Respiratory System Overview

The three steps in the human body for respiration: pulmonary ventilation (gas exchange between atmosphere and lungs), external respiration (gas exchange between lungs and blood), and internal respiration (gas exchange between blood and body tissues).

The respiratory system exchanges gases, regulates blood pH, permits vocal sounds and the sense of smell, filters inhaled air, and excretes wastes.

The respiratory system is divided into two functional zones: the conducting zone (airway to respiratory zone, filtering, warming, humidifying air as it enters) and the respiratory zone (gas exchange area of the lungs).

Part of the respiratory system including the nose, nasal cavity, pharynx, and associated structures.

Part of the respiratory system including the larynx, trachea, bronchi, and lungs.

The interior and anterior space of the nose, divided by a septum and containing paranasal sinuses, conchae for air swirling, and olfactory epithelium.

Air-filled spaces in the skull surrounding the nasal cavity, lined with mucus membranes for sound resonance and warmth/humidity.

Bony projections within the nasal cavity that swirl inhaled air.

Inside the nose, contains smell receptors.

The throat divided into nasopharynx, oropharynx, and laryngopharynx, each with differing functions.

The larynx contains nine cartilage rings, including the thyroid (Adam's apple), epiglottis, and cricoid.

A flap of cartilage that covers the larynx opening during swallowing to prevent food from entering the airway

Elastic ligaments in the larynx, that vibrate with air to produce sound.

The trachea is a tube with C-shaped cartilage rings to keep it open and is lined with cilia to move mucus.

A network of branching airways within the lungs, narrowing from the trachea

A serous membrane that wraps around the lungs, consisting of two layers: the parietal pleura and the visceral pleura. The space between these layers is called the pleural cavity and contains pleural fluid.

A lubricating fluid found in the pleural cavity, which reduces friction between the lungs and the chest wall during breathing.

The inferior portion of the lungs, which rests on the diaphragm.

The superior portion of the lung, extending slightly above the clavicle.

A groove on the medial surface of the lungs that serves as an entry point for the bronchi, blood vessels, nerves, and lymphatic vessels.

An indentation on the left lung that provides space for the heart.

Deep grooves that divide the lungs into lobes, allowing each lobe to expand independently.

A diagonal groove that separates the superior and inferior lobes of both lungs.

A horizontal groove that separates the middle and superior lobes of the right lung only.

Branches of the main bronchus that supply each lobe of the lungs.

A small, independent unit of lung tissue supplied by a segmental bronchus, artery, and vein.

Smaller compartments within the lung, each consisting of a terminal bronchiole, an arteriole, a venule, and lymphatic vessels, all surrounded by elastic connective tissue.

Microscopic branches of the bronchioles that lead to the alveoli, lined with simple cuboidal epithelium.

Tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide between the blood and air takes place.

Thin, squamous epithelial cells that form the walls of the alveoli, allowing for efficient gas diffusion.

Peripheral chemoreceptors detect low blood pH (acidosis) and send a signal to the respiratory center in the brainstem. This stimulates the dorsal respiratory group (DRG), which increases the rate and depth of breathing, leading to hyperventilation.

Hypocapnia is a condition of low carbon dioxide (CO2) levels in the blood. It can result from hyperventilation, where excessive breathing expels more CO2 than normal.

The inflation reflex prevents overinflation of the lungs during forceful breathing. Baroreceptors in the bronchi and bronchioles sense stretching of the lung tissue and send a signal to the DRG via the vagus nerve, inhibiting it and causing exhalation.

Exercise increases pulmonary perfusion (blood flow to the lungs) due to increased ventilation and the anticipation of exertion stimulating the limbic system and proprioceptors. During rigorous exercise, chemoreceptors sense increased hydrogen ions (H+), further stimulating the DRG.

Chronic obstructive pulmonary disease (COPD) is a group of lung diseases that block airflow and make it difficult to breathe. It is often caused by tobacco smoking.

COPD increases goblet cell number and mucus secretion, impairing ciliary function and causing chronic cough, shortness of breath, and wheezing. It also causes emphysema, the immune destruction of alveolar walls, which decreases oxygen acquisition.

Emphysema is a lung condition that damages the tiny air sacs (alveoli) in the lungs. This damage makes it difficult to breathe and can cause shortness of breath.

