physiology

‫الرحيم‬ ‫الرحمن‬ ‫ا‬ ‫بسم‬
”‫م‬ّ ‫ث‬ُ ‫ه‬ِ ‫ل‬ّ ‫ال‬ ‫لى‬َ ‫إ‬ِ ‫ه‬ِ ‫في‬ِ ‫ن‬َ ‫عو‬ُ ‫ج‬َ ‫ر‬ْ ‫ت‬ُ ‫ما‬ً ‫و‬ْ ‫ي‬َ ‫قوا‬ُ ‫ت‬ّ ‫وا‬َ
‫ل‬َ ‫م‬ْ ‫ه‬ُ ‫و‬َ ‫ت‬ْ ‫ب‬َ ‫س‬َ ‫ك‬َ ‫ما‬َ ‫س‬ٍ ‫ف‬ْ ‫ن‬َ ‫ل‬ّ ‫ك‬ُ ‫فى‬ّ ‫و‬َ ‫ت‬ُ
‫ن‬َ ‫مو‬ُ ‫ل‬َ ‫ظ‬ْ ‫ي‬ُ“
, ‫البقرة‬ ‫سورة‬‫آ‬‫ية‬281

Nutrition, Digestion, Metabolism
Nutrition
What is Nutrition:
Nutrition is the study of how our bodies use the food that we eat.
What are Nutrients:
Nutrients are chemical substances in food that require for performance of various
life activities, and necessary for reproduction and growth. One of the most important
function of macronutrient is the production of energy.
The balanced diet:
It is the diet which must be composed of carbohydrates, lipids, proteins, vitamins,
minerals and water in proportionate amounts.
We require food:
■ To provide fuel for our body or energy to accomplish daily activity (Carbohydrates
& Lipids).
■ To provide the necessary materials for building or maintenance of body tissue
and organs. (Proteins).
■ To provide the substances needed to regulate body functions and vital processes.
(Vitamins, Minerals & Water).
Food Types and Feeding Mechanisms:
Animals fit into one of the following three dietary categories.
Herbivores: such as cows and many snails, eat mainly autotrophs (plants, algae).
Carnivores: such as sharks, spiders, and snakes, eat other animals.
Omnivores: such as cockroaches, bears and humans consume animal and plant
or algal matter.

Nutrients are classified into:
Macronutrients: Nutrients required in relatively large amounts, e.g. carbohydrates,
lipids, and proteins.
Micronutrients: Nutrients required in smaller amounts, e.g. vitamins and minerals.
Carbohydrates
Carbohydrates are organic compounds which contain carbon, hydrogen, and
oxygen in which the last two elements are always present in the same
proportions as in water (CnH2nOn).
Classification of carbohydrates:They are classified according to the number of
units of mono-sugar into:
(1) Monosaccharides:
Monosaccharide composed of a single sugar unit. They are classified according
to the number of carbon atom into: trioses (3C), tetroses (4C), pentoses (5C) as
ribose sugar , hexose's (6C) as glucose (presents in diet in the form of
disaccharides and polysaccharides, Galactose (presents in the form of lactose)
& fructose [in fruits, honey (50% fructose, 50% glucose].
(2) Disaccharides:
Disaccharide is formed by the condensation of two monosaccharides with
elimination of a molecule of water and formation a glycosidic bond.
■ (Milk sugar) Lactose (glucose + galactose)
■ (Cane sugar) Sucrose (glucose + fructose).
■ (Malt sugar) Maltose ( glucose + glucose).

(3) Polysaccharides: On chemical bases, polysaccharides can be
divided into two broad classes:
a- Homopolysaccharides: The constituent sugars are the same.
Examples are:
■ Glycogen [12 -18 units of glucose]. It is found in animal cells (In
human and other vertebrates. Glycogen is stored primarily in the
liver and muscle cells.
■ Starch [200 - 300 units of glucose]. It is found in plant cells.
■ Cellulose [up 2000 units of glucose]. It is found in plant cell wall.
b- Heteropolysaccharides: The constituent sugars may take several
forms.
Examples are:
■ Chitin: It is found in arthropod shells, cuticle of mollusks and
annelids. It is a polymer of acetylglucosamines units.
■ Hyaluronic acid: It is found in synovial fluids of joints, vitreous
humor of eye,….. It contains N-acetylglucosamine and glucuronic
acid.
■ Chondroitin sulfate:It is found in tendons, cartilage, and bones.

An example shows the chemical structure of
glucose (a monosaccharide carbohydrate)

Biological significance of carbohydrates:
1- They form about 50-60% of human diet.
2- Stored as glycogen in both liver(6%) and
muscles(1%).
3- Act as a source of energy (4.2 Kcal/g).
4- They may be converted to fats or proteins.
5- The pentose (ribose) sugar is a part of DNA
and RNA.
6-Cellulose (dietary fibers) stimulates
contraction of the intestine, peristalsis
(wormy-like movement) that helps passage of
food a long through the digestive canal.

Lipids
Lipids (like carbohydrates) contain carbon,
hydrogen and oxygen, but the proportion of
oxygen in them is much less.
Classification of lipids:
Simple lipids………….[ fats as butter & waxes as
bee wax].
(Fats) are ester of fatty acids with glycerol.
(Waxes) are ester of fatty acids with alcohol
other than glycerol.
Compound lipids......................[phospholipids].
Derived lipids ...........[Cholesterol and bile acids].

Biological significance of lipids:
1- The most important source of energy. Oxidation
of 1g of fat (triglycerides)produces about 9.3 kcal.
3- Lipids are the most common storage materials,
and have the following functions:
a- Subcutaneous fats provide an insulating layer
that protects from heat loss in cold weathers.
b- Lipids have a role in protection and fixation of
internal organs as kidney.
4- Lipids are source of fat-soluble vitamins,
essential fatty acids & steroid hormones.
5- Lipids are essential components in the structure
of cell membranes.

Proteins
■ Proteins are composed of carbon,
hydrogen, oxygen, and nitrogen; and they
frequently contain sulfur, or phosphorous,
or iron.
■ Protein molecules consist mainly of amino
acids which linked together in chains
called polypeptide. The linkage between
the amino acids is called peptide bond.

The amino acids
• An important feature of the amino acid is that each
individual amino acid contains two characteristic groups
of atoms -COOH and -NH2. The simplest amino acid,
glycine which has the formula, CH2NH2COOH. There
are two types of amino acids:
The essential amino acids :
which can not be synthesized inside the body of either
animals and humans but synthesized by the plants. They
are: phenylalanine – histamine – isoleucine – lysine –
methionine – valine – threonine – leucine – tryptophan.
The non-essential amino acids: which can be
synthesized inside the body are: alanine - arginine -
aspartic acid – cysteine - glutamic acid – glutamine –
glycine – proline – serine – tyrosine – asparagine –
selenocysteine.

