Mammalian System

This section is a continuation of the study of “systems of life”, which was started in year one. Two of the mammalian systems, the circulatory and excretory systems, will be discussed in this section. These two systems play very vital roles in the proper functioning of the human body through their functions, which can be said to be closely related. The cardiovascular system is composed of the heart, blood vessels and blood tissue. The circulatory function of the cardiovascular system is necessary for maintaining a stable internal balance within the internal environment of the organism. The excretory system, which works in harmony with the cardiovascular system, is composed of the kidneys, skin, lungs and liver. The main function of these organs is primarily to remove waste from the body of the organism. For instance, the kidneys excrete urine while the skin excretes sweat.

As mentioned earlier, maintaining a stable internal environment (homeostasis) is vital to healthy living, and therefore, the need for these processes to take place.

Failure of these processes to occur will lead to the accumulation of toxins within the body of the animals, which, without treatment, may lead to eventual death.

The interactions of these two systems in their functions are key to ensuring the optimum functioning of the organism and, ultimately, its survival. This section ends with discussions on the transport system in plants and photosynthesis, which is the basic biological process used by plants, algae and some bacteria, e.g. Chlorobium, to turn light energy into chemical energy. This is an important process as it is the source of all the energy supply in all ecosystems, as well as maintaining a balance of the oxygen and carbon dioxide levels in the atmosphere.

KEY IDEAS

• Photosynthesis occurs in the chloroplasts of organisms in two stages, that is, the light stage and the dark stage.

• Plants use vascular tissues (xylem and phloem) to transport water, dissolved minerals and produced food substances.

• The photosynthetic process is performed by organisms that have the chlorophyll pigment in their systems and use light energy.

• The cardiovascular system, also known as the circulatory system, is responsible for transporting oxygen, nutrients, hormones and waste products throughout the body. It consists of the heart, arteries, veins, capillaries and blood tissue.

• The excretory system is made up of organs and structures responsible for removing waste materials from the body to ensure homeostasis.

The cardiovascular system is a complex network of organs and tissues that transports oxygen, nutrients, hormones, and other materials, such as carbon dioxide and urea, throughout the body to specific organs to be excreted. The structure of the various components relates to their function in attaining a functional system.

The Heart

This is a muscular organ that pumps blood throughout the body. it is divided into four chambers: the right atrium or auricle (RA), the left atrium or auricle (LA), the right ventricle (RV) and the left ventricle (LV). The RA and RV are separated from the LA and LV by a thick muscular wall called the septum. This prevents blood in the left side of the heart from mixing with that of the right side. The right side receives deoxygenated blood from the cells of the body and pumps it to the lungs for oxygen uptake and carbon dioxide release, while the left side receives oxygenated blood from the lungs and pumps it to all parts of the body. The atrioventricular septum separates the atria from the ventricles. The thick muscular wall, the ellipsoidal shape and large chamber volume of the left ventricle adapt it to its function of pumping blood to all parts of the body. Between the RA and the RV is the tricuspid valve, and between the LA and the LV is the bicuspid valve or mitral valve. Both valves ensure blood flows in one direction, preventing backflow and ensuring efficient circulation of blood.

A healthy blood pressure reading for most adults is less than 120/80 millimetres of mercury (mmHg), with the top number (systolic) representing the pressure when the heart beats or pumps, while the bottom number (diastolic), when the heart rests or relaxes. When the pressure at which the heart pumps rises to 140/90 mmHg or higher, it results in a condition called hypertension. This can occur because of ageing, family history, being overweight, being physically inactive, high salt intake or drinking too much alcohol.

Other common conditions that affect the heart include; coronary artery disease (CAD), which is a narrowing or blockage of the coronary arteries; heart failure (inability of the heart to pump enough blood), arrhythmia (abnormal heart rhythms), myocardial infarction (heart attack), cardiac arrest (sudden loss of heart function), endocarditis (infection of the heart valves and inner lining) and dilated cardiomyopathy (enlarged heart muscle).

Figure 4.1: Anatomy of the human heart Blood vessels Blood vessels are a crucial part of the circulatory system, responsible for transporting blood (oxygenated and deoxygenated) throughout the body. The three main types of blood vessels in humans and other mammals are arteries, veins and capillaries. The arteries (except for the pulmonary artery and umbilical artery) transport oxygenated blood from the heart to the body tissues. The thick walls enable them to withstand the high blood pressure flowing through them. Veins, on the other hand (except for the pulmonary veins), transport deoxygenated blood to the heart and have thinner walls with valves to prevent backflow of blood. Veins can be divided into large veins (e.g. vena cava, pulmonary veins), medium veins (e.g. femoral vein and jugular vein) and small veins (e.g. venules). jugular veins are a pair of veins which are located on either side of the neck. Femoral veins are in the thigh, starting from the knee through the groin to the abdomen. Capillaries are tiny blood vessels with very thin walls, usually one cell thick. This unique structure allows for efficient exchange of oxygen, nutrients, hormones and waste products between the blood and surrounding tissues.

