BI0005 - Lecture 5 - Endocrine system

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  1. What is endocrinology?
    The study of the endocrine system.
  2. What is the endocrine system?
    It is one of the two basic systems for communication and regulation throughout the body (the other being the nervous system) and has the function of chemical signaling by hormones.
  3. What is neuroendocrinology?
    The study of the control of the endocrine system by the nervous system.
  4. What is neuroendocrine integration?
    How the nervous system and the endocrine system interact in order to maintain homeostasis in the body.
  5. What is homeostasis?
    Homeostasis is the property of a system in which variables are regulated so that internal conditions remain stable and relatively constant.
  6. What is a hormone?
    • A hormone is a molecule that is secreted into the extracellular fluid, circulates in the blood or hemolymph, and communicates regulatory messages throughout the body.
    • A hormone elicits a specific response - such as a change in metabolism - from its target cells, whereas cells lacking a receptor for that particular hormone are unaffected.
  7. Where are hormones produced and secreted?
    Hormones are secreted into extracellular fluids by endocrine cells. Some endocrine cells are grouped into ductless organs called endocrine glands. 
  8. Ductless glands have...
    ...a rich blood supply
  9. Where do hormones bind?
    • To receptors on their target cells.
    • Although the circulatory system allows a hormone to reach all cells of a body, only its target cells have the receptors taht enable a response.
    • If the appropriate receptor is not present on a cell, the hormone cannot affect it.
  10. What types of chemical substances can hormones be?
    • Steroids,
    • Peptides/proteins
    • Amines
  11. Briefly describe steroid hormones.
    • Synthesized in the adrenal cortex, ovaries, testes, and placenta.
    • Not very soluble in blood - transported bound to proteins.
    • Fat soluble, cross membranes easily, diffuse out of cells, not much stored intracellularly
    • Have intracellular receptors
    • Easily absorbed in GI tract - administered orally.
    • E.g. Cortisol
  12. Briefly describe protein/peptide hormones
    • Synthesised as 'prehormones' or 'preprohormones'
    • Stored in membrane-bounded Vesicles/granules
    • Circulate in the blood unbound
    • Have cell membrane receptors
    • Cannot be administered orally
    • e.g. Insulin
  13. Briefly describe Thyroid amine hormones.
    • Derived from tyrosine
    • Cross cell membranes
    • Have intracellular receptors
    • Transported protein-bound
    • Stored in thyroid follicles
    • Administered orally
  14. Briefly describe Catecholamine amine hormones.
    • Derived from tyrosine
    • Do not cross the cell membranes
    • Have cell membrane receptors
    • Transported free
    • Stored in membrane-bounded vesicles/granules
    • Could be administered orally, but half-life is too short.
  15. Whilst transporting hormones to their target cells, why are hormones bound to proteins?
    • It prolongs their circulating half-life
    • It prevents them from entering the wrong cell type.
    • It prevents them from being lost through the kidneys
    • It maintains the right concentration of hormone
    • It acts as a "buffer" against a drop in the secretion of a hormone
  16. How do hormones act on target cells?
    • The binding of a hormone to a receptor protein triggers intercellular cell-signalling events.
    • This involves the synthesis of cyclic AMP (cAMP) as a short-lived secondary messenger
  17. What are secondary messengers?
    • Second messengers are molecules that relay signals from receptors on the cell surface to target molecules inside the cell, in the cytoplasm or nucleus.
    • They relay the signals of hormones like epinephrine (adrenaline), growth factors, and others, and cause some kind of change in the activity of the cell.
    • They greatly amplify the strength of the signal.
  18. What are some examples of endocrine glands?
    • Pituitary gland
    • Thyroid gland
    • Adrenal gland
    • Testis
    • Pineal gland
    • Thymus
    • Pancreas
    • Ovary
  19. Thyroid gland
    • Hormones
    • Thyroxine (T4) - 90%
    • Triidothyronine (T3) - 9%
    • Reverse T - 1%

    • Effect
    • Stimulates and maintains metabolic processes
    • Lowers blood calcium levels
    • For maturation, development and growth (bones, brain...)
    • Role in cardiovascular system
  20. Adrenal medulla
    • Hormones
    • Epinephrine and norepinephrine
    • (OR adrenaline and noradrenaline)

    Act on alpha and beta adrenoceptors

    • Effect 
    • Raises blood glucose level;
    • increases metabolic activities
    • constricts certain blood vessels
  21. Adrenal cortex
    Hormones and effect

    • Mineralocorticoids - e.g. aldosterone
    • Regulates mineral metabolism - retention of Na+ and water resorption by kidney

    • Glucorticoids - e.g. cortisol
    • Regulates blood glucose levels

    • Sex hormones
    • e.g. weak androgens that can be converted into more potent sex hormones such as testosterone and oestrogens, especially in women.
  22. Pancreas
    • The pancreas is both an exocrine and an endocrine gland.
    • The endocrine part of the Pancreas are called Islets of Langerhans.

