Transcript pregnancy
Pregnancy Begins with fertilization: • The sperm enter the vagina, swim through the cervix and the uterus and into the two fallopian tubes. • If an egg is present in the fallopian tube fertilization could take place. • Their speed averages one inch per hour. • They swim a total of about six inches Fertilization: • Also known as conception • Is the joining of an egg and a sperm. • Sperm are capable of fertilization for 48 hours or longer after ejaculation • Because of this the period during which intercourse can result in fertilization spans the two days before and the two days after ovulation Genetic determination • Once inside the egg, the material that makes up sperm joins with the egg. • Inherited characteristics are determined by units of information carried in the egg & sperm. Genetic material • The units which carry the genetic information are called genes • Genes link together to form chromosomes • Chromosomes and genes are made up of a chemical substance called deoxyribonucleic acid (DNA) DNA • Every human cell (except reproductive cells) contain 46 chromosomes arranged in 23 pairs • Egg and sperm contain only 23 chromosomes Parenting • Every gene on a chromosome contributed by one parent has a counterpart gene contributed by the other parent Dominant and Recessive genes: • Often one gene in a pair may be stronger or dominant. (curly hair, brown eyes) • One may be weaker or recessive. (straight hair, blue eyes) • Dominant gene is expressed Genetic disorders: • Any abnormal condition that a person inherits through the genes • Examples of common genetic disorders: hemophilia, cystic fibrosis, sickle cell disease • If a family member has a disorder it could be something that you carry but do not express. The Zygote • The fertilized egg (zygote) begins to divide within hours of fertilization. • While the cluster of cells are dividing they move through the fallopian tube toward the uterus. • When they reach the uterus, the cells have formed a blastocyst hollow ball of cells called a Implantation • The blastocyst floats freely in the uterus for a few days • Then it will begin to attach itself to the uterine wall this is called implantation • Implantation usually occurs about one week after fertilization. • Once the blastocyst is attached to the uterine wall it is called the embryo Implantation The Embryo • The place of attachment develops into a structure called the placenta • The placenta allows the exchange of nutrients, oxygen and waste between mother and embryo. Exchange of nutrients and waste • The embryo’s and the mothers blood do not mix. • The two substances are separated by thin membranes in the placenta that allow these substances to pass through The umbilical cord • The embryo’s blood travels to and from the placenta through blood vessels within a cord called the umbilical cord. • The cord acts as the baby’s lifeline until birth • After birth this cord is cut and tied The amniotic sac • The baby is enclosed in a bag of thin tissue called the amniotic sac • The embryo floats within the amniotic sac in a liquid called amniotic fluid The Trimesters • Pregnancy lasts for 40 weeks (approx.. 9 months) • This time is divided into three threemonth periods called trimesters The First Trimester • The fertilized egg develops into an embryo • Embryo grows to 3” long and has a recognizable human form • Facial features,limbs,hands, feet, fingers & toes become apparent • From this time until birth the embryo is called a fetus. The Second Trimester • The fourth through sixth month of pregnancy • Fetus grows to 12”long and about 1 pound • Hair and nails grow, the body facial features and ears develop • The fetus begins to move • The skeleton, muscles and nervous systems are developing The Third Trimester • The seventh through ninth months • The fetus continues to grow and develop until it is ready to be born • Body size grows to be in proportion with the head • Eyelids open, the lungs and the digestive system are developed • By the end 18-22 inches long, 6-8 pounds.