CIRCULATORY SYSTEM

Circulatory System Circulatory system: Efficient distribution system Network of 100,000 km of blood vessels Supplies cells with nutrients and oxygen and removes carbon dioxide and waste products Transports hormones Plays an important role repairing tissues and protecting the body from infection

Organs of the Circulatory System * Blood: Type of connective tissue (cells & liquid) * Heart: Multi-chambered, muscular organ - Overall flow of blood via blood vessels  from the heart to the tissues throughout the body back to the heart - Body contains 5 L of blood

3 Types of Blood Vessels 1. Capillaries: Microscopic blood vessels- make contact with all cells of the body Walls of capillaries consist of a thin layer of epithelial tissue  enables diffusion of nutrients and oxygen out of the blood & the diffusion of waste products into the blood 2. Arteries: Blood flows from the heart to the capillaries through thick walled blood vessels = arteries Walls of arteries = epithelial tissue wrapped in layers of smooth muscle and connective tissue Muscle tissue enables arteries to constrict & dilate; Blood in arteries is under pressure due to the heart’s pumping action

3 Types of Blood Vessels 3. Veins: Blood returns from the capillaries to the heart through vessels = veins Walls of veins consist of epithelial tissue surrounded by smooth muscle & connective tissue… but muscle layer is thinner than that in arteries Blood is under little pressure Contracting skeletal muscles squeezes the veins and forces blood back to the heart

Chemical Exchange between Blood & Body Tissues Most cells are no further than 10 micrometers from a capillary and the blood inside Capillary network Critical to accomplishing the main functions of the circulatory system Distribution of oxygen & nutrients, and removal of waste products Cells in body tissues  surrounded by interstitial fluid

Chemical Exchange between Blood & Body Tissues Substances in capillaries do not enter tissue cells directly 1. First: Substances in capillaries enter the interstitial fluid 2. Second: Substances in the interstitial fluid then enter the cells

Chemical Exchange between Blood & Body Tissues Exchange of substances between blood & interstitial fluid occurs in several ways: Small molecules (oxygen, carbon dioxide)  diffuse across the membrane or pass through gaps between the epithelial cells of the capillary wall Oxygen & nutrients move from the blood into the interstitial fluid Carbon dioxide & other small waste products move from the interstitial fluid into the blood Larger molecules move across the membranes by exocytosis and endocytosis

Chemical Exchange between Blood & Body Tissues Exchange of substances between blood & interstitial fluid occurs in several ways: Blood pressure  forces fluid through the capillary wall  At the artery end of a capillary  blood pressure forces water, small solutes, and some dissolved proteins through the gaps between the cells… However, blood cells & larger proteins are too large to pass easily through the openings  remain in the capillary  Result: Vein end of the capillary in hypertonic compared to the surrounding interstitial fluid  Thus, water reenters the vein end of the capillary via osmosis… Blood pressure is very low at the vein end of the capillary, so it does not oppose the flow of fluid back into the capillary

Blood consists of Cells suspended in Plasma * Blood Highly specialized tissue Part liquid, part cellular material * Plasma Composes 55% of the volume of blood Plasma = 90% water; Other 10% = dissolved salts, proteins, transport substances

Blood consists of Cells suspended in Plasma * Red blood cells (Erythrocytes): Constitutes the remaining 45% of the blood volume Carry oxygen from the lungs to all the tissues in your body Each RBC  contains 250 million molecules of hemoglobin (Protein that temporarily stores oxygen for delivery to cells) Hemoglobin  Contains iron  Oxygen molecules bind to the iron portion (heme group) of the hemoglobin molecule

Red Blood Cells * Red blood cells (Erythrocytes): Produced in the bone marrow Distinctive shape due to the loss of their nuclei and mitochondria  shape = flat disk, curves inward in the middle  structure provides increased surface area for oxygen transport Life span of a RBC = days

Blood consists of Cells suspended in Plasma * White blood cells (Leukocytes): Responsible for fighting infection and preventing the growth of cancer When an infection invades your body  # of WBCs increases Most of the action of the WBC takes place outside the blood vessels in the interstitial fluid

3 Functions of Blood Blood: Carries oxygen, nutrients, and hormones Removes waste (carbon dioxide) Fights infection

Blood consists of cells suspended in plasma Blood: Connective tissue Flows through blood vessels Five liters of blood Takes 1 minute to make a complete circuit Composed of: 55% Plasma 45% RBCs

Blood consists of cells suspended in plasma Plasma (45%) 90% water 10% dissolved salts, proteins, and other substances RBCs Erythrocytes Most numerous cells in blood 5 million RBCs in 1 drop of blood Contains hemoglobin Produced in the bone marrow (2 million per second) Replaced every 120 days

Blood consists of cells suspended in plasma Hemoglobin Protein that binds with oxygen for transport to cells Contains iron which contains a high affinity for oxygen

Blood consists of cells suspended in plasma WBCs Leukocytes Fight infection and prevents growth of cancer 4,000-11,000 WBCs in 1 drop of blood Infection increases the number of WBCs Most action takes place in the interstitial fluid

Blood consists of cells suspended in plasma Blood clotting: Platelets help with blood clotting Originate from the bone marrow 250,000 – 500,000 in a drop of blood Stick to damaged site Release clotting factors Fibrin produced (Protein) Patch forms and dries into a scab