Animal Reproduction and development

From speech of Aristophanes:
...The sexes were not as they are now...the primeval man...had four hands and four feet, one head with two faces...Terrible was their might and strength...and they made an attack upon the gods...Zeus...said: "Methinks I have a plan which will humble their pride and improve their manners; men will continue to exist, but I will cut them in two...After the division of the two parts of man, each desiring his other half, came together, and throwing their arms about one another, entwined in mutual embraces, longing to grow into one...
-Plato Symposium

Love (sweet Chloe) is a god, a young Youth, and very fair, and wing'd to flye... His power's so vaste, that that of Jove is not so great... For there is no med'cine for Love, neither meat, nor drink, nor any Charm, but only Kissing, and Embracing, and lying naked together.
-Daphnis & Chloe By Longus Translated out of Greek by George Thornley Anno. 1657

Fox Chapter 20

MALE

Meiosis and sperm

Fig. 20.16
Spermatogonia (mitosis and meiosis) - primary spermatocytes
- meiosis (both divisions) - spermatids (scrotum cooler)
Sperm (meioses throughout adult life) Seminiferous tubules
300 million/ ejaculation

Fig. 20.13
Testes - seminiferous tubules make sperm, stimulated by FSH, inhibin for feedback
Interstitial (Leydig) cells produce testosterone, stimulated by LH (ICSH), feedback

Fig. 20.12
Low mag section of testis, higher mag showing seminiferous tubule and interstitial cells
Testes in short day hamsters are smaller than in long day hamsters

Fig. 20.17
An even higher magnification showing Sertoli cell that supports spermiogenesis, has histology
(histology picture)

Semen

Fig. 20.20
male anatomy
Semen:
Bulbourethral (Cowper's) gland (early overflow from sexual excitement)
Seminal vesicle - fructose, amino acids, mucus, prostaglandins (uterine contractions)
Prostate - alkaline (infection, cancer most men > 50)
Capacitation of sperm
Epididymis
Vas deferens - peristalsis -(vasectomy 100% effective- permanent long term effects unknown)
Urethra (of course, it is output here for which condom is a form of contraception)

The prostate story.

Cancer in men >50, diagnosed by paplation
PSA=prostate specific antigen, 1 is low, 5 is high, but not specific to cancer, might be high after having sex
Several "remedies" including selenium
Surgery and radiation, etc.
Slowly developing cancer
Complications - incontinence (for #1, even #2), possibly impotence (ED)
For ED, Viagra, Levitra, Cialis

Fertilization

Many sperm attack one egg, only one fertilizes - fast (electrical) response prevents others

20.39
acrosome, nucleus, mitochondria (not go into egg), flagellum

Review:
Parasympathetic arterioles (unique, usu only symp.) - erection (sleep)
ACh - NO - smooth muscle dilate- viagra blocks breakdown enzyme
NO synthase in cavernous artery and corpus cavernosum
Robert F. Furchgott, Louis J. Ignarro, Ferid Murad Nobel 1998 "for their discoveries concerning nitric oxide as a signalling molecule in the cardiovascular system"
Sympathetic - ejaculation inhib erection

Fig. 20.21
Here is a picture from our histology course showing the spongy tissue of the corpus cavernosum which becomes engorged with blood to mediate erection.
rodents racoons walruses - bone
Sympathetic - ejaculation inhib erection

FEMALE

Review

Fig. 20.34
Here is the typical text book diagram depicting the menstrual (ovarian) cycle (covered earlier)

For convenience, I used the term "eggs" earlier, now I get more official

Meiosis, ovary, steroids

Fig. 20.32
I showed this to you before
primary oocyte in early follicle
secondary oocyte in mature follicle

Fig. 20.31
Here's how that relates to meiosis
Primary oocyte (2-4 million at birth, 1st meiotic prophase)
(400,000 at puberty, only 400 used)
(no oogonia after 3 mo)

Secondary oocyte + polar body
(Graffian follicle finish 1st meiosis) ovulation
if 2 ovulations - DZT - 2 amnions, 2 chorions
twins 1.2% of births, of these 70% "fraternal"
DZT run in family

Uterus, fertilization, and early development

Fig. 20.24
Review
I showed this to you before
anatomy of ovary, and relation of ovulation to fimbriae of uterine (Fallopian) tubule
Tubal ligation (laparoscopy) 100% effective. Reverse?
Cervix (diaphragm, cervical caps, foam, spermicidal jelly)

Fig. 20.42
Fallopian tube (fimbria capture ovulated egg - Sperm meets, 2nd meiosis makes ootid 3 polar bodies discarded nucleii
Division in Fallopian tubes
Blastocyst (trophoblast, blastocoel, inner cell mass)
(trophoblast - >chorion -> placenta)
(inner cell mass -> embryo -> fetus)
IUD prevent implantation, irritate, after previous child, not for everybody legal question
if inner cell mass divides, Monozygotic (identical) twins MZT (2 amnions, 1 chorion), 30% of twins

Fig. 20.44
Shows trophoblast, implantation and a little development

While I have this up, I will talk about "stem cell research"

This relates to cloning.