Classification of proteins
Proteins are classified according to the chemical structure
into:
(1) Simple proteins: which on hydrolysis give rise amino
acids only. e.g. albumin, globulin, collagen, and keratins.
(2) Conjugated proteins: which on hydrolysis give rise
amino acids and a non- protein group called prosthetic
group.
• Phosphoproteins……………….Casein of milk.
• Glycoproteins..………………….Heparin.
• Chromoproteins .. ……………...Haemoglobin.
• Nucleoproteins…………………..Nucleic acids.
• Hormoproteins…………………..Insulin –Prolactin.
(3) Derived proteins: which obtained as a result of partial
hydrolysis of natural proteins as: peptones, proteoses,
and peptides.

Biological significance of proteins:
1- Provide the body with essential amino
acids.
2- Build up new tissues during growth,
pregnancy, and lactation.
3- Proteins are important for synthesis of
some hormones and all enzymes.
4- Proteins maintain the pH of blood (7.4).
5- Proteins provide the body with energy
when needs [4 kcal/g].

Vitamins
Definition:
The vitamins are organic compounds, which must be present in the
food in minute quantities to enable growth, health, and maintenance
of life.
Nomenclature:
• The word vitamin is from vital amine, and it means amine of life .
• First named alphabetically vitamin A , B,C,D,E,K……….etc.
• Given common names also Thiamin, Riboflavin, Niacin,………etc.
• Chemical names, Ascorbic acid, Folic acid,……………… ….etc.
Sources:
• Foods, are the major dietary sources.
• Exposure to sunlight (UV), triggers vitamin D synthesis in the skin.
• Intestinal bacteria are able to synthesize a sufficient quantity of
some vitamins like vitamins E and K.

Classification of vitamins
There are two types of vitamins:
(I) Fat – soluble vitamins [A,D,E and K].
(II) Water – soluble vitamins [B and C].

Vitamins Purpose Sources
Vitamin A
(Retinal & Retinol)
(Produced from the
plant precursor ß-
Carotene).
1- Normal cell differentiation & growth.
2- Protects the linings of the digestive,
urinary and respiratory tracts (It helps
secretion the mucous).
3- Maintain healthy vision at night.
4- Antioxidant.(Fights free radicals that
causing DNA damage.)
Deficiency:
• Growth retardation.
• Changes in skin epithelia, dry, horny
and more susceptible to infections.
• Night blindness, as a result of rhodopsin
deficiency which responsible for night
vision.
Liver,
Carrots,
Sweet, potatoes,
Spinach,
Cantaloupe,
Broccoli,
Mangos
(I) Fat – soluble vitamins

Vitamin D
The active form
1,25-dihydroxy
cholecalciferol
■ Helps intestinal absorption of calcium and
phosphorus for healthy bones and teeth.
Deficiency:
* Rickets in children.
* Osteoporosis & Osteomalacia.
* Sunlight, promotes
synthesis of vitamin D
under the skin.
* Cod liver oil
* Salmon
* Sardines
Vitamin E
(Antisterility)
Alpha-tocopherol
is the most
biologically active
compound
■ Helps form blood cells.
■ Antioxidant, so it protects DNA from free
radical damage.
Deficiency:
■ Female abortion and male sterility, only in
experimental animals.
■ Hemolysis of red blood cells, degeneration
of sensory neurons.
■ Deficiency symptoms are rare occurrence
in human being because the intestinal
bacteria are able to synthesize the vitamin in
a sufficient amount.
■ Plant oils, seeds, nuts,
wheat germ, green leafy
vegetables.
■ Synthesized by
intestinal
microorganisms.

Vitamin K
Anti-hemorrhagic
Phylloquinone
■ It helps in the production of blood-
clotting-factor proteins that participate in a
series of reactions to form a blood clot
[prothrombin (factor II), factors VII, IX,
and X, and proteins C, S, and Z].
■ It also participates in the production of
bone proteins [osteocalcin, also called
bone Gla protein (BGP), matrix Gla
protein (MGP)].
Deficiency:
■ Prolongation of the time of blood clotting
formation (hemorrhage may occur).
■ A primary deficiency of vitamin K or E is
rare, but a secondary deficiency may result
from:
■ Fat malabsorption syndrome.
■ Prolonged use of antibiotics can
destroy the intestinal bacteria that produce
these vitamins.
Green
vegetables
Spinach,
Broccoli,
liver .
synthesis by
intestinal
microorganisms.

Vitamin C
Ascorbic Acid
■ It is used in the production of collagen
(bone, tendons, cartilage, and skin).
■ It improves the immune system.
(Moderate doses alleviate the symptoms
of colds).
■ Acts as an antioxidant (destroying free
radicals).
■ Strengthens blood vessel walls.
■ It enhances the absorption of iron.
Deficiency:
Scurvy disease
Its symptoms are:
• Loss of hair and teeth.
• Bleeding gums.
• Very slow healing of wounds.
citrus,
tomatoes,
broccoli,
potatoes,
green peppers,
cabbage
(II) Water – soluble
vitamins

Vitamin Purpose Sources
B1
Thiamin
■ Essential for energy production, because
it is required for the metabolic reactions of
foods, especially carbohydrate. The energy
is essential for the functions of nervous
system. The metabolic reactions catalyzed
by thiamin are decarboxylation reactions.
Deficiency:
Beri beri disease
• Pain and loss of sensation in the hands
and feet. So, paralysis of the legs may
occur.
• Muscle wasting (weakness) and gradual
loss of function.
• Brain damage and eventually death.
legumes,
whole grains,
wheat germ,
nuts

B2
Riboflavin
■ It converted in the body to the active forms
flavin adenine dinucleotide (FAD) and flavin
mononucleotide (FMN), which they act as
cofactors for dehydrogenase enzymes.
■ It plays an important role in the metabolism
of carbohydrates and proteins.
[dehydrogenation reactions]
Deficiency:
Dermatitis.
Thickening and rough skin, especially in the
mouth, with cracks and inflammation at the
corners of the lips, a painful tongue.
Milk Dairy
products.
Whole grains,
Eggs, Fish,
Green leafy,
Vegetables
B3
Niacin,
nicotinamide
■ In the form of NAD or NADP, the vitamin
plays a vital role in energy production in cells.
fat, protein, and carbohydrates metabolism.
[dehydrogenation reactions].
Deficiency:
Pellagra (Pella = skin, agra = rough)
Its symptoms are: diarrhea, dermatitis,
dementia ‫,خبل‬ and death.
Meat, fish,
poultry, eggs,
peanuts,
legumes
grains

B5
Pantothenic
Acid
■ It plays a vital role in metabolism of foods
(carbohydrates, lipids, and proteins),
particularly in the production of energy in
cells, because it represents a part from the
vital molecule coenzyme A.
Deficiency: In animal only:
■ Impaired growth and reproduction,
dermatitis, nervous symptoms.
■ Naturally occurring pantothenic acid
deficiency is very rare, since it is so
widespread in the diet.
Chicken, beef,
potatoes,
tomatoes,
liver, kidneys,
eggs, broccoli,
whole grains
(such as brown
rice)
B6
Pyridoxine
■ It catalyzes the reactions of conversion of
some amino acids (decarboxylation,
transamination, deamination……….)
■ It also plays a role in fat metabolism and in
carbohydrate metabolism.
Deficiency:
Impaired growth, anemia, dermatitis, and
neuromuscular problems such as convulsion
in children
Meat, poultry,
fish, grains, bran,
wheat germ,
egg yolk,
legumes, green
leafy
vegetables

