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• 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
• 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
• 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

  • where nervous and endocrine system interact
  • Hypothalamus regulates secretions of anterior pituitary
  • Posterior pituitary is an extension of the hypothalamus
  • pituitary gland produces nine major hormonesoes that regulate body functions and secretions of other endocrine glands

  
• Hypothalamic control of posterior pituitary

  1. Hormones produced in neurons in hypothalamus, stored in posterior pituitary

  2. Axons form hypothalamohypophysial tract

  3. Action potentials in these neurons cause hormone release
• Hypothalamic control of anterior pituitary

  1. Blood vessels make up hypothalamohypophysial portal system, connect the areas

  2. Hypothalamic releasing and inhibiting hormones stimulate or inhibit anterior pituitary hormone release
• Hypothalamus, Anterior Pituitary, Target Tissues

  1. Stimuli within nervous system regulate secretion of releasing hormones from neurons in hypothalamus

  2. Releasing hormones pass to anterior pituitary

  3. Releasing hormones stimulate the release of hormones from anterior pituitary

  4. Anterior pituitary hormones travel in blood stream to target tissue, which may be another endocrine gland
• Hypothalamic Hormones


  • Growth hormone-releasing hormone, causes increased secretion of GH
  • Growth hormone-inhibiting hormone, cause decreased secretion of GH
  • Thyrotropin-releasing hormone, causes TSH secretion
  • Melanocyte releasing hormone, causes MSH secretion
• 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

  1. Stimuli within nervous system cause neurons in hypothalamus to increase or decrease action potential frequency

  2. AP's conducted along neurons from hypothalamus to posterior pituitary. Axon terminals of these neurons store neuro-hormones

  3. AP's cause release of neurohormones into circulatory system

  4. Posterior pituitary hormones travel in blood stream to target tissue
• Control of hormone secretion - negative feedback

  1. Anterior pituitary secretes a tropic hormone which travels in blood to target endocrine cell

  2. Hormone from target endocrine cell travels to its target

  3. 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

  1. Anterior pituitary secretes a tropic hormone which travels in blood to target endocrine cell

  2. Hormone from target endocrine cell travels to its target

  3. 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
• ACTH – Adrenocorticotrophic hormone

  • 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
  • LH and FSH 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, positive feedback
• 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
• differences between nervous and endocrine

  • mode of transport: axon and blood
  • speed of response: nervous = instant, endocrine = delayed
  • duration of response: nervous = milliseconds, endocrine = mins or days
• thyroid stimulating hormone

  stimulates thyroid to secrete t3 and t4
• adrenocorticotropic hormone

  stimulates adrenal cortex to secrete cortisol and aldosterone
• melanocyte-stimulating hormone

  causes melanocytes to produce more melanin
• follicle-stimulating hormone

  regulate production of gametes and reproductive hormones
• prolactin

  role in milk production
• posterior pituitary hormone - antidiuretic hormone

  stimulates increased reabsorption of sodium and water from nephrons, so less urine is produced

  if blood pressure decreases, then ADH secretion is stimulated
• posterior pituitary hormones - oxytocin

  uterine contractions during birth, ejection of milk from lactating breast