Biology 102: (Chapter 36) Reproduction and Development

Embryonic development

Begins with fertilization; the process by which the embryo is formed and develops, until it develops into a fetus.

Both males and females produce what?

Both males and females produce androgens and estrogens but differ in their blood concentrations of particular hormones. For example, males have testosterone levels about 10 times higher than females.

Normally the Y chromosome ______ the SRY gene, and the X chromosomes _______ the SRY gene.

Normally the Y chromosome contains the SRY gene, and the X chromosomes lack the SRY gene.

How long it is after an ovum has been fertilized by a sperm that the blastocyst implants into the wall of the uterus?

Once the embryo reaches the blastocyst stage, approximately five to six days after fertilization, it hatches out of its zona pellucida and begins the process of implantation in the uterus.

What is one outcome of homologous recombination?

One outcome is for an X chromosome to gain the SRY gene (referred to as X(SRY+)). Conversely, through the same process, it is possible for the Y chromosome to lose the SRY gene (referred to as Y(SRY-)).

Male reproductive system

Overall function is production of offspring. Testes produce sperm and male sex hormone, and male ducts and glands aid in delivery of sperm to the female reproductive tract. Also has structures that deliver gametes.

Bulbourenthal glands

Paired glands that secrete a mucus-like fluid in response to sexual stimulation.

Apoptosis

Programmed cell death

Why are the protein receptors on the egg cell particularly important among aquatic animals that use external fertilization?

Protein receptors on the egg match species-specific proteins on the sperm; this ensures that sperm of a different species will not fertilize the egg.

Prostate gland

Secretes an alkaline fluid that supplies nutrients and lubrication for the sperm. It comprises ~70% of the ejaculate volume.

Within the embryo, what is the origin of the dorsal, hollow nerve cord that is common to all members of our phylum?

The neural tube, which becomes the brain and spinal cord, develops from a dorsal ectodermal plate that folds inward to form an interior tube.

FSH (follicle-stimulating hormone) and LH (luteinizing hormone) are what type of hormones and what do they do?

They are tropic hormones; meaning that they trigger endocrine tissues to release other hormones. FSH and LH act on the gonads and regulate the production of sex hormones.

What do the seminal vesicles, prostate gland, and the bulbourethral glands contribute to?

They contribute to semen, the fluid ejaculated from the penis during male orgasm.

During fertilization, what exactly occurs?

- A sperm releases enzymes contained in its acrosome that pierce the egg's coat, - Sperm surface proteins bind to egg receptor proteins, sperm and egg plasma membranes fuse, and the two nuclei unite, - Changes in the vitelline layer of the egg's membrane prevent entry of additional sperm, and the fertilized egg (zygote) develops into an embryo.

The Process of Sexual Reproduction

- Both sperm and egg are gametes, sex cells with a haploid (n) set of chromosomes. - The male gamete, the sperm, is a relatively small cell that moves by means of a whiplike flagellum. - The female gamete, the egg, is a much larger cell that is not self-propelled. - When egg and sperm join, they form a diploid (2n) zygote, or fertilized egg.

Fertilization results in a zygote and triggers embryonic development

- Combines haploid sets of chromosomes from two individuals to form a diploid zygote - Activates the egg by triggering metabolic changes that start embryonic development

What happens during the 3 trimesters of the growth of a fetus?

- During the first semester, the most rapid changes occur. At eight weeks, the embryo is called the fetus. - The second and third trimesters are times of rapid growth and preparation for birth

The formation of sperm and egg cells requires meiosis (Part 2)

- In females, each month, one primary oocyte forms a secondary oocyte, which, if penetrated by a sperm, completes meiosis and becomes a mature egg. - The haploid nucleus of the mature egg then fuses with the haploid nucleus of the sperm, forming a diploid zygote. - Women continue to produce secondary oocytes (gametes) until the age of 45+ when the ovaries stop producing progesterone and estrogen. This time is called menopause.

