LECTURE 8 (Fat soluble vitamins + B12, B9) Flashcards
Which vitamins are Non-B Vitamins?
Vitamins A, C, D, E & K
[all fat soluble except for Vitamin C)
Which vitamins are fat soluble?
Vitamins A, D, E & K
Describe the absorption of Non-water soluble vitamins
- Together with other lipids, fat-soluble vitamins form MICELLES in JEJENUM
[hydrophobic groups inside + hydrophilic groups outside] - Absorbed by ENTEROCYTES -> packaged into CHYLOMICRONS -> secreted into LYMPH
Describe Fat Malabsorption
Leads to deficiencies of fat-soluble vitamins
CAUSES:
- Abnormal bile/pancreatic secretions
- Disease/resection of intestine
MANIFESTATIONS:
- Cystic fibrosis (lack of pancreatic enzymes)
- Celiac sprue
- Crohn’s disease
- Primary biliary cirrhosis
- Primary sclerosing cholangitis
What are the properties of Vitamin A?
- Includes retinal, retinol and retinoid acid
- Found in liver and leafy vegetables
- Stored in liver -> it takes years to develop deficiency
What is the function of Vitamin A?
- Antioxidant
- Constituent of visual pigments (retinal)
- Essential for normal differentiation of epithelial cells into specialised tissues
- Prevents squamous metaplasia
What is the importance of Retinoic acid?
Acts like a hormone -> binds receptors in nucleus -> regulates/controls protein synthesis
Describe the important examples of Retinoic acid
KERATIN (important for maintenance of healthy skin)
- Limit/control keratin production
- Retinoic acid used in treatment of PSORIASIS
MUCOUS
- Limit/control production in epithelial cells
Describe Vitamin A deficiency
Vitamin A deficiency is when your body lacks the amount of vitamin A it needs to function properly
MANIFESTATIONS:
- Night blindness (NYCTALOPIA)
[often the first sign]
- Dry, scaly skin (XEROSIS CUTIS)
- Dry eyes (XEROPHTHALMIA)
[Keritinisation of cornea -> blindness]
- Corneal degeneration (KERATOMALACIA)
- Corneal squamous metaplasia -> Bitot spots (keratin debris + foamy appearance on conjunctiva)
- Immunosuppression
- Growth failure in children
In which disorders is Vitamin A therapy used?
- Measles
(used in resource-limited countries) - Psoriasis (skin disorder)
- Severe cystic acne (skin disorder)
- Acute promyelocytic leukaemia
What are the properties of Vitamin A therapy used in Acute promyelocytic leukaemia?
- All-trans-retinoic acid (ATRA/tretinoin) = synthetic derivative of retinoic acid
- Induced malignant cells to complete differentiation
Describe Hypervitaminosis A (Vitamin A excess)
Usually occurs from chronic, excessive supplements
ACUTE TOXICITY SYMPTOMS:
- nausea/vomiting
- Increased intracranial pressure (vertigo, blurred vision)
CHRONIC TOXICITY SYMPTOMS:
- Alopecia
- Dry scaly skin
- Hepatic toxicity and enlargement
- Arthralgias (joint pain)
Why is Accutane not prescribed to pregnant women?
Isotretinoin (Accutane) is a TERATOGEN (substances that cause congenital disorders in a developing embryo or fetus) -> A negative pregnancy test and 2 forms of contraception is required before it is prescribed
SIDE EFFECTS ON FETUS:
- Cleft palate
- Cardiac abnormalities
- Ear deformities
- Microcephaly
- Brain fluid accumulation
- Abnormal immune system development
- Learning disabilities
- Facial deformities
What are the two forms of Vitamin D?
- D3 (CHOLECALCIFEROL) from exposure of skin to sun, ingestion of fish, fortified milk & plants
- D2 (ERGOCALCIFEROL) from ingestion of plants, fungi and yeasts
What happens to both of the forms of Vitamin D?
Both are converted to 25-OH D3 (CALCIDIOL - storage form) in liver to the active form 1,25-(OH)2 D3 (CALCITRIOL) in kidney PCT
What is I alpha-hydroxylase regulated by?
PTH (Parathyroid hormone)
EXPLANATION: 25-hydroxyvitamin D(3)-1 alpha-hydroxylase (1 alpha-hydroxylase) plays an important role in calcium homeostasis by CATALYSING SYNTHESIS of the active form of vitamin D, 1,25-dihydroxyvitamin D(3), in the kidney.
What is the difference between 1,25(OH)2 D3 formed in the kidneys and in the tissues in the body?
KIDNEYS:
- Endocrine
- Maintains calcium economy
TISSUES IN THE BODY:
- Autocrine
- Prevent and/or treat Viral respiratory disease, Cancer, Osteoporosis, Heart disease, Multiple sclerosis, Diabetes, Hypertension