Page 267 - Textbook of Pathology, 6th Edition

1. Haemorrhagic disease of newborn. The newborn infants 251
are deficient in vitamin K because of minimal stores of
vitamin K at birth, lack of established intestinal flora for
endogenous synthesis and limited dietary intake since breast
milk is a poor source of vitamin K. Hence the clinical practice
is to routinely administer vitamin K at birth. CHAPTER 9
2. Biliary obstruction. Bile is prevented from entering the
bowel due to biliary obstruction which prevents the
absorption of this fat-soluble vitamin. Surgery in patients of
obstructive jaundice, therefore, leads to marked tendency to
bleeding.
3. Due to malabsorption syndrome. Patients suffering from
malabsorption of fat develop vitamin K deficiency e.g. coeliac
disease, sprue, pancreatic disease, hypermotility of bowel
etc.
4. Due to anticoagulant therapy. Patients on warfarin group
of anticoagulants have impaired biosynthesis of vitamin K-
dependent coagulation factors.
5. Due to antibiotic therapy. The use of broad-spectrum
antibiotics and sulfa drugs reduces the normal intestinal flora. Environmental and Nutritional Diseases
6. Diffuse liver disease. Patients with diffuse liver disease Figure 9.11 Lesions in scurvy.
(e.g. cirrhosis, amyloidosis of liver, hepatocellular carcinoma,
hepatoblastoma) have hypoprothrombinaemia due to maintenance of folic acid levels by preventing oxidation
impaired synthesis of prothrombin. Administration of of tetrahydrofolate; and
vitamin K to such patients is of no avail since liver, where role in iron metabolism in its absorption, storage and
prothrombin synthesis utilising vitamin K takes place, is keeping it in reduced state.
diseased.
LESIONS IN VITAMIN C DEFICIENCY. Vitamin C defi-
ciency in the food or as a conditioned deficiency results in
WATER-SOLUBLE VITAMINS
scurvy. The lesions and clinical manifestations of scurvy are
Vitamin C (Ascorbic Acid) seen more commonly at two peak ages: in early childhood
and in the very aged. These are as under (Fig. 9.11):
PHYSIOLOGY. Vitamin C exists in natural sources as L-
ascorbic acid closely related to glucose. The major sources of 1. Haemorrhagic diathesis. A marked tendency to bleeding
vitamin C are citrus fruits such as orange, lemon, grape fruit is characteristic of scurvy. This may be due to deficiency of
and some fresh vegetables like tomatoes and potatoes. It is intercellular cement which holds together the cells of
present in small amounts in meat and milk. The vitamin is capillary endothelium. There may be haemorrhages in the
easily destroyed by heating so that boiled or pasteurised milk skin, mucous membranes, gums, muscles, joints and
may lack vitamin C. It is readily absorbed from the small underneath the periosteum.
intestine and is stored in many tissues, most abundantly in 2. Skeletal lesions. These changes are more pronounced in
adrenal cortex.
The physiologic functions of vitamin C are due to its growing children. The most prominent change is the deranged
formation of osteoid matrix and not deranged mineralisation (c.f.
ability to carry out oxidation-reduction reactions:
the pathological changes underlying rickets already
L-Ascorbic Acid Dehydro L-Ascorbic described). Growing tubular bones as well as flat bones are
+
acid + 2H + 2e affected. The epiphyseal ends of growing long bones have
1. Vitamin C has been fond to have antioxidant properties cartilage cells in rows which normally undergo provisional
and can scavenge free radicals. mineralisation. However, due to vitamin C deficiency, the
2. Ascorbic acid is required for hydroxylation of proline to next step of laying down of osteoid matrix by osteoblasts is
form hydroxyproline which is an essential component of poor and results in failure of resorption of cartilage. Conse-
collagen. quently, mineralised cartilage under the widened and irregu-
3. Besides collagen, it is necessary for the ground substance lar epiphyseal plates project as scorbutic rosary. The skeletal
of other mesenchymal structures such as osteoid, chondroitin changes are further worsened due to haemorrhages and
sulfate, dentin and cement substance of vascular haematomas under the periosteum and bleeding into the joint
endothelium. spaces.
4. Vitamin C being a reducing substance has other functions 3. Delayed wound healing. There is delayed healing of
such as: wounds in scurvy due to following:
hydroxylation of dopamine to norepinephrine; deranged collagen synthesis;