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Option D Human Physiology
D.1 Human Nutrition
D.1
Essential idea: A balanced diet is essential to human health.
Nature of science: Falsification of theories with one theory being superseded by another – scurvy was
thought to be specific to humans, because attempts to induce the symptoms in laboratory rats and
mice were entirely unsuccessful.
D.1 U1 Essential nutrients cannot be synthesized by the body, therefore they have to be included in
the diet.
o Nutrients: chemical substances, found in foods, that are used in the human body.
o Essential: food is the only source of this nutrient. Such as amino acids, some unsaturated fatty
acids, some minerals, calcium, vitamins, and water.
o Non- essential: another nutrient can be used for the same purpose or because they can be
made in the body from another nutrient. Such as glucose, starch and other carbs because
they are used in respiration to provide energy and lipids can be used instead.
o Some essential nutrients are conditionally essential: In adults Vitamin K is produced by
metabolism of symbiotic bacteria in intestine, since infants don’t have colonies at birth they
are given supplementary injections of vitamin K.
Application D.1.1: Production of ascorbic acid by some mammals, but not others that need a dietary
supply.
o Vitamins C is ascorbic acid. Needed to make collagen fibers that form tissues of body (skin
and blood vessel walls).
o Most plants and animals can make vitamin C.
o Mutations have led to genes that no longer produce protein need to make vitamin C. This
inability is due to mutations in the GLO gene which codes to make the enzyme L-gulono-ylactone oxidase. (this catalyzes the final reaction to make vitamin C.
o Some fish called teleost (cod, salmon, and herring) have lost the ability to produce vitamin C.
Most mammals can (carnivores like dogs and cats) but primates (humans, chimps, and apes)
cannot but the more primitive ones can (like lemurs)
o Symptoms of vitamin C deficiency (scurvy) can be eliminated by dietary sources.
D.1 U4 Some fatty acids and some amino acids are essential.
o Of the 20 amino acids in proteins half are essential in humans. Other half can be made from
other simpler nitrogen compounds.
o Threonine and arginine are conditionally essential. Threonine can be synthesized if
phenylalanine is present. Arginine can be produced in a healthy individual but in premature
infants the pathway is not active so must get from diet.
o Some omega-3 and omega-6 fatty acids are essential in diet. Omega-3 and-6 refers to
position of double bond in relation to end of molecule. Alpha-linolenic acid and linoleic acid
are used to make a number of compounds so are needed in body but in large quantities in
brain and eye. However, diet supplements of these do not enhance brain or eye
development.
Histidine
Isoleucine
Leucine
Lysine
Methionine
Essential amino acids
Phenylalanine
Tryptophan
Valine
Threonine (only if phenylalanine is not in diet)
Arginine (required in the diet of infants)
D.1 U5 Lack of essential amino acids effects the production of proteins.
o If shortage of amino acids in diet then body can’t make enough of the proteins it needs.
Known as protein deficiency malnutrition.
o Essential a.a. may be lacking due to insufficiency of protein in diet or imbalance in types of
proteins. Ex. Can cause a lack of blood plasma proteins which results fluid being retained in
tissues causing swelling (edema) in abdomen. Child development can be mentally and
physically retarded with stunted growth and developmental disabilities. Adults undergo
serious weight loss (wasting)
D.1 U2 Dietary minerals are essential chemical elements.
o Needed in diet in small quantities (milligrams or micrograms)
o Can be distinguished from vitamins by chemical nature.
o Minerals: chemical elements, usually in ionic form. Ex. Calcium 2+ ions.
o Lacking in diet causes deficiency disease, can be serious. Ex. Iodine is needed by thyroid
gland to make hormone thyroxin which stimulates metabolic rated and release of energy. A
lack causes iodine deficiency disorder (IDD). If pregnant baby may be born with permanent
brain damage. Can cause mental development and impaired intelligence if baby born with
it. Many people affected by this and an iodine supplement can be given by adding mineral
salt to diet.
D.1 U3 Vitamins are chemically diverse carbon compounds that cannot be synthesized by the body.
o Vitamins are organic compounds needed in small amounts because can’t be made by body
but must be obtained from diet.
o Roles such as co-factors for enzymes, anti-oxidants and hormones.
o Vitamin C comes from monosaccharide, vitamin A is hydrophobic and has hydrocarbon ring
and chain, Vitamin B2 has nitrogen rings and is converted to Flavin mononucleotide by
addition of phosphate to carb. Within molecule.
o Can be fat or water soluble. Water have to be constantly consumed and any excess is lost in
urine. Fat can be stored in body.
