Unit 2 BHS: Endocrine Flashcards
Endocrine glands
Effectors/ responsive body parts under the stimulation from the autonomic nervous system
Hormones
- Chemicals that alter the metabolism of many cells, under negative feedback control.
- Secreted by a cell or group of cells
- Transported to target cells
- Acts by binding to receptors
- Regulates metabolic functions of other cells in the body
- Exerts effects at very low concentrations
- Action must be terminated
Target cells
Peripheral cells that respond to a particular hormone, hormones circulate all tissues but only activate target cells.
Receptors
A protein in the cell membrane or within the cytoplasm or nucleus. Target cells must have specific receptors to which the hormone binds to trigger its action.
Major regulatory functions of the endocrine system
- Growth, metabolism, tissue maturation
- Blood glucose and other nutrients in the blood
- Blood ion concentrations (Ca, Na, K)
- Water balance
- Heat rate and blood pressure
- Immune function
- Reproductive function
- Uterine contraction and milk release
Compare the nervous system and endocrine system
- Cells: Neurons vs. Glandular epithelium
- Chemical signal: Neurotransmitter vs. Hormones
- Specificity of action: Receptors on postsynaptic cell vs. receptors on target cell
- Speed of action: Seconds vs. Seconds to hours
- Duration of action: Very brief vs. Brief or may last for days
General characteristics of hormones
- Potent
- Produce long-lasting effects in the target cells
- Regulate metabolic processes (maintain homeostasis)
- Regulated by negative feedback mechanisms
Three groups of hormones
- Amino acid derivatives
- derived from tryptophan or tyrosine - Peptide hormones
- small chains of amino acids, mostly synthesised as pro hormones and some are glycoproteins - Lipid derivatives
a) steroid hormones
b) eicosanoids
- derivatives of lipids such as arachidonic acid and cholesterol
Two major classes of hormones
- Water-soluble hormones
- hydrophilic
- incl. proteins, peptides and amino acid derivatives
- amino acid based
- molecular size varies (peptides vs. proteins)
!! short half-life !! - Lipid-soluble hormones
- lipophilic
- steroids, thyroid hormones, eicosanoids
- bound to carrier molecules in the blood which allows transport of the hormone; protect hormone from enzymatic degradation. carriers are dissociated before hormone entering the cell.
!! long half-life !!
Determinants of blood hormone levels
- rate of secretion
- rate of metabolic activation or conversion
- mode of transport
- inactivation by
a) binding to cell receptors
b) removal by liver, kidney
c) breakdown by extracellular enzymes - excretion
Regulation of hormonal secretion
- Hormonal stimuli - endocrine glands activated by other hormones
- Humoral stimuli - changing blood levels of certain ions and nutrients stimulates hormone release
- Neural stimuli - nerve impulses stimulates hormone release, most under SNS control
Hormone interactions
Responsiveness of hormone on target tissue depends on:
- concentration
- effects of other hormones on the target tissue
Hormones may:
- antagonise each other or
- produce effects that are additive or complementary
INTERACTIONS
1. Permissive effect - one hormone cannot fully exert its effects without the presence of another. The second hormone can act to enhance the responsiveness of the target tissue or increase the activity of the another hormone. e.g. reproductive hormones and thyroid hormones
- Synergistic effect - the combined effect of two or more hormones is greater than the sum of each individual effect. e.g. glucagon, epinephrine, and cortisol
- Antagonistic effect - one hormone diminishes the effect of another. e.g. insulin vs. glucagon. Antagonists may compete for the same receptor, act on different cellular pathways or reduce the target cell sensitivity.
Outline the mechanisms of hormone action
- hormones acts on target cells by binding to their receptors.
- brings about effects on target cell by altering cell activity (increase of decrease in cellular activity)
- response depends on target cell type
- depends on the chemical nature of hormone (water vs. lipid soluble) and cellular location of receptor (plasma membrane or intracellular)
Effects of hormone stimulation
- alter membrane potential or plasma membrane permeability
- stimulates synthesis of proteins or regulatory molecules (enzymes)
- activates or deactivates enzymes
- induce secretory activity
- stimulate mitosis
Nonsteroid hormone action
- hormone binds to receptor on cell membrane and acts as first messenger
- results is either increase or decrease in some second messenger
- second messenger activates protein cascade, leading to cellular changes
- commonly G-protein - cAMP
