reproductive Flashcards
1
Q
function of the reproductive system
A
provides gametes for procreation of the species, mating, fertilization
2
Q
organs of the reproductive system
A
gonads
- pathway for gamete transport
- accessory organs and glands
3
Q
functions of gonads
A
organs which produce gametes
source of/secrete sex steroid hormones
4
Q
gonads of the male reproductive system
A
testis
5
Q
pathway of male reproductive system
A
testis -> epididymis -> vas deferens (ductus deferens) -> prostate gland -> accessory glands (seminal vesicle) -> urethra -> outside body
6
Q
urogenital
A
the organs concerned with reproduction and urinary excretion
7
Q
scrotal sac
A
outside the body
testes, blood vessels, nerves found here
- blood vessels allow for countercurrent blood flow to regulate temp
8
Q
spermatic cord
A
cord-like structure which passes through a slit in abdomen down into the scrotal sac
- a combo of the vas deferens, blood vessels, and nerves
- slit opening is in the inguinal canal and this continues down into the scrotal sac
9
Q
what is the physiological purpose of countercurrent blood flow
A
to house the testis at least 2 C below core body temp for optimal spermatogenesis (sperm production)
10
Q
descent of the testes
A
during development: the testes are first found in the abdominal cavity and descend to their final position in the scrotum
during the gestation period: at 8 weeks testes are high up, near kidneys
- first phase: btw 8-12wks testes will move down towards inguinal canal
- second phase: btw 7-9 months on intra-uterine life the testes pass through the inguinal canal and come to rest in the scrotum
at birth: the testes should have descended into the scrotal space and be housed in the proper manner
11
Q
testes
A
found inside scrotal sac
male gonads
divided into many compartments: seminiferous tubules (highly twisted or convoluted tubules - site of sperm production), rete testis. efferent ductules, epididymis
12
Q
seminiferous tubules
A
site of sperm production
sit on a basement membrane, contain a lumen and many cells called spermatogenic cells
spermatogenesis begins at puberty
13
Q
mumps
A
can cause the seminiferous tubules to become much smaller
- lumen becomes much bigger and the spermatogenic cells look very small
- the mumps pathogen can affect spermatogenesis process
14
Q
leydig cells
A
found in the connective tissues surrounding the seminiferous tubules
also called interstitial cells
produce testosterone
15
Q
sertoli cells
A
epithelial cells lining the circular seminiferous tubule
many functions including helping in the process of sperm development
laid out side by side and sit on a basement membrane
16
Q
smooth muscle cells
A
just outside the basement membrane
muscle-like or myoid cells
have contractile properties - help with peristalsis to move the sperm forward
17
Q
tight junctions
A
join epithelial cells
do not allow infections or other substances that might harm the growing sperm through
create and invisible ring-like structure through which nothing can permeate from the outside to the inside
important in forming blood-testis barrier: creates two physiological compartments
- basal compartment: from the basement membrane up to the tight junction
- luminal compartment: from the tight junction to the lumen (adluminal compartment)
18
Q
functions of sertoli cells
A
support sperm development “trophic role”
secrete luminal fluid for sperm housing
secrete androgen-binding protein - under the influence of follicle-stimulating hormone (FSH)
androgen buffer
helps maintain steady androgens in lumen
act as target cells for testosterone and fsh
secrete paracrine factors that stimulate spermatogenesis
secrete inhibin
hormone for negative feedback loop for fsh
phagocytosis of old and damaged sperm
site of immunosuppression (blood-testis barrier)
test
19
Q
testosterone
A
steroid hormone
synthesized from cholesterol
produced by adrenal cortex and the gonads, testes
20
Q
corticosteroid synthesis in the adrenal gland
A
an intermediary hormone, progesterone, is synthesized from cholesterol
depending on the enzymes present, progesterone is converted to mineralocorticoids, glucocorticoids, or androgens
21
Q
corticosteroid synthesis in the male gonads
A
progesterone is produced from cholesterol and the predominate enzymes channel the production towards testosterone
formation of mineralocorticoids and glucocorticoids is bypassed in the male gonads and more testosterone is produced
22
Q
testosterone receptors are primarily located in