Various factors can affect breathing, including emotions through the limbic system, temperature (e.g., cold shock can temporarily stop breathing), pain (can slow or speed breathing), airway irritation (increases respiration rate), and increased blood pressure (decreases respiration rate).

The diaphragm contracts and flattens, increasing the volume of the thoracic cavity, which decreases pressure and draws air into the lungs.

The intercostal muscles contract, pulling the ribs upward and outward, further increasing the volume of the thoracic cavity.

During strenuous inhalation, the diaphragm can move down by up to 10 cm, significantly reducing pressure and drawing in more air.

External intercostal muscles contract to elevate the ribs, contributing to the expansion of the thoracic cavity during inhalation.

The pressure within the pleural cavity is always slightly lower than atmospheric pressure, creating a suction that keeps the lungs expanded.

Exhalation is primarily passive, occurring when the respiratory muscles relax, causing the thoracic cavity to decrease in volume and force air out.

Elastic fibers in the lungs recoil, contributing to the pressure increase that forces air out of the lungs during exhalation.

During strenuous activities, the abdominal and internal intercostal muscles contract to force more air out of the lungs, facilitating active exhalation.

Surfactant reduces surface tension in the alveoli, preventing them from collapsing and ensuring efficient gas exchange.

Excess fluid in the pleural cavity can decrease lung volume and make breathing difficult.

Lung compliance refers to the ease with which the lungs and chest wall can stretch and expand.

Airway diameter, obstruction, and collapse are factors that influence the resistance to airflow in the respiratory system.

Lung volumes are specific measurements of air, while lung capacities are combinations of specific lung volumes.

The solubility of a gas in a liquid determines its ability to dissolve, impacting gas movement between blood and tissues.

Gases move from areas of high partial pressure to low partial pressure, driving gas exchange in the lungs and tissues.

Hemoglobin (Hb) is a protein in red blood cells that binds oxygen reversibly, transporting it throughout the body.

Hemoglobin saturation refers to the percentage of Hb molecules in the blood that are bound to oxygen. It indicates how much oxygen is being carried.

Various factors influence Hb's affinity for oxygen, impacting how readily it binds and releases oxygen. These include partial pressure of oxygen (PO2), acidity, partial pressure of carbon dioxide (PCO2), temperature, intermediate products of glycolysis, and the type of hemoglobin.

Increased acidity (lower pH) in the blood changes Hb's structure, decreasing its affinity for oxygen. This means Hb releases oxygen more readily.

High partial pressure of carbon dioxide (PCO2) lowers blood pH, which in turn decreases Hb's affinity for oxygen, promoting oxygen release.

Increased temperature in the blood, often due to muscle activity, reduces Hb's affinity for oxygen, making it easier to release oxygen to tissues.

2,3-bisphosphoglycerate (BPG), produced during glycolysis in red blood cells, binds Hb and changes its structure, decreasing its affinity for oxygen.

Fetal hemoglobin (Hb-F) has a higher affinity for oxygen than adult hemoglobin (Hb-A) and doesn't bind BPG, allowing efficient oxygen transfer from mother to fetus.

Carbon dioxide is transported in the blood in three main forms: dissolved CO2, bound to proteins (carbaminohemoglobin), and as bicarbonate (HCO3-) ions.

Most carbon dioxide (CO2) is transported as bicarbonate (HCO3-) ions. CO2 converts to carbonic acid (H2CO3) in red blood cells, which then dissociates into bicarbonate and hydrogen ions.

The chloride shift is a process where chloride ions (Cl-) move into red blood cells to maintain electrical balance as bicarbonate ions (HCO3-) diffuse out.

In the pulmonary capillaries, the reverse chloride shift occurs, with bicarbonate ions moving back into red blood cells and chloride ions moving out to facilitate CO2 elimination.

The respiratory centre in the brain controls breathing, consisting of two main areas: the medulla oblongata and the pons.

The medullary respiratory group in the medulla oblongata controls breathing rhythm, further divided into the dorsal respiratory group (DRG) for normal breathing and the ventral respiratory group (VRG) for forceful breathing.

The pontine respiratory group in the pons influences normal breathing by affecting the DRG in the medullary respiratory centre.