THE RESPIRATORY SYSTEM.

 THE RESPIRATORY SYSTEM.:

The respiratory system is responsible for the exchange of oxygen and carbon dioxide between the body and the environment. It consists of a number of organs, including the nose, mouth, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli.  

1. Nasal Cavity

• Structure:
• The nasal cavity is a hollow space within the nose.
• It is lined with mucous membranes and tiny hairs called cilia.
• Divided by a septum into two nostrils.
• Functions:
• Air Filtration: Filters dust, pathogens, and other particles from the air.
• Warming and Moistening Air: The mucous membrane moistens and warms the inhaled air.
• Sense of Smell: Contains olfactory receptors that are responsible for the sense of smell.

2. Pharynx (Throat)

• Structure:
• A muscular tube that connects the nasal cavity to the larynx and esophagus.
• Divided into three regions: nasopharynx, oropharynx, and laryngopharynx.
• Functions:
• Passageway for Air: Directs air from the nasal cavity to the larynx.
• Voice Production: Works with the larynx during speech.
• Immunity: Contains lymphoid tissues (tonsils) that help protect against infections.

3. Larynx (Voice Box)

• Structure:
• A cartilaginous structure located below the pharynx and above the trachea.
• Contains vocal cords, which are elastic bands of muscle.
• The epiglottis, a flap of cartilage, is located at the entrance of the larynx.
• Functions:
• Airway Protection: The epiglottis prevents food and liquids from entering the trachea during swallowing.
• Voice Production: The vocal cords vibrate to produce sound when air passes through them.
• Passageway for Air: Directs air into the trachea.

4. Trachea (Windpipe)

• Structure:
• A tube about 10-12 cm long, made up of C-shaped cartilage rings.
• Lined with ciliated mucous membrane.
• Located between the larynx and bronchi.
• Functions:
• Air Conduction: Provides a clear path for air to travel to the bronchi.
• Protection: Cilia trap and expel foreign particles and mucus.

5. Bronchi and Bronchioles

• Structure:
• The trachea splits into two main bronchi (left and right), one for each lung.
• Each bronchus further divides into smaller bronchi and bronchioles within the lungs.
• Bronchioles are the smallest airways, leading to alveolar ducts.
• Functions:
• Air Distribution: Conducts air from the trachea into the lungs.
• Regulation of Airflow: Bronchioles control airflow through the lungs by constricting or dilating.

6. Lungs

• Structure:
• A pair of spongy organs located in the thoracic cavity.
• The right lung has three lobes, and the left lung has two lobes.
• Enclosed by a double-layered membrane called the pleura.
• Contain millions of alveoli, small air sacs where gas exchange occurs.
• Functions:
• Gas Exchange: Oxygen is absorbed into the blood, and carbon dioxide is expelled from the blood in the alveoli.
• Regulation of pH: Helps maintain the acid-base balance of the blood.
• Protection: The pleura reduces friction during breathing and protects the lungs.

7. Diaphragm and Intercostal Muscles

• Structure:
• The diaphragm is a dome-shaped muscle located below the lungs.
• Intercostal muscles are found between the ribs.
• Functions:
• Breathing Mechanics: The diaphragm contracts and flattens to create negative pressure, pulling air into the lungs (inhalation). It relaxes to expel air (exhalation).
• Support for Lungs: Intercostal muscles help expand and contract the thoracic cavity, aiding in respiration.

Physiology of Respiration:

Respiration is the process by which oxygen is taken into the body and carbon dioxide is expelled. It involves both external and internal processes, ensuring that the body's cells receive oxygen for energy production and that waste gases are removed efficiently.

1. Pulmonary Ventilation (Breathing)

• Definition: The mechanical process of moving air into and out of the lungs, involving inhalation (inspiration) and exhalation (expiration).
• Inhalation (Inspiration):
• Diaphragm and Intercostal Muscles: During inhalation, the diaphragm contracts and moves downward, while the external intercostal muscles contract, lifting the rib cage. This increases the thoracic cavity's volume and creates negative pressure, allowing air to flow into the lungs.
• Air Flow: Air enters through the nasal cavity, passes through the pharynx, larynx, trachea, bronchi, and bronchioles, eventually reaching the alveoli.
• Exhalation (Expiration):
• Diaphragm and Intercostal Muscles Relax: During exhalation, the diaphragm relaxes and moves upward, and the rib cage returns to its original position. This decreases the thoracic cavity's volume and creates positive pressure, pushing air out of the lungs.
• Air Flow: Air is expelled from the alveoli, moving back through the bronchioles, bronchi, trachea, larynx, pharynx, and finally out through the nasal or oral cavity.

