Blood Circulation in the Fetus

Blood Circulation in the Fetus

• Fetus receives oxygen from the blood of its mother

  • Lungs not used for oxygen/carbon dioxide exchange

  • Lungs need only enough blood to keep growing tissues alive

• Oxygen received from mother's placenta through the umbilical vein

• After the first breath after birth:

  • Lungs inflate and the newborn oxygenates its own blood

  • Foramen ovale and ductus arteriosus close so that blood no longer bypasses the lungs

Circulatory Patterns in the Fetus and Newborn

• Fetus: ductus arteriosus is open (patent); oval foramen is open — allows blood to bypass the lungs

• Newborn: ductus arteriosus closes and becomes the ligamentum arteriosus; oval foramen closes and becomes the fossa ovalis

Pulse

• Rate of alternating stretching and recoiling of elastic fibers in an artery as blood passes through with each heartbeat

  • Left ventricle doesn't eject blood in a continuous flow

• Evaluates regularity of pulsations and their strength

• Auscultation is not a true pulse

• Rate equal to heart rate in healthy species

• Most often felt on superficial arteries lying against firm surfaces (bones)

  • Palpable arteries will change dependent on species

• Generally, large animals have slower pulses, and small animals have faster pulses

Blood Pressure

• Measurement of the amount of pressure that flowing blood exerts on arterial walls

• Dependent upon interactions with:

  • Heart rate

  • Stroke volume

  • Diameter and elasticity of the artery

  • Total blood volume

• Varies during the cardiac cycle:

  • Systolic blood pressure = highest number; pressure when heart contracts (related to aorta)

  • Diastolic blood pressure = lowest number; pressure when heart is relaxed

  • Mean arterial pressure (MAP) = average pressure during one cardiac cycle

Indirect Tests to Monitor Cardiovascular System

• Auscultation of the thorax

• Peripheral artery palpation

• Arterial blood pressure evaluation

• Thoracic radiography

• Electrocardiography

• Echocardiography

Electrocardiography

• Based on electrical activity of the heart

• Detects electrical impulses on the surface of the animal's body

• Produces an electrocardiogram (ECG or EKG)

Components of One Cardiac Cycle (on ECG)

• P wave - depolarization in the atriums (from SA node)

• QRS complex - depolarization in the ventricles

• T wave - repolarization

Venipuncture

• Superficial blood vessels are used to collect blood samples, administer medications intravenously, and place venous or arterial catheters

• Common sites by species:

  • Cat: jugular vein, cephalic vein, femoral vein (medial surface)

  • Dog: jugular vein, cephalic vein, saphenous vein (lateral surface)

  • Cattle: jugular vein, coccygeal vein

  • Horse: jugular vein

Other Venipuncture Sites

• In lactating dairy cattle: superficial caudal epigastric vein = milk vein (not used routinely)

• In ruminants and rodents: coccygeal vein