Lecture #5: Hormones of the anterior pituitary

Pituitary

Made up of an anterior & posterior lobe

What is the anterior part of the pituitary made up of?

Glandular tissue

What is the posterior part of the pituitary made up of?

Neural tissue (part of the brain)

Posterior pituitary

Made up of neurosecretory cells & is part of the brain
• Made up of axons of neurons from the
hypothalamus
• Hormones produced in soma
• Transport down axon
• Released into capillary bed in pituitary
• Taken into general circulation

What are the two hormones the posterior pituitary releases?

1. Oxytocin
2. ADH (Antidiuretic hormone)

What does oxytocin stimulate?

Stimulates smooth muscle contraction
• parturition (child birth)
• milk let down (pushing milk towards teats)
• ejaculation

Parturition

Child birth which is a positive feedback loop
(Ferguson reflex)

Ferguson reflex

1. Fetus pushes into cervix stimulate oxytocin
secretion
2. Oxytocin stimulates more smooth muscle
contraction
3. Fetus pushes harder into cervix

When does the Ferguson reflex stop?

The positive feedback loop is stopped when the child is finally out

Milk letdown

Positive feedback loop to push milk to teat

Oxytocin Analogs

Used in reproductive medicine
• Pitocin® - synthetic oxytocin
• Used to induce or speed up labor
• Used to expel placenta/debris
after giving birth
• Use to stimulates milk let down

What roles do oxytocin play?

- Hormone
- Neurotransmitter
(called the love hormone/plays a role in mate bonding)

Antidiuretic Hormone (ADH)

Stimulated by blood thickening or low BP (hypothalamus monitors that which stimulated ADH)

What does ADH do to water reabsorption?

ADH increases water reabsorption in the kidneys

How does ADH increase water reabsorption?

1. ADH stimulates expression
of aquaporins
2. Water diffuses into
interstitial tissue and back
into blood
*Decreases urine production
Less/more concentrated urine*

What does ADH do to blood?

Stimulates vasoconstriction

How does ADH stimulate vasoconstriction?

Stimulates contraction of
smooth muscle around blood
vessels
• decreases space in vascular
system
• Increases blood pressure

AVPR2 receptor

Regulation of the body water homeostasis by determining the level of reabsorption of water from prourine through Aquaporin-2 (AQP2) water channels.

What happens when ADH binds to AVPR2 receptor?

Increases aquaporin expression which not allows more water to flow out

What enzyme is involved with the increase of aquaporin expression?

Adenylyl cyclase

What happens when ADH binds to a VPR1A receptor?

It causes smooth muscle contractions

What enzyme is involves with AVPR1A causing smooth muscle contractions?

Alpha g protein binding to a Phospholipase C