ansc314 - vitamin A & D

vitamins

vital to life

• casimir funk (1905)

  • Cornelius Adrianus Pekelharing found animals fed purified proteins, carbohydrates, fats, inorganic salts, and water would thrive only if small amounts of milk were added to the diet

  • 1911, Casimir Funk isolated a concentrate from rice polishing that cured polyneuritis in pigeons

    • named the concentrate “vitamine” b/c it appeared to be vital to life and b/c it was probably an amine

vitamin functions

vitamins & minerals close interactions w/ macronutrients to accomplish metabolic functions

• co-enzymes → energy & protein metabolism

• cell regulators & hormones → growth & development

• anti-oxidants → health & disease

enzyme

protein that functions as catalyst to mediate speed of chemical reaction

cofactor

non-protein chemical compound

• bound to protein & needed for biological activity of protein

• helps enzymes

coenzyme

substance that enhances action of enzyme

• cofactors that are bound to an enzyme loosely

prosthetic group

tightly bound cofactor

• specific non-polypeptide unit needed for biological function some proteins

vitamin classifications

• fat soluble - stored in fatty tissues

• water soluble - no real storage site in body

fat soluble vitamins

stored in fatty tissues

• A → retinol

• D → cholecalciferol, ergocalciferol

• E → tocopherols

• K → phylloquinones, menaquinones, menadione

water soluble vitamins

no real storage site, go away when secreting water (urine, sweat, etc)

• dietary requirement MUCH higher

  • thiamin (B1)

  • riboflavin (B2)

  • niacin (B3)

  • pantothenic acid (B5)

  • pyridoxine (B6)

  • biotin (B7)

  • folate / Folacin (B9)

  • cobalamin (B12)

  • inositol, choline, ascorbic acid (C)

plant vitamins

vitamins, trace elements, & proteins are in the germ & bran of the plant

• germ is reproductive part

  • germinates → grow into plant

• in leaves: associated w/ chlorophyll

vit A sources

• vegetable sources (beta-carotene - precursor for Vit. A)

  • green, leafy vegetables

  • intensely colored fruits & vegies

• animal sources

  • eggs, meat, & dairy products

carotenoids

derived from plants & give them their color

• precursor for Vit. A

  • body enzymes turn it → Vit. A

    • 50/600 carotenoids are converted → Vit. A

vitamin A forms

• retinol

• retinal

• retinoic acid

  • Retinol & retinal converted → other forms

    • retinoic acid can’t

  • In general, animal foods provide most of the preformed Vit. A

    • plants provide most of the provitamin A carotenoids in diet.

vitamin A functions

group of related vitamins w/ multiple functions

• visual pigment - retinal

• growth (bone) retinoic acid (hormone)

• reproduction - retinoic acid

• cell differentiation/gene expression - retinoic acid

• immune cells - retinol/retinal

  • most prevalent vitamin deficiency

Vit A & carotenoids digestion & absorption

• stored in liver

  • travels w/ lipids → other tissues

• consuming:

  • animal product → Vit. A

  • plant product → carotenoids → enzymes → active Vit. A form (retinal)

15-15’-dioxygenase

cleaves carotenoids → 2 Vit. A units

• enzyme absent in cats & minks

• plasma protein

  • 70% plasma protein → albumin

albumin

transport protein

vitamin A storage

in liver

carotenoids

500 plant pigments

• ꞵ-carotene

  • enzymes → 2 Vit. A but 1 end gets chewed up

• lutein

  • not Vit A activity (eye sight)

vitamin A eye deficiency

visual cycle

light hits retina → Vit A prominent in rhodopsin (made of opsin & cis retinal) → light breaks it up → splits into opsin & trans-retinal

retinoic acid

cell differentiation & division

• vit A regulates gene coding for proteins needed for cell differentiation & maturation

vitamin A deficiency bulls

retinoic acid controls meiotic initiation & formation of seminiferous epithelium & regulate spermatogenesis

• normal testes

  • spermatogonia & sertoli cells visible

  • inwards → maturing spermatocytes & spermatids (precursors of spermatozoa)

• deficient testes

  • sperm production dmg

  • tubules shrunken

vitamin A deficiency cow

• born blind & weak

• improper skull growth (retinoic acid)

• optic nerves pinched where pass through optic chiasma

vitamin A toxicity

• chronic

  • > 10X RDA over weeks or months

  • headache, alopecia, dry skin, joint pain

  • birth defects (teratogen, esp. 13 cis-retinoate)

• Acute

  • > 100X RDA

  • nausea, vomiting, headache, vertigo, blurred vision, coma, death

vitamin D

• body makes vitamin D w/ sun exposure

  • cholesterol precursor

• cheese, butter, margarine, fortified milk, fish, fortified cereals

D3

synthesized in body

• cholesterol → cholecalciferol (D3)

  • 7-dehydrocholesterol intermediate

• not dietary requirement w/ enough sunlight

D2

synthesized in plants

• ergosterol → ergocalciferol (D2)

• exposure of harvested green grasses & hays to sunlight

D3 biosynthesis

spin epidermis

• cholesterol

  • liver synthesis, diet sources

• 7-dehydrocholesterol intermediate

  • w/ sun → pre-vitamin D

• cholecalciferol (D3)

  • from spontaneous isomerization

  • → blood stream

• DBP-D3

  • vit D3 binding protein transports D3 → hepatic cells

vitamin D activation

activation → calcitriol (regulates Ca+ lvls) in KIDNEY

• kidney convert calcidiol → calcitriol in response to PTH

• parathyroid gland produces PTH in response to ↓ Ca+

  • master regulator of producing calcitriol

  • stimulate liver to convert vit D3 → calcitriol in kidney

calcium homeostasis

vitamin D helps maintain Ca+ homeostasis

• calcitriol maintains Ca+ balance

  • ↑ Ca+ absorption in s. intestine

  • ↓ excretion by kidneys

  • ↑ resorption in bones

• pregnancy & lactation

  • new bones & tissue growth

  • milk production

vit D requirement factors

• Ca+ & P amt in diet

• Ca+ & P ratio in diet (1-2:1)

• Ca+ & P availability in diet

• physiological status - young animals (growth), lactation, pregnancy

vitamin D deficiency symptoms

• all animals

  • failure of Ca-salt deposited in cartilage matrix

  • ↓ bone calcification

  • cartilage cells fail to mature

  • compression of cartilage cells

  • invasion of cartilage by capillaries (swelling)

• Ca & P deficiency

  • rickets (young) & osteomalacia (old)

  • tetany (intermittent muscular spasms)

  • assessment:

    • Serum 25-OH-D3 , & 1, 25-(OH)2-D3, Ca2+, P, PTH

• calcidiol (25-OH-D3) is best indicator of D3 status

tetany

intermittent muscular spasms caused by malfunction of parathyroid glands & Ca+ deficiency

vitamin D toxicity chronic

> 20X required for more than 3 months

• over-supplementation (not from too much sun)

• calcification of organs (liver damage) and arteries

• hypertension

• irritable

vitamin D toxicity acute

> 600X required for 1 day

• Hypercalcemia

• Poor appetite, thirsty, bone pain, tired