Biswash Sapkota (M.Pharm) (B.Pharm)
Lecturer, MBAHS
Respiratory system

Course Content
 Anatomy of respiratory organs and its functions
 Respiration
 Mechanism and regulation of respiration
 Respiratory volumes and vital capacity
 Acid base balance and brief description of
respiratory system
 Bronchopulmonary system
 Bronchopulmonary segments
 Nervous control of respiration
 Hypoxia, anoxia, hyperventilation

 The respiratory system provides the route by which the
supply of oxygen present in the atmospheric air gains
entry to the body and it provides the route of excretion
of carbon dioxide.
 Blood provides the transport system for these gases
between the lungs and cells of the body .
 The exchange of the gases between the blood and the
lungs is called external respiration and between the
blood and cells is called internal respiration .

Organs of respiratory system
 It includes
1. Upper respiratory tract : Nose, Pharynx,larynx
2. Lower respiratory tract : trachea, Bronchi, lungs
3. Coverings: Pleura, muscle of breathing,
intercoastal muscles and diaphragm

Nose
Nose
External
Nose
Internal
Nose
(Nasal
Cavity)

Nose (external nose)
 It is only externally visible part of respiratory system . It has
followings parts
1. Root : the area between the eyebrows
2. Bridge: it is the area that connects the root to other parts of
nose
3. Dorsum nasi : it is the total length of the nose.
4. Nasal septum: it divides the nose into right and left part
5. Alae : the tip part of the nose is called alae and it forms the
lateral wall of nostril
6. Apex : it is the tip of nose
7. Nostril : it is the external opening of nose
8. philtrum : it connects the upper lips and the apex of nose

 The nose has a skeletal framework,which is partly
bony and partly cartillaginous.
 The bony part is contributed by the nasal bones
and frontal processes of maxilla.
 The cartilages are superior and inferior cartilages
and septal cartilage.

Internal Nose (Nasal Cavity)
 It contain the nasal cavity
 Nasal cavity has two parts
1. Superior Part : it has olfactory receptor for sense
of smell
2. Other part : it has respiratory mucosa. It has thin
wall vein which warm the air. It has mucus gland
which contains mucus . Mucus moist the air,
entrap the bacteria and the lysozyme present in
mucus destroy the bacteria.
The respiratory mucosa has ciliated epithelium
which moves the contaminated mucosa towards the
throat and reaches the stomach . It is finally digested
by juice present in stomach.

The LATERAL WALL OF NOSE
 The lateral wall of the nose is irregular,presence
of 3 bony projections called conchae or
turbinates.
 Their elevations are called superior, middle and
inferior nasal conchae according to their position
on the lateral wall of nasal cavity.
 Function
1. The conchae increases the surface area of
nasal cavity,
2. prevent dehydration,
3. disturb the air flow which clean the air and warm
the air .

Paranasal air sinuses
 Paranasal sinuses are a group of four paired air-
filled spaces that surround the nasal cavity.
 They are
1. The maxillary sinuses are located under
the eyes
2. The frontal sinuses are above the eyes
3. The ethmoidal sinuses are between the eyes
4. The sphenoidal sinuses are behind the eyes

Functions of paranasal sinuses
 1)They reduce the weight of the skull
 2)The inhaled air is warmed and humidified
 3)They add resonance to the voice
 4)The mucous secreted by the mucous glands
help to trap the dust particles in the inhaled air,
the cilia remove the dust particles

Pharynx
 12-14cm long muscular tube, extend from nose to
larynx
 The pharynx is divided into three portions
1. Nasopharynx : it connected with nasal cavity
2. Oropharynx : it is connected with oral cavity
laryngopharynx : connected to larynx

 The pharynx or the throat serves as a passage for the
two system- digestive and respiratory systems
 Air can enter the pharynx either from the two nasal
cavities or from the mouth to the larynx
 At the lower end air proceeds to the larynx, while food
is swallowed into esophagous
 The right and the left eustachian tubes open into the
nasopharynx, connecting the middle ear with upper
respiratory tract
 It also contains the pharyangeal (Adenoids) tonsil
 During swallowing the nasal and oral parts are
separated by soft palate , Uvula .

