Chapter-6
Proteins
Dietary protein performs all three functions of nutrients. It is needed for growth, maintenance and
repair of body tissue; it regulates key processes within the body and any excess protein is used as
source of energy.
The term protein meaning to take first place was introduced by the Dutch chemist Mulder in 1838. He
defined protein as a nitrogen-containing constituent of food and felt life was impossible without it.
About 50 per cent of protein is present in muscle, 20 per cent in bone, 10 per cent in the skin and the
rest is present in other parts of the body.
Chemical Composition
All proteins are synthesised from amino acid molecules and 20 different amino acids are used in
protein synthesis, although a protein can contain many hundreds of amino acid units (or residue)
overall. All the amino acids used in protein synthesis contain carbon, hydrogen and nitrogen atoms
and cysteine and methionine contain sulphur atom. Unlike carbohydrates and lipids proteins contains
nitrogen. The percentage composition of protein in general falls between the following limits: C-50-55;
H=6.0-7.3; 0-19-24; N=15-19; 5-0-4
All amino acids contain an amino group (NH) a carboxyl group (COOH) and a hydrogen atom (H)
attached to central carbon atom, which is also bonded to the side chain or side group of the amino
acid
Properties
Amphoteric Nature: – Amino acids and proteins are amphoteric in nature that is, they act on both
acids
And bases. Since proteins have electric charges, they migrate in an electric filed, the direction of
migration depending on the net charge on the molecule. For each protein, there is a pH at which the
positive and negative charge will be equal and protein will not move in an electric field. The pH is
known as the isoelectric point of the protein.
Solubility: Each protein has a definite and characteristic solubility in a solution of known salt
concentration and pH. Albumins are soluble in water. Globulins are soluble in neutral sodium chloride
solutions but are almost insoluble in water.
Some proteins like casein are soluble in alkaline pH. The differences in the solubility are made use of
in the separation of proteins from a mixture.
Colloidal nature of protein solutions: Proteins have large molecular weights and protein solutions are
colloids. They do not pass through semi-permeable membranes. This property of proteins is of great
physiological importance.
Nutritional Classification of Protein
The nutritive value of proteins is determined by the composition of essential amino acids. From the
nutritional point of view, proteins are classified into 3 categories:
Complete proteins: These proteins have all the ten essential amino acids in the required proportion by
the human body to promote good growth. Eg egg albumin, milk casein
Partially Incomplete protein: These proteins are partially lacking one or more essential amino acids
and hence can promote moderate growth, e.g., wheat and rice proteins (limiting Lys, Thr).
Incomplete Protein: These proteins completely lack one or more essential amino acids. Hence, they
do not promote growth at all e.g., gelatin (lack Trp), zein (lacks Trp, Lys).
Higher quality protein produces a faster growth rate. Such growth rate measurements evaluate the
actual factors important in a protein. Pattern and abundance of essential amino acids, relative
amounts of non-essential and essential amino acids, digestibility and of trypsin inhibitors all affect
the quality of proteins and in turn affect the growth rate
Nutritional Classification of Amino Acids
Essential Amino Acids
Essential amino acids are ones that canned be synthesized by the body at a rate sufficient to meet the
needs for growth and maintenance. The human body has certain limited powers of converting one
amino acid into another. This is achieved in the liver by the process of transamination, whereby an
amino group is shifted from one molecule across to another under the influence of amino
transferases, the co- enzyme of which is pyridoxal phosphate. Inability to synthesise the carbon
skeleton of these amino acids is the probable reason why they are dietary essentials.
Non-essential Amino Acids
Non-essential amino acids are ones that the body can make in adequate amounts if nitrogen is
available in the diet. They are non-essential only in the sense that they are not essential components
of the diet.
Conditionally Essential Amino Acids
These are needed in the diet unless abundant amounts of their precursors are available for they
synthesis the new born may not have enzymes in adequate amounts to synthesise non essential
amino acid. Or in intestinal metabolic dysfunction arginine may not be synthesised. Henice it
becomes conditionally essential amino acid. Amino nitrogen is not freely interchanged between all
amino acids
Functions
Virtually every biochemical reaction within the body is catalysed by a protein enzyme. All structural
tissues of the body contain protein so the importance of proteins to all aspects of life cannot be over
emphasised.
