Bone Structure and Function Quiz

Questions and Answers

What effect does PTH have on renal phosphate reabsorption?

It decreases renal phosphate reabsorption. (correct)

It increases renal phosphate reabsorption.

It has no effect on renal phosphate reabsorption.

It causes a complete cessation of renal phosphate reabsorption.

How does calcitriol influence renal reabsorption of phosphate?

It increases renal reabsorption of phosphate. (correct)

It leads to complete elimination of phosphate in the urine.

It decreases renal reabsorption of phosphate.

It has no effect on renal reabsorption of phosphate.

What overall effect does calcitonin have on phosphate levels in the body?

It increases renal reabsorption of phosphate.

It decreases phosphate levels due to increased renal loss. (correct)

It has no significant effect on phosphate levels.

It increases phosphate absorption from the diet.

What is the relationship between calcium and phosphate regulation in the body?

Hormones regulating calcium levels also regulate phosphate, but their actions differ. Signup and view all the answers

What is the primary action of calcitriol in relation to calcium levels?

It increases serum calcium levels by enhancing intestinal calcium absorption. Signup and view all the answers

What is the primary role of carbonic anhydrase in bone resorption?

It releases acid into Howship’s lacuna. Signup and view all the answers

How does the body maintain calcium homeostasis?

Through the regulation of hormones like PTH and OPG. Signup and view all the answers

What is the function of osteocytes in bone remodeling?

They provide gap junctions for signaling between bone cells. Signup and view all the answers

Which of the following hormones is NOT involved in regulating calcium levels?

Growth hormone Signup and view all the answers

What primarily keeps intracellular calcium levels low?

Sequestering calcium in organelles. Signup and view all the answers

Which statement best describes the concentration of calcium in the body?

Half of the extracellular calcium is ionized. Signup and view all the answers

PTH increases serum calcium levels by which of the following mechanisms?

Stimulating vitamin D activation in the kidney. Signup and view all the answers

What role do gap junctions in osteocytes play during bone remodeling?

They allow transfer of signals and nutrients between bone cells. Signup and view all the answers

What is the primary function of osteoblasts in bone physiology?

Bone formation Signup and view all the answers

Which component forms the main inorganic part of the bone matrix?

Hydroxyapatite crystals Signup and view all the answers

How do osteoblasts influence osteoclast activity?

By expressing RANK ligand (RANKL) Signup and view all the answers

Which of the following describes osteocytes?

Mechanosensors that transport nutrients Signup and view all the answers

What role does alkaline phosphatase (ALP) play in bone formation?

Breaks down pyrophosphate to promote mineralization Signup and view all the answers

What does Osteoprotegerin (OPG) do in bone metabolism?

Binds to RANKL and inhibits its action Signup and view all the answers

Which mineral is primarily involved in forming hydroxyapatite crystals in bone?

Calcium Signup and view all the answers

What is the effect of sustained high levels of parathyroid hormone (PTH) on bones?

Promotes bone resorption Signup and view all the answers

Study Notes

Types of Bones

Cortical Bone: Also known as compact or lamellar bone; dense and forms the outer layer of bone.
Trabecular Bone: Also referred to as medullary, cancellous, or spongy bone; less dense, found within the interior of bones.

Bone Matrix Composition

Composed of Organic (30-35%) materials:
- Osteoid, primarily made of Type I collagen.
- Glycosaminoglycans (GAGs) such as chondroitin sulfate, keratin sulfate, and hyaluronic acid.
- Non-collagen proteins including osteocalcin, osteonectin, and osteopontin.
Composed of Inorganic (65-70%) materials:
- Hydroxyapatite crystals (Ca10(PO4)6(OH)2) provide bone rigidity and strength.
- Includes additional minerals that enhance bone strength.

Major Bone Cell Types

Osteoblasts: Responsible for bone formation by secreting osteoid proteins.
Osteoclasts: Involved in bone resorption, breaking down bone tissue.
Osteocytes: Function as mechanosensors and facilitate mineral transport.

Osteoblasts Function

Secrete proteins, forming osteoid as a scaffold for mineral deposition.
Alkaline phosphatase (ALP) promotes bone mineralization by breaking down pyrophosphate (PPi).
RANK ligand (RANKL) produced by osteoblasts activates osteoclasts; osteoprotegerin (OPG) inhibits this process.
Parathyroid hormone (PTH) partially stimulates osteoclast activity through osteoblasts, while calcitriol enhances osteoblast differentiation and OPG release.

Osteoclasts Function

Stimulated by RANKL and inhibited by calcitonin temporarily.
Create Howship's lacunae by secreting acid and proteolytic enzymes to dissolve bone matrix components.

Bone Remodeling Process

Bone remodeling is a balanced cycle of formation and resorption regulated by RANK and OPG, along with hormone influences (PTH, vitamin D, calcitonin).
Essential for maintaining structural integrity of the skeleton and calcium homeostasis.

Osteocytes Role

Reside in a fluid-rich environment that aids calcium and phosphate transport.
Form gap junctions with other osteocytes and osteoblasts for communication and signaling.
Sense mechanical loading through the movement of bone fluid and exhibit piezoelectric properties.

Calcium Regulation in the Body

Major calcium reservoir is in bone, primarily as hydroxyapatite.
Intracellular calcium levels are low; tightly regulated due to its physiological importance.
Extracellular calcium concentration is significantly higher than intracellular, with approximately 50% in ionized form.

Hormonal Regulation of Calcium

Parathyroid Hormone (PTH): Increases serum calcium by promoting bone resorption and reabsorption in kidneys; initiates vitamin D activation.
Vitamin D (Calcitriol): Increases intestinal calcium absorption and renal reabsorption. Stimulates both osteoblastic and osteoclastic activities.
Calcitonin (CT): Reduces serum calcium by inhibiting osteoclastic activity and renal reabsorption.

Phosphate Homeostasis

Closely linked to calcium regulation; hormones affecting calcium also impact phosphate levels.
PTH raises serum phosphate initially by stimulating bone resorption but ultimately decreases overall phosphate due to renal excretion.
Calcitriol enhances intestinal phosphate absorption while promoting bone turnover.
Calcitonin generally results in a reduction of phosphate levels due to increased renal excretion.

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Description

Test your knowledge on the different types of bones, their matrix components, and the major cell types involved in bone tissue. This quiz covers the functions of cortical and trabecular bone and the roles of osteoblasts, osteoclasts, and osteocytes in maintaining bone health.