B9
Folic Acid
■ Synthesis of hemoglobin.
■ Synthesis of DNA & RNA.
Deficiency:
■ Failure of normal cell division. e.g. in the
cells lining the digestive system, this can
lead to loss of appetite and diarrhea.
■ In the bone marrow leads to a type of
anemia called megaloblastic anemia (large,
immature blood cells).
Meat, eggs,
fish, green
vegetables,
beans,
asparagus,
yeast
B12
Cobalamin
■ vital for cell division, especially in the bone
marrow.
Deficiency:
■ Leads to production of large, immature
blood cells which do not have the normal
oxygen-carrying capacity.
■ Damage in nervous system.
(Pernicious anemia)
Meat, liver
poultry, fish, dairy
products

Biotin
)Vitamin B7(
■ It plays a major role in metabolism,
addition of CO2 (synthesis of fats, urea
formation, ……..)
Deficiency:
Deficiency syndromes are not normally
seen in man. Experimentally, they
include hair loss, dermatitis, and
depression.
Egg yolk,
milk,
legumes,
peanuts,
bananas

Minerals
• Both vitamins and minerals are essential in the diet in
small quantities, so they are often grouped together as
micronutrients.
• Minerals cab be divided into:
(I) Major minerals: which required in relatively large
amounts such as calcium (Ca), phosphorus (P),
potassium (K), sodium (Na), chlorine (Cl), magnesium
(Mg), sulfur (S).
(II) Trace elements: which required in smaller amounts
such as iron (Fe), manganese (Mn), copper (Cu), iodine
(I), cobalt (Co), zinc (Zn), florine (Fl), selenium (Se),
chromium (Cr), molybdenum, bromide, aluminum.

Mineral Source Use in the body
Calcium
(Ca)
Dairy products,
dark green
vegetables
legumes.
• It is necessary for bone and
teeth formation.
• It contributes to nerve and
muscle action.
• It contributes to blood clotting.
Phosphorus
(P)
Meat, poultry,
whole grain
foods..
• It serves as components of
bones, teeth, phospholipids, ATP,
phosphoproteins, and nucleic
acids.
Magnesium
(Mg)
Whole grains
foods, green
leafy vegetables.
• It acts as coenzyme in several
enzymes such as adenosine
triphosphatase (ATPase),
phosphodiesterase, hexokinase,
…..
(I) Major minerals

Sodium
(Na)
Table salt,
widespread in the
diet.
• It is a major cation of extra-cellular
fluid.
• It participates in the muscle and nerve
functions.
• It contributes to maintenance of water
balance in the body.
Potassium
(K)
Widespread in the
diet, especially in
meats and grains,
fruits, vegetables.
• It is necessary for muscle and nerve
function,
• It represents a major component of
intracellular fluid.
Chloride
(Cl)
Table salt. • It plays a role in the acid-base balance.
• It is required for stomach acid
formation.
• It is necessary for maintenance of body
water balance.
Sulfur
(S)
Meat products • It is a component of some amino acids
and (like methionine and cysteine) and
many proteins (like insulin and keratine).

(II) Trace elements
Iron
(Fe)
Green leafy
vegetables, Whole
grains, legumes,
meats, eggs.
• It is needed for synthesis of hemoglobin,
myoglobin, and certain enzymes like
cytochrome P450.
• So, it required for oxi-reduction reactions.
Copper
(Cu)
Seafood, nuts,
legumes.
• It stimulates iron absorption.
• It activates many enzymes, particularly
oxidative enzymes.
• It represents a part of the respiratory pigment
of blue color called hemocyanin (similar to
hemoglobin) in invertebrates like crabs, shrimp,
……….etc.
Iodine
(I)
Iodized salt, marine
fishes.
• It is a part of the thyroid hormones (thyroxine
and triiodothyronine).
Zinc
(Zn)
Whole grain foods,
Meats, seafood.
• It is activates many enzymes such as
carbonic anhydrase.
Fluorine
(F)
Fluoridated water,
tea, seafood..
• It accounts for the maintenance of teeth from
decay (perhaps the maintenance of bone as
well).

Water
• The amount of water in a human body depends on age, gender, body type, and level
of physical activity.
• The body of an adult male is approximately 62 percent water, while an adult female is
51 percent water. 10-15% loss of water will result in death.
Water balance: It refers to the balance between the amount of water consumed and
the amount of water excreted.
Water functions :
• Both the spaces between cells (intercellular spaces) and the spaces inside cells
(intracellular spaces) are filled with water.
• Water is the medium in which materials are transport to and from cells and tissues.
• Water is the solvent of our nutrients through digestion.
• Water is the medium in which toxic substances are excreted from the kidney. Much of
the water lost each day is through the excretion of toxic waste materials.
• Water is a participant in hundreds of metabolic processes.
• Water lubricates and functions as a shock absorber for joints, spinal cord, and our
eyes.
• Water maintains appropriate blood volume.
• Water also helps the body maintain a constant temperature by acting as a thermostat.
• When a person is too hot, whether from being in a hot environment or from intense
physical activity, the body sweats. When sweat evaporates, it lowers the body
temperature.

The digestive system
• The digestive system consists of
(I)The alimentary canal.
(II)The accessory organs.
• The alimentary canal is a long tube that
extends from the mouth to the anus. It
includes the mouth, pharynx, esophagus,
stomach, small intestine, and large intestine.
• The major accessory organs are the salivary
glands, liver, and pancreas. These organs
secrete digestive juices into the alimentary
canal.

Structure of digestive system
(I) Alimentary canal: It consists of:
1. The mouth: It contains the teeth, the tongue, the salivary
glands.
2. The pharynx: In humans, it leads to both the trachea and
the esophagus. The epiglottis blocks the trachea and the
uvula blocks off the nose, while food is being swallowed.
3. The esophagus: It is the muscular tube which extends
from the pharynx to the stomach. Food is moved easily
along the esophagus by peristalsis, and mucus secretion.
There are sphincter muscles at the top and bottom of the
esophagus.
4. The stomach is a J-shaped muscular sac, which lies on
the left side of the upper abdomen. The stomach can
expand to hold about 2 L of food. The stomach has two
sphincters: the cardiac sphincter closes off the top end of
it and the pyloric sphincter, which closes off the bottom.

