Endocrine System 1 Flashcards
Endocrine System
- the second great communication system of the body
- allows the body to adapt to both internal and external change
- includes all the endocrine tissues and cells that secrete hormones
Nervous vs Endocrine System
Nervous System:
- direct communication
- quick response
- response to physical and chemical stimuli
- capable of secreting
Endocrine System:
- indirect communication
- slow acting, slow response
- responds to chemical stimuli
- capable of secreting
Characteristics of Nervous and Endocrine Systems
Mediator molecules:
NS - neurotransmitters which are released locally in response to nerve impulses
ES - hormones delivered to tissues throughout the body by blood
Site of mediator action:
NS - close to the site of release, binds to receptor in postsynaptic membrane
ES - far from the sire of release (usually) binds to receptors on or in target cells
Types of target cells:
NS - muscles, cells, gland cells, other neurone
ES - virtually all cells in the body
Onset of action:
NS: typically within milliseconds
ES: seconds or hours or days
Duration of action:
NS: generally brief
ES: generally longer
Functions of hormones
- Help regulate
- chemical composition and volume of internal fluids
- metabolism and energy balance
- contraction of smooth and cardiac muscle fivers
- glandular secretions
- some immune system activities - Control growth and development
- Regulate operation of reproductive systems
- Help establish circadian rhythms
- Mobilise body’s defence against stressors e.g. IL2
Endocrine Glands, Circulating Hormones, Autocrines and Paracrines
Endocrine Glands -ductless -well vascularised -secrete hormones into extracellular/interstitial fluid Circulating hormones -affect distant target cells Autocrines (work on itself) and Paracrines (act on neighbouring cell) -local hormones
Hormone Action
-Hormones are generally delivered to the target tissue via ECF
-Target tissue has specific receptors
-The biological activity of the target tissue is determined by
1. concentration of the hormone
2. receptor
3. receptor affinity (how tightly the hormone binds to the receptor
Up and down regulation: lots of hormone, saturation of receptors, lots of activity, down regulation of receptor, internalisation in membrane (degradation), reduces activity
Up is opposite
Effective plasma concentration
- effective plasma concentration of a hormone is regulated by
- rate of secretion
- transport
- metabolism
- excretion
- shifts in any one of these factors can lead to endocrine disorders e.g.
- hormonal excess
- hormonal deficiency
- decreased responsiveness of the target tissue
Acromegaly
- pronounced brow protrusion
- enlargement of mandible, tongue, teeth gapping
- growth of hands and feet
- soft tissue swelling
Hormone changes
- can alter intellectual capabilities, memory, learning, and emotional states
- affects behaviour when endocrine glands are over secreting or under secreting
Classes of hormones (based on chemical structure)
1. Amino acid derivatives
- small molecules structurally related to amino acids
- synthesized from the amino acids
- tyrosine eg. thyroid hormone, adrenaline, noradrenaline
- tryptophan eg. melatonin from the pineal gland, also serotonin
Classes of hormones (based on chemical structure)
2. Peptide hormones
- chains of amino acids
- synthesized as prohormones
- inactive molecules converted to active hormones before or after secretion
- 2 groups
1. glycoproteins eg. TSH, LH, FSH
2. short polypeptide chains and small proteins e.g. ADH, GH and prolactin
Classes of hormones (based on chemical structure)
3. Lipid derivatives
2 groups
- Eicosanoids
- derived from arachidonic acid e.g. leukotrines, prostaglandins - steroid hormones
- derived from cholesterol e.g. androgens, estrogens, corticosteroids
Transport of hormones
Circulate freely or bound to transport proteins
Free hormones
-remain functional for less than 1 hr
-diffuse out of bloodstream, bind to receptors on target cells
-are absorbed (broken down by cells of the liver or kidney
-are broken down by enzymes in plasma or interstitial fluids
Thyroid and Steroid Hormones
- remain in circulation much longer
- enter bloodstream (more than 99% become attached to special transport proteins)
Mechanism of hormone action
Water soluble hormones
-water soluble hormones act via second messengers
eg. cyclic AMP
-hormone binds to membrane receptor coupled to adenylate cyclase (AC) via G protein
-AC catalyses the synthesis of cyclic AMP
-cyclic AMP changes metabolism (eventually deactivated by phosphodiesterase)
Phosphorylates membrane proteins - opens channels eg ADH
Mechanism of hormone action
Lipid soluble hormones
- bind to and activate receptors in cytosol or nucleus
- activated receptor-hormone complex alters gene expression
- directs synthesis of new proteins
- alters cellular metabolism
