Introduction to endocrinology

1. Introduction to
Endocrinology
Dr. Sai Sailesh Kumar G
Professor
Department of Physiology
NRIIMS
Email: dr.goothy@gmail.com

2. Introduction
Endocrine Physiology – Study of processes involved in
regulation and integration of cells and organ systems by
specialized chemical substances called hormones
Hormones – synthesized by endocrine glands
Endocrines – ductless glands – secretes directly into
circulation

3. Introduction
Endocrine glands are small in size but great in importance
They are called duct less glands
Hormones circulate all over the body
But produces effects only in selected sites
Target organs may or may not be near the site of production of
the hormone

4. Endocrine glands
 Hypothalamus
 Pituitary ( Anterior and posterior)
 Thyroid
 Adrenal ( Cortex and medulla)
 Parathyroid
 Endocrine pancreas
 Gonads ( Testis and ovary)
 Pineal gland

5. Other endocrine glands
Thymus (Thymosin)
Kidney (Erythropoietin, renin etc.)
Heart (Atrial natriuretic peptide)
Lungs ( prostaglandlins)
GI tract (GI hormones)
Placenta (placental hormones)

6. Types of hormones
Three types
Proteins or peptides
Amino acids
Steroids

7. Proteins or peptides
 Insulin
 Glycoproteins – LH, FSH, TSH, hCG
 Growth hormone, prolactin
 Secretin
 Somatostatin
 Parathormone
 Calcitonin
 ADH

8. Amino acid derivatives
Amines – Epinephrine, Norepinephrine, Dopamine, Serotonin
Thyroxine
Triiodothyronine

9. Steroid hormones
Glucocorticoids
Mineralocorticoids
Estrogen
Progesterone
Testosterone
1,25 dihydroxy cholecalciferol

10. Hormone signalling

11. Endocrine
Hormone secreted from the endocrine gland reaches distant
target tissues via blood bloodstream.
Thyroid hormone

12. Paracrine
Hormone secreted from the endocrine gland diffuses into
extracellular space and signals the neighboring tissue
Somatostatin secreted by D cells of islets of the pancreas
Influence secretion of insulin and glucagon from same islets

13. Paracrine
Hormone secreted from the endocrine gland diffuses into
extracellular space and signals the neighboring tissue
Somatostatin secreted by D cells of islets of the pancreas
Influence secretion of insulin and glucagon from same islets

14. Autocrine
Hormone secreted from the endocrine gland binds with the
receptor located in the same cell that secrete the hormone
Platelet activating factor secreted from platelet
Activates platelet

15. Neurohormones
Secreted from axon terminals
Released into circulation
Hypothalamic-releasing hormones
Acts on anterior pituitary
Oxytocin and ADH released by posterior pituitary

16. Peptide hormone synthesis
First synthesized a preprohormone
Cleaved to form pro hormone
Transported to Golgi complex
Converted to hormone
Packed in secretory granules for storage

17. Amine hormone synthesis
All amine hormones except serotonin are synthesized from
tyrosine
Serotonin is synthesized from 5-hydroxytryptamine
Stored in granules
Secreted by calcium mediated exocytosis

18. Steroid hormone synthesis
Synthesized from cholesterol
Not stored in cell as granules
Present in cytosol –bound to proteins
On stimulation
Becomes free from intracellular proteins and transported outside
the cell by diffusion

19. Transport
Hormones – after secretion
Enters blood
Amine and protein hormones remains unbound ( free form)
Thyroxine and steroid hormones and Vitamin D circulate in
bound form

20. Ectopic hormone secretion
Non endocrine tissues secretes hormones ( Pathological)
Neoplastic tissues of lungs like small cell pulmonary carcinoma
produce several hormones
Paraneoplastic syndrome
Hormones usually secreted are ACTH, ADH and paratharmone
Cushing syndrome, water retention, hypercalcemia respectively

21. Regulation of hormone secretion
Feedback mechanisms
Neural regulation
Chronotropic regulation
Hormonal and chemical regulation

22. Feedback mechanisms
Negative feedback mechanism
Positive feedback mechanism

24. Neural regulation
 Endocrine glands are innervated by the autonomic nervous system
 Stimulation of these systems alters endocrine secretion
 Vagal stimulation – increase insulin secretion
 External stimuli like light, smell, taste, and sound.
 Internal stimuli like pain, stress, etc also alter endocrine secretions
 Example- Milk ejection reflex

25. Chronotropic regulation
Circadian rhythms
Sleep-wakefulness cycle
Menstrual cycle
Seasonal rhythms

26. Pulsatile
Lasting for few minutes to hours
Secretion of GnRH

27. Diurnal
Lasting for few hours in a 24 hours cycle
Secretion of ACTH

28. Periodical
Lasting for many days
Alteration in sex hormones in menstrual cycle

29. Seasonal
Occurring in a particular season of the year
More prominent in birds and animals
The center for the generation of these pulses is present in the
suprachiasmatic nucleus of the hypothalamus

30. THANK YOU