Lecture 5 General med_2nd semester

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Lecture 5 General med_2nd semester

• Development of external form of the embryo
• and fetus. The rule of Hasse
• Uterine growth during pregnancy
• Marks of the mature and full-term fetus
• Multiple pregnancy mono- and dizygotic
• twins arrangements of fetal membranes in
• twins
• Position, posture and presentation of the fetus

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• Development of the external form of the embryo
  and fetus
• 1st month
• growth of developing embryo is accompanied by
  changes of its shape and size
• the human development begins by spherical zygote
  that mitotically divides and gives rise to
  2-,4-,8-cell stage,- a morula
• up to the morula stage all blastomeres are
  totipotent
• more differentiated stage than morula is a
  blastocyst composed of two cell
• lines trophoblast and embryoblast

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• the embryoblast is soon differentiated into germ
  layers - the ecto- and endoderm
• by the third week, the formation
• of the third germ layer mesoderm
• begins
• the embryo becomes trilaminar
• disc called the embryonic disc

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the mesoderm then differentiates into somites,
intermediate and lateral mesoderm
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• by day 10, development of fetal membranes run
• by the end of the first month, the embryo becomes
  to form a tube that is C - shaped curved
• a convexity of the embryo is adjacent dorsally
  and the embryonic body can divide into three
  parts head, rump and tail
• embryo is connected via omphalomesenteric duct
  with vitelline sac
• length of the embryo is lesser than 1 cm

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• 2nd month
• the cephalic region (future head) is large with
  5 obvious prominences, from which a face of the
  embryo develops
• in the future cervical region, 4 pairs of
  branchial arches and between them branchial
  grooves lay down
• simultaneously limb buds differentiate and
  development of limbs starts (development of the
  upper limb precedes development of the lower one)
  
• at the end of this month the head is more rounded
  and shows human characteristics, external
  genitalia still have sexless appearance
• the embryo is about 20 mm long
• the term the embryo does not use longer and
  concept is termed the fetus

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• 3rd month
• main developmental processes are completed
• head is large and constitutes almost half of the
  fetus but later growth of body length accelerates
  and head becomes smaller
• face is broad, the eyelids are developed but they
  close to the end of this month
• upper limb reaches its final relative length
• the external genitalia are well developed and the
  sex of the fetus is possibly to identify
• in liver and then in spleen, the hematopoiesis
  begins
• fetus starts to excrete urine (into amniotic
  fluids)
• length - 9 cm, weight 20 grams

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• 5th month
• lower limbs reaches their final relative
  proportion
• the skin is covered with a greasy cheese - like
  material with protective function known as vernix
  caseosa and with fine hairs called lanugo
• mother feels the first fetal movement -
  quickening
• the length 25 cm, weight cca 300 grams
• 6th month
• the skin is usually wrinkled as the layer of the
  subcutaneous fat is missing
• it is translucent and pink-reddish coloured as
  blood capillaries and vessels are seen
• production of surfactant begins in lungs
• fetus is 30 cm long and weighs 650 grams
• 7th month
• accumulation of the subcutaneous fat starts, head
  and lanugo hairs well developed
• eyes reopen
• CNS is able to control rhythmic breathing
  movements and body temperature so that the fetus
  may survive if born prematurally
• length - 35 cm, weight - 1250 grams
• 8th month

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• 9th month
• nails reach to the ends of distal phalanges,
  hairs are short, skin is always pink and smooth
• the descent of the testes is completed
• length - 45 cm, weight - 2500 grams
• 10th month
• individual body parts show usual proportions
• hairs are minimally 1 cm long, labor of the fetus
  --- newborn
• fetus is 50 cm long and weighs 3200 - 3500 grams
• Rule of Hasse
• used for estimation of fetal age of a unknown
  fetus (important in forensic medicine)
• from the 3rd to 5th month, the length of fetus
  is equal with the second power of respective
  month (9, 16, 25 cm)
• from the 6th to 10th month, the length of fetus
  is equal with product 5 x respective month (30,
  35, 40, 45, 50 cm)

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• Uterine growth during pregnancy
• the uterus of a nonpregnant female lies in the
  pelvis minor, during pregnancy it increases in
  size to accommodate the growth of the fetus
• the increasing uterus is to touch through the
  ventral wall of the abdomen
• 3rd month - uterine fundus corresponds to the
  superior aspect of the pubic symphysis
• 5th month - uterine fundus occupies the half
  distance between the umbilicus and pubic
  symphysis
• 6th month - uterine fundus is just in the level
  of the umbilicus
• 8th month - uterine fundus lies at the half
  distance between the umbilicus and xiphoid
  process
• 9th month - uterine fundus is just in level of
  the xiphoid process
• 10th month - uterine fundus descends and is
  located for about two fingers below the xiphoid
  process

the increase in size of the uterus results
from hypertrophy of preexisting muscle cells
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• Estimation of the date of birth
• the date of birth is calculated according to the
  day of fertilization or the onset of the last
  normal menstrual period
• in the first case, birth follows after 266 days
  after estimated day of fertilization (38 weeks
  8 3/4 calendar months 9 1/2lunar months)
• in the second case, birth follows after 280 days
  after onset of the last menstrual period (LMP)
  (40 weeks 91/4 calendar month10 lunar month)