A
intracellular locations
- testosterone is lipophilic and can diffuse across the membranes and bind to intracellular receptors to exert its function
- testosterone acts by influencing gene transcription and affecting protein synthesis to produce a response in the target cell
23
Q
production of male hormones in the leydig cells
A
cholesterol -> pregnenolone -> progesterone
24
Q
DHT
A
converted from testosterone by 5-alpha reductase
- maintains prostate gland and secondary male sexual characteristics
25
testosterone may be converted to
estrogen by aromatase
- occurs in liver, adipose tissue, brain, testes
26
plasma testosterone levels through life span
before birth (gestation period): high peak of testosterone, plasma testosterone levels then decrease until time of birth
neonatal (right after birth): high peak (short duration), plasma testosterone levels decrease for the duration of the childhood years
puberty until adulthood: plasma testosterone levels slowly increase through the stages of puberty and remain high during adulthood, around age 40 levels of testosterone start to decline (andropause)
27
sperm production
begins at the onset of puberty with a sharp wise until adulthood is reached
maintained unto age 40-45 and then production starts to decline - parallels the decline in testosterone levels
28
pulsatile secretion
at the onset of puberty in males, there is a pulsatile secretion of gonadotropin releasing hormone (GnRH)
occurs every 90 mins
called the pulse generator
pulsatile release of GnRH then acts on the gonadotropic cells of the anterior pituitary to cause the pulsatile secretin of hormones
29
why is pulsatile secretion necessary
with a constant release of GnRH, the cells of the anterior pituitary will not respond to GnRH, the receptors do not respond to constant levels of GnRH
anterior pituitary cells will then secrete LH and FSH in a pulsatile manner
30
high frequency pulses of GnRH =
predominant secretion is luteinizing hormone (LH)
31
low frequency pulses of GnRH =
predominant secretion is follicle stimulating hormone (FSH)
32
hypothalamic-pituitary-leydig cell axis
testosterone acts as a negative feedback regulator at both the hypothalamus and the anterior pituitary
- testosterone acts at the level of the hypothalamus and dampens the amplitude of this pulsatile secretion, resulting in lower amplitude of waves or decreases responsiveness due to a down regulation of receptors for GnRH at the level of the anterior pituitary
33
onset of puberty
secondary sexual characteristics
hair growth (pubic, beard)
deepening of voice
rapid growth in height
34
at puberty
pulsatile secretion of the pulse generator which induces pituitary-linked pulsatile release of lh and fsh, which causes more secretion of testosterone
increased secretion of testosterone initiates spermatogenesis
35
effects of androgens
stimulate spermatogenesis
promote development of secondary sex characteristics during puberty and maintenance of these characteristics in adult life (functions of testosterone and DHT)
increased sex drive
promote protein synthesis in skeletal muscle (anabolic effect)
stimulate growth hormone secretion, which permits bone growth during adolescence
promote development of male reproductive structures during embryonic life
36
spermatogenesis
formation of the male gamete or the sperm
37
mitosis
enlarge and spit a cell into 2 identical daughter cells that are genetically identical to the original cell
formation of sperm begins close to the basement membrane in the seminiferous tubule
- germ cells found close to the basement membrane
38
meiosis
each daughter cell receives half of the chromosomes; the chromosome number is reduced from the normal 46 chromosomes (2n/diploid) down to 23 chromosomes (n/haploid)
39
spermatogonia
original germ cells that a male child is born with, cells from which a sperm cell arises
spermatogonium (singular)
diploid or 2n number of chromosomes
40
steps to produce sperm
spermatogonium first divides by mitosis (occurs in basal compartment in btw two sertoli cells) - one of the cells produced remains a spermatogonium to ensure that numbers of spermatogonia are not depleted and reverses back to join the pool of spermatogonia
- the other cell is a "committed cell" (primary spermatocyte) that undergoes a structural differentiation and progresses on into the direction of formation of mature sperm, has diploid number of chromosomes
