BI233 Lab Exercise 43

• Testis
• Ovary

• "n"
• Half the number of chromosomes seen in all other body cells
• = 23 in humans

• The process of gamete formation
• Reduces chromosome number by half

The alternative would be that each subsequent generation would have double the chromosomes of the previous generation

Egg/Sperm chromosomes that carry genes for the same traits

• "2n"
• 23 pairs of homologous chromosomes
• 46 chromosomes

• Nuclear division process which reproduces cells
• Creates a chromosome content exactly identical to all other cells in the body

• Specialized form of nuclear division producing the haploid number of chromosomes
• Occurs in teh ovaeries and testes during gametogenesis

• Initial cell of gametogenesis
• Stem cell which undergoes chromosomal replication (as in mitosis) immediately prior to untergoing meiosis I and II
• Produces 4 haploid daughter cells (rather than 2 diploid) from cytokinesis

• Event which occurs only in meiosis (not mitosis)
• Pairing in which each homologous chromosome pair lines up closely along the length of the chromosome
• Happens in prophase

• A grouping of four chromatids
• 23 formed during synapsis

• aka Chiasmata
• During synapsis these are the points at which "arms" of adjacent chromosomes coil around each other
• Point at which exchange may occur as homologues separate during Anaphase I
• Event which provides innumberable genetic combinations

Threads of chromatin held together by centromeres

Second maturation division of the cell in which chromosomes are NOT replicated

Holologous chromosomes

sister chromatids by breaking the centromeres

• Interphase
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Cytokinesis
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II
• Cytokinesis

Begins at puberty and proceeds continually throughout life

1/4 billion

Seminiferous tubules (of the testes)

• Found at perifery of seminiferous tubules
• Primitive stem cell from which sperm develop
• Mitotic division before puberty produces 2 spermatogonium
• Mitotic division after puberty produces 1 spermatogonium and on primary spermatocyte

Follicle-stimulating hormone (FSH)

Anterior Pituitary

Cell which is created due to mitosis of spermatogonia (under influence of FSH) and proceeds to meiosis (as opposed to mitosis)

• Haploid cells that are the actual product of meiosis
• Pre-gametes
• Nonmotile cells which have too much excess baggage to function well in a reproductive capacity

• Step which follows meiosis
• Point at which excess cytoplasm is removed from teh spermatid and a streamlined sperm is created
• Occurs in epididymus

• Seminiferous Tubules: from periphery --> lumen
• Spermatogonia (pale-staining nuclei w/centrally located nucleoli)
• Primary spermatocytes--undergoing nuclear division (contain coarse clumps of chromatin having coiled spring appearance)
• Secondary spermatocytes (b/w Meiosis I and Meiosis II
• (Sustentacular/Sertoli cells)
• Spermatids (small w/round nucleus which may look lopsided due to loss of cytoplasm)
• Immature sperm in lumen (have tails)

• aka Sustentacular
• Elongated cell in which spermatids are embedded
• Extend inward from the periperhy of the tubule
• Nourish the spermatids

• aka Leydig cells
• Lie external to (between) seminiferous tubules

• aka Interstitial cell-stimulateing hormone
• Triggers interstitial/Leydig cells to produce testosterone which acts synergistically w/FSH to stimulate sperm production

• Head (w/acrosome)--activating/genetic region
• Midpiece--metabolic region
• Tail--locomotor region

• Anterior to the nucleus in the head of the sperm
• Contains enzymes used to penetrate egg

Centriole which gives rise to filaments which structure the sperm tail and is wrapped tightly w/mitochondria whcih provide ATP needed for contractile activity of the tail

• Typical flagellum produced by a centriole
• Powered by ATP to propel sperm

Primary Oocyte

Relatively thick (appearing) cell membrane produced by the primary oocyte after sperm penetration

