Biology 30 - Chapter 15: Fertilization, Embryonic Development, and Birth

Parturition (Birth)

1. All associated events are called labour 2. Preceded by the release of the hormone relaxin to loosen the pubic bone and prolactin to stimulate milk production 3. Begins with uterine contractions that happen every 15-20min and last for about 40 seconds

Structures That Support the Embryo

1. Allantois 2. Amnion 3. Chorion 4. Yolk sac 5. Umbillical chord 6. Placenta THESE MAKE UP THE AFTERBIRTH

Implantation

1. Blastocyst implants with the ICM against the endometrium. 2. Trophoblast cells secrete enzymes that digest some of the tissues and blood vessels of the endometrium; and the blastocyst sinks into the uterine wall. 3. At this point, the trophoblast starts secreting hCG, which has high levels for about 2 months, and declines to a low level by the end of four months 4. Complete in about the 2nd week.

Placenta

1. By the end of the second week, finger-like projections from the chorion extend into the uterine lining (these are the chorionic villi) 2. A disk-shaped organ rich in blood vessels (placenta), attaches the embryo to the uterine wall, and metabolic exchange (nutrients, O2, wastes) happens through it. 3. Fully developed in 10 weeks (still 1st trimester) 4. Blood vessels and systems of the mother and baby never touch but lie close to each other

Endoderm (inner primary germ layer)

1. Cellular lining of the respiratory and digestive tract, urethra, and bladder 2. Most of the liver and part of tonsils 3. Gallbladder 4. Thyroid and parathyroid glands and thymus 5. Pancreas

Mesoderm (middle primary germ layer)

1. Dermis of skin 2. Cellular lining of blood vessels, lymphatic vessels, and body cavities 3. Muscle tissue 4. Connective tissue (bone, cartilage, AND BLOOD) 5. Adrenal cortex 6. Kidneys and ureters 7. Spleen, Heart, and Internal reproductive organs

Amnion

1. Develops from cells of the embryonic disk 2. Grows to enclose the embryo completely 3. Penetrated ONLY by the umbilical chord 4. Becomes filled with amniotic fluid, which protects the embryo from trauma and temperature changes, allows for freedom of movement, and prevents limbs from sticking to the body

3 Stages of Labour

1. Dilation of the cervix and thinning of he mucus plug 2. The fetus moves head-first out of the cervix 3. Blood vessels within the placenta and umbilical cord contract and block further blood flow, making the newborn independent of the mother. The placenta detaches from the uterine wall and is delivered minutes after the baby.

What's the difference between the embryonic and fetal period?

1. Embryonic period is from conception to the 8th week and morphogenesis is taking place 2. Fetal period is the 9th week on and more about growth and refinement

End of the First Trimester

1. Growth in the length of the body accelerates but growth of the head slows 2. Skeleton begins to harden from cartilage to bone 3. Sex is determinable 4. Weeks 3-16 is when the fetus is most susceptible to damage 5. Increased mucus in the cervix of the mother forms a plug, protecting from disease, the maternal part of the placenta grows, and the uterus gets larger 6. Ovulation and menstrual cycling stops via negative feedback 7. Breasts enlarge and morning sickness ensues 8. Baby is approx. 9cm long and weighs about 60g. Placenta is well-established and weighs more than the baby

Anatomy of the Ovum

1. It's surrounded by a clear layer of protein and carbohydrates called the zona pellucida 2. The zona pellucida is surrounded by jelly-like layers of follicle cells loosely attached to each other called the corona radiata (THIS LAYER IS WHAT NOURISHED THE EGG WHEN IT WAS AN OVARIAN FOLLICLE)

Explain how the notochord and the neural tube form

1. Notochord forms from mesoderm on the backside of the embryo 2. Neural tube starts as a plate of ectoderm just above the developing notochord 3. Edges of the neural tube plate fold inward, meet, and form a hollow tube surrounded by cells. The neural tube pinches off from the ectoderm and develops into the brain and spinal chord 4. Cells migrate from the meeting margins of the neural tube and eventually form other muscles, bones, and organs.

