WEEK 9 - RESIPIRATORY SYSTEM

Question 1

Functions of Respiratory System

Answer 1

Main role of respiratory system is to bring oxygen (O2) into body and expel carbon dioxide (CO2) from body

Question 2

What are the 4 functions of the respiratory system?

Answer 2

1. RESPIRATION
   Gas exchange - between lungs and pulmonary capillaries
   O2 delivery from lungs to blood
   CO2 removal from blood to lungs
   Note: this is different to ventilation (movement of air between the environment and the lungs)
2. METABOLISM
   Regulate acid-base balance by removing excess H+ ions
3. DEFENCE
   Protects against inhaled particles
4. MANUFACTURE
   Produces surfactant – important in preventing lung collapse

Question 3

What are the main anatomy of the respiratory system?

Answer 3

Major structures:
Nasal cavity (nose)
Pharynx
Larynx (+ epiglottis)
Trachea
Bronchi and branches
Alveoli
Air flows through each structure and on to next
Each structure has protective features like cilia or mucous secretion…

Question 4

CONDUCTING ZONE

Answer 4

AIR NOT INVOLVED IN GAS EXCHANGE

Contains trachea and bronchial tree - acts like a ‘gas pipe’ that contains: ‘DEAD SPACE AIR’ = 150ml

Air is moistened, warmed and filtered

Cartilage gradually replaced by smooth muscle in bronchioles, which is innervated by ANS to change their diameter

Parasympathetic = Bronchoconstriction
Sympathetic = Bronchodilation

Cilia (hair-like projections) line airways and beat rhythmically to move debris and microbes out of lungs

Goblet cells secrete mucus to enable cilia to move trapped microbes. Mucus and cilia clean and protect airways

Question 5

RESPIRATORY ZONE

Answer 5

AIR INVOLVED IN GAS EXCHANGE
Contains respiratory bronchioles and clusters of alveoli, 300 million! (makes up most of the lung volume)

Question 6

Respiratory membrane

Answer 6

Alveolar and capillary walls and their basement membranes
Alveoli contains:
Type I cells → involved in gas exchange
Type II cells → secretes surfactant (↓ surface tension)

Question 7

RATE OF DIFFUSION (GAS LAW #4: FICK’S LAW)

Answer 7

Surface area for gas exchange :140 m2 (extremely large)

Solubility of gases: CO2 has high solubility, O2 solubility 1/20 of CO2 and N2 is practically insoluble

Partial pressure gradient

Thickness of respiratory membrane: Extremely thin, 0.4 - 1 µm, ideal for gas exchange

Question 8

WHAT IS FICK’S LAW?

Answer 8

The rate of diffusion of a substance across unit area (such as a surface or membrane) is proportional to the concentration gradient.

Question 9

Surfactant and Surface Tension

Answer 9

At liquid-air interfaces surface tension occurs where there is a greater attraction of H2O molecules to each other via strong hydrogen bonds.
The surface of the H2O becomes ‘under tension’ and the net effect is an inward force.
A thin layer of H2O lines the alveoli wall.
Surfactant ↓ surface tension by interfering with cohesiveness of H2O molecules and keeps alveoli open.
Respiratory Distress Syndrome occurs when premature babies do not produce surfactant and are at risk of their alveoli collapsing.

Question 10

Mechanics of Breathing - ventilation

Answer 10

Ventilation relies on contraction of skeletal muscle to change the volume of the thoracic cavity (when the cavity expands so do the lungs). Air moves into and out of body based on pressure changes

Question 11

QUIET INSPIRATION: AIR IN

Answer 11

Diaphragm contracts and flattens out (inferiorly), external intercostals contract lifting ribcage up and out (anteriorly)
REQUIRES ENERGY
Lungs stretch
↑ Volume ↓ Pressure
Air flows into lungs, ‘down its pressure gradient’ (from high to low)
Pressure equalises (ends inspiration)

Question 12

QUIET EXPIRATION: AIR OUT

Answer 12

Diaphragm relaxes back into dome shape (superiorly), external intercostals relax (posteriorly)
PASSIVE MOVEMENT
Lungs recoil
↓ Volume ↑ Pressure
Air flows out of lungs, ‘down its pressure gradient’ (from high to low)
Pressure equalises (ends expiration)

Note: forced inspiration/expiration involves extra muscles including internal intercostals and other accessory muscles

Question 13

Lung Volumes and Capacities

Answer 13

Amount of air moving into and out of lungs varies
Pulmonary function can be measured by spirometry

Respiratory Volumes
Depends on conditions of inspiration and expiration
Respiratory Capacities
Involves two or more lung volumes
Ventilation
Rate of gas movement into or out of lungs

Question 14

Lung Volumes and Capacities cont.

