Human Physiology: Respiratory and Renin-Angiotensin Systems

Respiratory System Functions

• Provides extensive area for gas exchange between air and blood.
• Moves air to and from lung exchange surfaces.
• Protects respiratory surfaces from environmental variations (dehydration, temperature).
• Defends respiratory system and other tissues from pathogen invasion.

Non-Respiratory Functions

• Regulates blood pH by altering carbon dioxide levels.
• Produces sounds for communication (speaking, singing).
• Provides olfactory sensations to the central nervous system (CNS).
• Produces chemical mediators (HSC 113).

Renin-Angiotensin-Aldosterone System (RAAS)

• Regulates blood pressure and fluid balance.
• Activated when blood volume or sodium levels are low, or potassium is high.
• Kidney releases renin, which converts angiotensinogen to angiotensin I.
• Angiotensin I is converted to angiotensin II in the lungs by ACE.
• Angiotensin II constricts blood vessels and increases blood pressure.
• It also stimulates aldosterone release from adrenal glands.
• Aldosterone promotes sodium and water retention and potassium excretion.
• Overactive system leads to high blood pressure.

Anatomy of the Respiratory System

• Structurally: Upper and Lower Respiratory Tract.
• Functionally: Conducting zone (carries gases) and Respiratory zone (exchange of gases).
• Organs: Nose, Pharynx, Larynx, Trachea, Bronchi, Bronchioles, Lungs, Intercostal muscles, diaphragm.

Egyptian Hieroglyphs of the Respiratory System

• Depictions dating back to the 30th century BC show understanding of pulmonary anatomy, including trachea, bronchi, and lungs.
• Different depictions from various dynasties are documented.

Upper Respiratory Tract

• Nose and Nasal Cavity: Includes vestibule, conchae and olfactory region.
• Pharynx: Divided into nasopharynx (air passages), oropharynx (food and air), and laryngopharynx (food and air).
• Contains lymphatic tissue, eustachian tubes, and tonsils.
• Nasopharynx
  • Contains lymphatic tissue and eustachian tubes.
• Oropharynx
  • Contains tonsils and passage for food and air.
• Laryngopharynx
  • Part of both respiratory and digestive systems.

Larynx (Voice Box)

• A semi-rigid structure made of cartilage.
• Cartilages and muscles control vocal cord movement for speech.

Thyroid and Cricoid Cartilage

• Provide structural support to airways to prevent collapse.
• Epiglottis is a leaf-shaped cartilage that covers the larynx during swallowing.
• Glottis is the opening that leads to the larynx.
• Vocal cords are involved in sound production.

Adam's Apple

• Notch at top of thyroid cartilage, more prominent in men due to puberty.
• Related to larynx enlargement.

Internal Laryngeal Structure

• Detailed description of internal structures of the larynx.

Lower Respiratory Tract

• Trachea: Tubular structure with cartilaginous rings to prevent collapse.
• Primary Bronchi: Divides into right and left bronchi, one for each lung, further branching into secondary and tertiary bronchi, bronchioles.
• Structure
  • Fibrous and elastic outer layer.
  • Cartilage and smooth muscles in the middle layer.
  • Ciliated epithelium and mucus secretion in the innermost lining.
  • Nerve endings present.
• Function
  • Prevents kinks and obstructions as head and neck move.
  • Allows changing shape due to food bolus (swallowing).
  • Mucus traps inhaled debris.
  • Cilia move mucus towards the pharynx.
• Bronchial Tree (Trachea and Bronchi Structures):
  • Bronchi branch into smaller structures called bronchioles, ending up with alveoli.
  • Cartilage decreases and smooth muscle increases in smaller bronchioles.
  • Alveoli are the site of gas exchange.
• Lungs: The lungs have right and left lobes, with fissures separating the lobes.
• Alveoli:
  • Tiny air sacs (about 150 million in adults) in lungs.
  • Lined by simple squamous epithelium for gas exchange.
  • Type I cells perform gas exchange and Type II cells produce surfactant (reduces surface tension)
• Large surface area facilitates gas exchange.

Alveoli Adaptations for Gas Exchange

• Thin walls for efficient diffusion.
• Surfactant reduces surface tension to prevent collapse.
• Rich capillary network for rapid gas exchange.

Accessory Muscles of Respiration

• Muscles that aid in breathing, such as sternomastoids, scalenes, intercostals, and abdominal muscles.

Physiology of the Respiratory System

• Pulmonary Ventilation: Breathing (inhalation and exhalation).
• External Respiration: Gas exchange between alveoli and pulmonary capillaries (O2 in, CO2 out).
• Internal Respiration: Gas exchange between systemic capillaries and tissues (O2 out, CO2 in).

Respiratory Mechanics

• Important factors in breathing, such as Boyle's Law and pressures related to the lungs and chest cavity.

Pressures During Inspiration and Expiration

• Details on pressures involved in inhalation and exhalation, like atmospheric pressure, intra-alveolar pressure, and intrapleural pressure.

Mechanism of Breathing

• Processes of inhalation (diaphragm contracts) and exhalation (diaphragm relaxes).

Lung Volumes and Lung Capacities

• Measurement and definition of different lung volumes and capacities (eg. tidal volume, inspiratory reserve volume).

Control of Respiration

• The nervous system and chemical factors regulate respiration.
• Nervous control: Centers in the brain stem (medulla and pons) send signals to breathing muscles.
• Central chemoreceptors detect changes in pH of cerebrospinal fluid.
• Peripheral chemoreceptors (aortic and carotid bodies) monitor blood gases (pO2 and pCO2)
• Stretch receptors, located in the airways, respond to lung inflation and signal the brain to stop or slow deeper inspiration. (Hering-Breuer reflex).

Transport of Gases

• Oxygen transport in blood: bound to hemoglobin (98.5%) or dissolved in plasma (1.5%).
• Carbon dioxide transport in blood: bicarbonate ions (70%), carbaminohemoglobin (23%), dissolved in plasma (7%).

Oxygen-Hemoglobin Dissociation Curve

• Relationship between oxygen partial pressure and hemoglobin saturation.
• Factors that affect this curve: pH (acidity), temperature, and partial pressure of CO2.

Factors Affecting Oxygen-Hemoglobin Dissociation Curve

• Explains how factors like partial pressure of oxygen (pO2), carbon dioxide (pCO2), acidity (pH), and temperature affect the binding of oxygen to hemoglobin