What happens to a baby at birth

Before birth, oxygenated blood from the placenta flows into the child’s inferior vena cava and mixes with blood returning from the lower part of the body. The atria are, in effect, one chamber due to the open foramen ovale; however, laminar blood flow tends to supply the left atrium and ventricle (and hence the upper body) with more placental (oxygenated) blood than the right atrium receives. The ventricles also act as one and pump blood around the body. Blood from the right ventricle bypasses the lungs, flowing through the ductus arteriosus and joining blood from the left ventricle in the descending aorta. A large portion of this blood flow goes to the placenta through the umbilical arteries.

Although the pulmonary vessels are fully developed in the fetus, only a tiny amount of blood (about 5% of cardiac output) flows through them due to intense vasoconstriction of the pulmonary arterioles. The nutritive blood supply to the lungs is from the bronchial arteries that arise from the aorta. The collapsed alveoli (air sacs) are filled with amniotic fluid.

Oxygenated blood is red, de-oxygenated blood is blue, and at the moment of birth, a normal newborn is circulating a mixture of blue and red blood. The color (lips and tongue) of a healthy newborn at birth is a pinkish purple; the child has been this color for nine months and normal placental function (cord pulsating) will maintain this color until the lungs function.

When the lungs are functioning, the umbilical vessels close, the ductus venosis closes, the hepatic portal vein is open, the foramen ovale closes, the heart is two sided, the cardiac output from the right ventricle (blue blood) goes through the lungs and is oxygenated, the left ventricular output (red blood) goes through the body, the ductus arteriosus closes, the pulmonary arterioles are open, the alveoli are full of air and the child turns from purple to pink. All of this complicated process is coordinated and controlled by the child’s reflexes; it usually happens within three or four minutes of birth. What makes it happen?

All babies are born soaking wet, and on meeting the atmosphere, the skin cools; this triggers two reflexes:

The cold crying reflex - cold, wet diapers produce the same result, crying.
The cold pressor reflex - cold skin raises blood pressure.
In order to cry, the child must first take a deep breath, and an inspiratory "gasp" is often the first sign, triggered by cold, that a child is going to cry or breathe. Contraction of the diaphragm and intercostal muscles increase thoracic volume and create negative intra-thoracic pressure. Once air is in the lungs, another reflex is triggered that relaxes the pulmonary arterioles; this causes an enormous increase in pulmonary blood flow.

The cold pressor reflex increases the blood pressure in the aorta, and this may be sufficient to reverse blood flow through the ductus arteriosus causing more blood to flow through the lungs.

The cord is also cooling, and the cord is a well-designed self-refrigerator. It has no skin and blubber to keep it warm like the child. It contains only the cord vessels surrounded by a watery gel, Wharton’s jelly, covered by a single layer of cells, the amnion. Water evaporation cools it rapidly, causing the vessels, especially the muscular arteries, to constrict; this further helps to raise systemic blood pressure and to reverse ductus arteriosus flow.

At the same time, a large transfusion of placental blood is being forced into the child by gravity and/or by uterine contraction, greatly increasing cardiac output and pulmonary blood flow. The net result of these changes is a large amount of blood flowing into the left atrium from the lungs, which raises left atrial pressure and closes the foramen ovale - the heart changes from one-sided to two-sided. The lungs are now oxygenating blood that is pumped round the body by the left ventricle - the child turns pink.

If the child has not taken the first breath, or is depressed and cannot breathe, the massive increase in pulmonary blood flow generated by the placental transfusion may, of itself, initiate ventilation. Jaykka [1,2] showed that the fetal lungs are erectile tissues; by injecting serum through the pulmonary artery of excised animal fetal lungs, the engorged capillaries around the alveoli erected them and caused air to enter through the trachea. With establishment of pulmonary blood flow, the high colloid osmotic pressure of blood causes absorption of amniotic fluid from the alveoli and "dries out" the lungs, filling the "erected" alveoli with air.

Cold will eventually cause the cord vessels to close; however, a high arterial blood oxygen concentration is probably a key factor in umbilical artery closure - they close before the umbilical vein closes; it may also cause ductus arteriosus closure. After umbilical artery closure, the placental transfusion may continue through the cord vein in a very measured and controlled manner.

Information found at: http://whale.to/a/morley4.html

Powerful Picture

Click the title link to view the photo in a larger scale at its original location. This is a five-week-old embryo found in the case of an ectopic pregnancy. Ectopic pregnancies cannot survive and present great danger to the mother's health. The embryo was removed shortly after the photo was taken. The details in the photograph are amazing. At this stage it is difficult to distinguish a human fetus from the fetuses of other animals. Apologies as I reveal the horror movie lover in me, but we do look a bit like alien chestbursters during our earliest stages of development.

