3.1.1c Mammalian Respiratory System Flashcards
See images for labelling human gaseous exchange system
(slides, pg72)
How do gaseous exchange surfaces aid land animals that face a continual conflict between need for gaseous exchange & water
- Gaseous exchange surfaces are moist, so oxygen dissolves in the water before diffusing into the body tissues.
- As a result, the conditions needed to take in oxygen successfully are also ideal for the evaporation of water
In what ways have mammals evolved complex exchange systems
They have evolved complex systems that allow them to exchange gases efficiently but minimise the amount of water lost from the body
SA:V ratio of mammals?
Mammals are relatively big, so have a small SA:V ratio & a very large volume of cells
Do mammals have a high metabolic rate
Yes, mammals have a high metabolic rate bc they are active & maintain their body temp independent of their environment.
As a result, they need lots of oxygen for cellular respiration & they produce CO2, which needs to be removed.
What is the nasal cavity (human exchange system)
- Has a large SA & good blood supply, which warms the air to body temp
- A hairy lining, which secretes mucus to trap dust & bacteria, protecting delicate lung tissue from infection
- Moist surfaces, which increase the humidity of the incoming air, reducing evaporation from the exchange surfaces
What is the Trachea
- The main airway carrying clean, warm, moist air from the nose down into the chest
- A wide tube supported by incomplete rings of strong, flexible cartilage, which stops the trachea from collapsing
- The rings are incomplete so that food can move easily down the oesophagus behind the trachea
Structure of the Trachea
- The trachea & its branches are lined w a ciliated epithelium with goblet cells between & below the epithelial cells
- Goblet cells secrete mucus onto the lining of the trachea, to trap dust & microorganisms that have escaped w nose lining.
- The cilia beat & move the mucus, along w any trapped dirt & microorganisms, away from the lungs. Most of it goes into the throat & is swallowed & digested.
(One of the effects of cigarette smoke is that it stops these cilia beating)
see images for diagram of trachea
What is the Bronchus
In the chest cavity, the trachea divides to form the left bronchus (plural bronchi), leading to the left lung, and the right bronchus leading to the right lung.
- They are similar in structure to the trachea, w the same supporting rings of cartilage, but they are smaller
What are Bronchioles
- In the lungs, the bronchi divide to form many small bronchioles.
- The smaller bronchioles (dia 1mm or less) have no cartilage rings
- The walls of the bronchioles contain smooth muscle, which contracts causing the bronchioles to constrict (close up). When it relaxes, the bronchioles dilate (open up). This changes the amount of air reaching the lungs
- Lined w a thin layer of flattened epithelium, making some gaseous exchange possible
What is the Alveoli (singular Alveolus)
- Tiny air sacs (200-300pm dia), which are the main gas exchange surface of the body.
- Consist of a layer of thin, flattened epithelial cells, along w some collagen & elastic fibres. (allowing the alveoli to stretch as air is drawn in, and recoil to aid exhalation). When they return to their resting size, they help squeeze the air out. This is known as the ‘elastic recoil’ of the lungs
see diagram of gaseous exchange within an alveolus in images
Main adaptations of the Alveoli for effective gaseous exchange
- Large SA
- Thin layers
- Good blood supply
- Good ventilation
- Moist
- Short diffusion pathway
How does a large SA allow effective gaseous exchange in Alveoli
There are 300-500 million alveoli per adult lung. The alveolar SA for gaseous exchange in the two lungs combined is 50-75m^2. A large SA provides a large enough space for the amount of oxygen needed to diffuse into the body
How do thin layers allow effective gaseous exchange in Alveoli
Both the alveoli & the capillaries surrounding them have walls that are only a single epithelial cell thick, so the diffusion distances between the air in the alveolus & the blood in the capillaries are very short
There is a short diffusion pathway due to the walls of the alveoli being one cell thick & flattened (squamous)
How does good blood supply allow effective gaseous exchange in Alveoli
The millions of alveoli in each lung are supplied by a network of around 280mil capillaries.
The constant flow of blood through these capillaries brings CO2 & carries off oxygen, maintaining a steep concentration gradient for both CO2 & oxygen between the air in the alveoli & the blood in capillaries
How does good ventilation allow effective gaseous exchange in Alveoli
Alveoli are ventilated, allowing effective delivery & removal of oxygen (inhalation) and CO2 (exhalation). This leads to a steep concentration gradient –> increased diffusion
What is lung surfactant
The inner surface of the alveoli is covered in a thin layer of a solution of water, salts & lung surfactant. It is this surfactant that makes it possible for the alveoli to remain inflated.
What is ventilation
Air is moved in & out of the lungs as a result of pressure changes in the thorax (chest cavity) brought abt by the breathing movements. This movement of air is called ventilation
Purpose of the ribcage
Provides a semi-rigid case within which pressure can be lowered w respect to the air outside it
What is the diaphragm
A broad, domed sheet of muscle, which forms the floor of the thorax.
Where are the external & internal intercostal muscles
The external intercostal muscles & the internal intercostal muscles are found between the ribs
What is the thorax lined by
The thorax is lined by the pleural membranes, which surround the lungs. The space between them (the pleural cavity) is usually filled w a thin layer of lubricating fluid so the membranes slide easily over each other as you breathe
What is Inspiration
Taking air in or inhalation. It is an energy-using process
Process of Inspiration
The diaphragm contracts, flattening & lowering.
