True or False 

The hormones of the posterior lobe of the pituitary gland are arginine vasopressin (AVP), also called antidiuretic hormone (ADH), and oxytocin. These hormones are synthesized in specialized nuclei of the hypothalamus called the paraventricular and supraoptic nuclei (SON and PVN). The SON are located above the optic tracts and the PVN are located on either side of the 3rd ventricle. The hormones are transported in membrane-bound vesicles through the axons to the neural lobe, where they are stored and later released.  Processing of the prohormone to the mature peptide occurs in the vesicles. Nerve action potentials arising in the cell body are propagated along the axon and trigger the release of the hormones into the peripheral circulation.

True or False

ADH, also known as vasopressin, is a nine amino acid peptide secreted from the posterior pituitary. Within hypothalamic neurons, the hormone is packaged in secretory vesicles with a carrier protein called neurophysin, and both are released upon hormone secretion.  

True or False

ADH binds to receptors in the distal or collecting tubules of the kidney and promotes reabsorbtion of water into the circulation. In the absense of ADH , the kidney tubules are impermeable to water, and it flows out as urine.  

True or False

ADH inserts aquaporins in membranes of kidney distal tubules.  These channels transport solute-free water through tubular cells and into blood, leading to a decrease in plasma osmolarity and an increase in urine osmolarity.

True or False

Both ADH secretion and thirst appear to be stimulated by hypothalamic osmoreceptors, although probably not the same ones. The osmotic threshold for ADH secretion is considerably lower than for thirst. The hypothalamus does not invoke thirst unless the situation is bad enough that ADH cannot handle it alone. 

True or False

Secretion of ADH is also simulated by decreases in blood pressure and volume, conditions sensed by stretch receptors in the heart and large arteries. Changes in blood pressure and volume are not nearly as sensitive a stimulator as increased osmolarity, but are nonetheless potent in severe conditions. For example, loss of 15 - 20% of blood volume by hemorrhage results in massive secretion of ADH.  

The following is/are a stimulatant(s) for ADH seceretion:

a. Major blood loss (>10%)

b. nausea

c. change of plasma osmolarity

d. vomitting

e. all the above

True or False

Oxytocin is 9 amino acid and differs from ADH in 2 amino acids. 

True or False

In cases where uterine contractions are not sufficient to complete delivery, physicians sometimes administer oxytocin ("pitocin") to further stimulate uterine contractions. 

True or False

It may be best to view oxytocin as a major facilitator of parturition rather than a necessary component of these processes. (Mice that are unable to secrete oxytocin due to targeted disruptions of the oxytocin gene will mate and deliver their pups without apparent difficulty. However, they do show deficits in milk ejection and have derangements in social behavior.) 

1. vaginal stimulation by the fetus.

2. abruptly declining progesterone.

3. increasing level of estrogen that increases the level of myometrial oxytocin.