11.2 Human Endocrine System

There are two glandular systems such as the exocrine glands and the endocrine glands. The exocrine glands secrete enzymes, saliva and sweat and have ducts that carry their substances to the membrane surfaces. Example: salivary gland and gastric gland. The endocrine glands, called ductless glands produce hormones and lack ducts; they release their hormone to the surrounding tissue fluid.

The hormones circulate around the body and eventually reach the target organs. Endocrine glands (Figure: . ) include the pituitary, thyroid, parathyroid, pineal, adrenal, thymus and are also known as exclusive endocrine glands . The hypothalamus along with its neural function also produces hormones and is considered as a neuro endocrine gland.

In addition several organs such as pancreas, gastro intestinal tract epithelium, kidney, heart, gonads and placenta are also have endocrine tissues and are known as partial endocrine glands. Table. . .

Chemical nature of hormones Class Chemical properties Example Amines Small, water soluble derived from tyrosine or tryptophan Adrenalin, nor adrenalin, melatonin and thyroid hormone Protein/Peptides Water soluble Insulin, glucagon and pituitary hormones Steroids Derived from cholesterol mostly lipid soluble Cortisol, aldosterone, testosterone, oestrogen, progesterone. As the part of limbic system it influences various emotional responses. In mammals, the role of pars intermedia is insignificant, but in other vertebrates it secretes melanocyte stimulating hormone (MSH).