D.1 U6 Malnutrition may be caused by a deficiency, imbalance of excess of nutrients in the diet.
o Malnutrition results from a poor diet. Diets can be low in overall quantity with low protein and
caloric content, can be unbalanced and fail to provide essentials, or can contain excess gats
and carbs.
o Malnutrition often associated with poverty, starvation results from diet lacking in adequate
protein and carbs.
o Obesity observed in developing countries as well as lower classes as a result of unhealthy diets
with excess of fat and refined carbs.
D.1 U7 Appetite is controlled by a centre in the hypothalamus.
o Hypothalamus is located in brain and makes us feel satisfied when we have eaten enough.
Called appetite control center.
o Small intestine secretes hormone (PYY3-36) when it has food. Pancreas secretes insulin when
blood glucose concentration is high. Adipose tissue secretes hormone leptin when amounts of
stored fat increase. If appetite control center receives these hormones it reduces the desire to
eat. This aids in avoiding health problems due to overeating including excessive blood
glucose levels and obesity.
Hypothalamus in Brain
receives these signals and tells
us we are full
D.1 U8 Overweight individuals are more likely to suffer hypertension and type II diabetes.
o Unhealthy diets with excess fat and refined carbs. Have health consequences. Ex. Diabetes
and hypertension.
o Several diseases cause excessive excretion of urine, all of which are forms of diabetes. In
commonest form sugar is preset in urine (diabetes mellitus) and affects many. Can develop 2
ways:
o 1. Auto-immune destruction of insulin-secreting cells in pancreas (Type I)
o 2. Decreased responsiveness of body cells to insulin due to “burn-out” (Type II)
o Type II is rising in many countries. Epidemiology (study of rates and distribution of a disease)
have implicated increased blood conc. Of fatty acids, linked to the risk factors: diets rich in
fat and low in fiber, obesity due to overeating and lack of exercise, genetic factors that affect
fact metabolism.
o Big variation between ethnic groups in rates of type II. China has less than 2 percent and
Pima Indians having 50%. Symptoms are not always recognized so all people not diagnosed.
Symptoms include: elevated levels of blood glucose, glucose in urine, dehydration and thirst
resulting from excretion of large volumes of urine.
o Diabetes can cause health problems if not managed. Several complications relate to
cardiovascular system: atherosclerosis (narrowing of arteries by fatty deposits), hypertension
(raised blood pressure), coronary heart disease (narrowing of coronary arteries with risk of
heart attacks)
o Link between cardiovascular disease and blood lipid concentrations: links between high
conc. of cholesterol high conc. of LDL and low conc. Of HDL.
o Clear correlation between excessive weight gain and hypertension. Weight gain can
increase release of hormones as well as cause changed in body physiology and anatomy
which all can lead to hypertension: weight gain leads to higher cardiac output and can raise
blood pressure; abdominal obesity can increase vascular resistance which can raise blood
pressure; weight gain associated with arteries becoming stiffer and narrower which can raise
blood pressure.
o Hypertension can be caused by high salt intake.
D.1 U9 Starvation can lead to breakdown of body tissue.
o Occurs due to severe lack of essential and nonessential nutrients.
o In absence of energy sources the body will first access glycogen stores, then it will break down
its own muscle tissue to utilize amino acids as energy sources. The a.a. are sent to liver and
converted to glucose. This results in loss of muscle mass.
Application D.1.2: Cause and treatment of phenylketonuria (PKU)
o Phenylketonuria (PKU) is a genetic disease caused by mutations of a gene coding for the
enzyme that converts phenylalanine into tyrosine. Mutations produce alleles enzyme that is
unable to catalyze the reaction. Only one normal allele is needed for normal condition so the
disease is only inherited when two recessive mutant alleles are acquired.
o As a result phenylalanine accumulates in body and can also be a deficiency in tyrosine. High
levels cause reduced growth of head and grain, mental retardation of young children,
hyperactivity and seizures in older children.
o PKU babies are unaffected at birth because mother’s metabolism kept normal levels. Test are
carried out at 24 hours after birth when phenylalanine concentrations have started to rise.
o Treatment involves eating a diet low in phenylalanine. Meat, fish, nuts, cheese, peas and
beans eaten in small quantities. Tyrosine supplements may be needed. Harmful effects can
be avoided with diet.