5. The small intestine: It has a length of about 6
m. The surface of the small intestine is wrinkled
and convoluted to produce a greater surface area
for absorption. The total surface area is about 300
m2. The small intestine includes:
▪ the duodenum, the first portion.
▪ the jejunum, the second portion.
▪ the ileum, the third portion.
6. The large intestine or colon: It begins with a
blind pouch called the cecum. In humans, cecum
terminates in the appendix, a finger-like extension
which may function in the immune system. The
rectum is the terminal portion of the large intestine
and functions for storage of the feces. It leads to
external opening called the anus.

Accessory glands
■ Salivary glands
There are 3 pairs of salivary glands: the parotids,
submandibular, and sublingual. Salivary glands secrete
about 1-1.5 L/day of the saliva in the adult.
■ The liver.
The liver is the largest gland in the body, attached to the
under surface of the liver is a gall bladder containing a
green colored fluid called bile. When the chime from the
stomach enters the duodenum, the gall bladder contracts
and bile is discharged on the foods.
■ The Pancreas.
The pancreas is a slightly pink-colored glands which lies
between the stomach and the duodenum. but contains
cells that secrete in to the blood stream as well as those
that discharge via the pancreatic duct into the gut.

Digestion
Digestion is a biochemical process by which the complex compounds
in foods like carbohydrates, proteins, and lipids are changed into
more simple soluble units (glucose, fructose, galactose, amino acids,
fatty acids, and glycerol), which can be easily absorbed through the
intestinal wall.
• The breakdown of these food chemicals is brought about by
biochemical catalysts called enzymes. An enzyme is a chemical
substance (special proteins) which accelerates a chemical reaction
without itself being changed.
Factors affecting digestive enzymes activity:
• Each enzymes has an optimum temperature.
• Each enzyme has an optimum pH.
• Each enzyme acts upon a specific type of food called substrate.
• Each enzyme is secreted as a pro-enzyme (zymogen), inactive form.
• Each enzyme has an specific activator and specific inhibitor.
• Most enzyme names are written with the suffix-ase, e.g. Maltase –
Sucrase - Lactase.

Digestion in buccal cavity
Salivary glands:
• There are 3 pairs of salivary glands: the parotid,
submandibular, and sublingual.
• Salivary glands secrete about 1-1.5 L/day of the
saliva in the adult.
• The salivary glands pour there secretion in the
mouth cavity.
• The saliva is colorless, and has a pH 7.4.
Constituents of saliva:
• It consists of about 99.5% water, 0.2% inorganic
materials [chloride, phosphate, bicarbonate, Na, K,
and Ca] and 0.3% organic solids [mucin, albumin, and
enzymes].

Functions of saliva:
● The mucous acts as a lubricant which facilitates
mastication and swallowing.
● The food is moistened and softened.
● When the body loses too much moisture the flow of
saliva is stopped, a sensation of thirst is created and
the feel to drink water is created.
● Saliva dissolves certain substances which are then
able to stimulate the taste buds of the tongue and give
the sensation of taste.
● Saliva contains the following digestive enzymes:
Salivary amylase: It initiates the digestion of a part of
soluble starch into maltose.
Maltase: It converts maltose sugar into glucose.
Lysozyme: It has anti-bacterial effects, so it destroys
microorganisms which enter the mouth.

Digestion in the stomach
▪ Control of gastric juice secretion:
(1) Reflex stimulation of the vagus nerve.
(2) Hormonal stimulation:
- Gastrin stimulates acid secretion.
▪ The volume of the gastric juice is 2-3 L / day, pH 1-2.
▪ The gastric glands contain different types of secretory cells:
- Oxyntic (parietal) cells .………………....secret HCl.
- Mucous cells …………………………….secret mucin.
- Peptic (chief) cells…………………………….....secret enzyme
pepsinogen.
- G cells………………secret gastrin hormone which released to the blood.
▪ Functions of gastric digestive enzymes:

Functions of HCl:
• It gives the optimum pH of stomach (1-2).
• It activates the pepsinogen enzyme into pepsin.
• It has antibacterial action.
• It converts carbohydrates into mono-, di-, and
polysaccharides; and proteins to meta-proteins.

Digestion in the small intestine
Most of the digestive action that takes place in the small
intestine is carried out in the duodenum and brought
about by secretions from liver, pancreas, and intestine
itself.
Hormonal control of juices secreted into intestine:
• When the acidic chyme reaches to the duodenum, the
later secretes the following hormones from special cells.
- Secretin: It stimulates both pancreas and liver to secret
alkaline juices (rich with bicarbonate).
- Cholecystokinin (the old name is pancreozymin): It
stimulates secretion of the bile juice; and the pancreatic
juice rich with enzymes.
- Entrokinin: It stimulates the intestinal wall cells to
secret the intestinal juice.

The pancreatic juice
▪ The pancreatic juice is alkaline (pH 7.5-8.0), and its
volume is about ¾ L / day.
▪ It contains digestive enzymes for proteins, carbohydrates,
and lipids:

The bile juice
▪ It is secreted by the liver cells and stored in the gall
bladder .
▪ The bile is a viscous fluid which contains about 98%
water, mucin, bile salts (sodium salts), bile pigments (as
billirubin and billiveridin), and cholesterol.
Role of bile juice in digestion
▪ Sodium salts cause:
- alkalinity of digestive juice.
- breakdown the fats into minute droplets, so the fat
becomes emulsified.
▪ Mucous acts as a lubricant.

The intestinal juice
▪ It secrets from the wall of the intestine itself.
▪ The volume of the juice secreted per day is about 3 L.
▪ The juice contains the following enzymes.
[1] Peptidases: They convert peptides into amino
acids (aminopeptidase, tripeptidase, and dipeptidase)
[2] Intestinal lipase: It hydrolyzes the emulsified fats into
glycerol and fatty acids.
[3] Disuccharidases:
- Sucrase, which hydrolyzes sucrose into glucose
and fructose.
- Maltase, which hydrolyzes maltose into glucose
and glucose.
- Lactase, which hydrolyzes lactose glucose and
galactose.
▪ The juice contains also mucin which protects the intestinal
wall from either the digestive enzymes or the acidity of the
food coming from the stomach.

Absorption
Absorption means passage of the molecules of food from
the intestinal lumen into the body's interior after digestion.
Pathways of absorption: There are two pathways:
(1) The veins of the portal system. Where amino acids
and glucose pass into the bloodstream.
(2) The lymphatic (lacteal) vessels. Where the fatty acids
and glycerol are transported into the lymphatic system
and then to the blood stream at the thoracic region.
Mechanisms of absorption: Fluids and nutrients are
absorbed by different mechanisms (methods).
(1) Osmosis: Osmosis means the movement of water
through a partially permeable membrane down a
concentration gradient from a dilute solution (where there is
a high concentration of water) to a concentrated solution
(where there is a relatively low concentration of water).

(2) Diffusion:
▪ Diffusion means the movement of particles (solutes)
from an area of high concentration to an area of low
concentration down a concentration gradient.
Diffusion and osmosis are both types of passive
transport - i.e., no energy is required for the molecules
to move into or out of the cell.
Diffusion may be simple or facilitated. In facilitated
diffusion, a large molecules such as glucose and amino
acids cross the plasma membrane by the help of carrier
proteins. While in simple diffusion, a small molecules
(CO2 & O2) are passed through the membrane without
the need of carrier proteins.

