Reproductive 5 - Uterine cycle, Fertilization, Implantation

How long is the menstrual phase

5 days

What occurs to the uterus during the menstrual phase

Blood flow to tissue decreases, causing tissue death and slough into vagina causing menstrual flow.

Hormonal control of menstruation

Menstruation triggered by decreased estrogen and progesterone. Hormone decreases when corpus luteum degenerates

What occurs to the uterus in the proliferative phase

Endometrial lining develops and grows, endometrial layer grows and glands enlarge. Smooth muscle layer thickens and cervical glands secrete a thin mucus

Hormonal control of proliferative phase

Estrogens stimulate development of uterine lining

What occurs to the uterus during the secretory phase

The endometrium prepared for implantation: blood supply increased, glands enlarge and secrete glycogen-rich fluids, and cervical secretions more sticky forming a plug

How to contraceptives effect the cervical plug

Increased progesterone forms a thicker cervical plug

Hormonal control of secretory phase

Progesterone + Estrogen

Effects of estrogen on the ovary

Increased growth of follicles, increased receptors for estrogen, progesterone, FSH, LH

Effects of progesterone in the ovary

Decreased FSH-induced E production, decreased receptors for estrogen

Effects of estrogen on the fallopian tube

Increased growth, contractility, cilia activity, secretions

- Contractility and cilia activity for ovum movement

Effects of progesterone on the fallopian tube

Decreased contractility, secretions, cilia number

Effects of estrogen on the uterus

Grows endometrium and myometrium, increase contractility. Contractions don't allow ovum to sit on the uterus

Effects of Progesterone on the uterus

Increase endometrial secretions, decrease contractility, decreased sensitivity to oxytocin (less contractions to prevent loss of ovum)

Effects of estrogen on the cervix

Produces sperm friendly mucus - abundant, watery, alkaline

Effects of progesterone on the cervix

Sperm unfriendly mucus produciton - small, viscous, cellular

Effects of estrogen on the vagina

Proliferation and cornification (keratinization) of epithelium

Effects of progesterone on the vagina

WBC infiltration, decreased cornification

Effects of estrogen on the breasts

Increased duct growth, fat deposition, increased size and pigmentation of areola

Effects of progesterone on the breasts

Increased alveolar growth

What is fertilization

Fusion of male and female gametes to form a zygote

Use of male and female external genetalia for mating

Sperm deposited into female to fertilize the ovum

What is the fertilized zygote called in the first two months of gestation

Embryo

what is the zygote called after 2 months of gestation

Fetus

What is parturition

Child birth

Site of fertilization

Female oviduct (fallopian tube)

How long are sperm viable for

5 days

How long is an ovum viable for

12-24 hours

Sperm are initially incapable of fertilization. What do they requires?

Capacitation

Only a few hundred sperm make it to the uterine tubes of the initial 200-300 million. Why?

- Damage due to acidic pH of female tract

- Some loss due to cervix leakage

- Loss of energy

Only the best sperm gets access to the oocyte. What would be the best sperm?

The sperm that receives capacitation. Altered PM allows for exposure to membrane bound enzymes to make channel through zona pellucida

Why does polyspermy not occur?

Chromosome number is not maintained. Embryo has 3 sets of chromosomes

Pronucleus

the nucleus of a sperm or an egg cell during the process of fertilization, after the sperm enters the ovum, but before they fuse

How many sperm undergo acrosomal reaction?

Many sperm can undergo the acrosomal reaction when they bind to zona pellucida

Events of fertilization (steps)

1. Many sperm bind to receptors on the zona pellucida and undergo the acrosome reaction

2. Sperm move through zona pellucida

3. One sperm bind to egg plasma membrane

4. Three things occur

a. Egg releases contents of secretory vesivles into egg plasma membrane and zona pellucida. Enzymes enter zona pellucida and harden the zona to prevent polyspermy

b. Sperm is drawn into egg: egg completes 2nd meiotic division and zygote form

c. Egg enzymes activated when zona pellucida is breached. Zygote begins embryogenesis (zygote divides and forms embryo)

What are the blocks to polyspermy

- Change in membrane potential

- Release of contents from cortical granules

- Enzymes enter and harden zona pellucida

- Enzymes inactive sperm binding receptor

What is the sperm binding receptor on the ovum?

Glycoproteins

What happens to the oocyte during fertilization?

- Fusion of sperm with oocyte stimulates 2nd

meiotic division of oocyte

• oocyte -->ovum

- Sperm plasma membrane disintegrates

- Chromosomes from sperm and ovum migrate

to center

- DNA replicated --> zygote

Morula

A solid ball of cells that makes up an embryo; in humans, this stage occurs within four days of fertilization.

Is there cell division in early embryonic development?

No - only cell cleavage

Totipotent

Stem cells with the potential to differentiate into any type of cell.

How long does the embryo remain totipotent?

Up to 16-32 cell stage

What does the morula proliferate into?

Blastocyst

How are identical twins formed

Division of totipotent morula.

How are fraternal twins formed

Fertilization of two oocytes (released during the same cycle)

When does the blastocyst form

4-5 days after fertilization

What structure in the morula is lost in the blastocyst?

Zona pellucida

Anatomical components of the blastocyst

Outer cell layer is the trophoblast, and there is an inner cell mass. beside the cell mass is a fluid filled cavity blastocoele

What does the trophoblast become

Fetal placenta

What does the inner cell mass become

Embryo

Where in the female reproductive system is the blastocyst found

Uterine site

Which uterine phase does implantation occur?

Secretory phase

Role of glycogen in implantation

helps blastocyst anchor to endometrial lining

What allows trophoblast cells to implant

The trophoblast cells are sticky, and will adhere

When does implantation occur

6-7 days after fertilization

Syncytiotrophoblast

outer layer of trophoblast that enters the endometrium

Cytotrophoblast

inner cellular layer of the trophoblast that secrete hormones for growth

Decidual response

The uterine response to the presence of the embryo. The cells of the endometrium swell and become full of glycogen, lipids and other nutrients. The blood vessels branch and move closer to blastocyst

What age does the placenta function and heart beat?

By 5 weeks