Growth and Maintenance of Tissue
New growth, including the building of muscles, can occur only when an appropriate mixture of amino
acids is available over and above the amount needed for the maintenance and repair of existing
tissue. The vital process of cell division is also dependent on proteins. Specific proteins form the
intracellular scaffolding or cytoskeleton that is involved in moving the contents of the dividing cell,
especially the chromosomes containing the genes and distributing them properly between the two
new cells being formed. One-sixth of the wet cell mass contributed by proteins.
The structural matrix or framework, within bones and teeth is composed of protein molecules,
particularly the protein known as collagen. Collagen is also the main protein within tendons and
ligaments and it is the intercellular material that binds cells together. The contractile fibres of muscles
are composed of two kinds of protein, actin and myosin, which slide past one another in a process
powered by the hydrolysis of adenosine triphosphate to allow muscle to contract.
Proteins are continually degraded and then resynthesized in a process known as protein turnover
which is 0.3 to 0.4 per cent of body protein, Body reuses most of the amino acids released by the
breakdown of proteins. Protein is lost from the skin, hair and nails which are constantly shed from the
body’s surface. Protein is also lost from the continuously shed intestinal wall cells that are excreted in
faeces. In addition to the need to replace proteins during turnover, proteins must also be synthesized
for the repair of damaged tissue.
Formation of Essential Body Compounds
Enzymes, including those responsible for digestion are proteins, many of the hormones such as
insulin, gastrin and growth hormone produced by various glands in the body are proteins or peptides.
Hormones regulate metabolic functions of a cell. They also control very important biological
functions like reproduction. Epinephrine a hormone secreted by the adrenal gland is derived from the
amino acid tyrosine. Glycoproteins have specific binding function lor thyroxine and cortisol.
The oxygen molecules needed to oxidise food molecules during respiration are transported through
the blood by the protein haemoglobin, Almost all of the substances responsible clotting of blood are
proteins.
Contractile proteins, myosin and actin regulate muscle contraction. The photoreceptors in the eye,
which initiate the nerve signals responsible for the sense of vision when they absorb light are proteins.
The amino acid tryptophan serves as the precursor for the vitamin niacin and for serotonin, a vital
neurotransmitter that is involved in transmitting nerve signals from one nerve cell to another.
Transport of Nutrients
Proteins play an essential role in the transport of nutrients from the intestine across the intestinal wall
to the blood, from the blood to the tissues of the body and across the membranes of the cells of the
tissues. These transport and membrane bound carrier proteins are usually specific to one nutrient.
Retinol binding protein, for example, binds to and transports only retinol But, some like metallothione,
transports both copper and zinc ions. Lipoproteins can transport many different lipid molecules.
Regulation of Water Balance
Fluid in the body is distributed in intracellular and extracellular compartments. The extracellular is
divided into the intercellular (between the cells) and intravascular (within the blood vessels)
compartments. The balance between the compartments is achieved by dissolved proteins and
dissolved ions (electrolytes) primarily sodium and potassium ions. Protein molecules in the blood that
are too large to pass out of the blood into the intercellular space exert an oncotic pressure, drawing
water from the intercellular space back into the blood. A hydrostatic pressure, pushing fluid in the
opposite direction out of the blood and into the intercellular space is also present always because of
the pumping action of the heart. When the level of protein in the blood is low, the hydrostatic pressure
dominates and pushes fluid out of the blood. This causes accumulation of fluid within the tissues
resulting in oedema.
Maintenance of Appropriate PH
Normal processes of the body continually produce acids and bases that must be carried by the blood
to the organs of excretion. Acidosis or alkalosis can cause death. Proteins in the blood serve as
buffers. They can combine with both hydrogen ions and hydroxide ions if the concentration of either of
these determinants of the pH should rise.
Defense and Detoxification
The body’s ability to fight off infection depends on its immune system which has defensive proteins
known as antibodies. Specific antibody is required for specific antigen. Whenever required, the body
produces antibodies quickly. The toxins present in foods are detoxified by enzymes found mainly in
liver which convert them into harmless substances.
Source of Energy
Though proteins can also provide 4 kcal energy per gram like carbohydrates, they are used for energy
purpose only when the diet has inadequate carbohydrate and fat.
Specific Functions of Amino Acids
Glycine:
It is needed during periods of rapid growth
Biological systems incorporate glycine molecule into purines, glutathione, creatine and creatinine,
bile acids, hippuric acid and serine.
It is also essential for biosynthesis of porphyrin ring of haemoglobin.