1)Nasopharynx
 Nasopharynx:The nasal part of the pharynx lies
behind the nose above the level of soft palate
 The adenoids, also known as the pharyngeal
tonsils, are lymphoid tissue structures located in
the posterior wall of the nasopharynx. Waldeyer's
tonsillar ring is an annular arrangement of
lymphoid tissue in both the nasopharynx and
oropharynx.
 On its lateral walls are the two openings of the
auditory tubes,one leading to each middle ear.

2)Oropharynx
 The oral part of the pharynx lies behind the
mouth,extending from below the level of the soft
palate to the level of the upper part of the body of
the 3rd cervical vertebra.
 The lateral walls of the pharynx blend with the
soft palate to form two folds on each side.
 Between each pair of folds is a collection of
lymphoid tissue called the palatine tonsil

3)Laryngopharynx
 The laryngeal part of the pharynx extends from
the oropharynx above and continues as the
oesophagus below i.e from the level of the 3rd to
the 6th cervical vertebrae

Functions
 1)Passageway for air and food:The pharynx is
involved in both respiratory and digestive
systems.
 Air passes through the nasal and oral secretions
and food through the oral and laryngeal
secretions
 2)Warming and humidifying:By the same methods
as in the nose, the air is further warmed and
moistened as it passes through the pharynx

 3)Taste:There are olfactory nerve endings of the
sense of taste in the epithelium of the oral and
pharyngeal parts
 4)Hearing:The auditory tube,extending from the
nasopharynx to each middle ear,allows air to
enter the middle ear.
 Satisfactory hearing depends on the presence of
air at atmospheric pressure on each side of the
tympanic membrane

Functions of pharynx
 5)Protection:The lymphatic tissue of the
pharyngeal and laryngeal tosils produces
antibodies in response antigens e.g bacteria.
 The tonsils are larger in children and tend to
atrophy in adults
 6)Speech:The pharynx functions in speech,by
acting as a resonating chamber for sound
ascending from the larynx,it helps (together with
the sinuses)to give the voice its individual
characteristics

Larynx
 It extend from the root of the tongue to the trachea .
 It is a cartilaginous and muscular organ also known
as voice box .
 It is made up of nine cartilages, 3 paired and 3
unpaired united by muscles and liagements
 Paired : arytenoid, corniculate and cuneiform
 Unpaired : thyroid, cricoid and epiglottis
 The thyroid cartilages or Adams apple is the largest
cartilage in larynx. In male thyroid cartilage increase
in size at puberty
 The leaf shaped epiglottis is attached to the top
border of the thyroid cartilage . It has the hinged,
door-like action at the entrance of larynx
 During swallowing it acts as lid to prevent food from
entering the larynx.

Functions
 Sounds production
 Protects the lower respiratory tract during
swallowing
 Passage of air
 Warming and humidifying the air
 Speech

Trachea
 The trachea or windpipe is a cylindrical tube
 Is a continuation of larynx
 10-11cm long and lies in front of esophagous
 Made of up 16-20C shaped rings
 Inferiorly divided into two main bronchus at carina (the
lowest cartilage)
 It also contain ciliated epithelium which can propel the
mucosa filled with dust and other debris .
 The trachea functions as a simple passage way for air to
reach the lungs. When it becomes blocks blocked from
swelling or blocked a tracheostomy is necessary .
 It has open part and closed part. The closed part contain
cartilage and prevents from collapsing of trachea during
breathing while the open parts helps in expanding during
swallowing .

Function
 Maintains patency of airways
 Cilia on the wall helps in sweeping the mucus and
the foreign particles upwards towards the larynx
 Warm and humidify the air
 Helps in prevention of aspiration by cough reflex

Bronchi
 Two main bronchus formed by division of trachea
 They are the primary bronchi
 Right main bronchus : wider, shorter(2.5cm) and
more vertical
 Left main bronchus : Narrower, Longer (5cm)
 The bronchi enters into lungs through Hilum .
• The bronchi subdivides into the secondary
bronchi or the lobar bronchi which deliver the
oxygen to the lobes of lungs .
• The secondary divides into tertiary bronchi or the
segmental bronchi

 The tertiary bronchi divide further in another three
branching's known as 4th order, 5th order and 6th
order segmental bronchi which are also referred
to as subsegmental bronchi. These branch into
many smaller bronchioles which divide
into terminal bronchioles, each of which then
gives rise to several respiratory bronchioles,
which go on to divide into two to eleven alveolar
ducts. There are five or six alveolar
sacs associated with each alveolar duct.
The alveolus is the basic anatomical unit of gas
exchange in the lung.

