endorcrine

• Main ways that cells communicate

  • Direct communication
  • Paracrine
  • Endocrine
  • Synapses

  
• Mechanisms of cell communication

  • Gap junctions
  • Through extracellular fluid
  • Through blood
  • Across synaptic cleft
• Transmission of cell communication

  • Ions, small solutes, lipid-soluble molecules
  • Paracrine factors e.g. histamine
  • Hormones
  • Neurotransmitters
• Distribution of effects of cell communication

  • Limited to adjacent cells
  • Local area. Cells must have appropriate receptors
  • Target cells (with appropriate receptors) in other tissues
  • Very specific post-synaptic cells
• Endocrine system

  Chemical signal, slower, prolonged, indirect (through blood), dose-responsive
• Nervous system

  Electrical signal, fast, direct (synapses), all-or-nothing signal
• Endocrine and nervous systems maintain homeostasis
• Endocrine glands

  • Produce hormones that are secreted directly into the blood and can act on target cells
• Hypothalamus

  • Central controller of the endocrine system
  • It secretes releasing and inhibiting factors (chemicals) that control the function of the pituitary gland e.g. thyrotropin releasing factor (TRF)

  
• Pituitary gland

  • Located inferiorly to the hypothalamus, connected by the infundibulum
  • Anterior pituitary (glandular epithelium) - connected by hypothalamic-hypophyseal portal system
  • Posterior pituitary (nervous tissue) - connected by hypothalamic-hypophyseal tract

  
• Anterior Pituitary Hormones

  • Thyroid Stimulating Hormone (TSH)
  • Adrenocorticotropic Hormone (ACTH)
  • Follicle Stimulating Hormone (FSH)
  • Luteinising Hormone (LH)
  • Growth Hormone (GH)
  • Melanocyte Stimulating Hormone (MSH)
  • Prolactin
• Posterior Pituitary Hormones

  • Anti-Diuretic Hormone
  • Oxytocin
• Thyroid Gland

  • "butterfly" shaped gland in neck
  • Secretes T3 and T4 (stimulated by TSH)
  • T3 and T4 act on most body cells to increase metabolic rate. Needed for growth and maturation
• Hypothyroidism

  Condition where thyroid gland is underactive
• Hyperthyroidism

  Condition where thyroid gland is overactive
• Parathyroid Glands

  • Located within posterior part of thyroid gland
  • Secretes parathyroid hormone (PTH) to increases breakdown of bone by osteoclasts (increases blood calcium levels)
• Adrenal Cortex Hormones

  • Aldosterone (salt/water balance)
  • Cortisol (anti-stress hormone)
  • Androgens (sex hormone)
• Adrenal Medulla

  • Secretes Epinephrine/Norepinephrine (Sympathetic nerve response)
• Pancreas

  • Has exocrine (secretes digestive enzymes) and endocrine function
  • Islets of Langerhans secrete insulin, glucagon and somatostatin
  • Important for controlling blood glucose levels
• Diabetes

  Condition where there is no insulin or non-functional insulin
• Ovaries

  • Secrete estrogen and progesterone (stimulated by GnRH from hypothalamus, and LH & FSH from anterior pituitary)
  • Estrogen needed for development of sex organs, secondary sex characteristics. In menstrual cycle necessary for ovulation and thickening of uterine wall
  • Progesterone needed for continued thickening of uterine lining during menstrual cycle and if a pregnancy results
• Testes

  • Secrete testosterone (stimulated by GnRH from hypothalamus, and LH & FSH from anterior pituitary)
  • Development of sex organs, secondary sex characteristics and sperm
• Hormonal action

  1. ATP -> cAMP

  2. Cell response
• Lipid-soluble hormones

  Direct action
• Water-soluble hormones

  Indirect action
• Hormone receptors

  • Plasma membrane receptors
  • Cytosol or nuclear receptors
• Hormonal control - Negative feedback

  1. Response

  2. Negative feedback
• Hormonal control - Positive feedback

  1. Response

  2. Positive feedback