What is the Endocrine System?
A control system responsible for homeostasis and managing important body functions [1].
How do hormones help combat stress?
They respond to infection, trauma, and shock [2].
Why is it called "endocrine"?
Because it releases substances directly into the blood [1].
What are the homeostatic functions of hormones?
Managing energy, fluid/electrolytes, and blood pressure (BP) [2].
What is the endocrine role in growth and development?
Controlling cell hyperplasia (number) and hypertrophy (size) [2].
What are the endocrine functions in reproduction?
Development of primary sex organs and secondary sex characteristics [2].
What is the general definition of a hormone?
A substance secreted by an endocrine cell that affects another cell via a receptor molecule [2].
At what concentration are hormones usually present?
Extremely low concentrations, yet they remain biologically active [2].
What is the typical lifespan (half-life) of a hormone?
Generally short-lived, ranging from minutes to hours [3].
Which hormones have a longer half-life?
Thyroid hormones, which last for days [3].
Which Adrenal gland hormone is essential for life?
Cortisol [3].
Which Anterior Pituitary gland hormone is essential for life?
ACTH [3].
Which Parathyroid gland hormone is essential for life?
PTH [3].
What are the "3 Ps" of Polypeptide/Protein hormones?
Pituitary, Parathyroid, and Pancreas [3].
What is the structural basis of Steroid hormones?
They share a steroid nucleus derived from cholesterol [3].
Name two types of Steroid hormones.
Sex hormones and corticosteroids [3].
What are the two types of Amine hormones?
1. Single Amino Acid (Thyroid & Catecholamines). 2. Glycoprotein (contains a CHO group, e.g., FSH) [3].
What five factors does a hormone's chemical structure affect?
Storage, transport, mechanism of action, degradation, and replacement [3].
How are hormones disposed of?
Through metabolic degradation or inactivation [4].
Where are the primary sites of hormone disposal?
Target tissues, liver, and kidneys (via biliary or urinary secretion) [4].
Where are Steroid hormones mainly disposed of?
Primarily in the liver [4].
What is the effect of liver or kidney failure on hormones?
The level of hormones in the blood increases because disposal is impaired [4].
Where can hormone receptors be located?
Internal (cytoplasm/nucleus) or external (cell surface) [4].
What are the two primary functions of receptors?
1. Target recognition. 2. Signal transduction (triggering a physiological response) [4].
What are the three properties of receptors?
Specificity, Affinity, and Regulation (up & down) [4].
Define Down-regulation.
A high concentration of a hormone decreases the number of receptors via internalization and degradation [4, 5].
Define Up-regulation.
A low concentration of a hormone increases the number of receptors via increased synthesis/insertion from stores [5].
Which hormones behave like Polypeptides regarding their mechanism?
Catecholamines [5].
Which Amine hormones behave like Steroids regarding their mechanism?
Thyroid hormones [5].
What is the mechanism for Lipid-soluble hormones (Steroids/Thyroid)?
They diffuse across the membrane and bind intracellular receptors in the cytoplasm or nucleus [5].
What is the mechanism for Water-soluble hormones (Peptides)?
They bind surface receptors and activate second messenger systems [6].
Why are the effects of water-soluble hormones rapid?
They modify pre-existing proteins (takes seconds to minutes) rather than making new ones [6].
Explain the cAMP Pathway (Step 1).
Hormone binds receptor → Activates Adenylate Cyclase (AC) [6, 7].
Explain the cAMP Pathway (Step 2).
AC increases cAMP → cAMP activates Protein Kinase A (PKA) → PKA phosphorylates proteins [6, 7].
Which hormones use the cAMP Pathway?
Glucagon and Epinephrine (via β-receptors) [6, 7].
Explain the IP3/DAG Pathway (Step 1).
Hormone binds → Activates Phospholipase C (PLC) → Splits PIP2 into IP3 and DAG [7, 8].
Explain the IP3/DAG Pathway (Step 2).
DAG activates Protein Kinase C (PKC); IP3 releases Ca²⁺ from the ER [7, 8].
Which hormones use the IP3/DAG Pathway?
Oxytocin and ADH (via V1 receptors) [7, 8].
When is the IP3/DAG mechanism typically used?
For processes needing Ca²⁺, such as smooth muscle contraction or exocytosis [9, 10].
Explain the Tyrosine Kinase Pathway.
Hormone binds → Receptor autophosphorylation → Activates IRS (insulin receptor substrates) [7, 8].
Which hormones use the Tyrosine Kinase Pathway?
Insulin and Growth Factors [7, 8].
Explain the cGMP Pathway.
Hormone binds → Activates Guanylate Cyclase (GC) → Increases cGMP → Activates PKG [7, 8].
Which hormones use the cGMP Pathway?
ANP (Atrial Natriuretic Peptide) and Nitric Oxide (NO) [7, 8].
What is the primary function of cGMP pathway activation?
Vasodilation and smooth muscle relaxation [8].
Name another important second messenger complex.
Calcium-Calmodulin [9, 10].
Can Peptide hormones have long-term effects?
Yes, some have a long-term genomic mode of action [11].
What six types of cellular changes result from hormone action?
1. Permeability/transport. 2. Electrical state of membrane. 3. Metabolism. 4. Secretory activity. 5. Proliferation/differentiation rate. 6. Contractile activity [10, 11].
Define Synergistic effects.
One hormone enhances the effects of another (e.g., Glucagon + Epinephrine + Cortisol on blood glucose) [11].
Define Antagonistic effects.
One hormone counteracts the other (e.g., Insulin and Glucagon) [11].
Define Permissive effects.
One hormone "primes" a target for another (e.g., Estrogen primes the uterus for Oxytocin/Progesterone) [11].
What is the Hypothalamic-pituitary-target gland axis?
A system of slow control involving endocrine axis-driven feedback (e.g., Thyroid, Gonadal hormones) [11].
What is Response-driven feedback control?
Hormone control based on substrate levels (e.g., Insulin by blood glucose; PTH by calcium) [11].
What is an example of Direct neural control?
The Adrenal medulla controlled by sympathetic preganglionic nerves [11].
What are Diurnal/Circadian rhythms in hormones?
Daily cycles of hormone release, such as Cortisol [11].
Where are ADH and Oxytocin produced?
In the Hypothalamus (Paraventricular and Supraoptic nuclei) [12].
Where are ADH and Oxytocin released?
From the Posterior Pituitary [12].
How does the hypothalamus control the Anterior Pituitary?
By secreting regulatory hormones into the portal vessels [12].
What is the effect of TRH?
Release of TSH [12].
What is the effect of GnRH?
Release of LH and FSH [12].
What is the effect of GHRH?
Release of GH [12].
What is the effect of Somatostatin (SS/GHIH)?
Inhibition of GH [12].
What is the effect of CRH?
Release of ACTH [12].
What is the effect of Dopamine (DA)?
Inhibition of PRL (Prolactin) [12].
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