Circulatory System PDF

ZOO 112-Mammalian Body Circulatory System:Heart, Blood Motunrayo Coker 2023/2024 Session Mammalian Heart The heart is a complex muscle that pumps blood The three divisions of the circulatory system Systemic circulation-heart to body Pulmonary circula...

ZOO 112-Mammalian Body Circulatory System:Heart, Blood Motunrayo Coker 2023/2024 Session Mammalian Heart The heart is a complex muscle that pumps blood The three divisions of the circulatory system Systemic circulation-heart to body Pulmonary circulation-heart to lungs Coronary circulation- within heart The heart is composed of three layers; The epicardium (outer layer) Pericardium-surrounds and protects the heart The myocardium (middle layer and bulk of heart wall) The endocardium(inner wall) 2 Structure of the heart –Atria and ventricles The heart muscle is asymmetrical In humans, the heart is divided into four chambers: Two atria- receives blood into the heart Two ventricles- pumps blood out of the heart One atrium and one ventricle are on the right side One atrium and one ventricle are on the left side. The right atrium receives deoxygenated blood Superior vena cava-the jugular vein that comes from the brain and from the veins that come from the arms, Inferior vena cava- veins that come from the lower organs and the legs. The coronary sinus which drains from the 3 heart itself Structure of the heart –Atria and ventricles Deoxygenated blood then passes to the right ventricle The right ventricle pumps the blood through the pulmonary arteries, to the lungs for re-oxygenation The left atrium then receives the oxygen- rich blood from the lungs via the pulmonary veins The left ventricle is where the oxygen rich blood is pumped out through the aorta ( major artery of the body) to the organs and muscles of the body. 4 Structure of the heart –valves Valves are flaps that open and close to monitor the direction of blood flow in the heart Atrioventricular valve/ tricuspid valve Right atrium and right ventricle Mitral/bicuspid valve Left atrium and left ventricle Pulmonic valve Right ventricle to the lungs Aortic semilunar valve Left ventricle and aorta 5 Divisions of the circulatory system The pulmonary (heart and lungs) The systemic (heart to other parts of the body) The coronary (vessels that serve the heart) The right side of the heart is not as thick as the left side which must have enough pressure to pump blood all the way to the legs. 6 Blood vessels-Arteries The wall of an artery consists of three layers Innermost layer-tunica intima(squamous epithelium ) Middle layer- tunica media (smooth muscle - thickest layer) Outermost layer-tunica externa (connective tissue with varying amounts of elastic and collagenous fibers) Arteries carry blood away from the heart Pulmonary arteries transport blood that is low in oxygen from the right ventricle to the lungs Systemic arteries transport oxygen rich blood from the left ventricle to the body tissues. Blood is pumped from the ventricles into large arteries that branch into smaller arteries that results in arterioles The arterioles play a key role in regulating blood flow into the capillaries 7 Blood vessels-Veins The walls of veins have the same three layers as the arteries There is less smooth muscle and connective tissue Walls of veins are thinner than those of arteries Blood in the veins has less pressure than in the arteries Veins carry blood toward the heart After blood passes through the capillaries It enters the smallest veins, called venules It flows into progressively larger veins until it reaches the heart Pulmonary veins transport oxygen rich blood from the lungs to the left atrium of the heart Systemic veins transport blood from the body tissue to the right atrium of the heart 8 Blood vessels-capillaries The smallest and most numerous of the blood vessels Form the connection between the vessels that carry blood away from the heart (arteries) and the vessels that return blood to the heart (veins) The primary function of capillaries is the exchange of materials between the blood and tissue cells Capillary distribution varies with the metabolic activity of body tissues Metabolically active tissues such as skeletal muscle, liver, and kidney have extensive capillary networks Other tissues, such as connective tissue, have a less abundant supply of capillaries The epidermis of the skin, the lens and cornea of the eye completely lack a capillary network 9 Differences between veins and arteries Arteries Veins Location Closer to the heart Closer to the surface of the skin Wall structure thicker walls made of smooth thinner and less elastic muscles and elastic tissues Size Larger than veins Not as large as arteries Direction of blood Away from the heart Back to the heart flow Blood pressure Higher pressure Lower pressure Type of blood Oxygen rich (except pulmonary Oxygen poor (except artery) pulmonary vein) 10 Cardiac cycle The main purpose of the heart is to pump blood through the body It does so in a repeating sequence