Zoology and Environmental Biology: Transport in Animals PDF

## SECTION 3. Zoology and Environmental Biology ### Chapter 18 Transport in Animal **Dr. Nkiru F. Oparaku** ### 18.1 Introduction Animal circulatory system moves oxygen, CO₂ or nutrient from one part of the body to another through diffusion, extracellular fluid and animals' environment. All animal...

## SECTION 3. Zoology and Environmental Biology ### Chapter 18 Transport in Animal **Dr. Nkiru F. Oparaku** ### 18.1 Introduction Animal circulatory system moves oxygen, CO₂ or nutrient from one part of the body to another through diffusion, extracellular fluid and animals' environment. All animals must maintain a homeostatic balance in their bodies. Any system of moving gases, wastes, nutrients that reduce the functional diffusion distance using fluids may be referred to as an internal transport or circulatory system. This depends on the size, species and the life style of the animal. Simple animalssuch as protozoan, cnidarians, etc., lack specialized system for transport and circulation of nutrient and gases, diffusion alone is used and is enough for them. As organisms increase in size and complexity diffusion becomes in adequate. There are two circulatory systems; blood vascular system and the lymphatic system. Most circulatory systems also have other functions that assist homeostasis, circulatory fluid often contain phagocytic cells that can engulf microbes and other substances that are foreign to the body.Some blood cells assist immunity by producing antibodies when clotting occurs, it prevents the loss of blood fluids following minor injuries. ### 18.2 Transport In Invertebrates Unicellular organisms with a higher surface area to volume ratio rely on diffusion for gas exchange and waste exchange with the external environment that surrounds them. Some small invertebrates do not have an internal transport system because diffusion alone can do all that. Larger invertebrates usually have circulatory system, some have open and some others have close recirculatory system. ### 18.5 Transport In Vertebrates All vertebrate animals have a closed circulatory system, which is called a cardiovascular system. The blood systems of all vertebrates possess a muscular heart, lying in a ventral position near the front of the animal. The heart is responsible for pumping blood rapidly to all part of the body. Arteries carry blood away from the heart, and veins carry blood from the body back to heart. Oxygen is carried by haemoglobin in red blood cells the human blood system is an example for both a vertebrate and mammal. ### 18.6 Composition of Blood An average adult has about 5dm³ of blood. It is made up of several types of cell which are found bathed in a fluid matrix called plasma. The different types of blood cell can be seen in blood smear. The cells make up about 45% by volume of the blood. The other 55% is plasma, if blood is centrifuged, the cells (and platelets, which are really cell fragments) form a red pellet at the bottom of the tube, with plasma above which is colorless. Serum is plasma from which clotting protein has been removed. The pH of the blood is kept between 7.35 and 7.45. | Plasma | Function | Source | |:---:|:---:|:---:| | Plasma proteins (7-8% of plasma)) | Maintain blood osmotic pressure pH | Liver | | Gases; oxygen Carbon-dioxide. | Cellular respiration, End product of metabolism | Lungs, Tissue | | Nitrogenous waste urea uric acid | Excretion by kidneys | Intestinal villi, Liver | ### 18.7 Transport in Vertebrates All vertebrate animals have a closed circulatory system, which is called a cardiovascular system. It consists of a strong, muscular heart, in which the atria receive blood and the muscular ventricles pump blood out through the blood vessels. There are three kinds of blood vessels: arteries, which carry blood away from the heart; capillaries, which exchange materials with tissue fluid; and veins, which return blood to the heart. Arteries have thick walls, and those attached to the heart are resilient, meaning that they are able to expand and accommodate the sudden increase in blood volume that results after each heartbeat. Arterioles are small arteries whose diameter can be regulated by the nervous system. Arteriole constriction and dilation affect blood pressure in general. The greater the number of vessels dilated, the lower the blood pressure. ### 18.8 Comparing Circulatory Pathways Among vertebrate animals, there are three different types of circulatory pathways. In fishes, blood follows a one-circuit (single-loop circulatory) pathway through the body. The heart has a single atrium and a single ventricle. The pumping action of the ventricle sends blood under pressure to the gills where it is oxygenated. After passing through the gills, blood is under reduced pressure. However, the single circulatory loop has advantages in that the gill capillaries get deoxygenated blood and the systemic capillaries get fully oxygenated blood. As a result of evolutionary changes, the other vertebrates have a two-circuit (double-loop circulatory) pathways. The heart pumps blood to the