PHYSIOLOGY
=Ovulation.=—Ovulation is the process whereby the eggs are discharged
from the Graafian follicle which matures and protects them in the ovary.
The egg is a true cell with one, and sometimes more than one, nucleus.
The ripening of the eggs, as well as their discharge, is attended with
much general disturbance and great physical changes. This phenomenon
begins from the twelfth to the fifteenth year, depending on race,
climate, occupation and temperament, and marks the transition of the
individual from childhood into maturity.
This period is called _puberty_. At this time the breasts enlarge, the
hips round out, the vagina, uterus and external genitals increase in
size. Hair appears upon the vulva, the emotions become more evident, and
modesty develops through a consciousness of sexual difference and
attraction.
Simultaneously a new function appears—
=Menstruation.=—Menstruation may be defined as a process wherein a
bloody fluid is discharged from the uterus at regularly recurring
periods between puberty and the menopause, _except_ during pregnancy and
lactation. It is a hæmorrhage which in some way is closely associated
with ovulation, but it is not known positively which is the precedent of
the other, or whether one causes the other.
Menstruation is not essential to pregnancy, for pregnancy may occur when
the flow is normally absent, as before puberty, after the menopause, or
during lactation. Nevertheless, regularity of menstruation is the rule
in fertile women and clinicians agree that while conception _may_ occur
at any part of the menstrual cycle, it is _most likely_ to happen just
before or just after the menstrual flow.
The best authorities at present support the theory that ovulation
usually occurs soon after the close of the menstrual period. This is
confirmed by the similarity of the physical changes that take place in
the endometrium during menstruation and after conception.
[Illustration:
Fig. 12.—Development of the ovary (after Wiedersheim). _A_, an
ingrowth of the germinal epithelium, forming a cell-cord, which
breaks up into primitive Graafian follicles; _B_, a primitive
Graafian follicle, with its contained primitive ovum; _C_, _D_, _E_,
later stages in the development of the Graafian follicle. (Crossen.)
]
As the period of the flow approaches, the lining membrane of the uterus
becomes hyperæmic and swollen with blood, serum, and glandular
secretions. The blood vessels are engorged, the glands become longer and
more tortuous, little hæmorrhages appear, and the superficial epithelium
is thrown off. A large amount of mucus is produced by the increased
activity of the glands, and all is discharged into the vagina as a
bloody, incoagulable flow with an odor of marigolds. The process
continues usually from three to seven days, when the discharge ceases
and the endometrium slowly resumes its uncongested state.
[Illustration: Fig. 13.—Graafian follicles. One contains two ovules
which, if fertilized, will produce twins. If all three ovules are
fertilized, triplets will result. (Bumm.)]
Meanwhile, the psychic and bodily conditions have not remained
unaffected. The nervous system is disturbed, the disposition is
irritable and capricious and the head may ache. The woman takes cold
easily. She is indisposed to exertion from a sense of languor and
malaise. Pain may develop in the back, or cramps in the pelvis, so
severe as to keep the woman in bed. Frequently the approach of the
period is signalized by skin changes, such as a marked odor or an
eruption of acne pustules.
The flow usually returns every twenty-eight days, but it may vary within
normal limits from twenty-one to thirty days. The flow continues at such
intervals regularly from puberty to the menopause (change of life),
which occurs between the ages of forty-five and fifty.
=Conception, or Fertilization.=—This is the process wherein the male
element (spermatozoon) meets and unites with the female egg. From what
is known from investigations of lower animals, this meeting usually
takes place in the Fallopian tube.
[Illustration: Fig. 14.—Human spermatozoa. _h_, head; _c_, intermediate
portion; _t_, tail. (Williams.)]
The egg expelled from the ovary is carried into the open end of the tube
by peritoneal currents and passed on toward the uterus by the waving
action of the hair-like outgrowths of the cells (ciliæ) that line the
tube, aided, possibly, by the tubal muscle.
The spermatozoon makes its way upward from the vagina by means of its
tail. This activity, like the tail of a fish, or snake, or as a boat is
sculled, drives the cell forward through the thin layer of fluid that
covers the mucous membranes.
The arrow-shaped spermatozoon travels at a rate that completes the
passage to the ovary in twenty-four hours, but spermatozoa may lie in
wait for the egg a considerable time, as is shown by the fact that they
have been found alive in Fallopian tubes removed three and a half weeks
after copulation. As soon as the male and female elements approach each
other, they exercise a powerful magnetic attraction, which draws them
together, and as soon as they touch, the two cells unite and the
spermatozoon almost immediately disappears.
Only one spermatozoon is required for the fertilization of an egg, and
hence enormous numbers must perish without achieving their destiny.
The fertilized egg has become the _ovum_, and originally 1/125 of an
inch in diameter, it now begins to grow, and filled with a new energy,
it passes down the tube and enters the uterus. Here it comes into
contact with the soft mucosa and digs a hole for itself—a nest, very
much as a warm bullet might sink into ice or snow—and is soon completely
surrounded by a proliferating tissue called the decidua. The woman is
now pregnant. The menstrual flow does not appear, and local and
systematic changes are inaugurated.