Cloning

(Not cloning as in cloning a gene, but cloning an organism)

1950's work on amphibians - Since all nuclei should have all the genes, any nucleus should work to make whole organism, taken out of, for instance, an intestine cell. But not all cells work, so put the nucleus into an egg where it is certain that the nucleus already there has been destroyed.

work to make sheep Dolly. Nuclear transfer by removal of egg nucleus followed by fusion with cell with diploid nucleus. Need to implant into a surogate mother.

Cloning has been extremely controversial, and human "reproductive cloning" is banned. Some scientists hoping to advance medical treatments would like to distinguish "theraputic cloning" from cloning to produce a person genetically identical with the donor. Some think the issue would be simplified by use of the term "nuclear transplantation."

Stem cell research

Because cells lose their pluripotency, researchers have focussed on their discovery that embryonic stem cells are better at differentiating into cells that can repair cell damaged areas such as in the case of spinal cord injury; the issue is very controversial because it may encourage practitioners to create and destroy human embryos for no other purpose than to harvest stem cells. Of note, there may be "left-overs" (it is hard to find a diplomatic euphemism) from in vitro fertilization after a couple has had all the children they want (that might go to "waste"). For this reason, for humans, only the use of some 60 cell lines that are already in culture was dictated in the US by President Bush.

Several colleagues and I are collaborating to cure blindness in a mouse mutant with cells that started as embryonic and were induced to become precursors of nerve cells; identified by green fluorescent protein, here is a cell that has been put into the retina and is beginning to show a neuron-like phenotype.

Cursory overview of development

Fig. 20.46
trophoblast implants becomes chorion -
Chorionic villus biopsy - early genetic testing
Amniocentesis-later genetic screening
placenta - exchange, diseases like rubella, alcohol, drugs

Fig. 20.45
make HCG 2 wks - 4 mo (pregnancy test)
to maintain corpus luteum

Fig. 20.5
(not graphic)
2 sexes from 1 primordium
H-Y antigen = testes differentiating factor
then testosterone alters development
MIF (Mullerian inhibiting factor) contributes to development of male "plumbing" female pattern is the default pathway, clitoris is equivalent of penis

Prof Aldridge teaches several courses and does research on reproduction. Prof Ogilvie teaches developmental biology. Prof. Schreiweis teaches embryology.

Exam questions from 2004 - 2008 relating to this outline

How many oogonia does a woman have at puberty?

none

A ball consisting of trophoblast plus what other clump of cells becomes implanted in the endometrium?

inner cell mass

When is meiosis completed in the "egg?"

when sperm meets egg

A low PSA reading is around 1 while a high PSA is 5. What does PSA stand for?

prostate specific antigen

Where is the acrosome?

tip of spermatozoan

Why might a physician want to test a sample of amnionic fluid?

to test prenatally for gene or chromosomal defects

Semen has components from seminiferous tubules, seminal vesicles, bulbourethral (Cowper's) gland, and what other gland?

prostate

The trophoblast becomes the chorion, and the chorion, in turn, becomes what?

placenta

What divides to make monozygotic (identical) twins?

inner cell mass

Where does fertilization take place?

way up in uterine (Fallopian) tube

What becomes of the mitochondria of the spermatozoan during fertilization?

they do not go into the egg

Incontinence is a common consequence of what surgery?

prostate

What is the result of ligating and snipping the vas deferens?

man is no longer fertile

Where is the "egg" when meiosis is complete?

when the sperm fuses

What divides to make identical twins?

inner cell mass

Genetically, how are fully differented adult cells different from pluripotent stem cells?

They both have the same genes, though only a limited subset are being expressed in the former

One diploid primary oocyte undergoes two meitic divisions. How many cells that can be fertilized result?

only one

What part of the blastocyst will eventually (much later) become the placenta?

trophoblast

How can a physician test for defects earlier than amniocentesis?

chorionic villus biopsy

What happens if neither MIF (Mullerian inhibition factor) nor testosterone are present?

primordia of sex structures adopt female development

The PSA (prostate specific antigen) test is used to diagnose a predisposition for what disorder?

prostate cancer

Why is development of uterus and clitoris considered the default pathway?

testes-determining factor (TDF), Mulleriasn-inhibiting factor and testosterone actively cause indifferent gonad primordia to select the male pattern

Spermatogonia undergo meiosis to make sperm. In what way is this process different for formation of oocytes in the adult human?

