Honours / Discipline Specific Elective (DSE)
ENDOCRINOLOGY
►Unit 1: Introduction to Endocrinology
General idea of Endocrine systems, Classification, Characteristic and Transport of Hormones, Neuro-secretions and Neuro-hormones: Examples and Functions
Q. What are neurohormones? Give two examples.
Neurohormones are chemical messengers synthesized and secreted by nerve cells. Some neural messengers are relatively small molecules such as amino acids (glycine, glutamate) or molecules derived thereof, for example serotonin, norepinephrine and dopamine. Neurohormones can be released into a synaptic cleft to rapidly activate pre- and postsynaptic membranes. This neurocrine route of delivery transfers information from neurons to adjacent neurons, muscle cells or secretory (glandular) cells. Neurohoromones can also be released from less-specialized sites along the neuron to activate receptors on nearby cells.
Q.Who are the spare receptors?
In most cells, a maximum biological response is achieved when only a small percentage of receptors is occupied. For example, maximal stimulation of steroidogenesis by Leydig cells of the testis occurs when only about 1% of LH receptors are occupied. The additional receptors are referred to as spare receptors and are considered to be fully functional. The role of this receptor reserve may be to increase the sensitivity of target cells to activation by low levels of hormones. The term spare is used in a relative sense, as the degree of receptor excess differs according to the particular biological response measured.
►Unit 2: Hypothalamo-Hypophyseal Axis
Structure and functions of hypothalamus and Hypothalamic nuclei, Regulation of neuroendocrine glands, Feedback mechanisms, Hypothalamo-Hypophyseal-Gonadal Axis. Structure of pituitary gland, Hormones and their functions, Hypothalamo-hypophyseal portal system
Q. Discuss the endocrine control of Hypothalamo - Hypophyseal - Gonadal Axis in male.
Answer key:
►Unit 3: Peripheral Endocrine Glands
Structure, Hormones and Functions of Thyroid gland, Parathyroid, Adrenal, Pancreas, Ovary and Testis. Disorders of endocrine glands (Diabetes mellitus type I & Type II; Graves’ Disease).
Q. What is diabetes insipidus? What do you mean by SIAD?
(i)A rare clinical disorder of the hypothalamus is diabetes insipidus. The patient produces an abnormally large volume (3 to 30 liters/day) of dilute urine. This diuresis is most commonly due to the absence of AVP that normally controls water reabsorption in the kidney.
(ii)Physical damage (such as a brain lesion) or certain infections (e.g., encephalitis) account for the remainder. Nephrogenic diabetes insipidus is the result of a failure of the kidney tubules to respond to normal or above-normal levels of AVP.
(iii)Genetic modifications might be inherited or acquired and might be linked to other diseases: diabetes mellitus (DM), visual impairment, or deafness (Wolfram syndrome).
(iv)Diabetes insipidus might also occur as a consequence of other illnesses such as trauma, tumors, or infections.
(v)In nephrogenic diabetes insipidus, vasopressin binds in the kidney to the vasopressin receptor, which in turn stimulates adenylate cyclase and thus increases intracellular levels of cyclic adenosine monophosphate (cAMP). This increase of cAMP concentration is lacking in some patients; in other patients, cAMP levels increase, but the following events are inhibited.
Apart from genetic defects, metabolic anomalies (increased or diminished calcium concentration), drug use (e.g., lithium salts), sickle cell anemia, and chronic nephropathies have been reported as causal.
The syndrome of inappropriate antidiuresis (SIAD) is caused by excessive AVP release. High levels of AVP result in excessive water retention, elevated blood pressure, and reduced urine production. Drugs such as demeclocycline block the action of AVP (Vasopressin) on the kidney and are used to treat this condition. However, long-term use of such drugs induces nephrogenic diabetes insipidus. Medications that control AVP release from the pars nervosa often are not uniformly effective and can influence other hypothalamic functions.
►Unit 4: Regulation of Hormone Action
Mechanism of action of steroidal, non-steroidal hormones with receptors (cAMP, IP3-DAG), Calcium and Glucose homeostasis in mammals. Bioassays of hormones using RIA & ELISA, Estrous cycle in rat and menstrual cycle in human
Q. How does ELISA testing work?
There are variations of the ELISA test, but the most utilized type consists of an antibody attached to a solid surface (polystyrene plate). This antibody has affinity for the substance of interest, such as a hormone, bacteria, or another antibody.
For example, human chorionic gonadotropin hormone (HCG), the commonly measured protein that indicates pregnancy, can be detected by ELISA. A mixture of purified HCG linked to an enzyme and the test sample (blood or urine) are added to the test system. If no HCG is present in the test sample, then only the linked enzyme will bind to the solid surface. The more substance of interest that is present in the test sample, the less linked enzyme will bind to the solid surface. The more of the substance of interest is present it will cause a reaction and show up on the test plate in some way, such as a colour change of the solution (or like a pregnancy test "two pink lines" or a "+" mark).
►Unit 5. Non Mammalian Vertebrate Hormone
Functions of Prolactin in Fishes, Amphibia & Birds; Function of Melanotropin in Teleost fishes, Amphibians and Reptiles.
Q. How does prolactin help in maintaining the balance of water and electrolytes in fish?
(i)It helps in survival of hypophysectomized euryhaline freshwater species, restoration of water turnover in hypophysectomized fish, restoration of plasma Na+ and Ca2+ in hypophysectomized eels when given with cortisol, skin, buccal, and gill mucus secretion.
(ii)It reduces gill Na+ efflux (reduced permeability) and gill permeability to water.
(iii)It helps in inhibition of gill Na+/K+-ATPase.
(iv)It increases the urinary water elimination and decreases salt excretion.
(v)It causes stimulation of renal Na+/K+-ATPase and decreases water absorption and increases Na+ absorption in bladder.
(vi)It decreases salt and water absorption from eel gut.