hormone synthesis and action

Question 1

What are glands, hormones and target tissues?

Answer 1

• Glands
  ○ Endocrine -releases the secretions inside the body from cells (ductless glands)
  ○ Exocrine-releases the secretions outside the body e.g. sweat or digestive juices (into a ducts sometimes)
  ○ Mixed- e.g. Pancreas produced digestive juice + insulins, glucagon and somatisation
  
  • Hormones
    ○ Are secreted directly into the blood by specialised cells
    ○ Carried in the blood to receptors on target organs (can be endocrine, autocrine, paracrine)
    ○ Hormones are present in only minute concentrations in the blood and bind to specific receptors in target cells to influence cellular reactions
    § Must have a receptor for the hormone to have a response
    ○ Intracrine
    § Cell relaces hormone and it doesn’t exit instead acts on the same cell (often seen in cancers)
    ○ Autocrine
    § Cell relaces hormone and it does exit instead acts on the same cell (often seen in cancers)
    ○ Paracrine
    § Chemical communications between neighbouring cells within a tissue or organ
    ○ Endocrine and Neurocrine
    § released by specialised group or cells into the circulatory system to effect a different target organ
  • Target tissue
    The tissue that is effected by the hormone

Question 2

What are the 3 major groups of hormones and outline their synthesis, storage, transport to the target organs and how they react with specific receptors in or in the target organ?

Answer 2

• Protein/peptide hormones
  ○ Most common type
  ○ Hydrophobic so cant not diffuse into the cell but won’t need any help to move abound in the blood (no careers needed in the blood but will need surface receptors on the cell membrane as it is very large and can’t get in the cell)
  ○ Can be performed and stored in membrane bound vesicles readily for release by exocytosis
  ○ Produced on ribosomes (RER) as large precursor molecules (pre prohormone)
  ○ Pre prohormone turns into prohormone goes to hormone
  § Conversion take place by Big protein is chopped up into the active hormone (peptides will low molecular weights)
  ○
  • Steroid hormones
    ○ Made from cholesterol so is hydrophobic/lipophilic
    ○ From adrenal cortex and sex hormones
    ○ Hydrophobic so can’t be stored in the cell so when are synthesis are removed from the cell and doesn’t like to be in the blood as it is not water soluble and will need a transporter
    ○ Ca simply diffuse into cel so no receptor needed and can have intrinsic effect
    ○ Made in the smooth endoplasmic reticulum form cholesterol form diet o acetate
    ○ Not stored in body that much as they are rapidly secreted and then moved in the urine
    ○
  • Amine hormones
    ○ Act on the cell surface
    § Tyrosine derivatives bound together.
    § Contain 4 iodine atoms (T4).
    § Contain 3 iodine atoms (T3).
    § Small, non-polar molecules.
    □ soluble in plasma membranes
    ○ Water soluble
    ○ Steroid and thyroid hormones need to be transported in blood by carrier protein to:
    1. increase solubility in blood
    2. increase half-life
    3. create readily accessible reserve in blood
    ○ Specific binding proteins e.g.Thyroid binding globulin (TBG) and cortisol binding globulin (CBG).
    ○ Non-specific binding proteins e.g. Albumin - loose binding.
    ○ Aldosterone binds to albumin.
    ○ Bound and free hormone are in equilibrium
    ○ Receptors are within the cytoplasm (intracellular receptors)
    ○ Belongs to the thyroid/steroid hormone family
    ○ Hormone-receptor complex binds to specific ‘hormone response elements (HREs)’ in the promoter region of specific genes. This results in modification of gene transcription and protein synthesis
    ○ These receptors are therefore described as ‘ligand-inducible transcription factors

Question 3

What is the role of the feedback and endocrine axis in endocrine relation?

Answer 3

• Feedback= body will respond to a change
  ○ Negative = decrease change
  § process by which body senses change and activates mechanism to reduce it.
  § The final product of an endocrine cascade acts to inhibit the release of hormones higher up the cascade
  ○ Positive = increace change
  § process by which body senses change and activates mechanism to amplify it
  
  • Axis
    ○ How does the hormone effect the tissue
    ○ The target tissue for one hormone may be another endocrine gland (a tropic hormone stimulates another endocrine gland) This functional grouping of endocrine glands is called an endocrine axis (e.g. Hypothalamo-pituitary-adrenal (HPA) axis)
    ○ Faults may occur along this axis
    ○