Human Reproductive System Human Reproduction Human reproduction and

Human Reproductive System

Human Reproduction • Human reproduction and development are carried out by specialized organs. The function of these organs is regulated by hormones from the endocrine system. In humans, as in nearly all mammals, fertilization and development occur internally- within the mothers body. Reproductive organs in other mammals are similar in appearance and function.

Human Reproductive Systems (Gametogenesis) • Male reproductive system – secondary sex characteristics • testosterone- produced by the male gonads (testes) and is responsible for secondary sex traits gained during adolescence. – primary sex characteristics • development of sperm and delivery to female

Secondary Sexual Characteristics Male • Form during adolescence • Produced by testosterone – Deeper voice – Chest, groin and facial hair – Lengthen bones (growth spurt) – Increased size of testes for sperm production – Increased oil production and darkening of hair

Male Reproductive System Excretion of urine and delivery of sperm Storage and maturation of sperm Makes sperm and testosterone Adds mucus and glucose Smooth muscle that keeps testes at 2 -4 degrees less than body temp. Tube that connects epididymis to the urethra- stores sperm Adds alkaline substance Adds thin mucus to rid urethra of urine

Sperm Formation MEIOSIS forms sperm as gametes Sperm forms in testes Scrotum testes keeps cooler than rest Semen is sperm plus protecting fluid Semen leaves testes through the vas deferens (sperm ducts) to the urethra before it exits. • Sperm live one to three days • • •

Human Reproductive Systems (Gametogenesis) • Female reproductive system – secondary sex characteristics • regulated by estrogen released by the female gonads (ovaries). – primary sex characteristics • production of the ovum (egg), fertilization and development of the offspring.

Secondary Sexual Characteristics Female • Begins at adolescence • Induced by increased LH, FSH, estrogen, and progesterone hormone levels – Pubic hair – Widen pelvis – Enlarge mammary tissue (breasts) – Begin menstrual cycles – Darkening of hair and increased oil secretions

Female Reproductive System Egg lives 24 hours Fertilization occurs here The embryo implants and growth happens here Birth canal, entry for sperm Makes eggs and hormones- estrogen and progesterone Sphincter- ring of muscle that closes off the cervix Gestation- time from implantation to birth

Ovum Formation • MEIOSIS forms the eggs (ova) • Eggs are formed before birth • 1 egg per month is matured and released from ovaries, most of the time • Eggs travel through the fallopian tube where they may become fertilized

Biology and the Menstrual Cycle • Menstrual cycle is regulated by fluctuating levels of sex hormones • These hormones produce certain changes in the ovaries and uterus • Humans are nearly unique among species in having a menstrual cycle • Other species of mammals have estrous cycle.

Menstrual Cycle • approximately a 28 day cycle- uterine lining builds up to prepare for the implantation of an embryo. If no implantation occurs, the lining is shed, this is called menstruation. (3 -5 days) • Menstrual cycle begins again with the maturing of another egg. Cycle is regulated by hormones released by the hypothalamus, pituitary, and ovaries. • Cycle ceases during pregnancy and stops altogether at menopause which occurs in women between the ages of 45 -50 years old.

The Phases of the Menstrual Cycle • • • The menstrual cycle has 4 phases: 1. Follicular phase 2. Ovulation 3. Luteal phase 4. Menstruation

Hormones and What Happens in the Ovaries • Follicle stage- lasts 10 -14 days – Follicle stimulating hormone (FSH) is released by the pituitary causing several follicles (egg and surrounding tissues) to develop, but only one egg will mature fully. – As the follicle in the ovary develops it will release estrogen. Estrogen causes the build-up (vascularization) of the uterine lining.

Hormones and What Happens in the Ovaries • Ovulation- release of the ovary from the egg. Occurs midway through the cycle. – an increase in estrogen causes • (1) a decrease in FSH from the pituitary, and • (2) the secretion of luteinizing hormone (LH) from the pituitary. – High levels of LH causes the ovary to release the egg from the ovary.

