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Vitamin A

Vitamin A is a fat soluble vitamin which is derived from beta carotene which plays a significant role in the process of vision and other important metabolic pathways pertaining to cell division and genetic expression. The significant forms of vitamin A include retinol, retinal, retinoic acid and retinyl esters. There are approximately six hundred derivatives of beta carotenes and the most important form is retinol.

Functions of Vitamin A

Vitamin A is essential for many metabolic pathways in the body. It is the chief requirement for the function of the rhodopsin protein located in the retina to absorb light and to differentiate functions of the cornea and the conjunctival membranes. Vitamin A is essential for normal functioning of the retina. Apart from this, vitamin A plays a significant role in immune system functions, cell signaling and cellular communication and reproduction. The functions and pathways associated with vitamin A are directly related to the functionality of vital organs such as heart, brain, lungs, liver and kidneys. Hence vitamin A is also known as an important antioxidant. Besides it is required for the growth and differentiation of epithelial tissue, normal growth of bone and embryonic development. Most of our body's Vitamin A is stored in the liver in the form of retinyl esters.


Vitamin A Deficiency: Poor adaptation of vision to darkness or what is known as night blindness is an early symptom that may be followed by degenerative changes in the retina. Degenerative changes in eyes and skin are commonly observed in vitamin A deficiency. The predominant form of vitamin A deficiency is Nyctalopia or night blindness. This occurs as result of retinol imbalance which is the chief derivative of vitamin A. In third-world, vitamin A deficiency is the primary cause of blindness. Pregnant and lactating women, premature children, children living in rural areas of developing countries and patients who have a history of liver diseases such cirrhosis and cystic fibrosis are most susceptible to Vitamin A deficiency. Severe or prolonged deficiency may lead to dry eye or Xerophthalmia (dryness in conjunctiva and cornea of the eye) that can result in corneal ulcers, inflammation, ridge formation, scarring and eventually blindness. Xerophthalmia is due to lacrimal gland dysfunction. Other associated conditions include keratomalacia and follicular hyperkeratosis. Another important consequence of Vitamin A deficiency is acquired immunodeficiency disease, with an increased incidence of death related to infectious diseases. Vitamin A deficiency is associated with increased disease progression and mortality in HIV patients.

World Health Organization (WHO) Recommendations for Vitamin A:
Supplementation may be required in cases where the blood Vitamin A level falls below 20 µg/dL.
Severe deficiency is < 10 µg/dL


Food sources and recommended dietary allowance

Vitamin A is naturally available in dairy products such as milk, cheese, curd, cream. Meat products like liver and fish oil and leafy vegetables are excellent sources of vitamin A. Other sources include pumpkin, potatoes, broccoli, cereals, beans and cow peas. Studies indicate that the intensity of the fruit or vegetable color is directly proportional to the amount of vitamin A present in it. The recommended intake of vitamin A per day for children 500 micrograms, males 1000 micrograms and females 800 micrograms respectively.


RDAs (recommended dietary allowance) for vitamin A are given as mcg of retinol activity equivalents (RAE) to account for the different bioactivities of retinol and provitamin A carotenoids. FDA may introduce new labeling regulations in the near future which may result in listing Vitamin A with RAE values rather than in IU.
The following table shows conversion rates of mcg of RAE (retinol activity equivalents):

  • 1 IU retinol = 0.3 mcg RAE
  • 1 IU beta carotene from dietary supplements = 0.15 mcg RAE
  • 1 IU beta carotene from food = 0.05 mcg RAE
  • 1 IU alpha carotene or beta-cryptoxanthin = 0.025 mcg RAE

Essentially all dietary sources of vitamin A are converted into retinol by the body: 1 mcg of physiologically available retinol is equivalent to the following amounts from dietary sources:

  • 1 mcg of retinol
  • 12 mcg of beta carotene
  • 24 mcg of alpha carotene or beta cryptoxanthin

Hypervitaminosis A: Vitamin A in excess can be toxic. According to WHO, values in excess of 120 µg/dL is Hypervitaminosis A. Chronic vitamin A over dosage may be a serious issue in normal adults who take more than 15 mg per day and in children who take more than 6 mg per day of vitamin A over a period of several months. Symptoms can include :

