Nutrition Exam 4 - VITAMIN D

What does homeostasis do?

Controls the levels of calcium and phosphorus in the body

Vitamin D is synthesized in the skin of many _______

Herbivores and omnivores including: -Human -Rats -Pigs -Horses -Poultry -Sheep -Cattle

Vitamin D is thought of as the ___________

"Sunshine vitamin"

In addition to sunlight, what other factors may influence dietary vitamin D requirements?

-Amount of dietary Ca and P -Availability of Ca and P -Species -Physiological factors (age, growth, lactation, health, etc.)

Vitamin D plays a role in:

-Thyroid by producing PTH -Bone -Kidney -Intestine

What are the two major natural sources of vitamin D?

1. Cholecalciferol 2. Ergocalciferol

Where is CHOLECALCIFEROL synthesized?

In the outer skin layer

Vitamin D - Metabolism (synthesis) STEP 4:

The hormone acts to increase the active transport of Ca and P across the intestinal epithelial cells, and potentiates the action of (parathyroid hormone - PTH) hormone to increase bone Ca resorption

Calciferol

Vitamin D

Because Vitamin D is fat soluble, it is absorbed ___________

With other neutral lipids via CHYLOMICRON into the lymphatic system of mammals

Human -Blood calcium normal range: -Blood phosphorous normal range:

-Calcium: 8.6 to 10.2 mg/dL -Phosphorus: 3 to 4.5 mg/dL

Where is vitamin D absorbed? What is required for absorption?

-From the intestinal tract in association with fats -It requires the presence of BILE SALTS

What is the importance of vitamin D?

-Impacts bone health -Impacts calcium and phosphorus metabolism

What types of tests are done to test for what kinds of things?

-Liver biopsy to analyze for vitamin D -Blood test to analyze for calcium and phosphorus

Dietary and supplement sources of vitamin D3 and D2 include:

-Oils -Eggs -Milk

The disturbance of calcium and phosphorus metabolism produces other symptoms such as:

-Reduced performance -Hypocalcemia -Reproductive failure

It has been reported that only ____________ is absorbed

50% of a dose of vitamin D

Clinical signs of vitamin D deficiency ___________

Are similar to those produced by deficiency of Ca and (or) P

Rickets

Bone-deforming disease caused by a deficiency in vitamin D -Generally characterized by decreased concentration of calcium and phosphorus in the organic matrices of cartilage and bone

How does vitamin D indirectly control how much calcium and phosphorus is absorbed?

By controlling pH

Vitamin D brings about an elevation of plasma __________

Ca and P by stimulating specific pump mechanisms in the intestine, bone and kidney

Females lactating depends on __________

Calcium which comes from bones

Rickets in dogs raised in lack of sunlight was cured with what?

Cod liver oil (believed to reverse rickets disease) -Beagles were commonly used as a dog model for this disease

What happens when you feed high calcium diets before an animal gives birth? What to do instead?

Doesn't teach the body to mobilize calcium -Leads to hypocalcemia (calcium can't get out) -Instead, feed low calcium diets prior to giving birth to train the body to mobilize calcium after the pregnancy

Most animals and humans don't have a nutritional requirement for vitamin D, which animals are an exception to this? Why?

Dogs and cats (And perhaps other carnivores) -They have a requirement for vitamin D even when sufficient sunlight is available, since vitamin D3 is not produced in skin through action of UV irradiation on 7-dehydrocholesterol in sufficient quantities to prevent rickets *The first step is not very efficient in dogs and cats*

All sterols possessing vitamin D activity ______________

Have the same steroid nucleus -They differ only in the nature of the side chain attached to carbon 17

Vitamin D and Calcium homeostasis:

Hormones: -1,25 (OH)2D or Calcitriol -PTH Nutrients: -Ca -P -Vitamin D3 Major organs: -Kidneys -Bone -GI tract (intestines) -Liver -Parathyroid gland

If an animal can't get enough sunlight, what can be done?

Provide a vitamin D supplement

What are the symptoms of rickets?

Skeletal changes: -Weakened long bones, resulting in curvature and deformation -Enlarged, painful hock and knee joints -General stiffness of gait, arched back and a tendency to drag hind legs -Beaded ribs and deformed thorax

Vitamin D - Metabolism (synthesis) STEP 1:

Vitamin D, supplied by the skin or the diet, is rapidly transported to and sequestered by the liver

Ergocalciferol

Vitamin D2 -Form found in plants

Cholecalciferol

Vitamin D3 -Form found in animals

Vitamin D - Metabolism (synthesis) STEP 2:

Within the liver, vitamin D can be converted to 25-hydroxyvitamin D by vitamin enzyme D 25-hydroxylase and released into the blood (Adds the first OH group)

What is the outstanding disease of vitamin D deficiency?

Rickets

What do dogs and cats have little of in their skin?

7-hydrocholesterol

Calcitriol regulates high serum Ca levels by:

1. Regulating gut absorption 2. Regulating bone mineralization 3. Regulating kidney absorption *Feed goes to the small intestine/is filtrated in the kidneys *More calcium = kidney's filter to get rid of it

What type of vitamin is vitamin D?

Fat soluble vitamin -Fat soluble factor

With Osteomalacia, in adults, the progressive demineralization of bones eventually results in ___________

Fractures and breaks

Cholecalciferol is produced by ___________

Irradiation (occurs under the skin) of 7-dehydrocholesterol with UV light either from the sun or from an artificial source

Harry Steenbock

Realized that UV irradiation was causing the alteration of some substance in animals and proceeded to demonstrate that UV irradiation of not only animals but of their food could heal or prevent rickets

In 1822, Sniadecki suggested that RICKETS was caused by what?

Lack of exposure to the sunlight -Vitamin D deficiency -Almost 70 years later, Palm concluded from an epidemiology survey that the common denominator in rickets in children was lack of exposure to sunlight -However, the majority of scientists and physicians at the time did not believe that simple exposure to sunlight could cure or prevent rickets

More calcium =

Less absorption

What is the general function of vitamin D?

Regulate plasma Calcium (Ca) and Phosphorus (P) to a level that will support a normal bone mineralization

Vitamin D requirements?

Most animals and humans do not have a nutritional requirement for vitamin D when sufficient sunlight is available -Can get vitamin D through sunlight and diet

What happens in preserved materials such as silage in terms of vitamin D?

Most vitamin D is lost (vitamin D = not so stable)

DeLuca: Steenbock's student demonstrated _________

That vitamin D itself is inactive and identified active metabolites of vitamin D -Thought that it was activated by sunlight

Vitamin D - Metabolism (synthesis) STEP 3:

The 25-hydroxyvitamin D then circulates to the kidney where it can be converted to the hormone 1,25-dihydroxyvitamin D (Other OH groups added)

In 1922, Sir Edward Mellanby was credited for ___________

The discovery and importance of vitamin D in the prevention of rickets

Parathyroid hormone (PTH)

Thyroid hormone that activates the kidney's

In the adult animal, _________________ is the counterpart of rickets

Osteomalacia -Cartilage growth in the adult has ceased, and thus this condition is characterized by a decreased concentration of calcium and phosphorus in the bone matrix (demineralization)