Lecture 6.1 - The Hypothalamic-pituitary axis and growth hormone

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Questions and Answers

What is the primary function of CRH in the hypothalamus?

Regulation of thyroid hormone release

Regulation of growth hormone release

Inhibition of prolactin release

Stimulation of adrenal glands (correct)

Which of the following hormones is NOT produced by the anterior pituitary?

TRH (correct)

PRL

ACTH

TSH

What is the effect of somatostatin on growth hormone secretion?

Stimulation of growth hormone release

Regulation of thyroid hormone release

Stimulation of prolactin release

Inhibition of growth hormone release (correct)

What is the primary function of GH in adults?

Regulation of metabolism and body composition Signup and view all the answers

What is the result of growth hormone deficiency in childhood?

Pituitary dwarfism Signup and view all the answers

What is the effect of IGFs on lipid metabolism?

Increase in lipolysis in adipose tissue Signup and view all the answers

What is the function of GHRH in the hypothalamus?

Stimulation of growth hormone release Signup and view all the answers

What is the effect of GH on bone growth?

Stimulation of long bone growth before epiphyseal closure Signup and view all the answers

What is the mechanism of GH action on cells?

Activation of JAK/STAT pathway Signup and view all the answers

What is the function of PRH in the hypothalamus?

Stimulation of prolactin release Signup and view all the answers

Which of the following functions is NOT performed by the hypothalamic pituitary axis?

Regulation of body temperature Signup and view all the answers

What is the origin of the anterior pituitary gland?

Oral ectoderm Signup and view all the answers

Which hormone is NOT produced by the hypothalamus and released by the posterior pituitary gland?

Adrenocorticotropic hormone Signup and view all the answers

What is the role of the hypophyseal portal system in anterior pituitary function?

To transport hormones from the hypothalamus to the anterior pituitary gland Signup and view all the answers

Which of the following is a characteristic of neurocrine function?

Hormones are produced by the hypothalamus and released by the posterior pituitary gland Signup and view all the answers

What is the role of the posterior pituitary gland in the regulation of water homeostasis?

To synthesize and release antidiuretic hormone Signup and view all the answers

Which of the following hormones is NOT released by the anterior pituitary gland?

Oxytocin Signup and view all the answers

What is the relationship between the hypothalamus and the posterior pituitary gland?

They are physically connected through the infundibulum Signup and view all the answers

Study Notes

Hypothalamic Pituitary Axis

The hypothalamic and pituitary gland forms a complex functional unit that serves as the major link between the endocrine and nervous systems
Modulates a wide variety of processes: • Body growth • Reproduction • Adrenal gland function • Water homeostasis • Milk secretion • Lactation • Thyroid gland function • Puberty

Pituitary Gland

Consists of two parts: • Anterior pituitary gland (adenohypophysis) - endocrine tissue • Posterior pituitary gland (neurohypophysis) - nerve tissue
The anterior and posterior pituitary glands have distinct embryological origins and distinct functions: • Anterior pituitary arises from evagination of oral ectoderm (Rathke's pouch) - primitive gut tissue • Posterior pituitary originates from neuroectoderm - primitive brain tissue

Neurocrine Function of Posterior Pituitary

Hormones produced in the hypothalamus
Oxytocin and antidiuretic hormone (vasopressin) produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus
Transported down nerve cell axons in vesicles to the posterior pituitary
Stored and released from posterior pituitary nerve endings into the general circulation to act on distant targets

Anterior Pituitary Function

Hormones synthesized in the hypothalamus are transported down axons and stored in the median eminence before release into the hypophyseal portal system
These hormones stimulate (or inhibit) target endocrine cells in the anterior pituitary gland (neurocrine function)
Endocrine cells of the anterior pituitary secrete a variety of hormones into the bloodstream to act on distant target cells (endocrine function)

Tropic Hormones of the Hypothalamus

6 tropic hormones (stimulating) produced in the hypothalamus: • TRH (thyrotropin-releasing hormone) • PRH (prolactin-releasing hormone) = TRH (minor +ve control on prolactin) • PIH (prolactin-release-inhibiting hormone) (dopamine) • CRH (corticotropin-releasing hormone) • GnRH (gonadotropin-releasing hormone) • GHRH (growth hormone-releasing hormone) • GHIH (growth hormone-inhibiting hormone) (Somatostatin)

Hormones Produced by the Anterior Pituitary

TSH (thyroid-stimulating hormone)
ACTH (adrenocorticotropic hormone)
LH (luteinizing hormone)
PRL (prolactin)
GH (growth hormone)

Negative Feedback

The pathways by which hypothalamic and anterior pituitary hormones are produced are often regulated by negative feedback: • Short loop or long loop negative feedback pathways

Growth Hormone

Produced in the anterior pituitary: • Stimulated by hypothalamic GHRH • Inhibited by hypothalamic somatostatin
Protein hormone (191 aa) has signal peptide that must be cleaved before proper folding
Growth-promoting effects mainly exerted indirectly via insulin-like growth factors (somatomedins)

Control of GH Secretion

Principle control is via the hypothalamus: • GHRH -> increases GH secretion • Somatostatin -> decreases GH secretion
CNS regulates GH secretion via inputs into the hypothalamus effecting GHRH and somatostatin
GH secretion is regulated by long loop and short loop negative feedback

Growth Hormone Deficiency

In childhood, results in pituitary dwarfism
Proportionate type of dwarfism
Complete or partial deficiency
Both types respond to GH therapy

Growth Hormone Excess

In childhood, results in GIANTISM
In adulthood, leads to acromegaly: • Characterized by large extremities: • Hands • Feet • Lower jaw

Insulin-Like Growth Factors (IGFs)

2 IGFs in mammals (IGF1 and IGF2)
Binding proteins modulate their availability in the blood
Actions of IGFs can be paracrine and autocrine as well as endocrine
IGFs act through IGF receptors (distinct from GH receptors) to modulate: • Cell growth (hypertrophy) • Cell number (hyperplasia) • Increase in the rate of protein synthesis • Increase in the rate of lipolysis in adipose tissue

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Description

Explore the complex functional unit of the hypothalamic and pituitary gland, modulating various processes such as body growth, reproduction, and hormonal functions. Learn how they connect the endocrine and nervous systems.