Module 20 Flashcards
1
Q
Monotremes
A
The way reptiles, and some mammels, reproduce through egg-laying.
2
Q
Anatomical Features of the Male
A
- Testes
- Ducts
- Accessory sex glands
- Urethra (shared between urinary and reproductive systems
- Penis (shared between reproductive and urinary systems)
3
Q
Anatomical Features of the Female
A
- Ovaries
- Uterine (fallopian) tubes
- Uterus
- Cervix
- Accessory sex glands
- Vagina
4
Q
Functions of the Male Reproductive System
A
- Testes produce sperm
- Testes produce testosterone
- Ducts transport, store, and assist in maturation of sperm
- Accessory sex glands secrete bulk of seminal fluid
- Penis encloses urethra as passageway for excretion of urine
- Penis and urethra are used to introduce semen into female by coitus and ejaculation.
5
Q
Functions of the Female Reproductive System
A
- Ovaries produce oocytes
- Ovaries produce progesterone, estrogens, inhibin, and relaxin
- Uterine (fallopian) tubes transport oocyte to the uterus.
- Uterine tube is site of fertilization
- Uterus is site of implantation of fertilized ovum and supports development of fetus.
- Accessory sex glands secrete fluid during coitus
- Vagina receives penis during coitus
- Cervix and vagina are passageways for childbirth.
6
Q
Spermatazoa
A
Spermatazoa are produced in the hundreds of millions; a single one is called a spermatozoon. They are produced in the testes, mature in the epididymis, then, upon demand, travel through ducts to be ejaculated from the urethra of the penis.
7
Q
Scrotum
A
The scrotum supports and encloses the testes. It has 2 muscles:
- dartos: subcutaneous surrounds sac
- cremaster: in spermatic cord
8
Q
Testes
A
Testes make a continuous supply of sperm.
- spermatogenic cells make sperm
- Sertoll (sustenfacular) cells support spermatogenesis
Testes also secrete testosterone and other androgens
- Leydig (interstitial) cells
9
Q
Ducts and Accessory Glands for the Male
A
- Ductus deferens carries sperm from seminiferous tubules to prostate
- There, prostate and seminal vesicles add secretions and the mixture is dumped into urethra
- Bulbourethral glands add secretions just prior to ejaculation.
10
Q
Penis
A
Erectile tissue consists of sponge-like venous passages which fill up with congested blood to make the penis erect
- Corpora cavernosa (right and left)
- Corpus sponglosum
Urethra passes sperm or urine
Uncircumcised men have prepuce (“foreskin”) covering glans.
11
Q
Gamete production and Transport
A
- Gametes are critical for sexual reproduction
- Male gametes + female gametes = new member of the species
- Male gametes (spermatazoa) produced in the testes, matured in the epididymis, travel through ductus deferens and urethra to be ejaculated into the female.
- There, fertilization joins male and female gametes.
12
Q
Sperm Path through Male
A
Spermatazoa takes a complicated path to ejaculation:
- Released into lumen of seminiferous tubules of testes
- Mature in epididymis, wait for ejaculation
- Upon sexual stimulation leading to ejaculation, travel via ductus deferens (secretion from bulbourethral glands prepares urethra
- Critical fluids from seminal vesicles and prostate added
- Ejaculated through the urethra of erect penis.
13
Q
Spermatogenesis 1: A Spermatozoon is Born
A
- Spermatogonia are the stem cells. These cells divide at the basement membrane
- Gametes mature progressively as they move from basement membrane to lumen
1. Speratogonia
2. Primary spermatocytes
3. Secondary spermatocytes
4. Early spermatids
5. Late spermatids
6. Spermatazoa (sperm cells)
14
Q
Spermatoazoa on the Move
A
Sperm are the only cells in the human body with flagellae. This allows them to be motile. Spermatazoon is basically a “missle” (mitochondria for rocket fuel + flagellum) with a “payload” of paternal DNA.
15
Q
Spermatogenesis 2: The Waiting Room
A
- After being produced in seminiferous tubules of testes, spermatazoa move to rete testes and cross imaginary border into the epididymis.
