Biology Chapter 13: The Respiratory System

Chapter 13: The Respiratory System

• Respiration is the process of exchanging oxygen and carbon dioxide throughout the body
• Respiration involves three exchanges: air and lungs, lungs and blood, and blood and cells
• The respiratory system functions in gas transport in the blood and gas exchange between blood and cells
• The anatomy of the respiratory system reflects its physiological functions in gas exchange

Respiration

• Air and lungs exchange gases
• Lungs and blood exchange gases
• Blood and cells exchange gases
• Blood transport of gases (needs carriers like hemoglobin)

How Do Respiratory and Conducting Sections Differ?

• Airways are either conducting or respiratory
• Airways branch to reach alveoli
• Bigger airways contain more cartilage to prevent collapse
• Smaller airways are more numerous
• Conducting airways contain goblet cells, ciliated cells, clara cells, glands, cartilage, smooth muscle, and elastic fibers.
• Respiratory airways (alveoli) contain very thin epithelium for efficient gas exchange.

What Happens in the Conducting Airways?

• Mucociliary escalator helps warm and moisten airways, and clears foreign particulates
• Cilia in the bronchial epithelial wall moves mucus upwards towards the throat to clear the airways

The Airways in Cross Section

• Airways have muscle where inflammation can occur
• Airways have mucus glands
• Airways have cilia

Alveoli

• Alveoli are the primary site of gas exchange between air and blood
• Alveoli are tiny sacs in the lungs
• The alveoli wall is a single-layered epithelium to facilitate gas exchange
• Capillaries surround alveoli, allowing for efficient gas exchange between air and blood

Alveolar Cells

• Type I alveolar cells form the majority of the alveolar wall, facilitating rapid gas exchange.
• Type II alveolar cells produce surfactant which helps prevent alveolar collapse.

Arrangement of the Thorax (Muscle)

• Thoracic cavity, made of the rib cage, ribs, sternum, and diaphragm muscles work together to facilitate inhalation and exhalation.
• Accessory muscles of inspiration contract during forced inhalation.
• Muscles of expiration contract only during forced exhalation

Arrangement of Lungs in Pleural Sacs

• Lungs are in pleural sacs, containing fluid to reduce friction and tension.
• Pleural membranes help keep lungs close to the chest wall and reduce friction during breathing.
• Intrapleural pressure is always lower than alveolar pressure.

The Mechanics of Breathing: the role of Pleural pressure + Alveolar Pressure

• Atmospheric pressure is 760 mmHg
• Alveolar pressure is pressure in the alveoli
• Pleural pressure keeps the lungs attached to the chest wall

The Law of Laplace + Alveolar Stability

• Laplace's Law describes the pressure within a sphere.
• Surfactant reduces surface tension in the alveoli, thus preventing small alveoli from collapsing.
• Alveolar pressure is less in larger alveoli
• All alveoli in the same lung have the same pressure in normal breathing.

Pneumothorax

• Pneumothorax is a condition where air leaks into the pleural space; this causes lung collapse

Things that Make Respiration Possible

• Boyle's Law describes how pressure and volume are inversely proportional
• Gases move from higher to lower pressure.
• Lungs and thorax have compliance for expansion and recoil.
• Partial pressure gradients facilitate gas exchange.

Let's Put It All Together

• Inhalation involves expanding the thoracic cavity increasing volume and reducing intrapulmonary pressure.
• Exhalation involves decreasing the thoracic cavity volume increasing pressure and forcing air out.

Lung Volumes and Pressures

• Intrapulmonary pressure moves air into and out of the lungs
• Intrapulmonary pressure is lower during inspiration

Respiratory Cycle

• During inspiration, the volume of the thoracic cavity increases, and air moves into the lungs.
• During exhalation, the volume of the thoracic cavity decreases, and air moves out of the lungs.

The Role of Airway Diameter

• Airflow is proportional to pressure changes
• Resistance works against airflow and is inversely proportional to it.
• Airway diameter and resistance play an important role in respiration.

Now that We Have Gas in Lungs, How Do We Move it in the Body?

• Gases diffuse down partial pressure gradients
• Transport of gases.

Air is a Mixture

• Total pressure of a mixture is the sum of the partial pressures.
• Partial pressure is calculated by multiplying atmospheric pressure by the percentage of that gas in the air.

Review of the Respiratory Cycle

• Breathing is a process of inspiration and exhalation
• Inspiration is active and exhalation is passive, but both involve muscle contraction.
• Changes in chest size change the pressure inside the lungs, and air flows accordingly.

Let's Look at the Graphs Again!

• Alveolar pressure and flow rate have similar patterns
• A larger pressure gradient leads to faster airflow.

Why Does Air Change with Altitude?

• Air is always 21% oxygen
• Atmospheric pressure decreases with altitude, even though the proportion of gases remains the same.

These are Some Numbers to Know

• Lung function, pressure, volume, blood gas contents and exchange of the respiratory system.

How Is Oxygen Transported?

• Oxygen diffuses into red blood cells where it binds to hemoglobin; hemoglobin transports a vast majority of oxygen.
• Only a small percentage of oxygen is dissolved in plasma

Hemoglobin

• Hemoglobin has four polypeptide chains per molecule
• Each hemoglobin molecule contains iron atoms which bind to oxygen
• Oxygen binding to hemoglobin is cooperative, meaning the binding of one oxygen molecule to Hb facilitates the binding of more.
• Hemoglobin's conformation changes allow for oxygen binding and release.

Oxygen Saturation Curves

• Hemoglobin's oxygen-binding affinity changes according to factors like pH, temperature, and the presence of certain molecules
• When pH decreases (more acidic), the curve shifts to the right (lower affinity) and releases more O2
• When pH increases (more basic), the curve shifts to the left (higher affinity) and binds more O2.
• The shape of the curve highlights how hemoglobin's affinity for oxygen changes with various levels.

How Can Someone Have 100% Saturation but Poor Oxygen Content?

• Someone with lots of Hb but low red blood cell or Hb count may have normal saturation, but poor oxygen content.
• Hemoglobin saturation, or the percentage of hemoglobin bound to oxygen, can be 100% but oxygen transport still may be impaired

Oxygen Saturation Curve

• The relationship between oxygen levels and hemoglobin saturation varies with factors such as pH, temperature, and concentration of certain substances like 2,3-bisphosphoglycerate
• Binding changes allow for oxygen release in tissues where it's needed more.

Hemoglobin Saturation Curves Again

• Conditions such as high carbon dioxide concentrations, low pH, elevated temperature, and the presence of BPG shift the oxygen-hemoglobin dissociation curve to the right, resulting in a lower affinity for oxygen. Conversely, a shift to the left indicates an increase affinity for oxygen.
• Blood and tissue pH, temperature and 2,3-BPG levels influence the position of the curve.

Oxygen Gets Stored in Hemoglobin

• Oxygen is stored in the blood in the form of oxyhemoglobin, but oxygen needs to be released into tissues.
• Oxygen release is affected by factors such as PCO2, pH, temperature, and 2,3-BPG concentrations

What About Carbon Dioxide?

• Carbon dioxide transport involves three mechanisms: dissolved in plasma, bound to Hb and bicarbonate ion.
• Carbonic anhydrase in red blood cells converts CO2 to bicarbonate, which is then transported out of the cell, maintaining the pH balance.

Told You It Was Complicated!

• Carbon dioxide transport mechanisms in the respiratory system.