Module 11

Question 1

Vitamin D

Answer 1

• Previtamin D is made in skin (from cholesterol)
with exposure to sunlight
– Cholecalciferol
•Can also come from food
• Cholecalciferol goes to liver and is converted to a
more active form
– 25-hydroxy Vitamin D3
• 25-OH D3 goes to kidney where it is converted to
the most active form of the vitamin
– 1,25 dihydroxy Vitamin D3 (Calcitriol)

Question 2

Calcitriol

Answer 2

acts a steroid hormone in gene expression

Turns protein synthesis on and off

Question 3

Calcitriol Action

Answer 3

To stimulate protein 
synthesis
– calcitriol-VDR complex 
will cause synthesis of 
additional copies of 
specific mRNA
– mRNA will then be 
translated so that there 
are additional copies of 
specific proteins
• This will affect 
physiological 
function

Question 4

Vitamin D target organs

Answer 4

Vitamin D target organs are essential for maintaining 
blood calcium levels
– Intestine
–Synthesis of Ca binding protein (Increase 
absorption)
– Kidney
–Decreased Ca excretion
– Bone
–High doses activate osteoclasts
»Bone dissolving cells

Question 5

Vit D Deficiency

Answer 5

• Childhood Deficiency
– Rickets
•Bone 
deformities, 
bowed legs
•More of a 
problem when 
there is less 
sunlight; or 
dark skin

Question 6

Vit D Deficiency/Toxicity

Answer 6

• Adult Deficiency
– Osteomalacia
•soft (nonmineralized) bones
– Can also contribute to osteoporosis
• Toxicity of vitamin D
– Deposits of Ca in soft tissues

Question 7

Vitamin A

Answer 7

Retinal and 
retinoic acid (RA) 
are the derivatives 
of Vitamin A that 
act as hormones
– Also known as 
retinoids

Question 8

Retinoids

Answer 8

Naturally occurring retinoids perform a variety of
regulatory functions in the body
– Regulation of growth
– Cell differentiation via gene expression
– Act as morphogenic agents during embryonic
development

Question 9

Cell Differentiation

Answer 9

• A process where immature cells change in structure
and function to become mature and specialized
– Epithelial cells differentiate into mucus
producing cells
• Vitamin A affects cell differentiation through its
effect on gene expression
– Gene expression can turn on or turn off the
production of certain proteins that regulate
functions within cells and throughout the body
– By affecting gene expression, Vitamin A can
determine what type of cell an immature cell will
become

Question 10

Vit A Deficiency/Toxicity

Answer 10

• Vitamin A is necessary for maintenance of
epithelial tissue
– Covers external body surfaces and lines
internal cavities and tubes
•Includes skin, lining of eyes, intestines,
lungs, vagina and bladder

Question 11

Vit A Deficiency regarding epithelial cells

Answer 11

When deficient in Vitamin 
A, epithelial cells that are 
supposed to turn into 
mucus secreting cells 
instead turn into keratin 
secreting cells - 
Keratinization
• Keratin is hard 
protein of hair and 
nails

Question 12

Vit A Deficiency/Toxicity (2)

Answer 12

• Vitamin A regulates growth and differentiation of
cells for
– Normal reproduction
– Growth
– Immune function
• Vitamin A is also necessary for visual cycle
– But in visual cycle, it does not act as a hormone

Question 13

Vit A Deficiency/Toxicity (3)

Answer 13

Deficiency
– Night blindness (visual cycle related, reversible)
– Xerophthalmia (keratin coating in eyes, permanent)
– Poor growth
– Dry skin
– Impaired immunity

Question 14

Vit A Deficiency/Toxicity (4)

Answer 14

• Toxic in large amounts (pre-formed vitamin A)
– Weight loss
– Muscle and joint pain
– Liver damage
– Bone abnormalities
– Visual defects
– Dry and scaling lips
– Skin rashes
– Birth defects
• Medications made from vitamin A such as Retin A or 
Accutane, can cause serious side-effects