primary spermatocyte moves forward to the luminal compartment and meiotic division starts (produces two secondary spermatocyte) - chromosome number is halved
each secondary spermatocyte gives rise to two spermatids (4 spermatids produced)
spermatids must undergo differentiation to form the final sperm structure - spermatozoa
64 days from primary spermatocyte to spermatozoa
41
spermatogonia to primary spermatocyte occurs in
the basal compartment
42
primary spermatocyte moves to
luminal compartment
- tight junctions open allowing the primary spermatocyte move through to the next compartment
43
where do spermatozoa hide
create small little cavities in the luminal park of the sertoli cells to hide their heads to mature, conc of testosterone is high
44
spermatid
a circular cell containing a nucleus with half the number of chromosomes, many mitochondria, acrosomal vesicle
45
spermatid to spermatozoan
a flagella, or hair like structure, starts developing from inside the cell and protrudes outward
cytoplasm gets remodeled, circular spermatid begins to gain shape of sperm - some of the cytoplasm is shed and the mitochondria line up in the middle zone, which will become the neck piece of the sperm
approx 24 days
46
components of a sperm
head, mid-piece, tail
47
head
contains nucleus (chromosomes, genetic material) and acrosome (a vesicle positioned close of the plasma membrane at the tip of a sperm's head, contains enzymes necessary for fertilization, needed for crossing the egg's protective coat)
48
mid-piece
many mitochondria which generate ATP needed for movement of the tail
49
tail
whip-like movements propel sperm
50
immotile
incapable of movement and must reside in seminiferous tubule for about 20 days in order to gain full mobility
51
sperm maturation
as sperm are essentially immotile following spermiogenesis, fluid pressure generated by sertoli cells pushes the sperm forward towards the epididymis
sperm resides in the epididymis for 6-12 days where they undergo a process of maturation before they are capable of progressive motility and fertilization
sperm move to the vas deferens by the process of peristalsis where they are temporarily stored until ejaculation
52
gonadotropins
FSH, LH
53
FSH
stimulates spermatogenesis
54
LH
stimulates androgen secretion
55
inhibin
peptide hormone, regulates the axis at the level of the anterior pituitary to decrease secretion of fsh, does not act at the hypothalmic level
56
negative feedback control of of LH
testosterone released from leydig cells inhibits the secretion of lh at the level of the anterior pituitary and at the level of the hypothalamus
57
negative feedback control of fsh
release of fsh from the anterior pituitary is inhibited by inhibin released from sertoli cells
testosterone acts on seroli cells to stimulate spermatogenesis
fsh stimulates sertoli cells to release inhibin and androgen-binding protein
- androgen binding protein binds testosterone to keep the conc of testosterone high in the lumen of the seminiferous tubule
58
fluid comes from
seminal vesicle - provides bulk of fluid volume
prostate gland - help in maintaining the health of the sperm
bulbourethral gland
59
functions of seminal fluid
dilution of sperm
provides energy - fructose
formation of semen clot - fibrin like protein or clotting protein that helps in the formation of the semen plug
60
3 accessory glands
seminal vesicle, prostate gland, bulbourethral glands
61
seminal vesicle
secrete alkaline fluid with fructose, enzymes, and prostaglandins
- enzymes necessary to produce semen clot
- alkaline to balance the highly acidic environment in the female genital tract
- prostaglandins function primarily to cause contraction of the female tract for sperm to move forward
62
prostate gland
secrete citrate and enzymes (PSA)
- citrate provides energy for sperm
- PSA is a proteolytic enzyme (protease) that breaks down the protein in the seminal clot making the semen more fluid
- hypertrophy - a biomarker for cancer, PSA is a biomarker for detection of abnormal growth of prostate tissue
63
bulbourethral glands
secrete viscous fluid with mucus
64
male sexual response is controlled by
the autonomic nervous system, involves spinal reflexes
65
erection phase
mainly controlled by the parasympathetic nervous system
under resting condition, when the penile tissue is not undergoing erection, the dominant control is by the sympathetic nervous system
parasympathetic nervous system acts on the vascular smooth muscle to cause relaxation of the blood vessels; inc blood flow into the tissue causes an erection
66