Hormones and What Happens in the Ovaries • Corpus Luteum stage- lasts 10 -14 days – LH causes the ruptured follicle to fill with cells forming a yellow body called the corpus luteum. – Corpus luteum releases progesterone which maintains the uterine lining build-up. (hormone of pregnancy).

Hormones and What Happens in the Ovaries • Menstruation- shedding of the uterine lining, lasts 3 -5 days. – If no fertilization occurs, LH decreases causing progesterone levels to decrease. – Decreasing levels of progesterone results in the breakdown of the uterine lining and the extra layers of blood, uterine lining tissue, and the unfertilized egg pass out of the woman’s body.

Role of the Hypothalamus • Note: The hypothalamus in the brain influences the pituitary gland to release FSH and LH which in turn influence the ovaries to produce estrogen and progesterone. In a complex negative feedback mechanism the hormones from the ovaries influence the release of the pituitary and hypothalamus hormones as well.

Fertilization- fusion of the male (sperm nucleus) and female (egg nucleus) gametes (sex cells). 1. occurs in the upper part of the oviduct. 2. If egg is not fertilized within app 24 hours the egg deteriorates. 3. Cleavage (cell division by mitosis) begins in the oviduct and 6 -10 days later the embryo implants in the uterine lining.

Development • Cells divide and differentiate (specialize), forming tissues and organs and finally organ systems. • a proper balance of nutrients ensured correct development without abnormalities. Exchange of gases and nutrients occurs across the placenta.

Development • During the first 3 months, when essential organs are forming in the embryo, things can go wrong: • embryo’s inherited genes • harmful environmental factors which a woman should avoid during pregnancy, including alcohol, drugs, and tobacco. Abuse of these substances can lead to the birth of a baby with brain damage, drug addiction and/or low birth weight and the problems associated with it. • The embryo or fetus may also be harmed if the mother is exposed to toxic chemicals, or gets certain infections such as German measles.

1 st Trimester = 1 st 12 weeks • Heart develops first • Neural tube develops • All body systems appear by Week 8 – Now a Fetus

2 nd Trimester = up to 24 weeks • Most growth • Looks more like a baby • Some preemies survive at this stage

3 rd Trimester = Up to 40 weeks • • • More growth Kicking, rolling, stretching Eyes open – Week 32 Lungs mature Rotates to head-down position, unless baby is breech

Extra embryonic membranes

Birth • Cell differentiation and growth occur until adulthood. During adulthood, the body begins to age and eventually the organism weakens and dies. This same pattern applies to all organisms. • Labor – Uterine contractions begin – Cervix dilates to 10 cm. • Birth – Uterus pushes baby through vaginal canal – Placenta delivered after baby – Cesarean Section (c-section) is a surgery that cuts through the uterus to deliver the baby if it cannot be born vaginally

Applications of Reproductive Technology • Agriculture– through biogenetics, scientists have produced plants resistant to insects, weed killers and frost. These organisms have been cloned to produce thousands of genetically identical offspring. – Using artificial insemination, scientists can generate hundreds of offspring from one farm animal. – Sperm, eggs, or embryos from desirable farm animals can be frozen and transported to animals thousands of miles away, at far less cost than transporting the animals themselves.

Applications of Reproductive Technology • Ecology– Embryos from endangered species have been transplanted into related species, who later give birth to offspring that are no different than if they developed in the bodies of the endangered animals themselves. – Hormones of insects that regulate their reproduction and development have been studied in an attempt to find ways to control insect populations without using poisonous chemicals.

Applications of Reproductive Technology • Medicine- 1. doctors help infertile women to become pregnant by using hormone therapy to adjust their hormones to normal levels. 2. In vitro fertilization- doctors remove eggs from a woman’s ovaries and fertilize them with sperm in a laboratory dish. When these fertilized eggs are implanted in the woman’s uterus, a successful pregnancy may result. 3. Ultrasound and miniature video cameras can aid doctors in viewing ovaries, oviducts, and other reproductive structures, or even a developing fetus to determine where or if problems exist. 4. Amniocentesis- doctors remove a sample of amniotic fluid with fetal cells from around the fetus that can be analyzed for chromosomal abnormalities, or biochemical deficiencies that may threaten the health or development of the fetus.