D. 1 Human Nutrition
Essential nutrients cannot be synthesized by the body; therefore, they have to be
included in the diet.
o Essential nutrients- nutrients that cannot be synthesized in the body and have to be
ingested from food.
o Nonessential nutrients- nutrients that can be synthesized from other nutrients that are
present in the body or ones whose function can be performed by other nutrients.
o Conditionally essential- nutrients that may be needed to be ingested by a baby,
however as the organism develops it is then able to synthesize that nutrient by itself.
▪ Ex.: vitamin K
Dietary minerals are essential chemical elements.
o Minerals are different from vitamins in their structure.
▪ Minerals usually have an ionic form, for ex.: Ca+2 ions.
o Lack of intake of minerals can cause serious health problems.
▪ For ex.: the thyroid gland uses iodine to produce a hormone, which
stimulates metabolic rate and energy release in the body. The deficiency of
iodine may cause brain damage or have other negative effects on the body.
Vitamins are chemically diverse carbon compounds that cannot be synthesized by the
o Vitamins function as parts of enzymes, anti-oxidants and hormones and must be
acquired through the diet, as the body cannot synthesize them.
o There are two types of vitamins:
▪ Fat soluble- can be stored in the body;
▪ Water soluble- must be ingested regularly and any excess is gotten rid of
through urine (there are more water-soluble vitamins).
Some fatty acids and some amino acids are essential.
o Humans have 20 amino acids. Out of the twenty, around half of them are essential.
▪ Threonine and arginine are conditionally essential amino acids.
o Some fatty acids are also essential to humans and cannot be synthesized.
▪ Omega-3 and omega-6, which are needed throughout the body, however
are especially used in the development of the brain and the eyes.
Lack of essential amino acids affects the production of proteins.
o Protein malnutrition-when there is not enough of essential amino acids in the diet,
the body will not be able to produce all needed proteins.
▪ It can cause lack of blood plasma proteins, which results in the retention of
fluid in the tissues.
▪ It may have a negative impact on the development of children, having an
effect on mental and physical abilities.
▪ In an adult it may cause serious weight loss.
Malnutrition may be caused by a deficiency, imbalance or excess of nutrients in the
o Malnutrition- the outcome of a poor diet.
o There are two types of malnutrition:
▪ Lack of proteins and carbohydrates= starvation;
▪ Excess of fats and refined carbohydrates= obesity.
Appetite is controlled by a centre in the hypothalamus.
o the appetite control centre- responsible for making us feel satisfied when we have
o The appetite is supressed, when these hormones are secreted:
▪ The small intestine secrets a hormone when it contains food.
▪ Adipose tissue secrets the hormone leptin when the amount of stored fat
Overweight individuals are more likely to suffer hypertension and type II diabetes.
o Diabetes mellitus- sugar is present in urine.
▪ Caused by auto-immune destruction of insulin-secreting cells;
▪ Caused by decreased response of the body to insulin.
o Increased blood concentrations of fatty acids:
▪ Diets rich in lipids and low in fibre
▪ Overeating and lack of exercise
▪ Genetic factors that affect metabolism.
o Diabetes can cause:
▪ Hypertension (raised blood pressure)
▪ Coronary heart disease
o Weight gain results in a raise of blood pressure
o Abdominal obesity increases vascular resistance
o High intake of salt can cause hypertension.
Starvation can lead to breakdown of body tissue.
o Starvation occurs due to the severe lack of essential and non-essential nutrients.
o When there is a lack of glucose present, the body break down muscle for energy.
Production of ascorbic acid by some mammals, but not others which need a dietary
o Ascorbic acid = Vitamin C
▪ Needed for the synthesis of collagen fibres that are part of many tissues in
• Such as skin, and walls of the blood vessels.
o Animals that are able to synthesize Vitamin C:
o Animals that are unable to synthesize Vitamin C:
Cause and treatment of phenylketonuria (PKU).
o Consequences of PKU:
▪ Reduced growth of head and brain;
▪ Mental retardation;
▪ Hyperactivity and seizures.
