CHAPTER 12 – THE HUMAN BODY

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Note: It would be useful for the teacher to have access to a butchery during the teaching of this chapter. The organs of a goat, sheep or pig are quite similar to the corresponding human organs and are very suitable for demonstration. If organs from these or similar animals are not available, those of a small mammal such as a rabbit or of a domestic fowl (chicken) could be used as alternatives. It is not necessary to have such materials available for every module, but it is desirable for students to see real organs at some time.

12.1 THE SYSTEMS OF THE HUMAN BODY

Aims:

  • To make students aware of the systems of the human body and their general functions.
  • To remind students about cells (studied in Module 5.3 5.4) and introduce them to the notions of tissues and organs.
  • To review the general features and functions of the circulatory system (studied in Module 8.2).

Activities:

  • Introduce the idea of the systems of the human body and the organs that comprise them. Encourage students to discuss what they already know or believe they know. Throughout this topic, encourage students to refer to their own bodies as examples. Focus this initial discussion on the more obvious systems such as skeletal, muscular, digestive and respiratory.
  • Review previous work on cells (Modules 5.3 – 5.4) focussing on animal cells and growth in multi-cellular organisms. Then introduce the idea that organs are made of tissues, each of which is composed of millions of identical or similar cells.Use samples of red meat (muscle and fat), chicken thighs (muscle, bone, skin and connective tissues) to make sure they are familiar with examples of a few tissues. A heart with blood vessels attached would be useful for revising the circulatory system. Models or charts of the human body would also be useful if available.
  • Review previous work on the circulatory system (Module 8.2). Focus on the general functions of the system and do not allow students to become distracted or confused by too much detail!
  • Encourage students to try the questions at the end of the module. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers.

Answers:

  • Q1. (i) Cells are the tiny ‘building blocks’ from which all living things are made. There are many different kinds of cell, but all cells are surrounded by a cell membrane. All cellscontain a living jelly called cytoplasm and a control centre called the nucleus. (ii) Tissues are the materials that organs are made of. Each tissue is made of millions of cells all of the same kind, or of a few similar kinds. (iii) Organs are the working parts of a living organism. Each organ has a specific function.
  • Q2. A system of the human body consists of a group of organs that work together to perform a general function such as movement, respiration or transport of materials around the body. The systems of the body work closely together and depend on one another – they are inter-dependent, not independent!
  • Q3. Sensitivity means responding to conditions or situations – for example moving out of the sun if you are too hot, or ducking if something is thrown at you! Co-ordination means making different systems or organs work together. For example, to catch something that is thrown at you, you have to coordinate the movement of your hands with what your sight is telling you about the position of the object thrown!

12.2 THE RESPIRATORY SYSTEM

Aims:

  • To provide students with basic information about,and understanding of, the respiratory system, how it works and how it contributes to the needs of the body.

Activities:

  • Use an introductory lesson to review thoroughly with students, Module 6.11 about breathing and respiration, including the respiration equation. Emphasise the differences between inhaled and exhaled air and demonstrate or discuss the activities described in that module. Review also, the parts of Modules 8.2 and 8.4 that deal with the circulation of the blood to the lungs and to the rest of the body; also the functions of the red blood cells and the plasma in carrying oxygen, carbon dioxide and water.
  • Emphasise the fundamental importance of respiration in the cells to the functioning of the human body.
  • Discuss with students the information provided in the textbook regarding the structure and functioning of the respiratory system. If possible show them the lungs of a sheep, goat or pig; it may be possible to inflate the lungs by blowing down a tube inserted in the trachea. Make sure that students can identify the positions of the lungs and diaphragm in their own bodies and refer to any additional models and diagrams that may be available.
  • Encourage students to try the questions at the end of the module. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers.

Answers:

  • Q1. Compared to inhaled (normal) air, exhaled air contains less oxygen, more carbon dioxide and more water vapour. It is also warmer! (See Module 6.11).
  • Q2. Mucus is a sticky liquid that cleans the air passing through the trachea by trapping particles of dust and dirt. Cilia are like tiny hairs on the walls of the trachea that push the mucus towards the mouth where it can be swallowed. The mucus may also be coughed up. (You should take the opportunity to warn students that spitting spreads disease and should be avoided!).
  • Q3. When I run, my muscles are working hard. They need more energy than usual from respiration,so my lungs must work faster to send more oxygen. A molecule of oxygen is absorbed by a red blood cell, in a tiny sack called an alveolus in my lung. The molecule of oxygen is carried by the red cell along a vein to the left side of my heart.The heart pumps it out again through a huge artery. The artery has many branches and the molecule of oxygen eventually reaches my leg and goes along a tiny capillary leading to my leg muscle. It is taken by a muscle cell and used for respiration. Respiration gives the muscle the energy it needs to help me run. During respiration, the molecule of oxygen becomes part of a molecule of carbon dioxide. The carbon dioxide is absorbed by the plasma in the blood which carries it along a tiny capillary, into a vein, and back to the right side of the heart. Finally, the right side of my heart pumps the blood containing the carbon dioxide back to the lungs were it is released into an alveolus and I breathe it out. So the oxygen molecule, which is now part of a carbon dioxide molecule, returns to the air again. (See Modules 8.2 to 8.4 for details of the blood and its circulation).