Figure 4.2: Image showing the interior of a vein and an artery.

Figure 4.3: Cross section of an artery

Figure 4.4: Cross section of a vein

Table 4.1: Summary of differences between arteries, veins and capillaries.

Arteries Veins Capillaries

Function Carry oxygenated blood from the heart to various parts of the body except the pulmonary artery.

Carry oxygenated blood from various parts of the body to the heart.

Facilitates the

exchange of materials between blood and tissues.

Location Deeply seated in the body to protect them from damage.

Superficially located in the body because they play a crucial role in temperature regulation.

Form a network inside the body organs Pressure Blood flows at high pressure Blood flows at low pressure because of the presence of one- way valves, relaxed vessel walls and gravity’s effect.

Blood flows at very minimal pressure compared to that of arteries, but higher than in veins.

Lumen Diameter

Marrow Wide because of their thinner walls, the low pressure of blood flowing through them and the need to accommodate a larger volume of blood returning to the heart.

Extremely narrow (one cell wide) Wall Thickness Have thick elastic walls to withstand the high pressure of blood pumped by the heart Thin Extremely thin (single cell thick) to facilitate efficient exchange of substances between the bloodstream and surrounding tissues.

Wall Layers

Three layers Three layers One layer Arteries Veins Capillaries Muscle and Elastic Fibres Large amounts to allow them to expand and recoil with each heartbeat to withstand the high pressure of blood coming from the heart.

Small amounts None Valves Absent because the high pressure at which the heart pumps ensures one-way (unidirectional) flow of blood, giving less chance for a backflow.

Present to ensure that blood flows in one direction towards the heart, preventing backflow due to the low pressure of the blood.

Absent because of their extremely narrow diametre and the pressure at which blood flows prevents a backflow.

Blood Blood is a vital fluid in the human circulatory system, delivering oxygen and nutrients to cells and transporting waste products to specific organs for excretion.

The components of blood are the plasma (liquid portion) and corpuscles or cells (solid portion). The solid part is made up of:

1. The red blood cells (RBCs) or erythrocytes: These are biconcave, disk- shaped cells produced in the bone marrow. Mature RBCs, called corpuscles, do not have a nucleus and many organelles. Dissolved within the cytoplasm is haemoglobin, which is a globular protein, meaning it has a roughly rounded shape. Haemoglobin contains four heme groups, with each containing an iron atom (in the form of Fe²⁺). This iron atom in haemoglobin allows it to bind to oxygen in the lungs, transport oxygen to the body’s tissues and release oxygen where it is needed.

Figure 4.5: Red blood cells

2. The white blood cells (WBCs) or leucocytes: the function of WBCs is to fight infections or foreign materials in the body through an immune response. They form a key part of the immune system and are produced in the bone marrow with a variable lifespan of hours to days. Also, there is a nucleus within the cytoplasm. The types of WBCs are neutrophils, lymphocytes, monocytes, eosinophils and basophils. The structure of each type differs from the other due to variations in the shape of the nucleus and other materials found in the cell.

Figure 4.6: Types of white blood cells

3. Platelets (thrombocytes): Platelets are small, irregular non non-nucleated (without nucleus) fragments of cells produced in the bone marrow with a life span of about 8-12 days. Their primary function includes blood clotting, wound healing and homeostasis.

The liquid portion of blood, called plasma, is largely composed of water. Other materials present are proteins, dissolved food nutrients, dissolved gases, mineral salts, hormones, electrolytes and waste products. The functions include:

a. Transport of nutrients, hormones and waste products.

b. Regulation of blood pH, temperature and osmotic balance.

c. Blood clotting.

d. Blood pressure regulation.

Figure 4.6: Image of the cellular and fluid components of human blood

Activity 4.1 Anatomy of the human heart

1. Visit the following website (https://www.youtube.com/ watch?v=CWFyxn0qDEU on YouTube and watch videos of the anatomy or structure of the human heart. Do this together with your friends. (If unable to get access to the internet, use charts on the human heart.)