emission phase
sympathetic division = thoracolumbar division
sympathetic nervous system (SNS) acts on the muscular tissue of the prostate gland, the muscular tissue around the vas deferens and the muscular tissue of the seminal vesicle
SNS causes smooth muscle contraction, leading to the movement of sperm from the vas deferens with mixing of the seminal fluid into the common urogenital tract
67
ejaculation phase
rapid contraction of skeletal muscle for semen expulsion (somatic control)
this muscle contraction allows for ejaculation of semen to the outside of the body
68
parasympathetic control during erection
activity in the sympathetic neurons decreases
activity in the parasympathetic neurons to the penile structure increases, causing relaxation of the smooth muscle which inc blood flow
activation of the parasympathetic nerve causes the release of nitric oxide
- nerves to the erectile tissue releases NO
- NO stimulates production of cGMP
- inc cGMP can act on smooth muscle of blood vessels to cause vasodilation
- cGMP is broken down by the enzyme phosphodiesterase, once cGMP is broken down, vasodilation does not continue, there is no blood flow and the erection ceases
69
erectile dysfunction
treated with viagra (sildenafil)
viagra acts as an inhibitor of the enzyme phosphodiesterase
works by inhibiting phosphodiesterase actions of cGMP in and around the smooth muscle are prolonged, cGMP is not broken down when phosphodiesterase is inhibited by viagra maintaining the vascularization and the erection
70
fallopian tube
site where fertilization occurs
only a very low number of sperm actually reach the fallopian tube (~100) due to the high acidity, or pH, within the female reproductive tract that affects survival of the sperm
71
two processes involved in final maturation of sperm
capacitation and the acrosome reaction
72
capacitation
occurs as sperm move through the female reproductive tract
a physiological or functional maturation process of the sperm cell membranes
receptors are made available through the removal of the glycoprotein layer
the area of the acrosomal cap is altered during capacitation so that the acrosomal reaction can take place
membrane alterations also alter the motile properties of the sperm - tail movements change from wave-like to whiplash: hyperactivity
73
acrosomal reaction
female oocytes have an outer layer called the zona pellucida
sperm must penetrate the zone pellucida to gain access to the egg
binding of the sperm with the zona pellucida triggers the acrosome reaction
the acrosomal reaction involved the progressive fusion of the acrosomal membrane with the plasma membrane of the sperm in many locations, creating many openings or pores through which the acrosomal enzymes or contents can be released by exocytosis
the enzymes will then allow the sperm to digest a path through the zona pellucida to the oocyte to allow fertilization to occur
74
female gonads
ovaries
75
reproductive tract
uterus, uterine tubules, vaginal canal
76
uterine tubes
aka fallopian tubes, oviducts
transport ova from the ovaries to the uterus
fimbria are finger-like projections which stick out and sit very close to the ovary - contain small hair-like cells, or ciliated cells, which can actively move; once the female egg or gamete is released from the ovary it is captured by the fimbriae and the infundibulum, a cup-shaped structure
site of fertilization
77
movement of ovum through uterine tube
initially - peristaltic contractions
mostly - ciliary actions
duration - 4 days to uterus
78
3 layers of the uterus
perimetrium
myometrium
endometrium
79
perimetrium
outer layer
epithelial cells and connective tissues, providing a protective covering
80
myometrium
middle layer
myo = muscle
thickest layer composed of smooth muscle
81
endometrium
inner layer
layer of epithelial cells
layer of connective tissue
numerous glands which contain things such as glycogen
goes through a cyclic change every month under the influence of hormones
82
site of fetal development
body - upper portion
cervix - canal leading to vagina
cervix + vagina - birth canal
83
follicles
densely packed shells of cells containing an immature oocyte at all stages prior to ovulation
84
ovary
covered by a capsular structure
contains follicles, suspended in a background material of connective tissue
contains blood vessels
contains follicles in different stages of growth
- primordial follicles are very small
- primary follicles are in a medium stage of growth