The external intercostal muscles contract, moving the ribs upwards & outwards.
The volume of the thorax increases so the pressure in the thorax is reduced.
It is now lower than the pressure of the atmospheric air, so air is drawn through the nasal passages, trachea, bronchi & bronchioles into the lungs. This equalises the pressures inside & outside the chest
What is Expiration
Breathing out or exhalation. It is a passive process
Process of Expiration
The muscles of the diaphragm relax so it moves up into its resting domed shape.
The external intercostal muscles relax so the ribs move down & inwards under gravity.
The elastic fibres in the alveoli of the lungs return to their normal length.
The effect of all these changes is to decrease the volume of the thorax. Now the pressure inside the thorax is greater than the pressure of the atmospheric air, so air moves out of the lungs until the pressure inside & out is equal again
see images for inspiration & expiration of lungs
What are some everyday triggers to ppl w asthma
House dust mites, cigarette smoke, pollen, stress
What happens during an asthma attack
The cells lining the bronchioles release histamines, chemicals that make the epithelial cells become inflamed & swollen. Histamines stimulate the goblet cells to make excess mucus, and the smooth muscle in the bronchiole walls to contract. As a result, the airways narrow & fill w mucus, making it difficult to breathe
Is there medicine for asthma
Asthma medicines have been developed to reduce symptoms or prevent attacks.
The drugs are delivered straight into the breathing system using an inhaler
2 main ways to treat asthma
Relievers - give immediate relief from symptoms. They are chemicals similar to the hormone adrenaline. They attach to active sites on the surface membranes of smooth muscle cells in the bronchioles, making them relax & dilating the airways
Preventers - often steroids, taken everyday to reduce sensitivity of the lining of the airways
What is special about the first breath of a newborn
This requires a force 15-20 times greater than normal inhalation to inflate the lungs.
The lungs are enormously stretched as the air flows in, & the elastic tissue near returns to its go length.
What makes the first breath of a newborn possible
The intake of breath is only possible bc of special chemicals called lung surfactants containing phospholipids & both hydrophilic & hydrophobic proteins. The surfactant stops the alveoli collapsing & sticking tg as the baby exhales
One reason why premature babies struggle to breathe and die
Babies born at full term have alveoli coated in lung surfactant all ready for breathing.
However, the cells of the alveoli do not produce enough surfactant for the lungs to work properly until around the 30th week of pregnancy
What is being done in recent yrs to make breathing easier, help prevent lung damage & enable more babies to survive
Artificial lung surfactants have been produced. A tiny amount sprayed into the lungs of a premature baby coats the alveoli just like the natural surfactant, making breathing easier, help prevent lung damage & enable more babies to survive
How does the inside of an alveoli being moist allow effective gas exchange
The inside lining of the alveoli is moist, meaning oxygen can dissolve into the solution and dissolve more easily. It also contains a surfactant
How does a short diffusion pathway in alveoli allow effective gas exchange
The cells of the capillaries & the alveolus are connected. The capillary wall & alveolar wall are next to eachother therefore a short diffusion pathway
What is significant about the lumen of the capillary to the alveoli
The lumen of the capillary is abt the same diameter of the alveolar itself
Where is smooth muscle found
In the Trachea, Bronchi, Bronchioles
What does smooth muscle do
Able to CONTRACT, therefore causing airways to CONSTRICT
Where are elastic fibres found
In the alveoli
What do elastic fibres do
They STRETCH (preventing from bursting), and RECOIL (helps forcing air out in exhalation)
Structures in the gaseous exchange system
- Goblet cells
- Cilia
- Elastic fibres
- Smooth muscle
- Rings of cartilage
Structures in the gaseous exchange system: Goblet cells
Where?: lining the airways
- secrete mucus
- The mucus traps microorganisms & dust particles in the inhaled air, stopping them from reaching the alveoli
Structures in the gaseous exchange system: Cilia
Where?: on the surface of cells lining the airways
- Beat the mucus
- This moves the mucus (plus the trapped microorganisms & dust) upward away from the alveoli towards the throat, where its swallowed
- This helps prevent lung infections
Structures in the gaseous exchange system: Elastic fibres
Where?: in the walls of the trachea, bronchi, bronchioles & alveoli
- Help the process of breathing out
- When breathing in, the lungs inflate & the elastic fibres are stretched
- Then, the fibres recoil to help push the air out when exhaling
Structures in the gaseous exchange system: Smooth muscle
Where?: in the walls of the trachea, bronchi & bronchioles
- Allows their diameter to be controlled
- During exercise the smooth muscle relaxes, making the tubes wider.
- This means theres less resistance to airflow & air can move in & out of the lungs more easily
Structures in the gaseous exchange system: Rings of cartilage
Where?: in walls of the trachea & bronchi
- Provide support
- Its strong but flexible - stops the trachea & bronchi from collapsing when you breathe in & the pressure drops
Structures in the gaseous exchange system: Ciliated epithelium
Wafts the mucus & microorganisms up the trachea to the throat, to be swallowed & digested
SEE PG73 FOR TABLE OF PARTS OF LUNGS + COMPONENTS
