Hypothalamic-Pituitary Axis & Feedback Control

What is the function of Hypothalamus and Pituitary Gland

Hypothalamus controls endocrine signals

Pituitary gland has two parts, the anterior pituitary and the posterior pituitary

Anterior pituitary makes and releases hormones

Posterior Pituitary stores and releases hypothalamic hormones

How does the hypothalamus control the release of hormones from the Pituitary?

Posterior Pituitary: Nerve signals from the hypothalamus triggers the release of stored hormones.

Anterior Pituitary: Hormones from the hypothalamus travel through the hypophyseal portal system to control hormone release

What hormones does the posterior pituitary release?

ADH and oxytocin

Where are the hormones made in the hypothalamus and how is it transported

Hormones travel down axons from the supraoptic nucleus and paraventricular nucleus

Nerophysins carry ADH and oxytocin during transport

What’s the function of ADH?

Water retention- Concentrates urine when body needs to save up water

Blood vessel constriction- constricts blood vessels to help maintain blood pressure during stress or loss

What are osmoreceptors and stretch receptors and how does ADH release work depending on on when water is low and high

Osmoreceptors- detect changes in the blood concentration

Stretch receptors- detect changes in blood volume

When water is low:

Less water in the body makes the blood more concentrated

Osmoreceptors sense this change ans signal for more ADH to be released

ADH helps the kidney save water, reducing urine

When water is high:

Extra water dilutes the blood

Osmoreceptors stop signalling, and less ADH is released

The kidneys remove the extra water by producing more urine

What’s the role of Oxytocin

Oxytocin helps release milk during breastfeeding

Contracts the uterus

Released during breastfeeding and labour

What are the different cell types in the anterior pituitary?

Gonadotropes- Produce LH and FSH

Corticotropes- Produce ACTH helps body respond to stress

Thyrotropes - Produce TSH

Lactotropes- Produce Prolactin

Somatotropes- Produce Growth Hormone

How does the portal system work

Step 1: Hypothalamus releases small peptide hormones.

Step 2: These enter the first capillary bed.

Step 3: Portal vessels carry them down the pituitary stalk.

Step 4: They reach the anterior pituitary and act on specific cells.

Step 5: Pituitary hormones enter the bloodstream and act on target organs.