Endocrine 1

• What is the primary function of the endocrine system?

  It is a network of ductless glands that secrete hormones directly into the blood.
• How does the endocrine system regulate body processes?

  By releasing hormones that regulate complex body processes.
• What is the endocrine system considered to be?

  The regulatory system of the body.
• How is the endocrine system regulated?

  By means of control of hormone synthesis rather than by degradation.
• What are exocrine glands?

  • Glands that secrete their substances through ducts onto body surfaces.
  • Examples include saliva, sweat, breast milk, and digestive enzymes.
• What role do hormones play in an individual's growth and development?

  They play an important role in the growth and development of an individual.
• How do hormones reach their target tissues?

  They diffuse into the blood to be transported to their specific sites.
• How are hormones regulated in the body?

  By metabolic activity through either positive feedback or negative feedback mechanisms.
• How do the nervous and endocrine systems work together?

  They coordinate functions of all body systems.
• How does the nervous system communicate its signals?

  Through nerve impulses conducted along axons of neurons.
• What do neurotransmitters do at synapses?

  They trigger the release of mediators (messengers).
• What is the main difference between the control mechanisms of the nervous and endocrine systems?

  The means of control of the two systems are very different.
• What are some commonly used abbreviations in endocrine physiology?

  • ACTH: Adrenocorticotrophic hormone
  • ADH: Antidiuretic hormone
  • CRH: Corticotropin-releasing hormone
  • FSH: Follicle-stimulating hormone
  • GHRH: Growth hormone-releasing hormone
  • GnRH: Gonadotropin-releasing hormone
  • GH-IH: Growth hormone-inhibiting hormone
  • HCG: Human chorionic gonadotropin
  • GH: Growth Hormone
  • HPL: Human Placental lactogen
  • IGF: Insulin-like growth factor
  • LH: Luteinizing hormone
  • MSH: Melanocyte-stimulating hormone
  • PIF: Prolactin-inhibiting factor
  • PTH: Parathyroid hormone
  • T3: Triiodothyronine
  • T4: Thyroxine
  • TRH: Thyrotropin-releasing hormone
  • TSH: Thyroid-stimulating hormone
• How are hormones classified according to their structure?

  1. Peptides and Proteins

  • Synthesized and stored in secretory granules
  • Half-life: 10 - 30 minutes
  • Cannot cross cell membrane
  • Water soluble, not bound to carrier protein

  
  

  1. Steroids

  • Lipid molecules with cholesterol as a precursor
  • Half-life: 30 - 90 minutes
  • Produced by adrenal glands, placenta, ovaries, testes
  • Water insoluble, circulate bound to carrier protein

  
  

  1. Amines

  • Derived from an amino acid
  • Water soluble
  • Half-life: 7 to 10 days
• What is the half-life of peptide and protein hormones?

  10 - 30 minutes.
• What is the half-life of steroid hormones?

  30 - 90 minutes.
• What is the half-life of amine hormones?

  7 to 10 days.
• How is hormone release stimulated by direct neural innervation?

  Neurons release a neurotransmitter into the synapse with the cells that produce hormones.
• What are the mechanisms for inhibition of hormone release?

  1. Inhibition by Humoral stimuli

  • Companion hormone's release is inhibited by the same humoral stimulus.

  
  

  1. Inhibition by Neural stimuli

  • Neurons inhibit targets just as often as they stimulate them.

  
  

  1. Inhibition by Hormonal stimuli

  • Some hormones prevent the secretion of other hormones.
• What is the negative feedback mechanism in hormone regulation?

  • Most hormones are regulated by negative feedback.
  • Hormone secretion is initiated by the hormone itself once blood levels reach a certain point.
  • Hormones may inhibit the action of other stimulatory hormones.
• What is the positive feedback mechanism in hormone regulation?


  • Some hormones promote the synthesis and secretion of tropic hormones.
  • This stimulates further secretion of the original hormone.
• What is TSH produced by?

  The pituitary gland.
• What is TRH produced by?

  The hypothalamus.
• What is a tropic hormone?


  A chemical messenger that has another endocrine gland as its target.
• What regulates the secretion of anterior pituitary hormones?


  The hypothalamus.
• Which of the following is NOT a peptide hormone?

  Epinephrine.
• How are thyroid hormones classified?

  As amino acid derivatives.
• Where is ACTH produced?

  In the adenohypophysis (anterior pituitary).
• Where is GHRH produced?

  In the hypothalamus.
• Where is the hypothalamus located?

  In the walls and floor of the third ventricle of the brain.
• What is the role of the hypothalamus in the endocrine system?

  It is the link between the endocrine and nervous systems.
• How is the hypothalamus connected to the posterior pituitary?

  By the infundibulum.
• What are the three units of the hypothalamus?

  1. Anterior nuclei (Supraoptic)

  • Comprises the preoptic, medial, and lateral areas.

  
  

  1. Middle nuclei (Tuberal)

  • Responsible for the control of appetite.

  
  

  1. Posterior nuclei (Mammillary)

  • Regulate body temperature and play a role in memory function.
• What hormones are produced in the hypothalamus?

  1. Hypophysiotropic hormones
  2. Tropic hormones
• How does the hypothalamus communicate with the anterior pituitary?

  • It sends hormones via the portal hypophyseal vessels from the median eminence.