Mammalian gas exchange & specialised exchange surfaces

• how is the size of an organism proportional to its SA:V ratio?

  the larger the organism, the smaller the SA:V ratio
• What are the formulae of a sphere?

  SA= 4πr^2

  Vol= 4/3πr^3
• what do organisms exchange?

  material with surroundings
• What's the amount of material that we take in proportional to?

  To its volume
• What's the amount of material it's able to exchange proportional to?

  To its SA
• Why is diffusion alone sufficient for exchanging materials in unicellular organisms (amoeba)?

  1. Metabolic activity is low 

  2. Has a large SA: V ratio 

  3. Diffusion distance is small
• What is necessary when an organism has a small SA:V ratio?

  Specialised systems for efficient exchange surfaces
• What are the specialised exchange surfaces? Why are they necessary?

  1. Increased surface- overcomes limitations of small SA:V in large organisms (e.g. root hairs and villi)

  2. Thin layers- shortens diffusion distance (e.g. alveoli and villi)

  3. Good blood supply- maintains steep concentration gradient for faster diffusion

  4. Ventilation- to maintain diffusion gradient (for efficient gas exchange)
• What is mass flow?

  the movement of large volumes of substances within the transport systems
• Why do multicellular organisms need diffusion?

  They rely on diffusion for:

  1.Gas exchange   

  2. Nutrients 

  3. Excretion
• What do mammals have?

  •small SA:V

  •large volume of cells

  •high metabolic rate

  •maintain body temperature
• What do mammals require?

  Lots of oxygen and quick removal of carbon dioxide
• What are adaptions of the respiratory system?

  • nasal cavity

  •trachea
• What are the features of the nasal cavity?

  •Large SA with rich blood supply (warm blood)

  •Hairy lining with mucus (protective as it traps bacteria and dust)

  • Moist surface( increased humidity to reduce evaporation)
• What are the features of the trachea?

  •incomplete rings of cartilage (C-shaped) to prevent collapse of lungs and for easy food passage down the oesophagus

  • ciliated epithelium (present in bronchioles and bronchus too) to waft mucus backwards to be swallowed and destroyed in the stomach acid

  • Goblet cells- they secrete mucus to trap bacteria and dust (protective) and remove anything that the nose hasn’t
• What is the structure of the lungs?

  •trachea branches into the two bronchi which are in the lungs. both are covered in a smooth muscle, which can contract and narrow its diameter.

  •bronchus branches into bronchioles, which have no cartilage, and where some gas exchange takes place

  • these branch into alveoli where gas exchange happens between oxygen and carbon dioxide
• What are the features of the alveoli?

  • thin flattened epithelium- collagen and elastic fibres (elastic recoil/ diffusion - to make sure they never collapse as they can stretch)

  •millions of alveoli to give a large SA

  •Rich blood supply to maintain concentration gradient

  •Good ventilation (for a steep diffusion gradient)

  •Lining - water, salts and lung surfactant (reduce water evaporation and keep inflated)

  •the lining of the alveolus is one cell thick (so is the capillary), this means gas exchange happens quickly as there is a small diffusion distance
• What is there a network of on the alveoli?

  A network of rich capillaries, they are thin (one cell thick) for efficient gas exchange) so maintains the concentration gradient
• why do alveoli have moist and permeable walls?

  To allow gases to pass through
• What happens at the alveoli?

  Oxygen diffuses from the alveoli to into red blood cells, ready to be carried around the body. Carbon dioxide diffuses out of the blood plasma and into the alveoli.
• Why do the lungs need to be stretched during inhalation?

  To allow for the expansion of the lungs and facilitate breathing
• What is the chemical that makes breathing possible in the lungs?

  Lung surfactant
• What role do phospholipid and hydrophillic proteins play in lung function?

  They prevent the alveoli from collapsing and sticking together during exhalation
• When do babies typically have lung surfactant already coated in their lungs?

  at the 30th week of pregnancy
• Why might premature babies struggle to breathe?

  They may not have developed lung surfactant
• What is done to help premature babies breathe if they lack lung surfactant?

  Artificial lung surfactants are sprayed into their lungs
• What would happen without lung surfactants?

  Breathing would be impossible
• Why is the first breath hard for a newborn?

  Because the lungs have never expanded before
• What must the infant overcome during their first breath?

  The elastic recoil of the lungs and the adhesion of the surfaces
• How do lung surfactants assist during the first breath?

  They prevent the alveoli from collapsing and sticking together
• What cells secrete lung surfactant?

  Alveolar cells
• What is ventilation?

  • Movement of air in and out of the lungs due to pressure changes in the thorax
• Why is ventilation necessary in animals?

  To maintain a concentration gradient in the alveoli, where oxygen diffuses into the blood, and carbon dioxide diffuses out.
• What is the pleural cavity?

  The pleural cavity is the space between the two layers of the pleura, a thin membrane that surrounds the lungs, and contains pleural fluid that helps to lubricate the lungs so that they do not rub against each other when they expand and stay in place.
• What is inspiration?

  Breathing in
• What is expiration?

  breathing out
• What happens in inspiration?

  •it uses energy (active process)

  •the diaphragm contracts (flattens and lowers)

  •the external intercostals contract, and the internal intercostals relax.

  •the ribs move up and out

  •the thoracic volume increases as the chest expands

  •the inside pressure is lower than atmospheric, so air enters the lungs
• What happens in expiration?

  •doesn’t use energy (passive process)

  •the diaphragm relaxes (it widens and goes higher)

  •the internal intercostals contract, the external intercostals relax.

  • the ribs move down and in

  •thoracic volume decreases as the chest contracts

  •inside pressure is higher than the atmospheric, so air exits the lungs
• What happens during asthma?

  • cells of bronchioles release histamine (cells are inflamed and swollen)

  •there is a lot of secretion of mucus inside the bronchioles, so the lumen becomes narrower as the cells are inflamed and swollen.

  •the smooth muscle contracts
• what is treatment for an asthma attack?

  •Relievers (bronchodilators- Ventolin/adrenaline)

  •These widen the lumen of the bronchioles