Circulatory System – General Aspects - Usd

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					 Circulatory System – General Aspects
• In small invertebrate organisms, no circulatory
  system is necessary, as diffusion distances are
• With greater size, diffusion from the external
  environment becomes insufficient and a
  circulatory system is required to transport
  materials within the body.
 Circulatory System – General Aspects
• Two types of circulatory systems are present
  among invertebrates:
  – Open System = more primitive, heart pumps blood
    out through vessels to various parts of the body.
    Return vessels are absent so blood oozes back to
    heart via interstitial spaces.
  – Closed System = advanced condition, also present in
    all vertebrates; blood never leaves vessels. Delivery of
    nutrients occurs via diffusion across thin-walled
• Amphioxus shows intermediate condition = both
  outgoing and return vessels present, but no
  capillaries connecting them.
Fig 12.4 – Microcirculation in a closed vascular system
    Functions of Circulatory System
•   Facilitate gas exchange
•   Delivery of nutrients
•   Removal of wastes
•   Transport of hormones
•   3 Subcomponents (all mesodermal in origin):
    – Blood Vascular System = includes heart, arteries (carry
      blood away from heart), capillaries (gas and nutrient
      exchange), and veins (carry blood back to heart)
    – Hemopoietic Organs = sites of blood cell production
    – Lymphatic System = thin-walled vessels that carry fluid
      from interstitial spaces back to blood stream
Fig 12.2 – Blood pressure and cross-
sectional areas of the different vessels
of the blood vascular system.
Fig 12.11 – Basic vertebrate blood vascular system circulation,
as illustrated in a shark
    Single and Double Circulation
• Fishes = possess single circulation pattern
   – Blood passes through heart only once during each
     complete cycle
   – Sequence: Heart  Gills  Body  Heart
• Amniotes = possess double circulation pattern
   – Blood passes through heart twice during each
     complete cycle
   – Sequence: Heart  Lungs  Heart  Body  Heart
• Intermediate condition with characteristics of
  both present in lungfish, amphibians and some
Fig 12.6 – Single and double circulation circuits in vertebrates
       Developmental Anatomy
• General Principles:
• Main vessels develop in association with
  major centers for metabolic activity.
• Primitive adult conditions are demonstrated in
  transitory embryonic stages in advanced
  – “Ontogeny recapitulates phylogeny” works well
    for the circulatory system.
        Developmental Anatomy
• Developmental Stages
1. Primitive Condition = heart pumps blood anteriorly
   through ventral aorta  passes through paired aortic
   arches  into paired dorsal aortae  to capillary
   network of yolk sac  drain to vessels leading back to
  — Yolk sac is site of formation of first blood vessels and first
    blood cells in the embryo.
2. Systemic Arteries branch off dorsal aortae to supply
   developing organs and gut.
  — Each organ develops a capillary bed that merges into
    systemic veins leading back to heart.
3. Yolk Sac is supplied and drained by systemic veins
   (Portal System) in Osteichthyes and Amphibians. Yolk
   sac supplied via Vitelline Arteries and drained by
   vitelline veins in Chondrichthyes and Amniotes.
         Developmental Anatomy
• Developmental Stages
4. As the Liver develops, it is supplied by veins leaving
   the yolk sac (= Hepatic Portal System) which pass
   through the liver capillary network then coalesce into
   veins passing back to the heart.
5. In Amniotes the Allantois (=extraembryonic
   membrane functioning in waste storage) develops
   and is supplied by allantoic artery and drained by
   allantoic vein.
   – Allantoic vein initially passes directly to back of heart, but
     later becomes incorporated into capillary bed of liver.
     Some anatomical bypass of liver capillary network in birds
     and reptiles, but not in mammals.
   – Associated with nutritional role of chorioallantoic
     membrane of the placenta in mammals. Functions solely in
     respiration in birds and reptiles.
        Developmental Anatomy
• Accessory Circuits
• Embryonic stages of all vertebrates except most
  primitive (cyclostomes) possess a Renal Portal
  System supplying capillary beds of kidney.
   – Renal Portal System also present in all adult
     vertebrates, except for cyclostomes and mammals,
     although in birds and reptiles much of the portal
     supply bypasses the kidney capillary network.
• Aortic Arches shift from gill circulation positioned
  on main aortic trunk (gill-breathers) to side circuit
  associated with other structures (lung-breathers).
• A specialized connective tissue in which the
  intercellular material is entirely fluid (plasma)
• Plasma components include …
  – Stable components = inorganic salts and blood
    proteins (e.g., albumin = increases osmotic
    pressure of blood, fibrinogen = clot formation,
    globulins = immunological role).
  – Fluctuating components = glucose, fats, amino
    acids, waste products (e.g., urea, uric acid),
                   Blood Cells
• No blood cells present in Amphioxus
  – Restricted to low energy lifestyle
• Two general categories in all vertebrates:
1. Erythrocytes (RBCs) = involved in oxygen and
   carbon dioxide transport
  — Hemoglobin serves as respiratory pigment to
    dramatically increase O2 carrying capacity of blood
2. Leukocytes (WBCs) = many actions –
   immunological, phagocytic, etc.
  — Most of these roles accomplished outside of
    circulatory system
  — Use circulatory system for transport to sites of action
          Leukocytes (WBCs)
• Unlike RBCs, leukocytes contain nucleus and
  all other subcellular organelles
• Have capacity for ameboid movement, many
  of WBC functions are carried out after
  movement across vessel wall = diapedesis
        Other Blood Cell Types
• Platelets = disc-shaped cell fragments derived
  from megakaryocytes in bone marrow
  – Function in clotting
  – Found only in mammals
• Thrombocytes = spindle-shaped cells
  developmentally related to WBCs
  – Function in clotting
  – Found only in non-mammalian vertebrates
Human Blood Smear

