Intro Flashcards
definition of endocrine gland
group of cells which secrete hormone into blood
definition of hormone
bioactive “messenger” secreted by endocrine gland into the blood
(Effect is relatively long compared to nervous system, many target cells)
What are the three classifications of hormones and give examples/ details
1 - Protein/polyoeotide hormone/ a.a. derived
Ex: LH, Insulin, T4, cathecolamines
Synthesis of pro/pre hormone: ex POMC for ACTH then modified in Golgi
2- Steroid hormones
Derived from cholesterol
2 groups: intact steroid nucleus (adrenal/gonadal steroids) and broken steroid nucleus (vit D + metabolites)
Ex: cortisol
3- Miscellanous
Thyroid hormone because iodine
Cut-off between polypeptide and protein?
70 a.a.
Describe protein hormone synthesis
1) Transcription (DNA to mRNA)
2) mRNA migrates to RER.
3) Translation of Pre-Prohormone
4) The Pre-Prohormone migrates through RER and loses signal peptide sequence becomes Prohormone.
5) The Prohormone is stored in a Golgi (storage) vesicle.
6) The Prohormone is broken down into a hormone in golgi through cytoplasm with proteolytic enzymes
7) Secretion via exocytosis – associated with excitation of cells by stimulus and is triggered by Ca2+ influx
Describe steroid hormone synthesis
Derived from cholesterol
LDL’s carry cholesterol to cell which stores it as fatty acid esters
Cholesterol Esterase liberates the cholesterol
Cholesterol taken to mitochondria by Steroidogenic Acute Regulatory (StAR) protein.
Hormone production occurs in mitochondria and smooth endoplasmic reticulum (SER).
Lipid soluble steroid immediately diffuses out of cell
Steroid binds to protein in blood
List the 5 steroid hormones for which cholesterol is a precursor
1) Progestins (e.g. progesterone) - help mediate the menstrual cycle and pregnancy.
2) Glucocorticoids (e.g. coritsol) - affect metabolism of carbohydrate, protein and lipids.
3) Mineralcorticoids (e.g. aldosterone) - maintain salt and water balance.
4) Androgens (e.g. testosterone) - affect maturation and function of secondary sex organs.
5) Oestrogens - promote female sexual development.
Types of plasma proteins
Low affinity high capacity - albumin (so transports general proteins)
High affinity low capacity - binding globulins like CBG (transports specific protein)
Most hormones are secreted into the systemic circulation, except?
hypothalamus releases into hypophyseal portal circulation
Where are protein hormones stored? Steroid hormones?
- in vesicles waiting to be released
- in the blood, bound to plasma proteins (steroid)
Describe protein/polypeptide signalling
Most receptors are G proteins located in plasma membrane:
- The hormone binds to the receptor on the cell membrane.
- The G-Protein dissociates from the receptor (alpha subunit).
- The G-Protein activates the enzyme Adenylate cyclase (AC).
- AC converts adenosine triphosphate (ATP) to cyclic adenosine monophosphate (cAMP).
- cAMP activates protein kinase A (PKA).
- PKA acts as 2nd messenger producing an effect
Describe steroid signalling
IC receptors (cytoplasm/nucleus) Receptor + hormone act as a TF - can influence DNA to mRNA and mRNA translation on ribosome
Where are most steroid hormones produced?
Adrenals and gonads
What enzyme breaks down fatty acid esters?
Esterase
Where does steroid hormone synthesis take place in the cell?
Mitochondrion
