Human Breathing

Nose

Air can be taken in through the mouth (buccal cavity) or the nose.

The nose: Breathing in through the nose is beneficial because:

The nose: Breathing in through the nose is beneficial because: (1) The air is filtered by the hairs and the mucous in the nose.

The nose: Breathing in through the nose is beneficial because: The air is filtered by the hairs and the mucous in the nose. It is moistened.

The nose: Breathing in through the nose is beneficial because: The air is filtered by the hairs and the mucous in the nose. It is moistened. It is warmed as it passes across the nasal passages.

These 3 things make it easier for the air to diffuse from the lungs into the bloodstream.

Warm, moist air diffuses easier!!

The pharynx:

Pharynx is the part of the throat that begins from behind the nose to the beginning of the voice box and the oesophagus.

It is a common channel that both air and food pass through. Because of these two functions, the pharynx must open to allow air and food to pass through.

Epiglottis: Because of the need to swallow and breathe there is a flap of tissue called the epiglottis which closes off the trachea when your swallowing and closes off the oesophagus when breathing.

                                                                            

Thererfore when breathing this prevents food and drink entering the trachea (windpipe).

Larynx:

Contains two vocal cords. These vibrate when we force air across them. The vibrations produce sound which our tongue and lips convert to speech.

Area of the windpipe containing the larynx is called the glottis.

Trachea: The trachea, bronchi and bronchioles are all made of muscle and elastic fibres and incomplete rings of cartilage. Rings of cartilage prevents tubes from collapsing as air is drawn in.

Trachea  bronchi  bronchioles. Bronchioles become narrow during an asthma attack.

Cilia: Sticky. Beat  create an upward current. Moves the mucus into the oesophagus  to the stomach. Clearing our throats  force mucus up and away from the vocal cords.

All of these air pipes are lined with mucous secreting cells and tiny hairs called cilia.

These trap particles such as dust, bacteria and viruses.

Lungs: Large spongy structures. Where gaseous exchange takes place. Each lung is surrounded by the pleural membrane. The outer pleura lines the chest wall and diaphragm. The inner pleura lines the lungs.

The gap between these 2 membranes is the pleural cavity and it is full of liquid. This liquid lubricates the membranes and reduces friction during breathing.

Alveoli: Each bronchus divides into about a million bronchioles. These end in hollow, balloon-like air sacs called alveoli (or alveolus). 700 million alveoli in the 2 lungs.  Very large surface area for gas exchange = tennis court

Each alveolus is 1 cell thick. Moist. Enclosed in a network of blood cappilaries (like the villi).  When the gases are exchanged they only have to pass through the alveoli membrane and the capillary wall.

Function of the alveoli: Gas exchange.

Gas exchange: Respiration happens in cells to supply energy. Body cells use up oxygen and produce carbon dioxide and water. Eqn: C6H12O6 + 6O2 --- 6CO2 + 6H2O + energy. Enzymes

Gaseous exchange = diffusion!!! CO2 and H2O diffuse out of cells and into the blood because the cytoplasm has a high conc of CO2 and H2O compared with the blood. In the lungs, CO2 and H2O diffuse out of the blood into the alveoli  from ↑ conc to ↓ conc.

Diffusion is: the movement from a high conc to a low conc. In the same way, O2 diffuses from the alveoli into the blood and then from the blood into body cells. Exhalation: body cells  CO2  plasma (in blood)  alveolus  exhale. Inhalation: O2 from air  alveolus  blood  body cells.

Transport of gases: (1). O2 is mostly carried by haemoglobin (97%) + 3% carried in the plasma. (2). CO2 is dissolved in plasma and carried in blood. H2O is carried in plasma.

Inhaled v’s Exhaled air:

Mechanism of breathing: Normally involuntary. At rest: 15 times per minute. In: inhalation/inspiration. Out: exhalation/expiration.

The process: Medulla oblongata in the brain controls the rate of breathing. It sends a message to the diaphragm and intercostal muscles. Muscles contract = active process.

(1) Ribs pull up and out/ Diaphragm moves down. Inhalation. (1) Ribs pull up and out/ Diaphragm moves down. Pressure in the chest cavity falls. Internal air pressure is now higher than the pressure of air in the chest. Air is forced into the lungs = inhalation.

(2) Intercostal muscles and diaphragm relax. Exhalation. (2) Intercostal muscles and diaphragm relax. Ribs move down and in/ Diaphragm moves up. The volume of the chest cavity decreasesd. Thoracic pressure increases. Air is forced out = exhalation.

Note: Exhalation is said to be passive because the muscles only have to relax.  Nervous control is not needed.

Effect of exercise on the rate of breathing: Respiration is using food to make energy. Therefore, exercise ↑ the rate of respiration, esp in muscle cells (↑ energy is needed so respiration ↑). During exercise: The medulla oblongata detects the ↑ level of exercise and therefore ↑ the rate of breathing. Exhalation is normally passive becomes active during exercise. Extra muscles are used to ↑ the depth of breathing.

Asthma. Breathing disorder. Symptoms: -Narrowing of the bronchioles in the lungs. Appearance: -Noisy, wheezy breathing and a feeling of breathlessness.

Cause: Not clear. May be triggered by inhaled allergens. -pollen. -animal dander. -dust and dust mites. -lung infections. -exercise. -stress. -anxiety.

Incidence: 10% of children. Incidence is rising in developed countries. Around half of children affected grow out of it.

Prevention: Identifying and avoiding those allergens. Tests can be taken to identify the allergens.

Treatment: Inhalers:  Drugs that widen the bronchioles to make it easier to breathe. Injection:  In severe cases.

Control of breathing: Respiratory centres in the medulla oblongata. Monitor levels of CO2 in the blood and tissue fluid. CO2 is slightly acidic  it causes the pH to drop slightly.

These respiratory centres detect this drop and react by sending out impulses to the diaphragm and intercostal muscles to help us breathe. Exercise increases CO2 in blood.

We breathe in response to high CO2 not low O2!