- In epididymis, pass through efferent ducts to ductus epididymis.
- Ductus epididymis is where sperm wait up to 14 days to mature. During maturation, they acquire mobility and ability to fertilize ovum
- Smooth muscle layer surrounding epididymis responds to sexual arousal by contracting, expelling sperm
16
Q
Spermatogenesis 3: The Tubes
A
Upon leaving the epididymis, the spermatazoa are forced into the ductus deferens
- Meanwhile, the bulbourethral glands secrete a small amount of alkaline fluid to lubricate and buffer the pH of the urethra.
- The ductus meets the urethra at the prostate. Secretions from the seminal vesicles and prostate are added here.
- Now the fluid is semen
17
Q
Speratogenesis 4: Ejaculation
A
- Ejaculation is a sympathetic reflex coordinated by lumbar spinal cord
- Internal urethral sphincter closes to prevent leakage of urine and backflow of sperm
- Peristaltic waves in epididymis, ductus deferens, seminal vesicles, ejaculatory ducts, and prostate
- Contractions of muscles at root of penuis
bulbosponglosus
ischlocavemosus
superficial transverse perineus - Emission results
18
Q
Semen Facts
A
- About 2.5 to 5 mL of semen in the average ejaculation. - About 100 million (10^8) spermatazoa per mL. (below 20 million mL is usually defined as male infertility)
- Slightly alkaline: pH 7.2-7.7. This neutralizes the acidity of the male urethra and the female vagina
- Clots about 5 minutes after ejaculation. No one knows why. Has different clotting proteins than blood
- After another 10-20 minutes, it reliquifies. Prostate-specific antigen (PSA) is one of the anti-clotting agents.
19
Q
Seminal Fluids
A
Seminal fluid contributes nutrients, buffering, and fluid medium for delivery of ejaculate.
- Seminal vesicles contribute pH, fructose, prostaglandins (fructose is the major nutrient which powers sperm motility)
- prostate contributes zinc. citrate, and the enzyme acid phosphates (used in forensic testing) Prostate also gives a milky quality.
20
Q
Oocytes
A
Gametes are produced in the ovaries. The uterine tubes (fallopian tubes) convey the gamete (an ovum) from the ovaries to the uterus (Latin: womb).
- If fertilization occurs, implantation in the uterine wall will follow.
- If no fertilization occurs, then the uterine lining and ovum/embryo are flushed out of the uterus by the process of menstruation.
21
Q
Ectopic Pregnancy
A
When an ovum implants in any place other than the uterus. (Example: the uterine tubes) It’s a life threatening condition for both mother and child.
22
Q
Function of the Female Reproductive Organs
A
Ovary: stores and matures eggs. Secrets estrogen. Another name for ovary is oophor (Greek: producing)
Uterine Tubes: Conduct egg from overy to uterus. The usual site of conception. Also called fallopian tubes (Greek: Trumpet)
Uterus: Site for embryo implantation. Also called hystero (Greek: womb)
Vagina: Muscular opening to permit insertion of penis. Flexible channel for childbirth.
Vulva: External opening (Introitus) for reproduction. External urethral orifice allows urination.
23
Q
Follicular Development
A
In general, the female reproductive years lie between menarche (the time of first menstruation) and menopause (the time of last menstruation).
- Prescursors to the ova undergo their last cell division before birth and remain in a quiescent state as primary oocytes until after menarche.
- Under the influence of pituitary hormones, and hormonal feedback from ovaries, one of the follicles surrounding a primary oocyte begins to change.
- Granulosa cells surround the primary oocyte and the follicle is now called a primary follicle.
- Later, fluid fill pocket develops. As soon as it does, the follicle is then called a secondary follicle.
- Finally, when fluid predominates, the follicle is called a mature follicle, or Graafian follice. This name indicates that the follicle is due to rupture, a process called ovulation.
24
Q
The Follicular Cycle and Oocyte Formation
A
Confusingly, the stages for the oocyte and the follicle are called by the same names (primary, secondary) but they’re not the same thing. So, we have a primary oocyte sitting in a secondary follicle.
