine vasopressin)

    Thyroid gland produces:

    • T3 (triiodothyronine - a powerful type of thyroid hormone)
    • T4 (thyroxine - a less powerful type of thyroid hormone)
    • Calcitonin

    Parathyroid gland produces:

    • Parathyroid hormone

    The heart produces:

    • ANP (atrial-natriuretic peptide)

    The digestive system produces:

    • CCK (cholecystokinin)
    • Ghrelin
    • Gastrin
    • Somatostatin
    • Secretin
    • Neuropeptide Y

    The liver produces:

    • Angiotensinogen
    • IGF (insulin-like growth factor)
    • Thrombopoietin

    The Islets of Langerhans (located in the pancreas) produce:

    • Glucagon
    • Insulin
    • Somatostatin

    Adrenal glands produce:

    • Glucocorticoids (mainly cortisol)
    • Androgens (such as testosterone and DHEA)
    • Mineralocorticoids (mainly aldosterone)
    • Adrenaline (epinephrine)
    • Noradrenaline (norepinephrine)
    • Testosterone

    Kidneys produce:

    • Renin
    • EPO (erythropoietin)
    • Calcitriol (this is the active form of vitamin D3)

    Skin produces:

    • Vitamin D3

    Adipose tissue produces:

    • Oestrogens
    • Leptin

    Testes (only in males):

    • Androgens (mainly testosterone)

    Ovaries (only in females):

    • Oestrogen (mainly oestradiol)

    Corpus luteum (only in females):

    • Progesterone
    • Oestrogens

    Placenta (only in pregnant females):

    • Progesterone
    • Oestrogens
    • HCG (human chorionic gonadotropin)
    • HPL (human placental lactogen)
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