Chorion

1. Outermost membrane that encloses the extra-embryonic membranes and the fetus 2. FORMS THE FETAL PORTION OF THE PLACENTA

Umbilical Cord

1. Rope-like structure that's about 60cm long and leads to the centre of the placenta 2. Contains two arteries that transport DEOXYGENATED blood from the fetus to the placenta and one vein that brings OXYGENATED blood to the fetus 3. Usually wrapped around the neck of a baby because the vein is longer than the arteries

Effects of Diseases on the Fetus

1. Rubella: Enters respiratory tract and spreads to the lymphatic system 2. Genital Herpes: passing of the virus to the fetus, premature birth, death, and blindness

Oxytocin in the suckling response

1. Suckling stimulates nerve endings in the nipple 2. These nerve impulses travel to the hypothalamus to stimulate the release of OCT 3. OCT causes mammary lobules to contract, which causes the milk to flow 4. If suckling stops, milk production stops within a few days and increased suckling increases milk production

Effects of certain medications on the fetus

1. Thalidomide: blocks blood vessels that lead to limbs, reducing growth in them 2. Seizure meds: reduces blood flow to the CNS

Third Trimester (Weeks 25-38)

1. The fetus is about 50cm long and weighs 3-4kg 2. Moves less as space becomes limited 3. Mother's organs become compressed and this is why pregnant women pee a lot 4. Brain cells form rapidly and testes start to descend 5. Layer of fat develop as well as the digestive and respiratory systems

Second Trimester (Weeks 13-24)

1. Uterus grows enough that the bump becomes obvious 2. The baby is about 30cm long and starts to move a lot 3. Hormone levels stabilize as hCG declines and the corpus luteum degenerates and the placenta completely takes over the production of estrogen and progesterone 4. Skeleton and brain start to form quickly 5. During the 5th MONTH, the baby is covered in fine soft hair called LANUGO and an oily substance to protect the developing skin 6. 6th MONTH, the skin is wrinkled and pink as the blood-filled blood vessels start to expand. There is very little fat under the skin.

What happens when the sperm reaches the egg?

1. When the sperm meets the ovum, its acrosome helps digest a path through the corona radiata and zona pellucida. 2. Once the sperm enters the ovum with the help of its lashing tail, the egg's plasma membrane depolarizes preventing other sperm from binding to and entering the egg 3. Cells called cortical granules release enzymes that harden the zona pellucida to prevent penetration of more than one sperm

Allantois

1. forms the foundation of the umbillical chord 2. Degenerates in the second month 3. Remainder becomes part of the bladder

Explain what happens to the blastocyst after implantation

1. hCG increases to maximum levels until it reaches the end of the first trimester 2. Progesterone continues to increase until it levels near the end of the pregnancy. Secreted early in the pregnancy by the corpus luteum, but early in the second trimester, secretion shifts to the placenta 3. Estrogen levels increase slowly throughout the pregnancy and increase more quickly as the end of the pregnancy approaches. Early in the pregnancy, it's produced by the ovary, but production shifts to the placenta by the second trimester

Organ Formation

3rd-8th week the organs start to form

What happens after neurulation starts?

A reddish bulge containing the heart forms and by the third week (18th day), the heart starts beating

Colostrum

A thin yellowish fluid high in protein that contains less fat than milk

Effects of Alcohol, Cocaine, and Cigarettes on the Fetus

Alcohol: It can accumulate in amniotic fluid, and cause FASD, and premature Birth Cigarettes: reduce the amount of oxygen available for the baby (carbon monoxide effects on mom are the same for baby) Cocaine: increases the heart rate of the baby, depleting oxygen levels, slowing growth. It also may cause bleeding in the brain.