The hormones released are luteinizing hormone (LH) and follicle-stimulation hormone (FSH). They are secreted by the anterior pituitary as a response of the hypothalamus secreting gonadotropin releasing hormone (GnRH).
FSH is released early in the menstrual cycle and promotes the maturation of a primary follicle into a secondary follicle, then to a mature follicle.
Hormones control the follicular cycle, the follicular cycle controls hormones.
25
Rupture of the Mature Follicle
In response to a surge of luteinizing hormone (LH) once a month, the mature follicle ruptures and releases a secondary oocyte
26
Follicular Development Steps in the Ovary
1. Primordial follicle
2. Primary follicle
3. Secondary follicle
4. Mature (Graafian) follicle: about 2 cm diameter
5. Ovulation - secondary oocyte expelled
6. Corpus luteum
7. Degenerating corpus luteum
8. Corpus albicans (scar tissue)
- Secondary and mature follicles secrete estrogens
- After follicle ruptures and secondary oocyte is released, the follicle becomes filled with a yellowish waxy substance called corpus luteum. (Latin: yellow body)
- The corpus luteum secretes progesterone and estrogens to maintain the lining of the uterus to prepare the body for implantation.
- In any case, after about 14 days, the corpus luteum "burns out" and no longer secretes hormones and becomes a corpus albicans (white body), a knot of scar tissue.
27
Gamete Production and Transport in the Female at Release of Secondary Oocyte.
The female gamete is the ovum
- Secondary oocyte released from ovary at ovulation
- Swept up by fimbriae of uterine tube
- Oocyte may encounter sperm in uterine tube
- If it does, the secondary oocyte undergoes division to form ovum
- If spermatozoon and ovum unite, zygote is formed.
- Zygote travels to uterus where it implants.
28
Histology of Uterine Wall
The uterine layers are named from Greek: "metra" meaning "womb"
Endometrium: nearest the lumen and has 3 layers
1. simple columnar epithelium
2. stratum functionalis
3. stratum basalis
The stratum functionalis is shed monthly in the menstural cycle. Also contains glands.
Myometrium: muscular layer, very thick
Perimetrium: Serosa
29
Blood Supply of the Uterus
Understanding blood supply of the uterus is essential for understanding of menstrual cycle and implantation of embryo.
- Internal iliac arteries to uterine arteries to arcuate arteries to radial arteries
- Radial arteries branch into spiral arterioles (to stratum functionalis) and straight arterioles (to stratum basalis)
- Venous drainage: uterine veins to internal iliac VV.
30
Blood Supply of the Uterus During the Uterine Cycle of Menstruation
- Spiral arterioles supply stratum functionalis
- Stratum functionalis is shed during menstrual cycle
- Arterioles and venules of stratum functionalis are shed with endometrium during menstruation, then regrow from stratum basalis during proliferative phase.
31
The Uterine Cycle
1. Complete loss of stratum functionalis during menstruation
2. Stratum functionalis rebuilt during proliferative phase
3. During secretory phase, glands of endometrium proliferate and endometrium becomes a secretory organ as well as "potting soil" for zygote.
The amount of menstrual flow varies widely. The average is 36 mL per cycle; more than 80 mL is considered menorrhagia, or abnormal bleeding.
32
Correlation of Ovarian and Uterine Cycles
- Early in the menstrual cycle, during the last half of menstruation and at the beginning of endometrial proliferaion, FSH released from anterior pituitary causes one lucky primordial follicle in one ovary to start developing. It then becomes a primary follicle because it was stimulated by follicle stimulating hormone. As blood levels of FSH remain high, the primary follicle develops into a secondary follicle
- The maturing follicle in turn secretes estrogens to help maintain growth and development of stratum functionalis of the endometrium. At midpoint, 14 weeks, burst of FSH and LH trigger ovulation
- Ruptured follicle becomes a corpus luteum, a temporary endocrine organ that secretes progesterone and estrogens. These support endometrium while it awaits for implantation.
