Respiratory SystemRespiratory System The word respiration describes two processes:The word respiration describes two processes:Internal or cellular respirationInternal or cellular respiration: is the process by : is the process by

which glucose or other small molecules are which glucose or other small molecules are oxidized to produce energy: this requires oxygen oxidized to produce energy: this requires oxygen

and generates carbon dioxide. and generates carbon dioxide.

External respiration (breathing):External respiration (breathing): involves simply: involves simply: Inhaling (inspiration)Inhaling (inspiration) - taking in oxygen from - taking in oxygen from

the air.the air. Exhaling (expiration)Exhaling (expiration) - giving off carbon - giving off carbon

dioxide to itdioxide to it..

The respiratory system is The respiratory system is responsible for providing the blood responsible for providing the blood stream with life sustaining oxygen stream with life sustaining oxygen while removing toxic waste gases, while removing toxic waste gases, enables the production of sound by enables the production of sound by passing over the vocal cords which in passing over the vocal cords which in turn cause vibration, and is partially turn cause vibration, and is partially responsible for the compression of the responsible for the compression of the abdominal muscles which assist in abdominal muscles which assist in urinationurination, defecation, and child birth as , defecation, and child birth as well as assists in laughter and other well as assists in laughter and other basic bodily functions surrounding the basic bodily functions surrounding the abdomen. abdomen.

The respiratory system is made up of The respiratory system is made up of the organs involved in the interchanges the organs involved in the interchanges

of gases, and consists of the :of gases, and consists of the :

The upper respiratory tract: The upper respiratory tract: includes the: includes the: nose, nasal cavity, pharynx and larynx.nose, nasal cavity, pharynx and larynx.

The lower respiratory tractThe lower respiratory tract : : Airways Airways beyond the larynx are divided into 2 zones: beyond the larynx are divided into 2 zones:

(1)   (1)   The conducting zoneThe conducting zone where there is no where there is no gas exchange. This consists of the tracheal gas exchange. This consists of the tracheal tube, which branches into two bronchi, one tube, which branches into two bronchi, one

of which enters each lung and makes of which enters each lung and makes further branching. further branching.

(2)   (2)   The respiratory zoneThe respiratory zone where gas where gas exchange occurs. Consists of respiratory exchange occurs. Consists of respiratory

bronchioles with alveoli attached to them. bronchioles with alveoli attached to them.

Nose and Nasal CavityNose and Nasal Cavity

In humans, inspiration and In humans, inspiration and expiration usually takes place through expiration usually takes place through the nose. The nasal cavity is located the nose. The nasal cavity is located inside the nose and joins the pharynx. inside the nose and joins the pharynx. The external openings to the nasal The external openings to the nasal cavity are the external nares and the cavity are the external nares and the posterior openings from the nasal posterior openings from the nasal cavity into the pharynx are the internal cavity into the pharynx are the internal nares. nares.

Pharynx:Pharynx:

It is the common opening of It is the common opening of the digestive and respiratory the digestive and respiratory systems. Receives air from the systems. Receives air from the nasal cavity, and air, food and nasal cavity, and air, food and water from the mouth. Inferiorly, water from the mouth. Inferiorly, the pharynx leads to separate the pharynx leads to separate openings of the respiratory openings of the respiratory system (larynx) and digestive system (larynx) and digestive system (esophagus). system (esophagus).

Larynx:Larynx: The larynx consists of an outer The larynx consists of an outer

casing of nine cartilages connected casing of nine cartilages connected to each other by muscles and to each other by muscles and ligaments. Six of the cartilages are ligaments. Six of the cartilages are paired and three are unpaired. paired and three are unpaired.

Trachea:Trachea: The trachea is a membranous tube The trachea is a membranous tube

that consists of dense regular that consists of dense regular connective and smooth muscle connective and smooth muscle

reinforced with 15-20 "C"-shaped reinforced with 15-20 "C"-shaped pieces of cartilage. The cartilages form pieces of cartilage. The cartilages form

the anterior and lateral sides and the anterior and lateral sides and protect the trachea and maintain an protect the trachea and maintain an

open passageway for air. open passageway for air. The posterior wall contains no The posterior wall contains no

cartilage and consists of a ligamentous cartilage and consists of a ligamentous membrane and smooth muscle which membrane and smooth muscle which

can alter the diameter of the trachea. can alter the diameter of the trachea.

Bronchi:Bronchi:

The trachea divides into the The trachea divides into the right and left primary bronchi. right and left primary bronchi. The right bronchus is shorter The right bronchus is shorter

and wider and is more vertical and wider and is more vertical than the left bronchus. than the left bronchus.

The lining of the bronchi is the The lining of the bronchi is the same as the trachea and the same as the trachea and the

bronchi are supported by "C"-bronchi are supported by "C"-shaped cartilage rings.shaped cartilage rings.

The lungs:The lungs: Are the principal organs of respiration Are the principal organs of respiration

and on a volume basis, they are one of and on a volume basis, they are one of the largest organs of the body. the largest organs of the body.