Answer 14

IRV = volume of air that can be forcefully inspired after a normal tidal inspiration

TV = volume of air inspired and expired with each breath at rest = 500ml

ERV = volume of air that can be forcefully expired after a normal tidal expiration

RV = volume of air remaining after a forced expiration
(can never expire)

Question 15

Pulmonary (minute) Ventilation rate (VE)

Answer 15

Total volume of air that flows into or out of respiratory tract in 1 minute
VE = TV x f
VE = 500 ml/breath x 12 breaths/min
VE = 6000 ml/min (6.0 L/min)
not all air is involved in gas exchange

Question 16

Alveolar Ventilation rate (VA)

Answer 16

Total volume of air that flows into or out of ALVEOLI in 1 minute
Since dead space is taken into account, it represents volume of air involved in gas exchange
VA =(TV - dead space) x f
VA = (500 ml – 150 ml) x 12 breaths/min
VA = 4200 ml/min (4.2 L/min)

Question 17

Effects of Breathing Rate & Depth

Answer 17

TV DS f VE VA
(ml) (ml) (ml/min) (ml/min)
500 150 12 6000 4200
1000 150 6 6000 5100
250 150 24 6000 2400
150 150 40 6000 0

Deep slow breathing results in more air making it to respiratory zone to be used in gas exchange

Question 18

Factors Affecting Gas Movement

Answer 18

The atmosphere is mixture of different gases, which each exert their own pressures termed ‘partial pressure (P)’ - a % that it contributes to the overall pressure.
Example: %O2 = 21% → PO2 = 760 x 0.21 = 160 mmHg
These pressures are measured in mmHg
Inhaled air from the atmosphere mixes with air remaining in the alveoli, which changes their partial pressures in the lungs….

Question 19

What is Dalton’s Law?

Answer 19

GAS LAW #2: DALTON’S LAW
Total pressure exerted by a mixture of gases = the sum of each individual gas pressure

Question 20

Atmospheric air pressure

Answer 20

PO2 = 160mmHg (21%)
PCO2 = 0.3mmHg (0.04%)
N2 = 597mmHg (79%)
H2O = 3.5mmHg (0.05%)
760mmHg

Question 21

Gas Exchange

Answer 21

External Respiration
exchange of gas between alveoli and pulmonary capillaries
O2 diffuses from alveoli → blood
CO2 diffuses from blood → alveoli

Internal Respiration
exchange of gases between tissues and systemic capillaries
O2 diffuses from BLOOD → TISSUES
CO2 diffuses from TISSUES → BLOOD

Question 22

What is Henry’s Law?

Answer 22

GAS LAW #3: HENRY’S LAW
Gas dissolves in liquid in proportion to its partial pressure
Gas will flow from high pressure to low pressure (DIFFUSION) until partial pressures are same (EQUILIBRIUM)

Question 23

Oxyhaemoglobin Dissociation Curve: RIGHT SHIFT

Answer 23

All of these factors shift curve to RIGHT – they enhance O2 off-loading = Bohr effect
↓ pH
↑ PCO2
↑ temperature
↑ BPG (by-product of RBC metabolism)

IN THE LUNGS: where partial pressure of O2 is high, O2 is loaded onto Hb
IN THE TISSUES: where partial pressure of O2 is low, O2 is off-loaded by Hb to tissues

Question 24

Carbon Dioxide Transport

Answer 24

There are 3 ways that CO2 is carried in blood:
Dissolved in plasma (7%)
Bound to haemoglobin (23%) - binds to globin part of Hb in RBCs
As Bicarbonate (70%)

Question 25

What is the most important factor regulating breathing?

Answer 25

CARBON DIOXIDE due to its relationship to pH

↑ CO2 = ↑ H+ = ↓ pH (low pH = more acidic)

Question 26

Factors Influencing Rate and Depth of Breathing

Answer 26

Changes in CO2 and O2 is sensed by CENTRAL & PERIPHERAL chemoreceptors

Question 27

CENTRAL chemoreceptors

Answer 27

Most important centre located in medulla
Primarily respond to ↑ CO2
(can also respond to ↓PO2)
CO2 readily diffuses into brain and causes ↑ [H+] in CSF
(i.e. ↓pH)
Response = rapid ↑ rate / depth of breathing

Question 28

PERIPHERAL chemoreceptors

Answer 28

Located in aortic arch & carotid arteries
Primarily responds to ↓PO2 esp. < 50 – 60 mmHg (can also respond to ↑PCO2)
Response = ↑ rate / depth of breathing

Question 29

Elasticity and Compliance in Lung Function

Answer 29

Elasticity: ease with which lungs rebound or recoil after being stretched
Governed by elasticity of alveolar membrane and surface tension
Compliance: ability of lungs to expand

Question 30

Two main categories of lung conditions that can affect ability to breathe:

Answer 30

RESTRICTIVE:
Definition: lost elasticity (‘stiff lung’) Features: Irreversible, may be related to dust diseases
Example: Pulmonary fibrosis

OBSTRUCTIVE:
Definition: Blockage of bronchi
Features: Reversible, smooth muscle, mucus; pollutants may initiate episodes
Example: Asthma