Circulatory Systems in Animals and Plants PDF

DEPARTMENT OF BIOLOGY AND BIOTECHNOLOGY BIO 102 (GENERAL BIOLOGY) CIRCULATORY SYSTEMS IN ANIMALS AND PLANTS By C. A. OGBU Learning Objectives: at the end of the lecture th...

DEPARTMENT OF BIOLOGY AND BIOTECHNOLOGY BIO 102 (GENERAL BIOLOGY) CIRCULATORY SYSTEMS IN ANIMALS AND PLANTS By C. A. OGBU Learning Objectives: at the end of the lecture the students should be able to i. Explain the need for transportation in lower and higher organisms ii. State the materials and media needed for transportation iii. Explain the types of circulatory system iv. List and explain the components for the circulatory system. v. State the functions of the blood and explain common heart diseases vi. Explain the mechanisms of transport in plants CIRCULATORY SYSTEMS IN ANIMALS Circulatory systems are essential for transporting nutrients, gases, hormones, and waste products throughout the body. They help to maintain homeostasis, support cellular respiration, and enable immune response. Transport is necessary for every cell of the organism to obtain all the essential materials for its metabolism, e.g. nutrients, oxygen, water etc. Transport is necessary to move hormones in animals from where they are produced to the area of need. It is also necessary to remove and dispose metabolic wastes, e.g. carbon (IV) oxide, water, urea etc. Transport System in Lower Organisms Unicellular or lower organisms have a large surface area to volume ratio. Therefore the exchange of metabolic materials within their cell and between their cells and their environment occur effectively by diffusion. Need for Transport System in Large Organisms Multicellular organisms have a small surface area to volume ratio. This makes diffusion inadequate for the exchange of metabolic materials within their body cells and between their body and their surrounding environment. They therefore require transport system because of the following: 1. Many cells are situated far away from others, hence substances have to be moved over greater distances. 2. A conducting or linking system becomes necessary to connect isolated groups of cells. 3. Materials being transported are large in quantity for simple process of diffusion, osmosis or active transport to accomplish, hence the need for an efficient transport system in higher organisms. Materials for Transport in Animals i. Oxygen ii) Excretory products such as carbon (II) oxide, urea, water etc. iii. Digested soluble food substances such as amino acids, glucose, fatty acid and glycerol etc. iv. Hormones v) Antibodies. Media of Transportation In all organisms, a liquid or fluid is the medium of transportation of materials. The following are the media of transportation. 1. Cytoplasm: This is the medium of transportation of materials in lower or unicellular organisms e.g. Amoeba and Paramecium. 2. Blood: This is the medium of transportation of materials in most animals especially vertebrates. 3. Lymph: This is one of the media of transportation in higher animals. It is a fluid similar in composition to tissue fluid Types of Circulatory Systems 1. Open 2. Closed Circulatory Systems. Open Circulatory System A system where the circulatory fluid (hemolymph) is not always contained within blood vessels. Examples: Arthropods (e.g., insects, spiders), crustaceans, and most mollusks. The blood is not enclosed in the blood vessels but is pumped into a cavity called a hemocoel and is called hemolymph because the blood mixes with the interstitial fluid. As the heart beats and the animal moves, the hemolymph circulates around the organs within the body cavity and then reenters the hearts through openings called ostia. This movement allows for gas and nutrient exchange. An open circulatory system does not use as much energy as a closed system to operate or to maintain; however, there is a trade-off with the amount of blood that can be moved to metabolically active organs and tissues that require high levels of oxygen  Closed Circulatory System A system where the circulatory fluid (blood) is contained within blood vessels at all times. Blood is contained inside blood vessels and circulates unidirectionally from the heart around the systemic circulatory route, then returns to the heart again. Examples: Annelids (e.g., earthworms), cephalopods (e.g., octopuses), and vertebrates (e.g., mammals, birds, fish). Functions 1. Blood is pumped by a heart through a network of vessels. 