- If no implantation occurs, low progesterone, estrogen, LH, and FSH levels allow the shedding of the endometrium - menstruation.
33
Inhibin and Relaxin
- Inhibin: inhibits the release of FSH (mostly) and LH (somewhat) from anterior pituitary.
- Relaxin: secreted by corpus luteum, relaxes smooth muscle of the uterus. It also plays a key role in childbirth (parturition) by dilating the cervix and increasing flexibility in the pubic symphysis.
34
Development of Internal Reproductive Organs
All 5wk embryos start out with indifferent gender. Sex-determining region Y (SRY) gene on Y chromosome leads to development of male gonads and genitalia.
Errors in this process:
- classic congenital adrenal hyperplasia (0.008%)
- androgen insensitivity syndrome (0.008%)
- "true" hermaphrodites (0.001%)
- Total about 50,000 in USA
35
Development of Genitalia
- Products of the same gene (SRY of Y chromosome), working on the same set of receptors results in development of male genitalia.
- Note that "default" pathway in absence of SRY funtion or defective receptors results in person who is phenotypically female.
- Variations in this process result in intersex genitalia (Estimates of incidence depend on definition: range from 0.02 - 1.7%
- Observing this developmental process allows us to draw analogies between female and male structures.
36
Analogous Structures Between Males and Females
Gonads: Testes and Ovaries
Paramesonephric (Mullerian) ducts:
- degenerate
- uterine tubes, uterus, and vagina
Glans area of genital tubercle:
- Glans penis and corpora cavernosum
- Clitoris
Urethral folds of genital tubercle"
- penile urethra
- labia minora
Labioscrotal swellings of genital tubercle
- Penis, scrotum, corpus spongiosum
- Labia majora, Pubercervial (Halban's) fascia and vestibular bulb.
- Prostate
- Paraurethral (Skene's) glands
- Bulbourethral glands
- Greater vestibular (Bartholin's) glands
37
Male vs. Female Perineum
The perineum is the region surrounding the genitals and anus.
Please Review the Slide in Objective 13
38
Hormonal Control of Male and Female Gamete Productions
Gonadotropin releasing hormone (GnRH) from the hypothalamus directs the secretion of follicle-stimulating hormone (FSH) or luteinizing hormone (LH) from the anterior pituitary in both males and females.
- In males there are no follicles and no corpora lutea, so FSH acts as a stimulant to the spermatogenic cells and the sustentacular (Sertoli) cells of the testes.
- LH acts on the interstitial cells (Leydig cells) of the testes. These cells secrete the androgen testosterone, which may be converted to the active form dihydrotestosterone (DHT), a hormone that alters secondary sexual characteristics in the male.
- In the presence of FSH, testosterone and androgen-binding protein from the sustentacular cells, spermatogenesis is promoted. A negative feedback loop controlled by inhibin levels ensures that sperm are not over-produced.
39
Gametes Arise from Meiosis
Remember that meiosis is a reduction division where DNA content is reduced.
- In mitosis, DNA content doubles before division, so cells are diploid before and after division.
- In meiosis, DNA content is not doubled (no S phase) so DNA content is diploid before division and haploid after division.
40
Meiosis and Sexual Reproduction
- An important feature unique to meiosis is crossing over.
- In prophase of meiosis I, genetic recombination occurs (scrambling of the pieces of the chromosome)
- This ensures that you and your brother or sister are not twins born years apart.
41
Comparison of Mitosis and Meiosis
Somatic cells: all cells of the body except germ cells.
Dividing somatic cells undergo mitosis:
- DNA content doubled (4n) in S and G2 phase, but cells in all other phases are diploid (2n)
- mitosis is a cycle
Germ cells undergo meiosis:
- crossing over
- reduction division (gametes are haploid 1n)
- when haploid gametes (spermatozoon and oocyte) join at fertilization, a diploid zygote results
- meiosis is a "one-way street"
42
Correlation of Speratogenesis with Meiosis
In males, gametogenesis begins with a stem cell, spermatogonia. Spermatogonia undergo mitosis to produce a clonal population. As long as they stay near the basement membrane, they remain a stem cell and divide by mitosis.
