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  1. What cells produce pulmonary fluid?
  2. What happens to that fluid generally after it is produce?

  1. Produced by the Pleural membrane cells
  2. Drains into the lymphatic system through holes (stomata) in the parietal pleura


Regarding small animals (dogs and cats) pulmonary fluid exchange

  1. Do they have a thin or thick visceral pleura?
  2. How is pleural fluild created?
  3. Blood supply is from what?

  1. have a relatively thin visceral pleura;
  2. the pleural fluid comes almost entirely from the parietal side and is reabsorbed on the visceral side or into the lymphatics of the parietal side-
  3. The primary blood supply to the visceral pleura is from pulmonary artery. 


Regarding large animals (horse and cow) pulmonary fluid exchange

  1. Do they have a thin or thick visceral pleura?
  2. How is pleural fluild created?
  3. Blood supply is from what?

  1. thick visceral pleura;
  2. produce some fluid from visceral pleura-
  3. blood supply to the pleura is from the aorta via the bronchiole circulation (high pressure).


Describe the 2 sides of an alveolar septum

  • Top- on the “thin” side of the septum, capillary endothelium and alveolar epithelium share a basement membrane.
  • Bottom- on the “thick” side of the septum, endothelium and epithelium are separated by a layer of interstitial tissue. 


How is pleural fluid produced?

Fluid filtration: High to low pressure (mm Hg) due to high hydrostatic pressure in the capillary and low hydrostatic pressure in the interstitium.


How is pleural fluid removed

  • Fluid reabsorption: Low to high pressure (mm Hg) due to low oncotic pressure in interstitium and high oncotic pressure in the pulmonary capillary.
  • The pulmonary and lymphatic capillaries will eventually reabsorb the excess pleural fluid. 


Exercise Example. 

  • How does increasing ventilation impact the rate of filtration and fluid reabsorption?

  • Increased activity (exercise) --> capillary hydrostatic pressure increases --> increasing filtration of fluid into the interstitium (space between cells in a tissue- in this case the space in the alveolar septum- Figure 50-4). 
  • When the heart is functioning normally, enough pressure is generated to help with fluid filtration. 
  • Also assisting with filtration and reabsorption is capillary and interstitial hydrostatic and colloid pressure differences. 
  • The lymphatic vessels will reabsorb excess fluid (up to a certain point) that has accumulated in the interstitium due to increased circulation/increased activity using the skeletal muscle pump (skeletal muscles contract and push lymphatic fluid into the venous blood (at the junction of the subclavian v. and internal jugular v.) and the respiratory pump (diaphragm acts like a pump during ventilation to push excess fluid through the lymphatics and into the venous system.
  • There is an increase in lymphatic fluid return and venous return during inhalation- due to Boyle’s law (increase volume and decrease pressure).  The opposite occurs during expiration.


What happens during left congestive heart failure

  • During left CHF (congestive heart failure) pressure increases inside the left atrium --> congestion of blood in pulmonary veins --> congestion of blood in pulmonary capillaries. 
  • This increase in hydrostatic pressure forces the fluid from the capillary walls into the interstitium.
  • The capillary filtration > pulmonary capillary/lymphatic reabsorption. 
  • Infections can also occur in that area and pleural fluid production can increase dramatically --> lungs to collapse (hunting dogs are prone to this- tend to get puncture wounds to the chest and develop an infection); horses are notorious for pleural infections due to inhaled particulate matter.


What is the difference between pleural effusion and pulmonary edema?

Location. Location. Location.

  1. Pleural effusion- abnormal fluid accumulation between the visceral and parietal pleura. 
  2. Pulmonary edema- abnormal fluid accumulation inside the lung tissue- this fluid can build up in the conducting airways depending on the severity (pink frothy/foamy (from surfactant- because it acts like a detergent) fluid exuding from the nares = pulmonary edema). 


What are 4 types of hypoxia?

  1. Hypoxic hypoxia
  2. Anemic hypoxia
  3. Stagnant hypoxia
  4. Histotoxic hypoxia


What is the normal function of pleural fluid? 

To reduce the friction (pleurae can slide easily past one another) during ventilation (inspiration and expiration).


  1. What happens in hypoxic hypoxia?
    • give an example
  2. what happens in anemic hypoxia
    • give examples

  1. Hypoxic hypoxia- Decreased PaO2
    • High altitude, airway obstruction, pulmonary edema)
    • Diffusion distance will increase, so not much oxygen will get from alveolus to pulmonary capillary
  2. Anemic hypoxia- Anemia
    • there is too little functioning hemoglobin in the blood (hemorrhage, anemia, carbon monoxide poisoning).


