12.4 fcka$$ flashcards i hate this chapter

parturition

process by which the foetus is expelled from the mother’s body at the end of gestation

preceeded by a sequence of events called labour

prior to labour

hormones + changes in structures + position of baby

several hormonal changes that

• cause ligaments in pelvis to soften, making them more pliable to childbirth

• increase response of uterus to stimuli

• strengthen contractions of uterus

foetus has probably settled its head in mother’s pelvis

cervix has softened, shortened in legnth, likely to have opened a little

foetus is facing womens right/left hip bone, kneeds drawn up to abdomen and legs crossed (position takes up as little room as possible)

one side of head is usually pressed against mother’s bladder, the other against her bowel

first stage of labour

during final 3 months, uterus undergoes weak irregular contractions that become more and more frequent and stronger until they occur every 30 minutes. marks beginning of birth process and contractions are known as labour pains

first stage: dilation of cervix (time from onsent of labour to complete dilation of the cervix)

• average of 8-9 hours for first birth and 4 hours for birth of subsequent children

waves of contractions travel from upper part of uterus downwards towards the cervix (similar to peristalsis that occurs in alimentary canal to push food along)

• muscle fibres that mkae up uterus shorten a smal amount, pulling on cervix to shorten it so that it no longer projects down into the vagina.

• at the same time, cervix is opened and allows foetus to move more deeply into the pelvis

• head of foetus is pushed more forcefully against slowly dilating cervix as contractions become more freuqnet and stronger

• cervix becomes dilated to about 10cm

• uterus, cervix and vagina form single, curved passage called birth canal (route which foetus will pass aided by contraction fo uterus and voluntary contractions of abdominal muscles of the mother)

• complete dilation marks the end of the first stage

second stage

involves delivery of fetus and is often called stage of expulsion

bursting of membrane surrounding fetus and gush of lfuid from vagina

may occur much earlier in labour or occasionally may not occur until foetus is ready to be born

full dilation of cervix to birth lasts between 20 minutes to 2 hours

• fetus moves through fully dilated cervix, head stretching the vagina

• distension of vagina stimulates the woman to contract her abdominal muscles + contraciton of uterus push foetus out of the vagina.

• baby’s head turns to face mothers back

• each push = baby’s head advances a small amount and retreats a little bwetween cotnractions but moves overall

• eventually, head stretches vaginal enterance and tissues between it and the anus

• tissue becomes tightly stretched over foetus’s head as it is forced out of vagina

• head emerges, turns sideways again to face the mothers hips and this rotation allows the rest of th ebody o move more easily throughout the birth canal

As the foetus passes through the birth canal, the pressure on the head may push it out of shape.

The underlying brain is not damaged, as the bones of the skull are pliable and separated by joints that

allow some degree of overlap. The head resumes its normal shape a few days after birth.

The head of the foetus is downward in over 90% of births. This position allows the head to

be delivered first and to act as a wedge to force open the cervix and the vagina. The head-down

position also allows the foetus to begin breathing even before it is completely free of the birth canal

third stage

• baby begins to breathe with it’s own lungs even tho still connected to the placenta via umbilical cord

• amnion, chorion and palcenta are still inside the uterus at this stage

• umbilical cord is clamped, tied in two places and then cut between ties

• arteries and vein within umbilical cord contract, before or immediately after they are cut

• after a few ays, stump of cord dries up and falls away

• navel or umbilicus is all that remains

• uterus coninues. to contract

• about five mins after delivery, the placenta and other membranes and remains of umbilical cord are expelled

• together these are called the afterbirth

• After birth, uterine contractions constrict vessels supplying the placenta.

• Blood clots form to prevent bleeding.

• The large exposed tissue area increases risk of infection.

• Historically, this often caused death in women.

• Today, cleanliness and antibiotics make infection after childbirth rare

ductus venosus

• foetal blood is carried to and from placenta by blood vessels in umbilical cord

• baby’s blood is carried to palcenta in two umbilical arteries

• CO2 and other wastes are exchanged for oxygen and nutrients as it circulates through the placenta

• some blood returning to foetus flows through liver and into inferior vena cava (main vein taking blood to heart from lower body)

• remaining 30% bypasses liver and flows through vessel called ductus venosus and then into inferior vena cava

• The fact that much of the blood does not pass through the liver causes no problems at this stage, as the mother’s liver is serving the needs of the foetus.

ductus arteriosus and foramen ovale

blood returning to the foetal heart enters the right atrium , and from there can follow several pathways

1) can flow from right ventricles then to lungs in usual way, but lungs are collapsed and aren’t functioning so they offer considerable resistance to blood flow and little reaches the lungs

2) most blood from right ventricle follows through ductus arteriosus to aorta, which vessel that bypasses the lung and allows blood in the pulmonary artery to flow directly into the aorta

3) blood in right atrium of heart can flow directly into left atrium and through an oval opening between two chambers called foramen ovale (located so that most of the blood entering right atrium goes through it). beneficial as blood coming from placenta is highly oxygenated and can flow to developing foetal tissues via aorta very quickly

changes at birth

• At birth, the placenta no longer supplies food and oxygen → lungs and liver must become functional.

• This requires closure of ductus venosus, ductus arteriosus, and foramen ovale.

• First breath triggered by shock of birth (or slap on bottom). If delayed, clamping the cord ↑ CO₂ → stimulates breathing centre.

• Lungs expand → resistance to blood flow decreases → ductus arteriosus closes (later fibrous tissue).

• Increased blood to left atrium forces foramen ovale flap shut → later seals permanently.

• Cutting the cord stops umbilical blood flow → ductus venosus closes → all blood must pass through liver.

• If foramen ovale doesn’t close = “hole in heart”, baby appears bluish (low oxygen). Surgery can correct.

• After birth physiology:

  • Breathing rapid (~45 breaths/min for 2 weeks) → slows later.

  • Heart rate high (125–130 bpm, up to 180 bpm with excitement).

  • High rates due to ↑ oxygen demand for muscle activity + warmth.

  • Red blood cells increase (extra oxygen transport).

  • White blood cells very high at birth, drop rapidly by day 7.