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Respiratory system
Introduction:
# Respiration is a physiological process in which living organisms move oxygen into
their internal environment & give up carbon dioxide to the external environment.
# depending upon availability of oxygen, respiration may be:
A. anaerobic respiration: does not involve uptake of molecular oxygen.
B.aerobic respiration: involves of molecular oxygen.
# the respiratory system works with the other organs systems contribute to
homeostasis such as with the circulatory system to accomplish respiration, which
consists of:
A. Breathing: entrance & exit of the air into and out of lungs.
B. External respiration: exchange of gases (O2&CO2) between air and blood.
C. Internal respiration: exchange of gases between blood & tissue fluid.
D. Cellular respiration; production of ATP in cells.
Function of respiratory system:
1.
2.
3.
4.
5.
O2 up take & CO2 removal (main function).
Regulation of pH of blob.
Excretion of water vapor.
Regulation of body temperature.
Also have roles in; moving venous blood to the heart, vocalization, defense
against harmful air borne cell or particles, removing or modifying a number of
blood-borne substances, and in the sense of smell.
The basis of gas exchange:
Air is consider as mixture of gases, each gas exerts a partial pressure (p.p) of the total
atmospheric pressure (a.p)
E.x:
 Atmospheric pressure is about 760 mmHg.
 O2 partial pressure is about 160 mmHg.
 Co2 partial pressure is about 0.3 mmHg.
Each gas diffuses across a membrane from the side where its p.p is higher to the side
where its p.p is lower.
e.x1: pulmonary artery
atom. Air
Gas
O2
CO2
O2
CO2
P.P
40
45
e.x2: cells of B.T
Gas
O2
CO2
P.P
40
45
160
0.3
blood vessels
O2
CO2
100
40
Gases enter and leave the animal body by crossing a respiratory surface .efficient
respiratory system has four basic requirements for respiratory surface:
1. An adequate surface area to meet O2 needs.
2. Thin wall for fast exchange.
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3. Moist layer to dissolve gases.
4. Vascular layer to facilitate quick gas exchange.
Factors influence gas exchange:
1. Surface-to-volume ratio: all animals body plans promote favorable rates of in
wards diffusion of CO2 .Ex: large animals has respiratory system for
respiration & small (tiny or flattened) has no respiratory system and gases
diffuse across the body surface e.g. earth worm.
2. Ventilation: large-bodied animals have great demand for gas exchange.
Therefore, varieties of adaptations are more efficient. E.g. many fishes above
their gills have tissue flaps which stir the surrounding water to put more
dissolve O2 closer to gills & carry more CO2 away from them.
3. Transport pigment: rates of gas exchange get boost with respiratory pigments,
mainly hemoglobin.
Mode of respiration: differ among animals group (invertebrate & vertebrate).
Invertebrates:
1. Integumetary respiration e.g. flat & earth worm.
2. Gills respiration e.g. aplysia.
3. Tracheal respiration: e.g. most insects & some spiders.
Vertebrates:
1. Gills respiration e.g. fish & amphibians.
2. Lungs respiration e.g. some fishes & all amphibians, reptiles & mammals
(have pair of lungs), in birds there are 5 air sacs attach to each lung. Due to
high metabolic rates according to flight & muscular activities.
Human respiratory system:
The respiratory tract consists of the nose (nasal cavities), the pharynx, the trachea,
the bronchi, the bronchioles & the lungs (which are composed of air sacs called
alveoli).
Respiratory airways:
fig41.10
Lungs:


