Oxytocin and ADH – Posterior Pituitary Hormones (Nursing)

00:00 So now that we have discussed the mechanism of actions of hormones, let's take a look at the endocrine organs and the hormones associated with them. First, let's start with the hypothalamus and the pituitary gland. The hypothalamus is connected to the pituitary gland by a stalk known as the infundibulum. From there, the pituitary is going to secrete at least 8 major hormones. The pituitary gland has 2 major lobes. We have the posterior pituitary which is composed of mostly neural tissue and will secrete neural hormones. The posterior lobe along with the infundibulum makes up what's known as the neurohypophysis. The second major lobe of the pituitary gland is the anterior pituitary or the adenohypophysis. This is going to consist of glandular tissue instead of neural tissue. If we focus on the posterior pituitary or the posterior lobe of the pituitary gland, we find that it is made up of neural tissue that is derived from a down growth of the brain. This lobe is going to maintain neural connections to the hypothalamus by way of the hypothalamic hypophyseal tract. This tract is going to run through the infundibulum. The posterior pituitary secretes 2 neural hormones. These are oxytocin and antidiuretic hormone. Both of these hormones are going to be stored in the axon terminals in the posterior pituitary. When these neurons fire, these hormones are then released into the blood. These axon terminals come from the paraventricular neurons that produce oxytocin and the supraoptic neurons that produce antidiuretic hormone or ADH.

02:25 Taking a look at the posterior pituitary hormones, we start with oxytocin which is a strong stimulant of uterine contractions that are released during childbirth. These also act as hormonal triggers for milk ejection during lactation. Both of these processes are positive feedback mechanisms where the introduction of these hormones causes the activity to continue. This hormone also acts as a neurotransmitter in the brain and it uses the PIP2 calcium second messenger system. The second posterior pituitary hormone is ADH or antidiuretic hormone. The hypothalamus contains osmoreceptors that monitors the solute concentrations.

03:24 If the concentration of a solute is too high, the posterior pituitary is triggered to secrete antidiuretic hormone. This hormone targets the kidney tubules and causes the reabsorption of more water in order to inhibit or prevent urine formation. So this is where this hormone gets its name as diuresis, means urine formation, and this is antidiuresis. Release is also triggered by pain, low blood pressure, and certain drugs. Antidiuretic hormone can also be inhibited by alcohol and also certain drugs called diuretics. High concentrations of ADH can also cause vasoconstriction and so sometimes ADH is referred to as vasopressin.