9. Human Respiratory System Flashcards
Nostrils
Function
Entrance to respiratory tract
Nasal Cavity
Features and Functions
Function:
- Cleaning, moistening and warming the incoming air
Features:
- Hairs on walls of nostrils: filters dust and bacteria from the inhaled air
- Mucus-secreting cells/goblet cells: secrete mucus that traps dust and bacteria
- Blood capillaries: close to the surface of the cavity, warms inhaled air
Larynx
Function
Contains vocal cords
Trachea
Features and Functions
Supported by C-shaped rings of cartilage:
Prevent trachea from collapsing during breathing due to change in air pressure (keeps lumen of trachea open)
Bronchus, Bronchioles, Alveoli
Features
The trachea divides into two tubes, bronchi (plural of bronchus). Each bronchus divides into numerous fine tubes, bronchioles. Each bronchiole ends in a cluster of alveoli (singular: alveolus).
Inner walls of the trachea and bronchi
Features and Functions
The inner walls are lined with ciliated cells and gland cells.
- Gland cells secrete mucus that traps dust particles and bacteria
- Ciliated cells have hair-like structures, cilia, on their surface. They sweep the dust-trapped mucus up the bronchi and trachea away from the lungs into the pharynx, where they can be swallowed or expelled.
How is breathing achieved?
Breathing (ventilation) is achieved by changing the volume of the chest cavity and it is done by the movement of the ribs and diaphragm.
Movement of the ribs is controlled by the intercostal muscles.
Diaphragm
Structure and Function
Structure:
A sheet of muscular and elastic tissue, separates the thorax from the abdomen.
Function:
It contracts to expand the chest cavity and relaxes to allow the chest cavity to return to original volume.
What happens during inhalation?
During inhalation:
- The diaphragm contracts and flattens
- External intercostal muscles contract and internal intercostal muscles relax
- Ribcage moves upwards and outwards
- Lung expands, as volume of lung increases, air pressure within the lung decreases
- Air is drawn into lungs as air moves from higher atmospheric pressure to lower air pressure in lungs
What happens during exhalation?
During exhalation:
- The diaphragm relaxes and arches upwards (to form a dome shape)
- External intercostal muscles relax and internal intercostal muscles contract
- Ribcage moves downwards and inwards
- Lungs are compressed, as volume of lung decreases, air pressure within the lung increases
- Air is expelled out of lungs as air moves from higher air pressure in lungs to lower atmospheric pressure
Alveoli
Adaptations and Functions
- Alveolar walls are one-cell thick: Provide shorter distance for faster rate of diffusion of gases into the blood
- Each alveolus is covered with a thin film of moisture: Enable gases to dissolve, increasing rate of diffusion
- Each alveolus is surrounded by numerous blood capillaries: Blood capillarties transport diffused oxygen away from lungs and carbon dioxide from bloodstream to the lungs for removal. The continuous transport of gases maintains the concentration gradient of the gases for a faster rate of diffusion
- Alveoli present in large quantities: Provide a large surface area to volume ratio to increase rate of diffusion of gases
Oxygen transport from lungs
- Alveolar air contains a higher concentration of oxygen than blood
- Oxygen dissolves in the thin film of moisture on the surface of the alveoli
- Oxygen then diffuses through the walls of the alveoli and blood capillaries into blood, where it diffuses into the red blood cell
- Oxygen binds with haemoglobin in red blood cells to form oxyhaemoglobin (reaction is reversible, direction is dependent on conentration of oxygen in surroundings)
- When blood passes through oxygen-poor tissues, the oxyhaemoglobin releases oxygen which will then diffuse through the walls of the capillaries into the tissue cells
Carbon Dioxide Transport from the Body Cells
- Tissue cells produe a large amount of carbon dioxide as a result of aerobic respiration.
- As blood passes through these tissues, carbon dioxide diffuses into the blood. Most carbon dioxide enters the red blood cells. A small amount is carried in the plasma as dissolved carbon dioxide.
- The carbon dioxide then reacts with water in the cytoplasm of red blood cells to form carbonic acid(H2CO3). This reaction is catalysed by carbonic anhydrase (enzyme)
- Carbonic acid then dissociates to form hydrogen ions (H+) and hydrogencarbonate ions(HCO3-)
- Hydrogen ions remain in the red blood cells, while hydrogencarbonate ions diffuse out of the red blood cell to be carried in the plasma
Carbon Dioxide Transport at the Lungs
- Hydrogencarbonate ions diffuse back into the red blood cell and combine with hydrogen ions to form carbonic acid
- Carbonic anhydrase catalyse the conversion of carbonic acid to carbon dioxide and water
- Carbon dioxide diffuses out of the red blood cell, into the blood, through the capillaries and alveolar wall to be removed to the environment during exhalation.
Stimulus for breathing
Stimulus for breathing is a high concentration of carbon dioxide in the blood or alveolar air. When there is too little carbon dioxide in the lungs, breathing movements do not occur.
