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
- 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
