Physiology

Question 1

Fertilisation

Answer 1

• Primary oocyte meiosis
  
  • 46->23 haploid cell and polar body
  • Now a secondary oocyte
  • Sperm enter fallopian tube via vagina and uterus
  • Sperm penetrates corona radiata and zona pellucida to fertilise the egg
  • 23-> 46, then 46->23 and a second polar body

Question 2

Blastocyst formation

Answer 2

• 23+23-> zygote
• Cell divides rapidly to form morula
• Forms blastocyst with inner cell mass (embroyblast), blastocele, trophoblast
Gradually loses corona radiata and zona pellucida

Question 3

Implantation

Answer 3

• Blastocysts arrives at uterus
  
  • Blastocyst reaches endometrium 8-10days after ovulation
  • Trophoblast adheres to stroma of endometrium
  • Outer layer of trophoblast is syncytiotrophoblast mixed with stroma of endometrium
  • Stroma-> decidua to provide nutrients to trophoblast
  • When blastocyt implants in endometrium, syncytiotrohphoblast produces HCG
  • HCG: CL-> O/P

Question 4

Development of embryo

Answer 4

• Blastocyst differentiates a week after fertilisation
  
  • Embryoblast cells split into yolk sac and amniotic carrier
  • Embryonic disc sits between yolk sac and amniotic cavity
  • Embryonic disc forms foetus
  • Chorion surrounds this complex; cytotrophoblast and syncytiotrophoblast

Question 5

When does fetal heart form and start to beat

Answer 5

6 weeks

Question 6

Lacunae formation

Answer 6

○ Trophoblast invades endometrium
○ Signals sent to spiral arteries, reducing their vascular resistance and making them more fragile
○ Arteries break down, leaving lacunae (lakes)
○ Maternal blood flows from uterine arteries into lacunae, and back out through uterine veins
○ Lacunae form at 20 weeks gestation
○ Lacunae surround chorionic villi, separated by placental membrane, O2, CO2 diffuses across
Pre-eclampsia: high vascular resistance in spiral arteries, sharp rise in maternal blood pressure

Question 7

Placenta function

Answer 7

Respiration
Nutrition
Excretion
HCG
Oestrogen 
Progesterone 
Immunity

Question 8

Placenta respiration

Answer 8

○ Oxygen source for foetus, affinity

○ CO2, H, HCO3, lactic acid, acid-base balance

Question 9

Placenta nutrition

Answer 9

○ Glucose
○ Vitamins and minerals
○ Harmful substances: medications, alcohol, caffeine, cigarette smoke

Question 10

Placenta excretion

Answer 10

○ Urea and creatinine

○ Act as kidneys

Question 11

Placenta hCG

Answer 11

○ Syncytiotrophoblast produces HCG
○ Levels increase in early pregnancy, plateau at 10 weeks
○ HCG maintains corpus luteum until placenta can take over O/P production
○ HCG can cause nausea/vomiting
○ Higher levels of hCG occur with multiple pregnancy and molar pregnancy

Question 12

Placenta oestrogen

Answer 12

○ ○ Softens tissues and makes them more flexible
○ Oestrogen allows muscles and ligaments of uterus and pelvis to expand
○ Cervix becomes soft and ready for birth
○ Enlarges and prepares breasts and nipples for breastfeeding

Question 13

Placenta progesterone

Answer 13

○ Placenta takes over by 5 weeks gestation
○ Progesterone maintains pregnancy
○ It relaxes uterine muscles, preventing contraction and labour
○ Maintains endometrium
○ Causes side effects by relaxing other muscles: LOS heartburn, bowel constipation, blood vessels hypotension, headaches and skin flushing
○ Raises body temperature between 0.5-1degree

Question 14

Placenta immunity

Answer 14

○ Antibodies transfer across the placenta to fetus during pregnancy

Question 15

Cardiovascular changes in pregnancy

Answer 15

○ Increased blood volume 
		○ Increased plasma volume
		○ High CO
		○ Decreased vascular resistance
		○ Low BP
		○ Vasodilation
		○ Varicose veins

Question 16

Respiratory changes in pregnancy

Answer 16

○ High tidal volume

○ High resp rate

Question 17

Renal changes in pregnancy

Answer 17

○ High blood flow
		○ Increased GFR
		○ High Na reabsorption
		○ High water reabsorption
		○ High protein excretion
		○ Physiological hydronephrosis

Question 18

Blood changes in pregnancy

Answer 18

○ High RBC/WBC
		○ Low pt
		○ Low Ht
		○ Increased clotting factors
		○ Low albumin
		○ High ALP (placenta)

Question 19

Skin changes in pregnancy

Answer 19

○ Linea nigra
		○ Melasma
		○ Striae gravidarum
		○ Spider naevi
		○ Palmar erythema

Question 20

Hormonal changes during pregnancy

Answer 20

Increased ACTH
Increased prolactin 
Melanocytes-stimulating hormone
TSH normal, T3/4 rise
HCG rise 
Progesterone rises