3. Principles of Endocrinology Flashcards
What are the functions of the endocrine system?
- Regulates metabolism
- Regulates water and electrolyte balance
- Induces adaptive changes to help the body cope with stressful situations.
- Promotes smooth, sequential growth and development.
- Controls reproduction.
- Regulates red blood cell production.
- Together with the autonomic nervous system, controls and integrates both circulation and the digestion and absorption of food.
What are the three main chemical messengers of the endocrine system?
- Paracrines:
- Signals that bind to nearby receptors
- ex: growth factors, clotting factors, cytokines
- Neurotransmitters
- the electrical signal: Neurons transmit
- Hormones
What are hormones?
- Chemical substances that are secreted by endocrine system, transported in the blood stream, elicits a specific response in target tissues and responsible for homeostasis
What are hydrophilic hormones?
Hydrophilic hormones:
- highly water soluble, low lipid solubility
- stored in secretory granules
- Transported in blood and target receptors
How do hydrophilic hormones produce their effect?
- Changing the configuration of a protein channel
2. Activating a second messenger system to alter activity of protein to produce effect
What’s happening here?
Signal transduction
What are lipophilic hormones?
- Highly lipid soluble, low water solubility
- Transported in the blood
- Target receptors that are INSIDE the target cell
- effect produced by activating genes to synthesize NEW proteins
What causes endocrine dysfunction?
- Too much hormone activity
2. Too little hormone activity
What causes hyposecretion?
Hypo - not enough secretion
- Primary hyposecretion:
- too little hormone is secreted due to abnormality within gland (causes - genetic, dietary, cancer…) - Secondary hyposecretion
- Gland is normal but too little hormone is secreted due to deficiency of its tropic hormone
What causes hypersecretion?
- Primary hypersecretion: too much hormone is secreted due to abnormality within gland
- Secondary hypersecretion: too much stimulation from outside the gland
What are the ways that a hormone can influence the activity of other hormones at a given target cell?
- Permissiveness: one hormone must be present in enough amounts for full exertion of another hormone
ex: thyroid hormone for epinephrine to exert full effect - Synergism: Several hormones working together
ex: FSH and testoterone - Antagonism: One hormone causes loss of another hormones receptors
ex: used commonly in drugs
What are tropic hormones?
Hormones that regulate hormone secretion by another endocrine gland
ex: thyroid-stimulating hormone (TSH) secreted from pituitary stimulates hormone secretion from thyroid
What makes the endocrine system complex?
- a single hormone may be secreted by multiple endocrine glands
- the same messenger may be either a hormone or a neurotransmitter
- different cycles/time lengths
What factors affect the plasma concentration of hormones?
- Rate of hormone secretion by the endocrine gland
- Extent of binding to plasma proteins (for lipophilic)
- Rate of metabolic activation
- Rate of metabolic inactivation and excretion
What are the 3 mechanisms for controlling secretion of hormones?
- Negative feedback control (maintains plasma conc. set point)
- Neuroendocrine reflexes (sudden increase in hormone secretion in response to stimulus ex:cortisol when stressed, suckling reflex)
- Diurnal and Circadian Rhythms
