Gas exchange: in humans

Why have humans evolved to have a specialised gas exchange mechanism?

- smaller SA:VOL
- higher metabollic rate

State features needed for an efficient gas exchange mechanism?

- thin: diffusion paths are short
- permeable: for respiratory gases
- moist: easier diffusion of gases — humans have internal respiratory system to minimise loss of water and heat
- large SA: faster rate of diffusion (millions of alveoli)
- extensive capillary network: rapid diffusion and for transport to maintain diffusion gradient

Why does the trachea have cartilage?

- to prevent trachea from collapsing
- to keep air in

Why does the trachea have C-shaped cartilage?

- to allow oesophagus to expand while swallowing - peristalsis

What is the ciliated epithelium?

- the layer of cells (ciliated cells and goblet cells) that line the trachea and bronchi

Describe the process that helps clean out our lungs?

- goblet cells secrete mucus that traps dust, bacteria etc
- mucus is swept upwards to the mouth by cilia of the ciliated epithelial cells

Describe mucus?

- slimy material rich in glycoproteins
- if an irritating substance is breathed in this can stimulate a sneeze

Where are goblet cells found?

- membranes of nasal cavity and ciliated epithelium

Describe purpose of ventilation?

- taking in oxygen for diffusion
- maintains constant concentration gradient

Explain features of alveoli?

- millions: large SA
- lined with moisture: gases can dissolve
- thin walls: short diffusion distance
- extensive capillary network: rapid diffusion & maintain gradient
- have surfactant: reduces surface tension and prevents the laveoli collapsing during exhalation/ sticking together

What is surfactant?

- substance containing phospholipids and proteins
- produced by alveolar walls
- reduces surface tension of liquid lining alveoli. Means wet walls are less likely to stick together/collapse when we exhale

What is the disease caused by lack of surfactant production?

- respiratory distress syndrome
- premature babies

What is respiratory distress syndome? How is it treated?

- premature babies who havent yet started to produce sufficient amounts surfactant
- either needs ventilator or artificial surfactant administered (reduces time on ventilator)

Describe the process of inhalation?

- external intercostal muscles contract
- rib cage moves up and out
- outer pleural membrane is pulled out
- reduces pressure in pleural cavity and inner pleural membrane moves outwards
- pulls on surface of lungs and causes alveoli to expand
- diaphragm contracts and moves downwards & diaphragm pushes digestive organs down
- volume of thoracic cavity increases
- alveolar pressure decreases to below atm and air is drawn into lungs

Describe the process of exhalation?

- opposite of inhalation

Name the piece of equipment used to monitor lung function?

- Spirometer

Explain the method used by the two different spirometers?

— one: air filled chamber suspended over water, lid rises and falls, pen goes up in exhalation and down in inhalation. Soda lime filter to absorb CO2.
- pulley moves down when exhaling so pen moves down and pen moves up when inhaling

What is tidal volume?

- air breathed at rest

What is expiratory reserve volume?

- Amount of air that can be forcefully exhaled after a normal tidal volume exhalation (max exhalation - tidal vol)

What is inspiratory reserve volume?

- Amount of air that can be forcefully inhaled after a normal tidal volume inhalation (max inhalation - tidal vol)

What is vital capacity?

- max air that can be inhaled and exhaled (tidal vol + inspiratory reserve + expiratory reserve)

Why would alveolar air composition be different to both inhaled or exhaled air?

- there is always residual air in the alveoli that you cannot breath out

What is total lung capacity?

- residual air + vital capacity

How do you calculate ventilation rate?

- tidal volume * number of breaths/min

Name the cause of asthma?

- allergic reaction to allergens such as dust/animal hair/smoke

State the symptoms of asthma?

- difficulty breathing, wheezing

Explain the symptoms of asthma?

- muscle spasm/contraction caused by allergens causes bronchioles to constrict narrowing air ways
- also inflammation of bronchioles
- mucus membranes usually become irritated and secrete excess mucus worsening the attack

State and explain the treatment of asthma?

- bronchodilators cause muscles to relax to widen airways
- steroids reduce inflammation

State and explain the cause of emphysema?

- smoking stimulates white blood cells to release protein digesting enzymes that gradually break down the walls of alveoli leaving large open spaces
- loss of elasticity reduces ability of lungs to recoil after breathing in and so air cannot be forced out of alveoli effectively
- surface area of alveoli is reduced and sometimes they burst (reducing rate of diffusion/gas exchange)

State and explain the symptoms of emphysema?

- irreversible damage to alveoli
shortness of breath:
- loss of elasticity - ventilating lungs and exhaling is more difficult so harder to maintain diffusion gradient
- smaller SA results in lower levels of O2 so patient tries to breath faster
Chronic cough:
- reflex action to remove damaged tissue and mucus
Cyanosis (blueish skin):
- reduced intake of O2 into blood due to less efficient gas exchange

Describe spirometer traces of someone with emphysema and someone with asthma compared to a normal person?

- emphysema: increased breaths per minute and smaller tidal volume
- asthma: smaller tidal volume

What is the eppiglottis?

- Flap of skin that stops food entering the trachea when swallowing