called the cardiac cycle The cardiac cycle is the coordination of: filling and emptying of the heart of blood by electrical signals that cause the heart muscles to contract and relax In each cycle, the heart contracts (systole), pushing out the blood and pumping it through the body This is followed by a relaxation phase (diastole), where the heart fills with blood, Blood pressure measurement 120/80 Systolic pressure/Diastolic pressure 11 Electrical signals in the heart muscles Contraction of heart muscles is stimulated by depolarization when a cell's internal charge becomes less negative relative to the outside of the cell. It is caused by a shift in the distribution of electrical charge Heart contains specialized “self excitable” muscle cells called autorhythmic fibers Initiate periodic actions without neural activation Sinoatrial node (SA) in the wall of the right atrium serves as a pacemaker (generate electrical impulses) that produces a spontaneous action potential Due to constant leakage of Na+ ions into the cell that depolarize the membrane generates an electrical impulse 60–100 times per minute The electrical impulse spreads through the atria, causing them to contract and pump blood into the ventricles The electrocardiogram is used to measure the electrical 12 activity of the heart Blood Blood is a connective tissue composed of a fluid matrix-plasma, cells and other forms of elements Transportation-essential cellular metabolism. Red blood cells transport oxygen attached to haemoglobin, nutrient molecules are carried in plasma, metablolic waste are removed as blood passes through the liver and kidneys Regulation- transports regulatory hormones from the endocrine glands and also temperature regulation Contraction and dilation of blood vessels near the surface of the body beneath the epidermis, conserve or dissipate heat as needed Protection- against injury and foreign microbes or toxins. White blood cells/leukocytes disarm invaders Blood clotting prevents blood loss when vessels are damaged 13 The components of blood The four main components of blood are: Plasma Red blood cells/Erythrocytes White blood cells/Leucocytes Platelets 14 Plasma This is the matrix in which blood cells and platelets are suspended Although plasma is 92% water, it contains the following: Nutrients, waste and hormones Ions –Na+, Cl-, HCO3- and traces of Ca2+, Cu2+, Zn2+, K+ and Zn2+ Proteins Albumin: α and ꞵ globulins- carriers of lipids and hormones Fibrinogen (blood clotting) When fibrinogen is removed, plasma becomes serum Most plasma proteins are produced in the liver 15 Red blood cells-Erythrocytes A microliter of blood contains about 5 million red blood cells (RBC) The fraction of the total volume of blood occupied by RBC is called hematocrit ( around 45% in humans) A normal RBC resembles a doughnut shaped disk with a central depression Mature mammalian RBC lacks a nuclei RBCs of vertebrates contains haemoglobin-the pigment that binds and transports oxygen 16  White blood cells- Leukocytes Less than 1% of the cells in human blood are white blood cells (WBC) WBCs are larger than RBCs and possess nuclei WBCs can migrate out of capillaries through the intercellular spaces into interstitial fluid There are 2 main types of WBC Granular leukocytes- neutrophils, eosinophils, basophils Agranular(Nongranular)- monocytes, lymphocytes Granules in the cytoplasm contains: Lysozyme Defensins 17 antioxidants  Platelets Platelets are cell fragments formed from larger cells in the bone marrow They are about 3 μm in diameter In the case of an injury, platelets releases clotting factors into the blood In the presence of these clotting factors, fibrinogen is converted into insoluble threads of fibrin Fibrin then aggregates to form the clot 18  Formation of blood cells Formation of blood cells begins in the bone marrow Production of blood cells in the bone marrow is known as haematopoiesis They develop from pluripotent stem cells Erythropoietin stimulates the production erythrocytes (erythropoiesis) The kidneys produces erythropoietin in response to low oxygen levels in the blood in adults Liver during embryonic development Lymphocyte proliferation are activated when it encounters an 19 antigen that binds to its receptors Role of Bone Marrow Stem Cells Blood Cell Production – Hematopoietic Stem Cells (HSCs) continuously differentiate into the various types of blood cells the body needs. Immune System Function – HSCs give rise to lymphocytes (T- cells, B-cells, and Natural killer cells) for immune defence. Injury Response Mesenchymal Stem Cells (MSCs) can go to sites of injuries and inflammation and help in tissue repair through Differentiation (generic embryonic cells become specialized cells) Paracrine signaling (allows cells to communicate with nearby cells by releasing signaling molecules, or ligands, that bind to receptors on nearby cells). Bone/Cartilage Regeneration – MSCs play a vital role in the regeneration and repair of bone and cartilage tissue injury 20 21