Human Breathing

Chapter 31

Human Respiratory System:Human Respiratory System:

• Consists of a pair of lungs and a series of tubes

• Lungs located in the thorax (chest)

• Diaphragm (sheet of muscle) forms the floor of the thorax

• Ribs (protective cage) and intercostal muscles (attached between ribs) form the walls of the thorax

Parts of the Respiratory System:Parts of the Respiratory System:PART FUNCTION

Nostrils Allows air to enter the nose

Nose Warms, filters & moistens air

Pharynx (throat) Connects nose & mouth to larynx

Epiglottis Found in pharynxStops food/drink entering trachea (windpipe)

Glottis Opening to larynx

Larynx (Vociebox)

Contains vocal cords

Trachea ( windpipe)

Allows air to pass to lungs*Made of muscle & elastic fibres with incomplete rings of cartilage

Cartilage Strong material which keeps trachea and bronchi open

Bronchi Transport air from trachea into lungs

Bronchiole About 1 million per lungTransport air into the alveoli

Alveoli Thin walled, moist, surrounded by capillaries.Site of gas exchange, provides a large surface area (700 million in 2 lungs) for gaseous exchange

Lung Takes in O2 and gets rid of CO2

Pleural membranes

Allow friction free movement of lungs

Diffusion is the movement of molecules from a region of high concentration to a region of lower concentration

Remember:Gas ExchangeGas Exchange

Gas Exchange in an AlveolusGas Exchange in an Alveolus

Air enters the nose travels down the windpipe, the bronchus, and the bronchioles to the alveoli

Oxygen diffuses from the alveoli to the red blood cells in the blood.

At the same time carbon dioxide and water vapour diffuse from the blood (plasma) to the alveoli

Note: in both cases CO2 and O2 are moving from areas of high concentration to low concentration.

Gas Exchange in Alveolus and Body CellGas Exchange in Alveolus and Body Cell

Oxygen, carbon dioxide and water vapour diffuse in the reverse direction in the cells of the body:

- Oxygen diffuses from the blood to the body cells

- Carbon dioxide and water vapour diffuse out of the body cells and into the blood. (Note: cytoplasm of body cells has higher conc.

of CO2 & H2O than blood)

Adaptations to improve Gas ExchangeAdaptations to improve Gas Exchange

Alveoli:• have thin walls• are very numerous• are moist

Capillaries:• have thin walls• are numerous

Inhaled Vs. Exhaled AirInhaled Vs. Exhaled Air

Note: - 97% oxygen transported by haemoglobin- Carbon dioxide & water vapour transported by plasma

Mechanism of BreathingMechanism of Breathing•Breathing (ventilation) is normally an involuntary process.

•The brain controls the rate of breathing

•This process has two stages:

- inhalation/inspiration

- exhalation/expiration

The brain sends signals to the intercostal muscles and diaphragm to contract

The intercostal muscles contract and cause the rib cage to move up and out. At the same time the diaphragm flattens downwards.

The volume of the chest (thorax) increases, so air pressure drops. External air pressure is now higher than the pressure of air in the chest as a result more air is forced into the lungs and subsequently the alveoli.

Inhaling requires energy as it is an active process i.e. energy required in movement of muscles

Inhalation:

Exhalation:

There is no message so the intercostal muscles anddiaphragm relax springing back to their original positions:

- relaxed intercostal muscles cause rib cage to move down and in.

- diaphragm moves up.

Volume of the chest decreases so air pressure increases, and air is forced out of the lungs.

Exhaling does not require energy as it is a passive process i.e. muscles only have to relax

Effect of Exercise on Breathing RateEffect of Exercise on Breathing Rate

100

75

50

25

225

175

125

75

5 mins 10 mins 15 mins 20 mins

Rest Exercise

Breathing rate/min

Recovery

Heart rate/min

Effect of Exercise on Breathing RateEffect of Exercise on Breathing Rate

• Adult at rest breathes approx 15 times/min.

• Exercise results in increased respiration

• Brain detects increased level of exercise and so increases breathing rate to allow for:

- increase in oxygen inhaled (respiration)- increase in carbon dioxide exhaled (waste)

• Exhalation becomes an active process during exercise

Activity 19b: To investigate the effect of exercise on the breathing rate

• You have a choice to complete this activity or Activity 19a (pg. 266) – completed previously

Breathing DisordersBreathing DisordersYou are required to study 1 breathing disorder!!!

• *Asthma – inflammation & constriction of bronchi

• Bronchitis

• Emphysema – destruction of alveoli

• TB – elasticity reduced (bacteria)

• Pneumonia – fills with fluid

Asthma:Asthma results in the narrowing of the lower bronchioles due to some irritant (dust mite, pollen, cold, virus) and so the sufferer finds it difficult to inhale enough oxygen

Symptoms: Causes:

• coughing• wheezing • breathlessness• chest tightness

• pollen• animals• smoke • dust mites• chemicals • exercise

Prevention:Identify triggers – avoid or remove e.g. Allergens

Treatment:Specific drug treatments which generally cause the bronchiole to widen e.g. Inhalers, steroids

Control Of Human BreathingControl Of Human BreathingHigher Level Only

• Breathing is under the control of the medulla oblongata in the brain, which is sensitive to CO2 levels

• Nerve cells in the medulla are connected to the diaphragm and intercostal muscles

• When CO2 levels in the blood are high (as a result of increased respiration caused by exercise), the pH of the blood decreases• This is detected by the brain and messages are sent to the intercostal muscles and diaphragm and the rate and depth of breathing is increased