- mature follicles are in a larger stage of growth with a fluid filled cavity
- follilces from which the eggs have been released are called the corpus luteum
85
corpus luteum
formed in the ovary at the site of a follicle, or sac, which has matured and released its egg
remains for a while and acts as an endocrine gland
86
3 cycles in the female body
hormonal cycle, ovarian cycle, uterine cycle
87
ovarian cycle overview
looks at the development of an ovarian follicle, rupture of that follicle with discharge of the ovum, and formation and regression of a corpus luteum
- changes in the ovarian cycle are due to the hypothalamic-pituitary-ovarian axis
- accompanied by cyclic changes in the secretion of estrogen and progesterone, which cause changes in the endometrium of the uterus during a menstrual cycle
88
uterine cycle overview
also called the menstrual cycle
cyclic operation of the uterus whose function is to prepare the lining of the uterus, called the endometrium, to receive a possible embryo in case of fertilization
89
hormonal cycle overview
the ovarian and uterine cycles controlled by hormones
cyclic changes in the secretion of follicle stimulating hormone and luteinizing hormone secreted from the anterior pituitary cause ovarian changes during a monthly cycle
90
ovarian cycle
2 phases
first phase: follicular phase - 14 days, associated with development of the follicles in which the eggs are growing, duration may be variable
ovulation, or release of the egg, occurs on the 14th day
second phase: luteal phase - the next 14 days of the cycle, duration usually constant
91
uterine cycle
3 phases - menstrual, proliferative, secretory
menstrual phase: day 1 - first day of menstrual bleeding or shedding the surface of the endometrial layer; 4-5 days of menstrual bleeding
proliferative phase: phase of development or growth, layers become wider in the endometrium, and the blood vessels are growing, functional layer of the endometrium develops
- menstrual and proliferative are at the same time as the follicular phase of ovarian cycle
secretory phase: further vascularization and development of uterine glands
- same time as luteal phase of ovarian cycle
92
oogenesis
refers to the development of the female gamete, or the oocyte
93
folliculogenesis
maturation of the ovarian follicle
94
primordial follicles
single oocyte surrounded by a single layer of epithelial cells
95
granulosa cells
single layer of cells
96
primary oocyte stage
primary oocytes begin with the primordial follicle stage
- epithelial cell origin: can multiply and divide, undergo mitosis and form several layers of granulosa cells while the oocytes are developing
- as the follicle grows my mitosis of granulosa cells, connective-tissue cells surrounding the granulosa cells differentiate and form layers knows as the theca
97
folliculogenesis
describes the progression of a number of small primordial follicles into large preovulatory follicles that occurs in part during the menstrual cycle
98
primary follicle stage
larger than primordial follicle
proliferation, or growth
granulosa cells secrete proteins and glycoproteins which form a thick layer of material that is deposited right around the oocyte - zona pellucida
99
preantral follicle
mitosis of granulosa cells results in many layers of granulosa cells around the oocyte
- connective tissue cells surrounding the granulosa cells differentiate and become the early theca cells
- theca cells have two regions: internal and external region
- do not have an antrum (fluid filled space)
100
early antral follicles
a fluid filled space known as the antrum begins to form
101
mature follicle
major growth is due to growth of antral space
granulosa cells just outside the oocyte undergo changes
- granulosa layers just outside the oocyte are suspended in a bridge-like fashion from the rest of the granulosa cells - known as cumulus oophorus
102
corpus albicans
empty follicle which function as a temporary endocrine structure will die off
a dying structure which ultimately forms scar tissue will dissipate along with neighboring connective tissue
103
selection of a follicle
10-25 follicles are randomly selected
the follicle that secretes the highest amount of estrogen of the 10-25 will become the dominant follicle
the remainder will die off (atresia or apoptosis)
104
hormonal cycle
estrogenic phase: first 14 days of the hormonal cycle - predominant hormone effect is from estrogen
progestational phase: after ovulation - predominant hormone effect is from progesterone