Lungs
 The lungs are the two cone shaped organs lying
on each side of the midline in the thoracic cavity
extended from the diaphragm to about one half
inches above the clavicle.
 The lung are composed of bronchi and smaller air
passages, alveoli, connective tissue, blood
vessels, nerves .
 The right lungs has 3 lobes and the left lungs has
2 lobes
 The lungs is covered by pleura
 The area between two lungs is called
mediastinum
 The adult lung is a spongy mass and is frequently
blue-grey in color because of inhaled of dust but

Pleura
 It is the serous membrane that surrounds the lung
 Has two layers
 parietal pleura is the outer layer
 Visceral pleura is the inner layer
 The space between two layer is called pleural
cavity
 The pleural cavity is filled with pleural fluid
 This fluid helps two layers to glide over each
other, preventing the friction between them during
breathing .
 This double pleural membrane arrangement
allows respiration with minimal friction

Alveolus
 It is also called air sac
 The smallest bronchial tubes subdivide into very
tiny tubes called alveolar duts
 The alveolar ducts blossoms out several alveolar
sacs resembling clusters of grapes
 A strong network of capillaries surround each
alveolus and it is at this point in respiratory tract
that the exchange of gases between blood and
inhaled air takes place.

Respiration
 Respiration is the movement of oxygen from the
outside environment to the cells within tissues
and the transport of carbon dioxide in the
opposite direction.
 The respiration involves following processes
1. Breathing or pulmonary ventilation
2. External respiration
3. Transport of 02 to the tissue
4. Internal respiration
5. Transport of CO2 from tissues

1.Breathing or Pulmonary Ventilation
 This is movement of air into and out of the lungs.
 Breathing supplies oxygen to the alveoli, and
eliminates carbon dioxide.
 The main muscles involved in breathing are the
intercostal muscles and the diaphragm.
 There are 11 pairs of intercostal muscles occupying
the spaces between the 12 pairs of ribs. They are
arranged in two layers, the external and internal
intercostal muscles.
 The diaphragm is a dome-shaped muscular structure
separating the thoracic and abdominal cavities.
 Breathing depends upon changes in pressure and
volume in the thoracic cavity. Since air flows from an
area of high pressure to an area of low pressure,
changing the pressure inside the lungs determines
the direction of airflow.
 Breathing involves two process

i. Inhalation:
 It takes place when the volume of thoracic cavity is
increased and the air pressure is decreased.
 Simultaneous contraction of the external intercostal
muscles and the diaphragm expands the thorax.
 As the diaphragm + external intercostals contracts
(moves downward) lung volume increases.
It involves following events
 First of all, external intercoastal muscle contracts and
internal intercoastal muscles relaxes.
 Due to contraction of external intercoastal muscles, ribs
is pulled upward, resulting in increase in thoracic cavity
size
 The thoracic cavity further enlarges due to contraction of
diaphragm, lowering the diaphragm and increases the
size of thoracic cavity.
 With increase in size of thorax, lungs expand
simultaneously.
 As lungs expands, the air pressure is reduced inside, so

ii. Expiration
 It takes place when the size of thoracic cavity is
reduced and air pressure is increased.
involves following events
 The internal intercoastal muscle contracts and
external intercoastal muscles relaxes.
 Due to contraction of internal intercoastal muscle, ribs
are pulled inward, resulting in decrease in size of
thoracic cavity
 Furthermore the diaphragm is pushed upward due to
its relaxation
 With the decrease in size of thoracic cavity, lungs is
compressed
 As lungs is compressed, pressure increases, so the
air is forced outside.

2. External Respiration
 This is the exchange of gases by diffusion between
alveoli and blood in the alveolar capillaries, across
respiratory membrane.
 Diffusion of oxygen and carbon dioxide depends on
pressure differences, e.g. between atmospheric air
and the blood, or blood and the tissues.
 Gas exchange during the respiration process takes
place in the alveolus at its surface that separates the
alveolus with the capillary.
 The exchange of O2 and CO2 occurs through
diffusion which is the net movement of gas molecules
from a region that has a higher partial pressure to
another region that has a lower partial pressure.
 The venous blood in alveolar capillaries contains high
level of CO2 and low level of O2.
 Co2 then diffuses from higher level (venous blood) to
lower level (alveoli) until equilibrium is maintained. By
the same process O2 diffuses from alveoli to venous

