Anatomy and Physiology 2 Chapter 28 - Mitosis, Meiosis, and Male Reproductive Anatomy

mitosis vs. meiosis

mitosis: produces clones and division of nucleus

meiosis: cell division producing gametes; crossing over and independent assortment present

4 things about mitosis

1. essential for body growth and tissue repair

2. occurs continuously in some cells (skin, intestinal lining, etc.)

3. rare in some (nervous tissue, skeletal muscle, and cardiac muscle)

4. 4 stages to ensure each cell receives copy of replicated DNA

   1. prophase

   2. metaphase

   3. anaphase

   4. telophase and cytokinesis

control of cell division

G0 signals

• G1 checkpoint (restriction point) most important and if it doesn’t pass it goes to G0 (no further division)

• late in G2 MPF (M-phase promoting factor) required to enter M phase

other control signals

• P53 gene

daughter cells

newly formed cells that result from the division of a single parent cell

ploidy levels

the # of complete sets of chromosomes found in a cell

homologous chromosomes

2 sets of chromosomes (homologous pair); 1 maternal and 1 paternal; gene codes for something and may vary slightly (allele)

somatic vs. sex chromosomes

somatic (body) cells: homologous pair (2 sets), 22 pairs of autosomes and 1 pair of sex chromosomes; produced in mitosis

sex (eggs and sperm) cells: 22 autosomes and 1 sex chromosome, XX for female and XY for male (SRY gene); produced in meiosis

meiosis I

aligning of homologous chromosomes, crossing over controls

1. interphase: pair of homologous chromosomes grow and replicate to make sister chromatids (homologous pairs); includes G1, S, and G2 phases

2. prophase I: align homologous chromosomes with their pair, nuclear envelope breaks down, and centrosomes migrate to poles to form spindle fibers

3. metaphase I: tetrads (1 maternal and 1 paternal sister chromatid paired) align on metaphase pair

4. anaphase I: homologous chromosomes separate and moves towards poles, spindle fibers push cell apart to elongate it

5. telophase I and cytokinesis: nuclear membrane reforms, chromosomes uncoil, short interphase step, cells cleaved by actin

produces 2 haploid cells

meiosis II

similar to mitosis, separation of sister chromatids; NO DNA replication

1. prophase II: centrosomes migrate to poles, nuclear envelope degrades, chromosomes attach to spindle fibers, NO alignment of homologous pairs

2. metaphase II: centrosomes align on metaphase plate, sister chromatids attach

3. anaphase II: sister chromatids separate and move towards poles, spindle fibers push cell apart to elongate it

4. telophase II and cytokinesis: nuclear envelope reforms, DNA uncoils, and actin cleaves cells in half

produces 4 haploid cells

independent assortment

genes for different traits sort into reproductive cells independently of one another —> allele from 1 gene doesn’t influence which allele it gets for another; variation based on different possible alignments on the metaphase

crossing over

paired homologous chromosomes exchange segments of DNA during cell division

random fertilization

process where any single male gamete (sperm) fuses with any single female gamete (egg) by chance

aneuploidy

genetic condition characterized by an abnormal # of chromosomes in a cell caused by nondisjunction events

*meiosis I = all abnormal; meiosis II = 2 abnormal

4 types of mutations

1. deletion: segment breaks off and lost

2. inversion: segment breaks off and reattached but in reverse order

3. translocation: segment breaks off and attaches to different chromosome that’s nonhomologous

4. duplication: a chromosome is longer from extra copy

3 things about the reproductive system

• primary sex organs (gonads)

  • testes and ovaries

    • secrete steroid sex hormones

      • androgens (males)

      • estrogens and progesterone (females)

• accessory reproductive organs = ducts, glands, and external genitalia

• sex hormones play a role in…

  • development and function of reproductive organs

  • sexual behaviors and drives

  • growth and development of many other organs and tissue

testes (male gonads)

produces sperm and is delivered to exterior through system of ducts: epididymis > ductus deferens > ejaculatory duct > urethra

anatomy of the testes

• lower than body temp for sperm production

• each surrounded by 2 tunics (membranes)

  • tunica vaginalis (outer): lines the scrotal cavity and reduces friction between the parietal (outer) and visceral (inner) layer

  • tunica albuginea: composed of collagen fibers to support blood and lymphatic vessels that supply and drain the testes

• septa divides testes

  • contain seminiferous tubules which is the site of sperm production

what produces androgens?

interstitial cells of the seminiferous tubules

scrotum and muscles

sac of skin and superficial fascia that contains paired testes

7 structures sperm must travel through in order

1. seminiferous tubules

2. rete testis

3. efferent ductules

4. epididymis

5. ductus (vas) deferens

6. ejaculatory duct

7. urethra

spermatic cord

paired structures extending between the abdominopelvic cavity and the testes; begins at the entrance of the inguinal canal and descends into the scrotum; houses the ductus deferens, blood vessels, and lymphatic vessels

epididymis

• nonmotile (immature) sperm pass slowly through (~20 days) and become motile, can be stored for several months

• during ejaculation, contracts and expels sperm into ductus deferens

ductus deferens (vas deferens) and ejaculatory duct

• pass through inguinal canal

• joins ducts of seminal vesicle to form ejaculatory duct

vasectomy

cutting and ligating ductus deferens; nearly 100% effective form of birth control

urethra

• carries both urine and semen (at different times)

• 3 regions

  • spongy urethra (outermost)

  • intermediate part of urethra (membranous urethra)

  • prostatic urethra (innermost)

3 accessory glands

1. seminal glands: produces viscous alkaline (fructose, citric acid, prostaglanids, and coagulating enzymes) seminal fluid; duct of seminal gland joins ductus deferens to form ejaculatory duct

2. prostate: encircles urethra inferior to bladder; secretes milky, slightly acidic (citrate and enzymes) fluid to help with sperm activation and enters prostatic urethra during ejaculation

3. bulbo-urethral gland: pea-sized glands inferior to prostate; produces thick, clear mucus during sexual arousal to lubricate glans penis and neutralize traces of acidic urine in urethra

penis

organ of copulation and urination; includes the corpus spongiosum and corpora cavernosa

sympathetic vs. parasympathetic for male sexual function

arousal > erection > emission

sympathetic: shoot

• causes ejaculation

• stimulates contraction of reproductive ducts to push semen and sperm to prostatic urethra and seminal glands

• bladder and internal urethral sphincter contract to prevent sperm entering bladder

• associated with orgasm and semen expulsion

parasympathetic: point

• causes erection by dilating blood vessels in the penis

• increases blood flow to erectile tissue

• associated with sexual arousal

ejaculation > orgasm > resolution

• orgasm increases heart rate and blood pressure

• resolution follows with decrease in heart rate and blood pressure as well as decrease in blood flow to erectile tissue; refractory period makes it unlikely for additional orgasm during this time