12.3 THE DIGESTIVE SYSTEM

Aims:

  • To make students aware of the four food groups that constitute the bulk of what we eat, and of digestion as the process of breaking down these for distribution to meet the needs of all parts of our bodies.
  • To provide students with basic information about, and understanding of, the digestive system, how it works, and how it contributes to the needs of the body.

Activities:

  • Start off by discussing what students eat. Have local foods to show them and identify examples of good sources for each of the four bulk food groups. (Nutrition and the balanced diet will be studied later in Chapter 17. At this stage we are interested only in a much broader picture).
  • Emphasise the fundamental nature of digestion as a process of breaking down foods into simpler substances that our bodies can absorb, our blood transport, and our cells use.
  • Discuss with students the information provided in the textbook regarding the structure and functioning of the digestive system. Refer wherever possible to the students’ own bodies and experiences as examples, and make sure that they can identify the positions of the gullet, stomachand intestines in their own bodies. If convenient, show them the guts of a sheep, goat or pig and make use of any models/diagrams that may be available. Peristalsis can be demonstrated by forcing a pea or similar object through a rubber or plastic tube by squeezing it along. Focus on helping students to understand the basic ideas involved and do not confuse them with unnecessary details (unless required by your local syllabus).
  • Encourage students to try the questions at the end of the module. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers.

Answers:

  • Q1. (i) A gland is an organ that produces and secretes (delivers) one or more substances needed by the body for specific purposes. (ii) An enzyme is a substance that assists in the chemical break-down of food during digestion. (Enzymes also have other roles but this is an adequate definition at this stage). (iii) Peristalsis is the process used to move food through the gullet and intestines. It involves the muscles in the tube squeezing just behind the food and thus forcing it along.
  • Q2. The intestine digests food with the help of enzymes from the pancreas and bile from the liver. These all enter the duodenum, which is the first part of the small intestine. The enzymes help to turn carbohydrates into glucose and proteins into amino acids. Fats are emulsified by the bile and then turned into fatty acids by the enzymes. The digested food is absorbed through the villi on the walls of the small intestine and goes into the blood capillaries inside the villi. Water is absorbed through the walls of the large intestine. A feature of the small intestine that helps absorption is the villi that cover its walls. These greatly increase the surface area for absorption. Another feature is the great length of the intestine. This increases both the surface area and the time available for absorption.
  • Q3. Glucose is the soluble sugar used for respiration. It comes from the digestion of carbohydrates. Digestion of carbohydrates starts in the mouth where an enzyme in saliva starts converting starch to sugar. In the small intestine, more enzymes convert remaining carbohydrates into glucose.

12.4 THE LIVER, THE LYMPHATIC SYSTEM AND THE SPLEEN

Aims:

  • To make students aware of the position, size and importance of the kidney and spleen, and to inform them about some of their functions.
  • To make students aware of the lymphatic system as a drainage system that works throughout the body in support of the circulatory system, and to understand how it functions.

Activities:

  • Help students to identify the positions of the kidney and spleen in their bodies and discuss what they know about their functions. Discuss the information provided in the textbook and if convenient show them a liver and a spleen from the butchery. (They should be aware of the importance and of these organs, but it is not necessary for most of them to memorise detailed lists of functions).
  • Discuss with students the information provided in the textbook regarding the structure and functioning of the lymphatic system. If convenient, show them a lymph vessel from the butchery. Refer wherever possible to the students’ own bodies and experiences as examples.
  • Encourage students to try the questions at the end of the module. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers.

