Vitamins and hormones
Vitamins are needed in small amounts in the diet; lack of each causes a specific disease. Hormones are chemical messengers made by endocrine glands.
What vitamins are
Vitamins are organic compounds needed in small amounts in our diet. Lack of a vitamin causes a specific deficiency disease. Most vitamins cannot be made by our body, but plants can make almost all of them, so vitamins are essential food factors. Bacteria in the gut make some vitamins for us, and the skin makes vitamin D in sunlight. Vitamins are named by the letters A, B, C, D, E and K, and the B group is divided into B₁, B₂, B₆, B₁₂ and others.
Fat-soluble vs water-soluble vitamins
Vitamins, sources and deficiency diseases
| Vitamin | Good sources | Deficiency disease |
|---|---|---|
| A | Fish liver oil, carrots, butter, milk | Xerophthalmia (hardening of the cornea of the eye), night blindness |
| B₁ (thiamine) | Yeast, milk, green vegetables, cereals | Beri beri (loss of appetite, retarded growth) |
| B₂ (riboflavin) | Milk, egg white, liver, kidney | Cheilosis (cracks at the corners of the mouth and lips), digestive disorders, burning feeling of the skin |
| B₆ (pyridoxine) | Yeast, milk, egg yolk, cereals, grams | Convulsions |
| B₁₂ | Meat, fish, egg, curd | Pernicious anaemia (red blood cells lacking haemoglobin) |
| C (ascorbic acid) | Citrus fruits, amla, green leafy vegetables | Scurvy (bleeding gums) |
| D | Sunlight, fish, egg yolk | Rickets (bone deformities in children), osteomalacia (soft bones and joint pain in adults) |
| E | Vegetable oils such as wheat germ oil and sunflower oil | Increased fragility of red blood cells, muscular weakness |
| K | Green leafy vegetables | Increased blood clotting time |
What hormones are
Hormones are molecules that act as intercellular messengers. They are made by endocrine glands and released directly into the bloodstream, which carries them to the organs they act on. Chemically they fall into three groups: steroids (estrogens, androgens), polypeptides (insulin, endorphins) and amino acid derivatives (epinephrine, norepinephrine, thyroxine). Hormones keep the activities of the body in balance. Your syllabus needs only this elementary idea; you do not need their structures.
Some hormones and their roles
| Hormone | Made by | Role |
|---|---|---|
| Insulin | Pancreas (extra detail) | Released when blood glucose rises quickly; lowers it |
| Glucagon | Pancreas (extra detail) | Raises blood glucose; with insulin, keeps it within narrow limits |
| Epinephrine and norepinephrine | Adrenal glands (extra detail) | Bring about the body's responses to outside stimuli, such as fright |
| Thyroxine | Thyroid gland | An iodinated derivative of the amino acid tyrosine. Too little: hypothyroidism (lethargy, obesity). Too much: hyperthyroidism. Too little iodine in food can enlarge the thyroid gland, which iodised salt prevents (the name goitre is extra) |
| Glucocorticoids | Adrenal cortex | Control carbohydrate metabolism, inflammation and the response to stress |
| Mineralocorticoids | Adrenal cortex | Control how much water and salt the kidneys excrete. Failure of the adrenal cortex causes Addison's disease |
| Testosterone; estradiol; progesterone | Testes; ovaries | Secondary sex characters; estradiol helps control the menstrual cycle; progesterone prepares the uterus for the fertilised egg |
Iodised salt in Indian kitchens supplies the iodine the thyroid needs to make thyroxine, and so prevents goitre. Amla is one of the richest sources of vitamin C and protects against scurvy.
2 marks: “Why must water-soluble vitamins be taken regularly in the diet? Which vitamin is the exception?” They dissolve in water and are excreted in urine, so they cannot be stored in the body. Vitamin B₁₂ is the exception: it can be stored.
1 marks: “Name the deficiency disease caused by lack of vitamin B₁₂.” Pernicious anaemia.
2 marks: “What are hormones? Give one example each of a steroid hormone and a polypeptide hormone.” Chemical messengers made by endocrine glands and carried by the blood. Steroid: an estrogen or testosterone. Polypeptide: insulin.
Fat-soluble 'ADEK' stays in your fat; B and C wash out in urine (except B₁₂). A: eyes, B₁: beri beri, C: scurvy, D: bones, K: clotting.