3. Transport of Oxygen to Tissue
 Oxygen is carried in the blood to the tissue in two
from:
i) Oxyhaemoglobin (98.5%): it is a chemical
combination of O2 with haemoglobin
 Hb4 + 4O2…………………………………………
Hb4O8 (oxyhaemoglobin)
ii) Solution in plasma water (1.5%): O2 dissolve in
plasma of blood and carried to tissues.
 when the level of O2 is high in blood, it combines with
haemoglobin to from oxyhaemoglobin.
 Oxyhaemoglobin is unstable, and under certain
conditions readily dissociates releasing oxygen.
Factors that increase dissociation include low O2
levels, low pH and raised temperature.

4. Internal respiration
 internal respiration is exchange of gases
which takes places in tissue, so also known as
cellular respiration.
 In tissue, oxygen carried in the form of
Oxyhaemoglobin get dissociated to liberating free
O2.
 Hb4O8———dissociates to give ——— Hb + O2
 The free O2 then oxidized the glucose in the
presence of respiratory enzymes to liberate CO2,
water and energy.
 C6H12O6 + 6O2 ———- 6CO2 + 6H2O +
Energy

5. Transport of CO2 from tissue to
Lungs
 Carbon dioxide is one of the waste products of
metabolism.
 It is excreted by the lungs and is transported by
three mechanisms:
i) as Carbonic acid (H2CO3) (7%): some CO2
dissolved in the plasma to form carbonic acid
 carbon dioxide mixed with water of blood plasma
to form carbonic acid.
 CO2+ H2O——————H2CO3

ii) bicarbonate ions (HCO3−) in the plasma (70%)
 carbonic acid formed in blood plasma quickly ionizes
to from bicarbonates and hydrogen ions in the
presence of enzyme carbonic anhydrase.
 CO2 + H2O—————H+ + HCO3-
 bicarbonate ions combined with sodium or potassium
present in blood to form sodium bicarbonate
(NaHCO3) or Potasssium bicarbonate (KHCO3) and
transported in this form
iii) as carbaminohaemoglobin (23%): some CO2
combines with Haemoglobin to form
carbaminohaemoglobin in RBCs.
 CO2 + NHbNH2————–HbNH.COOH
(carbaminohaemoglobin).

Regulation of respiration
 Control of respiration is normally involuntary.
 Voluntary control is exerted during activities such
as speaking and singing.
 Special centres in the nervous system called ‘The
respiratory centres of the brain’ regulate different
aspects of respiration

Movements of thoracic cage
 Inspiration causes enlargement of thoracic cage .
 Change in the size of thoracic cavity occurs due to the
movements of four units of structure:
1. Thoracic lid
2. Upper costal series
3. Lower costal series
4. Diaphragm
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1. Thoracic lid (thoracic operculum) is formed by manubrium
sterni and the first pair of ribs. Due to contraction of scaleni
muscles, the first ribs move upwards to a more horizontal
position. The movement of first ribs draws the manubrium
sterni upwards and forwards increasing the anteroposterior
diameter of the thoracic cage.
2. Upper costal series is constituted by second to sixth pair of
ribs. The contraction of external intercostal muscles causes
elevation of these ribs and the sternum moves upwards and
forwards. It increases the anteroposterior diameter of the
thoracic cage.
Simultaneously, the central portions of these ribs (arches of
ribs) move upwards and outwards to a more horizontal
position. This increases the transverse diameter of thoracic
cage.
50

3. Lower costal series is formed by the seventh to tenth pair
of ribs. These ribs also show outward and upward
movements. This movement increases the transverse
diameter of the thoracic cage. The eleventh and twelfth
pairs of ribs are the floating ribs, which are not involved in
changing the size of thoracic cage.
4. Diaphragm before inspiration is dome-shaped with
convexity facing upwards. During inspiration, due to the
contraction, the muscle fibers are shortened. Diaphragm is
flattened. Flattening of diaphragm increases the vertical
diameter of the thoracic cage.
51

Respiratory center in Brain
 The neuronal signals transmitted between
respiratory centres of the brain and
the muscles in the chest and diaphragm modulate
respiration.
 There are three main centres of the brain that
regulate breathing.
 They are present in the medulla and the pons
region of the brain. They regulate breathing by
stimulating the contraction of the intercostal
muscles and the diaphragm.
 mainly two respiratory center are present one at
medullary center called medullary respiratory
center and another at pons called pontine

