Fetal physiology Flashcards

Question

Ductus venosus (from liver to IVC)

Answer 1

The DV = duct between UV and the IVC Arterial blood is shunted through the DV into the IVC The DV duct is very narrow DV is narrow = greater pressure ejection (faster) of arterial blood into IVC

Answer 2

The IVC now has 2 streams of differently oxygenated blood Oxygenated blood is travelling faster than the deoxygenated blood The speed prevents mixing of the 2 streams of blood Can do this effectively for the short distance from DV to right atrium

Answer 3

FO is a flap between left and right atria FO flap kept open by higher pressures in right atrium due to high-speed arterial blood flow. DV ejection blood flow This streams highest oxygenated blood into ascending aorta Circulation that feeds organs with highest metabolic demand - brain and heart

Answer 4

Stream one adds oxygenated blood to stream two in the right atrium This increases the oxygen saturation of stream two

Answer 5

IVC and SVC IVC, no mixing Right atrium – pick up some O2 in the RA from stream 1 Right ventricle Pulmonary artery Most blood bypasses lung through ductus arteriosus Descending aorta – pick up more O2 blood from the aortic arch spillover - aortic isthmus

Answer 6

Blood does not go to lung to be oxygenated Lungs need some blood for growth, around 8% of cardiac output Remaining blood is shunted past lungs and into the descending aorta via the ductus arteriosus. De-oxygenated blood returning to the heart from IVC and SVC picks up oxygen In the right atrium From aortic isthmus spill-over

Answer 7

Cord occlusion, cord knots, prolapse Placenta: impaired formation, abruption, haemorrhage Delivery in the wrong position – e.g. feet first Premature closure of the ductus arteriosus Maternal respiratory illness/anaemia

Answer 8

Peripheral chemoreceptors – carotid and aortic arch (fetus = carotid dominance) Central (brain) chemoreceptors - brainstem, midbrain Collectively they detect changes in O2, CO2 - pH Initiate quick chemoreflex responses Added to by slower acting factors (eg endocrine, endothelial factors) to change respiration and cardiovascular function

Answer 9

Fetal heart rate: Reduce heart rate to reduce metabolic demand - protect the heart Blood flow: Send more blood to key organs (e.g. brain, heart) to support organs with higher metabolic demand Reduce blood flow to liver: Increase blood flow from placenta (stream one) to key organs and stream more blood through foramen ovale Haemoconcentrate: reduce fluid in blood vessels – send it to extracellular space – this aggregates red blood cells and increases O2 delivery per unit of blood Behaviour: Reduce energy/O2 demands such as body and breathing movements

Answer 10

Role for parasympathetic in bradycardia can be demonstrated by 1. Cut the vagus nerves 2. Giving a parasympathetic muscarinic receptor blocker like atropine. Chemoreflex control can be demonstrated by 1. Cutting carotid sinus nerve Purpose of the fall in FHR? 1. Reduces cardiac work, protects the heart from injury during low O2 Prolonged bradycardia may also be caused by the heart becoming gradually hypoxic itself

Answer 11

Role for sympathetic in vasoconstriction can be demonstrated by 1. Giving an alpha adrenergic antagonist. Chemoreflex control can be demonstrated by 1. cutting carotid sinus nerve Why does peripheral blood flow fall? 1. Sends blood flow to vital organs with highest metabolic demand 2. Supports blood pressure when heart rate falls

Answer 12

Blood pressure = determined by CO (stroke volume and heart rate) + peripheral resistance. Fetal CO is mainly controlled by heart rate as immature heart structure limits stroke volume. The fall in heart rate can cause a big change in BP. Peripheral vasoconstriction supports BP during hypoxia. Blood pressure is vital for blood flow and O2 delivery and CO2 removal

Answer 13

The change in blood flow to the brain is not a chemoreflex Cutting the carotid sinus nerve does not change brain blood flow. It is not due to the increase in blood pressure It is actively mediated by vasodilatation due mainly to endothelial vasodilators like nitric oxide This is demonstrated by using nitric oxide donor inhibitors

Answer 14

Fetus will concentrate red blood cells. Does this by removing fluid out of the blood vessels to the extracellular space. This helps concentrate red blood cells, reduces diffusion area at the tissue site Ductus venosus – less blood to liver. Greater streaming into IVC – due to increased flow Less mixing in RA - due to increased flow More well oxygenated blood (stream 1) crosses the foramen ovale

Answer 15

Switch to non-REM brain activity or reduced brain activity NREM lower metabolic state – conserves energy Isoelectric (near complete suppression) if severe. Activity and growth Stop making breathing movements, licking, swallowing Not chemoreflex as carotid denervation does not change them. Apnea is due to brainstem centres. Stop making body movements Not chemoreflex. In fact the fetus makes some body movements to begin with to try and move away from cord obstructions. If hypoxia is prolonged and the fetus has adapted, some movements will return to help lungs and body prepare for birth but at the expense of somatic (body) growth

Fetal physiology Flashcards

(39 cards)