Many aromatic substances whether produced endogenously or consumed as drug or food additives
are conjugated in the liver with glycine and excreted in the bile or urine.
Glutamic acid
Glutamic acid, cysteine and glycine are components of glutathione, which function cellular oxidation
reduction reactions. It plays an important role in the metabolism ammonia. It is a precursor of the
neurotransmitter, y-aminobutyric acid in brain Cleavage of arginine results in the formation of urea in
the liver. It is a precursor of the neurotransmitter, Y-amino butyric acid in brain.
Arginine
Cleavage of arginine result in the formation of urea in the liver. It is a precursor amino acid for
neurotransmitters.
Lysine: It is the parent substance of carnitine, which transports fatty acids within the mitochondria
Methionine and Cysteine
Present in the keratin of hair and in insulin.
Involved in transmethylation.
Cysteine is a component of glutathione.
Fatty liver can be cured by methionine or choline which is formed from it. Methionine protects the liver
from damage by poisons such as carbon tetrachloride arsenic and chloroform
Taurine conjugated with bile acids, is derived from the metabolism of cysteine.
Phenylalanine and Tyrosine:
For foetal and childhood brain development, these amino acids are required.
Epinephrine and thyroxine are synthesised from tyrosine.
This helps in the synthesis of melanin pigment in hair, choroid lining of the eye and in the skin.
Histidine:
It is found in the muscle constituent carnosine.
It is probably a precursor of the red blood cell constituent ergothioneine. It is present to the extent of 8
per cent in haemoglobin.
Converted to histamine. Histamine is involved in allergic reaction. It also acts stimulus for acid
secretion in the stomach.
Tryptophan:
Nicotinic acid is synthesised from tryptophan. Milk is a good source of tryptophan.
Precursor of serotonin, 5-hydroxytryptamine, causes vaso constriction. When blood clot occurs,
platelets, release 5-hydroxy tryptamine which prevents bleeding by causing vasoconstriction. 5-
hydroxytryptamine is also a neurotransmitter.
Proline and Hydroxy Proline:
Present in haemoglobin and cytochromes.
Prevalent in the collagen of connective tissue.
Leucine, isoleucine and valine: These are branched-chain amino acids.
In the muscle they are oxidized and the nitrogen is used for the formation of alanine
Chapter-7
Vitamins, Minerals and Trace elements
Vitamins, minerals and trace elements are required for numerous functions within the body and
deficiencies can lead to serious health problems. They are required in much smaller amounts than
fats, carbohydrates and proteins and are therefore known as micronutrients. The department of
health recommends specific amounts of each micronutrient for certain sub groups of the population
known as dietary reference values (DRVS)
These recommendations only apply to healthy people and should only be used as a general guideline
as Individual requirements are likely to vary.
5.1 Classification of Vitamins
There are two types of vitamins, water-soluble and fat soluble:
5.1.1 Water-soluble vitamins
Water soluble vitamins travel around the body in the bloodstream and are picked up by cells when
they are needed. Water-soluble vitamins that are not required by the body are excreted in the urine.
5.1.2 Fat soluble vitamins
Fat soluble vitamins are stored in body fat (for a few days or as long as 6 months) until the body needs
them.
Water soluble vitamins:
Vitamin B1 (thiamin)
Vitamin B2 (riboflavin)
Vitamin B6
Vitamin B12
Folate
Niacin
Biotin
Pantothenic acid
Vitamin C
Fat soluble vitamins:
Vitamin A
Vitamin D
Vitamin E
Vitamin K
Minerals and Trace Elements
Minerals and trace elements are similar to vitamins and are required in very small or trace amounts to
maintain good health
Minerals tend to be required in milligram (mg) quantities and trace elements tend to be required in
much smaller amounts-microgram (ug) quantities
Some are found only in a few foods, so it is important that these foods are included in the diet on a
regular basis eg. The main providers of calcium in the diet are milk, cheese and yogurt. Some foods
are also fortified with minerals,
For example, iron is added to some breakfast cereals.
Minerals:
Calcium
Chloride
Fluoride
Iron
Magnesium
Phosphorus
Potassium
Sodium
Zinc
Trace elements:
Copper
Chromium
Lodine
Manganese
Molybdenum
Selenium
Consumption of a balanced and varied diet should ensure adequate levels of all vitamins, minerals
and trace elements are received.
