Question

Short / Long answer type questions.
Write the definition, chemical nature, specific characteristics, types and functions of hormones.

Answer 1

Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.

Chemically hormones may be steroids, proteins, peptides or amino acid derives.

• Steroid hormones : The hormones secreted by the testes, adrenal cortex, placenta and ovaries are composed of steroids. E.g. , testosterone, corticosterone, aldosterone, oestrogen and progesterone.
  
• Proteinaceous hormones : Hormones secreted by anterior lobe of the pituitary gland and hormones secreted by the pancreas are composed of proteins.
  
• Peptide hormones : Peptide hormone includes: MSH, vasopressin, oxytocin, ACTH, parathormone, calcitonin.
• Amino acid derivative hormones : Amino acid derivative hormones include: The hormones secreted by the thyroid gland. E.g., thyroxine. The hormones secreted by the adrenal medulla. E.g., adrenaline and nonadrenaline.

Following are specific characteristics of hormones -

• Hormones have low molecular weight so hormones can easily pass out through the capillaries.
  
• Hormones are soluble in water, so hormones can be easily transported with the bloodstream.
  
• Whenever their function is over, hormones are readily destroyed or inactivated or excreted.
• Hormones always act in very low concentration.
  
• Many hormones are produced in an inactive form called prohormone.
  
• A hormone in its primary action affects one or a limited number of reaction and does not influence directly all other metabolic activities of the cell.
  
• Secretion of the hormone is provoked in response to a given situation and its action is, therefore, to fulfil a given task.