Spermatogenesis and Oogenesis - Dr. Premanadan

Spermatogenesis

the continuous, hormone-regulated process in the male that converts diploid germ cells into haploid, motile spermatozoa

Three critical hormones controlling spermatogenesis:

1.) gonadotropin releasing hormone (GnRH)

2.) luteinizing hormone (LH)

3.) follicle stimulating hormone (FSH)

gonadotropin releasing hormone (GnRH) is secreted from...

the hypothalamus

gonadotropin releasing hormone (GnRH) target

anterior pituitary

gonadotropin releasing hormone (GnRH) action

simulates gonadotroph cells in the anterior pituitary to secrete LH and FSH

luteinizing hormone (LH) is secreted from...

anterior pituitary

luteinizing hormone (LH) target in the male

leydig cell in testes

luteinizing hormone (LH) action in the male

targets leydig cell in testes to produce testosterone

testosterone is needed for two things:

1.) the development of spermatozoa

2.) negative feedback loop for production of GnRH

follicle stimulating hormone (FSH) is secreted from...

anterior pituitary

follicle stimulating hormone (FSH) target in the male

sertoli cell in the testes

follicle stimulating hormone (FSH) action in the male

targets sertoli cell in the testes which function to encourage spermatogenesis

Sertoli cells

produce androgen binding protein which increases the testosterone concentration in the seminiferous tubules

Two hormones that regulate FSH:

1.) inhibin

2.) activin

Inhibin will _________ FSH secretion and activin will _________ FSH secretion

decrease; increase

Males are ________ producing spermatozoa. Why?

continuously; the male secretes a low level (tonic level) of LH that creates a base line secretion of testosterone, causing constant production of spermatozoa

The male reproductive tract is a ________ and ________ system

manufacturing

delivery

Manufacturing of spermatozoa takes place in the...

testes

Storage of spermatozoa takes place in the...

tale of the epididymis

Delivery of spermatozoa takes place in the...

penis

Where does spermatogenesis take place?

seminiferous tubules of the testes

seminiferous tubules

long convoluted tubules that make up the majority of the testicular parenchyma

What direction will maturation of spermatogonia take place in the seminiferous tubule?

from superficial to deep

Two cells of seminiferous tubules:

1.) sertoli (sustentacular) cells

2.) leydig cells

sertoli (sustentacular) cells

located on the inside of the seminiferous tubues; envelop and encourage development of germ cells

leydig cells

located on the outside of the seminiferous tubues; produce testosterone

When will spermatogenesis begin?

once puberty hits

Spermatogenesis takes place in three stages:

1.) spermatocytogenesis

2.) spermatidogenesis

3.) spermiogenesis

spermatocytogenesis

The stage of spermatogenesis that involves cell divisions; the proliferation of spermatogonia

At the beginning of spermatocytogenesis, sperm are in the form....

spermatogonia

During spermatocytogenesis, spermatogonia do either two things:

1.) constant rounds of mitosis, maintaining the germ pool

2.) replicate to form the next stage (primary spermatocytes)

After undergoing several rounds of mitosis during spermatocytogenesis, some spermatogonia will...

undergo meiosis

What are the spermatogonia chosen for meiosis called?

primary spermatogonia

During meiosis, __________ spermatogonia under go meiosis one, and then __________ spermatogonia undergo meiosis two

primary spermatogonia; secondary spermatogonia

Total process of spermatocytogenesis:

1.) spermatogonia undergo several rounds of mitosis to maintain the germ pool

2.) some spermatogonia undergo mitosis to produce primary spermatogonia

3.) primary spermatogonia undergo the first meiotic division to produce secondary spermatogonia

spermatidogenesis

secondary spermatogonia undergo the secondary meiotic division to produce spermatids (haploid)

After the second meiotic division of spermatidogenesis, secondary spermatocytes become...

spermatids

How many sets of chromosomes do spermatogonia have?

2N, diploid

How many sets of chromosomes do spermatids have?

haploid (N)

During spermatocytogenesis, primary spermatocytes divide into _____ secondary spermatocytes

During spermatidogenesis, secondary spermatocytes divide into _________ spermatids each

two

two

*so one primary spermatocyte (diploid) gives off four spermatids (haploid)

For mitosis, cells begin ______ and end ________

For meiosis, cells begin ________ and end _________

diploid; diploid

diploid; haploid

Spermiogenesis

morphologic transformation of spermatids (round cell) to spermatozoa (cell with mobility)

Five components of spermatozoa formed during spermiogenesis:

1.) head

2.) neck

3.) middle piece

4.) principle piece

5.) tail

During spermiogenesis, there is a loss of ______________

cytoplasm

Four phases of Spermiogenesis

1.) Golgi

2.) Cap

3.) Acrosomal

4.) Maturation

Golgi phase of spermiogenesis (2):

1.) golgi apparatus forms proacrosomic granules, which then fuse to form the acrosomic vesicle

2.) centrioles migrate to the caudal end of the nucleus and form the proximal and distal centriole

the acrosomic vesicle will eventually become the...

acrosome

proximal centriole

tail attachment point

distal centriole

gives rise to the axoneme

Cap phase of spermiogenesis (3):

