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 urinary system.
• Explain the processes involved in urine formation.
• Understand the role of excretion in homeostasis.

Lesson summary

Human respiration and excretion are fundamental processes for maintaining homeostasis within the human body. Respiration provides the energy needed for all life processes, while excretion removes metabolic waste products that could be harmful if accumulated. Understanding these processes is crucial for maintaining good health and preventing diseases. For South African learners, issues like respiratory illnesses (e.g., tuberculosis, asthma) and kidney problems are prevalent, making this knowledge particularly relevant. Understanding the underlying mechanisms allows for better awareness, prevention, and management of these conditions.

Lesson notes

2.1 The Human Respiratory System The respiratory system facilitates gas exchange, bringing oxygen into the body and removing carbon dioxide. It consists of the following key components: Nasal Cavity: Air enters the body through the nose, where it is filtered by hairs and mucous, warmed, and moistened. In a dusty environment like some areas in South Africa, the nasal cavity's function is vital in preventing lung irritation.

Pharynx: The throat; a passageway for both air and food.

Larynx (Voice Box): Contains the vocal cords, responsible for sound production.

Trachea (Windpipe): A tube reinforced with cartilage rings to prevent collapse. It conducts air to the lungs. Think of the trachea like a highway for air.

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

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

Alveoli: Tiny air sacs at the end of the bronchioles, surrounded by capillaries. Gas exchange occurs here. The alveoli are like millions of tiny balloons, allowing for a massive surface area for gas exchange.

Lungs: The main organs of respiration, containing the bronchioles, alveoli, and blood vessels.

Diaphragm: A large, dome-shaped muscle at the bottom of the thoracic cavity that plays a crucial role in breathing.

Rib Cage and Intercostal Muscles: The rib cage protects the lungs. Intercostal muscles between the ribs help expand and contract the chest cavity during breathing.

Microscopic structure of the alveoli: Each alveolus is a single cell layer thick and is surrounded by a network of capillaries. This proximity facilitates efficient diffusion of oxygen from the alveoli into the blood and carbon dioxide from the blood into the alveoli. 2.2 Mechanism of Breathing Breathing involves two main processes: inspiration (inhaling) and expiration (exhaling).

Inspiration: Diaphragm contracts and flattens: This increases the volume of the thoracic cavity. Imagine the diaphragm pulling downwards, creating more space.

Intercostal muscles contract: This raises the rib cage, further increasing the volume of the thoracic cavity. Increased thoracic volume leads to decreased pressure: The pressure inside the lungs becomes lower than the atmospheric pressure.

Air rushes into the lungs: Air moves from an area of high pressure (atmosphere) to an area of low pressure (lungs).

Expiration: Diaphragm relaxes and returns to its dome shape: This decreases the volume of the thoracic cavity.

Intercostal muscles relax: The rib cage lowers, further decreasing the volume of the thoracic cavity. Decreased thoracic volume leads to increased pressure: The pressure inside the lungs becomes higher than the atmospheric pressure.

Air is forced out of the lungs: Air moves from an area of high pressure (lungs) to an area of low pressure (atmosphere).

Worked example

Consider a person exercising vigorously. Their breathing rate and depth increase. Explain the physiological changes responsible for this.

Solution: During exercise, the body's demand for oxygen increases and the need to remove carbon dioxide also increases.

This leads to:

Increased rate of diaphragm and intercostal muscle contractions: This allows for faster inhalation and exhalation cycles, increasing the breathing rate.

Greater degree of diaphragm and intercostal muscle contractions: This leads to a larger increase in the thoracic cavity volume during inhalation and a larger decrease during exhalation, resulting in deeper breaths.

Increased blood flow to the lungs: This increases the efficiency of gas exchange in the alveoli.

2.3 The Human Urinary System

The urinary system removes metabolic waste products from the blood and maintains the body's fluid balance.

It consists of the following:

Kidneys: The main organs of excretion. They filter blood and produce urine. Humans have two kidneys located in the abdominal cavity.

Ureters: Two tubes that carry urine from the kidneys to the bladder.

Bladder: A muscular sac that stores urine.

Urethra: A tube that carries urine from the bladder to the outside of the body.

Structure of the Kidney: