Vertebrate chordates exhibit a closed circulatory system. Blood is transported around the body via veins and arteries. The blood is circulated by the pumping action of the heart. O2/CO2 in blood diffuse across the thin walls of the teeny vessels called capillaries in the tissues. Higher order vertebrates have a four-chambered heart, and a double circulation of the blood, which involves circulation for the heart and the lungs and another for the heart and the rest of the body =systemic circulation.

few in number/approx 3% of WBCs
bilobed nucleus
engulf antibody identified pathogens
release cytotoxic chemicals via exocytosis (can kill large
increase in # with allergen presence
reduce inflammation

The ductus arteriosus is a teeny blood vessel that connects the pulmonary artery to the aorta in a fetus. This vessel permits O2 rich blood bypass the pulmonary circulation, entering systemic circulation. In newborns, the ductus arteriosus closes and becomes the ligamentum arteriosum. If it does not close, it is called a patent ductus arteriosus.
The placenta secretes prostaglandins which keep the duct open in the fetus. With first breathe, the pulmonary vessels in the alveoli dilate changing the blood flow in the pulmonary circuit. Also, with the placenta no longer attached to the newborn, prostaglandin levels fall.  

    Heart rate is increased/decreased by changing the rate of depolarization in the pacemaker cells.
To decrease heart rate: ACh is released by parasympathetic neurons which alters K+ permeability of SA node cells. This delays the action potential slowing heart rate.
To increase heart rate: Sympathetic neurons release norepinephrine which opens the NA+/Ca+ channels increasing the rate of depolarization.

Fetal/placental circulation:
Low O2 blood flows from fetus to placenta via umbilical arteries which arise from fetal internal iliac arteries.
HIgh O2 blood flows from placenta to fetus via single umbilical vein which drains into the ductus venosus, a shunt that allows blood in the umbilical vein to bypass the fetal liver.
The ductus venosus drains into the inf. vena cava. 


btw...Low O2 stimulates erythropoietin/EPO
secretion from the kidney and for atrial natriuretic peptide (ANP) secretion from the heart. 


   Pressure (P) and Resistance (R) determines blood flow (f).
Flow is directly proportional to pressure and inversely proportional to resistance.
The pressure gradient is the difference in pressure from one end of a vessel to the other. ..think aorta to teeny capillary. The pressure gradient can be adjusted by altering cardiac output and capillary resistance. 

 is maintained using
  information such as blood pressure and O2/CO2 levels received via chemo/baroreceptors. 

White blood cells WBCs are also
called leucocytes.
1ml of blood exhibits 5ish x 10*6 RBCs and just 7500 WBCs.
​Most WBCs are found in the lymphatic tissue or connective tissue proper.  
WBCs that are in circulation are:

1. moved to the site of an infection/injury by + chemotaxis
2. sometimes capable of phagocytosis
3. capable of ameoboid movement
through endothelium into peripheral tissues via diapedesis.    

   Venous return aided by muscular compression and the respiratory pump

Blood Flow to the Brain...

12% cardiac output (CO) for 2% body weight!
Feed the brain at all costs!

  depolarization/ contraction/ systole
  repolarization / relaxation / diastole

kupffer cells line the sinusoids of the liver. they are phagocytes
that serve to breakdown "used" blood cells...

               Blood Pressure:
 Arterial pressure rises during ventricular systole and falls during ventricular diastole.

    The difference between diastolic and                systolic pressure = pulse pressure

       MAP = mean arterial pressure =
    diastolic pressure + pulse pressure/3

So: for BP of 110/80,
MAP = 80 + (110-80)/3 = 80 + 10 = 90

​MAP and pulse pressure decrease as the distance from the heart increases. 

              vein types
large veins:
    ex: inf vena cava
    thick tunica externa/thin tunica media
    lumen diameter: 2cm

medium veins:
    ex: peripheral veins
    thickish tunica externa/thin tunica media
    lumen diameter: 2-9 mm (.2-.9cm)
    ex: capillary bed
    no tunica media/resemble capillaries
    lumen diameter: 20 micrometers

all mollusks except those cephalopods exhibit an open circulatory system with a three chambered heart. one or two atria collect oxygenated blood from the gills, and the single ventricle pumps it to an aorta and then on into  small vessels which empty directly into tissues. mollusks are coelomates.
their main body cavity is a hemocoel through which blood and coelomic fluid circulate.  


a. foramen ovale becomes fossa ovalis
b. ductus arteriosus becomes
​ligamentum arteriosum

systemic and pulmonary circulation  

the blood vascular system first appeared in an ancestor of the triploblasts 520 million years ago as a way to overcome the time-distance constraints of diffusion.  Found in ​southwest China, where/when in the early Cambrian era evolution occurred rapidly and the main animal groups appeared for the first time, the animal had a tubular heart positioned with paired blood vessels that extended from the heart and were arranged along the body segments. In the head, blood vessels were concentrated around the brain, some of them extending towards the eyes and antennae, where most oxygen and nutrients would be required.
Consider the success of arthropods. They have the longest fossil record of any animal and are the largest phylum today.

         Capillary Exchange:
   *H2O, ions, glucose, aa diffuse                  between endothelial cells or via              channels in membrane
   *Large H2O soluable molecules                need fenestrations (kidneys,                  endocrine)
   *Lipid soluable molelcules and O2,              CO2 diffuse across plasma
          (phospholipid) membrane

  3.  Central Regulation/Endocrine Function:

evolution of the circulatory system

   Blood flow  equates to cardiac output... an increase of one increases the other.


Pressure/volume too high

2-8% of WBCs
large kidney bean shaped nucleus
become tissue macrophage after             24 hours in circ
release chemicals to attract other           WBCs

arthropods exhibit an open circulatory system. These animals have a dorsal heart and arteries that move blood into spaces within the tissues called hemocoels. vessels drain blood from these hemocoels back to the large pericardial cavity around the heart via ostia.

Types of WBCs

annelids have a closed circulatory system. blood is pumped by muscles in blood vessels. blood flows through the microscopic capillaries, picking up food molecules from the digestive tract and oxygen from the skin and transporting them to the cells of the body.

how did the circulatory system evolve?

      Control of Blood Flow




Stroke or TIA

      1. Autoregulation:


The Fetal Heart

         types of capillaries
continuous capillaries:
   most common
   complete endothelium (one to several cells)
   permit H2O, small solutes and lipid soluble
        molecules to diffuse into interstitial fluid    
   prevent blood cells and plasma proteins from
        exiting circulation

fenestrated capillaries:
   endocrine organs, filtration areas of kidney,
      absorbtive areas of intestine
   exhibit pores in endothelium
   permit exchange of H2O and solutes
   fenestration size/permeability vary by tissue

sinusoidal capillaries:
   liver, spleen, bone marrow
   flattened, non-continuous epithelium with
     thin/absent basement membrane 
   permit free exchange of H2O and larger                  solutes

Pressure/volume too low

               artery types:
elastic: closest to heart
              lumen diameter 1-2.5 cm
              ex: aorta
              tunica media very elastic
              high elastic rebound
muscular: most numerous
              lumen diameter 4mm (.4cm)                                  ex: brachial
              tunica media more muscular
smallest of arteries
              lumen diameter 30 micrometers                                                 (.03mm or .003cm) 
              poorly formed tunica media
              called resistance vessels 
              exhibit vasocontracition/vasodilation

during ​exercise, 
cardiac output (CO) increases from resting 5.8L/min to ...
run forest run...

platyhelminthes lack a  circulatory system. the functions associated with this system take place via absorption through the body wall. 

20-40% of WBCs
large round nucleus
exhibit three classes:
    t cells: cell mediated immunity
    b cells: antibody production
    natural killer cells: on patrol


                                                   Coagulation Phase
  extrinsic pathway: damaged endothelial cells begin the cascade   
  intrinsic pathway: activation of proenzymes in the blood begin the cascade

some mollusks have an 

In an open circulatory system, found in arthropods, blood is pumped into a cavity called a hemocoel where it surrounds the organs and then returns to the heart(s) through ostia (openings). The blood (hemolymph) found in arthropods is a mix of blood and interstitial fluid. 


Arteries gradually change as they get farther away from the heart.

vertebrate circulation

   Locked knees? Oops, no ,     no muscular compression       aiding venous return

 myocardial infarction
heart attacks occur when a coronary vessel is blocked
 commonly by plaque formation called coronary thrombus.
Diagnosis by:
pain (not always/silent killers)
ECG/blood tests for cardiac enzymes released by damaged cells

       blood viscosity 5x H2O
       vessel length
       vessel diameter

Neural Control of Homeostasis: Blood Pressure

In a closed circulatory system, blood is always contained within vessels. All mammals fish, birds, reptiles, and amphibians exhibit a closed system. 

    Blood clotting

      cardiac output = volume of blood pumped by the left ventricle in one minute

 The average heart pumps 2,000 gallons of blood per day without rest and will beat over 2.5 billion times in 70 years.

review of ABO/Rh compatibility

small and rare/ <1% of WBCs
release histamine (dilation) and heparin (< blood clotting)

 Stroke volume 

most abundant (60%)
segmented nucleus w/2-5 lobes phagocytic first strikers         that destroy bacteria by fusing  engulfed cell with                 lysozome containing defensins
release hormones that increase permeability
      of vessels and attract other WBCs 
short shelf life (30 min to 10 hours)

aortic transection

   Speaking of blood pressure....

 Heart Arrhythmias:
abnormal patterns of a heart's electrical activity which
​may reduce efficiency of heart

1.5-5 x 10*5/ml blood
shelf life approx 10 days
1/3 found in spleen where they are also
thrombocytopoiesis occurs via
     megakaryocytes; 1 = 4000 platelets 

evolution of the heart from...
two chambers - fish
three chambers - amphibians
four chambers - mammals

Cardiovascular center of medulla
responds to input
from baroreceptors and chemoreceptors.

  2. Central Regulation: Neural 
cardiovascular center of medulla exhibits:

a. cardiac center : inc/dec cardiac output via 
     cardioacceleratory center (sympathetic)
     cardioinhibitory center (parasympathetic)
b. vasomotor center: inc/dec lumen diameter
    vasoconstriction control: most peripheral
       vessels vascular via NE release
    vasodilation of muscle/brain vessels via         
       ACh release 

Most arterioles exist in a state of partial constriction. Max constriction reduces lumen by half of resting diameter increasing resistance x 80.  


          stroke volume =
volume of blood pumped out of the left ventricle during one contraction.
     SV = EDV - ESV 

   capacitance of a blood vessel =
        relationship of volume vs pressure
Veins have a higher capacitance as they are more expandable/distensable



Endothelial cells in the capillaries are smushed tightly together 
forming tight junctions which permits only teeny molecules, lipid-soluble molecules, and select gases to pass freely through the capillary to the brain cells.


Endocrine Control of Homeostasis:
Blood Pressure/Volume

           Innervation by                 parasympathetic and 
   sympathetic autonomic 
  system via cardiac plexus

plasma proteins

nematodes also do not have a circulatory system. they move gases and nutrients around their body through diffusion.

is a four chambered heart more efficient?
why or why not???

   Cardiovascular Pressure

      capillary structure
no tunica media or tunica externa

composed of endothilium with thin basement membrane (fibrous matrix secreted by endothium)
diameter : 8 micrometers (.008mm)        
                    (size of one red blood cell)


      Tissue Perfusion     The amount of blood flowing through capillary beds must be sufficient to feed adjacent cells with nutrients/O2 and remove CO2 and waste and is measure as Tissue Perfusion. 
Tissue perfusion is impacted by:
cardiac output, peripheral resistance and blood pressure. Blood flow must be regulated to ensure that certain tissues receive blood when they need it perhaps at the expense of others...
We have enough blood to fill only about 25% of the vessels in our capillary beds. Here's where regulation of blood flow comes in... 

with arterial and venous systems

Echinoderms rely on their water vascular system for movement, gas exchange and circulation. the water vascular system consists of a ring canal with radial canals extending along each arm. Water circulates through these canals, moving gasses, nutrients and waste.  the madreporite is like a valve that regulates the amount of water in the water vascular system. tube feet extend through openings in the endoskeleton. they use hydrostatic pressure to expand and contract.  

           heart rate =
​ heartbeats per minute

          Capillary Exchange:
             Filtration / Reabsorbtion
 to/from cells .125mm from capillary 

  artery structure
tunica intima:
endothilium, connective tissue w/elastic fibers, elastic internal elastic membrane
tunica media:
smooth muscle with connective tissue cover, external elastic membrane
tunica externa (adventicia):
connective tissue sheath w/ collagen and elastic fibers

functions of a
circulatory system

              venous valves
made of folds in tunica intima
point in the direction of blood flow = 
serve to compartmentalize blood and prevent
if weakened, lead to varicoceles /hemorrhoids
     DVT (deep vein thrombosis/clots form =

After that first breathe, the foramen ovale closes due to a change in the relative pressure of both atria ensuring the separation of O2 rich and O2 poor blood. 

Sometimes, the closure is incomplete or will take a week to several months to close. If the formaen ovale does not close, it is called a patent foramen ovale /PFO.

About 20% of adults have an incomplete closure. 

porifera don't exhibit the type of circulatory system seen in higher order animals.
There's no heart, veins/arteries or blood.
Gas/nutrient exchange occurs through the simple movement of water.

              vein structure
exhibit tunica externa, tunica media, tunica intima
thinner wall and larger diameter vs arteries
exposed to lower pressure

​may exhibit valves

coronary artery disease
ormation of atherosclerotic plaque reduces diameter of coronary artery/reducing blood flow=  coronary ischemia
reducing cardiac efficiency

angina pectoris often initial symptom

                     low cardiac output
    indicates poor peripheral circulation

cnidarians also lack
a circulatory system. Like
porifera, cnidarian cells
get oxygen directly from the water surrounding them.
Cnidarian cells exchange oxygen and carbon dioxide by diffusion. Nutrients are absorbed via the lining of the gastrovascular cavity.

connected by capillary beds


   Pressures affecting blood flow:
1. ​ Blood pressure (BP): arterial pressure measured in mmHg 
      BP range: 120mm at base of aorta to 35mm at start of capillary bed
2.  Capillary Hydrostatic Pressure (CHP): force exerted by blood against capillary wall
      CHP range: 35mm to 18mm through capillary bed
3. Venous Pressure (VP) pressure of blood in venous system.
      VP range: vena cavae exit at 2mm from venule pressure of 18mm, effective pressure
       of venous system = 16mm.

hemorrhagic shock

    vascular phase > platelet phase > coagulation phase



              capillary bed
one arteriole to dozens of capillaries to a few venules...exhibits thoroughfare channel and precapillary sphincters
permit exchanges of gasses/nutrients/wastes​
more than one artery supplying blood to  capillary bed = collateral arteries
two collateral arteries fusing to supply one capillary bed = arterial anastomosis

Neural Control of Homeostasis: O2, CO2, pH 

 Welcome to Dr. Kate Brilakis' Learning Portal

Artificial Pacemaker
uses electrical signals to prompt the heart to beat at a normal rate. Needed to treat arrhythmias.