Mechanisms of Asexual Reproduction

- Several simple forms of asexual reproduction are exclusive to invertebrates - One of these is budding, in which new individuals arise from outgrowths of existing ones - Also common among invertebrates is binary fission, the separation of a parent organism into two individuals of approximately equal size.

Sex hormones

- Sex hormones regulate gamete production both directly and indirectly - They serve many additional functions, including sexual behavior and the development of primary and secondary sex characteristics - Androgens and estrogens also stimulate specific sexual behaviors in males and females, respectively.

Human sperm cell

A highly differentiated sex cell consisting of three different regions: the head (containing a nucleus), the midpiece (with a large mitochondrion), and the tail composed flagellum.

Gonadotropin-releasing hormone (GnRH)

A hormone released from the hypothalamus that triggers the anterior pituitary to secrete FSH (follicle-stimulating hormone) and LH (luteinizing hormone).

Seminal vesicles

A part of the male reproductive system; paired glands that secrete a nutrient-rich fluid into the ejaculate to provide support for the sperm. This fluid includes enzymes, proteins, mucus, and fructose.

Budding

Asexual reproduction in which a part of the parent organism pinches off and forms a new organism. For example, this reproduction occurs in a hydra and coral.

SRY gene on Y chromosome directs what?

Directs the development of gonads into testes, particularly adult male characteristics such as a deeper voice, facial hair, and larger muscles.

Gastrulation

During gastrulation, - Cells migrate to new locations, - a rudimentary digestive cavity forms, and - the basic body plan of three layers is established with 1. Ectoderm outside-becoming skin and nervous systems 2. Endoderm inside-becoming digestive tract, and 3. Mesoderm in the middle-becoming muscle and bone.

Ectoderm

Epidermis of skin; epithelial lining of the mouth and rectum; sense receptors in epidermis; cornea and lens of eye; nervous system

Endoderm

Epithelial lining of digestive tract (except mouth and rectum); epithelial lining of the respiratory system; liver; pancreas; thyroid; parathyroids; thymus; lining of urethra, urinary bladder, and reproductive system

What are the major estrogens?

Estradiol and progesterone

Uterus

Female organ of reproduction used to house the developing fetus. It opens into the vagina, which receives the penis during intercourse and serves as the birth canal.

What is the first event to occur during embryonic development?

Fertilization, also called conception

Pregnancy Trimesters

First: weeks 1-13 Second: weeks 14-26 Third: weeks 27-40

Spermatogenesis

Formation of sperm

How do the levels of luteinizing hormone (LH) affect the corpus luteum in the ovary?

If the egg is not fertilized, the drop in LH shuts down the corpus luteum and its hormones. This triggers menstruation, the breakdown of the endometrium. - The hypothalamus and pituitary then stimulate another follicle, starting a new cycle. - If fertilization occurs, a hormone from the embryo maintains the uterine lining and prevents menstruation.

Cleavage

It is the first event that occurs during embryonic development and is a rapid series of cell divisions that produces: - More cells, - Similar cells, and - A fluid filled cavity, the blastocoel, in an embryo called a blastula.

Testes

Male gonads that are housed outside the abdominal cavity in a sac called the scrotum.

After gastrulation, the three embryonic tissue layers give rise to specific organ systems

- The stiff notochord forms the main axis of the body and is later replaced by the vertebral column in most chordates - The neural tube develops above the notochord from the ectoderm and will become the brain and spinal cord. - As the embryo elongates, paired somites - form along the sides of the notochord, - hollow out to form the body cavity, or coelom, and - eventually contribute to muscles, bone, and other connective tissues. - Other systems develop at the same time.

The reproductive cycle is actually two closely linked cycles. Explain more on this:

1. The ovarian cycle controls the growth and release of an egg. 2. During the menstrual cycle, the uterus is prepared for possible implantation of an embryo.

