Respiratory system

1. Respiratory system Structure, function and disease

2. One system, Two Portions, Many Structures.... • Conductive Portion • Warms • Moistens • Filters • Respiratory Portion • Remove waste CO2 • Bring in O2

3. Branching... • Nasopharynx • Larynx • Trachea • Bronchi • Bronchioles • Terminal bronchioles

4. Nasopharynx(Upper respiratory passage) • Warming • Bony projections (conchae or turbinates) increase S.A and turbulence (also site for olfactory receptors) • Filtering • Hairs in the vestibules (in the nose!) trap large particles • (Pseudostratified columnar) ciliated epithelia and goblet cells line the interior – known as respiratory epithelium • Cilia beat 250x/minute • about 20 mins to push debris from anterior (front) nostril to the end of the nasopharynx

7. Lower Respiratory Passages • Larynx • Vocal role • Contain striated muscle and ligaments • Supported by cartilage • Trachea • 10-12cm long, around 2cm in diameter • Lined with respiratory epithelium • 16-20 C-shaped cartilages (hyaline cartilage) support

9. Still on trachea... • Epithelium + lamina propria = mucosa • Lamina propria contains loose connective tissue • Many elastic fibres • Underneath = submucosa • Connective tissue • Why is the trachea so elastic?

11. Bronchi (1 = bronchus) • The trachea BIFURCATES to form main bronchi • Structure is very similar to the trachea • Difference: layer of smooth muscle between cartilage and epithelium • Bronchi split into different lobes and different segments of the lungs • Diameter down to around 1mm

13. A = arteryB = bronchuscart = cartilage platesep = epitheliumSM = smooth muscle of muscularisTM = tunica media of artery

14. Bronchioles • Thicker smooth muscle than in bronchi (relatively) • No glands or cartilage

15. Respiratory section • Bronchioles divide into respiratory bronchioles • These form alveoli – most are flattened Type I • 5% are Type II – these secrete a phospholipid to reduce surface tension and prevent collapse • Distance between neighbouring alveoli = 2µm • Walls made up of epithelia and connective tissue with elastic fibres, which contain pulmonary capillaries • Alveoli have no cilia but do have alveolar machrophages • Inside the human body?

16. al = alveolic = capillariesSC = septal cell

17. Identify the cell types on the next slide. • Look at the proportions of each - can you work out which part of the respiratory system this slide was taken from?

19. Remember the tissues are 3D – they can be cut through any section and so may appear slightly different

20. Mechanism of Breathing • Each lung surrounded by a pleural cavity • Diaphragm at the bottom, rib cage around the sides • Breathing in – inspiration - makes the rib cage bigger, increasing the volume and decreasing the pressure relative to the outside • In order to equalise the pressure, air rushes into the lungs

21. Diaphragm: • Muscular, domed, convex above, squashed in the centre by the heart • Contracts = flattens, increasing the space above it • Relaxes = pushed up by abdominal contents • Ribs: • 12 pairs, top 7 pairs joined to vertebrae behind and sternum in front, next 5 joined to one another and last two are ‘floating’ • 2 sheets of intercostal muscles – internal and external • Contracting intercostals brings the ribs closer together

22. Regulation • Mostly involuntary but can be overidden • Chemoreceptors • Medulla • Increased CO2, panic reflex • O2 receptors in carotid arteries only kick in when profound hypoxia eg high altitudes

25. Spirometer • Reflects lung capacity at different points in the ventilation cycle • Consist of a chamber (approximately 6 dm3) suspended freely over water and counterbalanced so that gas passed in or drawn out makes the chamber rise or fall. • A permanent record of the movements of the chamber can be recorded by attaching a pen to it and allowing it to write on a drum revolving slowly (kymograph)

27. What can it show? • The volume of air that a human breathes into and out of their lungs while at rest is called the tidal volume. This is a relatively small volume of air (around 500 cm3) and provides enough oxygen for a human’s resting needs.

