Respiratory System
1
Human Respiratory System
Components of the Upper Respiratory Tract
Functions:
 Passageway for
respiration
 Receptors for
smell
 Filters incoming air
to filter larger
foreign material
 Moistens and
warms incoming air
 Resonating
chambers for voice
Components of the Lower Respiratory Tract

Functions:
Larynx: maintains an
open airway, routes
food and air
appropriately, assists
in sound production
 Trachea: transports
air to and from lungs
 Bronchi: branch into
lungs
 Lungs: transport air to
alveoli for gas
exchange

Four Respiration Processes




Breathing (ventilation): air in to and out of
lungs
External respiration: gas exchange between
air and blood
Internal respiration: gas exchange between
blood and tissues
Cellular respiration: oxygen use to produce
ATP, carbon dioxide as waste
Process of Breathing: Pressure Gradient
Inspiration/Expiration: air in/air out
 Cycle:
 Relaxed state: diaphragm and intercostal muscles
relaxed
 Inspiration
(Inhalation): diaphragm contracts,
pulling muscle down, intercostal muscles contract
elevating chest wall and expanding volume of
chest, lowering pressure in lungs, pulling in air
 Expiration (Exhalation): muscles relax, diaphragm
resumes dome shape, intercostal muscles allow
chest to lower resulting in increase of pressure
in chest and expulsion of air

Respiratory Cycle: Mechanism of Breathing
Gas Exchange & Transport: A Passive Process

Gases diffuse according to their partial pressures




External respiration: gases exchanged between
air and blood
Internal respiration: gases exchanged with
tissue fluids
Oxygen transport: bound to hemoglobin in red
blood cells or dissolved in blood plasma
Carbon dioxide transport: dissolved in blood
plasma, bound to hemoglobin, or in the form of
plasma bicarbonate
Gas Exchange Between the Blood and Alveoli
Gas Exchange Between the Blood and Alveoli
Oxygen transport in Blood
• Oxygen transport
– 1.5% dissolved in plasma
– 98.5% bound to
hemoglobin (Hb)
• Oxyhemoglobin
Saturation Curve :
– higher PO results in
2
greater Hb saturation
CO2 Transport
• Carbon dioxide transport:
– ~9% dissolved in plasma
– ~13% as carbamino compounds
• Most combined with Hb
– ~78% converted to HC03• CO2 + H2O  H2CO3  H+ + HCO3-
• Haldane effect
– Inverse relationship between amount of Hb-O2 and
CO2 carrying capacity of blood
• Hb binds and transports more CO2 than O2
• Hb buffers more H+ than Hb-O2
– Promotes conversion of CO2 to HCO3- via carbonic anhydrase
reaction
Key Concept
• O2 mostly transported in blood bound to
hemoglobin
• CO2 mostly transported in blood as HCO3• Lesser amounts of CO2 are bound to Hb or
dissolved in plasma
Regulation of Breathing
As we exercise, the body needs to obtain more
oxygen and remove more carbon dioxide (CO2)
This is done by increasing the rate and depth of
breathing
An increase in carbon dioxide in the blood is the
main trigger that increases the rate and depth of
breathing
Regulation of Breathing
Chemoreceptors in the respiratory centre in the
brain stem’s medulla detect an increase in blood
CO2 levels
The intercostal and phrenic nerves increase the
rate and depth of breathing
Additional chemoreceptors on arteries near the
heart monitor oxygen and blood acidity
Regulation of Breathing
chemoreceptors
on aorta and
carotid artery
brain
respiratory
centres in
medulla
heart
intercostal
nerve to
external
intercostal
muscles
phrenic
nerve to
diaphragm
ribs
diaphragm
16