2. From the video you watched or the charts you studied, identify the organs and tissues that form the cardiovascular system in humans and relate the structures of the heart to their functions.

3. Work with two or three of your friends to design a mind map on the cardiovascular system, its structures and how the structures relate to their functions.

4. Display your design on your classroom wall as reference material.

Activity 4.2 Cardiovascular health

1. Search the internet or read medical journals for information on some common defects of the organs and tissues of the cardiovascular system in humans. (You may also speak with a medical professional for information on some common defects of the organs and tissues of the cardiovascular system in humans.)

2. Carefully note down the information you gathered from your source in your notebook.

3. Discuss with your friends the effects of a diseased or defective cardiovascular system and how it can affect the normal functioning of the body.

Excretory System of Humans

The excretory system in multicellular organisms is responsible for the removal of waste materials from the body and for regulating water and ion balance. It is made up of organs and structures that perform various functions to ensure that the body is balanced and healthy, to achieve homeostasis. Homeostasis is the ability to maintain internal stability in an organism despite any environmental changes.

The focus of this session is on the main excretory organs in humans, which are the kidneys, skin, lungs and the liver. Here we will study the structures of the excretory organs and their functioning to maintain a healthy balance in the human body. We will briefly mention some common diseases or infections that occur when these organs are not functioning properly.

Parts and structure of the excretory system in humans and their functions The Kidneys are a part of the urinary system. This system consists of other parts such as the ureter, the urinary bladder and the urethra, which all work together to produce and remove urine from the human body. The kidneys are a pair of bean- shaped organs in the upper abdominal region of the human body.

Figure 4.7: Front view of the Urinary tract.

Table 4.2: Parts and functions of the urinary system Parts of the Urinary System Function Kidney • Regulates blood volume and composition.

• Regulates blood pH.

• Regulates ions in the blood.

• Produces hormones, e.g. Erythropoietin (which stimulates bone marrow to produce red blood cells).

• Removes waste materials from the blood to form urine.

Ureter Transports urine from the kidney to the bladder.

Bladder Stores and expels urine through the urethra.

Urethra Discharges urine from the body.

Each pair contains millions of basic structural and functional microscopic units, called nephrons or kidney tubules. Each kidney tubule or nephron has several parts that perform various function. Some of these parts include the afferent arterioles and efferent arterioles that form a knot in the Bowman’s capsule, proximal/ first convoluted tubules, loop of Henlé, distal/proximal convoluted tubule, and collecting ducts.

The kidneys filter blood flowing from the renal artery into the afferent arteriole to the glomerulus to remove unwanted materials like urea and salts to form urine.

The glomerulus allows water, ions, small molecules and wastes to pass into the Bowman’s capsule and retains large molecules like blood cells and proteins. This process is called ultrafiltration. The kidneys reabsorb from the filtrate, essential nutrients, ions and water back into the bloodstream in the proximal convoluted tubule. Further reabsorption of water, nutrients and salts to concentrate the filtrate occurs in the loop of Henle. The distal convoluted tubule adjusts the composition of the filtrate by reabsorbing water and ions. The collecting duct further reabsorbs water to concentrate the urine and transports it to the bladder through the ureter.

These two main processes in urine formation, ultrafiltration and reabsorption, are regulated by anti-diuretic hormone (ADH), thus reducing urine output. Anti- diuretic hormone (ADH) is a hormone produced in the hypothalamus and released by the pituitary gland that regulates water balance in the body by controlling how much water the kidneys excrete.

Figure 4.8: Components of the urinary system.

The main components of urine are water (about 95%), nitrogenous compounds (urea, uric acids and ammonia), creatinine (waste produced from creatine by the natural and normal breakdown of muscle tissues), organic and inorganic salts and ions. Blood cells and proteins are not removed due to their large molecular size. Besides processing and removing metabolic waste, the kidney also produces hormones, regulate blood volume and ensure pH and ion balance by osmoregulation. Filtered blood leaves the kidney through the renal vein.

Some common diseases and infections of the kidney are kidney stones, kidney cancer and urinary tract infections (UTI’s). Kidney stones are formed when waste substances like extra salt, water, potassium, acid and nitrogen are sometimes in excess in the blood, and the kidneys cannot filter it all out. When these substances build up, they can form crystals in the kidneys, and these crystals can attract one another to form a solid object called a kidney stone. Kidney stones vary in size and shape. They can be as small as a grain of sand or as large as a golf ball. Kidney stones can be either smooth or jagged on the edges. If a kidney stone is not passed or removed from the body, it can continue to grow, and surgery would be needed to remove it. Kidney failure occurs when the kidneys have stopped working well enough for survival without dialysis or a kidney transplant. Kidney failure can be caused by severe infections and cancer. Urinary tract infection (UTI) is a common infection that affects any part of the urinary tract, including the bladder, urethra, or kidneys, and is often caused by bacteria entering through the urethra.