2. External Respiration (Gas Exchange in the Lungs)

• Definition: The exchange of gases (oxygen and carbon dioxide) between the alveoli and the blood in the pulmonary capillaries.
• Oxygen Diffusion:
• Oxygen from Alveoli to Blood: Oxygen from the inhaled air diffuses across the thin walls of the alveoli into the pulmonary capillaries. This occurs because the partial pressure of oxygen (PaO2) is higher in the alveoli than in the deoxygenated blood.
• Binding to Hemoglobin: Oxygen binds to hemoglobin in red blood cells, forming oxyhemoglobin, which is then transported to tissues throughout the body.
• Carbon Dioxide Diffusion:
• Carbon Dioxide from Blood to Alveoli: Carbon dioxide, a waste product of cellular respiration, diffuses from the blood into the alveoli. This occurs because the partial pressure of carbon dioxide (PaCO2) is higher in the blood than in the alveoli.
• Expiration: Carbon dioxide is then expelled from the body during exhalation.

3. Transport of Respiratory Gases

• Oxygen Transport:
• Hemoglobin: Most oxygen (about 98%) is transported in the blood bound to hemoglobin in red blood cells. A small amount of oxygen (about 2%) is dissolved in plasma.
• Oxygen Release: As blood reaches tissues with lower oxygen concentration, hemoglobin releases oxygen, which diffuses into cells.
• Carbon Dioxide Transport:
• Bicarbonate Ions: The majority of carbon dioxide (about 70%) is transported as bicarbonate ions (HCO₃⁻) in the plasma, formed when CO₂ reacts with water.
• Carbaminohemoglobin: About 20% of carbon dioxide binds to hemoglobin, forming carbaminohemoglobin.
• Dissolved in Plasma: The remaining 10% of carbon dioxide is dissolved directly in the plasma.

4. Internal Respiration (Gas Exchange in Tissues)

• Definition: The exchange of gases between the blood in systemic capillaries and the body’s tissues.
• Oxygen Diffusion:
• From Blood to Tissues: Oxygen diffuses from the blood (where PaO2 is high) into the tissues (where PaO2 is low). Cells use this oxygen for cellular respiration, producing energy.
• Carbon Dioxide Diffusion:
• From Tissues to Blood: Carbon dioxide produced by cellular metabolism diffuses from the tissues (where PaCO2 is high) into the blood (where PaCO2 is low). It is then transported back to the lungs for exhalation.

5. Internal Respiration (Tissue Gas Exchange)

• Oxygen Delivery:
• Oxygen Release: Oxyhemoglobin releases oxygen as it encounters tissues with lower oxygen partial pressure (Pₒ₂).
• Diffusion into Cells: Oxygen diffuses from the blood into the tissue cells where it is used for cellular respiration.
• Carbon Dioxide Removal:
• CO₂ Production: Cells produce carbon dioxide as a byproduct of metabolism.
• Diffusion into Blood: CO₂ diffuses from the cells into the blood, where it is transported back to the lungs for exhalation.

6. Regulation of Respiration

• Respiratory Centers:
• Located in the medulla oblongata and pons of the brainstem, these centers control the rate and depth of breathing.
• Medullary Respiratory Center: Regulates the basic rhythm of breathing.
• Pontine Respiratory Center: Modifies the rhythm and smoothes out the transition between inhalation and exhalation.
• Chemical Regulation:
• Chemoreceptors: Located in the medulla, aortic arch, and carotid bodies, these receptors respond to changes in blood levels of CO₂, O₂, and pH.
• Response to High CO₂: Increased CO₂ levels (hypercapnia) trigger an increase in the rate and depth of breathing to expel more CO₂.
• Response to Low O₂: Significant drops in blood oxygen levels can stimulate an increase in breathing rate.

NOTE :

The term pH stands for "potential of hydrogen" and is a scale used to measure the acidity or alkalinity of a solution. The pH scale ranges from 0 to 14:

• pH 7 is considered neutral, which means the solution is neither acidic nor basic. Pure water has a pH of 7.
• pH less than 7 indicates an acidic solution, where the concentration of hydrogen ions (H⁺) is higher.
• pH greater than 7 indicates a basic (alkaline) solution, where the concentration of hydroxide ions (OH⁻) is higher.