If they leave the basement membrane, they begin differentiation and become primary spermatocytes which then undergo meiosis I to become secondary spermatocytes. In meiosis II, they split up their DNA to individual chromatids (one copy of DNA per cell), so they end up haploid, 1n spermatids.
The spermatids undergo further differentiation but no further changes in DNA content, so they end up as haploid, 1n spermatazoa.
43
Correlation of Follicular Development, Ovulation and Fertilization with Events in Meiosis
In females, oogonia undergo their last mitotic division in the female fetus. Meiosis I begins at that time, generating primary oocytes which lie suspended halfway through meiosis I for 10 to 50 years. Each month after menarche, 5-12 primary oocytes respond to the hormonal signals from the pituitary. In general, only one of these progresses all the way through meiosis I to form a secondary oocyte. The remaining genetic material is tossed in the garbage disposal.
The secondary oocyte then starts, but does not complete meiosis II. Meiosis II is only completed if a spermatozoon penetrates the secondary oocyte. If it penetrates the egg, the secondary oocyte completes meiosis II and becomes an ovum. At the same time, the excess genetic material is again tossed in the garbage disposal.
To summarize: meiosis I starts before birth, finishes between menarche and menopause. Meiosis II starts at ovulation, finishes at fertilization
44
Men vs Women in Production of Gametes
- Men continuously generate sperm (300M/day), 10T over a lifetime)
- Women have millions of germ cells before birth, hundreds of thousands at birth, tens of thousands at menarche, zero at menopause.
45
Puberty
Androgens (testosterone) and estrogens (estradiol) change structure of the embryonic and newborn brain.
During puberty, a burst of GnRH from the hypothalamus leads to increased LH and increase FSH which in turn increase androgens and estrogens.
Sex steroids further alter behavior and drive development of secondary sexual characteristics
- Male: body hair (especially chest & face, pubic region, arms and legs), deeper voice, more prominent Adam's apple, muscular and skeletal growth
- Female: body hair (especially pubic region, arms & legs), breasts, wider hips
46
Average Age of Menarche
Menarche: age of first menstrual flow. This age can usually be determined with some certainty (relatively sudden)
Menopause: age at end of menstrual flow. This age cannot be determined with certainty (gradual process, not a single event)
47
Is there an Ongoing Decline in the Average Age of Menarche?
Studies indicate average age of menarche may be declining since 1960. We have not idea what is causing the decline.
48
Sexual Arrousal
- There are at least two components to sexual arousal
- Scientists prefer to study the mechanical, reflexive basis for arousal and sexual response.
- Clearly, a less-studied spiritual dimension to sexual arousal exists.
- Sexual response is easier to study and easier to understand in males: penile volume measurement with plethysmograph is a reliable well-used measure of sexual arousal in males.
- In females, sexual response is difficult to study and physiologically complex: instrumentation used to measure female sexual response is complex and subject to arguments about relevantsy.
- "In comparison to men, much less is known about the vascular mechanisms involved in the female genital response....there is no functional equivalent of the hydraulic system of the male penis in the human vagina."
49
Structures which Produce Sexual Arousal in Females
- Clitoris and clitoral sheath
- Labial/introital area
- Anterior vaginal wall, Pubocervical (Halban's) fascia (connective tissue between trigone of bladder and vaginal wall) and vestibular bulb.
- "Grafenberg spot" ("G-spot"): paraurethral (Skene's) glands and erectile tissue in paraurethral area
- Cervix
- Urethra
- Perineum and Thigh
- Anus and rectum
50
Structures which Produce Sexual Arousal in Males
- Glans/corpus cavernosum of penis
- Scrotum
- Corpus spongiosum of penis
- Prostate
- Urethra
- Perineum and thigh
- Anus and rectum
51
Nerves of Sexual Arousal
- Incoming sensory information from structures which produce sexual arousal comes into spinal cord at S1-S4
- Outgoing striated motor and parasympathetic autonomic at S2-S4.