It is always better to receive the recommended levels of vitamins, minerals and trace elements
through consumption of food sources rather than artificial supplements. However, supplements are
sometimes useful, particularly if you have an increased requirement for one or several nutrients e.g.,
pregnant women, infants, older people who don’t go out of doors or ethnic groups who wear coverall
clothing etc.
It is always a good idea to seek advice from a dietitian if you feel that supplements are necessary.
Deficiencies and Toxicity
An inadequate amount of a nutrient is a deficiency. Deficiencies can be due to a number of causes
including inadequacy in nutrient intake called dietary deficiency, or conditions that interfere with the
utilization of a nutrient within an organism. Some of the conditions that can interfere with nutrient
utilization include problems with nutrient absorption, substances that cause a greater than normal
need for a nutrient, conditions that cause nutrient destruction, and conditions that cause greater
nutrient excretion.
Nutrient toxicity occurs when an excess of a nutrient does harm to an organism. This toxicity may
cause some kinds of allergies but in some severe conditions these allergies and toxicity may cause
death as well.
VITAMINS AND THEIR SOURCES
Vitamins Function Food sources
Vitamin A Night vision
Healing epithelial cells
Normal development of
teeth and bones
Breastmilk, tomatoes,
cabbage, lettuce,
pumpkins
Mangoes, papaya,
carrots
Liver, kidney, egg yolk,
milk, butter, cheese
cream
Vitamin D Needed for absorption of
calcium from small
intestines
Calcification of the
skeleton
Ultra violet light from
the sun
Eggs, butter, fish
Fortified oils, fats and
cereals
Vitamin K For blood clotting Green leafy vegetables
Fruits, cereals, meat,
dairy products
B Complex Metabolism of
carbohydrates, proteins
and fats
Milk, egg yolk, liver,
kidney and heart
Whole grain cereals,
meat, whole bread, fish,
bananas
Vitamin C Prevention of scurvy
Aiding wound healing
Assisting absorption of
iron
Fresh fruits (oranges,
banana, mango,
grapefruits, lemons,
potatoes) and
vegetables (cabbage,
carrots, pepper,
tomatoes)
Breastmilk
Vitamin Health Benefit Deficiency Toxicity
Fat-soluble vitamins
Vitamin D (calciferols) Helps to maintain
constant levels of
calcium in the blood
Important in insulin
and prolactin
secretion, muscle
function, immune and
stress response,
Disease is rickets, not
a major problem in
U.S.; symptoms
include soft bones and
teeth
Most people do not
take in supplemental
form since the body
produces its own via
exposure to the sun
Toxic in doses larger
than 1,000-1,1500 I.U.s
daily for a month or
longer; produces
melanin synthesis, and
cellular differentiation
Vital for kidney and
parathyroid gland
function:
Necessary for healthy
bones
nausea, weakness,
and irritability
May lead to brain or
liver damage, jaundice,
and the destruction of
red blood cells
Vitamin E
(tocopherols)
Protects vitamin A
from oxidation during
digestion
Enhances immune
response
Inhibits carcinogens
from reaching target
sites
Can stop neurological
problems associated
with cystic fibrosis,
liver disease early in
disease process
Detoxifies free
radicals, prevents
damage to cell
membranes
No disease; may
produce vague
symptoms and anemia
Unlikely, although high
doses increase the
action of anticoagulant
medications
High doses also
interfere with the
absorption of other fatsoluble vitamins,
particularly vitamin K
Water-Soluble
Vitamins
Vitamin B-1 (thiamin) Vital for healthy
nervous
system and nerve
transmission
Essential in converting
glucose to energy
Disease is beriberi
Symptoms of a
deficiency include
depression, irritability,
attention deficit
Severe deficiency
leads to edema,
paralysis, and heart
failure
No toxicity has been
reported by those
taking large doses over
prolonged periods of
time
Vitamin B-2 (riboflavin) Essential for
metabolizing
carbohydrates, fats,
and lipids and for the
degradation of fatty
acids and the
synthesis of ATP
Acts as an
intermediary in the
transfer of electrons in
oxidation-reduction
reactions
Necessary for the
function of vitamins B6, folic acid, and niacin
Involved in formation
of red blood cells and
Symptoms are dry,
scaly skin on face, oral
swelling, and cracking
at the corners of the
mouth
No evidence that high
doses have toxic
effects
maintenance of body
tissues, particularly
the skin and eyes
Vitamin B-6
(pyridoxine)
Necessary for immune
system function,
hormone modulation,
gluconeogenesis
Essential in making
certain amino acids
and turning others into
hormones
Involved in
metabolizing
polyunsaturated fats
and proteins
Used to build red
blood cells and
maintain nerve tissue
Formation of niacin
Not common;
symptoms include
mouth sores, nausea,
nervousness, anemia,
convulsions
High doses over
prolonged periods are
very toxic and can
cause temporary or
permanent nerve
damage
Vitamin B-12
(cobalamin)
Works with folic acid to
produce red blood
cells
Helps build and
maintain protective
nerve sheaths
Needed for RNA and
DNA synthesis
Pernicious anemia,
muscle and nerve
paralysis
None reported
Health Benefits, Claims, Deficiency, and Toxicity of Leading Mineral Dietary Supplement Products
These claims have not been evaluated by the Food and Drug Administration. But the research on the
toxicity results id still under study. (As per IDA)
Table
Chapter-8
Hormones
Hormones are the chemical released by a cell or a gland in a part of body that transmit messages to
regulate the activities of other body parts; these hormones are transported in blood. These Hormones
have many different functions and modes of action: one hormone may have several effects on
different target organs, and, conversely, one target organ may be affected by more than one hormone.
