Week 2 - Respiratory System Flashcards
What is an Alveoli?
Air-filled pockets within the lungs where all gas exchange takes place.
Characteristics of an Alveolus?
Has an extensive network of capillaries, surrounded by elastic fibres. Fibres recoil during exhalation, reducing alveolar size and pushing air out lungs. Alveolar walls v thin <1um. Large SA (35x SA of body).
Describe Alveolar Epithelium
Simple squamos epithelium
Thin delicate Type 1 Cells
Patrolled by macrophages, also called dust cells.
Contains septal cells (Type 2 cells) that produce surfactant.
What is Boyle’s Law?
P=1/V
In a contained glass - external pressure forces molecules closer together, movement of gas molecules exerts pressure on container.
What is Henry’s Law?
When gas under pressure comes in contact w liquid, gas dissolves in liquid until equilibrium is reached.
At a given temp - Volume of gas in a solution is proportional to partial pressure of that gas.
Give 5 Reasons for efficient Gas exchange
- Substantial differences in partial pressure across the respiratory membrane.
- Distance involved in gas exchange are short
- O2 and CO2 are lipid soluble.
- Total SA is large.
- Blood flow and airflow are coordinated.
What causes CO2 to leave and O2 to enter blood?
Blood arriving has low Po2 and high Pco2. Conc Gradient causes O2 to enter blood and Co2 to leave
What are the partial pressures in the Pulmonary Circuit?
Entering: Po2- 40
Pco2 - 45
Alveolus: Po2-100
Pco2 - 40
Leaving: Po2 - 100
Pco2 - 40
What are the partial pressures in the Systemic Circuit
Entering: Po2- 95
Pco2 - 40
Interstitial Fluid: Po2-40
Pco2 - 45
Leaving: Po2 - 40
Pco2 - 45
What transports O2 and Co2
Red blood cells (erythrocytes) - Transport to and from peripheral tissues.
Remove O2 and Co2 from plasma allowing gases to diffuse into blood.
Describe Haemoglobin
Three types: Oxyhaemoglobin, Deoxyhaemoglobin, Carbaminohaemoglobin.
2 alpha chains
2 Beta chains
Heme group
Describe Oxy-haemoglobin saturation curve
Higher Po2 - Higher Hb Saturation
Curve because Hb changes shape when O2 binds
Each O2 bind makes next O2 bind easier
Allows Hb to bind O2 when O2 levels are low
Is standardised for normal blood (pH 7.4, 37 degrees)
How does Temp affect Hb?
Temp Inc - Hb releases more O2
Temp Dec - Hb hold O2 more tightly
Temp affects are significant only in active tissues that are generating large amounts of heat (eg active skeletal muscles)
What is the Bohr effect?
Bohr effect is the result of pH on Hb saturation curve.
Caused by Co2 diffusing into RBC
Carbonic anhydrase catalyzes reaction with H2O
Produces Carbonic acid
Dissociates into H+ and Bicarbonate
H+ diffuse out of RBC lowering PH
Describe the metabolic activity within RBCs
Hb and 2,3-bisphosphohlycerate (BPG)
RBCs generate ATP by glycosis forming lactic acid and BPG
BPG directly affects O2 binding and release- more BPG more O2 release.
BPG levels -
Inc - Ph increase, when stimulated by hormones
Dec - Haemoglobin will not release oxygen.
Carbon Dioxide Transport
Generated by aerobic metabolism
Three pathways: Dissolve in plasma
Bind to Hb
Converted into Carbonic acid
All three are reversible.
Describe Local control of respiration
At tissues - Inc activity of peripheral tissue
Dec Po2 Inc PCo2
Changes in gases exchange
Inc blood flow
Neural - CO inc, Respiratory rate inc
Voluntary, reflects activity in cerebral cortex, affects output of respiratory centres (medulla oblongata and pons) and motor neurons.
Involuntary, regulates respiratory muscle activity frequency and depth, responding to info from lungs and respiratory tract + others.
How does pons control respiration?
Apneustic and Pneumotaxic centres of the pons - paired nuclei that adjust output of respiratory rhythmicity centers
Regulating respiratory rate and depth of respiration.
What is the respiratory centre of medulla oblongata?
Used to establish basic pace and depth of respiration
1. Dorsal Respiratory Group (DRG)
Inspiratory centre, functions in quiet and forced breathing
2. Ventral Respiratory Group (VRG)
Inspiratory and expiratory centre, functions only in forced breathing.
Difference Between Quiet breathing and forced breathing
Quiet breathing (Eupnea) - Involve active inh and passive exh
Diaphragmatic breathing or deep breathing, dominated by diaphragm
Costal breathing or shallow breathing, dominated by ribcage movements.
Forced Breathing(hypernea) - Involve Active Inh and exh
Assisted by accesory muscles
Max levels occur in exhaustion
Summarise respiratory reflexes
Chemoreceptors - Detect changes in Po2, Pco2, pH of blood
Baroreceptors - Changes in BP
Stretch receptors - changes in lung volume
Irritating physical or chemical stimuli in nasal cavity, larynx, or bronchial tree
Other sensations including pain, changes in body temp, abnormal visceral sensations.
What is the Hering-Breuer Reflex?
2 mechanoreceptor reflexes involved in forced breathing.
Inflation reflex: Prevents overexpansion of lungs, as lung volume increases, DRG is inhibited, VRG stimulated.
Deflation reflex: Inhibits expiratory centres, stimulates inspiratory centres during lung inflation.
What causes Chemoreceptor Stimulation?
Drop in Po2 to 40mmHg inc resp rate by 50-70%
A rise of 10% in arterial Pco2 inc resp rate by 100%
Chemoreceptor stim is subject to adaptation: decreased sensivity due to chronic stimulation.
Increases in lactic acid affect respiration
What does age have to do w respiratory rate
Before birth - Pulmonary vessels are collapsed, lungs contain no air.
At birth - newborn overcomes force of surface tension to inflate bronchial tree and alveoli and take first breath.
Elderly - Deterioration in elastic tissue, compliance and VC, arthritic changes and decreased flexibility
Emphysema - smoking
