Physiology Lecture 4.5: Bone & Calcium

What are the three things does calcium regulate?

1. Neuromuscular excitability

2. Muscular contraction

3. Heart rhythms

Why is calcium vital for healing injuries?

Helps blood clotting

What does calcium help with for bones?

Building and maintaining

What form is phosphate present as in bone?

Calcium phosphate

Why is phosphate important for energy production?

Component of energy carriers

What are phosphates present in for membranes?

Phospholipids

What two body parts require phosphate for normal function?

1. Nerves

2. Muscle

What does phosphate help form for DNA and RNA?

Sugar-phosphate backbone

What are the three possible forms of calcium in plasma?

1. Ionized

2. Protein-bound

3. Anions constituents

What is the protein that most calcium is bound to in plasma?

Albumin

What is normal blood calcium levels?

8.5 to 10.5 mg/dL

What is normal ionized calcium levels?

4.65 to 5.25 mg/dL

Only what kind of calcium is biologically active and diffusible through the capillary membrane?

Free, ionized calcium

What is the most abundant protein in human plasma?

Human serum albumin

Where is human serum albumin produced?

Liver

What two things does protein binding to calcium protect against?

1. Precipitation

2. Ectopic calcification

How much calcium is lost in feces?

90%

How much calcium is lost in urine?

10%

What is 99% of calcium sequestered as in bone?

Hydroxyapatite

What is the reservoir for calcium salts?

Bone

How much calcium is exchanged between bone and ECF daily?

500 mg

Where is 80 - 85% of phosphorus found in the body?

Bones and teeth as hydroxyapatite

What is normal serum PO4- level in adults?

3-4 mg/dL

What is normal serum PO4- level in children?

4-5 mg/dL

What are the two forms Organic phosphorus is present in?

1. Phospholipids

2. Phosphates

What are the two hormones that increase calcium levels?

1. PTH

2. Vitamin D3

What is the hormones that decreases calcium levels?

Calcitonin

How does PTH and Vitamin D3 increase calcium levels?

Stimulate osteoclasts

How does calcitonin decrease calcium levels?

Inhibit osteoclasts

What are the three organs affected by calcitonin?

1. Bones

2. Intestines

3. Kidneys

Where are the parathyroid glands located?

Each corner of thyroid gland (4)

What are the two cell types in parathyroid glands?

1. Chief cells

2. Oxyphil cells

What do chief cells in parathyroid gland produce?

PTH

What is the major regulator of calcium homeostasis in humans?

PTH

How does PTH affect plasma? (2)

1. Increase calcium

2. Decrease Pi

What does PTH promote the formation of in the kidneys?

Vitamin D

What two processes related to bone does PTH stimulate?

1. Osteocytic osteolysis

2. Osteoclastic osteolysis

What is the fluid present in theperi-osteocytic space?

Bone fluid

What is Osteocytic osteolysis?

Transfer calcium from bone fluid to ECF

Is there change in bone mass during Osteocytic osteolysis?

No

Is the action of PTH on osteoclasts direct or indirect?

Indirect

Do osteoclasts have PTH receptors?

No

What are the two sources of vitamin D?

1. Ultraviolet radiation (Skin)

2. Ingested in diet

Why is vitamin D not a typical hormone?

Not produced by endocrine gland

What type of regulation is done for vitamin D?

Paracrine

What receptors does vitamin D bind to to evoke responses?

Intracellular receptors

Where does the first hydroxylation reaction for vitamin D occur?

Liver

Where does the second hydroxylation reaction for vitamin D occur?

Kidneys

What activates 1-alpha hydroxylase in the kidneys for vitamin D production?

PTH

What does vitamin D stimulate the absorption of? (2)

1. Calcium

2. Phosphate

What does vitamin D regulate by increased synthesis of calcium binding proteins?

Intestinal calcium absorption

What can vitamin D indirectly stimulate for bones?

Osteoclasts

What can vitamin D directly stimulate for bones?

Osteoblasts

Do osteoblasts or osteoclasts have vitamin D receptors?

Osteoblasts

How many amino acids are in calcitonin?

32

What two cells in the parathyroid gland produces calcitonin?

1. Parafollicular cells

2. C cells

What does calcitonin inhibit in kidneys?

Reabsorption of calcium

What does calcitonin increase in kidneys?

Excretion of phosphate through urine

What three things does calcitonin inhibit in bones?

1. Osteoclastic resorption

2. Active transport of calcium

3. Formation of new osteoclasts

What two things does calcitonin stimulate in bones?

1. Activity of osteoblasts

2. Synthesis of alkaline phosphatase

What does hypoparathyroidism result in?

Hypocalcemia

What are the two possible causes of Primary Hyperparathyroidism?

1. Adenomatous

2. Hyperplastic parathyroid tissue

What are the two possible causes of Secondary Hyperparathyroidism?

1. Vitamin deficiency

2. Kidney disfunction

What is the treatment method for hyperparathyroidism?

Vitamin D and Calcium supplements

What are the three diseases caused by vitamin D deficiency?

1. Rickets

2. Osteomalacia

3. Osteoporosis

What two conditions can high calcitonin levels signify?

1. Medullary thyroid cancer

2. C-cell hyperplasia

Does low level of calcitonin have a big effect on the body?

No