    In the Islets of Langerhans:

    Alpha cells produce glucagon - a catabolic hormone which can mobilise stores of glycogen, fat, and protein to act as energy sources during food deprivation.

    Beta cells produce insulin - an anabolic hormone which causes the uptake and use of glucose from the blood during times of excess nutrient availability.

    Delta cells - produce somatostatin (inhibits growth hormones) and gastrin.
  23. Briefly, how are blood sugar levels regulated by the pancreas?
    Low blood glucose --> Glucagon released by beta cells of pancreas --> Liver releases glucose into the blood --> Normal blood glucose levels achieved.

    High blood glucose --> Insulin released by alpha cells of pancreas --> fat cells take in glucose from blood --> Normal blood glucose levels achieved
  24. Briefly comment on calcium in the body.
    Calcium (Ca2+) has many vital roles in the body but the levels of Ca2+ MUST be tightly regulated otherwise it can become very toxic to cells.

    99% of Ca2+ is found in the bones and teeth. 0.9% Ca2+ occurs intracellularly and 0.1% Ca2+ is found in the ECM.

    • About half of the free Ca2+ is bound to proteins or with PO43- - only the remaining half of Ca2+ is freely diffusible and can take part in chemical reactions.
    • This is the part that must be regulated
  25. Briefly comment on the effect of calcium in the body.
    Decrease in Ca2+ results in over excitability of nerves and muscles

    Increase in Ca2+ depresses excitability of nerves and muscles

    Ca2+ entry into cardiac and smooth muscles initiates the contractile mechanism.

    Ca2+ entry into nerve terminals and cells that secrete peptide hormones triggers the secretory process.
  26. What does parathormone (PTH) do?
    Parathormone (PTH) produced by the parathyroid gland is vital for life as it increases Ca2+ levels and prevents hypocalcaemia

    • It regulates the exchange of Ca2+ between bone, kidneys and the intestine.
    • Calcitonin and vitamin D are also involved.
  27. What are sertoli cells and leydig cells in the testes?
    Sertoli cells are involved in the maturation of sperm by producing peptides that act as hormones.

    Leydig cells produce testosterone: steroid hormone, an androgen.
  28. What are the effects of testosterone?
    • Before birth
    • Regulates differentiation and development of internal and external genitalia

    • At puberty
    • Regulates growth and maturation of the internal and external genitalia
    • Development of secondary sexual characteristics (hair, deep voice, muscle growth)
    • Initiates and maintains spermatogenesis
    • Develops sex drive

    • Other effects
    • Aggression
    • Bone growth and fusion of epiphyses
  29. Ovaries
    • Produce eggs (oogenesis)
    • Secrete the female sex hormones oestrogen and progesterone
    • O and P help to promote fertilization and get reproductive system ready for pregnancy
    • Functions of oestrogen is similar to those of testosterone.
  30. Comment on female reproductive endocrinology.
    • Menstrual (ovarian) cycle
    • Controlled by a very complex series of interactions between hormones.
    • Synthesised by the ovary, the anterior part of the pituitary gland and the hypothalmus of the brain.

    • Endocrinology of pregnancy
    • Development of the placenta
    • Implantation of the fertilized ovum
    • Birth (parturition)

    • After birth
    • Breast feeding and lactation
    • Parental care
  31. The pituitary gland
    The posterior pituitary gland is attached to the hypothalmus at the base of the brain - stimulates contraction of uterus and mammary gland cells - promotes retention of water by kidneys

    The anterior pituitary gland (or adenohypophysis) regulates several physiological processes (including stress, growth, reproduction, and lactation)

    The pituitary gland secretes nine hormones that regulate homeostasis
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BI0005 - Lecture 5 - Endocrine system
2014-05-07 08:23:09
BI0005 Lecture
BI0005 - Lecture 5
BI0005 - Lecture 5
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