Endocrine slide 1

Primary Function: Maintains homeostasis alongside the nervous system.
System Comparison:
- Nervous System: Uses neurotransmitters, binds directly to target cells, yields rapid and short-lasting responses, acts locally.
- Endocrine System: Uses hormones transported via the blood, targets specific cell receptors, yields longer-lasting responses (seconds to days), acts widespread.
Organ Types:
- Primary Endocrine Organs: Anterior pituitary gland, thyroid gland, parathyroid gland, adrenal cortex, pancreas, thymus.
- Secondary Endocrine Organs: Heart, liver, kidneys.

Chemical Signaling Methods:
- Autocrine: Chemical targets the secreting cell itself or the same cell type.
- Paracrine: Chemical targets nearby, different cell types.
- Endocrine: Chemical travels through the bloodstream to target distant cell types.

Types of Secretion Stimuli:
- Hormonal: A hormone triggers release of another hormone (e.g., hypothalamic GHRH stimulates anterior pituitary GH release).
- Humoral: Blood/fluid ion or nutrient levels trigger release (e.g., high blood glucose stimulates insulin release).
- Neural: Nervous signals trigger release (e.g., sympathetic preganglionic axons stimulate adrenal medulla to release epinephrine and norepinephrine).

Solubility Properties:
- Hydrophilic (Water-Soluble): Travels freely in blood; degrades faster; cannot cross the cell membrane; binds plasma membrane receptors.
- Hydrophobic (Lipid-Soluble): Requires transport proteins in blood; lasts longer; freely crosses plasma membrane; binds cytosolic or nuclear receptors.
Chemical Classes:
- Amino Acid-Based: Includes amines (single amino acid), peptides, and proteins. Generally hydrophilic (exception: thyroid hormones are amino acid-based but hydrophobic).
- Steroids: Cholesterol derivatives with a hydrocarbon ring structure. Always hydrophobic.

Cellular Mechanisms:
- Hydrophilic Mechanisms: Membrane receptors trigger ion channel changes or second-messenger systems (e.g., G protein activation $\rightarrow$ adenylate cyclase $\rightarrow$ cAMP formation $\rightarrow$ protein kinase activation).
- Hydrophobic Mechanisms: Diffuses into cell $\rightarrow$ forms hormone-receptor complex $\rightarrow$ enters nucleus $\rightarrow$ regulates gene transcription and protein synthesis.
Receptor Regulation:
- Upregulation: Increases receptor count to boost cell sensitivity.
- Downregulation: Decreases receptor count to lower cell sensitivity.

Synergistic: Hormones work together to produce a stronger combined effect (e.g., estrogen and progesterone).
Permissive: One hormone requires the prior presence/action of another hormone (e.g., oxytocin action requires prolactin).
Antagonistic: One hormone opposes the action of another (e.g., insulin lowers blood glucose while glucagon raises it).

Hypothalamus: Anterior-inferior region of diencephalon; regulates hunger, thirst, fluid balance, body temperature, sleep-wake cycles, and reproduction.
Pituitary Gland (Hypophysis): Attached to hypothalamus via the infundibulum.
- Anterior Pituitary (Adenohypophysis): Glandular tissue.
- Posterior Pituitary (Neurohypophysis): Neural tissue.
Hypophyseal Portal System: Specialized capillary bed network on the infundibulum that delivers hypothalamic regulatory hormones directly to the anterior pituitary, bypassing systemic circulation.

Synthesized in hypothalamic neurosecretory neurons, transported along axons, and stored in posterior pituitary axon terminals.
Antidiuretic Hormone (ADH / Vasopressin):
- Function: Increases renal water reabsorption by inserting aquaporins into collecting duct cells; decreases urine output; constricts blood vessels.
- Regulation: Monitored by hypothalamic osmoreceptors detecting blood solute concentrations.
- Clinical Pathophysiology: Lack of ADH leads to Diabetes Insipidus (symptoms: extreme thirst, dehydration, polyuria; treated with synthetic ADH).
Oxytocin:
- Function: Stimulates uterine smooth muscle contractions during labor and milk ejection in mammary glands via positive feedback; aids sperm transport in males.

Regulated by hypothalamic releasing and inhibiting hormones via multi-tiered negative feedback control systems.
Thyroid-Stimulating Hormone (TSH / Thyrotropin): Stimulated by TRH; inhibited by somatostatin; targets thyroid gland.
Adrenocorticotropic Hormone (ACTH / Corticotropin): Stimulated by CRH; inhibited by cortisol; targets adrenal cortex to release glucocorticoids.
Prolactin (PRL): Stimulated by PRH; inhibited by PIH (dopamine); targets mammary glands for milk production.
Luteinizing Hormone (LH): Stimulated by GnRH; inhibited by sex steroids; triggers ovulation and sex hormone production.
Follicle-Stimulating Hormone (FSH): Stimulated by GnRH; inhibited by sex steroids/inhibin; regulates gamete production and follicle maturation.
Growth Hormone (GH / Somatotropin): Stimulated by GHRH; inhibited by GHIH (somatostatin); stimulates growth and insulin-like growth factor (IGF) production in liver, bone, and muscle.
Melanocyte-Stimulating Hormone (MSH): Stimulates melanosomes in melanocytes.
Endorphins: Inhibit pain perception, suppress cortisol, and elevate mood.

Question: Which statement is false regarding a hydrophobic hormone?
- A: It can easily pass through the cell membrane
- B: Its receptor can be in the cytoplasm
- C: It commonly utilizes second messenger systems
- D: Its receptor can be in the nucleus
- Response: C (Hydrophobic hormones diffuse through membranes and directly regulate gene expression; second messenger systems are utilized by hydrophilic hormones).
Question: Which hormone is not made in the pituitary gland?
- A: ADH
- B: LH
- C: GH
- D: ACTH
- Response: A (ADH is synthesized by neurons in the hypothalamus and stored/released by the posterior pituitary).
Question: What is the function of ACTH?
- A: Targets the thyroid gland to produce hormones
- B: Targets the adrenal gland to produce hormones
- C: Targets the testes and ovaries to produce hormones
- D: Targets general tissue to stimulate growth
- Response: B (ACTH stimulates the adrenal cortex to produce glucocorticoid hormones).