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
Which secondary sex characteristics are caused by testosterone? (5)
- Axillary, facial, pubic hair
- Enhanced hair growth on chest and some body areas
- Larynx enlargement (Adam’s apple) and deepening of voice (longer and looser vocal cords).
- Thick, oily skin
- Increased skeletal muscle size and mass- more dense bone structure to support the muscles
When aroused, what happens to blood flow in the erectile tissue?
When aroused- the parasympathetic system stimulates release of nitric oxide (NO). This is the only body region where PSNS has an effect on blood vessel diameter
How does nitric oxide work during arousal?
Filling of corpora cavernosa compresses drainage vessels- prevents blood from leaving. Corpus spongiosum also fills, but not as much
What can cause an erection?
Caused by tactile stimulation, higher mental concentration, sight, sound, etc
Ejaculation
Propulsion of semen from the duct system. Caused by initiation of spinal reflex- nerve impulses occur over sympathetic nerves serving genitals
What occurs during ejaculation? (4)
- Accessory glands contract and release contents to prostatic urethra
- Internal sphincter of the bladder closes
- Bulbospongiosus muscles of pelvis contract rapidly to propel semen out of the body
- Other changes occur- increased heartbeat and blood pressure, muscle contraction
What marks completion of ejaculation?
Completion marked by resolution- muscular and psychological relaxation. Sympathetic impulses constrict arterioles serving erectile bodies. Refractory period increases with age generally
What are the female gonads?
Ovaries
Suspensory ligaments
anchor the ovaries to the pelvic wall
Broad ligament
combines the 3 different mesenteries, supports the uterine tubes
Medulla of the ovary
supplies the vasculature and nervous system supply
Which blood vessels supply the ovary?
Ovarian artery and vein
Uterine tubes (fallopian tubes)
Receive ovulated oocyte from ovary and is the site of fertilization, supported by mesosalpinx
3 regions of the fallopian tubes
- Infundibulum- “end” of tube closest to the ovary. Fimbriae are fingerlike projections at end of each tube
- Ampulla- site of fertilization (typically)
- Isthmus- connect tubes to uterus
Structure of the fallopian tubes
Each tube contains smooth muscle and ciliated cells- cilia beat back and forth to create a current. Non ciliated cells of mucosa produce secretions to keep egg nourished
General function of the uterus
Receives, retains, and nourishes a fertilized egg- the egg will actually implant in the uterine wall.
3 regions of the uterus
- Fundus- most superior region that meets with each uterine tube
- Body- major portion
- Cervix
Cervix
Neck of uterus leading into vagina. Glands here secrete mucus to “block off” the uterus from the vagina
3 layers of the uterine wall
- Perimetrium- outermost serous layer
- Myometrium- contains bundles of smooth muscle
- Endometrium
Myometrium
Contains bundles of smooth muscle, takes up most of uterine wall by mass. Contracts during childbirth, Braxton Hicks contractions (practice for the uterus), period cramps
Endometrium
Mucosa of the uterine cavity. Embryo implants in this layer, remains here for duration of pregnancy
2 subdivisions of the endometrium
- Functional layer (stratum functionalis)- layer that is shed during menstruation
- Basal layer (stratum basalis)
Endometrium vasculature
Uterine arteries branch in uterine wall. Arcuate arteries enter myometrium, branch into small blood vessels called radial arteries
As the radial arteries enter the endometrium, they branch into (2)
- Straight arteries supply the basal layer
2. Spiral arteries- supply the functional layer
Spiral arteries
Supply the functional layer of the endometrium. Repeatedly regenerate and degenerate in response to changing hormone levels. With periods, hormone levels drop off and spiral arteries degenerate. Functional layer collapses and is nonfunctional. Once the functional layer is lost at the end of the period, the straight arteries in the basal layer will regenerate the basal layer as hormones increase.
Vagina
Female copulatory organ. Extends from cervix to body exterior and provides passageway for menstrual flow or infant. pH is slightly acidic- glycogen fermentation by local bacteria
Hymen
Forms incomplete partition at distal vaginal orifice. Normally breaks during first instance of intercourse, however, other things can break it as well. Function of the hymen is unclear, but it could be used to keep certain things out from the fetal body.
