Endocrinology
Endocrine System Nervous system
- Chemical communication - Electrical communication
- Hormones transported via bloodstream - Impulses transmitted by neurons
- Involuntary - Voluntary / involuntary
- Often distant - Localised
- Rapid or long-lasting effect - Rapid effect
A) Endocrinology
- Endocrine glands – ductless hormone secreting glands
- Hormones – chemical messengers released into bloodstream & affects activity of target cells
- Endocrine signalling – travels to distant target cell via bloodstream
- Paracrine signalling – travels to nearby cell via interstitial fluid
- Autocrine signalling – targets itself
a. Hormone Classification
i. Amines – small group derived from tyrosine
1. Catecholamines (e.g., adrenaline, norepinephrine)
a. Water soluble
b. Do NOT require carrier protein in plasma
c. Binds to receptor on cell surface membrane
2. Thyroid hormones (e.g., T3 + T4)
a. Poor water solubility
b. Need carrier protein in blood
c. Binds to receptor inside the cell
, ii. Peptide & Protein hormone (e.g., insulin, prolactin, glucagon, GH)
• Largest hormone class
• Water soluble
• Do NOT need carrier proteins in blood
• Binds to receptor on membrane surface
iii. Steroid hormones
• Synthesized from cholesterol
• Not stored in vesicles
• Rapidly diffuse out cell due to lipid solubility
• Poor water solubility → NEEDS carrier protein
• Free steroid hormones enter cell primarily by passive diffusion
B) Hypothalamus & Pituitary Gland
a. Hypothalamus (hypo)
i. Concerned with homeostasis
ii. In brain below thalamus
iii. Connected to anterior pituitary by hypophyseal portal system (blood vessel system)
iv. Connected to posterior pituitary by infundibulum (neurons within)
v. Secretes Liberins & Statins → regulate pituitary hormone secretion
1. Liberins - releasing hormones/factors
a. Thyrotropin releasing hormone (TRH) → stimulates TSH secretion
b. Corticotropin “ (CRH) → stim. ACTH secretion
c. Gonadotropin “ (GnRH) → stim. FSH + LH secretion
d. Growth Hormone “ (GHRH) → stim. GH secretion
2. Statins – inhibiting hormones/factors
a. Growth hormone inhibiting hormone (GHIH) / (somatostatin)
b. Prolactin inhibiting hormone (PIH)
3. Other
a. Oxytocin & vasopressin (peptide hormones) → produced in hypo →
transported down axons to posterior pituitary → bloodstream
Endocrine System Nervous system
- Chemical communication - Electrical communication
- Hormones transported via bloodstream - Impulses transmitted by neurons
- Involuntary - Voluntary / involuntary
- Often distant - Localised
- Rapid or long-lasting effect - Rapid effect
A) Endocrinology
- Endocrine glands – ductless hormone secreting glands
- Hormones – chemical messengers released into bloodstream & affects activity of target cells
- Endocrine signalling – travels to distant target cell via bloodstream
- Paracrine signalling – travels to nearby cell via interstitial fluid
- Autocrine signalling – targets itself
a. Hormone Classification
i. Amines – small group derived from tyrosine
1. Catecholamines (e.g., adrenaline, norepinephrine)
a. Water soluble
b. Do NOT require carrier protein in plasma
c. Binds to receptor on cell surface membrane
2. Thyroid hormones (e.g., T3 + T4)
a. Poor water solubility
b. Need carrier protein in blood
c. Binds to receptor inside the cell
, ii. Peptide & Protein hormone (e.g., insulin, prolactin, glucagon, GH)
• Largest hormone class
• Water soluble
• Do NOT need carrier proteins in blood
• Binds to receptor on membrane surface
iii. Steroid hormones
• Synthesized from cholesterol
• Not stored in vesicles
• Rapidly diffuse out cell due to lipid solubility
• Poor water solubility → NEEDS carrier protein
• Free steroid hormones enter cell primarily by passive diffusion
B) Hypothalamus & Pituitary Gland
a. Hypothalamus (hypo)
i. Concerned with homeostasis
ii. In brain below thalamus
iii. Connected to anterior pituitary by hypophyseal portal system (blood vessel system)
iv. Connected to posterior pituitary by infundibulum (neurons within)
v. Secretes Liberins & Statins → regulate pituitary hormone secretion
1. Liberins - releasing hormones/factors
a. Thyrotropin releasing hormone (TRH) → stimulates TSH secretion
b. Corticotropin “ (CRH) → stim. ACTH secretion
c. Gonadotropin “ (GnRH) → stim. FSH + LH secretion
d. Growth Hormone “ (GHRH) → stim. GH secretion
2. Statins – inhibiting hormones/factors
a. Growth hormone inhibiting hormone (GHIH) / (somatostatin)
b. Prolactin inhibiting hormone (PIH)
3. Other
a. Oxytocin & vasopressin (peptide hormones) → produced in hypo →
transported down axons to posterior pituitary → bloodstream