Respiratory Rhythm Centre (In
medulla)
 Inspiration is followed by expiration, thus creating a
regular, oscillating cycle of breathing.
 This is the respiratory rhythm. A special centre in the
medulla region of the brain is primarily responsible for
regulating respiratory rhythms.
 This is the ‘Respiratory Rhythm Center’. This centre
produces rhythmic nerve impulses that contract the
muscles responsible for inspiration (diaphragm and
external intercostal muscles)
 Normally, expiration happens when these muscles
relax
 They are two types called dorsal respiratory group
(DRG) and Ventral Respiratory group (VRG)

Dorsal Respiratory Group (DRG)
 Inspiratory neurons or ‘I’ neurons
 Situated on the dorsal aspect of medulla oblongata in and
around the nucleus of tractus solitarius (NTS)
 Sets the basic respiratory rate.
 It is autorhythmic and Produces inspiratory ramp
 Inspiratory ramp is type of electrical activity which gradually
increases and then stops suddenly.
 Stimulates the inspiratory muscles (diaphragm) to contract.

Ventral Respiratory Group
 Situated in the ventral aspect of medulla oblongata.
 Contains both Inspiratory and expiratory neurons.
 It is driven by DRG.
 Inactive during normal, quiet respiration.
 At times of increased ventilation, signals from the dorsal
group stimulate the ventral group.
 The ventral group then stimulates both inspiratory and
expiratory muscles. E.g., the abdominal muscles are
stimulated to contract and help force expiration.

Pneumotaxic Centre (in Pons)
 This centre regulates the functions of the
respiratory rhythm centre.
 It controls both the rate and pattern of breathing.
The pneumotaxic centre can send neural signals
to reduce the duration of inspiration, thereby
affecting the rate of respiration. The actions of
this centre prevent the lungs from over-inflating.
 It also regulates the amount of air that the body
takes in, in a single breath. If this centre is
absent, it increases the depth of breathing and
decreases the respiratory rate. It performs the
opposite function of the Apneustic centre.

Apneustic Centre (In Pons)
 This centre promotes inspiration by constantly
stimulating the neurons in the medulla region. It
sends signals that oppose the action of the
signals from the pneumotaxic centre. It sends
positive signals to the neurons that regulate
inspiration, thereby controlling the intensity of
breathing

Connections of respiratory centers
Efferent Pathway Afferent Pathway
 Nerve fibres from respiratory
centres
 Terminate on motor neurons in
the anterior horn cells of cervical
and thoracic segments of spinal
cord.
 From motor neurons two sets of
nerve fibres arise:
1. Phrenic nerves (C3 to C5)-
Supply diaphragm
2. Intercostal nerve fibres (T1 to
T11)- supply external
intercostals)
 Vagus nerves also contains some
efferent fibres from respiratory
centres
 Respiratory centres receive
afferent impulses from :
1. Peripheral chemoreceptors and
baroreceptors via branches of
glossopharyngeal and vagus
nerves
2. Stretch receptors of lungs via
vagus nerve
 By receiving afferent impulses
from these receptors,
respiratory centres modulate
the movements of thoracic
cage and lungs through efferent
nerve fibres

Hering-breuer inflation reflex
 It is a protective reflex that restricts inspiration and prevents
overstretching of lung tissues. It is initiated by the stimulation
of stretch receptors of air passage.

Chemoreceptors
 These are the receptors that respond to changes
in the partial pressure of oxygen and carbon
dioxide and also the change in pH in the blood
and cerebrospinal fluid .
 They are two types
a. Central chemoreceptors
b. Peripheral chemoreceptors

Central chemoreceptors
 These receptors are located in the central
nervous system more specifically close to the
surface of the medulla .
 The receptors are mainly monitored by the level
of CO2 and Hydrogen ion present.
 When the level of the CO2 increase it start firing
the signals to the respiratory system for breathing
faster and releasing the Co2 from body .
 Also when co2 levels increase the Hydrogen ion
levels (low pH) also increases and it stimulates
the respiratory centers.
 But it doesn’t respond to the increase oxygen

Peripheral chemoreceptors
 These are located in the arch of aorta and carotid
bodies.
 They are more sensitive to the small rise in
arterial CO2 then similar low arterial o2 levels.
 The impulses generated in peripheral
chemoreceptors are conveyed by
glossopharyngeal and vagus nerves to the
medulla and the stimulate the respiratory center.
 The rate and the depth of the breathing are then
increased .
 Also increase in blood Ph increase the activity of
peripheral receptors.