Characteristics of Normal Respiration and Deviations

Normal respiration refers to the typical pattern of breathing in a healthy individual. It involves a balanced, efficient process of inhalation and exhalation that maintains proper oxygen and carbon dioxide levels in the blood. Deviations from normal respiration can indicate underlying health issues or the body's response to certain conditions.

Characteristics of Normal Respiration

1.      Rate (Respiratory Rate):

o    Definition: The number of breaths taken per minute.

o    Normal Range: Typically, 12-20 breaths per minute for a healthy adult at rest.

o    Variations: Children and infants have a higher respiratory rate, typically 20-30 breaths per minute.

2.      Rhythm:

o    Definition: The regularity or pattern of breathing.

o    Normal Rhythm: Breathing is usually regular and evenly spaced, with consistent intervals between breaths.

o    Inhalation/Exhalation Ratio: The duration of exhalation is slightly longer than inhalation, with a ratio of about 1:2.

3.      Depth (Tidal Volume):

o    Definition: The amount of air inhaled and exhaled with each breath.

o    Normal Depth: Breathing should be deep enough to allow for adequate oxygen exchange but not excessively deep.

o    Tidal Volume: Approximately 500 milliliters (ml) of air per breath in an adult.

4.      Effort:

o    Definition: The amount of physical effort required to breathe.

o    Normal Effort: Breathing should be effortless and not require noticeable exertion. The muscles of the chest and abdomen work without strain.

5.      Sound:

o    Definition: The noise produced during breathing.

o    Normal Sound: Breathing should be quiet and barely audible, with no wheezing, crackles, or other abnormal sounds.

6.      Oxygen Saturation:

o    Definition: The percentage of oxygen-saturated hemoglobin in the blood.

o    Normal Range: 95%-100% oxygen saturation when measured using a pulse oximeter.

Deviations from Normal Respiration

1.      Tachypnea:

o    Definition: Abnormally rapid breathing, with a respiratory rate exceeding 20 breaths per minute.

o    Possible Causes: Fever, anxiety, pain, respiratory infection, or heart failure.

2.      Bradypnea:

o    Definition: Abnormally slow breathing, with a respiratory rate below 12 breaths per minute.

o    Possible Causes: Drug overdose (e.g., opioids), brain injury, or hypothermia.

3.      Dyspnea:

o    Definition: Difficulty or discomfort in breathing, often described as shortness of breath.

o    Possible Causes: Asthma, chronic obstructive pulmonary disease (COPD), heart failure, or anxiety.

4.      Apnea:

o    Definition: Temporary cessation of breathing.

o    Types: Obstructive sleep apnea (airway blockage during sleep), central sleep apnea (failure of the brain to signal breathing), and mixed apnea.

o    Possible Causes: Sleep disorders, head injuries, or respiratory depression.

5.      Hyperventilation:

o    Definition: Breathing that is deeper and more rapid than normal, leading to decreased carbon dioxide levels in the blood.

o    Possible Causes: Anxiety, panic attacks, pain, or metabolic disorders.

6.      Hypoventilation:

o    Definition: Shallow or slow breathing, leading to increased carbon dioxide levels in the blood.

o    Possible Causes: Respiratory muscle weakness, obstructive lung disease, or drug overdose.

7.      Cheyne-Stokes Respiration:

o    Definition: A pattern of gradual increase in breathing rate and depth followed by a gradual decrease, leading to a temporary stop in breathing (apnea).

o    Possible Causes: Congestive heart failure, brain injury, or high altitude sickness.

8.      Kussmaul Breathing:

o    Definition: Deep, labored breathing often associated with severe metabolic acidosis, particularly diabetic ketoacidosis.

o    Possible Causes: Diabetic ketoacidosis, kidney failure, or lactic acidosis.

9.      Wheezing:

o    Definition: A high-pitched whistling sound during breathing, usually on exhalation.

o    Possible Causes: Asthma, COPD, or airway obstruction.

10.  Crackles (Rales):

o    Definition: A crackling or rattling sound heard during inhalation, often caused by fluid in the airways.

o    Possible Causes: Pneumonia, heart failure, or pulmonary edema.

11.  Stridor:

o    Definition: A harsh, vibrating noise during breathing, typically caused by an obstruction in the upper airway.

o    Possible Causes: Croup, foreign body aspiration, or airway trauma.

12.  Cyanosis:

o    Definition: A bluish discoloration of the skin, lips, and nails due to low oxygen levels in the blood.

o    Possible Causes: Severe respiratory distress, hypoxia, or congenital heart disease.