Biology - Chapter 30: Human Breathing

pharynx

the throat

here, the epiglottis closes over trachea to prevent food or drink passing through

larynx

voice box - maintains open airway, routes food and air approximately, assists in sound production

nose

air can be inhaled here and is beneficial as air is:

• filtered or cleaned by hairs and mucus in the nostrils

• moistened

• warmed as it passes more easily from the lungs into the bloodstream

lungs

large, pink spongy structures where gas exchange occurs. Each lung is enclosed by a pair of pleural membranes (the pleura):

• outer pleura lines the chest wall and diaphragm

• inner pleura lines the lungs

pleural cavity

gap between the two pleura & contains a liquid that lubricates the membranes and reduces friction during breathing

alveoli - air sacs

used for gas exchange

adaptations:

• thin walled (one-cell thick) for efficient gas exchange

• huge number for large surface area for gas exchange

• moist surfaces for faster diffusion

• enclosed in a network of blood capillaries

gas exchange

Cells use up oxygen:

• diffuses in

• passes from alveoli into blood then blood into body cells

• diffusing from higher to lower concentration

Carbon dioxide and water:

• pass out of body cells by diffusion

• this is due to cytoplasm having higher concentration of CO2 and H2O than the blood plasms

• in lungs, carbon dioxide and water diffuse from the blood plasma into alveoli (high to low concentration)

transport of gases in gas exchange

• oxygen mainly transported (97%) combining w/ haemoglobin to form oxyhaemoglobin. Only about 3% oxygen carried dissolved in plasma

• carbon dioxide and water both carried in blood plasma

• carbon dioxide dissolved in plasma in the form of bicarbonate ions & very small amount of it is carried by RBCs

inhalation (inspiration)

active process:

• During inhalation the brain sends electrical impulses to the intercostal muscles and diaphragm, causing them to contract

• This causes the ribs to be pulled up and out, and the diaphragm to be flattens downwards, increasing the volume of the thoracic cavity.

• Volume of lungs increases

• Air pressure then drops

• external air pressure is now higher than air pressure in chest, hence air is forced into lungs

exhalation (expiration)

passive process:

• intercostal muscles relax and ribcage springs back down and in

• diaphragm relaxes and springs back up

• volume of lungs decreases

• air pressure rises

• air is pushed back

control of breathing rate

• special centres in medulla oblongata monitor CO2 levels in the blood

• rate of breathing is unconsciously controlled by medulla oblongata

• increase levels of carbon dioxide = increase rate of breathing (to get oxygen back)

effect of exercise on rate of breathing

• exercise is a factor of this (respiration), especially in muscle cells, hence body experiences lower levels of available oxygen

• brain detects increased level of exercise and increases level of breathing

• exhalation becomes active process & extra muscles are used to increase depth of breathing

asthma

symptoms: inflammation and narrowing of bronchioles/noisy, wheezy breathing/feeling of breathlessness

cause: allergens (lung infections, exercise esp. in cold air, stress or anxiety also)

prevention: avoid allergens//preventative inhaler and medication

treatment: inhaler, sometimes steroids or injections

trachea

transports air to and from lungs

bronchi and brochioles

branch into lungs and alveoli

lung defense

tubes in respiratory system lined with mucus and cilia

• mucus is sticky and traps small particles like dust, pollen grains, bacteria and viruses

• cilia beat and create an upward current - this moves mucus upwards and past epiglottis, which then passes down oesophagus and into stomach

veins

pulmonary vein - carries oxygenated blood from lungs

hepatic portal vein - carries blood between intestine and liver

renal vein - carries blood lowest in metabolic waste

vena cava - carries blood into right atrium of heart