Hormones

• Hormones


  Chemical substances produced by specialized glands that coordinate and regulate the activity of certain cells and organs
• Primary endocrine glands


  • Pituitary gland
  • Pineal gland
  • Thyroid gland
  • Parathyroid gland
  • Islets of Langerhans gland
  • Adrenal gland
  • Ovaries
  • Testes
• Endocrinology


  The study of hormones and the endocrine organs
• Endocrine system


  All of the glands that secrete hormones
• Endocrine glands are ductless glands which secrete their hormones directly into the bloodstream
• Exocrine glands release their secretions through ducts or tubes e.g. Sweat glands, salivary glands and tear glands
• Hormones


  • Carry signals to one or more organs or tissues in the body causing a series of biochemical processes inside the target organ
  • Only very small quantities are produced and secreted into the blood, but their impact in the target is huge
• Endocrine system characteristics


  • Access to every cell
  • Each hormone acts only on specific target cells
  • Target cells have receptors for specific hormones
  • Endocrine control is slower than the nervous system
  • Endocrine & nervous systems interact
• Endocrine glands stimulation


  1. Humoral stimuli

  2. Neural stimuli

  3. Hormonal stimuli (tropic hormones)
• Hormone


  A chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver
• Hormones like the nervous system coordinate the activities of the body
• Hormones are produced by endocrine glands such as the pancreas, pituitary gland, adrenal gland, testes, ovary etc.
• Endocrine glands are ductless glands i.e. they don't have ducts thus they release their secretions into the blood stream which carries the hormones to the target organs
• Hormones


  • Insulin, produced by the pancreas, alters the activity of the liver & skeletal muscles
• Hormonoids (tissue hormones)


  Compounds that are produced not in glands but in different tissues and regulate metabolic processes on the local level, but some of them (serotonin, acetylcholine) enters blood and regulate processes on the organism level
• Functions of hormones


  • Aid in cell communication and help regulate cell function
  • Affect other endocrine glands or body systems
  • Work with the nervous system
  • Promote or inhibit nerve impulses
  • Regulatory and homeostasis functions
  • Maintain consistency of interior of cell
  • Permissive functions; movement of substance in and out of cell
  • Integrative function; usually balance two systems
  • Developmental function; helps in development of fetus
  • Food metabolism
  • Growth and development
  • Controlling thirst and hunger
  • Maintaining body temperature
  • Regulating mood and cognitive functions
  • Initiating and maintaining sexual development and reproduction
• Cell signaling

  • Autocrine: The hormone acts on the cell that secreted it
  • Paracrine: The hormone acts on a nearby cell without having to enter the blood circulation
  • Intracrine: The hormone is produced in the cell and acts intracellularly
  • Endocrine: The hormone acts on the target cells once it is released from the respective glands into the bloodstream
• Hormones regulate the transport of ions, substrates and metabolites across the cell membrane
• Paracrine hormone


  A hormone that acts on cells which are nearby relative to the cell which released it
• Endocrine hormone


  A hormone that is released into the bloodstream by endocrine glands, where the receptor cells are distant from the source
• Hormones stimulate transport of glucose and amino acids
• Hormones influence ionic transport across the cell membrane
• Hormones influence epithelial transporting mechanisms
• Hormones stimulate or inhibit cellular enzymes
• Hormones influence the cells genetic information
• Factors affecting hormone production level

  • Fluid level
  • Infection
  • Physical injury
  • Emotional stress
• Factors affecting hormone impact on target tissue


  • Hormone production and secretion
  • Hormone concentration in the blood
  • Rate of blood flow to a target organ
  • Half-life of the hormone
• Half-life of a hormone


  The length of time in which a hormone remains viable in the blood before it is degraded by the liver or other tissues
• Hormone half-life can range from several hours to several days
• Characteristics of hormones


  • Low molecular weight
  • Small soluble organic molecules
  • Rate of diffusion is very high and are readily oxidized but the effect does not remains constant
  • Effective in low concentration
  • Travels in blood
  • Target site different from where it is produced and is specific to a particular target
• Hormones are non-specific for organisms and may influence body processes of other individuals
• Hormones affect only cells with appropriate receptors, initiating specific cell function(s)
• Hormones are excreted by the kidney, deactivated by the liver or by other mechanisms
• Hormone production


  1. Nerve impulses from the senses travel to brain

  2. Information is interpreted

  3. Brain sends a nerve impulse to a specific endocrine gland

  4. The specific gland releases hormone adrenaline to the bloodstream

  5. Heart beats rapidly until adrenaline level is normal
• Specific stimuli for hormone secretion are nervous impulses and concentration of certain compounds in blood passing through the endocrine gland
• Mechanisms of hormonal alterations

  • Elevated hormone levels
  • Depressed hormone levels
• Causes of hormonal alterations

  • Failure of feedback systems
  • Dysfunction of endocrine gland or endocrine function of cells
  • Altered rate of hormone degradation or inactivation by antibodies
  • Failure of target cells to respond to hormone
• Classification of hormones


  • Based on chemical nature
  • Based on mechanism of action
• Chemical classes of hormones

  • Amines
  • Peptide and protein
  • Steroid
• Amines


  Hormones derived from single amino acids, such as nor-epinephrine, epinephrine, and dopamine