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
2
Are elastic cone-shaped organs of gas exchange.
Enhances gas exchange between internal environment & outside air.
Protected by rib cage.
Surrounded by double folds of pleural membrane, which contain pleural
fluid between folds to minimize friction & also prevents collapse of lungs.
“There is a constant amount of air inside the lungs which does not change
(residual volume)".
Larynx (voice box):
Airway where sound is produced; closed off during swallowing.
@ Larynx has vocal cords & also has opening called glottis (gap between the
cord) which closed by epiglottis (is a tissue flap at the entrance to the larynx
during swallowing.
@ Air >nose>nasal cavity (where hair & ciliated epithelium filter the air,
capillaries warm the air & mucous moist it)>pharynx>larynx (an airway with 2
paired folds of mucous membrane..
@ The lower pair is vocal cords. When you breath, air is forced in & out through
the glottis) which is the gap between cords.
@ The epiglottis, a tissue flap at the entrance to the larynx. When it pointed
upward, air moves into trachea.
The epiglottis points downwards & slout off the trachea's entrance when you
swallow food or fluid, which enter esophagus) > trachea which branches into 2
airways bronchi ( each bronchus leading into the tissue of each lung)>
bronchioles >alveoli(the main site of gas exchange)
The respiratory cycle:
Normal quiet lung ventilation (movement of air in & out of lungs) mainly by
pressure gradient (increase in partial pressure of CO2in blood & decrease in
partial pressure of O2 in blood), this called respiratory cycle.
Each respiratory cycle consist of 2 actions:
1. Inhalation: a single breath of air down into air ways.
2. Exhalation: a single breath out.
Inhalation (inspiration):
fig 41.12
When inter costal muscles contract & lift rib cage upward & outward, the diaphragm
also contract & moves down ( flattens), the thoracic volume increases >pressure in
lungs decrease.>fresh air flow into lungs through the airways .(inhalation always an
active energy requiring action).
Exhalation (expiration:
fig 41.15
When the muscles relax & rib cage moves down and in, the diaphragm relaxes &
moves up (curves), the thoracic volume decreases. Pressure in lungs increases >air
expelled out of the lung through the airways>Exhalation (it is a passive action).
Note:



Inhale air contains more O2 and less CO2.
Exhaled air contains lessO2 and moreCO2.
The rate and depth of breathing may be increased by drop in O2concentration
in blood & increase in CO2 concentration in blood.
Gas exchange and transport;
Gas exchange is most efficient when rate of air flow is matched with rate of blood
flow.
 Each alveolus is a single layer of epithelial cells with a basement membrane at
its outer surface.
 Alveolar capillaries also have thin walls, and a thin flim of interstitial fluid
separates them from alveoli.
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
The diffusion distances are so small that gases can flow rapidly across
respiratory surface.
1. oxygen transport:






Inhaled air that reaches the alveoli has plenty of oxygen and not much
carbon dioxide.
In lungs, oxygen tends to diffuse into the plasma portion of the blood
(into pulmonary capillaries).
Then it diffuses into red blood cells & rapidly binds with hemoglobin.
O2+Hb>HbO2 (Oxyhemoglobin).
Oxygen is mostly transported as oxyhemoglobin & the circulatory
system takes it to body tissues then to the cell.
Oxyhemoglobin gives up oxygen faster when:
 pH is lower.
 Blood is warmer.
 Carbon dioxide partial pressure is high.
2. carbon dioxide transport:


a.
b.
Carbon dioxide from cells diffuses into blood capillaries.
From there three mechanism transport it to the lungs:
10 % dissolved in the blood.
30 % binds with hemoglobin to form carbon amino hemoglobin
(HbCO2).
c. 60 % is transported in the form of bicarbonate (HCO3-).
How do these (HCO3-) molecules form?
Carbon dioxide combines with water in blood to form carbonic acid, which then
dissociates into bicarbonate & hydrogen ions (H+)
What about (HCO3-) that forms in this reaction?
Move out of red blood cell & into blood plasma.
What about H+ ion?
Its reaction with hemoglobin (buffer) keeps blood from becoming too acidic.
* The reaction is reversed when blood reaches the alveoli, where the
partial pressure of CO2 is lower than it in the lung capillaries. CO2 &H2O
from here and diffuse into alveolar sacs, then the gas is exhaled from the
body.
Respiration unusual environment:
$ At high attitude when the oxygen partial pressure decreases, the body can adapt to
these conditions by:
 More air sacs & blood vessels developed in the lungs.
 Ventricles in their heart become enlarged to pump larger volumes of blood.
 Hemoglobin has a greater affinity for oxygen.
 For visitors have not time for adaptation. Therefore, can suffer from hypoxia
(cellular oxygen deficiency).
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 Respiration centre (brain) work to compensate for the oxygen deficiency by
hyper ventilation (breathing much faster & more deeply than normal).
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