Chemical coordination in humans

• Hormones are chemical messengers that regulate various physiological processes in the body.
• Why do we need chemical coordination along with neural

  To control and coordinate cells that are not innervated and controlled by our nervous system directly
• Chemical vs neural coordination

  1. Chemical coordination slow but long lived
  2. Chemical coordination involves hormones but neural coordination involves neurotransmitters and electrical impulses
• Endocrine glands are also called ductless glands that release their hormones directly into the bloodstream

  Exocrine glands are glands with ducts (includes sweat glands)

  Mixed or Heterocrine glands are glands with both endocrine and exocrine parts (includes gonads)
• Characteristics of hormones

  non-nutrient molecules

  intercellular messengers

  produced in trace amounts

  actively need chemical receptors to bind to
• The neural system provides a point-to-point rapid coordination among organs.
• The neural coordination is fast but short-lived.
• As the nerve fibres do not innervate all cells of the body and the cellular functions need to be continuously regulated, a special kind of coordination and integration has to be provided.
• This function is carried out by hormones.
• The neural system and the endocrine system jointly coordinate and regulate the physiological functions in the body.
• Endocrine glands lack ducts and are hence, called ductless glands.
• The secretions of endocrine glands are called hormones.
• The classical definition of hormone as a chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ has current scientific definition as follows: Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.
• Diabetes mellitus is a hormonal deficiency.
• Progestational hormone is a type of hormone.
• Hyperglycemic hormone and hypoglycemic hormone are types of hormones.
• FSH has a mechanism of action.
• Gonadotrophic hormones are a type of hormone.
• Blood pressure lowering hormone is a type of hormone.
• T4, PTH, GnRH, LH, and Parathyroid are all parts of the endocrine system.
• Androgens and estrogens are types of hormones.
• Goitre is a hormonal deficiency.
• Cretinism is a hormonal deficiency.
• Hypercalcemic hormone is also a type of hormone.
• Invertebrates possess very simple endocrine systems with few hormones whereas a large number of chemicals act as hormones and provide coordination in the vertebrates.
• The human endocrine system is described in this chapter.
• The endocrine glands and hormone producing diffused tissues/cells located in different parts of our body constitute the endocrine system.
• Pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus and gonads (testis in males and ovary in females) are the organised endocrine bodies in our body.
• In addition to these, some other organs, e.g., gastrointestinal tract, liver, kidney, heart also produce hormones.
• The hypothalamus is the basal part of diencephalon, forebrain and it regulates a wide spectrum of body functions.
• The hypothalamus contains several groups of neurosecretory cells called nuclei which produce hormones.
• These hormones regulate the synthesis and secretion of pituitary hormones.
• The hormones produced by hypothalamus are of two types, the releasing hormones (which stimulate secretion of pituitary hormones) and the inhibiting hormones (which inhibit secretions of pituitary hormones).
• A hypothalamic hormone called Gonadotrophin releasing hormone (GnRH) stimulates the pituitary synthesis and release of gonadotrophins.
• Somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary.
• These hormones originating in the hypothalamic neurons, pass through axons and are released from their nerve endings.
• Melatonin helps in maintaining the normal rhythms of sleep-wake cycle, body temperature, influences metabolism, pigmentation, the menstrual cycle as well as our defense capability.
• Thyroid hormones play an important role in the regulation of the basal metabolic rate, support the process of red blood cell formation, control the metabolism of carbohydrates, proteins and fats, and influence water and electrolyte balance.
• The thyroid gland is composed of two lobes which are located on either side of the trachea, interconnected with a thin flap of connective tissue called isthmus.
• Hyperthyroidism is a condition where the rate of synthesis and secretion of the thyroid hormones is increased to abnormal high levels, adversely affecting the body physiology.