  • Dry skin
  • Cheilosis
  • Glossitis
  • Hypercalcemia
  • Hyperlipidemia
  • Amenorrhea
  • Liver fibrosis with portal hypertension
  • pseudotumor cerebri
  • increased intracranial pressure and Papilledema
  • lymph node enlargement

Other than that some symptoms such as pain, vomiting, alopecia and bone demineralization may result due to excessive intake of Vitamin A. In pregnant women, an over dose of Vitamin A over a period of time may result in spontaneous abortions or Congenital malformations, craniofacial abnormalities and valvular heart disease in the baby.

However, unlike preformed Vitamin A, beta-carotene is not known to be teratogenic (reproductive toxicity). Even a relatively large supplemental doses of beta carotene or eating carotenoid rich food for long duration need not result in toxicity always. Rarely a reversible condition known as carotenodermia - where the skin turns yellow/orange might be the result of long term over dosage of beta carotene.


Plague

Plague is a bacterial infection caused by Yersinia pestis and is spread by rodents, especially rats. Exposure to rats, rabbits and squirrels increases the risk.


Types of Plague

Bubonic plague: is an infection of the lymph nodes. Symptoms of Bubonic plague symptoms include chills and high fever along with headache and swollen lymph glands (bubo).

Pneumonic plague: is an infection of the lungs. Symptoms of Pneumonic plague include severe cough, blood in sputum and difficulty in breathing.

Septicemic plague: is an infection of the blood. Symptoms of Septicemic plague include diarrhea, fever, low blood pressure, abdominal pain, bleeding and organ failure.

Diagnostic tests that are prescribed for plague are blood and sputum culture. Fluid from a lymph node is often examined. Antibiotics (streptomycin, gentamicin, doxycycline, or ciprofloxacin) are the first line of treatment. Pneumonic plague is infectious. If left untreated, plague can lead to meningitis or later death.


Lymphoscintigraphy

Lymphoscintigraphy is a special type of nuclear medicine imaging study; it provides images of the lymphatic system. A radio tracer is used to obtain the images. The images are known as scintigrams. Lymph nodes act like a filter for foreign bodies such as viruses, pollen and germs. Lymphoscintigraphy is used as an imaging study in people suffering from any of the following - breast cancer, malignant melanoma (stage 1&2), head, neck gastric, thyroid, vulvar, and penile cancers. The procedure is carried out by a certified nuclear imaging technician. Lymphoscintigraphy is performed to

  • Identify the sentinel lymph node i.e. the first node that drains a tumor.
  • Identify the number of sentinel nodes.
  • Mark the sentinel node over the skin for biopsy.
  • Locate the sentinel in unexpected locations.
  • Differentiate sentinel node from other subsequent nodes.
  • Plan a or surgery that helps assess the stage of cancer so as to plan treatment.
  • Identify points of blockage in the lymphatic system.

The study of the sentinel node is highly significant for the following reasons:


  • It is the first node to receive metastatic deposits in a malignancy.
  • A radio active channel leads to this node.
  • It is the node close to the primary lesion.
  • It is the first node to be visible during the lymphoscintigraphy study.

Lymphoscintigraphy became much sought after, after it was used to identify and study the breast sentinel nodes. This procedure is an important procedure because if the sentinel node is free of metastasis, then the subsequent nodes are also most likely to be disease free. This procedure permits the patient to skip axillary clearance surgery if the sentinel node shows negative for metastatic disease. This procedure becomes very useful for scores of people suffering from breast cancer across the world as it avoids a painful surgical procedure.

The patient is injected with the radioactive material; this radioactive material gives off gamma rays that are picked by the gamma camera. Pictures are taken for 1 hour to show the flow of the material through the lymph nodes. Anesthesia is not required, the patient is made to lie on a table and the gamma camera is positioned accordingly. As the gamma camera moves, it follows the radiation being emitted which in turn is mapped into a series of images. The doctor marks the skin at the sentinel node sites and these marks are later used during the surgery. The body passes out the small levels of radioactive material naturally.

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Bibliography / Reference

Collection of Pages - Last revised Date: November 22, 2019