▪ Eating a diet with low meat, fish and nuts intake;
▪ Tyrosine supplements.
Lack of Vitamin D or calcium can affect bone mineralization and cause rickets or
o Vitamin D:
▪ Component of fatty fish;
▪ Component of butter;
▪ Produced by the skin under UV light.
o Deficiency of Vitamin D leads to the inability to absorb Calcium (Ca), which then
weakens bone structure.
o Lack of Calcium leads to the inability of the bones to harden, especially in babies,
when the cartilage of the bone is hardening and being replaced by hard formed bone.
Breakdown of heart muscle due to anorexia.
o After there are no muscles left in the body to break down, the body starts breaking
down heart muscle.
Cholesterol in blood as an indicator of the risk of coronary heart disease.
o The liver can synthesize cholesterol
o Genetic factors affect cholesterol production and levels
o Positive correlation between intake of saturated fats and cholesterol levels.
Nervous and hormonal mechanisms control the secretion of digestive juices.
o Sight and smell of food:
▪ Releases salivary and gastric juices
▪ Gastrin- released by the wall of the stomach when food is felt or chemically
• Causes the release of gastric juices.
▪ Secretin- released by the wall of the duodenum, when there is a drop in pH
and when fats and proteins are chemically detected.
• Bicarbonate (HCO -3) is released, which neutralizes the acid.
▪ Cholecystokinin- released by the wall of the duodenum when there is a drop
in pH and when fats and proteins are chemically detected.
• Releases bile and pancreatic juice.
Exocrine glands secrete to the surface of the body or the lumen of the gut.
o Alimentary canal- the passage through which food passes from the mouth to the
o Secretion of digestive juices:
▪ Mouth- salivary glands secrete saliva (~pH 7)
• Starch broken down with amylase into maltose (a disaccharide sugar
composed of two glucose molecules)
▪ Stomach wall- gastric glands, in the wall of the stomach (~pH 2)
• Hydrochloric acid
• Enzymes- proteases
o Ex.: pepsin
• Mucus layer (produced from a polysaccharide) protects the wall of
the stomach from digesting itself.
▪ Pancreatic juices- secreted by the exocrine glands in the pancreas.
• Exocrine gland- secretes outside the gland through a duct;
o Ex.: sweat and digestive enzymes
• Endocrine gland- doesn’t have a duct, secretes the product into the
o Ex.: hormones
• Produces bile that is stored in the gall bladder
• Bile is secreted into the duodenum (the front of the small intestine).
• The pH of the food that just travelled from the stomach is raised to
a pH of 8.
• Bile emulsifies fat by breaking it down into smaller blobs of fat,
which increases the surface area of fats.
o Epithelial cells:
▪ Control what enters the body through active transport for which ATP is
needed. Thus, there is an abundance of mitochondria in epithelial cells, to
supply the needed energy.
Acid conditions in the stomach favour some hydrolysis reactions and help to control
pathogens in ingested food.
o Hydrochloric acid present in the stomach creates a highly acidic environment.
▪ This allows to kill bacteria and pathogens that may have entered with the
ingested food into the organism.
▪ Some enzymes, such as pepsin function only at extremely low pH levels,
thus this creates an optimum environment in which proteins are broken
The structure of cells of the epithelium of the villi is adapted to the absorption of food.
o Absorption takes place in the small intestine, through the villi that are covered by
o Structure of the villi:
▪ There are tight junctions between neighbouring villi, which ensures that
materials pass into the blood;
▪ Microvilli further increase the surface area that is available for absorption;
▪ Large amounts of mitochondria are present in the epithelial cells of the villi;
▪ Some foods that are too large to pass through active transport are absorbed
▪ Apical surface- the surface that is facing the lumen of the intestine;
▪ Basal surface- the surface that is facing the blood vessels.
The rate of transit of materials through the large intestine is positively correlated with
their fibre content.
o Dietary fibre- materials that cannot be readily digested
▪ Ex.: cellulose, lignin and pectin.