Endocrinology Flashcards
What is a hormone?
Chemical messengers released from one tissue, carried in the circulation that produces a specific, receptor-mediated change in another tissue
Name four major actions of hormones
Development: proliferation, growth, differentiation, organogenesis
Metabolism: Energy storage, metabolic rate, temperature
Reproduction: Sexual maturation, pregnancy, lactation
Fluid homeostasis: water balance, electrolye balance, blood volume and blood pressure
What are the characteristics of peptide hormones and catecholamines?
Rapid changes in plasma concentration
Short plasma half-life (secs to mins)
Receptors on the cell membrane
Act via second messengers to change enzyme activity
Promote secretion from granules/vesicles.
Effects are rapid
What are the effects of steroid hormones and thyroid hormones
Slow fluctuations in plasma concentration
Long plasma half life (mins to days)
Intracellular receptors
Passage is direct and rapid (related to secretion rate)
Alters gene transcription, Stimulates protein synthesis
Effects are slow (take hours to days)
Describe the synthesis of protein and peptide hormones
Peptide-derinved hormones are synthesised and stored in advance of need.
Most peptide hormones are synthesised from larger precursors (preprohormone)
After the gene is transcribed, the peptide is synthesised with a prepeptide or signal peptide at the N-term that directs it to the RER.
The prepeptide is cleaved off in the RER to form the prohormone.
This then undergoes post-translational procesessing by golgi apparatus and is proteolytically cleaved to yield the active hormone which is packaged into secretory vesicles.
Describe the synthesis of steroid hormones
Steroid hormones are synthesised and secreted on demand.
Cholesterol is the starting material for the synthesis of steroid hormones which is stored in the form of cholesterol esters within lipid droplets inside the cell.
Cholesterol esters are hydrolysed by enzymes to generate free cholesterol that enters the mitochondria.
Inside the mitochondria, cholesterol molecules bind to cholestrol cleaveage enzymes on the mitochondrial membrane where it is remodelled into pregnolone.
Pregnolone leaves the mitochondria and enters the SER where it is remodelled by enzymes into the relevant steroid hormone.
The final steroid hormone can then diffuse out of the cell.
Name three hormones that are derived from tyrosine
Dopamine
Norepinephrine
Epinephrine
Thyroid hormone
Name five hormones that are derived from cholesterol
Progesterone
Oestradiol
Testosterone
Aldosterone
Cortisol
What are the endocrine actions of cortisol (8 points)
Facilitates foetal maturation
Maintains cardiac output (decreases endothelial permeability and increases arteriolar tone)
Inhibits the inflammatory immune response
Increases GRF and water clearance in the kidneys
Stimulates the release of amino acids from muscles (decreases muscle mass)
Increases blood glucose: stimulates gluconeogenesis, inhibits glucose uptake by GLUT4
Inhibits osteoblast function, (decreases new bone formation, increases bone resorption)
Inhibits fibroblast proliferation and collegen synthesis
Hormones produced by the posterior pituatury gland
Oxytocin
Vasopressin
Hormones produced by the anterior pituatory gland
Adrenocorticotrophic hormone (ACTH): control secretion of adrenal steroids
Thyroid stimulating hormone:controls release of thyroid hormones. Controls growth, development and thermogenesis
Growth hormone: antagonises effects of insulin, promotes growth of bone, soft tissue and viscera
FSH
LH
control sexual differentiation (ovaries and testes), behaviour and fertility
Prolactin: promotes mammary growth, development and lactation
Hormones produced by the adrenal cortex
glucocorticoids (cortisol)
mineralocorticoids (aldosterone)
sex hormones (testosterone
Hormones released by the hypothalamus
Corticotrophin releasing hormone (ACTH release)
Thyrotrophin releasing hormone (TSH and prolactin release)
Growth hormone releasing hormone ( GH release)
Gonadotrophin releasing hormone (LH and FSH release)
Somatostatin/GHIH (inhibits GH and TSH release)
Dopamine (inhibits prolactin synthesis and release)
Hormones are released fromthe hypothalamus in response to neural inputs from other areas of the CNS
What are the four types of hormonal control?
Endocrine
Neuroendocrine
Paracrine
Autocrine
How do hormone receptors help to regulate endocrine responses?
Hormone effects are mediated by specific high affinity receptors and can therefore bind the hormone when levels in the circulation are low
Receptors are often inactivated or destroyed after binding its hormone. This decreases the responsiveness of the target cell to the hormone. Reactivation or upregulation re-sensitises the target cell.