HSF

• The Endocrine system
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• Specific Learning Objectives


  • State the main organs and functions of the endocrine system
  • Define a hormone
  • Understand the difference between neural and hormonal control of homeostasis
  • Describe negative and positive feedback
  • Describe the action of key hormones
  • Understand how the nervous system influences the endocrine system and vice versa
• Autocrine


  Released by cells and have a local effect on same cell type from which chemical signals released
• Paracrine


  Released by cells and affect other cell types locally without being transported in blood
• Neurotransmitter


  Produced by neurons and secreted into extracellular spaces by presynaptic nerve terminals; travels short distances; influences postsynaptic cells
• Endocrine


  Produced by cells of endocrine glands, enter circulatory system, and affect distant cells
• Characteristics of the Endocrine System


  • Body control system where regulation requires duration rather than speed
  • Glands that secrete chemical messengers (hormones) into circulatory system (blood)
  • Hormone characteristics: Produced in small quantities, Transported some distance in circulatory system, Acts on target tissues elsewhere in body
  • Hormone secretion can be: Acute - sudden release due to stimulus, Chronic – small variations over long periods, Episodic – e.g. estrogen & progesterone during menstrual cycle
  • Target cells respond to a hormone because they have the correct receptor
• Functions of the Endocrine System

  • Metabolism
  • Control of food intake and digestion
  • Tissue maturation
  • Ion regulation
  • Water balance
  • Heart rate and blood pressure regulation
  • Control of blood glucose and other nutrients
  • Control of reproductive functions (gametogenesis and pregnancy)
  • Uterine contractions and milk release
  • Immune system regulation
• The endocrine organs of the body
• Nervous vs Endocrine Systems

  • Similarities: Both systems associated with the brain, Endocrine – hypothalamus, May use same chemical messenger as neurotransmitter and hormone, Two systems are cooperative
  • Differences: Mode of transport - Axon vs Blood, Speed of response - Nervous – instant/milliseconds vs Endocrine – delayed/seconds, Duration of response - Nervous – milliseconds/seconds vs Endocrine – minutes/days
• Endocrine glands


  • pineal gland - sleep and wake cycles
  • hypothalamus - key hormones
  • pituitary gland - main
  • thyroid gland - stress and growth
  • thymus gland - immune system
  • pancreas - sugar metabolism
• Structure of the Pituitary Gland

  • Posterior pituitary (neurohypophysis): extension of the nervous system via the infundibulum, Secretes neuropeptides
  • Anterior pituitary (adenohypophysis): Develops from embryonic oral cavity; secretes traditional hormones

  
• Pituitary Gland and Hypothalamus


  • Hypothalamus regulates secretions of anterior pituitary
  • Posterior pituitary is an extension of the hypothalamus
  • The pituitary gland produces nine major hormones that Regulate body functions, Regulate the secretions of other endocrine glands
• Hypothalamic control of posterior pituitary

  Hormones produced in neurons in hypothalamus, stored in posterior pituitary, Axons form hypothalamohypophysial tract, Action potentials in these neurons cause hormone release
• Hypothalamic control of anterior pituitary

  Blood vessels make up hypothalamohypophysial portal system, connect the areas, Hypothalamic releasing and inhibiting hormones stimulate or inhibit anterior pituitary hormone release
• Hypothalamus, Anterior Pituitary, Target Tissues


  Stimuli within nervous system regulate secretion of releasing hormones from neurons in hypothalamus, Releasing hormones pass to anterior pituitary, Releasing hormones stimulate the release of hormones from anterior pituitary, Anterior pituitary hormones travel in blood stream to target tissue, which may be another endocrine gland
• Hypothalamic Hormones


  • Growth hormone-releasing hormone (GHRH)
  • Growth hormone-inhibiting hormone (GHIH)
  • Thyrotropin-releasing hormone (TRH)
  • Melanocyte releasing hormone (MRH)
  • Corticotropin-releasing hormone (CRH)
  • Gonadotropin-releasing hormone (GnRH)
  • Prolactin-releasing hormone (PRH)
  • Dopamine (prolactin-inhibiting hormone, PIH)
• Anterior Pituitary Hormones


  • Growth hormone (GH)
  • Thyroid stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
  • Melanocyte-stimulating hormone (MSH)
  • Luteinizing hormone (LH)
  • Follicle-stimulating hormone (FSH)
  • Prolactin
• Tropic vs Non tropic