Vulva
Any structures that lie external to vagina. Includes the labia majora, labia minora, vestibule, and mons pubis
Homologous structures
Arise from the same tissues between males and females
Mons pubis
overlies pubic symphysis
Labia majora
Extend from mons pubis posteriorly, homologous to the scrotum
Labia minora
Enclosed by the labia majora, homologous to the spongy urethra
Vestibule
Contains openings to urethra and vagina. Posterior portion of vestibule contains openings for greater vestibular glands- release mucus to vestibule surface
Clitoris
Composed mostly of erectile tissue and nerve endings. Homologous to the penis
Parts of the clitoris (3)
- Glans of clitoris- exposed portion
- Prepuce of clitoris- clitoral hood
- Body of clitoris- contains corpora cavernosa
Bulbs of vestibule
Engorge with blood during sexual stimulation. Function- closes off urethra during copulation
Female libido is driven by
Estrogens and DHEA
In females, which areas fill with blood during arousal?
During arousal- clitoris, vaginal mucosa, bulbs of vestibule, and breasts fill with blood. Females have no refractory period
Do females ejaculate?
Female orgasm is not accompanied by ejaculation, it is not necessary for conception to occur. Still a spinal reflex- females experience muscular contraction, blood pressure and heart rate increase, and the uterus contracts rhythmically.
Oogenesis definition
the production of ova (eggs), occurs in the ovaries
Oogenesis process (3 steps)
- Oogonia (diploid stem cell) divides by mitosis to form primary oocytes
- Primary oocytes undergo meiosis 1 to produce secondary oocytes
- Secondary oocytes undergo meiosis 2 to produce ova- polar body is useless
Differences in the oogenesis process from male gamete production (3)
- Meiosis 1 only occurs in a fetus
- Meiosis in primary oocytes stops in late prophase, may or may not resume after puberty.
- Meiosis 2 arrested in metaphase 2 in secondary oocytes, only continues if an egg is fertilized.
When are oogonia present in a female?
Oogonia are present in the fetus- gamete production in females begins during fetal development
Atresia
Programmed cell death, occurs throughout fetal development. A lot of cells are killed off during this time.
Ovarian follicle
Individual developing oocyte surrounded by cells and enclosed in basal lamina to form ovarian follicle. Function- support of ovum
Stages of development of follicles (4)
- Primordial follicle- first class of follicle formed
- Primary follicle- present throughout life until menopause
- Secondary follicle- present throughout life until menopause
- Vesicular follicle- present from puberty until menopause
Primordial follicle
First class of follicle formed. Contain single layer of cells surrounding a primary oocyte (arrested in prophase 1 of meiosis)
Primary follicle
Present throughout life until menopause. Contain single layer of granulosa cells surrounding primary oocyte (arrested in prophase 1). Oocyte secretes glycoprotein rich substance to form a transparent extracellular layer- zona pellucida
Secondary follicle
Present throughout life until menopause. Contain multiple layers of granulosa cells (they’ve divided) surrounding primary oocyte arrested in prophase 1
Vesicular follicle
Present from puberty until menopause, contains a fluid filled cavity called the antrum. Primary oocyte resumes meiosis, becomes secondary oocyte. A secondary oocyte is what’s ejected from the ovary
What are the products of oogenesis after meiosis 1? (2)
- First polar body
2. Secondary oocyte
First polar body
Smaller in size than the oocyte, contains almost no cytoplasm or organelles. Usually undergoes meiosis 2 to form 2 polar body daughter cells
Secondary oocyte
Contains almost all the cytoplasm of original primary oocyte. Secondary oocyte arrests in meiosis 2, is ovulated. If no fertilization occurs- oocyte degenerates, is shed with uterine lining. If fertilization occurs- oocyte completes meiosis 2
Ovarian cycle definition
monthly series of events at the ovary that leads to maturation of an ovum
GnRH
Hormone produced by the pituitary gland to make LH and FSH in females and testosterone in males
How is GnRH release prevented before puberty?