(3) Active transport:
▪ It means the movement of substances
against the concentration and electrical
gradient, with consumption of energy.
▪ In active transport, a special carrier
protein in the cell membrane is used to
transport the particle from one side to
the other side of the membrane.

Sites of food absorption
▪Stomach: Absorption of some short-chain fatty acids.
:▪Small intestine
-Duodenum: Absorption of vitamins A and B1, iron,
calcium, glycerol, fatty acids, monoglycerides, amino acids,
and monosaccharides.
-Jejunum: Absorption of glucose, galactose, amino acids,
glycerol, fatty acids, copper, zinc, potassium, calcium,
magnesium, phosphorus, iodine, iron, fat-soluble vitamins D,
E, and K, most of the B complex, and vitamin C.
-Ileum: Absorption of sodium, potassium, chloride,
calcium, magnesium, phosphorus, iodine, vitamins (e.g.,
biotin and vitamin K), and water.
▪Colon: Absorption of sodium, potassium, water, acids,
gases, some short-chain fatty acids metabolized from plant,
fibers and vitamins synthesized by micro-organisms.

Metabolism
Metabolism: It is the set of life-sustaining chemical trans-
formations within the cells of living organisms. In other
words, it refers to all chemical reactions that occur in living
organisms, including digestion, transport of substances into
and between different cells, and uses of these substances
in various biochemical activities.
Metabolism is usually divided into two categories:
* Catabolism: It refers to the breakdown of organic
matter into small intermediates with production of energy,
for example conversion of fats into carbon dioxide, water,
and ATP.
* Anabolism: It refers to the uses of energy and small
intermediates to construct components of cells such
as manufacture of proteins from amino acids.

Calculation of number of ATP molecules produced
during glycolysis of one molecule of glucose
I- During aerobic glycolysis:
ATP consumed = 2 ATP
ATP produced = 2 + 2 + (3x2) = 4 + 6 = 10 ATP
[Where, in the presence of O2, NAD → NADH+ + H+ → To
respiratory chain → 3 ATP (3 ATPX2 = 6 ATP)]
Net production of ATP = 10 – 2 = 8 ATP
II- During anaerobic glycolysis:
ATP consumed = 2 ATP
ATP produced = 2 + 2 = 4 ATP
Net production of ATP = 4 – 2 = 2 ATP

■ Number of produced ATP per oxidation of 2 moles of pyruvic
acid into acetyl-CoA = 2x3 = 6 ATP molecules

Total number of ATP produced per oxidation of one mole of glucose
into CO2 and H2O:
● In aerobic glycolysis: 8 ATP molecules
● In conversion of pyruvate to acetate: 6 ATP molecules
● In citric acid cycle (oxidation of acetate into CO2 and H2O): 24 ATP
molecules
Total number of ATP = 8 + 6 + 24 = 38 ATP molecules

Metabolism of Keto Acids:
1- It converted by decarboxylation to acetyl-coA
which enters citric acid cycle and produces
energy (ATP), in addition to CO2 and water.
2- It used in synthesis of glucose and glycogen.
3- It used in synthesis of fats.

Blood vessels
Arteries carry oxygenated blood away from the heart. Artery aorta, a massive
and thick-walled artery receives the blood from left ventricle Major
arteries Tissue arteries Arterioles Capillaries.
Veins carry oxygen-poor blood back to the heart. Deoxygenated blood is
collected by capillaries Venules Tissue veins Two major
veins: the superior vena cava (from areas above the heart) and the inferior vena
cava (from areas below the heart) Right atrium.
Capillaries
▪ Help to join tissue with arterioles.
▪ Help in distribution and passage of blood oxygen and nutrients to all body
cells.
▪ Help in collection of metabolic wastes from all body cells (e.g. CO2, urea,
…….).

Types of circulations
(1) Pulmonary circulation
● In this circulation, oxygen-depleted blood is
pumped away from the right ventricle of the heart,
via the pulmonary artery, to the lungs and
returned, oxygenated, to the left atrium of the heart
via the pulmonary veins.
● Gas exchange occurs in the lungs, where CO2 is
released from the blood into the lungs, and O2 is
absorbed from the lungs alveoli into the blood. The
pulmonary veins return the oxygen-rich blood to
the left atrium.

(2) Systemic circulation
● Systemic circulation transports oxygenated
blood through the aorta from the left ventricle to
the different parts of the body (except the lungs),
and returns oxygen-depleted blood back to the
heart.
● Arteries bring oxygenated blood to the tissues.
As blood circulates through the body, oxygen
diffuses from the blood into cells surrounding the
capillaries, and carbon dioxide diffuses into the
blood from the capillary cells.
● Veins bring deoxygenated blood back to the
heart.

(3) Coronary circulation
● The coronary circulation provides a blood supply to
the myocardium (the heart muscle).
● It arises from the basis of aorta by two coronary arteries,
the left and the right. The right coronary artery supplies
blood mainly to the right side of the heart. The left coronary
artery, which branches into the left anterior descending
artery and the circumflex artery, supplies blood to the left
side of the heart. The left side of the heart is larger and
more muscular because it pumps blood to the rest of the
body.
● After nourishing the myocardium, blood returns through
the coronary veins into the coronary sinus and from this
one into the right atrium. The smallest cardiac veins drain
the blood directly into the heart chambers.

Anatomy of the human heart
Weight: The heart weighs between 200 to 425 grams.
Size: The normal average size of adult heart equals to clenched adult fist.
Location: Human heart is located in the center of the chest between right
and left lungs, behind and slightly to the left of sternum.

Membranes of the heart:
▪ The heart is covered by the pericardium, which
is made of a double-layered membrane like a
sac that surrounds the heart and its major blood
vessels.
▪ The outer layer of the pericardium (parietal
pericardium), is slightly thicker, surrounds the
roots of the heart's major blood vessels and is
attached by ligaments to vertebral column,
diaphragm, and other parts of the body.
▪ The inner layer of the pericardium (epicardium
or visceral pericardium) is attached to the heart
muscle. It's a thin, glossy membrane.
▪ There is a small amount of fluid between the
pericardium membranes that acts as lubricant,
and to reduce friction between the heart and the
pericardium when the heart beats.
▪ Another smooth, glossy membrane, called the
endocardium, covers the inside surfaces of the
four chambers of the heart, plus the valves and
the muscles that attach to the valves.

The Exterior of the Heart &
Blood circulation in the heart
The Right Side of the Heart
◘ It contains both the right atrium and right ventricle, and the blood
vessels connected to them.
◘ The superior and inferior vena cavae are connected to the right
atrium, and carry the deoxygenated blood collected from the tissues
back to the atrium.
◘ The superior vena cava carries deoxygenated blood from the upper
parts of the body, including head, chest, arms, and neck. The inferior
vena cava carries deoxygenated blood from the lower parts of the
body.
◘ The deoxygenated blood from the vena cavae flows into the right
atrium and then into the right ventricle, from which the blood is
pumped through the pulmonary artery to the lungs, where
oxygenation of the blood occurs.
◘ The oxygenated blood passes from the lungs back to the heart
through the pulmonary veins.

