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