- Outgoing sympathetic autonomic at T10-L2
- The brain clearly influences this basic reflex pathway
52
Penile Erection Results from Congestion in the Corpora Cavernosa
Three processes, working together, cause penile erection:
1. Relaxation of smooth muscle in corpora cavernosa
2. Increase in arterial blood flow to penis
3. Restricted flow of blood out of penis
53
Nitric Oxide (NO) is a Neurotransmitter that Causes Vasodilation
- Mouse eNOS mutants: unable to make NO
- In these mice, mean arterial blood pressure (MABP) is significantly higher than in "normal" mice.
- Nitric oxide causes smooth muscle in blood vessels to relax
- This is why nitroglycerine is used in angina
54
Mechanism of Action of Viagra
- Nitric oxide (NO) causes dilation of smooth muscle in blood vessels
- As blood vessels dilate in corpora cavernosa, penile erection occurs
- Normally, the signaling molecule involved is inactivated by an enzyme called PDE5.
- Sildenafil (Viagra) blocks the PDE5 and prolongs smooth muscle relaxation.
55
Direct Imaging of Tissues of Female Sexual Arousal
Martin-Alguacil et al. have shown the neurochemistry of female clitoral erection is essentially identical to male penile erection
- NO causes dilation of vasculature which leads to erection of clitoris or penis
- Viagra, Levitra, and Cialis and other drugs act on this system
- These fail to produce a reliable sexual response in females; female sexual response is more than clitoral erection.
Suh et al. quantitatively imaged female genital and pelvic organs during arousal.
- clitoris and vaginal bulb are the only structures which demonstrate increased blood flow during sexual arousal.
For years, existence of the so called Grafenberg spot ("G-spot") has been controversial.
56
Kaplan Model of Female Sexual Response
Three stages to model: Stage 1 is added to Masters & Johnson model, 2&3 are similar to it:
1. Desire: when this system is active, a person is 'horny.' She may feel genital sensations, or she may feel vaguely sexy, interested in sex, open to sex, or even just restless.
2. Excitement
3. Orgasm: reflexive component, with reflexive pelvic muscle contractions
57
Models of Female Sexual Arousal
The female sexual arousal has been more difficult for scientists to model. Three competing models have emerged:
- Masters and Johnson (1966): based on "male", hydraulic model of sexual arousal
- Kaplan (1977): motivational model
- Basson (2001): women engage in sexual intercourse because of desire for emotional closeness (sexual neutrality)
58
Masters and Johnson Model of Female Sexual Response
- Focus of physiological response
- Based on innovative instrumentation
- Modification of male model of sexual response
- Ignores psychological and emotional aspects of female sexuality.
- Four sequential stages:
1. excitement
2. plateau
3. orgasm
4. resolution
59
Basson Model of Female Sexual Resonse
Just look at slide in Module 18
60
Nurses Sexuality Study
Sand and Fisher (2007)
Nurses were presented with all three models. About an equal number selected each model as most representative of their experience.
61
Coitus
- Coitus describes the process of sexual intercourse in humans
- The male penis is inserted into the female vagina
- When the male ejaculates, about 300M sperm released to begin journey in the females reproductive tract
- Very few, if any, of these will reach the secondary oocyte.
Fertilization usually occurs in the uterine tube
- only a few hundred sperm reach the uterine tube
- some complete the journey in a few minutes!