  Anucleate erythrocyte

                          Neutrophil (a WBC)

Frog Blood Smear
                                       Nucleated erythrocyte


 Hemopoietic (blood-forming) Tissues
• Formation of blood cells continues throughout
  lifetime (from stem cell precursors) to replace
  dying blood cells.
• Embryonic Blood-forming Sites:
  – Blood Islands in yolk sac in large-yolked eggs
  – Chorion of placenta in mammals
• Becomes more localized later in embryonic
  –   kidney (sharks to reptiles and birds)
  –   liver
  –   spleen
  –   thymus (not in hagfish ?)
  –   diffuse sites in intestinal walls
 Hemopoietic (blood-forming) Tissues
• Adult Blood-forming Sites
  – Spleen (except for mammals and birds)
  – Thymus (T-lymphocytes)
  – Kidney (lampreys, elasmobranchs, teleosts)
  – Gonads (elasmobranchs  leukocytes)
  – Liver (teleosts, amphibians, turtles)
  – Intestinal Walls  lymphoid elements (or walls in
    other regions of digestive tract – esophagus, pharynx,
  – Bone Marrow (amphibians [frogs] – mammals)
  – Bursa of Fabricius  lymphoid elements (birds) =
    dorsal pouch off of cloaca (combined urinary-
    reproductive-anal opening)
 Hemopoietic Tissues – Myeloid Tissue
Arrows = adipose cells   Arrows = developing blood cells

     Bone Marrow              Embryonic Liver
               Lymphatic System
• Functions to return interstitial fluid to blood stream
• Lymphatics not connected with arteries; have blind
  capillaries and vessels.
• In Cyclostomes and Sharks there is no typical lymphatic
   – Instead possess an open system of sinusoids (low b.p., so
     low interstitial fluid production in these groups).
• Teleosts possess paired lymph hearts (muscular
  structures along lymphatics and at junctions with veins
  that help propel lymph along vessels) and 2 major sets
  of ducts:
   – Paired subvertebral ducts (deeper)
   – Paired lateral ducts
   – A similar condition occurs in Tetrapod embryos.
            Lymphatic System
• Amphibians with well-developed lymphatic
  system, many with numerous lymph hearts
• Reptiles show complex system; reduction in
  the number of lymph hearts and development
  of valves in vessels to prevent backflow
• Birds & Mammals generally have no lymph
  hearts in adults (although present in bird
  embryos and in a few adult birds).
  – Series of valves present to prevent backflow.
  – Movement of lymph in conjunction with skeletal
    muscle contraction.
               Lymphatic System
• Intestinal region lymphatics particularly well developed
  in advanced vertebrates.
• Most of the fats entering circulation from the gut do so
  by way of the lymphatics (due to the large size of the
  fat molecules and the incomplete endothelial lining of
  lymphatic vessels, fatty lymph = chyle).
• Lacteals = lymphatic vessels leaving intestine carrying
• Thoracic Ducts = lymphatics running along back of
  body cavity, serve as collectors for lacteals.
   – Major duct in mammals (single, paired in many primitive
• Cisternae chyli = area where many tributaries feed into
  thoracic duct (occurs in lumbar region)
Fig 12.46 –
Formation of
Fig 12.49 – Lymphatic system in a salamander. Note the prominence of the
lymph hearts for moving lymph within the lymphatic system.
Fig 12.48 – Lymphatic system in turtles
Figure 12.47

               Fig 12.47 – Lymphatic circulation
               and lymph nodes
Valve in           Adipose tissue
Vessel in

            Lymph vessel

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