Exchanges with the Environment (UNIT 2RECAP)• - Understand what materials need to be exchanged: respiratory gases, nutrients and excretory products• Understand the relationship of size and surface area to volume ratio• Understand the features of exchange surfaces which aid passive and active transport• Understand the special features of gas exchange surfaces• Understand the need for ventilation mechanisms• Gas exchange in protozoa, humans, and plants
Gas exchange in Humans• Recall the structure of the thorax: understand the mechanism of ventilation, including the role of the pleural membranes• Understand how breathing is controlled:understand vital capacity and tidal volume• Recall the structure of an alveoli and understand their role in gas exchange, explain the function of surfactants:know that breathing is controlled but the respiratory centre in the brain.
Exchanges with the environment:• Relationship between surface area/volume (size of cells)• Need for ventilation mechanisms• Features of gas exchange surfaces• Gas exchange in protozoa• Gas exchange in humans • Mechanism of ventilation • Control of breathing • Vital capacity and tidal volume • Role of alveoli in gas exchange
Imagine if thesewere unicellularorganisms . .Problems?/solutions
Other examples ofcells/organismswhich are adaptedwith a larger surfacearea?
ProtozoaWhatmaterials dothey need toexchange?How is thisachieved?Why arethere notlargeunicelluarorganisms?
Features of gas Exchange surfaces• Large surface area to volume ratio• Partially Permeable• Thin (short distance for diffusion 0r active transport)• May be covered with a film of moisture (although this makes diffusion slower, but easier)• Diffusion gradients
Pulmonary System(unit 4) -Recall the structure of the structure of the breathing system and the mechanism of ventilation -Understand the histology of lung tissue -Understand how the ventilation mechanism is controlled: -the roles of respiratory gases: the control centres in the medulla, stretch receptors and cranial nerves
These 2 typesof specialisedepithelialcells arefound in therespiratorytract until thebronchiolesand alveoliduct. Can youthink whyyou wouldn’tfind themfurther?
Histology of the Lungs – detail alveoli and capillaries Squamous Epithelium
The table below refers to three differences of epithelia. Complete the table by writing the name of each type of epithelium and giving onelocation of each. Epithelium Name One location
• Describe two ways in which alveoli are adapted to their function
1. The diagram below shows a sectionthrough lung tissue, as seen using amicroscope.(a) Explain how the cells labelled A areadapted to their function.
• large surface area ; increases diffusion ;• thin (wall) / single cell ; reduces diffusion distance ;• reference to surfactant ; stops adhesion ;• reference to capillaries ; maintains, diffusion / concentration gradient
An Overview of Respiratory Processes andPartial Pressures in RespirationPO2 and PCO2 arearbitrary units andfor comparison ofconcentration
Diffusion and respiratory functionGas exchange across respiratory membrane is efficient due to: • Differences in partial pressure (concentration gradients) • Small diffusion distance 6μm • Squamous epithelium • Lipid-soluble gases • Large surface area of all alveoli • ( be careful - Moist membrane – although this actually slows down gas diffusion) • Coordination between blood flow and airflow
Ventilation of the lungs• Movement of air depends upon • Pressure and volume - inverse relationship • Volume depends on movement of diaphragm and ribs to create changes in volume and so pressure Changes in pressure cause movement of air in/out
Mechanisms of breathing • Normal breathing involves the diaphragm muscle, the external and internal intercostal muscles • Forced breathing involves additional contractions of the Abdominal muscles • Inhalation • Diaphragm and External intercostal muscles contract • Volume in thorax increases • Pressure lowers • Air is drawn into lungs
Exam Question• 1. (a) State three characteristic features of gas exchange surfaces.• 1 …………………………………………………………………………………….• 2 …………………………………………………………………………………….• 3 ……………………………………………………………………………………. • (3)• (b) Describe how the process of inspiration (breathing in) takes place in mammals. • (3) (Total 6 marks)
Answers!• 1. (a) State three characteristic features of gas exchange surfaces.• large surface area;• thin lining;• (partially) permeable (lining);• covered by film of moisture. • (3 marks)• 3 Describe how the process of inspiration (breathing in) takes place in mammals.• contraction of diaphragm muscles lowers / flattens diaphragm; contraction of external intercostal muscles raises ribcage; volume of thorax / lungs increases thus intrapulmonic pressure falls / eq. reference to control by medulla / eq. • (3 marks) • [Total 6 marks]••
Spirometer – calculations of ventilation volume and rateNeeds calibrationfirst with knowvolumes of oxygen Chamber filled with oxygen Soda lime removes CO2 which may be harmful if repeatedly breathed in and allows volume of oxygen used to be established With nose clip!