Ovarian Follicles

An ovarian follicle consists of a developing oocyte surrounded by one or more layers of cells called follicular cells. At the same time that the oocyte is progressing through meiosis, corresponding changes are taking place in the follicular cells. Primordial follicles, which consist of a primary oocyte surrounded by a single layer of flattened cells, develop in the fetus and are the stage that is present in the ovaries at birth and throughout childhood.
Beginning at puberty follicle-stimulating hormone stimulates changes in the primordial follicles. The follicular cells become cuboidal, the primary oocyte enlarges, and it is now a primary follicle. The follicles continue to grow under the influence of follicle-stimulating hormone, and the follicular cells proliferate to form several layers of granulose cells around the primary oocyte. Most of these primary follicles degenerate along with the primary oocytes within them, but usually one continues to develop each month. The granulosa cells start secreting estrogen and a cavity, or antrum, forms within the follicle. When the antrum starts to develop, the follicle becomes a secondary follicle. The granulose cells also secrete a glycoprotein substance that forms a clear membrane, the zona pellucida, around the oocyte. After about 10 days of growth the follicle is a mature vesicular (graafian) follicle, which forms a "blister" on the surface of the ovary and contains a secondary oocyte ready for ovulation.

Ovulation
Ovulation, prompted by luteinizing hormone from the anterior pituitary, occurs when the mature follicle at the surface of the ovary ruptures and releases the secondary oocyte into the peritoneal cavity. The ovulated secondary oocyte, ready for fertilization is still surrounded by the zona pellucida and a few layers of cells called the corona radiata. If it is not fertilized, the secondary oocyte degenerates in a couple of days. If a sperm passes through the corona radiata and zona pellucida and enters the cytoplasm of the secondary oocyte, the second meiotic division resumes to form a polar body and a mature ovum

After ovulation and in response to luteinizing hormone, the portion of the follicle that remains in the ovary enlarges and is transformed into a corpus luteum. The corpus luteum is a glandular structure that secretes progesterone and some estrogens. Its fate depends on whether fertilization occurs. If fertilization does not take place, the corpus luteum remains functional for about 10 days then it begins to degenerate into a corpus albicans, which is primarily scar tissue, and its hormone output ceases. If fertilization occurs, the corpus luteum persists and continues its hormone functions until the placenta develops sufficiently to secrete the necessary hormones. Again, the corpus luteum ultimately degenerates into corpus albicans, but it remains functional for a longer period of time.

http://training.seer.cancer.gov/module_anatomy/unit12_3_repdt_female1_ovaries.html

Meiosis

Normally, meiosis causes a halving of chromosome material, so that each parent gives 23 chromosomes to a pregnancy

A cool site about meiosis for you to enjoy:
http://www.sciencecases.org/mitosis_meiosis/mitosis_meiosis2.asp

Testes! One, two...three???

We are currently studying the reproductive system in class. Here is some fun trivia about the testes. The information was gathered from Wikipedia.

In land mammals, with the exception of the elephant the testes are located outside of the body, as they are suspended by the spermatic cord and within the scrotum. This is due to the fact that The cremasteric muscle is part of the spermatic cord. When this muscle contracts, the cord is shortened and the testicle is moved closer up toward the body, which provides slightly more warmth to maintain optimal testicular temperature. When cooling is required, the cremasteric muscle relaxes and the testicle is lowered away from the warm body and are able to cool. This phenomenon is known as the cremasteric reflex. It also occurs in response to stress (the testicles rise up toward the body in an effort to protect them in a fight), and there are persistent reports that relaxation indicates approach of orgasm. There is a noticeable tendency to also retract during orgasm.

The testicles can also be lifted voluntarily using the pubococcygeus muscle, which partially activates related muscles. This can sometimes be triggered by tightening or sucking in the stomach or abdomen.

Animals other than mammals do not have externalized testicles. Birds, despite having very high core body temperatures have internal testes: it was once theorized that birds used their air sacs to cool the testes internally, but later studies revealed that birds' testes function at core body temperature.[1] Marine mammals also have internal testes, but it has recently been shown (eg, for dolphins) that they use elaborate vascular networks to provide the necessary temperature lowering for proper operation.

The seminiferous tubules of the testes are the starting point for the process of spermatogenesis, where stem cells adjacent to the inner tubule wall divide in a centripetal direction - beginning at the walls and proceeding into the lumen to produce immature sperm.