Metabolism of bone and muscle

Question 1

What is bone composed of?

Answer 1

Bone is a connective tissue divided into an extracellular matrix, consisting of organic and inorganic parts

Question 2

What are the organic and inorganic components of the bone’s extracellular matrix?

Answer 2

The organic part includes a lot of collagen 1 and many proteins. The inorganic part consists of calcium phosphate and hydroxyapatite.

Question 3

What is the role of osteocalcin in bone?

Answer 3

Osteocalcin, found in the extracellular matrix of bone, helps build the inorganic part of the bone.

Question 4

Name the three types of bone cells on the surface of bone.

Answer 4

Osteoblasts, osteoclasts, and cuboidal cells on the surface are osteoblasts.

Question 5

Where are osteoclasts found, and what is their function?

Answer 5

Osteoclasts are found in lacunae and are macrophages that remove bone, leading to bone degradation.

Question 6

Where are osteocytes located, and what is their function?

Answer 6

Osteocytes are found inside the bone and form the majority of the bone. They play a crucial role in bone maintenance and function as mechanosensors.

Question 7

What is the role of RANKL and OPG in bone regulation?

Answer 7

RANKL is a ligand that activates osteoclasts, while OPG is a molecule that protects bone by blocking RANKL. Osteocytes secrete RANKL and OPG based on pressure.

Question 8

How do hormones (PTH, calcitonin, calcitriol) influence bone?

Answer 8

PTH increases blood calcium levels by acting in the kidneys, intestines, and activating osteoclasts. Calcitonin inhibits osteoclast activity, acting in opposition to PTH. Calcitriol has a dual role in bone metabolism based on dietary calcium availability.

Question 9

Name some medications used in bone-related conditions.

Answer 9

Denosumab (RANKL antibody), Teriparatide (PTH analog), Romosumab (sclerostin antibody) are used for conditions like osteoporosis

Question 10

What enzymes and proteins are markers of bone metabolism?

Answer 10

Alkaline phosphatase (enzyme in osteoblasts), osteocalcin (requires vitamin K), and procollagen propeptides are markers of bone formation, while collagen telopeptides and acidic phosphatase indicate bone degradation.

Question 11

What are the primary substrates used by skeletal muscles, and how does substrate crossover occur?

Answer 11

Fatty acids and glucose are used by skeletal muscles. Substrate crossover occurs at around 65% of maximum load, where muscles shift from using more fats to more carbs.

Question 12

How is glucose transported into muscle cells, and what stimulates GLUT-4 translocation?

Answer 12

Glucose enters muscle cells via the GLUT-4 transporter, stimulated by calcium signaling during muscle contraction.

Question 13

What is the role of BCAAs (branch-chain amino acids) in skeletal muscles?

Answer 13

BCAAs serve as signals for muscle growth, transaminated in skeletal muscles, and play a role in activating mTOR, a crucial switch for cell division.

Question 14

What are some markers of muscle damage?

Answer 14

Creatine kinase (CKMM in skeletal muscle), CKMB (cardiac muscle), and myoglobin are markers of muscle damage.

Question 15

What is the role of AMPK in muscle metabolism?

Answer 15

AMPK is activated in response to low ATP levels and plays a role in regulating energy balance in muscle cells.

Question 16

What is the significance of intramyocellular lipids?

Answer 16

Intramyocellular lipids are lipid triglyceride droplets in muscle cells, with highly trained athletes having more. They serve as an energy source during exercise.

Question 17

How is substrate crossover related to muscle energy utilization?

Answer 17

Substrate crossover occurs around 65% of maximum load, where muscles shift from using more fats to more carbs as an energy source.

Question 18

What is the role of insulin in GLUT-4 translocation, and how is it different from calcium signaling?

Answer 18

Insulin spikes stimulate GLUT-4 translocation, while calcium signaling during muscle contraction also induces GLUT-4 translocation independently of insulin.

Question 19

What are the two phases of vitamin D activity, and how does it influence bone health?

Answer 19

Vitamin D has a dual-phase activity: calcitriol increases bone mass in individuals with sufficient dietary calcium, and it induces bone breakdown in those with insufficient calcium.

Question 20

Name some hormones that influence bone health and their roles.

Answer 20

Estrogen, PTH (parathyroid hormone), and calcitonin play roles in regulating bone metabolism and maintaining calcium balance.

Question 21

What is the mechanism of action of denosumab in treating osteoporosis?

Answer 21

Denosumab is an antibody against RANKL, blocking the degradation of bone and is used in the treatment of osteoporosis.

Question 22

How does teriparatide work, and what is its role in bone health?

Answer 22

Teriparatide is a PTH analog given through injections, stimulating bone formation and used for conditions like osteoporosis.

Question 23

What is the role of sclerostin, and how does romosumab affect bone mass?

Answer 23

Sclerostin blocks the activity of osteoblasts. Romosumab, an antibody against sclerostin, has been shown to increase bone mass.

Question 24

What is the role of myoglobin in muscles?

Answer 24

Myoglobin is a protein in muscle that binds and stores oxygen, providing a reserve for muscle cells during periods of increased demand.

Question 25

What is the significance of oxidative metabolism in muscle cells?

Answer 25

Oxidative metabolism refers to the process of generating energy using oxygen and is essential for sustained, endurance-type muscle activities.

Question 26

How do muscle fibers differ among types I, IIA, and IIx?

Answer 26

Muscle fibers vary in characteristics, with Type I being slow-twitch, Type IIA intermediate, and Type IIx fast-twitch, representing differences in contraction speed and energy metabolism.

Question 27

What is the role of amino acids other than BCAAs in muscle metabolism?

Answer 27

Other amino acids play roles in protein synthesis, energy production, and as precursors for various metabolic pathways within muscle cells.

Question 28

How do lipids change states between the fed and fasted states?

Answer 28

In the fed state, lipids are present as lipoproteins, while in the fasted state, they exist as free fatty acids, serving as an energy source.

Question 29

What is the role of mTOR in cell division and growth?

Answer 29

mTOR (mammalian target of rapamycin) is a crucial signaling pathway that regulates cell growth, proliferation, and survival in response to various signals, including nutrients.

Question 30

What is the importance of creatine kinase and myoglobin as markers of muscle health?

Answer 30

Creatine kinase (CK) is an enzyme indicating muscle damage, with CKMM specific to skeletal muscle, CKMB to cardiac muscle. Myoglobin is a protein in muscle that can indicate muscle damage and, when elevated in the blood, may lead to kidney damage.