Their interference with the synthesis, secretion, transport, binding, action, or elimination of natural
hormones in the body are responsible of homeostasis, reproduction, development, and/or behavioral
changes same way as the endogenous produced hormones. Hormonal signaling involves the
following Biosynthesis of a particular hormone in a particular tissue Storage and secretion of the
hormone Transport of the hormone to the target cell(s) Recognition of the hormone by an associated
cell membrane or intracellular receptor protein Relay and amplification of the received hormonal
signal via a signal transduction process: This then leads to a cellular response.
There are certain studies done which actually investigated changes in voluntary food intake and fuel
selection in response to manipulations of macronutrients balance when energy balance was held
constant.
Effects of hormones
Hormones have the following effects on the body: stimulation or inhibition of growth, mood swings,
induction or suppression of apoptosis (programmed cell death) activation or inhibition of the immune
system, regulation of metabolism, preparation of the body for mating, fighting, fleeing, and other
activity, preparation of the body for a new phase of life, such as puberty, parenting, and menopause
control of the reproductive cycle, hunger cravings.
A hormone may also regulate the production and release of other hormones. Hormone signals control
the internal environment of the body through homeostasis.
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea
and weighing 0.5 g (0.02 oz.), in humans. It is a protrusion off the bottom of the hypothalamus at the
base of the brain, and rests in a small, bony cavity (sella turcica) covered by a dural fold (diaphragma
sellae). The pituitary is functionally connected to the hypothalamus by the median eminence via a
small tube called the infundibular stem (Pituitary Stalk). The pituitary fossa, in which the pituitary
gland sits, is situated in the sphenoid bone in the middle cranial fossa at the base of the brain. The
pituitary gland secretes nine hormones that regulate homeostasis. There is an analogous structure in
the octopus brain.
A major organ of the endocrine system, the anterior pituitary, also called the adenohypophysis, is the
glandular, anterior lobe of the pituitary gland. The anterior pituitary regulates several physiological
processes including stress, growth, and reproduction. Its regulatory functions are achieved through
the secretion of various peptide hormones that act on target organs including the adrenal gland, liver,
bone, thyroid gland, and gonads. The anterior pituitary itself is regulated by the hypothalamus and by
negative feedback from these target organs. Disorders of the anterior pituitary are generally classified
by the presence of over- or underproduction of pituitary hormones. For example, a prolactinoma is a
pituitary adenoma that overproduces prolactin. In Sheehan’s syndrome of postpartum
hypopituitarism, the anterior pituitary uniformly malfunctions and underproduces all hormones.
Proper function of the anterior pituitary and of the organs it regulates can often be ascertained via
blood tests that measure hormone levels.
The anterior pituitary synthesizes and secretes the following important endocrine hormones:
Adrenocorticotropic hormone (ACTH), release under influence of hypothalamic Corticotropin
Releasing Hormone (CRH).
Thyroid-stimulating hormone (TSH), release under influence of hypothalamic Thyrotropin Releasing
Hormone (TRH).
Growth hormone (also referred to as ‘Human Growth Hormone’, ‘HGH’ or ‘GH’ or somatotropin),
release under influence of hypothalamic Growth Hormone Releasing Hormone (GHRH); inhibited by
hypothalamic Somatostatin.