• Secondary Oocyte
• First Polar Body

Sac-like structure within an ovary which immature ovum develop in

Cells which encase the ovum and form a single-cell layer saclike follicle

Cells which encase the ovum and form a multi-cell layer saclike follicle

Gonadotropic Hormones

Female gamete formation

primitive stem cell which eventually develops into oocyte

ovarian cortices of the developing female fetus

Occurs thousands of times during female fetal development reaching a population of 2 million +

Single layer of squamouslike follicle cells which encapsulate each fetal oogonium

• Cell form which occurs due to growth of oogonium
• State of most gametogenic ovarian cells by the time of birth
• Represent Prophase I
• Cell form which is maintained until after puberty

Follicle Stimulating Hormone (FSH)

• Follicle resulting from the growth of the primordial follicle and a shift from squamous to cuboidal epithelium
• Begins production of estrogens when stimulated by FSH
• Stimulates the completion of Meiosis I when stimulated by FSH
• [pic]

• Follicle containing the primary oocyte (arrested in Prophase I) surrounded by granulosa cells
• Contains multiple layers of granulosa ("follicle") cells as opposed to the single layer found in the primary follicle
• Begins to show evidence of fluid accumulation and antrum formation
• May take more than one cycle to develop
• [pic]

• Result of the completion of meiosis I (along with first polar body)
• Contains nearly all the cytoplasm from the primary oocyte

• Along with the Secondary Oocyte it is the result of completion of meiosis I
• Contains a minimum of the cytoplasm from the primary oocyte and will eventually disintegrate d/t lack of cytoplasm
• May undergo meiosis II to produce two polar bodies which then disintegrate

• Initially it produces a negative feedback influence on the release of gonadotropins by the anterior pituitary
• At midcycle (~ day 14 as the follicle reaches the vesicular/Graafian stage) the estrogen becomes highly stimulatory to the anterior pituitary which releases a burst of LH (and some FSH) to trigger ovulation

About midcycle as the follicle moves from primary to vesicular/Graafian stage

A burst of LH as well as FSH

[pic]

It must be penetrated/fertilized by sperm in order to continue past metaphase II

In the first third of the uterine tube

The chromosomes of the egg and sperm combine to form the diploid nucleus of the fertilized egg

A single functional gamete and 3 polar bodies

• Ruptured follicle which has been transformed by LH after expelling an oocyte
• Solid glandular structure or scalloped lumen structure
• Structure which produces progesterone and estrogen thus inhibiting FSH production in the anterior pituitary
• [pic]

Inhibits FSH release

• Decreasing stimulatory effect on folliclular producion of estrogen
• Decreased stimulation of anterior pituitary to release LH
• Decreased stimulation of corpus luteum
• Declining progesterone production by corpus luteum
• Eventual degeneration of corpus luteum in to scar tissue--corpus albicans

• [pic]
• scar tissue which forms near the end of the 28-day cycle as a result of the degeneration of the corpus luteum

[pic] outermost layer of the ovary

• Central cavity of an ovarian follicle which begins to form in the secondary follicle and becomes prominent in the vesicular/Graafian stage
• [pic]

• Follicle containing a developing secondary oocyte which is pushed to the side by a large antrum filled with fluid from the granulosa cells
• [pic]

• Several layers of granulosa cells which surround the secondary oocyte within the antrum of the vesicular/Graafian follicle
• Structure which is retained as oocyte is ovulated

• Connective tissue stroma which forms a capsule enclosing the mature vesicular/Graafian follicle
• [pic]

• Cycle controlled by hormones (estrogen/progesterone) secreted by the ovary
• Divided into 3 stages--menstrual, proliferative, secretory

• Menstrual
• Proliferative
• Secretory

Shedding of the functional layer of endometrium (days 1-5 )

Estrogens influence the rebuilding of the (endometrial) functional layer (days 6-14)

Immediately after ovulation progesterone triggers the endometrium to receive an embryo by enriching the blood supply and increasing glandular secretion of nutrients (days 15-28)

Production of a hormone similar to LH will maintain the function of the corpus luteum preventing deterioration and inhibiting the secretion of ovarian hormones.  As a result the endometrial blood vessels continue to proliferate