Volumes and Capacities
 The lung volumes that can be measured using a
spirometer include tidal volume (TV), expiratory
reserve volume (ERV), inspiratory reserve
volume (IRV) and residual volume .
1. The tidal volume : The amount of air breathed in
or out during normal respiration. It amounts about
500ml in the adult male.

Volumes and capacities
Tidal volume (TV):
• The amount of air that enters or leaves the lung in a single
respiratory cycle at rest .
• The amount is about 500ml in the adult male.
Alveolar volume : out of 500ml of TV only 350ml reaches
the alveolar for gaseous exchange .
Dead space volume : out of 500ml of TV 150ml remains in
the anatomical dead space and not available for gaseous
exchange .
Inspiratory reserve volume (IRV) :
 The volume of which can be taken in forcefully after
normal inhalation .
 It is usually equals to 3000ml (3ltrs).

Inspiratory capacity (IC) :
 It is the TV plus IRV .
 This is the amount or air (3.5ltr) a person can
breathe in beginning at the normal expiratory
level and distending the lungs to maximum
amount.
Expiratory reserve volume (ERV):
 It is the maximum extra volume of air that can be
expired by forceful expiration after the end of a
normal tidal expiration
 This normally amounts to about 1.1 ltr.
Residual volume (RV):
 It is the amount of air remaining in the lungs after
the most forceful expiration.

Functional residual volume (FRV):
 ERV+RV
 This is the amount of air that remains in lungs at
the end of normal expiration (2.3ltr)
Vital capacity (TC) :
 IRV+TV+ERV
 Volume of air forcefully exhaled after forceful
inhalation
 It is the maximum amount of air a person can
expel from lungs after first filling the lungs to their
maximum extent and then expiring to maximum
extent .
 Its about 4.6ltr.

Total lung capacity (TLC):
 VC+ RV
 It is the maximum volume to which the lungs can
be expanded with the greatest possible effort
 It is about 5.8 ltr

Dead space
 The regions of the respiratory system that contain
the air but are not exchanging oxygen and carbon
dioxide with blood.
 Because of inheritent structure are not capable of
exchange with blood
 Conducting zone, till terminal bronchioles

Acid base balance
 The pH of blood is 7.35-7.45.
 Your blood needs the right balance of acidic and
basic (alkaline) compounds to function properly.
This is called the acid-base balance.
 Acid and alkaline levels are measured on a pH
scale. An increase in acidity causes pH levels to
fall. An increase in alkaline causes pH levels to
rise.
 When the levels of acid in your blood are too
high, it’s called acidosis. When your blood is too
alkaline, it is called alkalosis.
 Respiratory acidosis and alkalosis are due to a
problem with the lungs

 Acidosis is the condition in which there is too
much of acid in the blood. Since co2 is acidic, the
condition of acidosis will occur if there is too much
co2 inn blood. This occurs when respiration is
restricted and co2 given off by cells begin to build
up.
 Alkalosis in which there is too little acid in blood.
This occurs less frequently but can occur when
respiration is over active. In case of
hyperventilation the exchanges of gases occur
too rapidly, there is too little of co2 in blood and
pH moves towards alkaline .
 the acid level of the blood affects the
concentration of sodium and potassium level so
that abnormal acid level can produced serious

 The respiratory system has responsibility for
helping to maintain acid level of blood at normal
range. If any reason the blood become acidic the
respiratory system is stimulated to increase
activity to give off more co2 and thereby to lower
the acid level back to normal.
 If any reason the basic level increase then the
respiratory system hold the co2 expiration and
builds up its level and maintain the blood pH.

