Endocrine III

Flashcard 1

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

• Back: 99% of calcium is found in bones.

Flashcard 2

• Front: In what form is calcium stably stored in bones?

• Back: Calcium is stably stored as hydroxyapatite in bones.

Flashcard 3

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

• Back: Extracellular and intracellular calcium ions are essential for several normal biochemical processes including neuromuscular excitation, blood coagulation, hormone secretion, enzyme activity, and fertilization.

Flashcard 4

• Front: How is extracellular calcium regulated in the body?

• Back: Extracellular calcium is very tightly regulated. Approximately 50% is ionized (free), 40% is protein-bound, and 10% is complexed with phosphate and citrate.

Flashcard 5

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

• Back: The primary source of calcium intake is diet, and approximately 1/3 is absorbed in the small intestine.

Flashcard 6

• Front: What are the three hormones that regulate calcium movement between bone, kidneys, and intestine? Which are most important in adults?

• Back: The three hormones are parathyroid hormone (PTH), calcitriol (vitamin D3), and calcitonin. PTH and calcitriol (vitamin D3) are most important in adults.

Flashcard 7

• Front: Where is PTH produced, and is it stored?

• Back: PTH is a peptide made by the parathyroid gland and is secreted continuously (not stored). It is produced by chief cells in the parathyroid gland.

Flashcard 8

• Front: List the three mechanisms by which PTH acts to raise blood calcium levels when plasma calcium begins to fall.

• Back: PTH raises blood calcium by:

  • Stimulating osteoclasts to resorb bone (primary mechanism)

  • Stimulating kidneys to resorb Ca2+

  • Stimulating kidneys to produce the enzyme needed to activate vitamin D, which promotes better absorption of Ca2+ from food/drink across the intestinal epithelium.

Flashcard 9

• Front: What happens to PTH secretion when blood calcium levels are too low (hypocalcemia)? What about when they are too high (hypercalcemia)?

• Back:

  • Hypocalcemia (too low): ↑ PTH secretion (stimulates resorption)

  • Hypercalcemia (too high): ↓ PTH secretion

Flashcard 10

• Front: Describe the process of bone deposition and bone resorption.

• Back:

  • Bone deposition: Osteoblasts secrete a matrix of collagen protein, which becomes hardened by deposits of hydroxyapatite.

  • Bone resorption: Osteoclasts dissolve hydroxyapatite and return the bone Ca2+ (& phosphate) to the blood.

Flashcard 11

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

• Back:

  1. Vitamin D3 is produced from its precursor molecule, 7-dehydrocholesterol, under the influence of UVB sunlight.

  2. Vitamin D3 is secreted into the blood from the skin/intestine and functions as a pre-hormone (inactive).

  3. It goes to the liver, where a hydroxyl group is added to C25.

  4. It requires a hydroxyl group addition to C1 to become active, a process done by an enzyme in the kidneys that is stimulated by PTH.

Flashcard 12

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

• Back: Active vitamin D stimulates intestinal absorption of Ca2+ and directly stimulates bone resorption by promoting the formation of osteoclasts.

Flashcard 13

• Front: Where is calcitonin made and what stimulates its release? What is its primary role in adult humans?

• Back: Calcitonin is made in the C cells of the thyroid in response to high Ca2+. It is thought to play only a minor role in adult humans.

Flashcard 14

• Front: What are some consequences of hyperparathyroidism and hypoparathyroidism?

• Back:

  • Hyperparathyroidism: Hypercalcaemia (too much Ca2+ in blood), increased bone resorption (fractures), mineralization of soft tissues, increased thirst & urination.

  • Hypoparathyroidism: Hypocalcaemia (not enough Ca2+ in blood), muscular weakness, ataxia, cardiac arrhythmias.

Flashcard 15

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

• Back:

  • Children: Rickets (poor bone mineralization, bone pain, stunted growth, deformities)

  • Adults: Osteomalacia (bone pain, fractures)

Flashcard 16

• Front: What is osteoporosis and what are some known risk factors?