Answers:

  • Q1. The liver is a big organ because it has to perform many complex functions (as listed by the dot points in the textbook).
  • Q2. (i) Plasma is the clear, pale yellowish, liquid part of the blood. (ii) Lymph is the liquid that flows in the lymph vessels. It comes from the plasma and has a similar composition. (iii) Lymphocytes are white blood cells that destroy foreign bacteria and viruses. (iv) Lymph nodes are small, roundish organs where several lymph vessels come together. They contain lymphocytes and are situated especially in the neck, arm pits, groin and trunk.
  • Q3. Tissue fluids are released into the tissues and drain into the lymph vessels all over the body, all the time. Because there is no pump in the lymphatic system, movement of the lymph along the lymph vessels depends on general muscular activity. If you are sitting and not moving around, the leg muscles are not active and the lymph vessels in the feet fill up. When more tissue fluid is released in the feet, it has nowhere to go and the feet start to swell! (Passengers on long international plane flights often find their feet swelling. To avoid this, they should get up and walk around from time to time).

12.5 THE EXCRETORY SYSTEM

Aims:

  • To make students aware of the body’s need for an excretory system to remove the waste products of bodily processes, including the destruction of dead cells.
  • To inform students about the excretory functions of the lungs, liver and skin.
  • To provide students with basic information about the urinary system and its role in excretion.

Activities:

  • Discuss the importance of the proper disposal of waste materials in everyday life. This can lead on to discussing the same issue in regard to the human body and identifying of some of the main wastes to be disposed of. Emphasise the breakdown of dead cells as a process producing waste materials.
  • Discuss with students the information provided in the textbook regarding excretion, and the structure and functioning of the urinary system. If convenient, show students a kidneys and a bladder from the butchery. Refer wherever appropriate to the students’ own bodies and experiences as examples, and make sure that they can identify the positions of the kidneysand bladder in their own bodies.Use any additional models and diagrams that may be available.
  • Encourage students to try the questions at the end of the module. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers.

Answers:

  • Q1. Excretion is necessary to remove waste products from the body. If they were not removed they would accumulate and stop the body working properly (that is to say, they would poison it). (i) Carbon dioxide is carried away from the tissues by the blood and excreted in the lungs. (ii) Nitrogenous wastes are processed in the liver to form urea. The urea is carried by the blood to the kidneys where it is excreted in the urine.
  • Q2. (i) The kidneys remove water, urea, salt and other waste products from the blood and excrete it as urine into the ureters. (ii) The ureters carry urine to the bladder. (iii) The bladder stores urine. (iv) The sphincter muscle controls the exit from the bladder into the urethra. (v) The urethra carries urine from the bladder to the outside of the body.

12.6 THE SKELETAL-MUSCULAR SYSTEM

Aims:

  • To inform students about the structure and functions of the skeletal and muscular systems.

Activities:

  • Try to find any available animal bones, including vertebrae, to take to the class. If possible cut open a large bone such as a femur to show the marrow and spongy bone inside.
  • Discuss with students the information provided in the textbook regarding skeletal-muscular system. Refer wherever appropriate to the students’ own bodies and experiences as examples, and make sure that they can identify the positions of the more important bones and muscles in their own bodies. Show them any bones you have been able to bring to the class, stressing the importance of the backbone and its flexibility. Use any additional models and diagrams that may be available.
  • Encourage students to try the questions at the end of the module. Follow up by discussing their attempts. Make sure they are aware of, and understand, the correct answers. The answer to Q3 raises an important issue and should be discussed thoroughly.

Answers:

  • Q1. (i) The heart is protected by the ribs. (ii) The spinal chord is protected by the spinal (or vertebral column). (iii) The brain is protected by the skull. (iv) The lungs are protected by the ribs.
  • Q2. Cartilage is a tough, flexible material . It is found between the bones in joints and in the vertebral column. It allows the bones to move without wearing against one another.
  • Q3. The triceps muscle pulls a bent elbow straight. (Muscles are no good at pushing – they can only pull, so all joints need a muscle on each side, one to bend the joint and one to straighten it).
  • Q4. Since we gain about 6 times the distance moved, we lose 6 times the force. Therefore our biceps have to use a force of about 60 kg (or 600N) to lift 10 kg. (Review Module 10.9 if necessary!).

12.7 THE SENSORY-NERVOUS SYSTEM

Aims:

  • To make students aware of our sensory organs and their role in keeping us informed about our surroundings.
  • To provide students with basic information about structure and functions of the nervous system and its roles in (i) voluntary and reflex actions, and (ii) coordinating the actions of the human body.
  • To make students aware of the human brain as (i) an array of interconnected nerve cells, and (ii) a super-computer that gives us unique abilities as regards such things as awareness, language, thought and imagination.

Activities: