Pituitary Hormones and Hypothalamic Control

Comprehensive practice questions covering the anatomy, hormonal secretions, regulation mechanisms, metabolic functions, and clinical disorders associated with the pituitary gland and hypothalamus.

What are the two distinct parts of the pituitary gland (hypophysis)?

The anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).

Where is the pituitary gland located and what are its physical dimensions?

It lies in the sella turcica at the base of the brain, measuring about $1\,cm$ in diameter and weighing between $0.5$ to $1\,gram$.

How do the embryological origins of the anterior and posterior pituitary differ?

The anterior pituitary originates from Rathke's pouch (an embryonic invagination of the pharyngeal epithelium), while the posterior pituitary originates from a neural tissue outgrowth from the hypothalamus.

Name the six important peptide hormones secreted by the anterior pituitary.

Growth hormone, adrenocorticotropin (ACTH), thyroid-stimulating hormone (TSH), prolactin (PRL), follicle-stimulating hormone (FSH), and luteinizing hormone (LH).

Match the five anterior pituitary cell types to the hormones they secrete.

Somatotropes (hGH), Corticotropes (ACTH), Thyrotropes (TSH), Gonadotropes (LH/FSH), and Lactotropes (PRL).

Which anterior pituitary cells are considered acidophils because they stain strongly with acid dyes?

Somatotropes.

What are the approximate population percentages of somatotropes and corticotropes in the anterior pituitary?

Somatotropes account for $30$ to $40\%$ and corticotropes account for about $20\%$ of the cells.

Which two hormones are secreted by the posterior pituitary?

Antidiuretic hormone (ADH), also called vasopressin, and oxytocin.

How is the secretion of the anterior pituitary regulated?

It is controlled by hypothalamic releasing and inhibitory hormones conducted through the hypothalamic-hypophysial portal vessels.

How does the hypothalamus control the posterior pituitary differently than the anterior pituitary?

Secretion from the posterior pituitary is controlled by nerve signals that originate in the hypothalamus and terminate in the posterior pituitary.

Where do the hypothalamic-hypophysial portal blood vessels originate?

They form in the median eminence, the lowermost portion of the hypothalamus that connects with the pituitary stalk.

What is the function of Somatostatin (Growth hormone inhibitory hormone)?

It inhibits the release of growth hormone.

Describe the molecular structure of Growth Hormone.

It is a small protein molecule containing $191$ amino acids in a single chain with a molecular weight of $22,005$.

What are the three primary metabolic effects of Growth Hormone?

(1) Increased rate of protein synthesis, (2) increased mobilization of fatty acids from adipose tissue, and (3) decreased rate of glucose utilization.

Why is Growth Hormone described as a 'protein sparer'?

It mobilizes large quantities of free fatty acids to supply energy for the body's cells, which decreases the breakdown of cell protein.

What causes the 'ketogenic' effect of excessive growth hormone?

Excessive mobilization of fat from adipose tissue causes the liver to form large quantities of acetoacetic acid, leading to ketosis and frequently a fatty liver.

What is meant by the 'diabetogenic' effect of growth hormone?

It causes 'insulin resistance' characterized by decreased glucose uptake in tissues, increased glucose production by the liver, and increased insulin secretion.

How does growth hormone affect the growth of long bones in length?

It stimulates the deposition of new cartilage at the epiphyseal cartilages, followed by its conversion into new bone, which elongates the shaft.

What are Somatomedins (Insulin-Like Growth Factors)?

They are small proteins formed by the liver in response to growth hormone that mediate its effects on bone growth; the most important is Somatomedin C (IGF-1).

Compare the duration of action of Growth Hormone and Somatomedin C in the blood.

Growth hormone has a half-time of less than $20\,minutes$ due to weak plasma protein binding, while Somatomedin C has a half-time of about $20\,hours$.

List three stimuli that increase growth hormone secretion.

Decreased blood glucose, starvation/protein deficiency, and deep sleep.

What is panhypopituitarism?

A term meaning decreased secretion of all the anterior pituitary hormones, often resulting from a pituitary tumor.

Describe the characteristics of panhypopituitary dwarfism.

The body develops in appropriate proportion but at a greatly decreased rate; the person usually does not pass through puberty unless only growth hormone is deficient.

What is the specific cause of dwarfism in African pygmies and Lévi-Lorain dwarfs?

A hereditary inability to form Somatomedin C, despite normal or high rates of growth hormone secretion.

What are the common effects of adult panhypopituitarism?

Hypothyroidism, depressed production of glucocorticoids by adrenal glands, and lost sexual functions due to suppressed gonadotropic hormones.