Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the structure and function of the respiratory system.
• Explain the mechanism of breathing (inspiration and expiration).
• Describe the structure and function of the excretory system.
• Explain the process of urine formation.
• Identify common respiratory and excretory ailments.

Lesson summary

Respiration and excretion are fundamental life processes crucial for maintaining homeostasis in our bodies. Respiration provides the energy we need to carry out all activities, from breathing to running a marathon. Excretion removes metabolic wastes that, if accumulated, could be toxic and disrupt our bodily functions. Understanding these systems is vital for understanding overall human health and disease. In South Africa, respiratory ailments like tuberculosis and asthma are prevalent due to various factors, including air pollution and socioeconomic conditions.

Lesson notes

2.1 The Human Respiratory System The respiratory system facilitates gas exchange – taking in oxygen (O 2 ) and removing carbon dioxide (CO 2 ). This process is essential for cellular respiration, where energy is produced within cells.

Components of the Respiratory System: Nasal cavity: Filters, warms, and moistens incoming air. Cilia and mucus trap dust and pathogens.

Pharynx (throat): A passageway for both air and food.

Larynx (voice box): Contains the vocal cords, which vibrate to produce sound.

Trachea (windpipe): A cartilaginous tube that carries air to the lungs. It is lined with ciliated epithelium to trap and remove debris.

Bronchi: The trachea divides into two bronchi, one entering each lung.

Bronchioles: The bronchi further divide into smaller and smaller tubes called bronchioles. They lack cartilage and are surrounded by smooth muscle.

Alveoli: Tiny air sacs at the end of the bronchioles where gas exchange occurs. The alveoli are surrounded by capillaries. Their large surface area (approximately 70 m 2 in humans) maximizes gas exchange efficiency.

Mechanism of Breathing: Breathing involves two phases: Inspiration (Inhalation): An active process. The diaphragm contracts and flattens, increasing the volume of the thoracic cavity. The external intercostal muscles contract, raising the rib cage. This decreases the pressure in the lungs (below atmospheric pressure), causing air to rush in.

Expiration (Exhalation): A passive process (usually). The diaphragm and intercostal muscles relax, decreasing the volume of the thoracic cavity. This increases the pressure in the lungs (above atmospheric pressure), causing air to flow out. During forced expiration (e.g., during exercise), the internal intercostal muscles contract, actively depressing the rib cage.

Gas Exchange: Gas exchange occurs in the alveoli. Oxygen diffuses from the alveoli into the blood capillaries, while carbon dioxide diffuses from the blood capillaries into the alveoli. This is driven by the difference in partial pressures of the gases. The blood then transports the oxygen to the body tissues.