Human Respiratory and Cellular Respiration: Key Functions

Homeostasis and the Respiratory System

Homeostasis refers to the actions performed by the body to maintain a stable internal environment. The respiratory system plays a crucial role in this process.

Key Components of the Respiratory System

• Mucus: Contains water and lysozyme, an enzyme that kills bacteria.
• Trachea: A tube that carries air into the lungs, branching into bronchi and bronchioles.
• Diaphragm: A muscle that separates the chest from the abdominal cavity.
• Ribs: Protect the lungs, which have a spongy structure.

The trachea, bronchi, and bronchioles share similar anatomical characteristics. The trachea is horseshoe-shaped and located behind the liver.

Functions of the Respiratory System

• Gas exchange: The primary function, involving the intake of oxygen and the release of carbon dioxide.
• Blood acidity control: Helps regulate the pH of the blood.
• Excretion: Eliminates waste substances, including water and noxious substances.

The brainstem controls respiration. The alveoli are the functional units of the lungs where gas exchange occurs. Lung volume is inversely proportional to pressure.

Respiratory Mechanics

• Inspiration: The diaphragm contracts and lowers, abdominal and intercostal muscles contract, interpulmonary pressure decreases, and air enters, increasing the volume of the rib cage.
• Expiration: The opposite of inspiration; muscles relax, and air is expelled.

Respiratory Volumes and Spirometry

Spirometry is a test used to assess lung function, particularly in people with asthma. It measures the air we breathe.

• Tidal Volume: The amount of air inhaled and exhaled during normal breathing (approximately 500ml).
• Inspiratory Reserve Volume: The maximum additional air that can be inhaled after a normal inspiration.
• Expiratory Reserve Volume: The maximum air that can be exhaled after a normal expiration.
• Vital Capacity: Tidal volume + inspiratory reserve volume + expiratory reserve volume (approximately 5 liters).
• Residual Volume: The air that always remains in the lungs.

Regulation of Respiration

Respiration is regulated in the brainstem. Key neuronal centers include:

• Pneumotaxic Center: Inhibits the apneustic center to regulate breathing rate.
• Apneustic Center: Stimulates inspiratory neurons to promote inspiration.
• Inspiratory Neurons (NI): Located in the dorsal part of the medulla, they communicate with the muscles responsible for inspiration.
• Expiratory Neurons (NE): Interact with muscles to facilitate relaxation and expiration.

Respiratory arrest occurs when the brainstem is disconnected from the spinal cord. During pulmonary ventilation, increased respiratory rate leads to greater CO2 release, decreasing blood CO2 levels and increasing blood pH (making it more basic). Conversely, a decrease in respiratory rate increases blood CO2 and lowers blood pH.

The pneumotaxic center is located in the brainstem. Blood pH increases during exercise because CO2 is released.

Cellular Respiration

Cellular respiration is the process by which cells use glucose and other molecules as a source of energy. The objective is to produce ATP (adenosine triphosphate), the primary energy currency of cells.

Metabolism

Metabolism encompasses catabolic reactions (breaking down molecules to release energy, producing ATP) and anabolic reactions (building up molecules, using ATP).

Types of Cellular Respiration

• Aerobic Respiration: Requires oxygen (O2). Includes glycolysis, the Krebs cycle, and the electron transport chain.
• Anaerobic Respiration: Does not require oxygen. Includes lactic acid fermentation and alcoholic fermentation. Also called fermentation.

ATP is essential for various cellular functions, including anabolism, active transport, and movement. Catabolic reactions break down molecules, such as glucose, fatty acids, and amino acids, to generate ATP. (NAD: oxidized form, NADH: reduced form).

Lactic Acid Fermentation

Occurs in muscle cells and the cytosol. It does not release any byproducts other than ATP and lactate.

Alcoholic Fermentation

Performed by yeast, amoebas, and protozoa. Occurs in the cytosol. Releases CO2. Its goal is to obtain ATP, and it produces ethanol as a byproduct.