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

               location of heart in
     mediastinum of thoracic cavity

Neural Control of Homeostasis: Blood Pressure

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

              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

    Blood clotting

Electrocardiogram = EKG/ECG

  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

The Fetal Heart

      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... 

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

​may exhibit valves

Types of WBCs

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.

changes...

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

    vascular phase > platelet phase > coagulation phase

  Neutrophils
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)

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.    

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

ETC...

review of ABO/Rh compatibility

   cardiac physiology

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

    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. 

 Stroke volume 

hemorrhagic shock

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

  Cardiovascular System

plasma proteins

Exercise

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

RBCs

Chemoreceptors

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

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

   myocardium
​  endocardium

   its not just         
     about blood...

aortic transection

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.  

    Leucopoiesis

  Pacemaker cells are modified cardiac muscle cells that exhibit weak contractile filaments.

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

            veins

 Pathology:
 myocardial infarction
​MI
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

   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.

  More detail...
​Pacemaker cells do not require stimulation...they will  depolarize/initiate action potentials all by themselves.
Their membrane potential "at rest" is approx. -60mV which is unstable.  (Membrane potential is the imbalance of electrical charge between the interior and exterior of the cell...as the inside of the cell becomes less negative, the potential decreases (gets more +) below the resting potential and the cell depolarizes). So, this membrane potential of the pacemaker cell that never fully "rests" is called a pacemaker potential. Pacemaker cells have channels called "funny channels" that are permeable to both Na + and K+. The K+ permeability slowly and spontaneously decreases with time causing a slow depolarization as K+ ions exit the cell. At the same time, there is a slow, continuous, spontaneous inward flow of sodium. These actions are not the result of nerve stimulation hence the term autorhythmic. The influx of Na+ exceeds the efflux of K + so there is a net + movement. As the ion concentrations of these two ions slowly depolarize the cell, it eventually reaches threshhold (-40mV) and an action potential is generated.

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

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

Stroke or TIA

WBCs

systemic and pulmonary circulation  

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

           heart rate =
​ heartbeats per minute

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

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

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

              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)
    
venules:
    ex: capillary bed
    no tunica media/resemble capillaries
    lumen diameter: 20 micrometers
             (.02mm/.002cm) 
    

Blood Flow to the Brain...

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

      Control of Blood Flow

Blood

   Cardiovascular Pressure

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

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

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

           Innervation by                 parasympathetic and 
   sympathetic autonomic 
  system via cardiac plexus

Endocrine Control of Homeostasis:
Blood Pressure/Volume

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

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. 

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

  Why do cardiac muscle cells contract?
A muscle cell in a state of rest (resting potential) has a sarcolemma that is polarized (- inside/+outside).  As the cell depolarizes due to shifting concentrations inside/outside of K+/Na+, Ca 2+ is released from the sarcolemma (and also enters the cell) and binds to troponin. Cross‐bridge binding occurs. Actin filaments slide past myosin filaments. A contraction occurs. Repolarization occurs and membrane potential returns to its original polarization. A refractory period follows. The muscle cell cannot contract again until the cell is restored to its resting potential. 

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

 Pathology:
coronary artery disease
CAD
formation of atherosclerotic plaque reduces diameter of coronary artery/reducing blood flow=  coronary ischemia
reducing cardiac efficiency

angina pectoris often initial symptom

  3.  Central Regulation/Endocrine Function:

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. 

               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
arterioles:smallest of arteries
              lumen diameter 30 micrometers                                                 (.03mm or .003cm) 
              poorly formed tunica media
              called resistance vessels 
              exhibit vasocontracition/vasodilation
​

              The Heart

Pressure/volume too low

pericardium:
  1. stabilizes position of heart
  2. reduces friction
contains:
1. outer fibrous pericardium
2. inner serous pericardium:
    a.parietal layer
    b. visceral (epicardium) layer
    c. pericardial cavity with serous
        fluid between a and b.

Pressure/volume too high

                     low cardiac output
    indicates poor peripheral circulation

   Speaking of blood pressure....

...lymphatic circulation
   (more about this in                           Section 3!)

         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

   Venous return aided by muscular compression and the respiratory pump

Baroreceptors

   Resistance:
       blood viscosity 5x H2O
       vessel length
       vessel diameter
       turbulance 

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

   anatomy of a            capillary bed

         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

  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.  

Neural Control of Homeostasis: O2, CO2, pH 

  depolarization/ contraction/ systole
  repolarization / relaxation / diastole

      1. Autoregulation:

   vasoconstiction/vasodilation

   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. 

   artery vs vein

    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.

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

    blood flow through the heart

      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)