physiology of pregnancy. the perinatal care of the fetus. prepared by n. bahniy
TRANSCRIPT
Physiology of pregnancy. The perinatal care of the fetus.
Prepared by N. Bahniy
STAGES OF PRENATAL DEVELOPMENT Preembryonic stage - first 2
weeks. Products of conception are called as conceptus.
Embryonic stage - from the third week until the end of the eight week. From this period conceptus is called embryo.
Fetal period starts from the beginning of the ninth week through the full 41 weeks of development. Products of conception are called as fetus.
Preembryonic Stage fertilization zygote formation division of fertilized ovum morula formatiom formation of free blastocyst implantation of the ovum in
the uterine wall Primitive chorionic villi
formation Initial folding into layers –
gastrulation beginning.
Chorion and amnion begin to form during this period also.
A SPERM FERTILIZING AN OVUM
Formation of free blastocyst
Morula
From outer layer - trophoblast
From inner layer - embryoblast
Implantation- attachment of the blastocyst on the 7th day into uterine wall
called implantation.
EMBRYONIC STAGE Formation of supportive structures - include the placenta, umbilical
cord, and certain extraembryonic membranes. The yolk sac forms early and manufactures blood cells until the liver
takes over at 6 week. The allantois forms the part of the yolk sac; it produces blood cells and
eventually forms the umbilical arteries and veins. During the third week the primitive streak appears, and then, other
rudiments of organs form, including the central nervous system, notochord, neural tube, heart, limbs, finger, toes, eyes, ears, and nose.
AN AMBRYO IS ABOUT 5 WEEKS OLD
"FETUS OF ABOUT EIGHT WEEKS, ENCLOSED IN THE AMNION,"
FROM GRAY'S ANATOMY. PART OF THE PLACENTA IS SHOWN AS THE LOWEST FEATURE IN THIS IMAGE, AND THE AMNION EXTENDS
ABOVE THE FETUS.[1
Critical periods of fetal development
ImplantationMorphogenesis and organogenesisPlacentation
Growing and differentiation of the structures during the Fetal Period
Conceptus structure in the end of pregnancy
Fetus Umbilical cord Placenta Amniotic Fluid Amnion Chorion Decidua
Fetal characteristics
Classification Gestational age (weeks of
pregnancy
Weight, gram Length, cm Signs of maturity
“Deep pre-term fetus”
12 – 22 25 – 500 9 - 25 Absent
“Fetus pre-term” 22 –36+6 days 500 – 2500 25 - 46 Absent
“Fetus in-term” 37 – 41 > 2500(3200-3500)
47(50-52)
Present
“Fetus post-term” > 41 > 2500 47 Present
Signs of fetal maturity
Umbilical ring is between pubis and processes xyphoideus
Pink skin Well-developed subcutaneous tissue, Lanugo in the shoulders and upper part
of the back Length of the hair on the head is 2 cm Nails are present till the top of the fingers Well-developed ears and nose cartilage Testes are present in the scrotum in the
boys and labia major are covered labia minor in the girls
Active movements Loud cry of the infant
FETAL HEAD AT TERM
DIAMETERS OF THE FETAL HEAD AT TERM
1. The suboccipitobregmatic (9.5 cm, 32cm), which follows from the middle of the large fontanel to the undersurface of the occipital bone.
2. The suboccipitofrontalis (10cm,33 cm) – from subocipital fossa to border of the hair.
3. The occipitofrontal (12 cm, 34 cm), which follows a line extending from a point just above the root of the nose to the most prominent portion of the occipital bone.
4. The occipitomental (12.5-13 cm, 39-41cm), from the chin to the most prominent portion of the occiput.
5.The sublingquobregmatica (9,5 cm, 32 cm).
6. The biparietal (9.5 cm), the greatest transverse diameter of the head, which extends from one parietal boss to the other.
7. The bitemporal (8.0 cm), the greatest distance between the two temporal sutures.
DIAMETERS OF THE FETAL BODY AT TERM
Biacromial distance – 12cm, 34-35 cm
Bisiliacus distance – 9cm, 27-28 cm
DECIDUA - MATERNAL MEMBRANE, immunologically specialized tissue.
provides for embryo-fetal nutrition.