The Left Side of the Heart
● It contains both the left atrium and left ventricle,
and the blood vessels connected to them.
● The left atrium receives oxygenated blood from
the lungs via pulmonary veins, and pumps it into
the left ventricle.
● The left ventricle pumps oxygenated blood
through the aorta to the rest of the body.

The Interior of the Heart
The septum
▲The heart are divided internally into right and left sides by an
internal wall of tissue called the septum.
▲ The area of the septum that divides the atria is called the atrial
or interatrial septum.
▲ The area of the septum that divides the ventricles is called the
ventricular or interventricular septum.
The heart chambers
■ The inside of the human heart is divided into 4 chambers.
■ The two upper chambers of the heart are called the left and right
atria. The atria receive and collect blood.
■ The two lower chambers are called the left and right ventricles
(their walls are more thicker than the two atria). The left ventricle is
the largest and strongest chamber in the heart (its wall is thicker
than right ventricle), so it has enough force to push blood into the
circulatory system to other parts of the body.

This figure shows a cross-section of a healthy human heart and its inside
structures. The blue arrow shows the direction in which oxygen-poor blood flows
from the body to the heart then to the lungs. The red arrow shows the direction
in which oxygen-rich blood flows from the lungs to the heart, then to the rest of
the body.

The Heart valves
Heart contains four valves which regulate blood flow
through the heart. They permit the blood flow in ONE
direction only.
1-The tricuspid valve permits the deoxygenated
blood flow from right atrium to right ventricle, but not
vice versa.
2-The mitral valve permits the oxygenated blood flow
from the left atrium to left ventricle, but not vice versa.
3-The pulmonary valve permits deoxygenated blood
flow from the right ventricle into pulmonary artery.
4-The aortic valve permits the oxygen-rich blood to
pass from the left ventricle into the aorta.

Blood flow in the heart and the role of the valves
The right atrium pumps blood into the right ventricle the
pulmonary artery the lungs
pulmonary veins the left atrium the left ventricle the
aorta the rest of the body.
● The blood flows in the heart in one direction only, and the
valves make this possible.
● Healthy valves open and close in an exact coordination
with the pumping action of the atria and ventricles.
● Each valve has a set of flaps called leaflets or cusps that
seal or open the valves. This allows pumped blood to pass
through the chambers and into the arteries without backing
up or flowing backward.

A cross-section of a human heart showing the four types of the valves (1,2,3,and 4),
and their location inside the heart.

Electrical conduction
system of the heart
● The electrical signal begins in the
sinoatrial (SA) node, located at the top
of the right atrium. The SA node is
sometimes called the heart's "natural
pacemaker" ‫القلب‬ ‫ضربات‬ ‫.منظم‬
● When an electrical impulse is
released from this natural pacemaker, it
causes the atria to contract.
● The signal then passes to the
atrioventricular (AV) node. The AV node
sends the signal through the bundles of
His to the Purkinje fibers and finally to
the muscle fibers of the ventricles,
causing them to contract.

Heart Sounds
Heart sounds result from the closing of the heart
valves.
● When the heart beats, it makes a "lub-dub" sound. Between the
time of hearing "lub" and “dub", blood is pumped through the
heart and circulatory system.
● The first heart sound (lub) results from the closure of the
atrioventricular valves (tricuspid valve and mitral valve).
● The second heart sound (dub) produced when the semilunar
valves shut (pulmonary valve and aortic valve).
● The right and left atrioventricular valves do not close at precisely
the same time. Nor do the semilunar valves. A physician can,
therefore, listen to each valve individually and determine whether
it is functioning properly.

Heart rate
It is the number of heartbeats per unit of time,
typically expressed as beats per minute
(bpm). Each heartbeat has two basic parts: diastole or
relaxation, and systole or contraction.
Normal heart beat:
At rest, the SA node causes the heart to beat about 50 to
100 times each minute. Exercise, emotions, fever and some
medications can cause the heart to beat faster, sometimes
to well over 100 beats per minute.
Measurement of the heart rate:
You can tell how fast your heart is beating (your heart rate)
by feeling your pulse. You will need a watch with a second
hand.
▲ Place your index and middle finger of your hand on the
inner wrist of the other arm, just below the base of the
thumb, where the radial artery passes.
▲ You should feel a tapping or pulsing against your fingers.
Count the number of taps you feel in 30 seconds.
▲ Multiply that number by 2 to find out your heart-rate for
one minute.
Heart rate
It is the number of heartbeats per unit of time,
typically expressed as beats per minute
(bpm). Each heartbeat has two basic parts: diastole or
relaxation, and systole or contraction.
Normal heart beat:
At rest, the SA node causes the heart to beat about 50 to
100 times each minute. Exercise, emotions, fever and some
medications can cause the heart to beat faster, sometimes
to well over 100 beats per minute.
Measurement of the heart rate:
You can tell how fast your heart is beating (your heart rate)
by feeling your pulse. You will need a watch with a second
hand.
▲ Place your index and middle finger of your hand on the
inner wrist of the other arm, just below the base of the
thumb, where the radial artery passes.
▲ You should feel a tapping or pulsing against your fingers.
Count the number of taps you feel in 30 seconds.
▲ Multiply that number by 2 to find out your heart-rate for
one minute.

Blood Pressure
■ Blood pressure is the pressure (force) exerted by circulating blood
upon the walls of blood vessels. It is principally due to the pumping
action of the heart.
■ Blood pressure varies throughout the cardiovascular system, being the
highest in the aorta and the lowest in the capillaries and veins. Low
blood pressure in the capillaries enhances the rate of exchange between
the blood and the tissues.
■ Blood pressure is maximum during systole, when the heart is
contracted, and minimum during diastole, when the heart is relaxed. It is
therefore expressed in terms of the systolic pressure over diastolic
pressure, and is measured in millimeters of mercury (mmHg).
■ Normal values are: 120/80 in adult male, and 115/75 in
adult females.
■ Blood pressure changes in relation to a person’s activity and stress
levels, and the age.

Factors affecting the
arterial blood pressure
(1) Total blood volume in the circulatory system.
(2) Volume of cardiac output of blood.
(3) Peripheral resistance.
It is affected by some factors such as,
▪ The viscosity of the blood.
▪ Vasoconstriction , which decreases the radius of the
peripheral vessels.
(4) Elasticity of the blood vessels walls.