Hermaphroditism

A condition in which an individual has both male and female reproductive systems. - Any two hermaphrodites can mate, and some hermaphrodites can self-fertilize. This includes earthworms.

Fragmentation

A form of asexual reproduction; the breaking of the body into pieces, some or all of which develop into adults. This must be accompanied by regeneration, regrowth of body parts.

What is the most common bacterial STI?

Chlamydia; frequently produces no visible symptoms but develop into pelvic inflammatory disease in women

Penis

Consists mainly of cylinders of erectile tissue that can fill with blood to cause an erection during sexual arousal. - Sperm production by the testes is controlled by hormones from the hypothalamus and pituitary.

Human female reproductive system

Consists of a pair of ovaries, ducts that carry gametes, a uterus, and structures for copulation.

Sexually transmitted infections (STIs)

Contagious pathogens spread by sexual contact. Some that are caused by bacteria can often be cured, but those that are viral can only be controlled

Ovaries

Contain follicles that nurture eggs and produce sex hormones.

Oviducts

Convey eggs to the uterus, where an embryo develops.

Homeotic genes

Genes that contain homeoboxes, nucleotide sequences that determine basic features of where a body part is.

One in five Americans is infected with ___________, caused by the herpes simplex virus type 2 (HSV-2), a variant of the virus that causes oral cold sores (HSV-1).

Genital herpes

In the absence of expression of SRY, what happens?

Gonads develop into ovaries

During meiosis, chromosomes exchange genetic material with one another though a process called what?

Homologous recombination

Childbirth

Induced by hormones and other chemical signals: - Estrogen makes the uterus more sensitive to oxytocin, which acts with prostaglandins to initiate labor. - The cervix dilates, the baby is expelled by strong muscular contractions, and the placenta follows.

What is the viteline membrane and what is its function?

It is an inner membrane of an egg; very flexible and surrounds the cytoplasm.

What does the acrosome of the sperm contain?

It is an organelle that develops over the anterior half of the sperm cell. It contains hydrolytic enzymes to penetrate the egg.

Oogenesis

It is one part of a female mammal's reproductive cycle, a recurring sequence of events that produces gametes, makes them available for fertilization, and prepares the body for pregnancy.

What is an advantage of sexual reproduction?

Sexual reproduction allows for genetic diversity.

Sexual reproduction results in what?

Sexual reproduction results in genetic variation among offspring. This may enhance survival of a population in a changing environment.

Mesoderm

Skeletal muscle, bones, circulatory system, excretory system, connective tissue, adipose tissue, dermis

The formation of sperm and egg cells requires meiosis

Spermatogenesis and oogenesis produce sperm and eggs, respectively. - Primarily spermatocytes are made continuously in the testes. - These diploid cells undergo meiosis to form four haploid sperm. - Men can produce sperm (gametes) throughout their lives.

What are the long-term differences between spermatogenesis and oogenesis?

Spermatogenesis leads to the formation of sperms, whereas oogenesis helps in the formation of ova. The fertilization of sperm and ova leads to the formation of a zygote which further develops into an embryo.

Which form of contraception is reliable only when combined with other methods?

Spermicide

Epididymis

Stores sperm as they develop further. During ejaculation, sperm leave the epididymis through the vans deferens.

What is the major androgen?

Testosterone

Regeneration

The ability to regrow a missing part of the body

Sexual Reproduction

The creation of offspring through the process of fertilization, the union of sperm and egg.

Parthenogenesis

The development of a new individual from an unfertilized egg; this form of asexual reproduction also occurs in some vertebrates.

Mammalian reproduction is coordinated by hormones from the _________, __________, and ____________. (*Remember HAG)

The hypothalamus, anterior pituitary, and gonads

IVF (in vitro fertilization)

The medical process during which LH and FSH are injected into the woman to stimulate multiple egg releases from the ovaries. The eggs are then taken from the ovaries and fertilized with the father's sperm in a petri dish. The process is done for those having troubles with conception/ fertilization.