Fetal membranes
Structure
chorion and amnion Amnion
A double-layered
translucent membrane
Become distended
with fluid
Amniotic fluid 1000-1500ml at 36th-38th week (peak) Absorb
1. Fetal membrane
2. Umbilical cord
3. Fetal skin
4. Fetal drinking
Source
1. Fetal urine
2. Fetal lung
3. Exudation of amnion and fetal skin
Functions:
Protection of the fetus
Protect mother, prevent infection
Formation of the forebag
Umbilical Cord
Structure
amnion, yolk sac, one vein, two artery and Wharton jelly
Length
30-70cm
Placenta at section
Fetal and maternal parts.
Cotyledon –
is a small
compound of placenta.
Placental villi
At term, the placenta contains approximately 12 m2 of villous surface area for maternofetal exchange.
Placental functions
Endocrine Transfer of nutrients Excretory - removal
of the products of fetal catabolism
Barrier Oxygen-transport
Placental hormones1. Protein hormones of the placenta: chorionic gonadotropin (cHG)– it is maintain the function of the corpus
luteum during early gestation, promote uterine vascular vasodilation and myometrial smooth muscle relaxation, relaxin secretion by the corpus luteum, stimulate thyroid activity, and some more basic forms also stimulate iodine uptake
human lactogen – its actions include lipolisis and an increase in the levels of circulating free fatty acids, thus providing a source of energy for maternal metabolism and fetal nutrition
2. Steroid hormones of the placenta: estrogens; progesterone.3. Chorionic adrenocorticotropin and thyrotropin, growth hormone
variant, parathyroid hormone-related protein (PTH-rP), calcitonin, and relaxin – no significant role has been established for this substance in normal human pregnancy.
4. Hypothalamic-like-releasing hormones of the placenta
Type of human placentation - hemochorioendothelial
Role of Estrogen in Pregnancy:
Increasing blood flow to the uterus by promoting vasodilation.
Changing the sensitivity of the respiratory system to carbon dioxide.
Softening of the cervix, initiating uterine activity, and maintaining labor.
Developing the breasts in preparation for lactation and secretion of prolactin by the pituitary gland.
Role of Progesterone in Pregnancy:
Ready the uterus for implantation. Relaxes smooth muscle to prevent
spontaneous abortion. Works to prevent a maternal immunologic
response to the fetus. Relaxes smooth muscle
– to decrease motility & improve absorption of nutrients.
– Enlarges the ureters & bladder to increase capacity.
Plays a role in development of the alveoli & ductal system to prepare for lactation.
Physiologic changes in pregnant woman
Genital organs1. Uterus1) capacity: 5ml-5000ml.weight: 50g-
1000g2) Hypertrophy of muscle cells3) Endometrium→decidua: basal
decidua, capsular decidua, true decidua
4) Contraction: Braxton Hicks5) Isthmus uteri: 1cm→ 7-10cm6) Cervix: colored7) Ovary: placenta replaces ovary
(10th week)8) Vagina: dilated and soft, pH↓(anti-
bacteria)9) Ligaments: relaxed
Physiologic changes in pregnant woman
Cardiovascular system1. Heart: move upward, hypertrophy of cardiac muscle2. Cardiac Output increase by 30%, reach to peak at 32nd –
34th week3. Blood pressure early or mid pregnancy Bp↓.late pregnancy
Bp↑ .Supine hypotensive syndrome
Physiologic changes in pregnant woman
Hematology1. Blood volume1) Increase by 30%-45% at 32nd –34th (peak)2) Relatively diluted2. Composition1) Red cells Hb:130→110g/L, HCT:38%→ 31%.2) White cells: slightly increase3) Coagulating power of blood: ↑ 4) Albumin: ↓,35 g/L
Physiologic changes in pregnant woman
The Respiratory system
1. R rate: slightly ↑2. vital capacity: no
change
3. Tidal volume: ↑ 40%
4. Functional residual capacity:↓
5. O2 consumption: ↑ 20%
Physiologic changes in pregnant woman
1. Kidney
1) Renal plasma flow (RFP):↑35%
2) Glomerular filtration rate (GFR):↑ 50%
2. Ureter
Dilated (P↑)
3. Bladder
Frequent urination
Physiologic changes in pregnant woman
Gastrointestinal system
1) Gastric emptying time is prolonged→ nausea.
2) The motility of large bowel is diminished → constipation
3) Liver function: unchanged
Physiologic changes in pregnant woman
Endocrine1. Pituitary (hypertrophy)1) LH/FSH: ↓2) PRL:↑3) TSH and ACTH:↑2. Thyroid1) enlarged (TSH and HCG↑)
2) thyroxine↑ and TBG↑ → free T3 T4 unchanged