Measurement of blood pressure
■ The cuff ‫طرف‬of the sphygmomanometer is wrapped
around the arm just above the elbow and pumped up to block
off blood flow (the pressure exerted by the cuff is higher than
the systolic pressure).
■ The pressure in the cuff is gradually decreased, and when it
equals the person’s systolic pressure, the heart can force
blood under the cuff, and a sound is heard (systolic pressure).
Here, record the value of systolic pressure on the column of
mercury.
■ As the pressure in the cuff is lowered, when it equals the
diastolic pressure, blood can flow freely, so the sound
disappears (diastolic pressure). Here, record the value of
diastolic pressure on the column of mercury.

Hypertension
■ Hypertension occurs when either the systolic pressure is greater than 145
to 160 mm Hg and/or the diastolic is greater than 90 to 100.
■ Major contributing factors include the high level of salt intake ,
cholesterol (and other lipids), and sugar in the diet; and the lack of exercise
the person gets.

Thrombus & Embolus
Definition: Thrombus is a blood clot which is formed within a blood vessel
(vein or artery) and blocks the blood flow.
▪ These can result from surgery or from conditions like atrial fibrillation.
▪ When a clot (thrombus) breaks off and travels to another part of the body, it
may cause vessel obstruction elsewhere and called embolus.
▪ If thrombi or emboli stabilize in an artery supplying blood to the heart, this
can cause a coronary embolism or heart attack or myocardial infarction.
▪ If one of these becomes lodged in an artery in the lungs, it is also a life-
threatening pulmonary embolism, and if in the brain, a cerebral (or
cerebellar) embolism or stroke or cerebro-vascular accident.
▪ When a thrombus occupies more than 75% of cross-sectional area of the
lumen of an artery, blood flow to the tissue supplied is reduced enough to
cause symptoms because of decreased oxygen (hypoxia) and accumulation of
metabolic products like lactic acid. More than 90% obstruction can result
in anoxia, the complete deprivation of oxygen, and infarction, a mode
of cell death.

A hemorrhage is bleeding, which can be severe if it
occurs internally.
A hematoma is a local swelling or tumor filled with
blood; e.g. a bruise ‫,كدمة‬ especially a large one.
Sometimes, if the injury is extensive, it can calcify
leading to a hard lump‫صلبة‬ ‫كتلة‬ , which may need to
be surgically removed.

The Respiratory System
Functions of respiratory system
1- The primary role of the respiratory system is to maintain a
continuous supply of tissues with atmospheric oxygen (O2) for
oxidation of foodstuffs in the cells and excreting carbon dioxide (CO2)
and water (H2O) from cells to atmosphere.
2- The secondary roles of the respiratory system include:
a- Control of acid-base balance (blood pH), by utilizing the
bicarbonate buffer. Acidosis activates the respiratory center to increase
respiratory rate and depth, which eliminates more CO2 and causes
blood pH to rise. Alkalosis depresses the respiratory center, resulting in
CO2 retention and a fall in blood pH.
b- Protection of the body against inhaled particles, e.g. bacteria.
c- Regulation of body temperature especially in panting animals
(= animals without sweat glands) during summer.
d- Supply of air to the larynx for purpose of voice production.

Divisions of respiratory processes
(1) External respiration: It includes;
a- Exchange of gases between the environment
and the lungs.
b- Exchange of gases between the lungs and the
blood, across the respiratory membrane.
(2) Transport of respiratory gases: The carriage of
O2 and Co2 by the blood to and from the body cells.
(3) Internal respiration: The exchange of O2 and Co2
between the blood and tissues. It is also involves the
intracellular O2 utilization through the metabolic
biotransformations, and production of CO2.

Divisions of the respiratory tract
Anatomically:
I- The upper Respiratory Tract: It includes the nostrils, nasal cavities,
pharynx, epiglottis, and the larynx.
II- The Lower Respiratory Tract: It consists of the trachea, bronchi,
bronchioles, and the Lungs.
Physiologically:
I- Conducting zone
▪ Respiratory passages that carry air to the site of gas exchange.
Filters, humidifies, and warms air.
▪ It includes the nostrils, nasal cavities, pharynx, epiglottis, larynx,
trachea, bronchi, terminal bronchioles.
II- Respiratory zone
Sites of gas exchange, which composed of:
Respiratory bronchioles
Alveolar ducts
Alveolar sacs

The diaphragm
▲The diaphragm is a sheet of muscles that lies across the bottom of the chest
cavity.
▲ As the diaphragm contracts and relaxes, breathing takes place. When the
diaphragm contracts, oxygen is pulled into the lungs, while when it relaxes,
carbon dioxide is pumped out of the lungs.
▲ In mammals, the diaphragm divides the body cavity into two parts:
(1) Abdominal cavity, which contains the viscera (e.g., stomach and intestines).
(2) Thoracic cavity, which contains the heart and lungs.

The pleural (A two-layered structure)
▲ The parietal pleura, which lines the walls of the chest
cage and covers the upper surface of the diaphragm.
▲ The pulmonary pleura, or visceral layer, which tightly
covers the surface of the lungs.
▲ The two layers, which are in fact one continuous sheet
of tissue, are generally connected (adhered) to each other.
▲ There is a slight amount of watery fluid within the pleural
cavity that lubricates the pleural surfaces and allows the
lungs to slide freely over the inner surface of the thoracic
wall during breathing.
▲ If air is introduced between them, the adhesion is broken
and the natural elasticity of the lung causes it to
collapse‫تنهار‬ . This can occur from trauma‫صدمة‬ .

Breathing (Respiration)
There are two phases of breathing:
Inspiration (inhalation) – air in
Expiration (exhalation) – air out
Mechanisms of Quiet Respiration (Eupnoea)
During eupnoea (respiration during rest in healthy subject),
respiration is underlying 2 mechanisms:
A- Central mechanisms: They involve the changes in the
activity of the respiratory centers in the brain which control the
peripheral activity. This will be discussed later.
B- Peripheral mechanisms: They involve the changes in the
size of the thoracic cavity and lungs leading to rush of the air
into or out of the lungs.

Peripheral mechanisms
I- During inspiration (inhalation)
The external intercostal muscles contract, causing the ribs to
move upward and laterally. The sternum moves out. This
increase the thoracic cavity laterally and in anterior and posterior
dimention (circumference).
The dome shaped diaphragm flattens as it contracts. This
increases the height (superior to inferior dimension) of the
thoracic cavity.
II- During expiration (exhalation)
The processes occurred during inspiration are passively
reversed.
The natural elasticity of the lungs returns them to their normal
volume.
At rest, we breath 15-18 times per minute exchanging about 500
ml of air per one time.

Boyle's Law: As the volume occupied by a gas
increases, the pressure of that gas decreases. This means
that the pressure of any gas and the volume it occupies are
inversely proportional (P = 1/V).
The entry and exit of air during breathing
■ When the lung stretches out, its volume is increased
thereby the pressure of air in the intrapulmonic space
decreases to a level below atmospheric pressure (760
mmHg), causing air moves into the respiratory tract from
the outside producing inspiration.
■ When the respiratory muscles relax, the thorax cavity
becomes smaller. This causes the pressure of the air in
the intrapulmonic space to exceed the air pressure
outside. This results in air moving out of the respiratory
tract producing passive expiration.