Before puberty- release of small amounts of estrogens prevents GnRH release- leptin (from fat tissue that increases with age) makes hypothalamus insensitive to estrogen. Females begin releasing FSH and LH- continues to rise for several years and then reach an adult cycle. Once adult cycle is reached, menarche occurs
Menarche
Menarche is the first menstrual period
How does the HPG axis regulate the ovarian cycle? (7 steps)
- Hypothalamus releases GnRH
- Anterior pituitary releases FSH and LH
- FSH and LH stimulate follicles to grow, mature, release sex hormones
- Rising estrogen plasma levels inhibit GnRH release
- Dominant follicle continues development to a mature vesicular follicle
- LH surge triggers ovulation and formation of corpus luteum
- If fertilization does not occur- LH levels drop, corpus luteum degenerates
How do FSH and LH stimulate follicles to grow and mature?
FSH causes granulosa cells of vesicular follicles to release estrogen. LH stimulates androgen release- androgens are converted to estrogens
Once estrogen inhibits GnRH release, what happens to FSH?
FSH release drops rapidly. Only the “dominant” follicles survive this drop in FSH- continues development, remaining follicles fail to develop
What happens to the dominant follicle?
Dominant follicle continues development to a mature vesicular follicle. Cells of the follicle releases large amounts of estrogens- cause a surge of GnRH release and LH release
LH surge from dominant follicle triggers
LH surge triggers ovulation and formation of corpus luteum. Primary oocyte in follicle completes meiosis 1. Ovary wall weakens- ovulation occurs, oocyte exits the ovary. Ruptured follicle forms corpus luteum- releases large amounts of progesterone and estrogens- progesterone maintains uterine lining
After the corpus luteum forms, how is GnRH release inhibited?
Rising progesterone and estrogen levels inhibit GnRH release. FSH and LH drop- follicle development stops
What happens to LH and the corpus luteum if fertilization does not occur?
If fertilization does not occur- LH levels drop, corpus luteum degenerates. This means that blood estrogen and progesterone drop. FSH and LH secretion can begin again- ovarian cycle begins again
Phases of the ovarian cycle
- Follicular phase
- Ovulation
- Luteal phase
Follicular phase
Many large vesicular follicles grow in ovaries, this when FSH drops off. FSH rescues a single follicle- the most mature/developed one. Rescues follicle continues to grow and develop. The end of this phase is marked by completion of meiosis 1 to form secondary oocyte and first polar body
Ovulation
Rupture of ovary wall and release of secondary oocyte. Sometimes more than 1 egg can be ovulated, and sometimes oocytes can be released independently of the hormonal cycle
Luteal phase
Occurs after ovulation- ruptured follicle collapses. Always lasts 14 days and never varies. Granulosa cells that remain after ovulation enlarge- forms corpus luteum. The corpus luteum may or may not persist
At the end of the luteal phase, what determines what happens to the corpus luteum?
Corpus luteum degenerates in 10 days if pregnancy does not occur. Release of progesterone ends, and corpus albicans remains- white scar on ovary surface. Corpus luteum remains and continues to release hormones if pregnancy does occur. Persists until placenta formation, then degenerates
Uterine cycle definition
Also called the menstrual cycle. Coordinated with ovarian cycle and hormones associated with it.
Phases of the uterine cycle (3)
- Menstrual phase
- Proliferative phase
- Secretory phase
Menstrual phase
Days 0-4, occurs during follicular phase. Uterus sheds most of the endometrium- functional layer detaches in absence of hormones
Proliferative phase
Days 5-14, occurs during follicular phase. Endometrium is rebuilt- estrogen stimulates formation of new functional layer from basal layer. Cervical mucus becomes thinner- will allow sperm through. Ends when ovulation occurs
Secretory phase
Days 15-28, occurs during luteal phase. Endometrium prepares for implantation of fertilized egg. Progesterone levels rise early in phase
What is caused by the rise in progesterone levels in the secretory phase? (2)
- Endometrial layer thickens, endometrial glands supply lining with nutrients for embryo
- Cervical plug thickens to prevent entry of extra (if any) sperm, bacteria, pathogens
If fertilization doesn’t occur, what happens to the corpus luteum?