There come to be no oogonia in women, thus the entire meiosis does no occur throughout life, way fewer gametes are formed, 4 sperm vs 1 oocyte and polar bodies, sperm constant oocyte meiosis regulated when sperm meets egg

Name one of the glands that adds to sperm to make semen.

bulbourethral (Cowper's), seminal vesicle, prostate

Nitric oxide activates an enzyme that makes cGMP. (Maybe you did not know this.) Why might some people take a drug to inhibit the enzyme that breaks down cGMP?

for erectile dysfunction

Why is the IUD (intrauterine device) particularly controversial?

prevents implantation, not fertilization

Say where (or when) the second meiotic division occurs for the oocyte

uterine tubule, when sperm meets egg

What technique provides earlier information on genetic or chromosomal abnormalities than amniocentesis?

chorionic villus biopsy

What specific body of cells divides to make monozygotic (identical) twins (and also is a source of embryonic stem cells)?

inner cell mass

What is the "egg" called officially at the time of ovulation, and what stage of meiosis or mitosis is it at at that time?

secondary oocyte, before meiosis II is complete

Tell me about oogonia in the human female between the first menstrual period and menopause.

there are none

Why do proponents think that embryonic stem cells might be useful to treat Parkinson's disease.

such cells are pleuripotent

An embryonic structure becomes the penis if testosterone is present. What does it become without testosterone?

clitoris

Tell me about spermatogonia in the adult male.

diploid, replace themselves by mitoses, give rise to diploid primary spermatocytes

Ligation and cutting of what tube is a common elective surgery for men to achieve sterility?

vas deferens

Why might an elderly man decide not to have surgery after first being diagnosed with prostate cancer?

it progresses slowly, surgery has side effects

Ovulation comes after a striking surge in what gonadotropin from where?

LH from anterior pituitary

Where (anatomically) does fertilization take place in the human.

in the uterine (fallopian) tube

How do dizygotic (fraternal) twins come about?

2 ovulations

Birth control prevents fertilization. Why is the intrauterine device qualitatively different?

prevents implantation meaning that fertilization (and many cell divisions) have already taken place

In cloning (Dolly, for example) what do you put into the surrogate mother and where?

blastocyst to uterus

"Spermatogenesis: the formation of spermatozoa, including meiosis" (from the glossary in your book). How is spermiogenesis distinguished from spermatogenesis?

spermiogenesis is just the stripping of the cytoplasm of spermatids and the streamlining of spermatozoa

For purposes of family planning, some men elect to have a straightforward surgery that results in sterilization. What is done?

vasectomy = ligate and sever the vas deferens

Why might an elderly man decide not to have surgery for prostate cancer?

it is a slowly developing cancer, and possible side effects of impotence and incontinence detract from the quality of life

As the sperm cell is about to fertilize the "egg," how far along in its meiotic divisions is the egg?

arrested at metaphase II (i.e. meiosis I is complete, but not II)

When are primary oocytes formed from oogonia in the human female?

before birth

With the intrauterine device, which irritates the uterus, the likelihood of an ectopic pregnancy is increased. How does ectopic differ from normal?

way up in uterine (fallopian) tube (instead of uterus)

What is the specific source of embryonic stem cells?

inner cell mass

What is the difference between identical vs fraternal twins in how they are formed?

two ovulations both fertilized fraternal, inner cell mass divides identical

Why do researchers have high hopes for the use of embryonic stem cells for eventual therapies for disorders like retinal degeneration and Parkinson's disease?

they are pluriotent, amazingly form into needed cells if placed where they are needed

Why should cells in the amniotic fluid give us information about genetic (and chromosomal) abnormalities of the fetus (and not the mother)?

the amnion (and of course the fetus) are of zygotic (as opposed to maternal) origin, so the fluid is surrounded only by cells from the fertilized egg

Under the influence of Mullerian inhibition factor (MIF) and (what else?) male development is initiated instead of the female default pathway.

testosterone

How do the mitochondria in the sperm cell contribute to the DNA in the zygote?

They do not

Two meiotic divisions in the female result in only one "egg." What did the other nuclei produced by meiosis become?

Polar bodies

In cloning Dolly, an egg was obtained, its nucleus was removed, a somatic cell nucleus was put in, and cell divisions create an embryo (a hollow ball of cells) in vitro. What did they have to do after that so that a sheep was born?

Implant into a surrogate mother

Why would the intrauterine device (IUD) be considered to be particularly controversial?

Well, even blocking fertilization might be controversial, but blocking implantation is a really early abortion

Why does in vitro fertilization come up in discussions of the benefits and controversities of stem cell research?

One possible source of embryonic stem cells would be "left overs" once a couple has decided they have had enough children

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this page was last revised 7/28/09