Reproduction in lower and Higher Animals
Pregnancy , Placenta, Parturition, Lactation
Pregnancy
Condition of carrying one or more embryos in the uterus
called pregnancy.
Also called gestation.
Period between fertilization of the egg, up to the parturition
Average period is 266 days from fertilization or 280 days (266+14)
counted from l mc- last mensuration cycle. (nine months)
Pregnancy are steps into three trimesters of three months each.
First Trimester
(From fertilization to
12th week)
Radical changes in mother and embryo.
In the first 2-4 weeks embryo receives nutrients directly
from the endometrium
Main period of organogenesis
At end of eight weeks major structures in a rudimentary form now
embryo is called foetus
About 3cm long arms,
hands, fingers, feet, toes are formed it can open and close mouth and fists.
CNS, excretory and circulatory
systems begins
Movements of fetus
starts but mother cannot feel it
Heartbeat can be heard
from 6th week
At the end of first trimester fetus is about 7-10 cm long
Progesterone level becomes high it initiates changes in her
reproductive system. And menstrual cycle is suspended
The maternal part of
placenta grows, the uterus becomes larger
Mother experiences ‘morning sickness’ (like nausea, vomiting, mood swings, etc).
Second Trimester
(from 13th to
26th week)
Rapid growth of fetus takes place it is very active and grows
to about 30 cm
Uterus grows enough for the pregnancy to become obvious.
Development of brain
begins
Hormone levels stabilize as hCG declines, the corpus luteum
deteriorates (regresses)
Placenta completely
takes over the production of progesterone which maintains the pregnancy
At the18-20 week delivery date can be established by observing
baby’s growth and position with the help of ultrasound (sonography)
Head has hair, eyebrows and eyelashes appear; ear pinnae are
distinct.
The baby reaches half
the size of a newborn
Movement of Baby
easily felt by the mother.
Third (final) Trimester
(from 27th week
till the parturition)
The fetus grows to about 3-4 kg in weight and 50cm in length.
Eyes are open
The uterus expands, the mother’s abdominal organs become
compressed and displaced, leading to frequent urination, digestive blockages
and strain in the back muscles.
At the end fetus fully developed and ready for parturition
Placenta
It is Temporary structural and functional connection between
foetal and maternal circulation.
It is Flattened, discoidal organ in the uterus of a pregnant
woman.
It Attached to the wall of the uterus and to the baby’s
umbilical cord.
It Formed from mother and the foetus tissues.
Part contributed by the foetus is called the foetal
placenta and it is the chorionic villi.
Other part, termed as maternal placenta is
rich in blood supply shared by the mother. It is a part of uterine wall.
So human placenta is called haemochorial.
The umbilical cord is of these three
blood vessels, two are small arteries (carry blood towards placenta) one is a
large vein (returns blood to the foetus)
It supplies of oxygen and nutrients and also for removal of carbon dioxide and excretory wastes produced by the foetus
Acts as an endocrine tissue produces hormones
hCG increases upto the end of first
trimester and then it declines.
Progesterone is produced at the end of
first trimester
Relaxin is secreted by the ovary in the
later phase of pregnancy. For foetal growth and maintenance of pregnancy.
Parturition
Process of giving birth to a baby.
Humans are viviparous (give birth to their young ones)
Uterine and abdominal contractions,
dilation of cervix and passage of baby are collectively called labour.
Discomfort or agony called labour
pains.
It is a complex neuroendocrine
mechanism.
The signals arise from foetus and
placenta cause mild uterine contractions.
It gives rise in estrogen- progesterone
ratio, increase in oxytocin receptors in uterine muscles.
They cause vigorous contractions of
myometrium of uterus at the end of pregnancy.
The
fully developed foetus gives signals for the uterine contractions by secreting Adrenocorticotropic
Hormone (ACTH) pituitary and corticosteroids from adrenal gland. Oxytocin from
mother’s pituitary gland,
Uterine muscles of mother and causes
vigourous uterine contractions.
Expulsion of the baby from the uterus.
It
involves the following three steps
1.
Dilation stage
2.
Expulsion stage
3. After birth
1. Dilation stage
Contraction starts from top uterus ,
forcing the baby towards the cervix.
Accompanied by pain caused by
compression of blood vessels.
Oxytocin induced uterine contractions
become stronger and stronger due to stimulatory reflex.
Baby is pushed down in the uterus, its
head comes to lie against cervix.
Cervix and vagina show dilation.
This stage of labour can normally last
upto few hours.
Ends in rupturing of amniotic membrane of foetus.
2. Expulsion stage
Uterine and abdominal contractions
become stronger.
In normal delivery, the foetus passes
out through cervix and vagina with head in forward direction.
It takes 20 to 60 min.
The umbilical cord is tied and cut off close to the baby’s navel.
3. After birth
After the delivery of the baby the
placenta separates from the uterus and is expelled out as “after birth”, due to
severe contractions of the uterus.
This process happens within 10 to 45 minutes of delivery.
Lactation
Mammary glands produce milk called
lactation.
Hormone responsible for production of
milk is Prolactin
Helps in Feeding the newborn baby.
Colostrum fluid secreted by the mammary glands soon after childbirth
Colostrum
Sticky and yellow fluid as soon as
after childbirth.
It contains Proteins, lactose low fat. And
mother’s antibodies e.g. Iga.
Antibodies helps in baby at a time when
its own immune response is not fully developed
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