Chapter 27- Reproduction Flashcards
General function of reproductive system
Production of offspring
Which 4 processes allow reproduction to happen?
- Gamete formation- formation of sperm and ova (egg) in the gonads
- Copulation- sperm and egg must be brought together
- Fertilization- combining genetic content of the sperm and the egg
- Gestation and parturition- development and birth of the fetus
Meiosis definition
Nuclear division that occurs only in the gonads and results in the formation of gametes
Meiosis importance (2)
- Reduces the number of chromosomes in gametes by one half
2. Produces genetic variability
What must happen before meiosis begins? (which cells are formed?)
Before meiosis begins, chromosomes in diploid (2n) parent cells replicate. This cell is basically a stem cell. When cells replicate, they make a clone- produce a sister chromatid. When sister chromatids form, we can start meiosis.
Steps of meiosis 1 (4)
- Prophase- homologous chromosomes synapse to form tetrads. Crossing over occurs
- Metaphase- tetrads align randomly on spindle plate
- Anaphase- homologous chromosomes separate, move to opposite poles. Sister chromatids do not separate here
- Telophase- cleavage occurs
Crossing over
Some information from the maternal chromosome ends up on the paternal chromosome and vice versa. If crossing over didn’t occur, there would be reduced genetic variability in our population- genetic variation necessary for disease survival on a population level, etc.
What happens when meiosis 1 is complete?
When meiosis 1 is complete, homologous chromosomes have been separated into 2 distinct daughter cells. The daughter cells are haploid- have half of the typical amount of genetic information (23 chromosomes)
What occurs during meiosis 2? (4 steps)
- Prophase- formation of new spindle
- Metaphase- chromosomes line up at equator
- Anaphase- sister chromatids separate and move to opposite poles
- Telophase- cleavage occurs
What happens if cleavage doesn’t occur during meiosis 2?
Genetic conditions such as down syndrome- people have a third 21st chromosome.
Hypothalamic-Pituitary-Gonadal (HPG) axis definition
The interaction of hormones released by the hypothalamus, anterior pituitary, and gonads
Important structures and their role in the HPG axis (3)
- Hypothalamus- releases gonadotropin-releasing hormone (GnRH)
- Anterior pituitary gland- releases follicle stimulating hormone (FSH) and luteinizing hormone (LH) in response to GnRH presence.
- Gonads- release sex hormones and produce gametes. Testosterone (males), estrogen and progesterone (females)
Which organs are the male gonads?
Testes
Scrotum
Enclose and protect the testes (which are external). Composed of skin and superficial fascia. Importance- body temp is too high to produce viable sperm. Allows production of viable sperm when on the outside, since temp is 3 degrees cooler. Musculature allows testes to maintain this optimal temperature
Muscles of the testes (2)
- Dartos muscle- wrinkles scrotal skin. Contraction reduces surface area
- Cremaster muscle- elevate the testes. Contraction pulls testes closer to the body
Vasculature of testes
Testicular arteries supply each testis. Testicular veins drain testes, and help to maintain optimal temperature. Blood from abdominal cavity is warm, so blood in the veins absorbs some heat from the arteries
Innervation of testes
Sympathetic and parasympathetic divisions serve each testis- sperm production inhibited by SNS
Spermatic cord
Nerve fibers, blood vessels, ductus deferens, and lymphatics form the spermatic cord
Seminiferous tubules
Found in each testis- tubules are location of sperm production. Immature sperm move through rete testis to epididymis
Epididymis
Stores immature sperm. Stereocilia on cells on epididymis wall remove excess testicular fluid and pass nutrients to sperm. As sperm travel through duct- develop ability to swim. Sperm can only remain in the epididymis for a few months before they’re killed off.
Ductus deferens- where does sperm go from here?
Transports sperm out of epididymis during ejaculation- muscular layers create peristaltic waves to push sperm. Ductus deferens ends at ampulla, ampulla ends at ejaculatory duct, ejaculatory duct empties into the urethra
Vasectomy
The ductus deferens can be cut or cauterized. No influence on sperm production- reversible procedure, although maybe not 100%.
3 divisions of the urethra (3)
- Prostatic urethra- portion surrounded by prostate gland
- Intermediate part- connects (1) to (3)
- Spongy urethra- runs through penis and opens to exterior of the body
Function of the penis
deliver sperm to female reproductive tract during copulation