Respiratory volumes• Alveolar volume -Amount of air reaching the alveoli each minute• Tidal Volume (VT) -Amount of air inhaled or exhaled with each breath• Vital capacity -Tidal volume plus expiratory and inspiratory reserve volumes• Residual volume -Air left in lungs after maximum exhalation
Respiratory volumes• Tidal Volume (VT) -Amount of air inhaled or exhaled with each breath. In normal Quiet breathing (male) 500cm3. • Alveolar volume -Amount of air reaching the alveoli each minute – 350cm3. (remaining is in trachea, bronchi etc and is called the dead air volume). Mixes with the air from previous inspiration and air undergone gaseous exchange – this keeps the oxygen level constant throughout the breathing cycle • Inspiratory/Expiratory Reserve volume When maximum breathing in (up to 2000cm3) Maximum breathing out (up to 1500cm3) Residue air (prevention of lung collapse 500cm3) • Vital capacity -Tidal volume plus expiratory and inspiratory reserve volumes (up to 400cm3)• Residual volume -Air left in lungs after maximum exhalation
Respiratory control and reflexes Respiratory centers – which control breathing rates- are modified by sensory information including: 1. Chemoreceptors from carotid arteries(from heart) -Level of carbon dioxide (partial pressures of CO2) cause increase of respiration rates. pH changes 1. Baroreceptors (blood pressure)in carotid arteries 2. Stretch receptors in Lungs which controls the Hering-Breuer reflexes -Prevents over-inflation and potential damage
Exercise Causes:Increased adrenalinIncrease in CO2 in bloodLowering of pHDetection by chemoreceptors in Carotid arteryStimulates breathing centres in MedullaMedulla Responses:Increase the frequency of impulses todiaphragm and intercostal muscles forincreased contraction/relaxation
Effect of Exercise on ventilation rate• Breaths per min increases• Ventilation rate increases• Tidal volume increases• Greater variation in volumes between inspiration and expiration• Decreases the inspiratory reserve volume as tidal volume increases
Before the race… Adrenaline Constriction of released skin and gut arterioles Glycogen Glucose gluconeogen -esis Dilation of Fatty acids muscle mobilised from arterioles fat stores …your system starts to prepare.
Anaerobic respiration Several minutes later… produces Lactate – this stimulates further dilation of Adrenaline dilates arterioles bronchioles Increased CO2 raises breathing Vo2 reaches and pulse rates Vo2max …you return to aerobic respiration and “get yoursecond wind”.
Effects of training on ventilation rate• Increase in tidal volume after exercise not as great• Increase in ventilation after exercise not as great• Faster return to normal breathing patterns• Respiratory muscles stronger (intercostal, diaphragm, abdominal muscles)• Alveolar capillary network increased
The Chemoreceptor Response to Changes in P CO2
Figure 23.24 Carbon Dioxide Transport inBlood Figure 23.24
Gas absorption/generation balanced by capillaryrates of delivery/removal• Homeostatic mechanisms maintain balance• Local regulation of gas transport and alveolar function include • Lung perfusion • Alveolar capillaries constrict in low oxygen • Alveolar ventilation • Bronchioles dilate in high carbon dioxiRespiratory Centers and Reflex Controls