Chapter 16- The endocrine system Flashcards
Hormones
Long distance chemical messengers that cause a change in metabolic activity of a cell. Effects are usually long lasting and are diverse
What factors do hormones control (4)
- Reproduction- gametes
- Growth and development- bone growth, mitotic activity, etc.
- Immune system activation- when pathogens get in
- Maintenance of various blood components (glucose, electrolytes, water, etc.).
Autocrine
Short distance chemical messengers- affect the same cells that secrete the messenger
Paracrine
Short distance chemical messengers- affect different cells that secrete the messenger in the same tissue
What does the chemical structure of hormones determine? (3)
Chemical structure determines longevity, transport in blood, and receptivity
Two major classifications of hormones
- Amino acid based
2. Steroids
Amino acid based hormones
Molecular size varies- amino acid derivatives, peptides, proteins. Epinephrine is an example of an amino acid derivative. Water soluble- can circulate without a carrier (chaperone to get to target cells/tissues). This is because blood is water based.
Steroid hormones
Synthesized from cholesterol. Lipid soluble- circulate with a carrier molecule. Can pass straight through the membrane of the target cell
What are the only steroid hormones in the body?
Gonadal hormones and adrenocortical hormones are the only steroid hormones in the body
Hormones can only affect a cell if
Hormones can only affect target cells with appropriate receptors. Different receptors= different response
Changes produced by hormone binding (5)
- Altering plasma membrane permeability or membrane potential, caused when ion channels open
- Stimulates synthesis of enzymes/proteins inside cell
- Activates/deactivates enzymes
- Induces sensory activity
- Stimulates mitosis
Two mechanisms of hormone action
- Second messenger systems
2. Intracellular systems
Second messenger systems
Uses receptors found on surface of plasma membrane. A ligand (hormone in this case) binds to a receptor, which then activates the G-protein inside the cell. The G-protein activates intracellular second messenger- causes response in cell. This is extremely efficient- a single hormone binding a receptor results in millions of product molecules being produced
Mechanism of action for amino acid based hormones
Second messenger systems
Intracellular systems
Hormone enters cell, binds to intracellular receptors. Receptor hormone complex- binds specific regions of DNA- DNA transcription occurs. Effect- certain proteins produced in larger numbers
Intracellular systems steps (5)
- The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor
- The receptor hormone complex enters the nucleus
- The receptor hormone complex binds a specific DNA region
- Binding initiates transcription of the gene to mRNA
- The mRNA directs protein synthesis
How is hormone synthesis and release controlled?
Hormone synthesis and release is controlled by negative feedback mechanisms. Importance- hormone levels need to be precisely regulated. If we produce too much or too little, homeostatic imbalances would result very quickly.
Stimulus mechanisms for hormone release (3)
- Humoral stimuli
- Neural stimuli
- Hormonal stimuli
Humoral stimuli
Changing blood levels of critical ions and nutrients. Ex- monitoring calcium levels by the parathyroid gland
Neural stimuli
Nerve fibers stimulate hormone release, this is infrequent. Ex- norepinephrine and epinephrine release by sympathetic nervous system
Hormonal stimuli
Hormone released in response to other hormones. Ex- hypothalamic hormones stimulate or inhibit anterior pituitary gland
Target cells only respond to a hormone if
It has a specific receptor protein for that hormone. Can be specific (only cells of a certain tissue) or broad (all body cells)
Hormone activation of a cell depends on
- Blood levels of hormone
- Number of receptors for specific hormone on/in cell
- Affinity of receptor to hormone
Up regulation
Increased receptor number in response to low hormone levels. This increases the sensitivity of the receptors to the hormone, so the receptors are more likely to respond.