  • Tropic hormones: stimulate the secretion of other hormones from target tissues
  • Non tropic: initiate an effect
• Hypothalamus, Posterior Pituitary, Target Tissues

  Stimuli within nervous system cause neurons in hypothalamus to increase or decrease action potential frequency, AP's conducted along neurons from hypothalamus to posterior pituitary. Axon terminals of these neurons store neuro-hormones, AP's cause release of neurohormones into circulatory system, Posterior pituitary hormones travel in blood stream to target tissue
• Posterior Pituitary hormones


  • Antidiuretic hormone (ADH)
  • Oxytocin
• Control of hormone secretion - negative feedback

  Anterior pituitary secretes a tropic hormone which travels in blood to target endocrine cell, Hormone from target endocrine cell travels to its target, Hormone from target endocrine cells has negative feedback (opposite) effect on hypothalamus and anterior pituitary to decrease secretion of tropic hormone
• Control of hormone secretion - positive feedback

  Anterior pituitary secretes a tropic hormone which travels in blood to target endocrine cell, Hormone from target endocrine cell travels to its target, Hormone from target endocrine cells has positive feedback effect on hypothalamus and anterior pituitary to increase secretion of tropic hormone
• Growth Hormone


  • Stimulates uptake of amino acids; protein synthesis, Stimulates breakdown of fats to be used as an energy source, Promotes bone and cartilage growth, Regulates blood levels of nutrients after a meal, GH stimulates liver and skeletal muscle to make IGF-1, Peak GH levels during deep sleep
• Thyroid Gland


  • One of largest endocrine glands, Highly vascular, Only gland that stores hormone, Composed of follicles: follicular cells surrounding thyroglobulin/thyroid hormones, Iodine and tyrosine necessary for production of T3 and T4, Increase rate of glucose, fat, protein metabolism in many tissues thus increasing body temperature, Normal growth of many tissues
• Triiodothyronine or T3


  Tetraiodothyronine or T4 or thyroxine
• ACTH


  • Near superior poles of kidneys, Inner medulla; outer cortex, CRH from hypothalamus causes release of ACTH from anterior pituitary which, Causes cortisol secretion from the adrenal cortex (a glucocorticoid), Causes aldosterone secretion from the adrenal cortex (a mineralocorticoid), Causes androgen (weak sex hormone)
• Adrenal Medulla


  • Epinephrine = adrenaline, Norepinephrine = noradrenaline, Stress, physical activity, and low blood glucose levels act as stimuli to the hypothalamus, resulting in increased sympathetic nervous system activity, An increased frequency of action potentials conducted through the sympathetic division of the autonomic nervous system stimulates the adrenal medulla to secrete epinephrine and norepinephrine into CVS, Secretion of hormones prepares body for physical activity. Short lived responses, Epinephrine and norepinephrine increase heart rate and force of contraction; cause blood vessels to constrict in skin, kidneys, gastrointestinal tract, and other viscera
• Melanocyte stimulating hormone - MSH


  • Acts on receptors in skin cells (melanocytes) and stimulates melanin (colour pigment) in the skin, MSH also has a role regulating appetite and sexual behaviour, Poorly understood
• LH & FSH


  • GnRH from hypothalamus stimulates LH and FSH secretion, Gonadotropins: glycoprotein hormones that promote growth and function of the gonads, Both hormones regulate production of gametes and reproductive hormones, From testes - Testosterone: spermatogenesis, secondary sex characteristics, From ovaries - Estrogen and progesterone: sex organ development and characteristics, menstrual cycle, pregnancy

  
• Prolactin


  • Non tropic hormone, Breast milk production, Supply and demand
• Oxytocin


  • Posterior pituitary, Non tropic hormone, Positive feedback, Breast milk release (let down), Supply and demand
• ADH


  • Anti diuretic hormone (vasopressin), Reduced urine formation, Keeps water in the body, Increases blood volume and thus blood pressure, Hot day / dehydrated = lots of ADH, Diuretic – tea, coffee, alcohol
• Pancreas – regulation of insulin secretion


  • Located along near intestine and stomach; retroperitoneal, Exocrine gland: Produces pancreatic digestive juices, Endocrine gland: Consists of pancreatic islets, Alpha cells - secrete glucagon, Beta cells - secrete insulin
• Endocrine Pancreas - Regulation

  After a meal, Hungry / fasting