Lesson Notes By Weeks and Term v5 - Grade 11
Transport systems in humans – Week 9 focus
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Transport systems in humans – Week 9 focus
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Subject: Life Sciences
Class: Grade 11
Term: 2nd Term
Week: 9
Theme: General lesson support
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The transport system in humans is critical for delivering essential substances like oxygen, nutrients, and hormones to every cell in the body, and for removing waste products like carbon dioxide and urea. This intricate network ensures the survival and proper functioning of all our organs and tissues. Understanding how the human transport system works is not only fundamental to understanding human biology, but also helps us understand the causes and prevention of various diseases prevalent in South Africa, such as heart disease, hypertension, and stroke. Understanding these systems empowers us to make informed decisions about our health and lifestyle.
2.1 The Components of the Human Circulatory System The circulatory system is composed of three main parts: the heart, blood vessels, and blood.
The Heart: This muscular organ acts as a pump, propelling blood throughout the body. It’s located in the thoracic cavity, between the lungs.
Blood Vessels: These form a network of tubes that transport blood.
There are three main types: Arteries: Carry blood away from the heart. They have thick, elastic walls to withstand the high pressure of the blood being pumped from the heart. The largest artery is the aorta.
Veins: Carry blood back to the heart. They have thinner walls than arteries and contain valves to prevent the backflow of blood, especially in the limbs, working against gravity. The largest veins are the vena cavae.
Capillaries: Tiny, thin-walled vessels that connect arteries and veins. They are the site of exchange of nutrients, gases (oxygen and carbon dioxide), and waste products between the blood and the body's cells. Their walls are only one cell thick to facilitate diffusion.
Blood: A fluid tissue that transports oxygen, nutrients, hormones, and waste products.
It consists of: Red Blood Cells (Erythrocytes): Carry oxygen, due to the presence of haemoglobin, an iron-containing protein. They are biconcave in shape, increasing surface area for oxygen absorption.
White Blood Cells (Leukocytes): Defend the body against infection. There are different types, each with specific functions in the immune response.
Platelets (Thrombocytes): Involved in blood clotting. They are small cell fragments.
Plasma: The fluid portion of blood, mainly water, carrying dissolved nutrients, hormones, waste products, and proteins. 2.2 The Structure and Function of the Heart The heart is a double pump, consisting of two sides, each with an atrium and a ventricle.
Atria (singular: Atrium): Receive blood returning to the heart. The right atrium receives deoxygenated blood from the body via the superior and inferior vena cavae, and the coronary sinus (draining blood from the heart muscle itself). The left atrium receives oxygenated blood from the lungs via the pulmonary veins.
Ventricles: Pump blood out of the heart. The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery. The left ventricle pumps oxygenated blood to the rest of the body via the aorta. The left ventricle has thicker walls than the right ventricle because it needs to generate more force to pump blood to the entire body.
Valves: Ensure that blood flows in only one direction through the heart.
Atrioventricular Valves (AV Valves): Located between the atria and ventricles. The tricuspid valve is on the right side, and the bicuspid (mitral) valve is on the left side.
Semilunar Valves: Located at the exit of the ventricles. The pulmonary valve is at the entrance to the pulmonary artery, and the aortic valve is at the entrance to the aorta. 2.3 Types of Blood Vessels and their Structure-Function Relationship Arteries: Thick, elastic walls to withstand high pressure. Elastic fibres allow the artery to stretch and recoil, maintaining blood pressure. Smooth muscle in the walls can constrict or dilate, regulating blood flow to different parts of the body.
Veins: Thinner walls than arteries. Contain valves to prevent backflow of blood, especially in the limbs, where blood has to travel against gravity.
Capillaries: Very thin walls (one cell thick) to allow for efficient exchange of gases, nutrients, and waste products between the blood and the body's cells via diffusion. The capillary network is extensive, increasing the surface area for exchange. 2.4 Composition of Blood and the Functions of Each Component | Component | Function | |-------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------| | Red Blood Cells | Transport oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. | | White Blood Cells | Defend the body against infection and disease through phagocytosis (engulfing pathogens) and antibody production. | | Platelets | Initiate blood clotting by forming a platelet plug at the site of injury and releasing clotting factors. | | Plasma | Transports nutrients, hormones, antibodies, and waste products. It also helps regulate body temperature and maintain blood volume and blood pressure. | 2.5 Systemic and Pulmonary Circulation Pathways Pulmonary Circulation: The pathway of blood from the heart to the lungs and back to the heart. Deoxygenated blood is pumped from the right ventricle to the lungs via the pulmonary artery. In the lungs, carbon dioxide is removed from the blood, and oxygen is absorbed. Oxygenated blood returns to the left atrium via the pulmonary veins.
Systemic Circulation: The pathway of blood from the heart to all parts of the body and back to the heart. Oxygenated blood is pumped from the left ventricle to the body via the aorta.