Activity 4.3 Understand the parts of the kidney and the nephron.

1. Build a chart of the kidney

a. Use papers, colours to draw the structure of the kidney.

b. Label the drawn structure.

c. Write a one-sentence note describing each labelled part.

d. Paste your diagram on the walls in your classroom.

2. Labelling the Nephron

Activity:

a. Print out or draw the diagram of the nephron

b. Use these key words or phrases to label the diagram of the nephron above: Bowman’s capsule, Glomerulus, Proximal convoluted tubule, Loop of Henle, Distal convoluted tubule, Collecting duct, ascending limb of the loop of Henle, descending limb of the loop of Henle.

Skin The skin is a continuous, flat layer that covers the entire body. It is composed of three main layers: the epidermis, the dermis and the hypodermis. The epidermis is the outermost layer formed from stratified epithelial cells, and contains some blood vessels, nerves, hair follicles and glands; the epidermis is interlocked with the dermis, which is an inner layer and has the same composition as the epidermis.

The hypodermis is a subcutaneous structure, which is the deepest layer of the skin, primarily composed of adipose and connective tissues.

Through the sweat glands, the skin produces sweat, which evaporates, drawing heat away from the body and cooling it down to regulate body temperature. This is evidenced by the cooling effect experienced by the body after sweat evaporates from the skin. The skin also detects stimuli through the numerous nerves scattered within it. It also protects the body and internal organs and tissues from pathogens and mechanical injuries The main components of sweat are water, salts, traces of urea, uric acids and ammonia. The exact composition of sweat may vary due to factors such as diet, level of hydration and the specific physiology of the individual.

Figure 4.9: The human skin Some common diseases of the skin are acne, eczema and vitiligo. Acne is a common skin condition that happens when hair follicles under the skin become clogged with sebum (an oil that helps keep skin from drying out) and dead skin cells, which leads to outbreaks of lesions, commonly called pimples or zits.

Eczema (dermatitis) is an inflammation that causes the skin to become dry and itchy with bumpy patches, weakening the skin as a barrier of protection. This condition happens when the skin comes into contact with substances that trigger eczema, e.g. dry weather, fabrics, skin care products, smoke and pollutants and other substances one may be allergic to. Vitiligo (resulting in white patches on the skin or hair) occurs because of a lack of the skin pigment, melanin. This can cover parts of the skin or sometimes the entire body. What causes vitiligo is unknown, but it is not contagious.

Activity 4.4 Action of Sweating

Objective: Understand the role of sweat glands in maintaining homeostasis.

Materials needed

• Exercise equipment (e.g., jump rope)

• Paper towels

• Stopwatch.

Procedure

1. Work with your team to observe and record the dryness of the skin before exercise, using paper towels or tissue.

2. Perform a physical activity with your team members, like jumping rope or skipping rope, for 5-10 minutes.

3. Observe and record the presence of sweat on the skin, using another paper towel.

4. Discuss with your team how sweating helps cool the body and maintain temperature homeostasis.

5. Share your discussions and observations with other teams in the class.

Note

Be careful not to share paper towels, as this may lead to the spread of infectious skin diseases.

The Lungs

The Lungs are paired organs located within the thoracic cavity, at the chest region, extending from the clavicle (collar bones) at the upper side and the diaphragm at the lower part above the abdomen. They are a part of the respiratory system.

These cone-shaped organs have a broad base and a pointed apex containing tiny air sacs called alveoli, surrounded by capillaries.

Figure 4.10: Air enters the lungs through the nasal cavity and then passes through the pharynx and the trachea into the alveoli.

The lungs are primarily responsible for the exchange of gases. Carbon dioxide from body tissues diffuses into the blood and is transported in the capillaries and veins to the alveoli. Carbon dioxide diffuses into the alveoli and is excreted through the bronchioles and bronchi to be exhaled through the nasal passage.

Water in the form of vapour is also excreted.

Some common diseases associated with the lungs are pneumonia, bronchitis, lung cancer and asthma.