Yolk Sac

An evolutionary holdover. Has no nutritive function whatsoever, BUT, it contributes to the formation of the digestive tract and produces the first blood cells

Hormonal Component of Birth

An increase in estrogen and OCT in the mother's blood has to happen: 1. High level of estrogen stimulates the production of OCT receptors within the smooth muscle of the uterus 2. Meanwhile, the baby's head pressures the cervix, stretching the uterus, signaling the hypothalamus to signal the pituitary gland to release OCT 3. OCT is produced by both the baby and the mother 4. The binding of OCT to its receptors stimulates the release of prostaglandins, which cause chemical changes in the smooth muscles of the uterus (lowering their threshold to become more sensitive) 5. Stronger contractions elicit more OCT from the mother's post-pituitary, causing stronger contractions and setting up a positive feedback loop

Teratogens

Any agent that causes a structural abnormality due to exposure during pregnancy

When is sex of the baby distinguishable

BETWEEN THE END OF THE FIRST TRIMESTER AND THE BEGINNING OF THE SECOND

Why is the natural decline of hCG not deadly to the endometrium?

Because after the 2nd month, the placenta completely takes over hormone secretion and becomes self-sufficient in maintaining the pregnancy

Why doesn't the fetus mix blood with the mother?

Because of the possibility of the baby's blood being different to the mother's

Fetal Alcohol Spectrum Disorder (FASD)

Cause is alcohol ingestion and the effects on the baby include: 1. Cognitive delays 2. Structural change in the forehead 3. Miscarriage

Neurulation

Development of the neural tube: 1. A thickened band of mesoderm cells develop along the back of the embryonic disk and lie along the baby's future spine, binding together to form the notochord (foundation of the skeleton: skull, vertebrae, intervertebral disks) 2. The nervous system develops from ectoderm located above the notochord to develop the neural tube (foundation of the central nervous system)

Split the trimesters up by weeks

First Trimester: Weeks 1-12 Second Trimester: Weeks 13-24 Third Trimester: Weeks 25-Birth

In Vitro Fertilization (IVF)

For women with blocked oviducts, in which ultrasound machines are used to identify specific follicles that are close to ovulation. Immature eggs can be retrieved directly from these follicles. The eggs are combined with sperm in laboratory glassware. After fertilization, the developing embryo is placed in the uterus

Ectoderm (outer primary germ layer)

Forms: 1. Outer skin (epidermis) and associated structures (hair, nails, sweat, mammary glands) 2. Nervous tissue and sensory organs 3. The pituitary gland 4. Tooth enamel 5. Adrenal medulla 6. Eye lens

Explain the negative feedback in the end of the first trimester

High levels of estrogen inhibit the anterior pituitary from releasing LH and FSH, which means that no follicle grows, and ovulation doesn't happen.

Surrogate Mothers

In which a woman is hired to carry the baby for an infertile couple. Using AI or IVF, one or both gametes from the couple can be contributed

Artificial Insemination (AI)

In which sperm are collected and concentrated before being placed in the woman's vagina. In some cases, the sperm are donated by the woman's male partner. In other cases, the sperm are from a stranger. Sperm banks provide a source of sperm samples that have been gathered for this purpose.

Physical or Chemical Barriers

Physical: Male or female condoms (effectiveness about 85%), a latex cap (diaphragm) that fits over the cervix (effectiveness about 90%), and the contraceptive sponge (effectiveness ranging from 70-90%) Chemical: Spermicide in jellies, foams and creams (75%),

Hormone Treatments

Pre: Hormones taken orally, through an injection, or other means that change the chemical balance of the body. Side effects include a higher risk of blood clotting, strokes, and breast cancer. It's the artificial intake of estrogen and progesterone, inhibiting LH and FSH. Post: A more intensive method is through hormones that deliver high doses of estrogen and progesterone, delaying and even preventing ovulation. If fertilization has already occurred, it can prevent implantation. Side effects include vomiting and painful cramps.

