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Biology 12
Respiratory System Notes
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Oxygen is moved to lungs →
CO2 moved away from cells of body→ _______ → outside of body
Inhalation—
Exhalation—
Air is filtered, warmed and hydrated as moves along air passages
throughout the system
A. Nose
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Made of 2 _______ ________
_________ are openings to nasal cavities
Separated by bone or cartilage
Inside nasal cavities have hairs and cilia which filter out
contaminants such as dust, pollen, etc.

 Have sensory receptors in nasal cavities for smell
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 Nasal cavities connected to sinuses in the head—i.e. bony cavities
lined with mucous membrane
 Nasal cavities open up into the ___________
Figure 1: Nasal Cavity
B. Pharynx

 Composed of ___________, ___________ and _____________
 Where ________, _________ and ________ are found
C. Larynx
 ______ found on top of trachea—Adam’s apple at front of larynx
 ______ is opening lying above larynx→ moves up and against
____________ when swallowing to block trachea
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Figure 2: Larynx
 Larynx contains ________ _______ (mucus membranes and elastic
ligaments) which vibrate as air passes them→ sound
 More narrow cords→
Figure 3: trachea in relation to esophagus
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D. Trachea

 Surrounded with cartilaginous c-shaped rings that help maintain
open airways
 Lined with cilia that help keep airway clean by sweeping up
contaminants caught in mucus to throat where swallowed
 ______________—procedure where opening is made in trachea if
blocked
 At end of trachea are main ___________
Figure 4: Trachea and larynx
Figure 5: Tracheostomy
4
E. Lungs
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2 lungs—
Each divided into lobes
R lung has 3 lobes and left has 2→
Lobes are further divided into smaller lobules
F. R & L Bronchus (pl.= Bronchi)
 Right and Left main __________→ lead into lungs
 Maintain cartilaginous rings
 Divide to form smaller and smaller diameter and thinner _____
eventually losing cartilage
 Eventually, bronchi become structures called bronchioles which
end in small sacs called _________
Figure 6: Lung structure
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G. Alveoli

 Thin structures only 1 cell layer thick—simple squamous
epithelium
 Covered by capillaries
 Alveoli covered by a thin film of a ____________ __________—
chemical that lowers surface tension—prevents them from
collapsing and clinging due to surface tension of water lining
alveoli which would cause alveoli to collapse
 Infant ___________ ________ __________—where babies do not
produce this and have collapse of alveoli—result is trouble
breathing; treatment = surfactant replacement therapy
Figure 7: Alveoli
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Mechanism of Breathing Overview
 Different kinds of respiration
a) Breathing

 Expiration (breathing out)
b) External respiration

c) Internal respiration
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d) Cellular Respiration
 ATP production in mitochondria: C6H12O6 + O2 → ATP + CO2 +
H2 O
Respiratory Volumes
a) Tidal Volume
 Volume of air inhaled and exhaled at rest

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b) Inspiratory reserve volume

 Forced inspiration
 3.0 L
c) Expiratory Reserve Volume

 About 1.4 L
Note: both inspiratory reserve volume and expiratory reserved volume
are used with physical activity
d) Residual Volume
 Air remaining in lungs even after forced expiration (1.0 L)
 ____________—residual volume builds & not used for gas
exchange and thereby reducing vital capacity
e) Vital Capacity

 Sum of tidal volume + inspiratory reserve volume + expiratory
reserve volume (about 4.5 to 5.7 L)
f) Functional Residual Capacity

 i.e. E.R.V. + R.V. (2.5 L)
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g) Dead Space

 E.g. nasal cavities, pharynx, larynx, etc.
Mechanism of Breathing
 Air passes from outside to pharynx → alveoli
 Lungs are in sealed _________ ________
 ____ ______ (with intercostals muscles) forms ____ and ______ of
this cavity
 _____________ (domed muscle) forms lower part of thoracic cavity
 _________ ___________ is double membrane associated with lungs
and thoracic cavity
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 One layer attached to lungs exterior and other layer closely adheres
to chest wall and diaphragm
 In between 2 pleural membranes is thin layer of fluid (mostly H2O)
 __________ _________ is about 4mm Hg less than atmosphere—
keeps them together
 _____________—condition whereby air enters intrapleural space
and causes lungs to collapse
Inspiration
 Active process—i.e. requires energy
 _________ center in medulla senses CO2 and H+ levels in blood
plasma→ automatically causes inspiration
 Levels of mostly H+ and CO2 as well as O2 are also sensed by _____
bodies (in carotid arteries) and _______ bodies (in aorta) which are
_______________ that send signal to respiratory center in medulla
via nerves
 The more CO2 and H+ in blood, the higher the rate and depth of
breathing
 _________ nerve → nerve to diaphragm that causes contraction
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 ___________ nerves → send nerve impulses to intercostals muscles
to contract
 When diaphragm and intercostals muscles contract → expand
volume of thoracic cavity→ lungs expand → negative pressure in
lungs → air enters lungs
 If inhale deeply → stretch receptors in alveoli → inhibitory nerve
impulses to respiratory centre → stops sending signals to diaphragm
and intercostals
Expiration

 Respiratory center → stops signal to diaphragm and rib muscles →
diaphragm and muscles relax → abdominal organs press against
diaphragm → volume of chest cavity decreases → pressure builds up
→ air is forced out
External Expiration
 Gas exchange (CO2, O2 and H20) in alveoli and pulmonary capillaries
occurs due to ___________
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Internal Respiration

External Respiration and 02 Exchange
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Blood temp. =
pH of blood = 7.4
Hb has 4 binding sites for oxygen
Oxygen bound to Hb called HbO2 or ______________
Internal Respiration and O2 Exchange
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Blood temp =
pH of blood = 7.35 (from cell metabolism)
Hb-02 →
Hb becomes unbound again
Internal Respiration and CO2 Exchange

 CO2 + H20 react in red blood cells to give H2CO3 –a reaction catalyzed
by enzyme __________ anhydrase

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Reaction: CO2 + H20 → H2CO3 → [HCO3-] + H+
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H+ ions are bound by Hb to produce HHb or _________ Hb
Above allows blood to be buffered against changes in pH
Some CO2 binds to Hb to give ______________________ (HbCO2)
Some very small amount transported as dissolved gas in plasma as
well
External Respiration and CO2 Exchange
 At alveolar capillaries:


 pH higher and temp. lower than at tissues→ release of CO2 and H+
from Hb
 next HCO3 and H+ combine to form carbonic acid by ___________
______________ enzyme
Reaction: HCO3- + H+ → [H2CO3] → CO2 + H2O
 then carbonic acid is converted into H2O and CO2 by enzyme _____
anhydrase
13

 Some CO2 also leaves from HbCO2 as well as dissolved CO2 in plasma
leaving the plasma for the alveoli

Driving Force of Gas Exchange
 Recall that gas exchange occurs by diffusion

 This gradient is accomplished by partial pressure differences of PCO2
and PO2

 Blood in pulmonary capillaries has higher PCO2 and low PO2
concentration
 Thus, CO2 diffuses out of capillaries into alveoli and O2 diffuses out
from alveoli into capillaries
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Effect of PO2/Temperature/pH on Hemoglobin Saturation
a. Oxyhemoglobin Dissociation Curve & PO2

 Notice that as PO2 increases, the oxygen saturation of Hb
increases to a point
 Notice also that at any given PO2, a rise in temperature or a
lowering of pH will result in a lower Hb saturation and therefore
more oxygen given off
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