systemic circulation

Examples of systemic circulation in the following topics:

• Types of Circulatory Systems in Animals

  • The circulatory system varies from simple systems in invertebrates to more complex systems in vertebrates.
  • The blood then continues through the rest of the body before arriving back at the atrium; this is called systemic circulation.
  • In amphibians, reptiles, birds, and mammals, blood flow is directed in two circuits: one through the lungs and back to the heart (pulmonary circulation) and the other throughout the rest of the body and its organs, including the brain (systemic circulation).
  • For this reason, amphibians are often described as having double circulation.
  • Describe how circulation differs between fish, amphibians, reptiles, birds, and mammals

• Dead Space: V/Q Mismatch

  • The pulmonary circulation pressure is very low compared to that of the systemic circulation; it is also independent of cardiac output.

• Structures of the Heart

  • The heart is a complex muscle that pumps blood through the three divisions of the circulatory system: the coronary (vessels that serve the heart), pulmonary (heart and lungs), and systemic (systems of the body).
  • Coronary circulation intrinsic to the heart takes blood directly from the main artery (aorta) coming from the heart.
  • For pulmonary and systemic circulation, the heart has to pump blood to the lungs or the rest of the body, respectively .
  • This pattern of pumping is referred to as double circulation and is found in all mammals.
  • The mammalian circulatory system is divided into three circuits: the systemic circuit, the pulmonary circuit, and the coronary circuit.

• Open and Closed Circulatory Systems

  • In a closed circulatory system, blood is contained inside blood vessels, circulating unidirectionally (in one direction) from the heart around the systemic circulatory route, then returning to the heart again.
  • In contrast to a closed system, arthropods (including insects, crustaceans, and most mollusks) have an open circulatory system.
  • As the heart beats and the animal moves, the hemolymph circulates around the organs within the body cavity, reentering the heart through openings called ostia (singular: ostium).
  • Most vertebrates and some invertebrates, such as this annelid earthworm, have a closed circulatory system.
  • Arthropods, such as this bee and most mollusks, have open circulatory systems.

• Cytotoxic T Lymphocytes and Mucosal Surfaces

  • Although the immune system is characterized by circulating cells throughout the body, the regulation, maturation, and intercommunication of immune factors occur at specific sites that are known as lymph nodes.
  • The blood circulates immune cells, proteins, and other factors through the body.
  • Recall that cells of the immune system originate from stem cells in the bone marrow.
  • On maturation, T and B lymphocytes circulate to various destinations.
  • These antigens are filtered through lymph nodes before the lymph is returned to circulation.

• The Nervous System

  • The nervous system is composed of the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves).
  • The nervous system of higher vertebrates (the group that includes humans) is a widely-distributed communication and processing network that serves controlling functions over other organ systems.
  • Two major divisions of the nervous system are the central nervous system (CNS) and the peripheral nervous system (PNS).
  • CSF also functions to circulate chemical substances throughout the brain and into the spinal cord.
  • The autonomic nervous system, also part of the peripheral nervous system, controls internal body functions that are not under conscious control.

• Immunological Memory

  • Immunological memory allows the adaptive immune system to very rapidly clear infections that it has encountered before.
  • The adaptive immune system has a memory component that allows for a rapid and large response upon re-invasion of the same pathogen.
  • In contrast, the memory cells persist in circulation.
  • If the pathogen is not encountered again during the individual's lifetime, B and T memory cells will circulate for a few years or even several decades, gradually dying off, having never functioned as effector cells.
  • However, if the host is re-exposed to the same pathogen type, circulating memory cells will immediately differentiate into plasma cells and TC cells without input from APCs or TH cells.

• Skin, Gills, and Tracheal Systems

  • In this case, blood with a low concentration of oxygen molecules circulates through the gills.
  • Insects have a highly-specialized type of respiratory system called the tracheal system, which consists of a network of small tubes that carries oxygen to the entire body.
  • The tracheal system, the most direct and efficient respiratory system in active animals, has tubes made of a polymeric material called chitin.
  • Air enters and leaves the tracheal system through the spiracles.
  • Some insects can ventilate the tracheal system with body movements.

• Immunodeficiency

  • Immunodeficiency occurs when the immune system cannot appropriately respond to infections.
  • Neutropenia is one form in which the immune system produces a below-average number of neutrophils, the body's most abundant phagocytes.
  • As the illness progresses, it interferes more and more with the immune system.
  • This response is accompanied by a marked drop in the number of circulating CD4+ T cells, cells that are or will become helper T cells.
  • This weakens the immune system, allowing opportunistic infections.

• Other Hormonal Controls for Osmoregulation

  • The renin-angiotensin-aldosterone system (RAAS) stabilizes blood pressure and volume via the kidneys, liver, and adrenal cortex.
  • The renin-angiotensin-aldosterone system (RAAS) is a hormone system that regulates blood pressure and water (fluid) balance .
  • This system proceeds through several steps to produce angiotensin II, which acts to stabilize blood pressure and volume.
  • Renin is a circulating enzyme that acts on angiotensinogen, which is made in the liver, converting it to angiotensin I.
  • The renin-angiotensin-aldosterone system increases blood pressure and volume.