Endocrine III

What percentage of the body's calcium is found in bones?

99% of calcium is found in bones.

In what form is calcium stably stored in bones?

Hydroxyapatite in bones.

What are the essential functions of extracellular and intracellular calcium ions?

They are crucial for neuromuscular excitation, blood coagulation, hormone secretion, enzyme activity, and fertilization.

How is extracellular calcium regulated in the body?

With approximately 50% ionized, 40% protein-bound, and 10% complexed with phosphate and citrate.

What is the primary source of calcium intake for the body? What percentage is typically absorbed?

Diet is the primary source, with approximately 1/3 absorbed in the small intestine.

What are the three hormones that regulate calcium movement and which are most important for adults?

Parathyroid hormone (PTH), calcitriol, and calcitonin; PTH and calcitriol

Where is PTH produced, and is it stored?

Parathyroid gland, specifically chief cells, and is secreted continuously without storage.

List the three mechanisms by which PTH raises blood calcium levels.

1. Stimulates osteoclasts to resorb bone. 2. Stimulates kidneys to resorb Ca2+. 3. Promotes activation of vitamin D for better Ca2+ absorption.

What happens to PTH secretion when blood calcium levels are too low (hypocalcemia) or too high (hypercalcemia)?

Hypocalcemia increases PTH secretion; hypercalcemia decreases PTH secretion.

Describe the process of bone deposition and bone resorption.

Bone deposition involves osteoblasts secreting a collagen matrix, while bone resorption involves osteoclasts dissolving hydroxyapatite.

Describe the synthesis of vitamin D3 starting from its precursor molecule.

Synthesized from 7-dehydrocholesterol via UVB light, converted in the liver and kidneys to its active form.

What are the main actions of active vitamin D in the body?

It stimulates intestinal absorption of Ca2+ and promotes bone resorption through osteoclast formation.

Where is calcitonin made and what stimulates its release?

Produced in the thyroid's C cells in response to high calcium levels.

What are some consequences of hyperparathyroidism and hypoparathyroidism?

Hyperparathyroidism can cause hypercalcemia and fractures; hypoparathyroidism can lead to hypocalcemia and muscular weakness.

What are the potential results of Vitamin D deficiency in children and adults?

Children may develop rickets; adults may suffer from osteomalacia.

What is osteoporosis and what are some known risk factors?

Characterized by reduced bone quality leading to fractures; risk factors include sex and calcium-deficient diets.

What hypothalamic hormones regulate Growth Hormone (GH) secretion?

GHRH stimulates GH secretion; somatostatin inhibits it.

Where is Growth Hormone (GH) synthesized, stored, and secreted?

By somatotropic cells in the anterior pituitary gland.

What are the two main periods of rapid growth in children?

Postnatal and puberty.

How does bone length increase?

Increases at epiphyseal plates where chondrocytes produce collagen.

What are the direct and indirect ways in which GH stimulates bone growth?

GH directly stimulates chondrocytes and promotes IGF-1 production in the liver.

Provide examples of GH over-production disorders in children and adults.

Children may experience Pituitary Gigantism, while adults may develop Acromegaly.

What are some characteristic features of acromegaly?

Features include lengthened jaw, coarse facial features, and enlarged hands and feet.

What is Laron-Type Dwarfism (Pygmies)?

It is characterized by decreased responsiveness to GH due to receptor deficiency.

What are some controversial uses for Growth Hormone (GH)?

Maintaining muscle mass in AIDS patients and athletic enhancement

What are the two cell types in the parathyroid gland?

Chief cells produce PTH; the function of oxyphils is unknown.

What is the most common form of calcium phosphate in bone?

Hydroxyapatite.

What is the role of 1-α-hydroxylase in calcium homeostasis?

It activates vitamin D in the kidneys and is stimulated by PTH.

What is the difference in vitamin D acquisition between humans and dogs/cats?

Humans synthesize vitamin D with UV light and dietary sources; dogs and cats only acquire it from their diet.

What are somatomedins, and what is a key example?

They are IGFs produced by the liver in response to GH; a key example is IGF-1.

What are some metabolic effects of Growth Hormone (GH)?

GH decreases glucose utilization, stimulates lipolysis, and plays a role in growth regulation.

What are some metabolic effects of IGF-1 that oppose those of GH?

IGF-1 decreases liver glucose release and increases sensitivity to insulin.

Describe the two ways in which bone diameter increases.

Increases through growth around the bone and matrix deposits on the outer surface.

What is the underlying cause of Pituitary Dwarfism in dogs of "toy" breeds (Ateliotic)?

It is caused by GH deficiency, resulting in a uniformly small body.

What are some potential adverse effects of treating cattle with synthetic GH?

Include impacts on reproduction and possible effects on humans.