[09.08] Gametogenesis and Implantation V2

Oogenesis Before birth

When does oogenesis begin?

Migration and mitosis

What two processes do primordial germ cells (oogonia) originating from the secondary yolk sac undergo as they migrate towards the genital ridge?

5th month of fetal life

Until when does oogonia undergo continuous mitosis?

Oogonia differentiate into primary oocyte

What do oogonia differentiate into?

Prophase I

At what stage of meiosis I are primary oocytes arrested?

2 million

Around how many primary oocytes are present at birth?

Puberty

What marks the start of ovulation?

Secondary oocyte and first polar body

What two haploid daughter cells does a primary oocyte produce during meiosis I?

Metaphase II

At what stage of meiosis II is the secondary oocyte arrested?

Fertilization

What needs to occur for meiosis II to be completed?

Second polar body

What does the secondary oocyte form when it reunites with the sperm?

First meiotic division

At what meiotic division does division of chromosomal number occur?

Oocyte and granulosa cells

What are the components of a follicle?

Primordial follicle

What is the only follicle present at birth?

Prophase I

At what stage is the primary oocyte arrested in a primordial follicle?

Single layer of flattened (squamous) follicular cells

What type of cells surround the primary oocyte in a primordial follicle?

Cortex

As follicles mature, do they move towards the cortex or medulla of the ovary?

Cuboidal and undergo stratification

What change do the granulosa cells undergo as primordial follicles mature into primary follicles?

Cavity (antrum)

What distinguishes a secondary/antral follicle?

Theca interna and theca externa

Into what two layers does the theca develop in a secondary/antral follicle?

Graafian follicle

What does a secondary follicle mature into?

Secondary oocyte

What does a Graafian follicle release?

Corpus luteum

What does a Graafian follicle transform into after ovulation?

Least amount of FSH

What is the Graafian follicle most sensitive to?

Corpus luteum

What temporary endocrine gland is formed from the Graafian follicle after it releases the secondary oocyte during ovulation?

Corpus albicans

What does the corpus luteum degenerate into if the oocyte is not fertilized?

Follicular atresia (degeneration)

What happens to the rest of the antral follicles that do not become Graafian follicles?

Puberty

When does spermatogenesis occur?

Seminiferous tubules of the testis

Where do spermatogonia increase in number at puberty?

Mitosis and meiosis

Through what processes do spermatogenic cells undergo continuous replication?

Primordial sperm cell

What is a spermatogonium?

Type B spermatogonia (spermatogonia B) and type A spermatogonia (spermatogonia A)

What two daughter cells do spermatogonia form through mitosis?

Reserve cells

What do spermatogonia A act as?

Primary spermatocytes

What do spermatogonia B undergo growth and differentiation to become?

Secondary spermatocytes

What do primary spermatocytes produce after meiosis I?

Spermatids

What do secondary spermatocytes produce after meiosis II?

Spermatids differentiate without further division

What occurs during spermiogenesis?

Spermatozoa

What do spermatids become?

Intercellular bridge

In the division of spermatogenic cells, what connects the daughter cells?

Communication between cells and coordinates sequence of spermatogenesis

What are the functions of intercellular bridges?

Spermiogenesis

When do intercellular bridges disappear?

Mature sperms

Into what do spermatids transform?

Differentiation or a sequence of post-meiotic changes

What do spermatids undergo to produce spermatozoa?

Phagocytosed by Sertoli cells

What happens to intercellular bridges that disappear?

Golgi phase, acrosomal phase, maturation phase

What are the three phases of spermiogenesis?

Small, rounded spermatid (7-8 μm)

With what does the Golgi phase begin?

Golgi apparatus

What organelle is prominent and adjacent to the nucleus during the Golgi phase?

Acrosomal vesicle

In what are small, membrane-limited pro-acrosomal granules enclosed?

Anterior half of nucleus

What does the acrosomal vesicle cover during the acrosomal phase?

