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
Parts of the penis (2)
- Root- attaches to body wall
2. Body- external portion
Glans
End of the body part of the penis. Surrounded by prepuce (foreskin)
Spongy urethra
Extends from root through the glans to exit the body- internal anatomy
Erectile tissue contains (3)
Contains connective tissue, smooth muscle, vascular space. Vascular spaces fill with blood during arousal
2 erectile bodies
- Corpus spongiosum- immediately surrounds urethra. Forms glans distally
- Corpus cavernosa- paired structures that make up most of penile tissue
Seminal glands
Combines with ampulla of ductus deferens at ejaculatory duct. Secretions produced here make up most of the total semen volume. Contains alkaline component, fructose sugar, coagulating component, citric acid, prostaglandins, and substances to initiate/improve sperm motility and fertilizing capabilities.
Prostate
Composed of 20-30 tubuloalveolar glands. Produces citrate, prostate-specific antigen (PSA), and substances that help activate sperm. Smooth muscle walls contract during ejaculation to release contents into prostatic urethra
Prostate cancer
Ranges from slow growing to highly aggressive. Men usually die with it, not because of it, even with more aggressive forms. Age is the only predicting factor of the development of prostate cancer- more commonly found in men ages 50+
Symptoms of prostate cancer
Asymptomatic in early stages. Late stage symptoms- frequent urination, strain to empty bladder, blood in urine, erectile dysfunction
Benign prostatic hyperplasia
Excessive growth of glands in the prostate- prostate just grows too large. Constricts prostatic urethra. Symptoms- frequent urination, difficult and painful urination. Not really any way to reverse it, but drugs can relax the smooth muscle in the walls of the prostate so it won’t press on the urethra
Bulbo-urethral glands
Produces alkaline mucus that neutralizes the acidic urine in the urethra before ejaculation. Sperm don’t do well with acidic pH
Semen
The combination of sperm with accessory gland secretions. Normal pH range 7.1-8
Components of seminal secretions (5)
- Prostaglandins
- Relaxin (and other enzymes)
- Fructose
- Antibiotic components
- Clotting factors
Prostaglandins
Decrease viscosity of mucus in female cervix, stimulate reverse peristalsis in the uterus
Relaxin
Along with other enzymes, promotes and enhances sperm motility
Fructose function in semen
Catabolized for sperm ATP synthesis
Antibiotic components in semen
destroy bacteria that could harm sperm
Clotting factors in sperm
coagulate sperm after ejaculation
Why does semen suppress the female immune system?
The sperm don’t belong in the reproductive tract, but they need to survive for fertilization
Spermatogenesis definition
production of male gametes
Important cell types of seminiferous tubules (4)
- Sustentocytes
- Spermatogenic cells
- Myoid cells
- Interstitial endocrine cells
Sustentocytes
Surround, support, and nourish developing sperm. Adjacent sustentocytes joined by tight junctions- prevent sperm from “escaping”.
Spermatogenic cells
sperm forming cells
Myoid cells
Smooth muscle like cells- contract to move immature sperm from tubules and into epididymis
Interstitial endocrine cells
Secrete testosterone (with small amount of estrogen- negligible effects)
Spermatogenesis process (3 steps)
- Spermatogonia (diploid stem cell) divide by mitosis
- Primary spermatocyte undergoes meiosis 1 to form a secondary spermatocyte
- Secondary spermatocyte undergoes meiosis 2 to form spermatids
Where do males get spermatogonia from?
All males are born with all spermatogonia they’ll ever need
What do spermatogonia divide into?
They continue to divide after birth, but what they’ll become depends on the age of the male. Before puberty, divides to make more spermatogonia. After puberty, form type A daughter cells or type B daughter cells. Type A becomes more spermatogonia, type B becomes primary spermatocytes.
Spermiogenesis
not meiosis- takes the spermatid and produces functional sperm
Sperm has 3 general areas
- Head
- Midpiece- metabolic area- contains mitochondria
- Tail- locomotor region with flagellum- allows sperm to move
Head of sperm
Holds genetic material (haploid). Forms a cap called the acrosome- helmet like structure that holds hydrolytic enzymes
How does the HPG axis work specifically in males? (3 functions)
- PG- LH stimulates interstitial endocrine cells of testes to secrete testosterone
- PG- FSH stimulates sustentocytes to release androgen binding protein (ABP)
- Release of sex hormone testosterone stimulates spermatogenesis, maturation of sex organs, development of secondary sex characteristics and libido
ABP
Androgen binding protein (ABP)- ABP stimulates spermatogenesis by keeping local testosterone levels in testes high
Why would a fetus have a surge of gonadotropins and testosterone?
Fetus also has a surge of gonadotropins and testosterone shortly before birth- stimulates development of reproductive organs. This surge drops quickly, does not appear again until around puberty. Surge is short because you just want to mature the sex organs, not produce sperm
In which organs does testosterone need to be converted? (2)
- Prostate- dihydrotestosterone (DHT). The more DHT, the more the prostate will grow.
- Brain, bone, fat- estradiol
Secondary sex characteristics definition
Features induced in nonreproductive structures due to influence of sex hormone