Chapter overviewChapter overview
TABLE 2.5.1 SUMMARY OF CAUSES AND EFFECTS OF NUTRIENT DEFICIENCIES
Nutrient Effect of deficiency Symptoms Cause of deficiency
Vitamin A (retinol)
• Reduced rhodopsin production
• Night blindness Food supplies low in carotene
• Dryness of mucous membranes
• Excessive skin dryness
• Xerophthalmia (dry eyes)
• Lack of mucous membrane secretions Vitamin C
(ascorbic acid)
Reduced formation and maintenance of collagen
Scurvy: bleeding and weakening of gums, tooth decay and loss of teeth
Lack of fruit and vegetables in diet
Vitamin D (calciferol) Low calcium and
phosphorus retention and bone malformation
Rickets: deformity of ribcage, skull and legs
Lack of dairy foods
Proteins Marasmus • Dry skin, loose skin folds
• Drastic loss of adipose tissue from normal areas of fat deposits
Diet low in all nutrients
Kwashiorkor • Swollen abdomen
• Weight loss
Weaned from breast milk onto a low protein diet
Iron Anemia Low energy Diet low in meat, dairy or
green leafy vegetables
Iodine Low levels of thyroid
hormones
• Goitre (increased growth of thyroid gland)
• Mental retardation
Diet low in iodine
• Tryptophan (an amino acid)
• Niacin (vitamin B3)
Tryptophan is converted into niacin, which is needed to help production of energy from food
Pellagra: diarrhoea, dermatitis, dementia and death
Diet low in dairy, meat, eggs, wheat flour, maize flour
Thiamine (vitamin B1) • Inefficiencies in converting carbohydrates into energy
• Reduced functioning of the heart, muscles, and nervous system
Beriberi: weight loss, emotional disturbances, weakness and pain in limbs, irregular heart beat
THEORY OF KNOWLEDGE
On 10 December 1948 the General Assembly of the United Nations adopted the Universal Declaration of Human Rights. Article 25 states that: ‘Everyone has the right to a standard of living adequate for the health and well-being of himself and of his family, including food, clothing, housing and medical care and necessary social services, and the right to security in the event of unemployment, sickness, disability, widowhood, old age or other lack of livelihood in circumstances beyond his control.’ In 2000, a UN resolution adopted the Millennium Development Goals. Article 19 resolves to reduce by half the proportion of people living on less than a dollar a day and reduce by half the proportion of people who suffer from hunger.
• You are a chemist interested in using your expertise to understand world hunger. You have many
questions on your mind like: What is hunger? What are the causes of hunger? What are the effects of hunger? What are the solutions? Carefully think about the things you need to know and suggest a possible research question for investigation. Try and narrow your focus. ‘Can rice be enriched with vitamin D?’ is an example of a good focused question.
• Consider some of the challenges scientists might face from experts in other areas of knowledge in the process of fi nding scientifi c solutions to world hunger. What sort of questions might a human scientist (economist, psychologist, sociologist, geographer) working in this fi eld ask? How would these questions differ from those of a chemist?
1 Describe the structural features of vitamin C that make this vitamin water-soluble.
2 Explain why carbohydrates are regarded as a macronutrient.
3 Describe one function of micronutrients.
4 Compare the structure of ascorbic acid with that of retinol (vitamin A).
5 Consider the following vitamins and use their structures to deduce whether they are water-soluble or fat-soluble.
a thiamine b ribofl avin
N
N NH2
H3C
N+ S
H3C
OH
c phylloquinone
CH3
CH3 3
O CH3
Section 2.5 Exercises
N
N
NH
N O
O
OH
HO
OH
OH H3C
H3C
CHAPTER 2 HUMAN BIOCHEMISTRY d tocopherol
H3C
CH3
CH3
CH3 CH3
CH3
CH3 HO
O
6 Explain why a child might contract each of the following conditions.
a Scurvy b Rickets c Beriberi d Anemia e Kwashiorkor
A hormone is a regulatory compound that is released by cells of one tissue and which acts to regulate the metabolism of target cells in another tissue.
Hormones are often described as ‘chemical messengers’.
Hormones are secreted directly into the blood by endocrine glands such as the hypothalamus, the pituitary gland, the thyroid gland,
the pancreas, the adrenal glands and the ovaries. The range of hormones produced is large, so we will only look in detail at a small number of them.
The sex hormones, testosterone, progesterone and estradiol, are the hormones that control sexual function in males and females, including production of sperm, ovulation and support of pregnancy. Secondary sex characteristics such as muscle bulk, hairiness and deepening of the voice in males and the growth of breasts, widening of hips and an increased amount of body fat in hips, thighs, buttocks and breasts in females are also supported by the sex hormones. These
hormones are all present in both males and females;
however, the relative amounts vary between the sexes.
For example, levels of progesterone in adult males are similar to those in women during the follicular phase (the fi rst part) of the menstrual cycle.
Estrogens are a group of steroid compounds of which the three naturally occurring members are estradiol, estriol and estrone. They are the primary female sex hormones, promoting the development of female secondary sex characteristics, such as breasts. They are also involved in the thickening of the lining of the uterus and in other regulatory aspects of the menstrual cycle. In males, estrogen plays a role in the maturation of sperm and is thought to be necessary for a healthy libido. Progesterone belongs to a class of hormones called progestogens, but is the major
2.6 HORMONES
B.6.1
Outline the production and function of hormones in the body. © IBO 2007
pituitary gland
testes (males only)
pancreas
ovaries (females only)
adrenal glands
thyroid gland
parathyroid glands
kidneys
hypothalamus pineal gland
Figure 2.6.1 Hormones are chemical messengers that travel through the bloodstream from endocrine glands to other parts of the body where they act.
naturally occurring member of the class. Progesterone is the hormone that helps pregnancy to continue by preparing the uterus for the fertilized egg.
High levels of progesterone are maintained throughout pregnancy.
Testosterone is the primary male sex hormone. It is present in both males and females, but there are much higher levels in males (about 40–60 times more).
Females are more sensitive to testosterone than males. Testosterone plays a key role in health and wellbeing as well as in sexual functioning. Testosterone is the precursor of progesterone in the human body.