The Circulatory System Overview

The Circulatory System

• Divided into two main parts: the cardiovascular system and the lymphatic system
• The cardiovascular system includes the heart and blood vessels
• The lymphatic system includes lymph vessels, lymph nodes, lymphatic organs and lymph

Major Parts of the Cardiovascular System

• Blood: a specialized fluid connective tissue, more viscous than water, slightly sticky
• Functions: transports oxygen, carbon dioxide, nutrients, hormones, heat, wastes; regulates pH, body temperature and water content of cells; protects against blood loss and disease

Components of Blood

• Plasma: 55%, primarily water, with proteins, electrolytes, nutrients, respiratory gases, regulatory proteins, and waste products
• Formed elements (cells): 45%, including erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets)

Erythrocytes (RBCs)

• Lack nuclei and organelles
• Contain hemoglobin, the oxygen-carrying protein, contributing to 33% of cell weight
• Biconcave disks for a large surface area to volume ratio and facilitate gas exchange
• Life span of approximately 120 days

Leukocytes (White Blood Cells)

• Two main classifications:
  • Granulocytes (polymorphonuclear): Neutrophils, eosinophils, basophils (contain granules)
  • Agranulocytes (mononuclear): Lymphocytes, monocytes (lack granules)
• Neutrophils: Constitute 60-70% of circulating leukocytes, highly dynamic, active phagocytes
• Eosinophils: Constitute 2-4% of leukocytes, cytotoxic effects on parasites, increased in allergic reactions
• Basophils: Less than 0.5-1% of leukocytes, contain granules of heparin and histamine (inflammation mediators)
• Lymphocytes: Constitute 20-25% of WBCs, agranular, play a key role in the immune system
• Monocytes: Constitute 3-8% of WBCs, largest of WBCs, differentiate into macrophages

Platelets (Thrombocytes)

• Non-nucleated, disk-like cell fragments derived from megakaryocytes
• Play a role in clot formation (blood clotting) to prevent loss
• Normal count: 200,000-400,000 per μL of blood
• Life span: approximately 10 days

The Heart

• A muscular organ with four chambers: right and left atria, right and left ventricles
• Protected by the pericardium, a fibrous sac around the heart
• Major parts include the pericardium (fibrous and serous), layers of the heart wall (epicardium, myocardium, endocardium), sulci (coronal, interventricular), and valves (atrioventricular and semilunar)
• Blood supply through the coronary arteries

Conducting System of the Heart

• Specialized system for rhythmic heart contractions
• Includes the Sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular bundle (bundle of His), bundle branches, and Purkinje fibers

Blood Vessels

• Three layers (tunics): tunica intima, tunica media, tunica externa
• Arteries: carry blood away from the heart, thick tunica media
• Veins: carry blood back to the heart, thin tunica media
• Capillaries: the smallest vessels for exchange of materials between blood and tissues; thin walls, one cell layer thick, three types of capillaries

Arteries of the body

• Aorta: main artery, divided into ascending aorta, aortic arch, and descending aorta (thoracic and abdominal)
• Coronary arteries: supply the heart muscle
• Arteries of the neck and head: internal and external carotid arteries, vertebral arteries
• Arteries of the upper limbs: subclavian, axillary, brachial, radial, and ulnar arteries
• Arteries of the lower limbs: common iliac, internal iliac, external iliac, femoral, popliteal, tibial, and peroneal arteries

Branches of the abdominal aorta

• Three unpaired branches: celiac trunk, superior mesenteric artery, inferior mesenteric artery
• Several paired and unpaired branches

Venous Drainage of the Body

• Systemic veins return blood back to the heart, draining into the superior vena cava and inferior vena cava
• Hepatic portal system: unique drainage system for the digestive tract to the liver

Fetal Circulation

• Different circulatory pathways in a developing fetus, with several important shunts to bypass the lungs
• Shunts: foramen ovale, ductus arteriosus, ductus venosus

Lymphatic System

• System of vessels, nodes, and organs that supports the immune system and fluid balance
• Functions: fluid balance, absorption of fats, immunity

Lymph Nodes

• Filter lymph; vital for immune response; found throughout the body along lymphatic pathways; important for purifying fluid before it returns to the blood
• Types of lymph nodes: Cervical, Axillary, Inguinal

This quiz covers the key components and functions of the circulatory system, including the cardiovascular and lymphatic systems. Learn about blood composition, functions of plasma and formed elements, and the role of erythrocytes in oxygen transport.