human gas exchange

• 1. as breathe in air enters trachea
  2. trachea splits into two bronchi-one bronchus lead to each lung
  3. each bronchus branch off into smaller tubes called bronchioles
  4. bronchioles end in small air sacs called alveoli
  5. ribcage, intercostal muscle and diaphragm work together and move air in and out

  A) nasal cavity

  B) pleural cavity

  C) intercostal muscle

  D) ribs

  E) diaphragm

  F) trachea

  G) lung

  H) bronchius

  I) bronchiole

  J) alveoli

  
• Gas exchange happens in thorax
• Lungs

  Supported by ribcage, moved by muscles
• Lungs ventilation

  Tidal stream of air constantly replenished
• cartilage


  strong and flexible tissue

  rings of cartilage in trachea: helps support and flex
• ciliated epithelium

  specialised tissue along trachea to bronchi

  sweeps mucus, dust, and bacteria upwards from lungs and epithelium
• goblet cells

  throughout ciliated epithelium in trachea

  mucus secreting cells- to trap dust and other microorganisms

  swept along cilia and swallowed

  then destroyed by acid in stomach
• smooth muscle

  in bronchi and bronchioles

  regulate air flow

  dilate to increase air flow

  constrict to decrease air flow
• capillary network


  surrounds alveoli for efficient gas exchange

  small lumen that is wide enough for one red blood cell to travel one at a time- ensures sufficient time and opportunity for gas exchange

  capillary is single cell thick- made of endothelium cells- for efficient gas exchange
• ventilation and gas exchange

  • consists of inspiration (breathing in) and expiration (breathing out)gas exchange in lungs require concentration gradient
  • ventilation(mass flow of gas) in lungs and continuous flow of blood in capillaries help ensure always a high concentration of oxygen in alveoli than in blood
  • exercise cause oxygen demand to increase which is facilitated by increased rate of diffusion
  • movements controlled by diaphragm, internal & external intercostal muscle and ribcage
• passage of air

  • nose/ mouth
  • trachea
  • bronchi
  • bronchioles
  • alveoli
• inspiration


  causes volume in chest to increase and air pressure in lungs to decrease

  air moves down pressure gradient and rushes into lungs

  mechanism at rest:

  • diaphragm contracts and flattens, increase chest volume

  mechanism when exercising

  • flattening diaphragm as well as external intercostal muscle contract, cause ribcage to move upwards and outwards
• inspiration mechanism

  • external intercostal and diaphragm contracts
  • causes ribcage to move upwards and outwards and diaphragm to flatten, increases volume of thoracic activity (space where lungs are)
  • as volume of thoracic activity increases, lung pressure decreases
  • air always flow from high pressure to low pressure, so air flows down trachea into lungs
  • inspiration is active process and require energy
• expiration

  at rest breathing occurs due to recoil of lungs after being stretched

  volume in chest decreases and pressure increases, cause air to be forced out

  mechanism at rest:

  • external intercostal muscles relax
  • recoil of elastic fibres surrounding alveoli cause air to be forced out
  • diaphragm relax

  mechanism when exercising

  • internal intercostal muscle contract which pulls ribs down and back
  • abdominal muscle contract and push organs upwards and outwards against diaphragm, increase internal pressure
  • causes forced exhalation
• expiration mechanism

  • external intercostal and diaphragm muscle relax
  • ribcage move down and inwards
  • volume of thoracic activity decrease, cause air pressure to increase
  • air forced down pressure gradient and out of lungs
  • normal expiration is passive process, no energy required
  • expiration can be forced (e.g. exercise)
  • external intercostal muscle relax and internal intercostal muscle contract, ribcage pulled further down and in. movement of two intercostal muscles is working antagonistically
• main types of intercostal muscles

  internal intercostal muscles: for expiration (where intercostal contracts)

  external intercostal muscles: for inspiration (where intercostal muscles contract)
• alveoli



  made of collagen and elastic fibres

  • elastic fibres allow stretch for when air enters so max amount of oxygen can flow into alveoli

  lined with epithelium cells

  • one cell thick for short diffusion pathway of oxygen to capillary or carbon dioxide from capillary

  many alveoli in lungs

  • for more gas exchange to occur- increase surface area available

  each surrounded by capillary network

  • efficient gas exchange from alveoli to blood
  • short diffusion pathway
  • maintains concentration gradient
• pulmonary ventilation rate (PVR)


  volume of air inspired per breath at rest is: tidal volume

  breathing rate: number of breaths taken per minute

  using results from spirometer trace can be created to show volume changes in lungs

  calculating PVR:

  • PVR: volume of air breathed in or out in one minute
  • calculated by:
  • PVR= tidal volume x breathing rate
• Lung disease


  Effects lungs function
• Lung disease


  • Can affect structure of alveolar walls and damage airways involved in ventilation
• Lung cancer


  Occurs if mutations affect regulation of mitosis in cells
• Lung cancer

  1. Mutation in oncogenes/ tumour-suppressor genes of epithelial cell

  2. Uncontrolled mitosis

  3. Develops in mass of cells in lumen of airways

  4. Tumour interferes with normal function of lungs

  5. May enter lymphatic system and develop another tumour
• Tumour

  • Larger than normal size
  • No programmed cell death
  • Survives and develops own blood supply (vascularisation)
• Symptoms of lung cancer

  • Coughing up blood
  • Persistent cough
  • Increased mucus
  • Back/shoulder pain
  • Wheezing and shortness of breath
• COPD


  chronic obstructive pulmonary disease- involves many lung- based diseases, e.g. chronic bronchitis and emphysema
• pulmonary tuberculosis- example of lung disease

  • infected with tuberculosis bacteria
  • tissues infected die and gaseous exchange surface damaged, tidal volume decreased
  • also causes fibrosis
  • reduced tidal volume- less air inhaled
  • symptoms: persistent cough, coughing up blood and mucus, chest pains, shortness of breath, and fatigue
• fibrosis- example of lung disease


  • formation of scar tissue in lungs- result in infection
  • scar tissue thicker and less elastic than normal lung tissue
  • lungs less able to expand and can't hold as much air as normal- tidal volume decreased
  • reduction in rate of gaseous exchange- diffusion slower across thicker scarred membrane
  • symptoms: shortness of breath, dry cough, chest pain, fatigue, weakness
• asthma- respiratory condition

  • airways become inflamed and irritated
  • asthma attack: smooth muscle lining bronchioles contract and large amount of mucus produced
  • cause constriction of airways, difficult for sufferer to breath, air flow reduced
  • symptoms: wheezing, tight chest, sortness of breath
  • can be relieved by inhalers which cause muscle in bronchioles to relax, opens up airways
• emphysema- lung disease

  • caused by smoking or long term exposure of air pollution- become trapped in alveoli
  • inflammation, attracts phagocytes to area, phagocytes produce enzyme that break elastin (protein in alveoli walls) down
  • loss of elastin= alveoli can't recoil to expel air
  • destruction= SA reduced rate of gaseous exchange decrease
  • symptoms: shortness of breath, wheezing