Week 6 (endocrine system) Flashcards
What does the endocrine system do?
Controls many/most aspects of physiology, via the secretion of hormones.
Name the 2 systems that are considered to be the major control systems of the body?
Endocrine
Neuronal (nervous)
What systems does the endocrine system interact with?
Nervous
Cardiovascular
Digestive
Immune
What is a hormone?
A chemical messenger that is secreted and transported into the blood to act on distant targets.
Why are hormones found at low concentrations in the blood?
Due to the specific receptor binding on the target cell.
How are hormones grouped?
By biochemistry and physiological function
Describe endocrine signalling
Hormones travel from the endocrine cell into the blood supply and act on the target cell.
Describe neuroendocrine signalling
Some nerves act as hormones producing cells.
They release hormones into the bloodstream instead of neurotransmitters.
Describe autocrine signalling
Cell that produces a signalling molecule.
Hormone is released and acts on the same cell.
Describe paracrine signalling
Hormone acts on the adjacent cell in the tissue from the cell that the hormone was released from.
Name the 3 main groups of hormones in terms of their biochemical function
Amino acid derivatives (tryptophan, tyrosine)
Peptides (TRH, growth hormone)
Steroids
Name the 4 main groups of hormones in terms of their physiological function
Reproduction
Energy balance
Growth and development
Homeostasis
What are endocrine glands?
Ductless glands that secrete hormones into the blood.
Located throughout the body.
Often contain multiple cell types, which have different function.
Name the major endocrine organs
Hypothalamus
Pituitary gland
Thyroid gland
Adrenal gland
Pancreas
Testes
Ovaries
Name and describe 3 other important endocrine organs
- Pineal gland (secretes melatonin and is important for biological rhythms)
- Adipose tissue and gastrointestinal tract (secrete many hormones involved in energy balance and metabolism)
- Placenta (secretes hormones involved in foetal and maternal development)
Define heterogeneity
Amount of variation within a subject
Define homogeneity
Uniformity of a subject
What is required to allow proteins to become fully functional?
Further processing after translation.
Variety of modifications.
Name and describe two post translational modifications
Preprohormones: inactive precursor from a single gene is cleaved into active compounds.
Dimerization: subunits from different genes combine to form an active product.
Describe the secretion of steroid hormones
Steroids are lipophilic.
They are synthesised from cellular lipid stores only when required and not stored as active hormone within cells.
They diffuse across the cell membrane into the blood, so no active secretory mechanisms.
One in the blood they are mostly transported bound to plasma proteins.
How do intra-cellular signalling molecules regulate target cells?
By binding to specific proteins, called receptors.
Name the two types of receptors
Membrane-bound receptors
Intracellular receptors
What type of receptors do peptide hormones bind to?
Membrane bound
What type of receptors do steroid hormones bind to?
Intracellular
Describe the membrane-bound receptors
Mechanisms of action for hydrophilic peptide and amine hormones.
Many different types but all have 3 basic domains; extracellular, transmembrane, intracellular.
Describe the intracellular receptors
Mechanism of action for steroids and thyroid hormones.
Stimulate gene expression.
What is the pituitary gland important for?
Acting as a gateway between central and peripheral endocrine organs.
How many major endocrine cell types are there?
5
What do the major endocrine cell types have?
A regulatory control from hypothalamus via inhibitory and/or releasing factors.
Describe the hypothalamic regulation of the anterior pituitary gland
Pituitary portal system transfers releasing and inhibitory hormones from hypothalamus to anterior pituitary.
Describe the hypothalamic regulation of the posterior pituitary gland.
Hormones are secreted directly from the cells in the hypothalamus down the axon to the posterior pituitary, and then into the systemic blood supply.
Describe the negative feedback loop
Imposes ‘brakes’ on system.
Important for homeostasis.
Common in physiology.
Takes things back to normal conditions.
Describe the positive feedback loops
Amplifies orginal signal.
By itself, not compatible with homeostasis.
Rare, but useful in certain circumstances (e.g., childbirth) when a large response is required.
Requires cut-off mechanism.
Takes things further away from normal conditions.
Describe the LH surge (positive feedback loop)
Oestrogen usually inhibits LH secretion via negative feedback.
But oestrogen surge occurs around day 12 of cycle.
High oestrogen drives change from negative to positive feedback.
Positive feedback causes LH surge, which induces ovulation.
After ovulation, drop in oestrogen concentration causes resumption of negative feedback and thus LH/FSH secretion falls.
