2.
Vitamin A is one of four lipid soluble vitamins
present in our body.
Vitamin A and its metabolites play diverse roles in
physiology, ranging from incorporation into vision
pigments to controlling transcription of a host of
important genes. Health depends on maintaining
vitamin A levels within a normal range, as either too
little or too much of this vitamin lead to serious
disease.
Vitamin A (RETINOL)
3.
Retinol is the immediate precursor to two important
active metabolites:
• retinal, which plays a critical role in vision
• retinoic acid, which serves as an intracellular
messenger that affects transcription of a number of
genes.
• Vitamin A does not occur in plants, but many plants
contain carotenoids such as beta-carotene that can be
converted to vitamin A within the intestine and
other tissues.
STRUCTURE
4.
5. Physiologic Effects of Vitamin A
Vitamin A and its metabolites retinal and retinoic acid appear to serve a
number of critical roles in physiology, as evidenced by the myriad of disorders
that accompany deficiency or excess states. In many cases, precise mechanisms
are poorly understood. Some of the well-characterized effects of vitamin A
include:
Vision: Retinal is a necessary structural component of rhodopsin or visual
purple, the light sensitive pigment within rod and cone cells of the retina. If
inadequate quantities of vitamin A are present, vision is impaired.
Resistance to infectious disease: In almost every infectious disease studied,
vitamin A deficiency has been shown to increase the frequency and severity of
disease. Several large trials with malnourished children have demonstrated
dramatic reductions in mortality from diseases such as measles by the simple
and inexpensive procedure of providing vitamin A supplementation. This
"anti-infective" effect is undoubtedly complex, but is due, in part, to the
necessity for vitamin A in normal immune responses
6.
7. •Epithelial cell "integrity": Many epithelial cells appear to require vitamin A
for proper differentiation and maintenance. Lack of vitamin A leads to
dysfunction of many epithelia - the skin becomes keratinized and scaly, and
mucus secretion is suppressed. It seems likely that many of these effects are
due to impaired transcriptional regulation due to deficits in retinoic acid
signalling.
•Bone remodelling: Normal functioning of osteoblasts and osteoclasts is
dependent upon vitamin A.
•Reproduction: Normal levels of vitamin A are required for sperm production,
reflecting a requirement for vitamin A by spermatogenic epithelial (Sertoli)
cells. Similarly, normal reproductive cycles in females require adequate
availability of vitamin A.
9. Sources of Vitamin A
Vitamin A is present in many animal tissues, and is readily absorbed from
such dietary sources in the terminal small intestine. Liver is clearly the richest
dietary source of vitamin A.
Plants do not contain vitamin A, but many dark-green or dark-yellow plants
(including the famous carrot) contain carotenoids such as beta-carotene that
serve as provitamins because they are converted within the intestinal mucosa
to retinol during absorption.
Storage:
Vitamin A is stored in the liver as retinyl esters and, When needed, exported
into blood, where it is carried by retinol binding protein for delivery to other
tissues.
11. Deficiency:
Blindness due to inability to synthesize adequate quantities of rhodopsin. Moderate
deficiency leads to deficits in vision under conditions of low light ("night blindness"),
while severe deficiency can result in severe dryness and opacity of the cornea
(xeropthalmia).
Increased risk of mortality from infectious disease has been best studied in
malnourished children, but also is seen in animals. In such cases, supplementation with
vitamin A has been shown to substantially reduce mortality from diseases such as
measles and gastrointestinal infections.
Abnormal function of many epithelial cells, manifest by such diverse conditions as dry,
scaly skin, inadequate secretion from mucosal surfaces, infertility, decreased synthesis
of thyroid hormones and elevated cerebrospinal fluid pressure due to inadequate
absorption in meninges.
Abnormal bone growth in vitamin A-deficient animals can result in malformations and,
when the skull is affected, disorders of the central nervous system and optic nerve.
Toxicity
Amount exceeding 7.5 mg/day can lead to toxicity
Vitamin A excess states, while not as common as deficiency, also lead to disease.
Vitamin A and most retinoid are highly toxic when taken in large amounts, and the
most common cause of this disorder in both man and animals is excessive
supplementation
12.
13.
14.
Vitamin K is a fat soluble vitamin. It plays an important role in
coagulation of blood so is also called “clotting vitamin”.
Vitamin K exists both natural and synthetic forms. The natural
forms of vitamin K include vitamin K1(Phllyoquinone) and
vitamin K2(menaquinone), while synthetic forms are vitamin
K3(menadione) and vitamin K4(menadiol).
Vitamin K1 is made by plants while vitamin K2 is made by
bacteria in large intestine.
VITAMIN K
15.
Absorption takes place in intestine in presence of bile
salts.
The transportation from intestine is carried out
through chylomicrons.
Storage occurs in liver and from liver transportation
to peripheral cells is carried out bound with beta
lipoproteins.
Absorption,
Transportation and Storage
16.
Vitamin K and Blood Clot
Formation
Blood clots through a process called
the ‘coagulation cascade’. It’s
referred to as a cascade as it involves
a cascade of enzymes activating each
other. The activation of some of the
enzymes in the coagulation cascade
is also dependent on vitamin K.
Vitamin k is needed as a cofactor to
activate clotting factors:
a. Clotting factor II(prothrombin)
b. Clotting factor VII(proconvertin)
c. Clotting factor IX(thromboplastin)
d. Clotting factor X(Stuart factor)
FUNCTIONS
18. Gas6 is a protein that is important for regulating cell growth,
proliferation and preventing cell death. Its function is dependent
on vitamin K. It also helps cells to communicate with each other.
Vitamin K Prevents Cardiovascular Disease
When there is a deficiency of vitamin K, osteocalcin does not bind
calcium. This means that calcium cannot bind to the bone matrix.
With the lack of calcium bones eventually become porous.
Calcium is then also free to travel in the blood, and eventually
gets deposited in the arteries. This causes a hardening of the
arteries, a condition also known as atherosclerosis.
Vitamin K and Cell Growth
19.
Anticoagulant drug overdose
Reduces excessive menstrual flow
Inhibiting cancer tumours
Overcoming inability to absorb vitamins
Protection against osteoporosis
Overcoming effects of antibiotics on intestinal
bacteria
Vitamin K used for:-
20.
21. •Vitamin k deficiency results from extremely inadequate intake,
fat malabsorption use of anticoagulants. Deficiency is particularly
common among breastfed infants. It impairs clotting. Diagnosis is
suspected based on routine coagulation study findings and
confirmed by response to vitamin k.
•Vitamin k deficiency decreases levels of prothrombin and other
vitamin k-dependent coagulation factors causing defective
coagulation and potentially bleeding