  1. What happens in stagnant hypoxia
    • give an example
  2. what happens in hystotoxic hypoxia
    • give example

  1. Stagnant hypoxia- heart failure
    • results from the inability of blood to carry oxygen to tissues fast enough to sustain their needs
  2. Histotoxic hypoxia- Cyanide poisoning
    • the blood delivers adequate oxygen to the tissues, but the tissues are unable to use it properly
    • Cynanide blocks an enzyme required for the use of O2 during ATP synthesis


do the lungs in fetal ciculation function as gas exchangers



The fetus depends on the placenta for 

the exchange of gas, nutrients, and metabolic byproducts.


Three shunts for oxygenated blood from the placenta to enter the aorta

1. Patent Ductus arteriosus 
2. Foramen ovale
3. Ductus venosus or similar structure (umbilical vein to caudal vena cava)


Pulmonary vascular resistance and pulmonary arterial pressure are high or low in fetal circulation

  1. High
  2. Pulmonary artery pressure > aortic


Why is pulmonary  vascular resistance and pulmonary arterial pressures high in fetal circulation (3 reasons)

  1. Pulmonary artery pressure > aortic
  2. Hypoxic pulmonary vasoconstriction
  3. Lack of lung expansion (small collapsed)


  1. Placenta serves as what to the fetus
  2. Does it have high or low vascular resistance?
  3. does it receive a lot or little part of cardiac output

–Low vascular resistance
–Receives a substantial part of cardiac output 

  1. Placenta serves as the “fetal lung”
  2. Low vascular resistance
  3. Receives a substantial part of cardiac output 


What is this diagram saying?

  • Fetal O2 transport is assisted by fetal hb, which has a high affinity for oxygen. 
  • Takes a lower partial pressure to saturate fetal hemoglobin than adult


The fetal circulation mixes oxygenated blood with deoxygenated blood at several points, so the fetus exists in a state of



  1. What are the 4 possible arrangements of fetal and maternal blood vessels
  2. what does this depend on?

  2. depends on species


What type of arrangement of fetal and maternal blood vessels do horses have?

Have a countercurrent exchange


Explain the arrangement of the equine placenta

  1. The maternal artery (oxygenated blood) and fetal artery (deoxygenated blood) are countercurrent (flow in opposite directions).
  2. The O2 is delivered via the maternal artery to the placenta (microcotyledon).
  3. The placenta is a unique vascular organ that receives blood supplies from both the maternal and the fetal systems and thus has two separate circulatory systems for blood:
    • (1) the maternal-placental (uteroplacental) blood circulation, and
    • (2) the fetal-placental (fetoplacental) blood circulation.
  4. The uteroplacental circulation starts with the maternal blood flow into the intervillous space through decidual spiral arteries.
  5. Exchange of oxygen and nutrients take place as the maternal blood flows around terminal villi in the intervillous space.
  6. The in-flowing maternal arterial blood pushes deoxygenated blood into the endometrial and then uterine veins back to the maternal circulation. 
  7. The fetal-placental circulation allows the umbilical arteries to carry deoxygenated and nutrient-depleted fetal blood from the fetus to the villous core fetal vessels.

  8. After the exchange of oxygen and nutrients, the umbilical vein carries fresh oxygenated and nutrient-rich blood circulating back to the fetal systemic circulation. 


What must be present at birth for the alveoli to expand upon the first inspiration.

pulmonary surfactant 


  1. what is a Patent Ductus Arteriosus
  2. where is it located 
  3. What would it have normally become?

  1. When ductus arteriosus does not close shortly after birth
    • Connects pulmonary artery and aorta (will bypass the lungs)
  2. Caudal to coronary a. and brachiocephalic trunk
  3. ligamentum arteriosum


  1. what does the ductus arteriosus allow in fetus?
  2. how does blood generally flow in fetus with a ductus arteriosus?
  3. when does patent ductus arteriosus close?

  1. Developing heart and brain get higher PO2
  2. Blood flows from R-to-L in the fetus
  3. Closes at birth – muscular contraction initially


What is the most common congenital heart defect in dogs?

Patent Ductus Arteriosus


  1. What is the foramen ovale
  2. What blood flow does it allow
  3. What is the point of having one in fetus?

  1. Opening between the atria
  2. Thin flap on the left side allows one-way R-to-L shunt
  3. Positioned to allow venous return in the caudal vena cava to stream into the left atrium