The endocrine system physiology includes hormones involved and how they are transported in the blood. Also, the effect that hormones have on other hormones is through permissiveness, synergism, and antagonism. the hormone classifications, chemical classes, and solubility along with the stimulation ...
Endocrine System: Communicates to target cells through secreted hormones
- Hormones are released from endocrine glands & transported in the blood
- Target cells are characterized by having the appropriate receptor for that hormone
- Response:
- Longer response time, Longer-lasting, and Wide-spread response
Hormones:
- A chemical secreted by a cell or group of cells into the blood for transport to a distant
target where it exerts its effects at very low concentrations
- The boundaries between hormonal and nonhormonal activity is rather blurred due to
advances in research
- Origin of secretion
- Most secreted by glands, tissue derived from epithelium
- Some secreted by individual cells, neurons (neurohormones), and immune system
(cytokines)
- Secretion: Most hormones are secreted into the blood stream
- Ectohormones are special class of hormones that serve as signal molecules
secreted into the external environment; ex: pheromones
- Targets: Can act locally or at a distance away depending on the location of target cells
- Concentrations: Act in the nano- (10-9) to picomolar (10-12) ranges
Functions of Endocrine System:
- Maintaining homeostasis of blood composition and volume
- Regulates the amount of specific substances dissolved in the blood
- Regulate the characteristics of blood (including cell #’s)
- Controlling reproductive activities
- Regulating development, growth, & metabolism
- Controlling digestive processes
Location of Major Endocrine Glands:
- Single organ with only an endocrine function
- Adrenal gland, parathyroid gland, pineal gland, pituitary gland, & thyroid gland
- Cells housed in small clusters within organs w/ other non-endocrine function
Negative Feedback: Common mechanism of regulation
- Causes the variable to change in a direction opposite of the initial change
Positive Feedback: Less common mechanism of control
- Causes the variable to be enhanced in the direction of the initial change
The Effect that Hormones Have on Hormones:
- Permissiveness
- Effect of a hormone is dependent on the presence or activity of a second hormone
- Ex: Thyroid hormone promotes reproductive development by the gonadotropins
and sex steroids
- Synergism: Complementary effect
, - Sum of the combined effects of hormones is greater than the sum of the individual
effects
- Ex: Epi ↑blood glucose, Glucagon ↑blood glucose, Epi & Glucagon ↑↑↑blood
glucose
- Antagonism
- The effect of one hormone results in the loss of another hormone’s receptors,
thereby reducing the 2nd’s effectiveness
- Ex: Progesterone (decreases contractions during pregnancy) inhibits uterine
responsiveness to estrogen (increases contractions during pregnancy)
Number of Receptors: Fluctuates under strict control
- Number of receptors influences the degree of cellular response
- Up-regulation increases cell sensitivity to hormone
- Down-regulation decreases cell sensitivity to hormone
- Cells modulate receptor number in response to available hormone
- E.g., if hormone level drops, then increasing # receptors increases probability of
hormone-receptor interaction
- Helps to maintain normal level of cellular response
Hormone Classifications: Source of secretion
- Mechanism of action (type of receptor used)
- Solubility in H2O
- Chemical classes
- Peptide/protein hormones
- Steroid hormones (derivatives of cholesterol)
- Amine hormones (modified amino acids)
Hormonal Chemical classes:
- Steroids: Androgens, estrogens, progestins, corticosteroids
- Protein/peptide hormones
- Polypeptides (14 to 199 aa), oligopeptides (3 to 10 aa), glycoproteins (proteins
with attached sugar chains)
- Biogenic amines: Also called monoamines
- Includes catecholamines (H2O soluble) & thyroid hormone (lipid-soluble)
Hormones Solubility:
- Hydophilic: H2O soluble
- Very low to low lipid solublility
- Lipophilic: Fat soluble
- Little to no water solubility
- Solubility influences synthesis & storage, transport in the blood, and how it interacts with
its target cell (& receptor)
Stimulating Hormone Synthesis and Release
- Hormonal stimulation
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