The lungs are enveloped in a The lungs are enveloped in a membrane called the pleura. The right membrane called the pleura. The right lung is larger than the left lung as the lung is larger than the left lung as the

right lung has three sections, called right lung has three sections, called lobes while the left lung has two lobes.lobes while the left lung has two lobes. Each lobe is divided into lobules Each lobe is divided into lobules

( Nine lobules in the left lung and ten ( Nine lobules in the left lung and ten lobules in the right lung) that are lobules in the right lung) that are

separated from each other by separated from each other by connective tissue but the separations connective tissue but the separations

are not visible as surface fissures. are not visible as surface fissures.

Alveoli: The Site of Gas Alveoli: The Site of Gas ExchangeExchange

Alveoli are hollow sacs having open Alveoli are hollow sacs having open ends continuous with lumens of airways. ends continuous with lumens of airways.

A pair of human lungs has about 300 A pair of human lungs has about 300 million alveoli, providing a respiratory million alveoli, providing a respiratory

surface of about 70 m2 arranged in surface of about 70 m2 arranged in clusters like bunches of balloons.clusters like bunches of balloons.

The alveolar inner walls lined by a The alveolar inner walls lined by a single layer of flat epithelial cells called single layer of flat epithelial cells called

type I alveolar cells, interspersed by type I alveolar cells, interspersed by thicker, specialized cells called type II thicker, specialized cells called type II

alveolar cells. alveolar cells.

Mechanics of BreathingMechanics of Breathing::

Breathing is an active processBreathing is an active process - - requiring the contraction of skeletal requiring the contraction of skeletal

muscles. muscles. The The muscles of inspirationmuscles of inspiration include the include the external intercostals muscles (located external intercostals muscles (located

between the ribs) the diaphragm (a between the ribs) the diaphragm (a sheet of muscle located between the sheet of muscle located between the

thoracic and abdominal cavities), thoracic and abdominal cavities), sternocleidomastoids and scalenes.sternocleidomastoids and scalenes.The The muscles of expirationmuscles of expiration includes includes

internal intercostals and the abdominals.internal intercostals and the abdominals.

• Inspiration: Inspiration: 1- Contraction of external intercostals 1- Contraction of external intercostals

musclesmuscles elevation of ribs & sternum > elevation of ribs & sternum > increased front- to-back dimension of increased front- to-back dimension of

thoracic cavity. thoracic cavity. 2- 2- Contraction of diaphragmContraction of diaphragm diaphragm diaphragm

moves downward moves downward increases vertical increases vertical dimension of thoracic cavity.dimension of thoracic cavity.

3- Increased volume (about 0.5 liter) --3- Increased volume (about 0.5 liter) -->Decreased pulmonary pressure ( -1 mm >Decreased pulmonary pressure ( -1 mm

Hg) air rushes into lungs to fill alveoli.Hg) air rushes into lungs to fill alveoli.4- Deep/forced inspirations – as during 4- Deep/forced inspirations – as during

exercise and pulmonary disease – scalenes, exercise and pulmonary disease – scalenes, sternocleidomastoid, pectorals are used for sternocleidomastoid, pectorals are used for

more volume expansion of thorax.more volume expansion of thorax.

• Expiration: Expiration: 1- Quiet expiration (exhalation) – simple 1- Quiet expiration (exhalation) – simple

elasticity of the lungs, relaxation of elasticity of the lungs, relaxation of external intercostals muscles and external intercostals muscles and diaphragm diaphragm return of diaphragm, ribs, return of diaphragm, ribs, and sternum to resting position> restores and sternum to resting position> restores thoracic cavity to preinspiratory volume.thoracic cavity to preinspiratory volume.

2- Decreases volume increased pulmonary 2- Decreases volume increased pulmonary pressure pressure movement of air out of the movement of air out of the lungs.lungs.

3- Forced expiration – contraction of 3- Forced expiration – contraction of abdominal wall muscles (i.e. obliques and abdominal wall muscles (i.e. obliques and transverses abdominus) further transverses abdominus) further decreases volume beyond relaxed point decreases volume beyond relaxed point --- > further increased in pulmonary --- > further increased in pulmonary pressure -pressure - more air moves out. more air moves out.

Pulmonary Ventilation:Pulmonary Ventilation:Ventilation is exchange of air between Ventilation is exchange of air between

atmosphere and alveoli. Air moves by bulk atmosphere and alveoli. Air moves by bulk flow, from a high pressure to a low flow, from a high pressure to a low

pressure region. Flow rate can be found pressure region. Flow rate can be found with:with:

F = (Patm - Palv)/RF = (Patm - Palv)/Rwhere, Patm, is the atmospheric pressure and Palv is the alveolar where, Patm, is the atmospheric pressure and Palv is the alveolar

pressure.pressure.

During ventilation, air is moved in and During ventilation, air is moved in and out of lungs by changing alveolar pressure out of lungs by changing alveolar pressure

through changes in lung dimensions. through changes in lung dimensions.