 MORE ON ACID BASE BALANCE

Acid base balance
 The concentration of hydrogen ions (H+) in a solution is a
measure of the acidity of the solution.
 Control of hydrogen ion in body fluids is an important factor in
maintaining a stable internal environment.
 An acid substances releases hydrogen ions when in solution.
 A basic (alkaline) substance accepts hydrogen ions often with the
release of hydroxyl (OH-) ions.
pH scale
 It is the standard scale for measurement of hydrogen ion
concentration in solution.
 The scale measures from 0 to 14.
 pH > 7 = basic; pH<7 = acid; pH = 7 = neutral

pH values of body fluids
BODY FLUIDS pH
BLOOD 7.35 TO 7.45
SALIVA 5.4 TO 7.5
GASTRIC JUICE 1.5 TO 3.5
BILE 6 TO 8.5
URINE 4. TO 8.0

Buffers
 A buffer solution is an aqueous solution consisting of a mixture
of a weak acid and its conjugate base, or vice versa.
 Buffers resists the change in pH when small amount of acid or
alkali are added to it.
 Despite the constant cellular production of acid and alkaline
substances, body pH is kept stables by systems of buffering
chemicals in body fluids and tissues.
 The organs most active in this way are the lungs and the kidneys.
 CO2 increases(H+) in the body fluids because it combines with
water to form carbonic acid, which then dissociates into a
bicarbonate ion and hydrogen.
CO2+H2O = H2CO3 = H+HCO3

BUFFERS-lungs and kidneys
• Lungs regulate the blood pH as they excrete carbon dioxide (CO2)
and regulates its level.
 The brain detects rising H+ in the blood and stimulates breathing
causing increase CO2 loss and fall in H+.
 Conversely, if blood pH becomes too alkaline, the brain can reduce
the respiration rate to increase C02 levels and increase (H+),
restoring pH towards normal.
 The kidneys regulate blood pH by increasing or decreasing the
excretion of hydrogen and bicarbonate ions as required.
 If pH falls, hydrogen ion excretion is increased and bicarbonate
conserved, the reverse happens if pH rises.
 Other buffer system include body proteins, which absorb excess H+
and phosphate which is important for controlling pH inside cells.`

Acidosis and Alkalosis
 When the pH falls below 7.35 and all the reserves of
alkaline buffers are used up, the condition of acidosis
exists.
 When the pH rises above 7.45, the increased alkali uses up
all the acid reserve and state of alkalosis exists.

Metabolic and respiratory acidosis
Metabolic acidosis
 The metabolic acidosis is diagnosed with decrease HCO3.e.g
diabetic ketoacidosis, alcoholic ketoacidosis, lactic acidosis
 Drugs- salicylate intoxication, methanol,
 Loss of bicarbonate-diarrhea
Respiratory acidosis
 Respiratory acidosis is a medical emergency in which decreased
ventilation(hypoventilation) increases the concentrations of CO2
in the blood and decreases the blood pH.
e.g. acute Myasthenia gravis, chronic COPD

Metabolic and respiratory alkalosis
Metabolic alkalosis
 It is characterised by high HCO3.
 Loss of HCl from vomiting, antacids intake, severe potassium
depletion, intestinal alkalosis-chloride diarrhea.
Respiratory alkalosis
 It occurs when hyperventilation reduces the pCO2,increasing
serum pH.
 CNS mediated=Trauma , infection hyperventilation syndrome-
voluntary, anxiety.
 hypoxia-high altitude, hypotension, severe anemia
 Pulmonary disease-pneumonia, pulmonary edema, pulmonary
embolism

Hypoxia, anoxia and hyperventilation
 Hypoxia is defined as reduced availability of oxygen to the
tissues.
 Causes of hypoxia:
 Oxygen tension in arterial blood
 Oxygen carrying capacity of blood
 Rate of blood flow
 Utilization of oxygen by the cells
 Anoxia refers to the absence of oxygen.
 Anoxia means a total depletion in the level of oxygen ,
an extreme form of hypoxia or low oxygen.
 Since there is no possibility for total absence of oxygen
in living conditions, the use of this term is abandoned.
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Features Hypoxic
hypoxia
Anemic
hypoxia
Stagnant
hypoxia
Histotoxic
hypoxia
PO2 in
arterial blood
Reduced Normal Normal Normal
O2 carrying
capacity of
blood
Normal Reduced Normal Normal
Rate of blood
flow
Normal Normal Reduced Normal
Utilization of
O2 by tissues
Normal Normal Normal Reduced
Efficacy of
O2 therapy
100% 75% 50% Not useful
Characteristics features of different types of hypoxia

 Hyperventilation is the increased pulmonary ventilation
due to forced breathing.
 It is an increase in alveolar ventilation that leads to
hypocapnea.
 Both rate and force of breathing are increased.
 It causes apnea (temporary cessation of breathing).

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