Physiology Flashcards
What is the role of the placenta
Provide oxygen and nutrients to fetus, function as lungs in utero.
What do the arteries do
They carry deoxygenated blood to the placenta
What is the role of the vein
Carries oxygenated blood to the fetus
What does the autonomic nervous system do
Controls the heart rate, breathing, bowel function and generates baseline
What nervous systems generate variability
The interplay between the parasympathetic and sympathetic NS
What nervous system generates movements and accelerations
Somatic NS
What nervous system creates decelerations and when are they seen on CTG
Parasympathetic NS, and mostly seen later in pregnancy
What is the pacemaker of the heart
Sinoatrial node
Explain the physiology of a baro receptor response
Baroreceptors are located in the aorta and carotid sinus. These are stimulated by changes in arterial pressure. When a contraction occurs a rise in pressure is sensed.
Occlusion of umbilical arteries during the compression of the cord. This increases parasympathetic activity, by slowing the heart rate to reduce the pressure. Hypotension then occurs and increases the sympathetic activity increasing the heart rate. Caused by cord compression during contraction (variable decels)
Explain the chemoreceptor response
Chemoreceptors are located in the aortic arch and carotid sinus.
The chemoreceptors detect a drop in oxygen levels in the blood, and a rise in carbon dioxide this leads to a sympathetic response, increasing the heart rate.
Once these stabilise the parasympathetic NS then slows the heart rate.
Caused by head compression (early and late decels)
Briefly explain the different types of decels
Early Decelerations: (2 marks) o Typically benign.
o Mirror contractions.
• Late Decelerations: (2 marks)
o Occur after contractions.
o Concerning - suggest fetal distress.
• Variable Decelerations: (2 marks)
o Abrupt and unpredictable.
o Often due to cord compression. •
Prolonged Decelerations: (2 marks)
o Significant, prolonged drops in FHR. o Requiring immediate attention.
Explain what happens in an early deceleration
Associated with compression of the head during a contraction. (3 marks)
• Compression causes increase in intracranial pressure which increases parasympathetic NS which causes a fall in HR to reduce intracranial pressure. (2 marks)
• When the pressure is released, the HR returns to normal. (1 mark)
• FHR returns to baseline at the end of the contraction. (1 mark)
• White/Reassuring Feature. (1 mark)
What is hypoxemia
Decrease in oxygen content of the arterial blood alone
What is hypoxia
Decrease in the oxygen content that affects the peripheral tissues
What is asphyxia
A general oxygen deficiency that affects the central organs
What is the fetal response to hypoxemia
Maintained energy balance
Decrease in growth
Reduced activity
More effective uptake of oxygen
This can be maintained for days or weeks
What is the fetal response to hypoxia
Maintained energy balance
Anaerobic metabolism in the peripheral tissues
Redistribution of blood flow
Surge of stress hormones
This can be managed for several hours
What is the fetal response to asphyxia
Brain and heart failure
Anaerobic metabolism in peripheral tissues
Alarm reaction
Max activation of sympathetic nervous system
This can last MINUTES !!
What are the types of hypoxia and what are the rates of PH drops
Acute - PH drop rate of 0.01/min (7.2-7.1 in 10mins)
Subacute - PH drop of 0.01/ 2-3 min (7.2-7.1 in 20-30 mins)
What is HIE
Brain injury, babies brain doesn’t receive enough oxygen or blood flow. May be suspected if there’s a significant risk factor during labour and delivery.