Application D.1.3: Lack of Vitamin D or calcium can affect bone mineralization and cause rickets or
osteomalacia
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Vitamins D needed for calcium absorption from food in the intestines. Symptoms are similar to
those of calcium deficiency.
Vitamin D is synthesized in the skin when exposed to sunlight or another light source containing
ultraviolet light with wavelengths in the range 290-310nm.
Children, pregnant women and elderly need to eat 10ug per day to supplement amount in
their skin. Dietary sources include oily fish (herring, mackerel, sardines and tuna), eggs, liver
good with margarine, milk are artificially fortified with vitamin D.
Ultraviolet light has harmful consequences: mutations in skin (dark skin gives protection
against cancer but it also reduce vitamin D synthesis) In indigenous human pop. skin color
balances the twin risks of vitamin D deficiency and cancer or other damage due to ultraviolet
light.
After population migrations there can be problems. In 1970 immigrants with dark skin from
Indian subcontinent living in United Kingdom showed symptoms of vitamin D deficiency.
Immigrants from northern Europe with light skin living in Australia, were found to have high rates
of malignant melanoma. Australians with light skin were then advised to stay of bright sunlight,
cover their skin or apply sun-block.
Application D.1.4: Breakdown of heart muscle due to anorexia
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Anorexia means reduced appetite. Anorexia nervosa is a psychiatric illness which involves
voluntary starvation and loss of body mass. The amounts of carb. and fats consumed are too
small to satisfy body’s energy requirements so protein and other chemicals in body are broken
down resulting in a wasting of muscles and loss of strength. Hair becomes thinner, skin
becomes dry and bruises easily. Fine growth of hair all over body. Blood pressure reduced,
poor circulation. In females infertility is common and no ovulation or menstrual cycles.
As body weight falls heart muscle deteriorates. Skeletal muscle mass reduces
disproportionately faster than cardiac mass.
Lack of protein, electrolytes and micronutrients result in muscle fiber deterioration, and alters
conc. Of calcium, potassium, and sodium and muscles do not contract normally.
Reduced blood pressure, slower heart rate and reduced heart output is also observed.
Application D.1.5: Cholesterol in blood as an indicator of the risk of coronary heart disease.
o Cholesterol is a normal component of plasma membranes in human cells.
o Research has shown a correlation between high levels of cholesterol in blood plasma and an
increased risk if coronary heart disease.
o Advice is often given to minimized dietary cholesterol intake, but is it not certain that this will
actually lower risk of CHD for a variety of reasons:
o Research has involved total blood cholesterol levels, but only cholesterol in LDL (lowdensity lipoprotein) is implicated in CHD.
o Reducing cholesterol often has small effect on blood cholesterol levels
o Liver can synthesize cholesterol so dietary cholesterol is not only source.
o Genetic factors are more important and some families have high cholesterol and low
dietary intake.
o Drugs can be more effective than reducing dietary intake
o Positive correlation between dietary intake of saturated fats and intake of cholesterol,
so possible that saturated fats, not cholesterol cause the increased risk of CHD in
people with high cholesterol intakes
Skill: Determination of the energy content of food by combustion.
o Calorimetry: determination of the energy content of a substance.
o The specific heat of water: it takes 4.186J of heat energy to raise the temperature of 1 gram of
water by 1 degree Celsius.
o Q= mass of water x specific heat capacity x change in temperature
o The apparatus consists of a thermometer to detect change in temp. A vessel contain a
known mass of water (1ml of water has a mass of 1g). The sample to be tested for its energy
content is ignited and placed below the container containing the water and the temperature
change is noted.
 Use these results to estimate the energy content the nut per gram:
o Data: Mass of nut = 0.60g; volume of water = 25ml; initial water temperature = 20oC; final
water temperature = 65oC
o
Your answer: ___________________________________
Skill: Use of databases of nutritional content of foods and software to calculate intakes of essential
nutrients from a daily diet.
o Balanced diet: combination of foods that will provide essential and non-essential nutrients in
the correct balance.
o Fresh fruit and vegetables should make up largest part of diet followed by carbs, proteins and
then dairy products. Fata and sugars are on charge because they should make up smallest
part of diet. (See food wheel below)
o Computer applications can be used to keep record of food consumed. Check our “Super
Tracker” available from the US Department of Agriculture (USDA)