Prolactin (PRL), also known as ‘Luteotropic hormone (LTH), release under influence of multiple
hypothalamic Prolactin Releasing Factors (PRH). The two ‘Gonadotropins’;
Luteinizing hormone (also referred to as ‘Lutropin’ or ‘LH’, or in males, “Interstitial Cell Stimulating
Hormone (ICSH)), and Follicle stimulating hormone (FSH), both released under influence of
Gonadotropin Releasing Hormone (GnRH) and; melanocyte-stimulating hormones (MSH’s) or
“intermedins” as these are released by the pars intermedia which is “the middle part”; adjacent to the
posterior pituitary lobe, pars intermedia is a specific part developed from the anterior pituitary lobe
These hormones are released from the anterior pituitary under the influence of the hypothalamus.
Hypothalamic hormones are secreted to the anterior lobe by way of a special capillary system, called
the hypothalamic-hypophysial portal system. The anterior pituitary is divided into anatomical regions
known as the pars tuberalis, pars intermedia, and pars distalis. It develops from a depression in the
dorsal wall of the pharynx (stomodial part) known as Rathke’s pouch.
Posterior pituitary
The posterior pituitary (or neurohypophysis) comprises the posterior lobe of the pituitary gland and is
part of the endocrine system. Despite its name, the posterior pituitary gland is not a gland, per se;
rather, it is largely a collection of axonal projections from the hypothalamus that terminate behind the
anterior pituitary gland.
The posterior pituitary consists mainly of neuronal projections (axons) extending from the supraoptic
and paraventricular nuclei of the hypothalamus. These axons release peptide hormones into the
capillaries of the hypophyseal circulation. In addition to axons, the posterior pituitary also contains
pituicytes, specialized glial cells resembling astrocytes. Classification of the posterior pituitary varies,
but most sources include the three regions below
Pars nervosa
Also called the neural lobe or posterior lobe, this region constitutes the majority of the posterior
pituitary, and is sometimes (incorrectly) considered synonymous with it. Notable features include
Herring bodies and pituicytes.
Infundibular stalk
Also known as the infundibular or pituitary stalk, the infundibular stalk bridges the hypothalamic and
hypophyseal systems.
Median eminence This is only occasionally included as part of the posterior pituitary. Other sources
specifically exclude it from the pituitary. A few sources include the pars intermedia as part of the
posterior lobe, but this is a minority view. It is based upon the gross anatomical separation of the
posterior and anterior pituitary along the cystic remnants of Rathke’s pouch, causing the pars
intermedia to remain attached to the neurohypophysis.
Hormones known classically as posterior pituitary hormones are synthesized by the hypothalamus.
They are then stored and secreted by the posterior pituitary into the bloodstream.
Peptide hormones
Peptide hormones are a class of peptides that are secreted into the blood stream and have endocrine
functions in living animals. Like other proteins, peptide hormones are synthesized in cells from amino
acids according to an mRNA template, which is itself synthesized from a DNA template inside the cell
nucleus. Peptide hormone precursors (pre-prohormones) are then processed in several stages,
typically in the endoplasmic reticulum, including removal of the N-terminal signal sequence and
sometimes glycosylation, resulting in prohormones. The prohormones are then packaged into
membrane-bound secretary vesicles, which can be secreted from the cell by exocytosis in response
to specific stimuli, e.g increase of calcium concentration in cytoplasm. These prohormones often
contain superfluous amino acid residues that were needed to direct folding of the hormone molecule
into its active configuration but have no function once the hormone folds. Specific endopeptidases in
the cell cleave the prohormone just before it is released into the bloodstream, generating the mature
hormone form of the molecule. Mature peptide hormones then diffuse through the blood to all of the
cells of the body, where they interact with specific receptors on the surface of their target cells. Some
peptide/protein hormones (angiotensin II, basic fibroblast growth factor-2, parathyroid hormonerelated protein) also interact with intracellular receptors located in the cytoplasm or nucleus by an
intracrine mechanism. Several important peptide hormones are secreted from the pituitary gland. The
anterior pituitary secretes prolactin, which acts on the mammary gland, adrenocorticotrophic
hormone (ACTH), which acts on the adrenal cortex to regulate the secretion of glucocorticoids, and
growth hormone, which acts on bone, muscle, and the liver. The posterior pituitary gland secretes ant
diuretic hormone, also called vasopressin, and oxytocin. Peptide hormones are produced by many
different organs and tissues, however, including the heart (atrial-natriuretic peptide (ANP) or atrial
natriuretic factor (ANF)) and pancreas (insulin and somatostatin), the gastrointestinal tract
cholecystokinin, gastrin), and adipose tissue stores (leptin). Some neurotransmitters are secreted
and released in a similar fashion to peptide hormones, and some ‘neuropeptides’ may be used as
neurotransmitters in the nervous system in addition to acting as hormones when released into the
blood. When a peptide hormone binds to receptors on the surface of the cell, a second messenger
appears in the cytoplasm, which triggers intracellular responses.
