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 (inhalation and exhalation).
• Describe the structure and function of the excretory system.
• Explain the role of the kidneys in waste removal and osmoregulation.
• Identify common respiratory and excretory disorders in a South African context.

Lesson summary

In Grade 10, you learned about cellular respiration and the basic needs for life. This year, we delve deeper into how humans specifically obtain oxygen and eliminate waste products – processes vital for maintaining homeostasis and overall health. Understanding respiration and excretion is crucial for several reasons. For example, respiratory illnesses like tuberculosis (TB) and asthma are prevalent in South Africa. Knowing how the respiratory system functions helps us understand these diseases better and promote healthier lifestyles. Similarly, kidney diseases are a growing concern.

Lesson notes

2.1 The Human Respiratory System The respiratory system's primary function is gas exchange: taking in oxygen (O₂) and releasing carbon dioxide (CO₂). This exchange occurs in the alveoli of the lungs.

Let's break down the structure: Nasal Cavity and Mouth: Air enters the body through these openings. The nasal cavity warms, moistens, and filters the air. Hairs and mucus trap dust and other particles.

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

Larynx (Voice Box): Contains the vocal cords, which vibrate to produce sound.

Trachea (Windpipe): A tube reinforced with C-shaped rings of cartilage to prevent collapse.

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

Bronchioles: Inside the lungs, the bronchi branch into smaller and smaller tubes called bronchioles.

Alveoli: Tiny air sacs at the end of the bronchioles. These are the functional units of the lungs where gas exchange occurs. The alveolar walls are very thin and surrounded by capillaries, facilitating diffusion of O₂ into the blood and CO₂ out of the blood.

Lungs: The main organs of respiration. They are spongy and elastic. The right lung has three lobes, and the left lung has two lobes (to accommodate the heart).

Pleura: A double-layered membrane that surrounds each lung. The space between the layers contains pleural fluid, which reduces friction during breathing.

Diaphragm: A large, dome-shaped muscle located at the base of the chest cavity. It plays a crucial role in breathing.

Intercostal Muscles: Muscles located between the ribs, also involved in breathing. These are the external intercostal muscles which contract during inhalation, and the internal intercostal muscles which contract during forceful exhalation.

Example: Imagine trying to filter water from the Vaal River before drinking it. The nasal cavity is like the first stage of filtration, removing large debris. The mucus and cilia act as finer filters to trap even smaller particles. This is especially important in polluted areas of Gauteng or the industrial regions of KwaZulu-Natal where air quality can be poor. 2.2 Mechanism of Breathing (Ventilation)

Breathing involves two phases: inspiration (inhalation) and expiration (exhalation).

Inspiration (Inhalation): Diaphragm contracts: It moves downwards, increasing the volume of the thoracic cavity.

External intercostal muscles contract: They lift the ribs upwards and outwards, further increasing the volume of the thoracic cavity.

Volume of the thoracic cavity increases: This decreases the pressure within the thoracic cavity below atmospheric pressure.

Air rushes into the lungs: Air moves from an area of higher pressure (outside the body) to an area of lower pressure (inside the lungs).

Expiration (Exhalation): Diaphragm relaxes: It moves upwards, decreasing the volume of the thoracic cavity.

External intercostal muscles relax: The ribs move downwards and inwards, further decreasing the volume of the thoracic cavity.

Volume of the thoracic cavity decreases: This increases the pressure within the thoracic cavity above atmospheric pressure.

Air is forced out of the lungs: Air moves from an area of higher pressure (inside the lungs) to an area of lower pressure (outside the body).