Lecture 1: Introduction to the Endocrine System Flashcards
What is 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 from the site of hormone synthesis, where they influence the activity of that target organ.
what systems communicate with and control all body functions?
endocrine and nervous
describe the process of endocrine communication
- hormones travel in the blood to their target organs/tissues.
- tissues detect hormones through the presence of specific receptors for that chemical on/in the cells. No receptor = no response.
describe the process of neural communication
- neurotransmitters released frm presynaptic neurons travel across the synaptic cleft to the postsynaptic cell to influence its activity.
- neurotransmitter is the chemical released by the neuron but, in contrast to hormones, acts locally within the synaptic cleft.
describe the process of neuroendocrine communication
- endocrine and nervous systems combine.
- nerves release hormones which enter blood and travel to their target cells e.g. hypothalamic - posterior pituitary axis.
give an example that demonstartes that the same hormone can have different effect in different target cells
what are the three categories of endocrine hormones?
- peptide or protein hormones - composed of chains of amino acids (most common)
- amine hormones - all derived from one of two amino acids (tryptophan or tyrosine)
- steroid hormones - all derived from cholesterol
give examples of peptide hormones
- thyrotropin releasing hormone (TRH)
- follicle-stimulating hormone (FSH)
- INSULIN
what are peptide hormones synthesised as and then cleaved into?
- synthesised as preprohormone in advance of need then cleaved into prohormone and stored in vesicles until required.
how are peptide hormones activated from their inactive storage form (prohormone)?
- 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 plasma (co-secretion).
describe C-peptide
- C-peptide is the inactive fragment cleaved from the insulin prohormone.
why are levels of C-peptide in plasma or urine measured?
- to indicate endogenous insulin production from the pancreas (produced in equal amounts).
- however, because insulin is metabolised faster, levels of c-peptide are typically about 5x higher than endogenous insulin.
why measure c-peptide levels and not insulin directly?
C-peptide doesn’t affect your blood glucose levels, but it stays in your blood longer than insulin, so it’s easier to measure accurately.
are peptide hormones hydrophobic or hydrophilic?
hydrophilic, water-soluble
most peptide hormones target which types of receptors?
GPCR or tyrosine-kinase linked receptors
