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The Respiratory System

Structure and Function

Pharynx: common passage for respiratory and digestive systems above the epiglottis.

Larynx: Structure that contains the vocal cords, voice box (just below epiglottis)

Trachea: the windpipe (cartilaginous ridges)

Bronchi: the first branches of tubes from the windpipe to the lungs. Each bronchi subdivides into bronchioles.

Bronchioles: the smaller branches of tubes in the lungs. Each bronchiole ends in an air pocket sac called alveoli.

Diaphragm: a sheet of muscle that separates the chest cavity from the abdominal cavity. A muscle used for breathing.

Alveoli:

• Saclike structures that are the air sacs in the lungs.

• Makes up the lungs

• 300 000 000 alveoli in human lung, 40x the surface area of the skin.

• Thin walled sacs covered with a capillary network

• Carbon dioxide and oxygen can diffuse directly through the walls

• Site of oxygen and carbon dioxide exchange.

Ribs: bones hinged to the vertebral column and sternum, which, with muscle, define the top and sides of the chest cavity.

Pleural Membranes:

• Membranes that enclose the lungs

• Outer pleural membrane sticks closely to the walls of the chest and the diaphragm

• Inner pleural membrane is stuck to the lungs

• The two lie very close to each other

• Pressure between the two is less than out air pressure or lungs collapse

• Lubrication

Thoracic Cavity

• Sealed off chest where lungs are

• Ribs form top and sides, diaphragm forms bottom

• Used in inspiration and expiration

Cilia and Mucous: cilia line the tubes of the respiratory tract. The tubes also produce mucus, which traps bacteria and dust particles. The cilia sweep the mucus upward,

Breathing

• The taking in of air in and out of the lungs

o In – inspiration

o Out – expiration

• The lungs lie in a sealed cavity – chest or thoracic cavity

• The ribs make up the top and sides, the diaphragm makes up the bottom, the pleural membranes seal it.

Inspiration (inhalation)

1. Diaphragm contracts (lowers)

2. Rib muscles contract (pull up and out)

3. This expands the thoracic cavity which causes a lower (negative) pressure; air is “sucked in”.

Expiration (exhalation)

1. Diaphragm relaxes (raises)

2. Ribs relax

3. Thoracic cavity relaxes (gets smaller) and air is forced out (positive pressure)

The pleural membranes seal the thoracic cavity so the negative pressure formed during inhalation forces air to be sucked in through the trachea.

Controlling breathing rate

1. The urge to breathe is brought about primarily by the level of carbon dioxide and Hydrogen ions in the blood.

2. Level is monitored in the blood by the medulla oblongata – respiratory center of the brain.

3. Chemo receptors in the carotid/aortic artery also respond to pH changes in the blood (due to elevated H+ levels ) and report to the medulla

4. High carbon dioxide and H+ stimulates breathing center, which stimulates the diaphragm and rib muscles to contract. You breathe in.

5. When lungs are filled, stretch receptor on the alveoli send messages to the breathing center, which shut down signals to the diaphragm and rib muscles. They relax and you breathe out.

Levels of respiration

• Breathing

• External respiration (in the lungs)

• Internal respiration (in the tissues)

• Cellular respiration (in the mitochondria of cells)

External respiration (O2 enters the blood)

• The CO2, O2 exchange at the alveoli

• Relies on diffusion (gases moving from high concentration to low

• Oxygen moves from lungs (alveoli) where concentrations are high into the low concentration lung capillaries

• binds to hemoglobin to move through circulatory system

1. Hb + O2 → HbO2 when O2 leaves alveoli and moves into blood to go to tissues.

2. Hb + CO2 → HBCO2 when CO2 (from cellular respiration) leaves cells and heads to lungs

• Binding of O2 to hemoglobin occurs best at lower temp, higher (neutral) pH and higher pO2 (oxygen pressure) of the lungs

• CO2 is transported in blood in three ways

1. As bicarbonate ion (approximately 70%)

▪ H+ + HCO3-→ H2CO3 →CO2 + H2O

▪ Bicarb in blood → lungs

Internal respiration (O2 enters the tissue)

• CO2, an O2 exchange in body tissue

• Also relies on diffusion

• CO2 levels are high in the body tissue and low in the capillaries

• CO2 is transported in blood in three ways

1. Most combines with water to form carbonic acid which dissociates to form hydrogen ions and bicarbonate ions

▪ CO2 + H2O → H2CO3 →H+ + HCO3-

▪ Cells →lungs

▪ This reaction is catalyzed by the enzyme carbonic anhydrase (found in red blood cells)

▪ The H+ combines with hemoglobin which acts as a buffer

• HHb →H+ and Hb

• HHb is called reduced hemoglobin

2. Dissolved CO2 directly in the plasma

3. CO2 is carried on hemoglobin as HbCO2 (carbaminohemoglobin)

4.

Oxygen is carried in the blood in only one way

• 02 is carried directly on hemoglobin

Hb + 02 HbO2 (oxyhemoglobin)

• Hemoglobin accepts O2 easier at cooler, neutral pH in lungs and gives up at warmer more acidic (lower pH) environment of the tissues.

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