tissues, called systemic circulation, and also pumps blood to the lungs, called pulmonary circulation. The double pumping action is an adaptation to breathing air on land. In amphibians, the heart has two atria, but there is only a single ventricle. The same holds true for most reptiles, except that the ventricle has a partial septum. The hearts of crocodiles, which are reptiles, and all birds and mammals are divided into right and left halves. The right ventricle pumps blood to the lungs, and the left ventricle, which is larger than the right ventricle, pumps blood to the rest of the body. The arrangement provides adequate blood pressure for both the pulmonary and systemic circulations. ### 18.9 Transport in Humans In the cardiovascular system of humans, the pumping of the heart keeps blood moving in. the arteries. Skeletal muscle contraction pressing against veins is primarily responsible for the movement of blood in the veins. ### 18.10 The Heart Pumps Blood The heart is a cone-shaped, muscular organ about the size of a fist. It is located between the lungs directly behind the sternum (breastbone) and is tilted so that the apex is directed to the left. The major portion of the heart, called the myocardium, consists of cardiac muscle tissue. The muscle fibers of the myocardium are branched and tightly joined to one another. The heart lies within the pericardium, thick, membranous sac that contains pericardial fluid, which has a cushioning and lubricating effect. The inner surface of the heart is lined with endocardium, which consists of connective tissue and endothelial tissue. Internally, a wall called the septum separates the heart into a right side and a left side. The heart has four chambers: two upper, thin-walled atria and two lower, thick-walled ventricles. The atria are much smaller and weaker than the muscular ventricles, but they hold the same volume of blood. The heart also has valves, which direct the flow of blood and prevent its backward movement. These valves are supported by strong fibrous strings called chordae tendineae. The chordae, which are attached to muscular projections of the ventricular walls, support the valves and prevent them from inverting when the heart contracts. The atrioventricular valve on the right side is called the tricuspid valve because it has three cusps, or flaps. The valve on the left side is called the bicuspid (or mitral) because it has two flaps. There are also semilunar valves between the ventricles and their attached vessels. A semilunar valve has three pockets of tissue, and each pocket resembles a half-moon.. The pulmonary semilunar valve lies between the right ventricle and the pulmonary trunk. The aortic semilunar valve lies between the left ventricle and the aorta. ### 18.11 How the Blood Moves * The superior vena cava and the inferior vena cava, both carrying deoxygenated blood, enter the right atrium. * The right atrium sends blood through an atrioventricular valve (the tricuspid valve) to the right ventricle. * The right ventricle sends blood through the pulmonary semilunar valve into the pulmonary trunk and the pulmonary arteries to the lungs. * The pulmonary veins, carrying oxygenated blood from the lungs, enter the lett atrium. * The left atrium sends blood through an atrioventricular valve (the bicuspid or mitral valve) to the left ventricle. * The left ventricle sends blood through the aortic semilunar valve into the aorta and to the body proper. From this description, you can see that blood must go through the lungs in order to pass from the right side to the left side of the heart. The heart is a double pump because the right side of the heart sends blood through the lungs, and the left side sends blood throughout the body. Since the left ventricle has the harder job of pumping blood to the entire body, its walls are thicker than those of the right ventricle. ### 18.12 Function of mammalian blood Blood performs many major functions. In the following list, the first four functions are carried out-solely by the plasma. 1. Transport of soluble organic compounds (digested food) from the small intestine to various parts of the body where they are stored or assimilated (used), and transport from storage areas to places where they are used, such as transport of glucose from the liver to the muscles when glycogen is converted to glucose. 2. Transport of soluble excretory materials to organs of excretion. Urea is made in the liver and transported to the kidneys for excretion, and carbon dioxide is made by all cells and taken to the lungs to be excreted. 3. Transport of hormones from the glands where they are produced to target organs, for example insulin from the pancreas to the liver. This allows communication within the body. 4. Distribution of excess heat from the deeply seated organs. This helps to maintain a constant body temperature. 5. Transport of oxygen from the lungs to all parts of the body, and transport of carbon dioxide produced by the tissues in the reverse direction. This involves red blood cells. 