28. • The maximum amount of air that may be inspired, above tidal inspiration, is called the inspiratory reserve volume. The typical adult value is 2 to 3.2 dm3.• The maximum amount of air that can be breathed out, above tidal expiration is called the expiratory reserve volume. The typical adult value is 0.75 dm3 to 1 dm3.

29. The vital capacity is the sum of tidal volume, inspiratory reserve volume and expiratory reserve volume. Total lung capacity can be estimated by multiplying the expiratory reserve volume by 6; residual volume can be calculated by subtracting vital capacity from total capacity

33. Images used in this powerpoint have been taken from: • http://www.courseweb.uottawa.ca/medicine-histology/Default_En.htm • http://www.lab.anhb.uwa.edu.au/mb140/Big/Big.htm • http://www.emptynosesyndrome.org/ • http://www.teachpe.com/anatomy/respiratory_system.php

34. Lung disease • Fibrosis, asthma and emphysema • All these conditions affect the efficiency of gas exchange at the alveoli

35. Pulmonary fibrosis • Fibrous tissue grows and divides the lung into separate spaces • This is known as “honeycomb lung” • No-one knows what exactly causes this • It’s possibly a reaction to microscopic lung injuries to which some people are more genetically susceptible • (what might cause “microscopic lung injury”?)

36. The consequences of PF • The lung epithelium becomes scarred and thickened • So oxygen cannot diffuse efficiently into the blood • The diffusion pathway has lengthened considerably • The volume of air that the lungs can contain is reduced • The lungs lose their elasticity

37. The symptoms of PF • What do you predict the symptoms to be? • Shortness of breath, especially during exercise • Chronic dry cough – the fibrous tissue obstructs the airway but nothing is expelled • Chest pain – Due to pressure from the fibrous tissue and further damage due to coughing • Weakness and fatigue – Due to reduced oxygen intake

38. Asthma • The EM shows dust and pollen particles on the ciliated epithelium of the lungs • Asthma is an allergic reaction to these and similar particles • These are called allergens

39. Asthma Allergens • Dust mite faeces • Pollen • Animal fur • Also asthma triggered/made worse by… • Air pollutants • Exercise • Cold air • Infection • Anxiety and stress

40. The effect of allergens • White blood cells on the lining of the bronchi and bronchioles release histamine • Histamine has the following effects: • The lining of the airways becomes inflamed • Large amounts of mucus are secreted • Fluid leaves the capillaries and enters the airways • Muscles in the bronchioles contract and constrict the airway

41. The consequences of histamine release • The above cause resistance to air flow in and out of the lungs • This makes it difficult to maintain a diffusion gradient across the respiratory membranes

42. Asthma symptoms • What do you think the symptoms may be? • Difficulty breathing • Wheezing when breathing – due to the constriction of the tubes • Tightness in the chest – due to inability to ventilate the lungs properly • Coughing – in response to obstruction

43. Susceptibility to asthma • The reasons why some people are more susceptible than others are complex and unclear • The incidence of asthma is increasing (USA data shown)

44. Why the increase? • Asthma tends to run in families (genetic) • Increased air pollution? • Increased stress of modern living? • Increased variety of chemicals in food and manufactured products? • “Cleaner” lifestyles do not expose children to as many antigens and so do not develop resistance?

45. Emphysema • Emphysema develops in 1 in 5 smokers • It can develop over 20 years • This makes it difficult to diagnose until the lungs are irreversibly damaged

46. What are the effects? • Healthy lungs are springy • They contain elastic tissue made from the protein elastin • In emphysema, the elastin has become permanently stretched • The lungs cannot force all the air out of the alveoli when we exhale

47. Alveoli in an emphysematous lung • The surface area of the alveoli becomes reduced • Sometimes they burst • So little or no gaseous exchange takes place

48. Symptoms of emphysema • Shortness of breath – due to reduced elasticity and reduced surface area • Chronic cough – damaged tissue and mucus are difficult to remove because the ciliated epithelium has been destroyed • Bluish skin colouration – due to low oxygen levels (the next slide contains an upsetting image)

49. Treatment • None • Lung function cannot be restored and the damage is permanent • However, giving up smoking significantly reduces the rate of further deterioration