Chapter 18: The Pituitary Gland

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Questions and Answers

What is the location of the pituitary gland?

In a pocket of the occipital bone

In a pocket of the frontal bone

In a pocket of the parietal bone

In a pocket of the sphenoid bone at the base of the brain (correct)

What is the function of the pituitary gland?

To produce insulin

To regulate blood pressure

To regulate body temperature

To coordinate control of many downstream endocrine glands (correct)

Which hormone secreted by the anterior pituitary acts on the breast?

Thyroid-stimulating hormone (TSH)

Growth hormone

Adrenocorticotropic hormone (ACTH)

Prolactin (correct)

What is the source of almost all of the blood supply to the anterior pituitary?

The portal hypophysial vessels Signup and view all the answers

What type of hormones are TSH, ACTH, FSH, LH, and growth hormone?

Tropic hormones Signup and view all the answers

How many separate endocrine organs are present in the pituitary gland in some species?

Three Signup and view all the answers

What is the location of the growth hormone-hCS cluster?

Long arm of human chromosome 17 Signup and view all the answers

How many genes are present in the growth hormone-hCS cluster?

5 Signup and view all the answers

Which of the following is NOT a gene in the growth hormone-hCS cluster?

Insulin Signup and view all the answers

What is the name of the variant form of growth hormone?

hGH-V Signup and view all the answers

What type of modification can occur in growth hormone peptides?

Glycosylation Signup and view all the answers

What is a challenge in understanding the physiologic significance of the various growth hormone peptides?

Their structural similarities Signup and view all the answers

What is the effect of hypophysectomy on young animals?

Growth is inhibited Signup and view all the answers

What is the result of prolonged treatment with growth hormone in animals?

Gigantism Signup and view all the answers

What is the effect of growth hormone on the epiphysial plates?

They widen Signup and view all the answers

What is the result of an overabundance of growth hormone in humans?

Acromegaly Signup and view all the answers

Which of the following signaling pathways is activated by growth hormone?

JAK–STAT pathway Signup and view all the answers

What is the effect of growth hormone on the sizes of visceral organs?

They increase in size Signup and view all the answers

What is the primary source of hGH-V and hCS in the circulation?

Placenta Signup and view all the answers

What percentage of circulating growth hormone is bound to a plasma protein?

50% Signup and view all the answers

What is the normal basal plasma growth hormone level in adult humans?

Less than 3 ng/mL Signup and view all the answers

What is the half-life of circulating growth hormone in humans?

6-20 min Signup and view all the answers

What is the daily growth hormone output in adults?

0.2-1.0 mg/d Signup and view all the answers

What is the function of the growth hormone receptor?

To bind to growth hormone, producing a homodimer Signup and view all the answers

What is the indirect effect of growth hormone on β cells of the pancreas?

It increases the ability of the pancreas to respond to insulinogenic stimuli Signup and view all the answers

What is the role of insulin in protein metabolism?

It has a protein anabolic effect Signup and view all the answers

What is the name of the first somatomedin isolated?

Sulfation factor Signup and view all the answers

What is the difference between insulin and IGF-I?

IGF-I has an extension of the A chain called the D domain Signup and view all the answers

Which of the following is a member of the same family of growth factors as somatomedins?

Relaxin Signup and view all the answers

What is the significance of IGF-I in the brain?

It is a variant form of IGF-I lacking three amino terminal amino acid residues Signup and view all the answers

Study Notes

The Pituitary Gland

Located in a pocket of the sphenoid bone at the base of the brain
Acts as a coordinating center for control of many downstream endocrine glands
Can be considered to consist of at least two (and in some species, three) separate endocrine organs

Hormones Secreted by the Anterior Pituitary

Thyroid-stimulating hormone (TSH, thyrotropin)
Adrenocorticotropic hormone (ACTH)
Luteinizing hormone (LH)
Follicle-stimulating hormone (FSH)
Prolactin
Growth hormone
Prolactin acts on the breast
Remaining five hormones are tropichormones, stimulating secretion of hormonally active substances by other endocrine glands or the liver and other tissues

Growth Hormone Biosynthesis & Chemistry

The growth hormone-hCS cluster contains five genes on the long arm of human chromosome 17
One gene codes for the most abundant (“normal”) form of growth hormone
A second gene codes for the variant form of growth hormone
Two genes code for human chorionic somatomammotropin (hCS)
The fifth gene is probably an hCS pseudogene
Growth hormone secreted into the circulation by the pituitary gland is a complex mixture of different peptides with varying degrees of posttranslational modifications

Plasma Levels, Binding, & Metabolism

Circulating growth hormone is bound to a plasma protein that is a large fragment of the extracellular domain of the growth hormone receptor
Approximately 50% of the circulating pool of growth hormone activity is in the bound form
Basal plasma growth hormone level measured by radioimmunoassay in adult humans is normally less than 3 ng/mL
Growth hormone is metabolized rapidly, at least in part in the liver
Half-life of circulating growth hormone in humans is 6–20 min
Daily growth hormone output in adults is 0.2–1.0 mg/d

Growth Hormone Receptors

Growth hormone receptor is a 620-amino-acid protein with a large extracellular portion, a transmembrane domain, and a large cytoplasmic portion
Member of the cytokine receptor superfamily
Growth hormone has two domains that can bind to its receptor, and dimerization is essential for receptor activation
Growth hormone activates many different intracellular signaling cascades, including the JAK2–STAT pathway

Effects on Growth

Growth hormone stimulates growth in young animals by accelerating chondrogenesis and increasing bone matrix deposition
In animals with closed epiphyses, growth hormone produces the pattern of bone and soft tissue deformities known as acromegaly
Growth hormone does not stimulate β cells of the pancreas directly but increases the ability of the pancreas to respond to insulinogenic stimuli

Somatomedins

Growth hormone effects on growth, cartilage, and protein metabolism depend on an interaction between growth hormone and somatomedins
Somatomedins are polypeptide growth factors secreted by the liver and other tissues
There are a variety of different somatomedins, including insulin-like growth factor I (IGF-I, somatomedin C) and IGF-II
These factors are closely related to insulin, except that their C chains are not separated and they have an extension of the A chain called the D domain

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Description

This quiz covers the introduction to the pituitary gland, its location, and its functions in controlling downstream endocrine glands. It also explores the hormones secreted by the anterior pituitary.