- spermatozoa may survive up to 3 days
- egg survives up to 2 days after ovulation
62
Sperm Capacitation
- In the uterine tube, sperm undergo capacitation
- Flagella beat more vigorously
- Plasma membrane of spermatozoa prepared to fuse with plasma membrane of secondary oocyte. Cholesterol, glycoproteins, and proteins scrubbed off spermatozoon's membrane
63
Slow Block to Polyspermy
Two layers surround oocyte
- corona radlata of granulosa cells (outer)
- zona pellucida, clear layer between granulosa cells and oocyte (inner)
Cortical Reaction:
- not well-studied in mammals, data from invertebrates
- Ca++ release from cortical granules in egg
- this lifts zona pellucida
- when contact between zona pellucida and oocyte is lost, sperm cannot penetrate the oocyte membrane
64
The First Week (Days 1-5): Fertilization to Implantation
Fertilization: sperm and egg unite
- this forms a diploid zygote
- it also starts our developmental "clock"
Two-cell stage
Four-cell stage
Morula ("raspberry")
Blastocyst (hollow ball of cells)
65
Day 6: Implantation
- Blastocyst makes contact with the endometrial wall
- Inner cell mass develops
- Problem: embryo is "foreign" tissue (half of genes not from mother)
- Implantation involves evading mother's defense mechanisms.
66
8-12 Days: Implantation
Upon implantation, the blastocyte divides into three parts:
- trophoblast (pink)
- inner cell mass which will become embryonic disc (blue)
- yolk sac (yellow)
The endometrial lining becomes the decidua
67
Day 16: Gastrulation
Gastrulation is a folding process that creates three germ layers in the embryo:
1. Ectoderm: becomes skin, teeth & jaws, posterior pituitary, and nervous system
2. Mesoderm: becomes connective tissue, muscles, and bones. Kidneys, heart, reproductive system, and gonads.
3. Endoderm: becomes gut tube, lungs, urinary bladder, thyroid, liver, pancreas, and lining of digestive tract.
Grastrulation is necessary for organogenesis to begin.
Clinicians classify cancer type based on embryonic origin of tissues.
- Carcinomas come from ectoderm
- Sarcomas come from mesoderm
68
Extraembryonic Membranes
- Implantation marks a change; embryo goes from being a free-livin zygote to being in a partnership with the lining of the mother's uterus (decidua).
- This means working with the maternal tissues to form a joint project - the placenta.
The placenta will:
- provide food to embryo
- provide oxygenated blood to embryo
- protect embryo from invaders with maternal antibodies
69
Extraembryonic Membranes Form the Placenta
Placenta is half embryonic and half maternal tissue. It begins with development of lacunae (open spaces) immediately after implantation. Chorionic villi are derived from the embryo:
- chorionic villus sampling (or chorionic villus biopsy) can be done as early as 8 weeks
- this allows detection of chromosomal abnormalities in the fetus with minimal risk (about 0.2% fetal mortality)
- Researchers estimate 50% of spontaneous abortions from nondisjunction syndromes (like trisomy 21)
- Trisomy 21 incidence increases exponentially with maternal age.
70
Chromosomal Abnormalities
Trisomy 21 and other chromosomal abnormalities result from nondisjunction.
- In meiosis, all four chromatids of 21 are supposed to arrive in different daughter cells
- In nondisjunction, both go to the same cell: one gamete gets two copies of chromatid 21
- At fertilization, the male contributes one copy, the female contributes two copies, so child gets three copies.
71
Placenta Blood Circulation
- maternal circulation
- maternal endometrial arteriole
- fetal blood vessels in chorionic villi
- umbilical vein
- embryo
- umbilical artery
- fetal blood vessels in chorionic villi
- maternal endometrial venule
72
Embryonic Folding Organogenesis Begins: Days 20-28
After gastrulation is complete (Day 16), development of organs can begin.
- The time when systems are sensitive is called the critical period. During this time, teratogens (substances which cause birth defects) can strongly influence development:
- rubella (german measles)
- cytomegalovirus
- toxoplasma (common in cat feces)
- radiation
- some chemicals
73
Embryonic Period
Is defined as fertilization (conception) to 8 weeks. After that time, the fate of most organ systems is set. The critical period for the development of most organ systems is during the embryonic period.
74
Fetal Period
Is defined as 9 weeks to birth. There is growth and development of the fetus, but most of the fetal period involves the organs carrying out a developmental plan set out during the embryonic period.
Normal gestation (time in womb) is 40 weeks.
