Diabetes & Endocrinology Welcome - Introduction and Case Launch Flashcards
Define the endocrine system
- A system that integrates and controls organ function via the secretion of chemicals (hormones) from cells, tissues or glands which are then carried in the blood to target organs, distal to the site of hormone synthesis, where they influence the activity of that target organ
Which 2 systems communicates with and controls all body functions?
- Endocrine system
- Nervous system
(a) What type of cell is shown on the left?
(b) What is represented by the red diamonds?
(c) Why does the cell on the right produce no response
(a) Endocrine cell
(b) Hormones (being secreted into the blood)
(c) Does not contain the specific receptor for the hormone to bind to therefore no response (therefore it is NOT the target cell)
What type of cell is shown here?
- Target cell (becuase it contains the specefic receptor for the hormone to bind to, therefore producing a specefic response)
What is shown by the red diamonds in this picture?
- Neurotransmitter
(neuronal communication shown here)
(a) What type of communication is shown here?
(b) Describe what is going on here
(a) Neuroendocrine communication
(b) Nerves release hormones which enter the blood and travel to their target cells e.g hypothalamic - posterior pituitary gland
All hormones circulate throughout the body in the blood.
True/False
- True
The same hormone has the same/different effects in different target cells.
DIFFERENT EFFECTS
What are the 2 responses at the bottom?
Glycogenesis = The formation of glycogen from sugar
Endocrine hormones exert their effects at very low/high concentrations
VERY LOW CONCENTRATIONS
(act in the range 10-9 - 10-12 M)
How can endocrine hormones have their actions terminated?
- Via negative feedback loops
State the 3 classifications of endocrine hormones and give a short description of each
- Peptide hormones (composed of chains of amino acids)
- Amine hormones (derived from 1 or 2 amino acids, mainly tyrosine)
- Steroid hormones (derived from cholesterol)
Peptide hormones: Preprohormones and prohormones
- The initial peptide hormone prodcued by ribosomes is large and inactive: PREPROHORMONE
- Preprohormones contain 1 or more copies of the active hormone in their in their amino acid sequence
- Preprohormones are cleaved into smaller units in the endoplasmic reticulum to leave smaller but still inactive proteins called prohormones
- Prohormones are packaged into vesicles in the golgi apparatus, along with proteolytic enzymes which break the prohormone down into active hormone and other fragments
- Hormones and fragments are stored in vesicles in the endocrine cells until release is triggered then all vesicle contents are released into the plasma (co-secretion)
- Measuring inactive fragments in plasma can be clinically useful e.g C-peptide in diabetes
What is C-peptide?
- Inactive fragment cleaved from insulin prohormone that is measured to indicate endogenous insulin production from the pancreas
State why levels of C-peptide are typically about 5x higher than endogenous insulin
- Insulin is metabolised faster
Descibe the mechanism of action of peptide hormones
- Peptide hormones are water soluable therefore are easily transported in the blood
- Water solubility however means the peptide hormone CANNOT cross the cell membrane therefore they bind to membrane bound receptors on the target cell
- Once the peptide hormone binds to the receptor, this activates either a G protein coupled receptor or tyrosine kinase linked signalling pathways
- G proteins activate a 2nd MESSENGER leading to the modification of existing proteins
- Tyrosine kinase alters gene expression but works much slower than G proteins
Most amine hormones are derived from what?
- Tyrosine
Which amine hormone is not derived from tyrosine?
- MELATONIN (derived from tryptophan)
How are steroid hormones transported in the blood and why is this needed?
- Transported via the carrier protein ALBUMIN or Thyroxine-binding globulin
- Needed because steroid hormones are poorly soluble in water
- This also stabalises their transport through the plasma and protects them from enzymatic degredation, phenomenally inreasing their half-life (60-90 mins vs 2 mins for amine hormones)
(e. g the protein carrier in this picture in ALBUMIN)
State some places in the human body where steroid hormones are produced.
- Placenta (hCG, sex steroids)
- Adrenal cortex (corticosteroids)
- Kidneys (Vitamin D3)
- Gonads (testes and ovaries - sex steroids)
Descibe the mechanism of action of steroid hormones
- Steroid hormones are hydrophobic therefore they cross the plasma membrane easily
- Therefore the receptors for steroid hormones are located inside the cell (either in the cytoplasm or nucleus) and activate or inhibit gene function within the nucleus (genomic effect)
- Becuase genes control the synthesis of proteins, these hormones either increase or decrease protein synthesis
(this is a slow process so there is a lag between the hormone release and biological effect but the effect persists for about the same time)
State the importance of some steroid hormones being unbound in the plasma membrane
- To allow them to cross the membrane to enter the cell
(remember: the bound:unbound ratio must be maintained)
- Endocrine pathways respond to (2)
- Negative feedback reflexes e.g parathyroid hormones
- Neural feedback loops e.g adrenaline