6. Defence against disease. This is achieved in three ways: * Clothing of the blood by platelets and fibrinogen which prevents excessive blood loss and entry of pathogens; * Phagocytosis, performed by the neutrophils, monocytes and macrophages, which engulf and digest bacteria which find their way into the bloodstream and body tissues; * Immunity, achieved by antibodies and lymphocytes. There is maintenance of a constant blood solute potential and pH as a result of plasma protein activity. As the plasma proteins and haemoglobin possess both acidic and basic amino acids, they can combine with or release hydrogen ions and so minimize pH changes over a wide range of pH values. In other words, they act as buffers. ### 18.13 Blood groups When a patient receives a blood transfusion it is vital that they receive blood that is compatible with their own. If it is incompatible, a type of immune response occurs. This is because the donor's red cell membranes passes glycoproteins (known as agglutinogens) which act as antigens and react with antibodies (agglutinins) in the recipient's plasma. The result is that the donor's cell are agglutinated (in other words, the cells link or attach to each other when the antigens on their surfaces interact with the antibodies). Two antigens exist, named A and B. The complementary plasma antibodies are named a and b, and are present in the plasma all the time; they are not produced in response to the donor's antigen as is the case in the immune reactions already studied. A person with a specific antigen in the red cells does not possess the corresponding antibody in the plasma. For example, anyone with antigen A in the red cell membranes has no antibody a in the plasma and is classified as having blood group A. If only B antigens are present the blood group will be B. If both antigens are present the blood group is AB, and if no antigen are present the blood group is O. When transfusion occurs it is important to know what will happen to the cells of the donor. If there is a likelihood of them being agglutinated by the recipient's plasma antibodies then transfusion should not take place. Individuals with blood group O are termed universal donors because their blood can be given to people with other blood groups. It possesses cells which will not be agglutinated by the recipient's plasma antibodies. Although group O possesses a and b antibodies. | Blood groups | 0 | A | B | AB | |:---:|:---:|:---:|:---:|:---:| | Percentage of population | 46% | 42% | % | 3% | | Antigen | - | A | B | A+B | | antibody | a+b | b | a | - | Individuals with group AB can receive blood from anyone and are called universal recipients. They can only donate to blood group AB. The blood donated must be tested and matched accurately before transfusions. ### 18.14 The rhesus factor 85% of the total population possess red cells termed rhesus positive. The remainder of the population lack the rhesus antigen and are therefore described as rhesus negative. Rhesus negative blood does not usually contain rhesus antibodies in its plasma. However, if rhesus positive blood enters a rhesus negative individual the recipient responds by manufacturing rhesus antibodies. The practical importance of this is made obvious when a rhesus negative mother bears a rhesus positive child. The rhesus factor is inherited. (Rhesus positive is dominant and rhesus negative recessive). During the later stages of the pregnancy, fragments of the rhesus positive red blood cells of the fetus may enter the mother's circulation and cause the mother to produce rhesus antibodies. These can pass across the placenta to the fetus and destroy fetal red cells. Normally the antibodies are not formed in large enough quantities to affect the first-born child., subsequent rhesus positive children can suffer destruction of their red cells. A rhesus baby is usually premature, anemic and jaundiced and its blood needs to be completely replaced by a transfusion of healthy blood. The condition is known as hemolytic disease of the newborn. It can be fatal, especially if the baby is born prematurely and often happens. Although a blood transfusion can now be undertaken whilst the baby is still in the womb, with modern screening methods the problem can be avoided, as explained below. ### 18.14.1 Protection against rhesus reaction * If an intravenous injection of anti-rhesus antibodies, called anti-D, is given to a rhesus mother within 72 hours of her giving birth, sensitization of rhesus negative mother by rhesus positive fetal cells is prevented. The anti-rhesus antibodies attach themselves to the rhesus antigens on the fetal cells which are in the mother's circulation and prevent them from being recognized by the mother's antibody forming cells. This means of prevention obviously depends on careful screening of all pregnant women. Testing blood groups is part of antenatal care. * If a rhesus negative mother of blood group O is carrying a rhesus positive child of any blood group than O, the problem will not arise. This is because if fetal cells enter the mother's circulation, the mother's a and b antibodies will destroy the blood cells before the mother has time to manufacture anti-rhesus antibodies.