2. Allows for more efficient and faster transport of substances. Components of the Closed Circulatory System 1. The Blood: It is composed of red blood cells, white blood cells, platelets, and plasma. The Red Blood Cells (Erythrocytes): Contain a red pigment called heamoglobin which aids in oxygen and carbon dioxide transportation. The White Blood Cell (Leucocytes): Helps in protecting against germs and fighting diseases. They are primarily involved in the immune response to identify and target pathogens, such as invading bacteria, viruses, and other foreign organisms. White blood cells are formed continually; some only live for hours or days, but some live for years. The Platelets (Thrombocytes): They help in blood clothing. They work with other factors to promote blood clotting at sites of tissue damage. The Plasma: This is the liquid part of the blood which contains water, proteins, salts, lipids, and glucose. Functions of the Blood 1. Transportation: The blood transports oxygen, hormones and nutrients (digested food) 2. Defense: The blood provides a strong immune defense mechanism 3. Temperature regulation 4. Production of antibodies 5. It helps in blood clotting 6. Exchange of Gases: The gases involved in this process are oxygen and carbon dioxide. The blood system has many capillaries in close contact with the air sacs (alveoli) of the lungs. The wall of the capillaries and air sacs enable oxygen to be exchanged for carbon dioxide through the process of diffusion. 7. Absorption of Digested Food: The digested food materials are absorbed by the villi of the small intestine. The mesenteric arteries take the food from the small intestine to the liver  through the hepatic portal vein. The liver then regulates the amount of food going into the blood. 8. Removal of Excretory Products: The blood is able to collect waste material like urea, nitrogenous materials, carbon dioxide, water, etc from the cells by simple diffusion. The waste products are then transported to the various organs like liver, lungs and kidney from where they are removed from the body Blood Vessels 1. Arteries: Carry blood away from the heart. 2. Veins: Carry blood towards the heart. 3. Capillaries: Tiny vessels where exchange of substances occurs between blood and tissues. Arteries These are thick-walled vessels that carry oxygenated blood away from the heart (except pulmonary artery) under high pressure. Arteries are defined by the fact that they carry blood away from the heart, not their oxygenation status: not all arteries carry oxygenated blood. Arteries are lined with thick connective tissue and muscle tissue that support the artery wall and help to regulate the amount of pressure sustained by the artery. Arteries diverge into smaller arteries, which then diverge into smaller arteries called arterioles, to reach more deeply into the muscles and organs of the body. Arterioles diverge into capillaries. Veins These are thinner-walled vessels that carry deoxygenated blood towards the heart (except pulmonary vein). Veins return blood to the heart under low pressure. Veins are defined by the fact that they return blood to the heart: not all veins carry deoxygenated blood. Veins are lined with connective and muscle tissue, but these linings are thinner than in arteries. In addition, veins have valves to prevent the backflow of blood. Because veins have to work against gravity to get blood back to the heart, contraction of skeletal muscle assists with the flow of blood back to the heart. Capillaries Microscopic vessels where exchange of gases, nutrients, and waste occurs. Gas exchange in capillaries occurs both in the lungs, where capillaries acquire oxygen and release carbon dioxide, and also in the tissues where the opposite process occurs. Capillaries are very narrow, allowing for a single red blood cell to pass through at a time. Capillaries are also very thin, allowing for exchange of gas, nutrients, and fluid. Fluid that leaks out of capillaries can return back to the capillaries, and can also be brought back to the heart via the lymphatic system. The capillaries converge again into venules (small veins). 2. The Heart The heart is a muscular organ that pumps blood through the circulatory system. Its structure varies among different animals (e.g., two-chambered heart in fish, four-chambered heart in mammals). Structure and Function of the heart The heart is an organ that pumps the blood in the blood vessels. It is located within the chest cavity. The heart has four chambers; the two upper chambers are called Auricles, while the two lower chambers are called the ventricles. The auricles (atria) receive blood; ventricles pump blood out. The partition of the chambers help to avoid mixing up of blood rich in oxygen with the blood rich in carbon dioxide. Valves prevent backflow of blood. In mammals, the right and left ventricles of the heart are completely separated, so that pulmonary (lung) and systemic (body) circulations are completely independent. Oxygenated blood arrives in the left atrium from the lungs and passes to the left ventricle, whence it is forced through the aorta to the systemic circulation. Deoxygenated blood from the tissues returns to the right atrium via a large vein, the vena cava, and is pumped to the pulmonary capillary bed through the pulmonary artery. Heart Variations among Different Organisms - Fish: Two-chambered heart (one atrium, one ventricle). - Amphibians: Three-chambered heart (two atria, one ventricle). - Reptiles: Partially divided ventricle. - Birds and Mammals: Four-chambered heart (two atria, two ventricles), allowing complete separation of oxygenated and deoxygenated blood. Circulatory Pathways 1. Single Circulation: this is found in fish. Blood passes through the heart once per circuit (heart → gills → body → heart). 