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• Marks of the mature (full-term) fetus
• in the human, the pregnancy lasts 280 days or 40
  lunar weeks from the 1st day of LMP (266 days or
  38 weeks after fertilization)
• fetuses born 10 to 14 days before or after
  term are called mature or full-term
• if they born before 37th week - premature and
  born after 42 weeks - postmature ones
• criteria or signs of maturity of the fetus are
  major and the auxiliary ones
• Major marks
• length of fetus - about 50 cm,
• weight of fetus - 3200 to 3500 g,
• in males testes are within the scrotum, in
  females labia minora are covered with labia
  majora
• dimensions of the new-born head should be in
  norm
• (head circumference to circumference of
  shoulders or chest should be 3534)

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• Auxiliary marks
• skin of the fetus is pink
• only residues of fine lanugo hairs are found
• hairs on head are at minimal 1 cm long
• nails have grown beyond the tips of the digits
• in the distal epiphysis of the femur is a
  distinct ossification centre
• baby is plump and cries

• Rule of Hasse
• used for estimation of fetal age of a unknown
  fetus (important in forensic medicine)
• from the 3rd to 5th month, the length of fetus
  is equal with the second power of respective
  month (9, 16, 25 cm)
• from the 6th to 10th month, the length of fetus
  is equal with product 5 x respective month (30,
  35, 40, 45, 50 cm)

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• Dimensions of head in newborns
• are transverse and longitudinal
• transverse dimensions
• - bitemporal distance - 8 cm (there is a distance
  of two points on the coronal suture lying each
  other as far as possible)
• - biparietal distance - 9.5 cm (there is a
  distance between the centres of both parietal
  tubera)

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• Dimensions of head in newborns
• longitudinal dimensions
• - frontooccipital distance - 12 cm (there is a
  distance between the centre of the forehead and
  external occipital protuberance), frontooccipital
  circumference - 34 cm,
• - distance subocciput-bregma - 9.5 cm (from
  bregma to the external occipital protuberance),
  circumference subocciput-bregma 32 cm,
• - mentooccipital distance - 13.5 cm (from the
  centre of the chin to the external occipital
  protuberance), mentooccipital circumference 35 to
  36 cm.

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• Multiple pregnancies Mono- and dizygotic twins
  arrangement of fetal membranes in twins
• multiple pregnancies occur in the human
• labor of
• twins falls on 90 pregnancies
• triplets on 90 x 90 pregnancies
  (902)
• quadruplets on 90 x 90 x 90 (903)
• pregnancies
• Twins may be of two categories
• dizygotic or fraternal - two zygotes
• monozygotic or identical - one zygote

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• Dizygotic twins result from fertilization of two
  ova by two different
• spermatozoa
• three possible ways of origin are supposed
• 1) both ova have developed in the same follicle
  - fertilized simultaneously
• 2) the ova derive from two follicles in the same
  ovary
• 3) one ovum was developed in the left and the
  other in the right ovary
• dizygotic twins may be of the same sex or
  different one
• genetically, they are no more alike than brothers
  or sisters born at different times
• dizygotic twins always have
• separate fetal membranes
• two amnions
• two chorions
• two placentas
• chorions and placentas may be
• fused in various extent

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• Monozygotic twins
• are always of the same sex because result from
  fertilization of one ovum
• they are genetically identical and very similar
  in physical appearance
• an arrangement of fetal membranes in these twins
  depends upon the twinning time
• twinning may occur in
• immediately after the first mitosis of zygote -
  twinning on two-cell stage
• (the zona pellucida is precociously dissolved,
  blastomeres then loose close contact and may
  develop independently each other
• each fetus has proper fetal
• membranes (separate)

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• Monozygotic twins
• around the end of the first week in time
  developing of inner cell mass
• (it can develop two embryonic primordia or the
  inner cell mass or embryoblast secondary divides
  into two parts)
• subsequently, two embryos develop, each in its
• own amniotic sac but within one chorionic sac -
• such twins have
• two amnions
• one common chorion and placenta

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• Monozygotic twins
• around the end of the second week (between day
  13- 15) if the duplicated primitive streak and
  chordomesodermal process develop
• twins have common all fetal membranes
• one common amnion
• one common chorion and placenta

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• Position, posture and presentation of the fetus
• (in the uterus)
• Position of the fetus (situs fetus) is defined
  as a relation of its longitudinal axis to the
  longitudinal axis of the uterus
• 3 positions are distinguished
• - longitudinal position - both axes run parallel
  - in 99,5 per cent
• - transverse position - both axes are rectangle
• - oblique position - axes are passing (instable
  position)
• The longitudinal position
• by head (96,5 ) or
• by breech (pelvic end of the fetus) - 3 .
• The back of the fetus is most often oriented to
  the left edge of the uterus
• Posture of the fetus (habitus fetus) is defined
  as a relation of fetal body parts to each other
• may be regular and irregular
• regular posture the head is in flexion, the
  chin is in close contact with the chest, upper
  and lower limbs are flexed in both articulations
  and are folded

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• Presentation of the fetus (praesentatio fetus) is
  defined as a relation of the fetal body part to
  the pelvic aditus
• cases that occur
• - cephalic presentation - is physiological or
  normal
• - breech presentation - by pelvic end of the
  fetus - rare,
• - foot or knee presentation - very rare,
• - malpresentation - any abnormal presentation

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Dimensions of the female pelvic aditus
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