75
Hormonal Changes During Pregnancy
Human chorionic gonadotropin (hCG)
- maintains corpus luteum
- corpus luteum continues to secrete progesterone and estrogens (does not become corpus albicans)
Relaxin:
- increases flexibility of pubic symphysis and aids in cervical dilation
Human chorionic somatomammotropin (hCS)
- alterations in maternal metabolism
Corticotropin-releasing hormone
- timing of birth
- increase in secretion of cortisol.
76
Hormone Levels vs Gestational Age
Spike of hCG is earliest. (Peak between 8-10 weeks)
Slow rise in progesterone and estrogens from maintenance of corpus luteum
- levels of estrogens rise steadily through pregnancy
- levels of progesterone rise steadily, but begin to drop slightly at the end of pregnancy.
77
Physiological Changes in Pregnancy: Cardiovascular System
Due to increased blood flow to placenta
- increased stroke volume, about 30%
- increased cardiac output, about 25%
- increased heart rate, about 10-15%
- increased blood volume, about 40%
- compression of inferior vena cava causes edema in legs and varicose veins
- compression of renal artery may lead to renal hypertension
78
Physiological Changes in Pregnancy: Respiratory System
- Increase in tidal volume, about 35%
- Decrease ERV, about 40%
- Increased ventilation, about 40%
- Increased total O2 consumption, about 15%
- dyspnea may result
79
Physiological Changes in Pregnancy: GI and Urinary Systems
GI System
- increased appetite
- decreased bowel motility leading to GI symptoms
Urinary System
- pressure on urinary bladder
- Increased GFR, about 40%
80
Stages of Labor
Dilation Stage:
- Onset of labor to dilation of cervix
- About 6-12 hours
- Regular contractions
- Usually rupturing of amniotic sac ("breaking water")
- Ends with complete dilation of cervix to 10 cm
Expulsion Stage:
- 10 minutes to several hours
- Ends with delivery of the baby
Placental Stage:
- 5-30 minutes or more
- Ends with expulsion of placenta ("afterbirth")
- Powerful uterine contractions expel placenta and help control bleeding
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Homeostatic Control of Labor
Rare homeostatic loop: Positive Feedback
- Input: stretching of cervix sends sensory information to brain
- Processing and output: brain interprets signal, releases oxytocin from posterior pituitary which causes uterus to contract more forcefully.
- Forceful contractions push baby further into cervix, increasing stretch
- Delivery of baby stops positive feedback loop
- Synthetic oxytocin (Pitocin) can be used to stimulate this homeostatic loop
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Suckling: Another Positive Feedback Loop
Curiously, there is another positive feedback loop associated with childbirth. This one is for suckling.
- Input: baby sucks nipple
- Processing and output: hypothalamus and posterior pituitary
- Releases oxytocin which in turn stimulates "milk let-down relex"
- Cycle continues until baby stops suckling
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Mammary Glands
Milk is produced in mammary glands. Is really modified sweat (sudoriferous) glands.
15-20 lobes separated by adipose (fat) tissue:
- structure maintained by suspensory ligaments (Cooper's ligaments)
- lobes have lobules
- lobules have alveoli
Contraction of myoepithelial cells ejects milk from alveoli. milk travels from:
- alveoli to
- mammary ducts to
- lactiferous sinusus to
- lactiferous ducts to
- nipple
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Birth Control
Probability of pregnancy from a single, unprotected act of intercourse is 2-4%.
- Probability is not the same throughout the menstrual cycle
- Peak probability is 8% on days 12-14
- Lowest probability is zero on days 1-2 (during menstrual flow)
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Male Birth Control Surgical Methods
Vasectomy: ductus deferens (vas deferens) is isolated and resected.
- Sometimes causes nerve damage
- May not be reversible
In a vasectomy, a small section of the as deferens is removed and the ends are tied
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Female Birth Control Surgical Methods
Tubal Ligation: uterine tubes (fallopian tubes) cut and tied off.
- Complicated, expensive surgery
- not reversible
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Birth Control Failure Rates
- Only truly reliable method is complete abstinence
- Surgical methods next best in terms of efficacy
- Female hormonal control methods also highly effective if used properly
- Intrauterine device (IUD) prevents implantation of zygote
