Human gas exchange system

• where does gas exchange occur in humans

  occurs in thorax
• structure of thorax 


  trachea

  lungs

  bronchi

  bronchioles

  Alveoli

  capillary network
• function of trachea 


  leads from mouth and nose to bronchi

  lined with mucus and goblet cells and cilia

  cilia sweeps microorganisms and dust away from lungs
• function of lungs 


  where gas exchange occurs in humans
• structure of bronchi 


  at bottom of trachea and lead into bronchioles
• structure of bronchioles 


  narrow tubes which carry air from bronchi to alveoli

  have no supporting cartilage so can collapse
• Structure of Alveoli 


  main site of gas exchange in lungs

  tiny sacs with thin walls large surface area to volume ratio for diffusion
• structure of capillary network 


  surrounds alveoli

  surface of gas exchange between lungs and blood

  oxygen diffuses from alveoli into capillaries

  carbon dioxide diffuses from capillaries into alveoli and exhaled
• function of cartilage 


  strong and flexible tissue , found in rings in trachea (tracheal rings )

  helps support trachea and ensures it stays open when flexing during breathing
• what is ciliated epithelium cells 


  specialised tissue found along trachea down to bronchi .

  Each cell has small projections of cilia which sweep mucus, dust and bacteria upwards and away from the lungs 
• what are goblet cells and how to they prevent microorganisms reaching lungs 


  mucus producing cells , secrete viscous mucus which traps dust bacteria and microorganisms from reaching lungs

  mucus sweat away by cilia from ciliated epithelium cells upwards and swallowed

  mucus then destroyed by acid in stomach
• Alveoli gas exchange adaptions 


  Thin lining of thin and squamous epithelium that allows for gas exchange .

  squamous epithelium very thin and permeable for easy diffusion
• smooth muscle adaptions


  found through walls of bronchi and bronchioles

  regulate ventilation

  dilates when air needed

  constricts when less air needed
• capillaries diffusion adaptations 


  diameter of 3-4um so only one cell thick for sufficient time and opportunity fir gas exchange
• Alveoli adaptions in lungs 


  large number of alveoli which increases surface area available for gas exchange

  Thin walls only one cell thick and cells flattened so creates short diffusion distance so gas exchange quicker

  surrounded by extensive capillary network that is one cell thick and flattened for short diffusion distance : constant blood flows maintains concentration gradient for gas exchange
• why is ventilation important for gas exchange 


  Helps ensure concentration gradient is maintained as it supplies new oxygen to alveoli and removes co2
• process of breathing in

  :external intercostal muscles contract and internal intercostal muscles relax

  :ribcage moves up and out

  :diaphragm contracts and flattens

  :Volume of thorax increases

  :pressure inside thorax/lungs decreases bellow atmospheric pressure

  :Air drawn in and moves down pressure gradient into lungs
• What is process of breathing out

  :External intercostal muscles relax

  :internal intercostal muscles contract pulling ribs down and back

  :Diaphragm relaxes and becomes dome shaped

  :volume of thorax decreases

  :abdominal muscles contract to push organs upwards on diaphragm to increase pressure

  :pressure inside thorax increases

  :air forced out of lungs
• What is breathing rate 


  Number of breaths per second
• what is pulmonary ventilation rate 


  volume of air breathed in or out in one minute
• calculation for pulmonary ventilation rate (PVR)


  PVR=tidal volume x breathing rate
• how can lung disease affect lungs

  can affect structure of alveolar walls for gas exchange and damage airways involved in ventilation
• How does lung cancer develop

  Mutations occur and cause uncontrolled mitosis of bronchial epithelial cells

  :tumour becomes larger no method of cell death and develops own blood supply (vascularisation)

  :tumour then interferes with lungs like squeezing blood vessels
• symptoms of lung cancer 


  Coughing up blood , persistent cough , wheezing , back and shoulder pain
• what is chronic obstructive pulmonary disease (COPD)

  a range off lung based diseases , such as chronic bronchitis and emphysema.

  : goblet cells in ciliates epithelium enlarge and produce excess mucus

  :damages cilia in trachea so increase pathogens in lungs

  :mucus has pathogens that can cause infections and narrow bronchioles

  :infection attracts phagocytes to the lungs and the phagocytes release elastase which damages alveolar walls

  :Without enough elastin, the alveoli break down and may burst. This creates large air spaces in the alveoli
• symptoms of COPD

  shortness of breath

  wheezing

  difficulty breathing
• how does smoking cause lung disease

  Tar: carcinogen that causes cancer and destroys cilia causing mucus build up which can lead to bronchitis

  Nicotine :narrows blood vessels

  carbon monoxide : reduces oxygen carrying capacity of blood
• how does tar damage alveoli

  merges alveoli together ,reducing surface area to volume ratio for gas exchange

  can also build up on alveoli increasing diffusion distance
• When was doll and hill study of smoking

  1951