The egg enlarges rapidly. Little glove-finger-like projections (the
villi) appear on its surface and dip down into the maternal tissues.
Through these villi the egg gets nourishment until about the twelfth
week, when the placenta forms. Externally the ovum resembles a chestnut
burr. As the egg grows, the villi on the surface find it more and more
difficult to secure nutriment, and _except at one place_, all gradually
shrink and disappear. At this significant point, they increase greatly
in size, number, and complexity to form the thick, cake-like placenta.
The egg or ovum is simply a growing cyst, filled with a fluid, normally
sterile, in which the developing embryo lives and swims. This fluid is
the liquor amnii and it is retained by a cystic wall made up of two
layers—the chorion, which represents the original cell membrane, and the
amnion, which develops out of the fœtus. At maturity, the ovum will
contain from one to two pints of liquor amnii.
[Illustration: Fig. 15.—The chorionic villi about the third week of
pregnancy. (Edgar.)]
=The Liquor Amnii.=—The liquor amnii is of vast importance to the child.
It allows free movement for the growing limbs and body, protects the
child from sudden changes of temperature, prevents injury both from
without and within, saves the child from birthmarks and deformities by
keeping it from contact with the surrounding walls, and in labor
lubricates the passages for the advancing part. In a measure, too, it
probably serves as a food. In labor it forms a pouch called the _bag of
waters_, which aids in dilating the os.
[Illustration: Fig. 16.—Diagram illustrating relations of structures of
the human uterus at the end of the seventh week of pregnancy. (American
Text Book.)]
Gradually, as nutrition becomes more abundant at the site of the growing
placenta, a stalk-like structure thrusts out from the fœtal abdomen and
forms an attachment with the formative placenta. This is called the
ventral stalk and as soon as the communication with the placenta is
established, it is combined with other parallel structures and becomes
vascularized, to form the umbilical cord.
[Illustration: Fig. 17.—Maternal surface of the placenta and membranes.
The cord protrudes from the cavity which held the fœtus. (Edgar.)]
=The Umbilical Cord.=—The umbilical cord at maturity measures from five
to fifty inches in length and from one-half to one inch in thickness.
The cord is composed of a gelatinous connective tissue, called Wharton’s
jelly, in the midst of which lie the twisted vessels (two arteries and a
vein) that supply the embryo with air and food and carry off the waste.
=The Placenta.=—The placenta or “after-birth” is an oval or circular
somewhat flattened disc, six to ten inches in diameter, and
three-quarters to one and one-half inches thick. It weighs about a pound
and a half. It is the organ of respiration and nutrition for the fœtus.
[Illustration: Fig. 18.—Fœtal surface of human placenta. (Eden.)]
[Illustration: Fig. 19.—The egg at term with uterus removed and child
showing through the membranes. (Edgar.)]
It is formed about the third month _outside_ the membranes covering the
child and is more or less loosely attached to the uterine wall. The
umbilical cord is attached to its fœtal surface, inside the ovum. Like a
flat sponge it takes oxygen, blood, and the nourishing fluids from the
blood vessels in the uterine wall, carries them to the child by means of
the umbilical vein, and carries back the carbonized blood and waste
products by the umbilical arteries to the placenta, and there returns
them to the maternal blood for disposal. The blood of the veins is
bright red, and of the arteries, dark and turbid.
[Illustration: Fig. 20.—Normal attitude of fœtus (complete flexion).
(Barbour.)]
There is no direct communication between the maternal tissues and the
placenta, hence all the changes occur by osmosis, and by the activity of
the cells which form the walls of the villi.
=The liver= of the child is large and active. The stomach and intestines
functionate mildly. The kidneys act, and urine is discharged into the
liquor amnii, which the child occasionally swallows.
During development, the movements of the child become more and more
pronounced. Arms, legs, and entire body participate in turn. Periods of
rest are also observed. Gradually the child assumes a definite attitude
in the uterus. It becomes more and more folded and flexed to accommodate
its size to the limitations of space. The head bends on the chest, the
arms are folded, the thighs flex against the abdomen, the legs on the
thighs, and even the back ultimately becomes convex. It attains a
complete flexion, the normal attitude of the child. As maturity
approaches, the head becomes more and more palpable and seeks its usual
location in the lower pole of the uterus, resting on the pelvic brim.
[Illustration: Fig. 21.—Fœtal skulls showing sutures. Note the
differences between the anterior and posterior fontanelles. (Eden.)]
[Illustration: Fig. 22 _A_.—Child’s head at term (from side), showing
diameter. (American Text Book.)]
[Illustration: Fig. 22 _B_.—The child’s head at term (from above),
showing diameters and fontanelles. (American Text Book.)]
=The fœtal skull= at maturity (at term) is still incompletely ossified.
The bones are thin and pliable and separated at their edges by intervals
of unossified membrane which form the sutures and fontanelles. Thus the
skull is compressible to a slight degree and capable of much change in
shape. It can be measurably moulded by the uterine contractions to suit
the pelvis.