Factors Influencing Pulmonary Factors Influencing Pulmonary VentilationVentilation

A. Respiratory Passageway ResistanceA. Respiratory Passageway Resistance : :1. Upper respiratory passageways - relatively 1. Upper respiratory passageways - relatively

large, very little resistance to airflow (unless large, very little resistance to airflow (unless obstruction such as from food lodging or obstruction such as from food lodging or cancer).cancer).

2. Lower respiratory passageways - from 2. Lower respiratory passageways - from medium-sized bronchioles on down, can alter medium-sized bronchioles on down, can alter diameter based on autonomic stimulation:diameter based on autonomic stimulation:

a. Parasympathetic - causes a. Parasympathetic - causes bronchioconstriction.bronchioconstriction.

b. Sympathetic - inhibits bronchioconstriction.b. Sympathetic - inhibits bronchioconstriction. "Epinephrine" - used to treat life-threatening "Epinephrine" - used to treat life-threatening

bronchioconstriction such as during asthma bronchioconstriction such as during asthma and anaphylactic shock (carried by people and anaphylactic shock (carried by people susceptible to sudden constrictionsusceptible to sudden constriction).).

B- Transpulmonary pressure = Palv - PipB- Transpulmonary pressure = Palv - Pip PPalvalv is zero, which means it is same as is zero, which means it is same as

atmospheric pressure. atmospheric pressure.

PPipip (intrapleural pressure) is negative, or less (intrapleural pressure) is negative, or less than atmospheric pressure because the than atmospheric pressure because the

elastic recoil of the lung inwards and the elastic recoil of the lung inwards and the elastic recoil of chest wall outwards increases elastic recoil of chest wall outwards increases

volume of intrapleural space between them volume of intrapleural space between them and decreases the pressure within.. and decreases the pressure within..

Therefore, transpulmonary pressure is greater Therefore, transpulmonary pressure is greater

than zero and this pressure puts an than zero and this pressure puts an expanding force equal to the force of elastic expanding force equal to the force of elastic recoil of lung and keeps it from collapsing. recoil of lung and keeps it from collapsing. Volume of lungs is kept stable and there is Volume of lungs is kept stable and there is

air inside lungs. air inside lungs.

•C- Lung Compliance :C- Lung Compliance : Lung compliance is a measure of Lung compliance is a measure of

elasticity or the magnitude of change in elasticity or the magnitude of change in lung volume (ΔVL) that can be produced lung volume (ΔVL) that can be produced by a given change in transpulmonary by a given change in transpulmonary pressure. CL = ΔVL / Δ (Palv - Pip) pressure. CL = ΔVL / Δ (Palv - Pip)

Determinants of Lung ComplianceDeterminants of Lung Compliance1- The elastic recoil of the lung tissue 1- The elastic recoil of the lung tissue

itself which determined by the elastic itself which determined by the elastic forces of the elastin and collagen fibers forces of the elastin and collagen fibers among the lung tissue.among the lung tissue.

2-The elastic force caused by the surface 2-The elastic force caused by the surface tension of the fluid that lines the inside tension of the fluid that lines the inside walls of the alveoli and other lung air walls of the alveoli and other lung air spaces.spaces.

Gas Exchange in AlveoliGas Exchange in Alveoli It is the process of exchange of O2 and It is the process of exchange of O2 and CO2 between external environment and the CO2 between external environment and the

cells of the body. cells of the body. In steady state, volume of oxygen In steady state, volume of oxygen consumed by body cells per unit time is consumed by body cells per unit time is

equal to volume of oxygen added to blood equal to volume of oxygen added to blood in lungs, and volume of carbon dioxide in lungs, and volume of carbon dioxide produced by cells is identical to rate at produced by cells is identical to rate at

which it is expired. which it is expired. The ratio of CO2 produced / O2 The ratio of CO2 produced / O2

consumed is called respiratory quotient consumed is called respiratory quotient (RQ), which depends on type of nutrients (RQ), which depends on type of nutrients

being used for energy. being used for energy. It occurs by simple diffusion along It occurs by simple diffusion along

partial pressure gradients.partial pressure gradients.

What is Partial What is Partial PressurePressure:?:? It's the individual pressure exerted It's the individual pressure exerted

independently by a particular gas within independently by a particular gas within a mixture of gasses. a mixture of gasses.

The partial pressure exerted by each gas The partial pressure exerted by each gas in a mixture equals the total pressure in a mixture equals the total pressure times the fractional composition of the times the fractional composition of the gas in the mixture. So, given that total gas in the mixture. So, given that total atmospheric pressure (at sea level) is atmospheric pressure (at sea level) is about 760 mm Hg and, further, that air is about 760 mm Hg and, further, that air is about 21% oxygen, then the partial about 21% oxygen, then the partial pressure of oxygen in the air is 0.21 pressure of oxygen in the air is 0.21 times 760 mm Hg or 160 mm Hg. times 760 mm Hg or 160 mm Hg.