BIOL126 Lecture Notes - Lecture 2: Osteomalacia, Homeostasis, Libido
8 Jun 2018
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Endocrine System
• Briefly compare the roles of the nervous and endocrine systems in maintaining homeostasis
o Endocrine system
• Made up of endocrine glands which secrete their products (hormones) into the
bloodstream
• Coordinated with the nervous system to provide an integrated control of
homeostasis
• Exocrine glands secrete substances onto an epithelial surface through ducts, e.g.
saliva, sweat, mammary, mucus
• Endocrine glands secrete directly into bloodstream
• Hormones act as blood-borne chemicals for information transfer
• Long distance fast/slow signal transduction (milliseconds - seconds - minutes - hrs
- days - yrs)
• Functions
▪ Regulates metabolism, water and electrolyte balance
▪ Allows body to cope with stress, trauma, infection
▪ Regulates growth
▪ Control reproduction
▪ Regulates circulation and RBC production
▪ Control digestion and absorption of food
o Nervous system
• Neurotransmitters act as local chemicals to transfer information from cell to cell
• Integrates tissue by a network of cell connections
• Short distance, fast signal transduction (milliseconds - seconds)
o Cell-cell communication
• Coordination of cell activities and continuation of life requires cells to communicate
with one another
• Neurotransmitters
▪ Short-range chemical messengers
▪ Diffuse across narrow space to act locally on adjoining target cell (another
neuron, a muscle, or a gland)
▪ e.g. acetylcholine
• Rapidly inactivated by local enzymes (acetylcholinesterase)
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• Hormones
▪ Long range messengers
▪ Secreted into blood by endocrine glands in response to appropriate signal
▪ Exert effect on target cells some distance away from release site
• Neurohormones
▪ Hormones released into blood by neurosecretory neurons
▪ Distributed through blood to distant target cells
▪ e.g. ADH released in response to increase osmolarity and significant BP drop
• Water reabsorption
• Vasoconstriction
• Briefly summarise the main classes of hormones and their mechanism of action
o Peptide, amine and steroid hormones
• Peptide hormones (proteins and peptides)
▪ Hydrophilic hormones
▪ Stored in secretory granules
▪ Majority of hormones are peptide hormones (e.g. insulin, GH)
• Amine hormones
▪ Synthesised from a single amino acid
▪ Often from tyrosine
▪ e.g. catecholamines
• Hydrophilic hormones
• Adrenaline for example
▪ e.g. thyroid
• Iodinated Tyr derivative
• Lipophilic hormone
• Steroid
▪ Cholesterol derivative
▪ Lipophilic hormones
▪ E.g. cortisol, aldosterone, sex hormones, vitamin D
• Only the "free" form of hormones are available to tissues and therefore exert their
effects
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o Cell surface and intracellular receptors
• Intracellular receptors
▪ Some messengers enter the cell and bind to receptors in the cytoplasm
• Information is processed directly without intermediate steps
• e.g. thyroxine, testosterone, oestrogen
▪ Some messengers enter the cell and bind to cell surface receptors an can
induce signal amplification
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Long distance fast/slow signal transduction (milliseconds - seconds - minutes - hrs. Short-range chemical messengers: diffuse across narrow space to act locally on adjoining target cell (another neuron, a muscle, or a gland, e. g. acetylcholine, rapidly inactivated by local enzymes (acetylcholinesterase, hormones. Synthesised from a single amino acid: often from tyrosine, e. g. catecholamines, hydrophilic hormones, adrenaline for example, e. g. thyroid. Steroid: cholesterol derivative, e. g. cortisol, aldosterone, sex hormones, vitamin d. Lipophilic hormones: only the free form of hormones are available to tissues and therefore exert their effects, cell surface and intracellular receptors, intracellular receptors. Some messengers enter the cell and bind to receptors in the cytoplasm. Information is processed directly without intermediate steps: e. g. thyroxine, testosterone, oestrogen. Some messengers enter the cell and bind to cell surface receptors an can induce signal amplification. Integrated by neurons of cns: hormone produced, negative feedback loops rarely seen in plants, but common in animals, the ns and es are tightly integrated.