2. Double Circulation: This is found in amphibians, reptiles, birds, and mammals. Blood passes through the heart twice per circuit (heart → lungs → heart → body → heart). It is more efficient in oxygen delivery and waste removal. Regulation of Circulatory System a. Nervous Control - Autonomic nervous system regulates heart rate and vessel constriction/dilation. - Sympathetic and parasympathetic branches influence cardiac activity. b. Endocrine Control - Hormones (e.g., adrenaline, aldosterone) affect heart rate, blood volume, and vessel diameter. c. Responses to Exercise and Stress - Increased heart rate and blood flow to muscles. - Redistribution of blood flow from digestive organs to skeletal muscles. Diseases and Disorders Common Heart Diseases 1. Hypertension (high blood pressure): Can lead to heart disease and stroke. 2. Atherosclerosis: Hardening of the arteries due to plaque buildup. 3. Heart Attack: Blockage of blood flow to the heart muscle. 4. Stroke: Disruption of blood supply to the brain.  CIRCULATORY SYSTEMS IN PLANTS Plants, like animals, have circulatory systems to transport water, nutrients, and other substances from the roots to the stems and leaves. These systems are crucial for plant growth, survival, and reproduction. Materials for Transport in Plants i. Manufactured food ii. Mineral salts iii. Excretory products e.g. carbon (II) oxide, water etc. iv. Hormones v. Water Media of Transportation In all organisms, a liquid or fluid is the medium of transportation of materials. The following are the media of transportation. Cell Sap or Latex: This is the medium of transport in many plants. Main Components 1. Xylem: Transports water and minerals from roots to leaves. 2. Phloem: Transports sugars and other metabolic products from leaves to other parts of the plant. The Xylem Xylem is a type of vascular tissue in plants responsible for the transport of water and dissolved minerals. Structure Composed of tracheids and vessel elements. a. Tracheids are long, thin cells with tapered ends. b. Vessel elements are shorter and wider, forming continuous tubes. Function i) Conducts water and minerals from the roots to the rest of the plant. ii) Provides structural support due to lignin in cell walls. Mechanism of Xylem Transport 1. Transpiration Pull: Water evaporates from the leaf surfaces (transpiration). The xylem creates a negative pressure that pulls water upward from the roots. 2. Capillary Action: - Water molecules stick to the walls of the xylem vessels (adhesion) and to each other (cohesion). It helps in the upward movement of water. 3. Root Pressure: Pressure generated in the roots as water moves into the roots from the soil. The xylem can push water up through the xylem vessels. The Phloem Phloem is a type of vascular tissue responsible for the transport of sugars and other organic nutrients. It is composed of sieve tube elements and companion cells. The sieve tube elements are elongated cells with sieve plates at their ends. The companion cells support the sieve tube elements. Function i) Transports the products of photosynthesis (sugars) from the leaves to other parts of the plant. ii) Distributes nutrients to growing tissues and storage organs. Mechanism of Phloem Transport Source-to-Sink Theory: Sugars are produced in the leaves (source). Transported to areas of growth or storage (sink), such as roots, fruits, and seeds. Pressure-Flow Hypothesis: Sugars are actively transported into the sieve tubes at the source. Water follows by osmosis, creating pressure that pushes the sugar solution through the phloem. At the sink, sugars are removed, reducing pressure and allowing flow to continue. Loading and Unloading of Sugars: Loading: Sugars are actively loaded into the phloem at the source. Unloading: Sugars are actively or passively removed at the sink. Comparison between Xylem and Phloem S/N Xylem Phloem Transports water and minerals. Transports sugars and organic nutrients Movement is unidirectional (roots to Movement is bidirectional (source to sink) leaves) Composed of dead cells at maturity Composed of living cells Provides structural support Does not provide structural support. Importance of Circulatory Systems in Plants 1. Growth and Development: Efficient transport of water, minerals, and nutrients is essential for plant growth. 2. Photosynthesis: Water transported by xylem is a key reactant in photosynthesis. 3. Nutrient Distribution: Phloem distributes the products of photosynthesis to all parts of the plant, ensuring energy supply. Challenges and Adaptations Challenges i) Transporting water and nutrients over long distances. ii) Maintaining water balance and preventing desiccation. Adaptations i) Xerophytes (dry environments): Thick cuticles, deep roots, reduced leaf area. ii) Hydrophytes (aquatic environments): Air spaces in tissues, reduced xylem.