Hypothalamus Pituitary (H-‐P) Axis

HYPOTHALAMUS PITUITARY (H-P) AXIS Learning objecves

1. Describe the physiologic & anatomic relaonship between the hypothalamus and the pituitary gland. 2. Idenfy the appropriate hypothalamic factors controlling secreon of each of the anterior pituitary hormones. 3. Explain the importance of pulsale and episodic secreon from the hypothalamus. 4. Diagram the short loop and long loop negave feedback control of the anterior pituitary hormone secreon. 5. Predict the changes in secretory rates of hypothalamic anterior pituitary and target gland hormones caused by over (or under) secreon of any of these hormones and by target organ resistance. REGULATES HOMEOSTASIS

• Pituitary regulates energy and water balances, growth, responses to stress, and reproducon. • Pituitary secretes 8 hormones which - act directly on non-endocrine ssues - act to modulate other endocrine glands and are called tropic pepdes. • Pituitary is regulated by the hypothalamus (brain). • Hypothalamus integrates aﬀerent signals from the brain, viscera, and circulang levels of substrates and hormones.

EMBRYONIC DEVELOPMENT

Anterior pituitary = glandular ssue Posterior pituitary = neural ssue HYPOTHALAMUS- PITUITARY PORTAL SYSTEM H-P AXIS TARGET CELLS REGULATION OF H-P AXIS GROWTH HORMONE (GH)

• Pulsale, 24 hour circadian rhythm

• Increases in response to stress and to sleep

• Decreases in response to increased blood glucose H-P- GH AXIS GH BIOLOGICAL ROLE GH EXCESS

Before puberty: GIGANTISM

Aer puberty: ACROMEGALY Coarsening of facial features, widening of ﬁngers, toes, hands, feet; prominent eyebrow ridge and Jaws. All organs increase in size.

*** Predict the serum IGF-1 levels- increased, decreased or unaﬀected? GENERAL CONCEPTS

Hypothalamus regulates hormone secreon from the pituitary to regulate water and energy balances, as well as reproducon and growth.

Pituitary consists of two disnct lobes (anterior & posterior) that have diﬀerent embryonic origins, are regulated separately, and produce diﬀerent hormones.

Anterior pituitary is regulated by negave feedback via hormones from the target organs. There are four major feedback loops: GH, TSH, ACTH, LH and FSH.

Many pituitary hormones are tropic for their target cells.