Chapter 7 Exchange Surfaces and Breathing Flashcards
What is the need for exchange surfaces?
Diffusion isn’t enough alone to supply the needs of single celled organisms because - 1. Metabolic activity of single cell is low
2. SA:V of an organism is large.
How does SA:V change?
As organisms get bigger the surface area to volume ratio decreases.
What features of large organisms are specific for specialised exchange surfaces?
Increased surface area - gives the area needed to overcome the limits of low SA:V
Thin layers - less distance for substances to travel through
Good blood supply - keeps the concentration gradient is steep always
Ventilation to maintain diffusion gradient - helps maintain concentration gradient
The human gas exchange system explained
Mammals are big - small SA:V, large number of cells
also have a high metabolic rate
they need lots of oxygen for cellular respiration and they produce carbon dioxide which needs to be removed.
Exchange takes place in the lungs.
Nasal Cavity features and functions
large surface area with a good blood supply, which warms the air to body temperature
a hairy lining - secretes mucus to trap dust and bacteria
moist surfaces - increase the humidity of incoming air reducing evaporation from the exchange surfaces.
Trachea
The main airway - a wide tube supported by strong flexible cartilage, which stop it from collapsing. incomplete rings so food can move down oesophagous easily.
Trachea lined with ciliated epithelium with goblet cells. Cigarette smoke stops these cilia beating.
Bronchus
Similar structure to trachea but smaller.
They divide into two leading to each lung.
left bronchus and right bronchus.
Bonchioles
small with 1mm diameter. no cartilage
made of smooth muscle.
when smooth muscle contracts the bronchioles constrict.
This changes the amount of air reaching the lungs.
They have a thing layer of flattened epithelium making some gas exchange possible.
What are the alveoli
tiny air sacs.
0.2mm in diamter
has a layer of epithelial cells, along with some collagen and elastic fibres
elastic tissues allow it stretch when air is drawn in.
This is known as elastic recoil of the lungs
Adaptations of the alveoli
large surface area - 300 million alveoli per adult lung.
thin layers - one cell thick
good blood supply - keeps steep concentration gradient
good ventilation - breathing keeps high concentration gradient.
Ventilation
Ventilation is the movement of air caused by pressure changes in the lungs
What are the following:
- rib cage
- the diaphragm
- the external/ internal intercostal muscles
- the thorax
rib cage - provides a semi-rigid case
diaphragm - domed sheet muscle, forms the floor of the thorax
external / internal intercostal - found between the ribs
thorax - lined bey the pleural membranes, which surround the lungs.
pleural cavity is filled with a thin layer of lubricating fluid so membranes can slide over each other.
Inspiration
it is when you take in air or inhale and uses energy
the diaphragm contracts causing it to lower.
external intercostal muscles contract, moving the ribs upward and outward. the volume of the thorax increases, so pressure is reduced until it is lower than the pressure of the air. so air is drawn in through the nasal passages, trachea, bronchi, and bronchioles into the lungs. Equalises pressure.
Expiration
breathing out or exhaling - passive process.
diaphragm relaxes
external intercostal muscles relax
elastic fibres in alveoli return to normal length.
decreases the volume of the thorax.
pressure in thorax is greater than air, so air move out of the lungs until the pressure inside and out is equal again.
Forced expiration
uses energy
internal intercostal muscles contract, and abdominal muscles contract, diaphragm goes up increasing pressure in lungs rapidly.
