Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe gas exchange in the lungs.
• Explain the process of ventilation (breathing).
• Describe the structure and function of the kidney and nephron.
• Discuss the homeostatic control of blood glucose.
• Explain the liver's role in detoxification.

Lesson summary

This week we delve into the crucial processes of human respiration and excretion. Respiration is the process by which our bodies extract energy from food, while excretion is the elimination of metabolic waste products. Understanding these systems is vital not only for understanding how our bodies function but also for making informed choices about our health and well-being. In South Africa, respiratory diseases like tuberculosis and asthma are significant health challenges, and understanding the respiratory system can help us better prevent and manage these conditions.

Lesson notes

2.1 Human Respiration Respiration vs.

Breathing (Ventilation): It's crucial to distinguish between breathing (or ventilation) and respiration. Breathing is the physical process of moving air in and out of the lungs. Respiration, on the other hand, is the chemical process of using oxygen to break down glucose to release energy, producing carbon dioxide and water as waste products. Cellular respiration occurs in all cells of the body, while breathing is the mechanism that allows gas exchange to support cellular respiration.

The Respiratory System: The human respiratory system comprises the following main parts: Nose/Mouth: Where air enters the body. The nose filters, warms, and moistens the air.

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

Larynx: The voice box; contains the vocal cords.

Trachea: The windpipe; a tube that carries air to the lungs. It is reinforced with rings of cartilage to prevent collapse.

Bronchi: Two branches of the trachea that lead to the lungs.

Bronchioles: Smaller branches of the bronchi within the lungs.

Alveoli: Tiny air sacs at the end of the bronchioles where gas exchange occurs. This is where oxygen enters the bloodstream and carbon dioxide leaves.

Mechanism of Ventilation (Breathing): Inhalation (Inspiration): The diaphragm (a large muscle at the base of the chest cavity) contracts and flattens, moving downwards. The external intercostal muscles (muscles between the ribs) contract, raising the rib cage up and outwards. This increases the volume of the thoracic cavity (chest cavity). The increased volume decreases the air pressure in the lungs below atmospheric pressure. Air rushes into the lungs from the atmosphere, down the pressure gradient.

Exhalation (Expiration): The diaphragm relaxes and moves upwards, returning to its dome shape. The external intercostal muscles relax, allowing the rib cage to move down and inwards. This decreases the volume of the thoracic cavity. The decreased volume increases the air pressure in the lungs above atmospheric pressure. Air rushes out of the lungs into the atmosphere, down the pressure gradient. Forced exhalation involves the contraction of internal intercostal muscles and abdominal muscles to further decrease thoracic volume.

Gas Exchange: Gas exchange occurs in the alveoli. The alveoli are surrounded by a dense network of capillaries (tiny blood vessels). Oxygen diffuses from the air in the alveoli across the thin alveolar and capillary walls into the blood. Carbon dioxide diffuses from the blood across the capillary and alveolar walls into the alveoli. The driving force for diffusion is the partial pressure gradient. Partial pressure refers to the pressure exerted by a specific gas in a mixture of gases. Oxygen has a higher partial pressure in the alveoli than in the blood, so it diffuses into the blood. Carbon dioxide has a higher partial pressure in the blood than in the alveoli, so it diffuses into the alveoli.

Alveolar Adaptations for Gas Exchange: Large surface area: The lungs contain millions of alveoli, providing a very large surface area for gas exchange.

Thin walls: The alveolar and capillary walls are only one cell thick, minimizing the distance for diffusion.

Moist surface: The alveoli are lined with a thin layer of moisture, which allows gases to dissolve and diffuse more readily.

Rich blood supply: The alveoli are surrounded by a dense network of capillaries, ensuring a constant supply of blood to carry oxygen away and bring carbon dioxide. 2.2 Human Excretion Excretion vs.

Egestion: Excretion is the removal of metabolic waste products from the body (products of cellular processes). Egestion is the elimination of undigested food (faeces) from the digestive system, which is not a metabolic waste product.

Organs of Excretion: Kidneys: Filter blood to remove nitrogenous wastes (urea), excess salts, and excess water, forming urine.

Lungs: Excrete carbon dioxide and water vapor (products of cellular respiration).

Skin: Excretes sweat, containing water, salts, urea, and other waste products.

Liver: Detoxifies harmful substances and produces urea.

The Kidney: The kidney is the primary organ of excretion. It filters blood and produces urine. Each kidney contains millions of microscopic filtering units called nephrons.

Structure of the Nephron: Bowman's capsule: A cup-shaped structure that surrounds the glomerulus.

Glomerulus: A network of capillaries where filtration occurs.

Proximal convoluted tubule: The first section of the tubule, where reabsorption of glucose, amino acids, salts, and water occurs.

Loop of Henle: A U-shaped structure that helps to concentrate the urine by reabsorbing water and salts.

Distal convoluted tubule: Another section of the tubule, where further reabsorption of water and salts occurs, as well as secretion of certain wastes.

Collecting duct: A duct that collects urine from multiple nephrons and carries it to the renal pelvis.