This document provides an introduction to the study of endocrinology. It defines hormones as chemical entities secreted by cells into the bloodstream to act on distant targets. Hormones can be peptides, amines, steroids, and many other substances. Their synthesis and secretion is regulated through feedback mechanisms and other internal and external factors. Hormones are transported through the bloodstream and metabolized in various tissues. They act through cell surface receptors or nuclear receptors to signal intracellular changes. Endocrine diseases can involve hormone excess, deficiency, hypersensitivity, or resistance and may present with non-specific symptoms like weight changes, fatigue, or changes in metabolism.

1. Endocrinology
Brig (Dr) A B Khare
Asso.Prof (Med)

2. Introduction to endocrinology
• Study of hormones
• Evolved from – certain cells secrete –chemical entities –hormones – directly
into blood stream to act on specific distant targets.
• ? Synthesis, secretion , regulation , transportation , metabolism , mechanism
of action on target tissues

3. What is hormone ?
• Definition based on physiology rather than chemistry.
• First example secretin enteroendocrine cell (dispersed)in GIT acting on
pancreas(exocrine glands).
• Discrete collections e.g.: adrenals ,gonads, thyroid ,parathyroid soon
recognized & chemically characterized.
• Peptides ,amines , steroids &many other fits definition of hormones.
• Paracrine , autocrine
• Tissues secreting hormones e.g. :kidneys, adipose cells.

6. Regulation of synthesis & secretion
• Two broad categories: 1- peptide , 2- steroid including thyroid,
catecholamine, active vit D &other non peptide hormones.
1- Peptide: genetically coded.
• Translation preprohormone cleaved  mature secreted product.
• post translational modification e.g.: disulfide bonding, C-peptide cleavage,
glycosylation.
• Stored in secretory granule exocytosis :regulated by Ca2+
2- Steroids & non peptide hormones : series of enzymatic steps on precursors
like cholesterol & aromatic amines

7. Contd…
Regulation
 main : negative feedback with or without HPA axes.
Additional : metabolic , neural & other internal and environmental inputs.
Temporal regulation related to diurnal rhythms , menstrual cycle & puberty.

8. Thyroid axis

11. Hormone transport & metabolism
Transport :Most peptide hormone circulate in free form except IGF-1.
• Steroids & thyroid : lipophilic circulate in protein-bound form. Free level is fraction
of total hormone . liver disease may affect carrier protein.
Metabolism : critical determinant for some hormone. Testosterone , thyroxine , vit D
enzymatic conversion to more potent hormones.

12. Mechanism of hormone action
How ?
• Through receptors :
1. Cell surface receptor
2. Nuclear receptors in nucleus or cytoplasm
Signal transduction

14. Steroid hormone receptors

15. Endocrine pathology
• Classification
 Hormone excess ;
1- Primary gland overproduction.
2- Secondary to excess trophic substance
 Hormone deficiency
1- Primary gland failure
2- Secondary to deficient trophic substance

16. Contd…
 Hormone hypersensitivity
1- Failure of inactivation of hormone
2- Target organ overactivity/hypersensitivity
 Hormone resistance
1- failure of activation by hormone
2- Target organ resistance
 Non functioning tumours
1- Benign
2- Malignant

17. Investigations
• Biochemical investigations – central role
Timing of measurement : release of many hormones rhythmical
(pulsatile , circadian or monthly) so sequential dynamic tests are
applied.
 Choice of dynamic biochemical test :
1- Abnormalities are often characterised by loss of normal regulation of
hormone secretion
2- If hormone deficiency suspected – stimulation test
3- If excess – suppression test

18. Contd…
4- The more tests there are to choose from , the less likely it is that
single test is infallible , so avoid interpreting one result in isolation
 Imaging :
1- Functional as well as conventional structural imaging can be
performed as secretory endocrine cells can also take up labelled
substances : 131Iodine
2- Most endocrine glands have a high of incidentalomas so do not scan
unless biochemistry confirms dysfunction or primary problem is tumor.

19. Contd…
 Biopsy :
many endocrine tumours are difficult to classify histologically
( e.g. adrenal carcinoma & adenoma

20. Examples of non specific presentations of
endocrine disease
Symptom
 Lethargy &
depression
 weight gain
Most likely endocrine disorder
Hypothyroidism , diabetes mellitus
hyperparathyroidism , hypogonadism,
adrenal insufficiency, Cushing’s
syndrome
Hypothyroidism, Cushing’s syndrome

21. Contd…
 Weight loss
 Polyuria and
polydipsia
Heat intolerance
Palpitations
Muscle weakness
(usually proximal)
• Thyrotoxicosis, adrenal insufficiency, diabetes
mellitus
• Diabetes mellitus,diabetes insipidus,
hyperparathyroidism, hypokalaemia(Conn’s
syndrome)
• Thyrotoxicosis, menopause
• Thyrotoxicosis, phaeochromocytoma
• Thyrotoxicosis, Cushing’s syndrome,
hypokalaemia, hyperparathyroidism,
hypogonadism

22. Contd …
Coarsening of
features
• Acromegaly , hypothyroidism