In front, the two coronary sutures meet the frontal and sagittal sutures
to produce a kite-shaped figure, called the large or anterior
fontanelle, or the bregma. Behind, the lambdoidal suture meets the
sagittal suture to form the small or posterior fontanelle.
The large fontanelle is made up of four bones and four angles; the
small, of three bones and three angles, and are usually easy to
differentiate. Furthermore, the difference between these fontanelles is
of great importance in labor, since by it the observer is enabled to
determine the position of the head. In America, the shape of the head is
that of an ovoid with the long diameter anteroposterior
(Dolico-cephalic). Thus it happens that when the head is completely
flexed, the smallest diameters are presented for delivery.
The important diameters of the head, with their measurements and names,
are as follows:
Nape of neck to center of bregma, 9.5 cm.—Suboccipito-bregmatic
diameter. Occipital protuberance to root of nose, 11.25
cm.—Occipito-frontal diameter. Between the eminences of parietal bones,
9.25 cm.—Biparietal diameter. Between anterior ends of coronal sutures,
8 cm.—Bitemporal diameter.
The smallest circumference is that of the suboccipito-bregmatic plane,
which comes into relation with the brim of the pelvis when the flexion
of the head is complete. It measures 27.5 centimeters.
The fœtus grows at a definite rate throughout gestation and so regularly
that the increase is rarely simulated by any other condition.
To find the probable length of the fœtus at any given time, square the
month of the pregnancy (up to five) and the result is the fœtal length
in centimeters. After the fifth month, multiply the number of the month
by five. Thus:
7th month ×5=35 cm., the approximate length of the fœtus at the lunar
month.—(Hasse’s rule.)
=The Mature Fœtus.=—Although subject to considerable variation, the
fœtus at term will weigh about seven and one-fourth pounds, and measure
50 cm. in length. The weight is far more uncertain than the length, and
therefore not so reliable as a sign of maturity.
To obtain an estimate of the weight of the child at any given month of
the pregnancy, the number of lunar months minus 2, is squared and
divided by 2, and the result is the average weight of the child at that
time in hundreds of grams. Thus:
8th month −2=6. 6×6=36. 36÷2=18, or in hundreds of grams, 1800, the
weight of the child.—(Tuttle’s rule.)
Differences between the mature and immature fœtus:
_Mature_ _Immature_
1. Skin smooth, plump, pink 1. Skin lax, wrinkled, dull red in
covered with vernix caseosa. color; little vernix caseosa.
2. Generous amount of subcutaneous 2. Subcutaneous fat scanty.
fat.
3. Hair abundant and from 1 to 2 3. Hair on scalp short.
inches long.
4. Lanugo mostly absent. 4. Lanugo present all over body.
5. Nails project from finger tips. 5. Short nails on fingers and
toes.
6. Skull bones in contact except 6. Skull sutures open.
at fontanelles.
7. Length 50 cm. born. 7. Moves and cries feebly when
8. Weight five to eight pounds. 8. Weight less than five
pounds.
9. Cartilage in ear well
developed.
10. Navel in middle of body.
11. Testes have descended in the
male, and the labia majora in
the female usually cover the
labia minora.
12. Moves and cries vigorously when
born.
=The Fœtal Circulation.=—The placenta is an organ of nutrition as well
as respiration, and through the umbilical vessels the food materials are
brought to the fœtus and the waste products removed.
Surrounded by the jelly of Wharton that fills out the cord, and running
in and out between the two arteries, the umbilical vein passes into the
fœtal abdomen and divides into two branches, one, the larger,
short-circuits directly into the inferior vena cava. This branch is
called the ductus venosus. The other joins the portal vein and passes
through the liver, after which it also enters the vena cava.
Thus the heart is fed with a mixed blood, part coming fresh from the
placenta and part coming up from the lower half of the fœtus. This blood
is poured into the right auricle, where it becomes mixed again with the
blood coming down from the upper pole of the fœtus through the superior
vena cava.
[Illustration: Fig. 23.—The fœtal circulation. (Edgar.)]
Now a small part goes down into the right ventricle and is forced into
the pulmonary arteries to supply the lungs. But the lungs are not
functionating, hence the greater part is again short-circuited through
the ductus arteriosus into the arch of the aorta, where it meets with
the great volume of blood which passed over into the left auricle
through the hole in the septum between the right and left auricles,
called the _foramen ovale_, thence down into the left ventricle and out
through the aorta to supply the rest of the fœtal body.
With the exception of the ductus venosus and the ductus arteriosus and
the foramen ovale, the circulation is the same as in the adult.
The blood in the descending aorta again divides and part goes on to
supply the lower extremities while the greater part leaves the internal
iliac arteries by means of the hypogastric vessels and returns through
the umbilical arteries to the placenta for oxygenation.
As soon as the child is born, the fœtal structures are altered. The
child breathes, the pulmonary circulation is established and the ductus
arteriosus is closed. The placental circulation is abolished, and the
ductus venosus and the hypogastric arteries are converted into solid
fibrous cords. Owing to the immediate change of pressure in the
auricles, the foramen ovale closes and the circulation assumes the adult
type.