Axoneme

What do the centrioles initiate the formation of?

9 doublet microtubules + 2 unfused microtubules in the center

What is the structure of the axoneme?

Elongation of the sperm tail

What does the axoneme serve as the template for?

Posteriorly

Where is the bulk of cytoplasm displaced during the acrosomal phase?

Mitochondrial sheath

What do mitochondria form when they spiral around the initial portion of the axoneme?

Sertoli cells

What phagocytose the excess cytoplasm (residual body) and intercellular bridges during the maturation phase?

Spermiation

What is the release of mature spermatozoa into the lumen of seminiferous tubules called?

Spermatogonium A

Which spermatogenic cells are NOT attached to the lateral border of the Sertoli cells?

Base

Where are the most immature cells located?

Lumen

As spermatogenic cells mature, where do they ascend towards?

Process of formation and development of specialized cells called gametes

What is gametogenesis?

Haploids

Are mature germ cells haploids or diploids?

Mitosis, growth and differentiation, and meiosis

What occurs during spermatocytogenesis?

Alteration in shape and size of mature sperm

What occurs during spermiogenesis?

Phagocytosis of Sertoli cells

How do intercellular bridges disappear during spermiogenesis?

Golgi, acrosomal, and maturational

What are the three phases of spermiogenesis?

Primitive germ cells (oogonia and spermatogonia)

What cells undergo a series of mitotic and meiotic divisions?

Primary oocyte and primary spermatocyte

What is formed through the growth and differentiation of primitive germ cells?

Meiosis I

What type of meiotic division do the primary oocyte and primary spermatocyte undergo?

Secondary oocyte and spermatocyte

What cells are produced through meiosis I?

Haploid

Are secondary oocytes and spermatocytes haploid or diploid?

Continuous

Is spermatogenesis continuous or does it have arrests?

Small and motile

What are the characteristics of sperm in terms of size and movement?

Large and immotile

What are the characteristics of a secondary oocyte in terms of size and movement?

Sparse

How much cytoplasm is found in sperm?

Abundant

How much cytoplasm is found in a secondary oocyte?

23X, 23Y

What are the sex chromosomes of sperm?

23X, 23X

What are the sex chromosomes of a secondary oocyte?

During puberty

When does spermatogenesis begin?

Before birth

When does oogenesis begin?

Two arrests

How many arrests does oogenesis have?

FSH

What stimulates the growth of primary follicles into secondary follicles?

Estrogen and inhibin

What do secondary follicles produce more of?

Negative feedback, drop of FSH concentration

What do high levels of estrogen and inhibin start?

Most sensitive to the least amount of FSH

What is the follicle destined to be a mature or Graafian follicle?

Atresia

What happens to the rest of the follicles?

400

Out of 400,000 follicles present in the ovary at birth, how many will develop?

Macula pellucida or stigma

What is the pale area in the ovary called that is a sign that ovulation will start to occur?

Luteinizing hormone (LH)

What hormone increases or surges to cause ovulation?

Collagenase

What does luteinizing hormone activate?

Breaks down connective tissue of the tunica albuginea

What does collagenase do?

Smooth muscle fibers in theca externa

What contracts to cause expulsion of the oocyte?

Secondary oocyte, first polar body, zona pellucida, and corona radiata

What is released from the ovary during ovulation?

Fimbriae of fallopian tube

What catches the secondary oocyte?

Ampulla

Where does the secondary oocyte stay in the oviduct?

24 hours

If not fertilized in how long does the secondary oocyte degenerate and is reabsorbed in the oviduct?

Corona radiata and zona pellucida

What are the two layers of the secondary oocyte that have to be penetrated by the sperm for fertilization?

Epididymis

Where do sperm migrate to for maturation?

Ampulla of vas deferens

What is the dilated part of the vas deferens called?

Seminal vesicles

What contributes secretions to the formation of semen?

Ejaculatory duct

What do the vas deferens and seminal vesicle form?