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes
cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the
liver and muscle. Insulin stops the use of fat as an energy source by inhibiting the release of glucagon.
When insulin is absent, glucose is not taken up by body cells and the body begins to use fat as an
energy source or gluconeogenesis; for example, by transfer of lipids from adipose tissue to the liver for
mobilization as an energy source. As its level is a central metabolic control mechanism, its status is
also used as a control signal to other body systems (such as amino acid uptake by body cells). In
addition, it has several other anabolic effects throughout the body. When control of insulin levels fails,
diabetes mellitus will result. As a consequence, insulin is used medically to treat some forms of
diabetes mellitus. Patients with type 1 diabetes depend on external insulin (most commonly injected
subcutaneously) for their survival because the hormone is no longer produced internally. Patients with
type 2 diabetes are often insulin resistant, and because of such resistance, may suffer from a
“relative” insulin deficiency. Some patients with type 2 diabetes may eventually require insulin if other
medications fail to control blood glucose levels adequately, though this is somewhat uncommon.
Insulin also influences other body functions, such as vascular compliance and cognition. Once
insulin enters the human brain, it enhances learning and memory and benefits verbal memory in
particular. Enhancing brain insulin signaling by means of intranasal insulin administration also
enhances the acute thermoregulatory and glucoregulatory response to food intake, suggesting central
nervous insulin contributes to the control of whole-body energy homeostasis in humans. Insulin is a
peptide hormone composed of 51 amino acids and has a molecular weight of 5808 Da. It is produced
in the islets of Langerhans in the pancreas. The name comes from the Latin insula for “island”.
Insulin’s structure varies slightly between species of animals. Insulin from animal sources differs
somewhat in “strength” (in carbohydrate metabolism control effects) in humans because of those
variations. Porcine insulin is especially close to the human,
Glucagon
Glucagon causes the liver to convert stored glycogen into glucose, which is released into the
bloodstream. Glucagon also stimulates the release of insulin, so glucose can be taken up and used by
insulin-dependent tissues. Thus, glucagon and insulin are part of a feedback system that keeps blood
glucose levels at a stable level, Glucagon belongs to a family of several other related hormones.
Glucagon is a 29-amino acid polypeptide. Its primary structure in humans is: NH2-His-Ser-Gln-GlyThr Phe-Thr-Ser-Asp-Tyr-Ser-Lys-Tyr-Leu-Asp-Ser-Arg-Arg-Ala-Gln-Asp-Phe-Val-Gln-Trp-Leu-Met-AsnThr-COOH. The polypeptide has a molecular weight of 3485 daltons. Glucagon is a peptide
(nonsteroid) hormone.
Production of Glucagon
The hormone is synthesized and secreted from alpha cells (a-cells) of the islets of Langerhans, which
are located in the endocrine portion of the pancreas. In rodents, the alpha cells are located in the
outer rim of the islet. Human islet structure is much less segregated, and alpha cells are distributed
throughout the islet.
Regulatory mechanism
Increased secretion of glucagon is caused by:
Decreased plasma glucose (indirectly)
Increased catecholamines – norepinephrine and epinephrine
Increased plasma amino acids (to protect from hypoglycemia if an all-protein meal is consumed)
Sympathetic nervous system
Acetylcholine
Cholecystokinin
Decreased secretion (inhibition) of glucagon is caused by:
Somatostatin
Insulin
Increased free fatty acids and keto acids into the blood
Increased urea production.
Adrenaline
Epinephrine (also known as adrenaline) is a hormone and a neurotransmitter. It increases heart rate,
constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the
sympathetic nervous system. Chemically, epinephrine is a catecholamine, a monoamine produced
only by the adrenal glands from the amino acids phenylalanine and tyrosine.