The Liver

This is a wedge-shaped organ with broad, rounded edges, responsible for producing bile, deamination and detoxification. The organ performs these functions mainly by specialised cells called hepatocytes (liver cells). Bile is produced from red blood cells and contains bilirubin (a yellowish-orange pigment) and Biliverdin (a green, water-soluble bile pigment), which are the waste products from the breakdown of haemoglobin in red blood cells. Bile itself is not a waste product but a digestive juice which is stored in the gall bladder. Bile is released into the intestine to break down fats into fatty acids, to absorb fat-soluble vitamins and is excreted from the body through egestion with faeces. The liver helps detoxify the body by breaking down harmful substances, e.g. drugs and alcohol and excreting them. Deamination is the conversion of ammonia (a toxic by-product from the breakdown of proteins) into urea and released into the blood to be excreted in the urine. These functions play a major role in maintaining homeostasis.

Figure 4.11: The front view of the human liver.

Figure 4.12: Homeostatic functions of the liver.

Some common diseases of the liver are cirrhosis (where the liver tissue is replaced by scar tissue) and hepatitis.

Activity 4.5 Homeostatic Functions of the Liver and Lungs Objective: Summarise and compare the homeostatic functions of the liver and lungs.

Materials needed

• Sheets of paper

• Pens or digital devices for notetaking Instructions

1. Find your team members and create a summary table with organ, homeostatic function and description as the columns. Decide with your team on information that fits as a homeostatic function.

2. Use textbooks, online resources, or class notes to research homeostatic functions and the description of the liver and lungs.

3. Fill in the summary table created with the information gathered.

4. Discuss with your team the findings and ensure that the information gathered is accurate and comprehensive.

5. Review the completed tables as a class and discuss the key points.

6. Reflect on the importance of the liver and lungs in maintaining homeostasis and how these organs work together to keep the body functioning properly.

Activity 4.6 Health Awareness

Objective: Raise awareness about kidney, skin, lung, and liver diseases and prevention.

Materials needed

• Posters

• Brochures

• Digital tools Instructions

1. Research common kidney, skin, lung, and liver diseases.

2. Create informational materials like flyers, brochures and charts to educate others about causes and prevention of the various diseases.

3. Share the informational materials with the school community.

1. What is the role of the heart in the cardiovascular system, and how do its structural components contribute to its function?

2. What are the solid components of blood, and what function does each serve in maintaining overall health?

3. How do the structures of arteries, veins and capillaries support their distinct functions within the cardiovascular system?

4. What are the symptoms and prevention strategies for a major cardiovascular disease, such as hypertension?

5. Describe the function of alveoli.

6. List the main parts of a nephron.

7. Describe how the kidneys maintain homeostasis in the body.

8. Name the three main layers of the skin.

9. Explain the role of sweat glands in the skin.

10. Evaluate the importance of the skin’s barrier function.

11. Describe the role of the liver in detoxification.

12. Analyse how the liver contributes to homeostasis.

13. What is the primary cause of kidney stones?

A. Bacterial infection B. Excessive calcium in the urine C. Low blood sugar D. Viral infection

14. Which of the following is a common symptom of eczema?

A. Itchy, inflamed skin B. Increased appetite C. Improved vision D. Weight gain

15. What is the primary cause of acne?

A. Bacterial infection B. Excessive sweating C. High glucose levels D. Low cholesterol levels

16. Identify the main components of the xylem.

17. Describe the function of phloem in plants.

18. Explain how the structure of vessels in the xylem contributes to their function.

19. List three environmental factors that can affect the rate of transpiration in plants.

20. Explain how high humidity affects the rate of transpiration.

21. Analyse the impact of wind on the rate of transpiration in plants.

22. What is translocation in plants?

23. Explain the role of companion cells in translocation.

24. List three factors that can affect the rate of translocation in plants.

25. What is the primary function of photosynthesis?

26. Identify the main pigment involved in photosynthesis.

27. Describe the role of light in the light-dependent reactions of photosynthesis.

28. What is the main purpose of the Calvin cycle?

29. List three factors that can affect the rate of photosynthesis.

30. Analyse how increasing carbon dioxide concentration affects the rate of photosynthesis.

31. How important is photosynthesis to the survival of plants and other organisms?

32. Professor Nebo has an array of indoor plants in her classroom and forgot to keep the windows in her class open during a two-week break from school. How would this room condition affect the indoor plants after the school break?

33. An experiment was conducted on the effect of temperature on the rate of photosynthesis, and the following data were obtained

a. Use the data to plot a graph.

b. Explain why the rate begins to drop off after twenty-five degrees Celsius.

Temperature (°C) Rate of Photosynthesis (O2

produced in ml/min) 10 2 15 4 20 8 25 12 30 10 35 6 40 2