1.) acrosomic vesicle begins to elongate and cover the cranial end of the nucleus, forming the acrosome

2.) remainder of the golgi migrates to the caudal end of the nucleus

3.) distal centriole gives rise to the axoneme

axoneme

microtubules that elongate off the distal centriole and develop into the tail

acrosome

A vesicle at the tip of a sperm cell that helps the sperm penetrate the egg

Acrosomal phase of spermiogenesis (3):

1.) acrosome continues to elongate over the top of the nucleus

2.) middle piece starts to develop more distinctly

3.) cytoplasm begins to be removed

Maturation phase of spermiogenesis (3):

1.) all the cytoplasm is gone

2.) acrosome covers the cranial half of the nucleus

3.) mitochondria aggregate into the middle piece

Three parts of the sperm tail

1.) middle piece

2.) principle piece

3.) terminal piece

middle piece

attaches to the head; contains mitochondria that provide the spermatozoa energy and axoneme

principle piece

length of the tail; made up of axoneme

terminal piece

end of the tail; made up of axoneme

Where are mature spermatozoa located?

in the most apical aspect of the seminiferous tubules

Mature spermatozoa are embedded ______-_______ in the apical surface of the seminiferous tubules

head-first

Length of spermatogenesis in the following species:

canine:

bovine:

equine:

canine: 62 days

bovine: 62 days

equine: 55 days

Therefore, if injury occurs at some point during spermatogenesis...

the entire process will be delayed, and reappearance of normal sperm will occur if there is the germ pool from spermatogonia

Which stage of spermatogenesis takes the longest?

primary meiotic division

Which stage of spermatogenesis takes the shortest?

maturation (secondary spermatocyte to spermatid)

True or false: along the length of the seminiferous tubules, spermatogenesis will be taking place in many different stages

true

Oogenesis

the production, growth, and maturation of an egg, or ovum

The ovaries will develop from...

primitive sex cords

primitive sex cords

mesothelial cells that invaginate into gonadal ridges; form plates/cords of tissue that facilitate germ cell incorporation

Two functions of the ovaries:

1.) production of ova

2.) endocrine gland

Three critical hormones controlling oogenesis:

1.) gonadotropin releasing hormone (GnRH)

2.) luteinizing hormone (LH)

3.) follicle stimulating hormone (FSH)

luteinizing hormone (LH) target in the female

theca cells

theca cells

cells surrounding ovarian follicles that respond to LH and produce androgens (estradiol and testosterone)

luteinizing hormone (LH) action in the female

targets theca cells to eventually cause production of estradiol and testosterone

follicle stimulating hormone (FSH) target in the female

granulosa cells

granulosa cells

cells surrounding the developing oocyte that respond to LH and produce androgens (estradiol and testosterone)

follicle stimulating hormone (FSH) action in the female

targets granulosa cells to eventually cause production of estradiol and testosterone

Function of testosterone and estradiol in the female

regulate cyclicity and behavior

Follicles

clusters of cells surrounding a single oocyte within the ovary that nurture and develop the oocyte

Where does follicle development occur in the ovary?

the cortex (outside layer of the ovary)

How is oogenesis different from male germ cell development?

in males, spermatogonia continuously divide to maintain a pool of germ cells throughout life

in females, a pool of germ cells is built during gestation and no longer replenished after birth

Does mitosis or meiosis primarily occur during oogenesis?

meiosis

Stages of meiosis during oogenesis:

1.) primary oocyte undergoes first meiotic division to form secondary oocyte

2.) secondary oocyte undergoes second meiotic division to form mature oocyte

How is meiosis different during oogenesis compared to spermatogenesis?

After each meiotic division, an oocyte is produced, but the second division becomes leftover genetic material

Polar body

left over genetic material formed after each meiotic division during meiosis; not utilized

Three stages of female gamete development from germ cells:

1.) fetal oogenesis

2.) prepuberty oogenesis

3.) puberty oogenesis

Fetal oogenesis

stage of oogenesis that involves primordial germ cells developing into primary oocytes

Fetal oogenesis begins when...

sex cords begin to break down and free primordial germ cells

Primordial germ cells will then differentiate into...

oogonia

Oogonia

undergo several rounds of mitosis in order to build the gene pool for the entirety of a female's life

After undergoing mitosis, oogonia will...

begin to undergo and become arrested in prophase of meiosis I

Once oogonia are arrested in meiosis I, they become...

primary oocytes

As the primary oocyte is developed during fetal oogenesis, so are the...

follicles

What type of follicle surrounds a primary oocyte?

primordial follicle

Primordial follicle structure

made up of a single layer of follicular cells surrounding the primary oocyte

follicular cells

flattened epithelial cells that make up the follicle

Two components of a follicle:

1.) oocyte

2.) supporting cells

Two supporting cells of a follicle:

1.) interstitial (theca) cells

2.) granuolsa cells

Prepuberty oogenesis

resting phase of oogenesis; time during primary oocyte arrest in meiosis I until puberty begins

Not much happens during prepuberty oogenesis except....

atresia

Atresia

degeneration and loss of follicular structures and the oocyte