Hormone Synthesis And Action Flashcards
Definition of endocrine system
A system of ductless glands and cells that secrete hormones
Regulates - metabolism, homeostasis and reproduction
List of endocrine glands
Pineal glands
Hypothalamus
Pituitary
Thyroid
Parathyroid
Thymus
Pancreas
Adrenal
Kidney
GIT
Ovaries/ testis
What are Endocrine Glands
Release secretions (hormones) into blood directly from cells - ductless glands
What are exocrine glands?
(Not part of endocrine system) release their secretions outside the body and may be ducted e.g. gut secretions, sweat glands
What are mixed glands?
Pancreas produces digestive juice + insulin, glucagon and somatostatin
What is a hormone?
Hormone is a substance secreted directly into the blood by specialised cells
Hormones are present in only minute concentrations in the blood and bind to specific receptors on target cells
What are the 2 major regulatory systems of the body
Nervous
Endocrine
Comparisons between nervous and endocrine systems
Few NT vs many hormones
Generally rapid vs generally slow
Generally short lived vs generally long lasting
Localised vs widespread
Three mechanisms of chemical signalling
Intracrine
Autocrine
Paracrine
What is intracrine signalling
Generated by a chemical acting within the same cell
What is autocrine signalling
Chemical or hormone secreted
And binds to autocrine receptors on the same cell
What is paracrine signalling
Chemical communication between neighbouring cells
What is the “classical” endocrine and neuroendocrine signalling mechanism
A chemical released by a specialised group of cells int circulation and acting on a distant target tissue
What is feedback control of hormonal release
Process by which body senses change and responds to it
What is negative feedback
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
What is positive feedback
Process by which body senses change and activates mechanism to amplify it
3 main groups of hormones?
Peptide hormones
Steroid hormones
Amine hormones
What is the most common hormone
Peptide hormone
Features of peptide hormones
Made of amino acids
Hydrophilic
Preformed and stored in membrane bound vesicles ready for release by exocytosis
How are peptide hormone synthesised?
Produced on RER as large precursor molecule - “preprohormone”
Matures into prohormone via cleavage of N terminal signal sequences
Bioactive hormone prod as result of enzymatic processing
What are the subunits of pituitary glycoprotein hormones
Alpha subunit - genetic subunit for all hormones
Beta subunit - specific to each hormone
Released from anterior PG
Some hormones secreted from anterior pituitary gland
Thyroid stimulating hormone TSH
Luteinising hormone LH
Follicle stimulating hormone FSH
Growth hormone GH
ACTH
Prolactin
Precursor of steroid hormones
Cholesterol
What is the rate limiting step in the production of steroid hormones
Pregnenolone
CYP11A
Examples of steroid hormones
Adrenal cortex (glucocorticoid and mineral corticoids) and sex hormones (testosterone/ oestrogen)
Features of steroid hormones?
Hydrophobic
Not stored - synthesised as required, then diffuse out of cell
How are steroid hormones synthesised
Hydrolysis of esters and release of cholesterol
Cholesterol to pregnenolone in mitochondria (steroid hormones cannot be stored so stored as precursor)
Processing of pregnenolone in SER
How is the movement of cholesterol to mitochondrion regulated
Regulated by steroid acute regulatory protein (StAR)
ACTH regulates StAR activity and processing of cholesterol
The secretions of different zonas in the adrenal cortex
Zona glomerulosa - aldosterone
Zona fasciculata - cortisol
Zona reticularis - adrenal androgens
How are enzymes involved in the synthesis of specific hormones
Specific tissue contains cells expressing enzymes leading to specific hormone synthesis
What does increase in secretion reflect?
Reflects accelerated rates of synthesis
How are steroid hormones eliminated
By inactivating metabolic transformations and excretion in urine or bile
Features of thyroid hormones
Amine hormones
Small
Non polar
Hydrophobic
Soluble in plasma membranes
Transportation of steroid & thyroid
Binding increases:
- solubility
- half life
Reservoir in blood
Specific binding proteins TBG and CBG
Or non specific binding proteins Albumin - loose binding
Receptors of protein hormones
Cell surface receptors
Activate second messenger cascade and change cellular function
What are the receptors of steroid hormones
Intracellular receptors
Cytoplasm or nuclear
Hormone-receptor complex binds to HRE
Types of endocrine disorders
Hormones in excess
Hormone deficiency
Causes and treatment of excess primary disorders
Hormones in excess:
Often caused by tumours/ exogenous intake of hormone
Treatment - surgical removal of gland
Causes and treatment of insufficiency
Hormones in deficiency:
Primary - primary organ inadequate
Secondary - tropic hormone deficient/ autoimmune destruction
Treatment - replacement therapy
Orally absorbed, long half life
Injection - otherwise degraded in GIT
What is the outcome of deficiency or excess of growth hormone
Deficiency: Dwarfism
Excess: Gigantism
What is the outcome of deficiency or excess of ADH
Deficiency diabetes insipidus
Excess hypervalemia
What is the outcome of deficiency or excess of insulin
Diabetes mellitus
Coma
Examples of peptide hormones
GH
CRH corticotropins
