Physiology Review -II

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Hypophyseal portal system connects - which structures?
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Hypophyseal portal system - connects the hypothalamus with the anterior pituitary.

What is the main function of Hypophyseal portal system?
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Main function of Hypophyseal portal system is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland.

How many amino acids are there in Vasopressin?
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Vasopressin- is an oligopeptide containing nine amino acids

Posterior pituitary secretes ------ hormones
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Posterior pituitary secretes two important hormones: ADH and Oxytocin

Where the ADH and Vasopressin are formed ?
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ADH and oxytocin. These hormones are formed in supraoptic and paraventricular nuclei of hypothalamus and released into posterior pituitary.

What is cleaved enzymatically to release ADH?
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Prepropressophysin is cleaved enzymatically to release
ADH,
neurophysin II ,
glycoprotein molecules.

What is the function of Neurophysin?
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Neurophysin - serves as carrier protein
transport the hormone from the cell body to the axon terminals

What are the Herring bodies?
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Herring bodies
These are neurosecretory bodies or neurosecretory terminals.
Found in the posterior pituitary.
They represent the terminal end of the axons from the hypothalamus
Hormones are temporarily stored in these locations.

What is the carrier protein for oxytocin?
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Neurophysin I is the carrier protein for oxytocin.

What is the carrier protein for vasopressin (ADH)?
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Neurophysin II is a carrier protein for vasopressin (ADH)

What are the Two important Stimuli for ADH?
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Plasma osmolality and ECF volume.

Increased plasma osmolality above--------------- increases ADH secretion
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Increased plasma osmolality above 285 mOsm/kg increases ADH Secretion

ADH causes water retention and brings osmolality back to normal. ADH secretion

What are the stimuli that Inhibit ADH Secretion?
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Decreased plasma osmolality,
Increased ECF volume,
Decreased temperature,
Ethanol,
Cortisol,
ANP,
Thyroxine
α-adrenergic agonist
All of above factors decrease ADH secretion.

What is the biologic half-life of ADH?
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Biologic half-life of ADH is about 18 min

ADH increases permeability of the tubular cells by acting on which receptors?
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V2 receptors

Which Aquaporins found in Brain?
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Kidney - Aquaporins 1, 2 and 3
Brain - Aquaporin 4
Salivary and Lacrimal glands and respiratory tract- Aquaporin 5
Human leucocytes -Aquaporin 9

Diabetes Insipidus
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There is deficiency of ADH
polyuria and polydipsia.
Polyuria occurs due to ADH deficiency that promotes water diuresis. Polydipsia occurs secondary to dehydration caused by polyuria.

What is the difference in osmolality of the urine in Diabetes Insipidus and Diabetes mellitus?
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Diabetes Insipidus -Urine osmolality is <300 mOsm/L,
Diabetes mellitus- Urine is hyperosmolal due to loss of glucose in urine [>1200 mOsm/L]

What are the Types of Diabetes Insipidus?
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Two types of DI:
Nephrogenic Diabetes Insipidus- kidneys fail to respond to ADH
Neurogenic Diabetes Insipidus- deficiency of ADH secretion .
Neurogenic DI is also called central DI

What are the drugs causing Nephrogenic DI -
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Demeclocycline,
Rifampicin,
Aminoglycoside,
Lithium,
Cisplantin
Amphotericin B.

Genetic disorders that cause Nephrogenic DI -
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X-linked recessive defect -V2 receptor gene is deficient
Autosomal defect - aquaporin gene is deficient

What is the Drug of choice for nephrogenic diabetes insipidus?
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The first line of treatment is hydrochlorothiazide and amiloride

What is the Drug of choice for Central diabetes insipidus?
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Vasopressin analogs such as Desmopressin.

What is SIADH (syndrome of inappropriate ADH secretion)?
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ADH secretion is inappropriately high relative to serum osmolality.

Drugs That Can cause SIADH?
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Drugs such as -
desmopressin, chlorpropamide, high dose of oxytocin, vincrisitine, phenothiazine, carbamazepine

What is vasopressin escape?
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ADH is counteracted by a process called vasopressin escape that limits the degree of hyponatremia.
This escape phenomenon occurs due to down regulation of aquaporins production in collecting duct
Urine output increases despite high ADH levels in plasma

How many amino acids are present in OXYTOCIN?
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Oxytocin is an oligopeptide containing nine amino acids.

Oxytocin secretion occurs in response to which physiological stimuli?
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Suckling - at the time of breastfeeding,
Cervical dilatation - at the time of parturition

Which Reflexes are mediated by OXYTOCIN?
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Oxytocin mediates two physiological reflexes:
1. milk ejection reflex
2. parturition reflex.

Which infusion is given to facilitate the progress of labor?
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OXYTOCIN INFUSION

Which injection is routinely injected immediately following delivery of placenta, to prevent excessive postpartum hemorrhage?
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OXYTOCON INJECTION
Mechanism-
uterus contracts severely in response to oxytocic and bleeding vessels are compressed in the contracted uterus that prevents bleeding.