Fetal Physiology

Question 1

Describe the amniotic fluid at different stages of pregnancy?

Answer 1

1. Early pregnancy - ultra filtrate of maternal plasma
2. Second trimester - extracellular fluid (diffuses through fetal skin)
   - composition: fetal plasma
3. After 20 w: fetal urine

Question 2

What are the functions of amniotic fluid?

Answer 2

1. Cushion fetus
2. Protects from trauma
3. Maintain temp
4. Growth and development of tissues
5. Minimal nutritive function

Question 3

What does the heart require to act efficiently as a pump?

Answer 3

1. The ability to beat
2. Intact electrical connections to ensure that the chambers contract in order
3. An intact structure to ensure that blood passes in the correct direction
4. Intact vascular connections for the inflow and outflow of blood

Question 4

When is blood flow seen through the fetus?

Answer 4

end of 3rd week

Question 5

What is the fetal heart rate at 12 weeks and what can it now get affected by?

Answer 5

140 –180 bpm
inputs from the brain (nerves) and from the blood stream (hormones) Adrenaline, Noradrenaline (Catecholamines) affect the heart rate
- These inputs alter the fetal heart rate and variability

Question 6

Describe the intrinsic control of the fetal heart?

Answer 6

1. Sino Atrial node is the pacemaker with a rate of 100bpm
2. Atrio Ventricular node can initiate a rate of 40-60bpm
3. Rest of the system will initiate a rate of 15-40bpm

Question 7

Describe the intrinsic control of the fetal heart?

Answer 7

Regulated by the autonomic nervous system

1. Parasympathetic (↓) Sympathetic (↑)
2. Adrenaline, stretching of the atria, temperature and drugs

Question 8

The fetal heart pumps deoxygenated blood back to the placenta via?

Answer 8

2 umbilical arteries

Question 9

Oxygenated blood is returned to the fetus via?

Answer 9

umbilical vein

Question 10

What is the role of the placenta?

Answer 10

facilitate exchange of blood gases and nutrients

- The exchange of gases is dependent on normal blood flow through the placental bed

Question 11

Describe aerobic metabolism in normal fetal gas exchange?

Answer 11

• The fetus uses O2 in the metabolism of glucose to provide energy and waste products Carbon Dioxide (CO2) and Water (H2O)
• The fetus’ supply of O2 is carried via haemoglobin
• Haemoglobin levels are higher in a fetus than an adult and fetal haemoglobin has a greater affinity for O2
• The waste products - Carbon Dioxide (CO2) and Water (H2O) are then further broken down to form a hydrogen ion (H+) and a bicarbonate ion (HCO3-)
• The toxic H+ is buffered by haemoglobin within the red blood cells and HCO3- passes out into the extracellular fluid
• Deoxygenated blood is then returned to the placenta via the 2 umbilical arteries

Question 12

Describe the process of anaerobic metabolism in fetal gas exchange?

Answer 12

Occurs when a fetus can no longer achieve normal gas exchange and when there is a reduction in available oxygen
The process of anaerobic metabolism uses up the fetal glycogen stores and the waste product of this metabolism is lactate and H+

Question 13

Describe the state of the fetus during an acute hypoxic event?

Answer 13

the fetus will suddenly drop its heart rate and a bradycardia will occur

Question 14

Describe the mechanism behind fetal acid base balance?

Answer 14

H+ is buffered by haemoglobin within the red blood cells and HCO3- passes out into the extracellular fluid
- The exchange of gases is dependent on normal blood flow through the placental bed

Question 15

Describe the physiological response of hypoxia in a fetus?

Answer 15

1. The sympathetic nervous system response causes an initial adrenaline release
   – tachycardia and autonomic nervous system response : vasoconstriction
2. As less O2 is available the blood vessels further constrict, central nervous system hypoxia develops and the fetal heart rate variability decreases.

Question 16

Where does hemopoiesis take place in the fetus?

Answer 16

Yolk sac: early embryo
Liver
Bone marrow

Question 17

Describe fetal blood?

Answer 17

initially nucleated RBCs
Hb 12g/dl at midpregnancy
Hb 18 g/dl at term
Short life span: high reticulocyte count
Erythropoiesis: fetal erythropoietin
Fetal blood flow: fetoplacental blood volume 125 mL/ kg of fetus.
Fetal Hemoglobin: Hb F falls during latter weeks of pregnancy. At term ¾ Hb F
Hb F bind more O2 at any given O2 tension and identical pH

Question 18

When do different parts of the nervous system start functioning?

Answer 18

At 10 weeks: Local stimuli evoke response
Swallowing:10 w
Respiration :14-16 w
Mature taste buds receptors;12 w
Ability to suck: 24 w
Integration of nervous and muscular function increase rapidly in third trimester
Hears sound:24-26 w
Eye sensitive to light: 28 w

Question 19

What do different parts of the GIT start functioning?

Answer 19

Swallowing: 10-12 w
Peristalsis and transport of glucose: 10-12 w
- Amniotic fluid regulated by swallowing
- Movement of fluid in GI may enhance growth and development of GI tract

Question 20

When does the urinary system start functioning?

Answer 20

14 w, loop of Henle functional
Kidneys start producing urine at 12 w
Kidneys :Not essential for survival in utero,
Impotant in contol in composition and volume of amniotic fluid

Question 21

When does the pulmonary system start functioning?

Answer 21

Psudoglandular stage: 5-17 w
Terminal sac stage: type ii cells begin to produce surfactant
At birth only 15% of adult alveoli are present,lungs continue to grow up to 8 years

Question 22

Describe the function of surfactant?

Answer 22

At birth,with first breath, an air to tissue interface is produced in the alveolus.
Surfactant uncoils from lammeller bodies and then spreads to line alveolus to prevent collapse during expiration

Question 23

When do endocrine glands develop?

Answer 23

Pituitary : ACTH,GH,TSH, and LH 13 w
Posterior pituitary: 10-12 w
Thyroid : 10-12 w
Adrenal glands : fetal zone disappears after birth