Gamete Vitro Fertilization

Similar to In Vitro Fertilization, except the ovum and the sperm are brought together in the oviduct

Abstinence

Simply not having sexual intercourse. It protects from STIs and it's the only 100% effective contraceptive method

What happens to the sperm inside the female reproductive system?

Some are destroyed by the acidic environment, others take the wrong tube, only one makes it to the egg.

Morphogenesis (Organogenesis)

Started by gastrulation, it forms distinct structures of the developing organism. Further differentiation into specialized tissues that will later become the organs of the body.

Vasectomy

Surgical sterilization in men where the vas deferens is cut and tied. The man can still have an erection and ejaculate, but the semen doesn't have sperm.

Tubal Ligation

Surgical sterilization in women where the oviducts are cut and tying the cut ends to prevent the oviduct from ever coming into contact with the sperm. The ovum disintegrates in the oviduct.

Explain lactation

The creation and secretion of breast milk: 1. High level of progesterone stimulates production of mammary alveoli while high level of estrogen stimulates the development of alveolar ducts 2. High levels of estrogen and progesterone inhibits the production and release of prolactin 3. Happens shortly after birth in response to declining estrogen and progesterone levels 4. Until milk production begins, the breasts produce colostrum 5. Colostrum and milk contain antibodies from the mother that protect baby against infectious agents

Blastocyst

The form that implants into the endometrium made up of two groups of cells: 1. Trophoblast (nourishment of the germ): Forms the outer layer of the blastocyst, will develop into a membrane called the chorion, which will turn into the placenta 2. Inner Cell Mass (embryoblast): what develops into the embryo itself

Gastrulation

The formation of the three primary germ layers: 1. Amniotic cavity develops (a space between ICM and trophoblast) this is where the baby will develop 2. As the amniotic cavity forms, the ICM is flattened into the embryonic disk, which initially only contains ectoderm and endoderm, but the mesoderm forms in between shortly after. 3. Takes about a week. All tissues, organs, and systems develop from this germ layer

Fertilization

The joining of the male and female gametes to form a single cell that contains 23 chromosomes from each parent for a total of 46, resulting in a zygote. Fertilization is said to be complete once the gametes have joined.

What are the last organs to form in a fetus?

The lungs and digestive system because you're not breathing or eating anything

Superovulation

The production of multiple eggs due to hormone treatment. Often used in conjunction to other fertility treatments.

Natural Family Planning

The tracking of a woman's cycle. Lowest success rate at about 70%, in which the couple pays attention to the changes in the woman's body to track when she's most fertile.

Negative feedback of prolactin in birth

Throughout the pregnancy, the mother's been releasing prolactin-inhibiting hormone

Distribution of weeks 4-9 of the first trimester

Week 4: Blood cells form and fill blood vessels, lungs and kidneys take shape, arms and legs appear, head, eyes, and nose are just visible Week 5: Brain cells develop, eyes are open but have no eyelids or irises Week 6: Brain continues rapid development, limbs strengthen and flex, gonads are starting to produce hormones that influence development of external genitalia Week 7-8: TESTOSTERONE SPIKE, organs form, nervous system starts to coordinate activity, eyes are developed but lids are closed, nostrils are plugged by mucus, external genitalia are forming but sex isn't visible Week 8-9: You're the size of a paperclip and 90% of your organs are developed YOU'RE NOW A FETUS

Cleavage (cell division without cell growth)

When cells skip through the growth phases and go straight to the synthesis phase: 1. Within 30 hours of being fertilized, mitosis happens over and over again. 2. The cells don't get bigger. The zygote remains at about the size of 0.1mm 3. At 16 cells, the zygote is called a morula, which reaches the uterus 3-5 days after fertilization (day 0) 4. During this time, it begins to fill with fluid that diffuses from the uterus, forming two different groups of cells. It's now called a blastocyst. This is what implants into the endometrium.