• Back: Osteoporosis is the most common disorder of bone, characterized by a reduction of bone quality due to excess resorption, leading to a risk of bone fractures. Known risk factors include sex (females, especially after menopause), lack of exercise, and a calcium-deficient diet.

Flashcard 17

• Front: What are the learning objectives related to the somatotropic axis?

• Back: The learning objectives are to identify growth hormones & their origins and understand clinical applications.

Flashcard 18

• Front: What hypothalamic hormones regulate Growth Hormone (GH) secretion from the anterior pituitary?

• Back: GHRH stimulates GH secretion, and somatostatin (GHIH) inhibits GH secretion.

Flashcard 19

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

• Back: GH is synthesized, stored, and secreted by somatotropic cells in the lateral wings of the anterior pituitary gland.

Flashcard 20

• Front: What are the two main periods of rapid growth in children, and what tissues does GH stimulate growth in?

• Back: The two main periods of rapid growth are postnatal and puberty. GH stimulates growth of bone and cartilage, and soft tissue (through hypertrophy and hyperplasia).

Flashcard 21

• Front: How does bone length increase, and what role do chondrocytes and osteoblasts play?

• Back: Bone length increases at epiphyseal plates. The epiphyseal plate contains chondrocytes that produce collagen. As this layer thickens and calcifies, chondrocytes degenerate. Osteoblasts then invade and lay bone matrix on top of the cartilage base.

Flashcard 22

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

• Back: GH directly stimulates chondrocytes and stimulates the production of IGF-1 in the liver, which in turn helps stimulate chondrocyte and osteoblast activity.

Flashcard 23

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

• Back:

  • Children: Pituitary Gigantism

  • Adults: Acromegaly

Flashcard 24

• Front: What are some characteristic features of acromegaly?

• Back: Acromegaly is characterized by a lengthened jaw, coarse facial features, and growth of hands & feet.

Flashcard 25

• Front: What is Laron-Type Dwarfism (Pygmies)?

• Back: Laron-Type Dwarfism is characterized by decreased responsiveness to GH (receptor deficiency).

Flashcard 26

• Front: What are some controversial other uses for Growth Hormone (GH)?

• Back: Maintaining muscle mass in individuals with AIDS and bodybuilding/athletic enhancement are controversial uses for GH.

Flashcard 27

• Front: What are the two cell types found in the parathyroid gland, and what is the known function of each?

• Back: The two cell types are:

  • Chief cells: produce PTH

  • Oxyphils: function unknown

Flashcard 28

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

• Back: The most common form of calcium phosphate in bone is hydroxyapatite.

Flashcard 29

• Front: What is the role of 1-α-hydroxylase enzyme in calcium homeostasis, and what stimulates its production?

• Back: The 1-α-hydroxylase enzyme is needed to activate vitamin D in the kidneys, and its production is stimulated by PTH.

Flashcard 30

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

• Back: Humans can synthesize vitamin D from 7-dehydrocholesterol with UV light in the skin and obtain it from dietary sources. Dogs and cats cannot synthesize vitamin D in their skin and must obtain it only from their diet (it is an essential vitamin for them).

Flashcard 31

• Front: What are somatomedins, and what is a key example mentioned in the text?

• Back: Somatomedins are insulin-like growth factors (IGFs) produced by the liver in response to GH. A key example is IGF-1.

Flashcard 32

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

• Back: GH can lead to decreased glucose utilization in most tissues, lipolysis in adipose tissue, and release of fatty acids. It also plays an important role in the endocrine regulation of growth (muscle & bone).

Flashcard 33

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

• Back: IGF-1 can lead to decreased liver glucose release, decreased plasma glucose concentration, and increased sensitivity of tissue to insulin, which are opposite to some effects of GH.

Flashcard 34

• Front: Describe the two ways in which bone diameter increases.

• Back: Bone diameter increases through growth occurring around the bone and matrix deposits on the outer surface of bone.

Flashcard 35

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

• Back: Ateliotic Pituitary Dwarfism in "toy" breeds is due to GH deficiency, resulting in a uniformly small body.

Flashcard 36

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

• Back: Potential adverse effects on cattle include impacts on reproduction. The text also raises the question of potential adverse effects on humans.