Respiratory SystemBiology 12

• The respiratory systems main function is to exchange oxygen from the air with carbon dioxide from the blood

• Respiration- process of supplying O2 to body cells– Linked to cellular respiration

C6H12O6 + 6O2 6CO2 + 6H2O + 38 ATP

• The respiratory and circulatory systems work together to:– Exchange gases between blood and air

(at lungs)– Transport gases from lungs to tissues– Exchange gases at tissues

Respiration can be broken down into 4 parts

– Breathing – movement of air into and out of lungs

• inspiration(inhalation) + expiration(exhalation)– External respiration – in alveoli,

exchange of O2 + CO2 between air and blood

– Internal respiration – exchange of O2 and CO2 between blood and tissue fluid

– Cellular respiration – production of ATP in mitochondria in cells

Respiratory TractAs air travels through the air passages 3 things occur:1. Filtering

– Done by hairs, cilia, and mucus in nose and cilia in trachea

– Cilia create an upward wave which moves mucus and dirt particles up towards the pharynx (throat)

2. Moistening – done by wet surface of passageways

3. Warming – done by heat from blood vessels lying

close to surface lining the air passages

Flow of Air• Nose/mouth pharynx larynx

trachea bronchi bronchioles alveoli (gas exchange of O2 for CO2 occurs here)

INSPIRATION- breathing air inEXPIRATION- breathing air out

1. Air enters the nasal passages.– hairs and CILIA trap dust and debris– the air is warmed and moistened.

2.The warmed and moistened air passes through the PHARYNX.

3. The air enters the larynx.– Vocal cords located here

4. The air enters the TRACHEA (windpipe).

– Held open by cartilaginous rings and lined with ciliated mucous membranes.

5. The trachea divides into two BRONCHI

6. Bronchi branch into many smaller passages called bronchioles that extend into the lungs.

7. The bronchioles branch out, and their walls get thinner and diameter smaller.

8.Each bronchiole ends in sacs called ALVEOLI.

• The left and right lung are divided into lobes (3 and 2)

• Each lobe is divided into lobules, each of which has a bronchiole with many alveoli

• The lungs are enclosed by two pleural membranes (one on chest cavity, one that lines lung)– Lubricates and makes air tight

Alveoli• Sac-like clusters at ends of bronchioles

6 features which help in function:1. number of alveoli – millions in each lung,

provide great surface area for exchange/diffusion of gases

2. thin-walled – one – cell thick, also aids in diffusion

3. lipoprotein “film” on inner surface – reduces surface tension of lining inside alveoli and prevents them from collapsing

4. Stretch receptors – nerve endings that signal alveoli are full

5. Moisture – ensures efficient diffusion of gases

6. pulmonary capillaries – surround alveoli and provide rich supply of blood for optimum gas exchange

The Diaphragm• Sheet of muscle that extends across

the bottom of the rib cage• Controls the volume of the thoracic

cavity to allow air to be drawn in or out of the lungs

Inspiration- The Active Stage• Chemoreceptors in the arteries signal to

breathing center in the medulla oblongata– Carotid bodies (in carotid arteries) and aortic

bodies (in aorta)

• Detects rising levels of CO2 and H+

• Not affected by oxygen levels

• Chemoreceptors detect levels of H+ (indirectly CO2) and send messages to respiratory centre in medulla oblongata (brain)

• Medulla oblongata sends impulses to diaphragm and intercostal (ribcage) muscles to contract

• Contraction of these muscles increases the chest cavity volume, which then causes air pressure in the chest cavity to decrease

• This causes the lungs to expand and as a result of the “negative pressure” air rushes into the lungs to equalize the pressure

Expiration- The Passive Stage• When the alveoli are filled, the

stretch receptors on the walls of the alveoli send signals to the medulla oblongata

• The medulla oblongata stops sending impulses to the diaphragm and intercostal muscles

• As these muscles relax, the volume in the chest cavity decreases and the pressure increases

• This causes the lungs to contract and forces air out of the lungs and the cycle starts over

Inhalation and Expiration  Inhalation ExhalationRib Cage Moves up and

outMoves down and in

Diaphragm Contracts (lowers)

Relaxes (moves up)

Air Pressure in Lungs

Decreases Increases

Movement of Air

Into lungs Out of lungs

• Hyperventilation – increased breathing rate leads to decreased levels of CO2 and H+ in blood and pH of blood increases (i.e becomes basic)

• Hypoventilation – decreased breathing rate leads to increased levels of CO2 and H+ in blood and pH of blood decreases (i.e becomes acidic)

Internal/External RespirationHCO3

- bicarbonate ion (in plasma)Hb hemoglobin or deoxyhemoglobinHbO2oxyhemoglobin- found in RBC’sHbCO2 carbaminohemoglobinHHb reduced hemoglobinH+ hydrogen ion

External Respiration• Happens in lungs between alveoli and

pulmonary capillaries• Exchange of O2 and CO2 • Movement of both gases is due to

concentration gradients diffusion

[O2 ] high in alveoli, [CO2] high in blood  [O2] [CO2]

capillaries low high

alveoli high low

• CO2 returns to the lungs (from tissues) in 2 forms:

1. Dissolved in water as bicarbonate ion: HCO3

- + H+ H2O + CO2

*catalyzed by carbonic anhydrase in plasma

2. Transported by hemoglobinHbCO2 Hb + CO2

Hemoglobin• Hemoglobin is an

iron-containing polypeptide found within red blood cells.

• It is more attracted to oxygen in cool, more basic lungs, and less attracted to oxygen in the more acidic, warmer tissues. – Hb will bind O2 in the lungs, and release it

in tissues.

  LUNGS  

Hb + O2 -----------> HbO2

reduced Hemoglobin

<----------- oxyhemoglobin

dark purple TISSUES bright red

• Temperature Effects: Hb takes up O2 more readily in low temperatures (lungs), gives up O2 more readily at higher temperature.

• pH Effects: Hb takes up O2 more readily in the more basic or neutral lungs, and gives it up more readily in the more acidic tissues.

Internal Respiration• Between blood and tissues

• Exchange of CO2 in tissue fluid and O2 in bloodHbO2 Hb + O2

• Tissue fluid is low in oxygen, high in carbon dioxide, therefor carbon dioxide diffuses into blood

The Fate of Carbon Dioxide

A small amount of carbon dioxide is take up by hemoglobin

Hb + CO2 HbCO2

• Most CO2 combines with H2O to form carbonic acid, which then dissociates to H+ and HCO3-.CO2 + H2O H2CO3 H+ + HCO3-

        to Hb to Plasma

• Hemoglobin combines with the excess H+ that this reaction produces.

Hb + H+ HHb–Maintains blood pH levels