Gaseous Exchange
Gaseous exchange and the respiratory system
- Created by: WinchesterD
- Created on: 12-12-14 00:02
Gaseous Exchange
Gaseous exchange refers to the exchange of respiratory gases between the cells of the organsim and the environment.
Animals and plants respire aerobically - oxygen is taken in and CO2 is produced as a waste product
The respiratory surface is the area where gas exchange takes place e.g. alveoli of the lungs in humans
Gaseous exchange takes place by diffusion
Ideal respiratory surface:
- permeable; so gases can pass through
- thin; diffusion is only effective over very short distances (short diffusion pathway)
- large surface area to volume ratio; so sufficient volumes of gases can be exchanged
- have an extensive capillary network; to maintain a steep diffusion gradient across the respiratory surface (keeps removing oxygen to maintain a concentration gradient)
A given volume of air has more oxygen than an equal volume of water
There are specialised respiratory structures in larger animals as their surface area to volume ratio decreases
A respiratory pigment in the blood further increases oxygen carrying capacity e.g. haemoglobin
Respiratory System
Make sure you can label these on a diagram
note: '*' means must learn!!
- nasal cavity
- pharynx
- epiglottis
- larynx
- *trachea
- Rib
- *intercostal muscle
- *bronchiole
- pleural membranes
- *right lung
- *diaphragm
- *oesophagus
- *cartilage of the trachea
- *bronchus
- *left lung
- *heart
Squamous and Ciliated Epithelium
Squamous Epithelium
- very flat, thin cells
- capillaries and alveoli are lined with squamous epithelium giving a short diffusion pathway
Ciliated Epithelium
- found in the trachea
- waft mucus away from the lungs wih trapped dust and bacteria (to be coughed up or swallowed)
Gas Exchange in Humans
1. Air passes along the following structures:
- Nasal passages to throat (pharynx/larynx) to trachea, to bronchi, to bronchioles, to the alveoli of the lungs
2. Trachea:
- C-shaped ring of cartilage prevents trachea collapsing during ventilation and for the oesophagus to expand as food is swallowed
- Epiglottis (flap of cartilage) closes over the trachea when we swallow
- Lined with ciliated epithelium and goblet cells -> goblet cells produce mucus which traps bacteria and dust particles; ciliated epithelium sweeps mucus to the throat
3. Bronchi:
- Trachea branches into two bronchi which then branch into bronchioles
- Bronchi and bronchioles have cartilage, smallers ones have only muscle and elastic tissue
note: muscle tissue expands and contracts; elastic tissue stretches and recoils.
This allows the tubes to expand and contract during ventilation
Gas Exchange in Humans Cont.
4. Alveoli:
- Smallest bronchioles end in clusters of hollow air sacs called alveoli
- Alveoli are lined with squamous epithelium and collectively form the gas exchange surface; covering a huge surface area
- Between the alveoli and capillaries is a very thin layer of tissue fluid containing elastin (elastic fibres) which allows them to stretch as they fill with air and recoil
- Also contain collagen (fibrous protein)
- The alveoli are covered in an extensive capillary network which have very thin walls (one cell thick) -> red blood cells are slowed as they pass through the capillaries allowing a greater time for uptake of oxygen (diffusion); red blood cells are squeezed through to present more of their surface area
Overview of alveoli key features:
- large surface area for increased diffusion
- thin wall of alveoli and capillaries (short diffusion pathway)
- Blood flow from extensive capillary network maintains steep diffusion gradient
Gas Exchange in Humans Cont.
5. Mechanism of Ventilation:
- Structures involved - external intercostal muscles (slant forwards and downwards); internal intercostal muscles (slant backwards and downwards); diaphragm (circular and radial muscles)
- Inspiration (Active process)
- External intercostals contract (internal intercostals relax)
- Rib cage moves forwards and outwards
- Diaphragm muscles contract and flatten (pulls down)
- Pressue inside decreases; volume of thorax increases
- Air rushes in to equalise the pressure
- Expiration (Passive process)
- Largely due to elastic recoil of lung tissue and respiratory muscles
- External intercostals relax (internal intercostals contract)
- Diaphragm muscles relax
- Volume of thorax reduced; pressure inside increases
- Air forced out of lungs
Pulmonary ventilation = tidal volume (dm^3) x ventilation rate (min^-1)
Ventilation rate = the number of breaths in one minute
Tidal volume = the volume of air breathed in and out at rest (approx 0.5 dm^3)
Related discussions on The Student Room
- Dee’s A*AA Journey »
- A-level chem enthalpy question »
- a question about respiration »
- What is DNA repair »
- OCR BIOLOGY PAPER 3 Predictions? »
- Electrospray Ionisation A level »
- Help! I have no idea of what career I want do do! »
- Chemistry question- enthalpy of formation »
- The movement of substances within living organisms. »
- enthalpy change of solution »
Comments
No comments have yet been made