Hormone synthesis and action Flashcards
The endocrine system
A system of ductless glands and cells that secrete hormones, regulating many physiological processes eg. metabolism, homeostasis and reproduction.
Organs of the endocrine system
- hypothalamus
- pituitary gland
- pineal gland
- thyroid gland
- parathyroid glands
- thymus
- heart
- adrenal glands
- kidney
- digestive tract
- pancreas
- adipose tissue
- testes
- ovaries
Types of glands
- endocrine; secrete hormones directly into the blood, ductless
- exocrine; release their secretions outside of the body, may have ducts
- mixed glands; have both endocrine and exocrine function eg. pancreas
Homeostasis
The monitoring and maintenance of a constant internal environment, coordinated by the nervous and endocrine systems.
Endocrine/nervous system comparison
- endocrine; uses hormones, effect is slow, long-lasting and more widespread
- nervous; uses neurotransmitters, effect is rapid, short-lived and very localised
Hormone action
Hormones are secreted directly into the blood, where they travel to their target organ and bind to specific receptors on target cell membranes, effecting a response.
Mechanisms of chemical signalling
- intracrine; acts within the same cell
- autocrine; acts on the same cell
- paracrine; communication between neighbouring cells
- endocrine; involves the secretion of hormones directly into the bloodstream for transport to a target organ
Negative feedback
The process by which the body senses change and activates a method to reduce it.
Positive feedback
The process by which the body senses change and activates a method to amplify it.
Endocrine axis
The functional grouping between endocrine glands eg. the hypothalamo-pituitary-adrenal axis (HPA axis). The target tissue for one hormone may be another endocrine gland on the same axis.
Tropic hormone
A hormone that stimulates another endocrine gland.
3 main groups of hormones
- protein/peptide hormones
- steroid hormones
- amine hormones
Protein/peptide hormones
- made of chains of amino acids
- hydrophilic=can be transported in the blood, but cannot pass through the cell membrane (require a receptor)
- produced on RER ribosomes as large precursor molecules
- preformed and stored in vesicles, ready for release by exocytosis
eg. TRH, ACTH
Steroid hormones
- made from cholesterol
- lipophilic= can pass directly through the cell membrane but cannot be stored
- synthesised in the smooth ER as required and diffuses out of cell
- eliminated by inactivating metabolic transformations and excretion in urine or bile
eg. aldosterone, cortisol, androgens, sex hormones
Amine hormones
- made from tyrosine derivatives bound together
- small, non-polar molecules= soluble in plasma membranes
eg. T3, T4
Hormone transport in the blood
Peptide hormones are freely water soluble, so can be transported in the blood. Steroid and amine hormones need to be transported by either a specific or non-specific binding protein.
Action of hormones
Peptide hormones bind to cell surface receptors, activating a secondary messenger cascade within the target cell. Steroid hormones are recognised by intracellular receptors, where they bind to effect a response.
Causes of endocrine disorders
- Overproduction of hormone
- Underproduction of hormone
- Insensitivity to hormone
