Endocrine system

Endocrine gland

  • Ductless gland, therefore directly transmitted to capillary or blood vessel

Classification of hormones

1) Peptides

  • Composed of complex protein follicles includes Hypothalamic, pituitary, pancreatic, parathormone.

2) Monoamines

  • One type of amino acid is present in molecular.

  • It could be tyrosine amino acid( Epinephrine and Thyroid hormones) and tryptophan amino acid( melatonin and serotonin)

3) Steroidal

  • All gonadal hormones except relaxin; adrenal hormones

    • Relaxin hormone(peptide type) - promotes relaxation of pelvic ligaments during parturition.

4) Lipid

  • Prostaglandin

Endocrine glands

1) Hypothalamus

  • Ventral to thalamus and secretes releasing hormones (RH).

  • Releasing hormones have direct effect to hormones secreted by pituitary gland

2) Hypophysis / pituitary gland

  • Attach to base of hypothalamus; secretes simulating hormones

  • pars distal, pars tuberalis, pars nervosa, pars intermedia

Pars distal

  • Secretes growth hormone/ somatotropin

  • ACTH

  • FSH

  • TSH

  • LH

  • Prolactin (lactogenesis)


3) Thyroid gland

  • 2 distinct lobes connected to isthmus near thyroid cartilage; secretes T3 and T4

    • T4 - Regulates basal metabolic rate of animal

4) Parafollicular cells of thyroid

  • Scattered among follicular cells of thyroid and secretes calcitonin (lower the calcium)

5) Parathyroid gland

  • Small aggregates of endocrine tissue near thyroid gland and secretes PTH/ Parathormone

    (increases blood calcium)

6. Pancreas

  • Scattered throughout this bilobed gland are small masses of endocrine tissue called

    islets of Langerhans, which secretes insulin and glucagon


7. Adrenal gland

  • located close to the kidney and composed of outer adrenal cortex (glucocorticoids

    and mineralocorticoids) and inner medulla (epinephrine & norepinephrine)

8. Ovary

  • paired ovoid structures in females which secretes estrogen (graafian follicles)

    and progesterone (corpus luteum)

9) Testes

  • Paired organs covered and protected by scrotum; secretes testosterone

    • Testosterone is responsible for development of secondary sexual characteristic in animals



    • Placenta

  • Secretes progesterone and placenta lactogens


Ultimobrachial body

  • present in bird and secretes calcitonin