endocrine system

• Human endocrine glands:

  • Hypothalamus
  • Pineal gland
  • Pituitary gland
  • Thyroid glans
  • Parathyroid gland
  • Thymus
  • Adrenal glands
  • Pancreas
  • Ovary
  • Testis
• functions of hypothalamus

  • secretes regulatory hormones to control activity of anterior pituitary
  • control sympathetic output to adrenal medullae
  • production of ADH and oxytocin
• infundibulum is the stalk of the pituitary and is composed of neuroectodermal tissue
• pars intermedia develops from roof plate tissue
• posterior pituitary derives from

  neuroectoderm tissue
• circulatory system in relation to endocrine

  • capillary beds to get blood through tissue and hormones in/out of tissues
• pituitary has capillary beds linked with portal veins through

  hypophyseal portal system
• hypophyseal portal system allows regulatory hormones to be transported from hypothalamus to anterior pituitary
• regulation by hypothalamus and pituitary

  • releasing hormone
  • causes hormone 1 to be released from anterior pituitary
  • hormone 1 causes hormone 2 release from target endocrine organ
  • hormone 2 inhibits release of RH and hormone 1
  • hormone 2 has effect on target cells
• tropic hormones 


  regulate function of endocrine cells/glands
• hormones released from anterior pituitary

  TSH, ACTH, FSH, LH, prolactin, growth hormone, melanocyte stimulating hormone
• melanocyte response to MSH

  • produce melanin
  • exported to keratinocytes
  • arranged above nuclei to protect from sun
• MSH is involved in regulating appetite

  • acts on neurons in mammals in their brain, inhibits hunger
• TSH (thyrotropin)

  • TRH controls release of TSH
  • TSH stimulates release of T3 and T4 from thyroid
• ACTH (corticotropin)

  • ACTH is peptide
  • CRH causes ACTH release
  • ACTH stimulates adrenal cortex to release glucocorticoids
• FSH and LH (gonadotropins)

  • Are glycoproteins
  • Gonadotropin releasing hormone (GnRH) control FSH and LH production
  • Promote egg and sperm production and secretion of sex steroids
  • Inhibin inhibits FSH production (both sexes)
  • Inhibin may inhibit GnRH release
• Prolactin:

  • Peptide
  • Prolactin releasing factor (PRF) and inhibited by prolactin inhibiting hormone (PIH, dopamine)
  • Stimulates milk production
  • Stimulates mammary glands
• Growth hormone: (somatotropin)

  • Is a peptide
  • Stimulated by growth hormone releasing hormone
  • Inhibited by growth hormone inhibitory hormone
  • Stimulates somatomedins (insulin- like growth factor production)
  • Stimulates bone and cartilage growth, fat and glycogen breakdown, increasing blood glucose levels
• growth hormone abnormalities

  • Pituitary gigantism- excess GH before puberty
  • Acromegaly- excess GH after puberty->> thickening of bones of hands, feet, cheeks and jaws
  • Pituitary growth failure- lack of GH
• Supraoptic and paraventricular neurosecretory cells release both oxytocin and ADH
• Oxytocin ->> mammary glands, uterine muscles (target)

  • Peptide
  • Milk ejection by mammary glands
  • Uterine contractions during childbirth
  • Targets in brain =: influencing behaviour
• posterior pituitary gland

  • ADH released to kidney tubule
  • oxytocin released to mammary glands and uterine muscles
• thyroid is a butterfly like structure
• centre of thyroid is the isthmus
• left and right lobes of the thyroid
• thyroid function 


  make T3 and T4 hormones
• T4 has 4 iodine atoms, T3 has 3 iodine atoms
• thyroid

  labels

  A) thyroid follicle

  B) follicle cells

  C) thyroglobulin

  D) C cell

  E) capillary

  F) capsule

  
• C cells are important for calcium homeostasis
• synthesis of thyroid hormones

  • Pump on surface of follicle imports iodide ion from blood into cell
  • Diffuse from basil to apical surface
  • Synthesise thyroglobulin which is rich in tyrosine amino acids
  • Iodide ions are oxidised to atoms, via thyroid peroxidase
  • iodine atoms enter the thyroid follicle
  • thyroglobulin is released via exocytosis into thyroid follicle
  • iodine reacts with tyrosine
• TSH stimulates

  • iodide uptake
  • thyroglobulin and thyroid peroxidase synthesis
  • uptake of thyroglobulin
• thyroid hormones function

  • development (metamorphosis in frogs, bone formation, brain)
  • metabolism (metabolic rate increase, ATP production, stimulate glycolysis, increase HR and BP)
• congenital hypothyroidism

  • poor skeletal and nervous system development
  • low body temperature
  • low metabolic rate
• hypothyroidism in adults

  • lethargy
  • muscle weakness
  • subcutaneous swelling
  • enlarged thyroid
  • can be caused by low dietary iodine
• hyperthyroidism

  • high HR and BP
  • CNS effected-excitability, restlessness, mood swings
• C cells

  • produce calcitonin
• calcitonin function

  • released when high calcium levels in the blood
  • inhibits osteoclast activity (bone breakdown)
  • increases uptake of calcium into bones
  • decreases blood calcium levels
• parathyroid hormone and calcitonin control calcium levels
• parathyroid is behind the thyroid
• parathyroid gland contains

  • chief cells (PTH)
  • oxyphil cells