The term adrenaline is derived from the Latin roots ad- and Renes and literally means “on the kidney”,
in reference to the adrenal gland’s anatomic location on the kidney. The Greek roots epi and nephros
have similar meanings, and give rise to “epinephrine”. The term epinephrine is often shortened to epi
in medical jargon. Adrenaline is synthesized in the medulla of the adrenal gland in an enzymatic
pathway that converts the amino acid tyrosine into a series of intermediates and ultimately
adrenaline. Tyrosine is first oxidized to L-DOPA, which is subsequently decarboxylated to give
dopamine. Oxidation gives norepinephrine, which is methylated to give epinephrine.
Adrenaline is synthesized via methylation of the primary distal amine of noradrenaline by
phenylethanolamine N-methyltransferase (PNMT) in the cytosol of adrenergic neurons and cells of the
adrenal medulla (so-called chromaffin cells). PNMT is only found in the cytosol of cells of adrenal
medullary cells. PNMT uses S-adenosylmethionine (SAMe) as a cofactor to donate the methyl group
to noradrenaline, creating adrenaline. The biosynthesis of adrenaline involves a series of enzymatic
reactions.
For noradrenaline to be acted upon by PNMT in the cytosol, it must first be shipped out of granules of
the chromaffin cells. This may occur via the catecholamine-H+ exchanger VMAT1. VMAT1 is also
responsible for transporting newly synthesized adrenaline from the cytosol back into chromaffin
granules in preparation for release.
In liver cells, adrenaline binds to the B-adrenergic receptor which changes conformation and helps
Gs, a G protein, exchange GDP to GTP. This trimeric G protein dissociates to Gs alpha and Gs
beta/gamma subunits. Gs alpha binds to adenyl cyclase, thus converting ATP into cyclic AMP. Cyclic
AMP binds to the regulatory subunit of protein kinase A: Protein kinase A phosphorylates
phosphorylase kinase. Meanwhile, Gs beta/gamma binds to the calcium channel and allows calcium
ions to enter the cytoplasm. Calcium ions bind to calmodulin proteins, a protein present in all
eukaryotic cells, which then binds to phosphorylase kinase and finishes its activation. Phosphorylase
kinase phosphorylates glycogen phosphorylase which then phosphorylates glycogen and converts it
to glucose-6-phosphate.
Nutrition and Genetics
Once nutrients and other dietary components are taken up by cells, they may interact with our genes
and have an effect on gene expression. The growth, development, and maintenance of cells, and
ultimately of the entire organism, are directed by genes present in the cells. Each gene essentially
represents a recipe, noting the ingredients (amino acids) and how those ingredients should be put
together (to make proteins). The products (proteins) of all the recipes in the cookbook (the human
genome) would then make up the human organism. The genome and the epigenome, the way the
genome is marked and packaged inside a cell’s nucleus, control the expression of individual traits,
such as height, eye color, and susceptibility to many diseases. Epigenetics refers to inherited changes
in gene expression caused by mechanisms other than changes in the underlying DNA sequence.
While our genome contains the code for the proteins that can be made by our bodies, our epigenome
is an extra layer of instructions that influences gene activity. In many cases it is the epigenome that
can be repaired by treatments, or affected by diet, rather than the genetics. The causes of chronic
diseases are complex and include a significant genetic component. Fortunately, the science of
genetics is moving swiftly such that medical breakthroughs are beginning to touch our lives. Genetic
discoveries are leading to new drugs that disrupt disease processes at the molecular level and to
tests that predict our risk for disease. In 2008, scientists discovered more than 100 genetic variations
associated with many medical conditions associated with aging, including type 2 diabetes,
Alzheimer’s disease, osteoporosis, high blood pressure, and heart disease.
Nutrition refers to the nurturing of our body, in our ability to keep it healthy and functioning as it is
supposed to do. Our ability to provide the body with all the necessary food, vitamins, and minerals so
that we continue to thrive in our daily life processes. Thus, a sound knowledge of nutrients and their
precise consumption in body is very important. Nutrition is a concept that should be as important to
our educational process as our ability to count. The ability to recognize our nutritional requirements,
one need to understand the right nutrients and find the foods we need to fulfill those requirements,
and differentiate between healthy food consumption and “unhealthy” eating habits is not an option.
Not for a healthy, happy, long, and quality life. What we should absorb as we travel along life’s daily
path is a way to incorporate good nutrition into our lifestyle. There is generally just as much room for
good as there is bad, it just so happens that bad nutritional habits hold more appeal. So the
competition is tough but the results of good nutrition are fairly understood.