If fertilization does not occur- corpus luteum degenerates, progesterone levels drop at the end of the phase. Spiral arteries in functional layer degenerate, spasm- loss of blood and nutrients causes lining to collapse. Functional layer will be shed (day 0).
What effects do rising estrogen levels have on the body? (4)
- Promote oogenesis and follicle growth
- Promotes growth and maturation of female reproductive structures
- Causes sudden growth spurt and cessation of bone growth
- Appearance of secondary sex characteristics- breast development, increased body fat, wider and lighter pelvis (helpful for delivering a baby)
What effects do rising progesterone levels have on the body? (3)
- Work in tandem with estrogen to establish/maintain ovarian cycle
- Promotes changes in cervical mucus
- Maintains pregnancy
Chlamydia
A bacterial infection that is one of the most common STIs. Typical age group most affected: 18-24, and older people living in nursing homes, but can affect anyone. Usually more severe in females- can result in damage to reproductive structures (pelvic inflammatory disease), sterilization, and/or fatal ectopic pregnancy. Treatment- simple antibiotic
Chlamydia symptoms (4)
- Abnormal discharge
- Burning sensation during urination- usually only in males, since urethra is in the same area as the reproductive tract
- Abdominal pain or pain in testicles
- Unusual bleeding- usually only in females
Can be asymptomatic
Gonorrhea
Bacterial infection. Also common- 3 million new cases/year, occasionally passed along with chlamydia. Typical age group affected- 18-24, but can affect anyone. Can lead to infertility, infection can spread to other parts of the body. Treatment- simple antibiotic
Gonorrhea symptoms (4)
- Unusual discharge
- Painful urination
- Abdominal pain, swelling of penis and/or testicles
- Unusual bleeding
Can be asymptomatic
Syphilis
200,000 new cases per year. Multiple stages- includes primary, secondary, and tertiary syphilis. Affects anyone. Treatment- antibiotic (usually penicillin)
Primary syphilis
3-90 days after exposure. Marked by appearance of open lesions/sores called chancres. The sores aren’t painful
Secondary syphilis
4-10 weeks after exposure. Marked by skin rash, swollen lymph nodes, fever. This stage enters a latent period- no signs or symptoms of infection are present
Tertiary syphilis
Occurs years after infection. The bacteria have entered the bloodstream and can go and infect anywhere- most people don’t make it to this phase. Causes damage to central nervous system (neurosyphilis), heart, eyes (ocular syphilis), blood vessels, liver, bones, joints. Symptoms correlate with where the infection occurs- numbness, loss of fine motor skills, vision problems, eventual dementia
Trichomoniasis
Parasitic infection, 3 million cases per year. More common in females than in males- can infect males, but very rarely have symptoms. Usually infects lower reproductive structures in women. Usually no symptoms, but can have a yellow-ish discharge. Can cause preterm labor in pregnant females. Treatment- antibiotics even though it’s not a bacteria
Human papillomavirus (HPV)
More than half of the adult population is infected- is usually not a permanent problem. No medication necessary- body eventually fights it off. More than 40 forms exist, and most cause genital warts.
What cancers can be caused by HPV?
3 forms can lead to cervical cancer in females- prevented by use of vaccine (in both females and males). Can also lead to penile, anal, and oropharyngeal cancer in males
Herpes simplex virus (HSV)
Difficult to assess frequency- only 15% of infected people show symptoms. Symptoms- blister like lesions on mouth or genitals, virus can be spread without an active outbreak via viral shedding. Forms include HSV 1 (cold sores) and HSV 2 (genital herpes). Treatment- none- infection is permanent. Medication shorten outbreak duration
For which 2 groups can an HSV infection be dangerous?
- Anyone with immune deficiency- can’t fight off an outbreak
- Fetus/newborn- virus can be spread from mother to fetus/infant in utero or during birth. Affects CNS development, eyes
