The respiratory system
Main Muscles of Respiration
1.
Diaphragm
2.
Intercostal Muscles (internal/external - 11 pairs)
Accessory Muscles of Respiration
1.
Sterno-mastoid
2.
Serratus anterior
3.
Pectoralis major - front of chest
Airway Structures of the Lungs
Nose and Mouth Larynx
Trachea Bronchi
Bronchioles Alveoli
Pleura
External repriration
The movement of air in and out of the
lungs
The exchange of gases between the
blood in the lung capillaries and the air in the alveoli of the lungs.
The blood takes up oxygen from the
atmospheric air and gives out carbon dioxide.
This is achieved by breathing.
Breathing consists of three phases
Inspiration Expiration Pause
Act of Inspiration
Contraction of intercostal muscles
Ribs are pulled outwards and upwards
At the same time the diaphragm
contracts and flattens, thus pushing abdominal contents downwards.
The effect of
this action causes the volume of the thorax to increase, therefore pressure of
air inside the thorax decreases below atmospheric (760 mmhg.). This decreasing pressure causes air from the
outside to rush in thorax by suction. When air pressure inside thorax is equal to
the air pressure outside, the flow of air stops. Inspiration is an active
process. The air pressure in the pleura is negative (- 4mmHg). During
inspiration this pressure may decrease
to - 12mmHg. Without this negativty the lungs will remain collapsed after
expiration.
Expiration
This is a passive process.
-
Does not require expenditure of energy.
-
It is the reversal of inspiration.
-
Diaphragm relaxes and returns to dome shape.
-
Lungs recoil due to elastic properties.
-
Intercostal muscles relax.
-
Pressure in the thorax increases.
-
Air is blown out
This process is followed by a PAUSE.
The Purpose of Respiration (Breathing)
i)
To supply the cells of the
body with oxygen and get rid of carbon dioxide.
ii)
To maintain normal blood pH.
iii)
Helps to maintain normal body
temperature.
The composition of air
Inspired
Air Expired Air Alveolar
Air
Oxygen 20% 16% 14%
Carbon Dioxide 0.04% 4% 6%
Nitrogen 79% 79% 79%
Diffusion of Gases in Alveloi
Cell membrane
has tiny pores (semi-permeable) through which substances, e.g. water, gases and
some solutes can pass. Diffusion always takes place down the concentration
gradient, i.e. from a high concentration side of the membrane to the low until
both are equal.
Diffusion from blood to tissues
As tissue
cells use up oxygen they produce carbon dioxide. By diffusion this carbon
dioxide passes into the oxygenated blood which contains less CO2
whilst simultaneously the O2, which is more plentiful, diffuses into
the cells.
Internal respiration
The ulilisation of oxygen in the
mitochondria
The Control of Respiration.
The Respiratory centre in the medulla
oblongata - if it is destroyed respiration ceases.
Normal rate is between 12-14 /min.
Two important factors control this:
1.
Nervous 2. Chemical
Nervous
Nerve centre
lies in the medulla oblongata. This centre sends regular impulses along the
phrenic nerves (motor) to the diaphragm and also along the intercostal nerves
to the intercostal muscles. These muscles contract, causing inspiration.
When the lungs expand stretch receptor nerve endings in the bronchioles send impulses to the respiratory centre via the vagus nerve, these inhibit the centre and cause relaxation of the respiratory muscles.
Herring-Breuer
Fibres inhibit the inspiratory part of the respiratory centre and stimulate the expiratoty part.
Chemical
Control - Normal respiratory rate = 12-14 per minute.
In this the
level of carbon dioxide (Co2) and oxygen (O2) concentration in the arterial
blood control respiration. An increase of Co2 concentration in the blood
stimulates the chemoreceptors in the CAROTID arteries. Impulses via the vagus
nerve and glosso-pharangeal nerve are passed to the respiratory centre to
stimulate respiration to rid of Co2 from the blood. The respiratory centre can
also be controlled by voluntary means (Brain Cortex).
Hydrogen ions
and Sodium Bircabonate concentrations may also influence respiration.
How are
pressure changes in the thorax involved in inspiration and expiration
How are these
pressure changes facilitated
What is the
role of the pleural membranes
What is the
role of the alveoli
Draw a diagram
of an alveoli showing the oxygenation of the capillary blood
Draw a
macroscopic diagram of the respiratory system
What factors
are involved in the control of respiration
What are the
effects of ageing on the respiratory system
Secreted from
type 2 pneumocytes in alveoli
A lipid which
reduces surface tension
Secretion
starts at 22 weeks gestation, surges at 30 – 35 weeks and at birth
Can be found
in amniotic fluid
Clucocorticoids
secreted during foetal stress increase production
Mothers can be
given betamethasone if delivering prematurely
Baby can be
given surfactant via ET tubes if needed
Foetal lungs
are filled with fluid
During passage
through the vagina much of this is squeezed out
Residual
mucous may need to be sucked out of the mouth at birth
Residual lung
fluid is absorbed through pulmonary capillaries and lymphatics
Reduced levels
of oxygen and increases in carbon dioxide will stimulate the first breath
Air entry into
lungs prevents fluid formation
Up to 4 weeks
babies are obligate nose breathers
Newborn 30 – 50 too
high above 60
1 year 26 – 40 too high above 50
2 years 20 – 30
4 years 20 – 30 too high above 40
6 years 20 – 26
8 years 18 – 24
10 years 18 – 25
Adult 12 – 20 too high above 30
NREM –
breathing is regular and slowed due to reduced metabolic demand
Parasympathetic
activity slows breathing rates and constricts bronchial lumen
REM –
breathing becomes irregular
Young babies
have longer periods of REM than older children so their sleeping breathing is
often irregular
Look for
normal respiratory associated movements, young children are more diaphramatic
breathers
Pallor and
cyanosis
Nasal flaring
Grunting and
stridor
Intercostal
recession
Increased
diaphragmatic breathing