Lung Volumes (Respiratory Air Volumes)
Lung volumes refer to the physical differences in lung volume during
inspiration or expiration in relation to differences in the respiratory
conditions.
There are 4 terms of air volumes (lung volumes). Most of them are
determined by the Spirometer.
1) Tidal volume (TV): It is the volume of air inspired or expired during
rest. It equals 5oo ml.
2) Inspiratory Reserve volume (IRV): It is the maximum volume of air
which can be inspired after normal inspiration. It equals 3000 ml.
3) Expiratory reserve volume (ERV): It is the maximum volume of air
which can be expired after normal expiration. It equals 1000 ml.
[N.B. The above 3 volumes can be measured by the Spirometer.]
4) Residual volume (RV): It is the volume of air that remains in the
lungs after maximal expiration. It can't be expelled to atmosphere except
after opening of the chest wall and squeezing the lungs. It equals 1200
ml.

Lung capacities:
Lung capacity equals 2 or more of lung volumes.
Most of the lung capacities are also determined by the Spirometer.
1. Inspiratory capacity (IC): It is the maximum volume of air which
can be inspired after normal expiration. It equals T.V (500) + I.R.V
(3000) = 3500 ml.
2. Functional Residual capacity (FRC): It is the volume of air
remaining in the lung after normal expiration. It equals ERV (1000) +
RV (1200) = 2200 ml. This air is used for gases exchange.
3. Total lung capacity (TLC): It is the volume of air contained in the
lungs after deepest inspiration (maximum expansion of lungs). It
equals all lung volumes = 5700 ml.
4. Vital capacity (VC): It is the volume of air given out by maximal
expiration after maximal inspiration. It equals IRV (3000) + TV (500)
+ ERV (1000) = 4500 ml.
VC = IRV+TV+ERV=TLC-RV

Anatomic Dead Space:
It is the portion of the airways, (from the mouth or
nose to the terminal bronchioles) which conducts
gas to the alveoli. No gas exchange is possible in
this space. The volume of this space is
approximately 150 ml in the average adult human.
Physiologic Dead Space:
It is the anatomic dead space plus the volume of
any non-functional areas of the lungs (alvioli which
are less efficient in gas exchange). In young,
health lungs, the volume of the anatomic dead
space and physiologic dead space are equal.

Lung capacity and high altitudes
● A person who is born and lives at sea level will develop a
slightly smaller lung capacity than a person who spends their life
at a high altitude.
● This is because the partial pressure of oxygen is lower at
higher altitude which, as a result means that oxygen less readily
diffuses into the bloodstream. In response to higher altitude, the
body's diffusing capacity increases in order to process more air.
● When someone is living at or near sea level travels to locations
at high altitudes (e.g. The Tibet & The Himalayas) that person
can develop a condition called altitude sickness. The severity of
these conditions varies from a minor headache to life threatening
swelling of the brain and lungs. because their lungs remove
adequate amounts of carbon dioxide but they do not take in
enough oxygen. (In normal individuals, carbon dioxide is the
primary determinant of respiratory drive).

Oxyhemoglobin dissociation curve
● This curve describes the relationship between partial
pressure of oxygen (PO2) on the horizontal axis, and the
amount of hemoglobin saturated with oxygen (SO2 or %
saturation) on the vertical axis .
● At high PO2, hemoglobin binds to oxygen to form
oxyhemoglobin, as in the pulmonary capillaries, hemoglobin is
nearly 100 % saturated.
● When the blood is fully saturated all the red blood cells are in
the form of oxyhemoglobin.
● As the red blood cells travel to tissues the oxyhemoglobin
releases the oxygen to form hemoglobin, due to decreased
PO2 in the tissues.
The reaction of oxygen with the iron molecule of the haem
group is an oxygenation reaction, not oxidative, and the iron
remains in the ferrous (2+) state.

The sigmoidal shape (S-shaped) of the oxygen
dissociation curve is a result of the co-operative
binding of oxygen to the four polypeptide chains.
Co-operative binding is the characteristic of
hemoglobin to have a greater ability to bind oxygen
after a subunit has bound oxygen. This means that
binding of the 1st O2 molecule increases the affinity of
hemoglobin for oxygen and hence facilitates the
binding of the 2nd O2 molecule. Binding of the 2nd O2
molecule facilitates the binding of the 3rd O2 molecule
and so on. The affinity of hemoglobin for the 4th
O2 molecule is approximately 300 times that for the
1st.

Factors that affect oxygen dissociation curve
1. Hydrogen ion concentration
◘ A decrease in pH from a value of 7.4 (increase
in H +
ion concentration) shifts the standard curve to
the right, while an increase shifts it to the left.
◘ The reason for this is that H+
and O2 both
compete for binding to the hemoglobin molecule.
Therefore, with increased acidity, the hemoglobin
binds less O2 for a given PO2 (Bohr effect).

2. Effects of carbon dioxide
• Most of the CO2 content (80–90%) is transported as bicarbonate ions.
• The formation of a bicarbonate ion will release a proton into the
plasma.
• Hence, the elevated CO2 content creates a respiratory acidosis and
shifts the oxygen–hemoglobin dissociation curve to the right (Bohr
effect). i.e. it decreases the affinity of hemoglobin to bind to O2.

In exercising tissues, PCO2 is high and hydrogen
ion concentration, [H+
], is also high due to the
formation of carbonic acid which dissociates to
form bicarbonate ions and hydrogen ions. This
increase in CO2 and decrease in pH shifts the
dissociation curve to the right for a given PO2,
releasing more oxygen to the tissues.
In the lungs, PCO2 is low and hydrogen ion (H+
)
concentration is also low. This decrease in
CO2 and increase in pH shifts the dissociation
curve to the left for a given PO2, enhancing oxygen
uptake.

3. Effects of 2,3-disphosphoglycerate (2,3-DPG)
◘ 2,3-DPG is an organo-phosphate, which is
created in erythrocytes during glycolysis.
◘ High levels of 2,3-DPG in red blood cells shift the
curve to the right, while low levels of 2,3-DPG shift
the curve to the left.
◘ This is because 2,3-DPG lowers hemoglobin's
affinity for oxygen by binding preferentially to
deoxyhemoglobin.

4. Temperature
● Increases in temperature, such as in
exercising tissues, causes a rightward
shift, while hypothermia causes a leftward
shift.
● This is because increasing the
temperature denatures the bond between
oxygen and hemoglobin.

5. Carbon monoxide
● Carbon monoxide (CO) binds with hemoglobin (hem
group) forming carboxyhaemoglobin (COHb). CO has
about 200–250 times the affinity of O2 for Hb.
● The presence of CO on one of the 4 hem sites
causes the oxygen on the other hem sites to bind with
greater affinity with O2.
● This causes either difficult for the hemoglobin to
release oxygen to the tissues or shifting the curve to
the left.
● With an increased level of CO, a person can suffer
from severe tissue hypoxia while maintaining a normal
PO2.

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