105
fsh
acts on the granulosa cells to inc the mitotic index, or the rate of mitosis, causing the granulosa cells to multiply and become bigger
106
role of theca cells during early to mid-follicular phase of the ovarian cycle
theca cells have receptors for LH, FSH causes an upregulation of receptors for LH on the theca cells
- lh acts on its receptors on the theca cells to stimulate the theca cells to secrete androgens
theca cells convert cholesterol -> progesterone -> androgens
- androgens permeate the granulosa cells
- inside the granulosa cell, androgens are converted to estrogen - some moves into blood stream, some stays in antrum, starts influencing the immediate neighborhood
107
role of granulosa cells
cells that make estrogen but cannot make estrogen beginning with cholesterol
- FSH upregulates an enzyme (aromatase) that converts androgens -> estrogen in the granulosa cells
- the granulosa cells get the androgens from the theca cells
108
in the late follicular phase
the rise in estrogen causes granulosa cells to start developing LH receptors
- under the influence of LH, the granulosa cells can now convert cholesterol -> progesterone
- small rise in progesterone occurs towards the late follicular phase
- as the corpus luteum phase begins, large amount of progesterone is made due to the granulosa cells expressing LH receptors and converting cholesterol to progesterone under the influence of LH binding to its receptors
109
meiosis 1
becomes arrested a 7 months of fetal life through birth until puberty
- monthly from puberty to menopause the dominant follicles is selected and that oocyte is released from arrest and completes its meiosis 1 division
110
meiosis 2
the second meiotic division occurs after ovulation and only if the secondary oocyte is fertilized by a male gamete
111
net result of oogenesis
production of 1 egg with n number of chromosomes
112
net result of spermatogenesis
production of 4 spermatozoa with n number of chromosomes
113
the uterine changes during a menstrual cycle are caused by changes in plasma concentrations of
estrogen and progesterone
114
day 1-5
menstrual phase
the epithelial lining of the uterus degenerates resulting in menstrual flow
115
day 5-14
proliferative phase
under the influence of estrogen, the endometrial lining starts growing and blood vessels become enlarged, grow and branch out
116
day 14
ovulation
after ovulation, glands begin to secrete and become larger
117
at the beginning of the cycle
estrogen has an inhibitory effect (negative feedback) on gonadotropin secretion when plasma estrogen levels are relatively low, as during the early and mid-follicular phase
- the inc in FSH secretion that occurs as one cycle ends and the next begins produces a stimulation and a group of preantral and early antral follicles enlarge
- inc in FSH is due to dec progesterone, estrogen and inhibin levels
118
during early proliferative phase
estrogen slowly being inc - comes from growing follicles
- there is a very quick rise in estrogen levels before day 14 bc one follicle grows and secretes a lot of estrogen
estrogen then starts decreasing before lh peaks
119
LH surge
rapidly increasing estrogen causes a sharp rise in LH
- estrogen at high levels causes a positive feedback effect on the gonadotropins
causes ovulation -> follicle ruptures and oocyte completes its 1st meiotic division
120
why do the gonadotropins, LH and FSH, remain low all throughout the luteal phase
in the presence of estrogen the high plasma conc of progesterone causes a decrease in the secretion of the gonadotropins by the pituitary gland
- estrogen and progesterone produce a negative feedback effect to suppress lh and fsh
- soon after ovulation, the corpus luteum begins to release large amounts of progesterone and from this point the progesterone pattern is similar to that of estrogen
121
where does estrogen come from
estrogen levels inc during the late follicular phase as the dominant follicle secretes mor and more estrogen
122
menstrual phase
day 1-5
shedding of uterine lining
tissues die and slough into vagina causing menstrual flow
hormonal control
- triggered by dec estrogen and progesterone (when corpus luteum degenerates)
123
proliferative phase
uterus prepares for fertilized ovum
- endometrial lining develops
- endometrial layer grows
- endometrial glands enlarge
- smooth muscle layer thickens (myometrium)
- cervical glands secrete a thin mucus
hormonal control: estrogen stimulate development of uterine lining
124
secretory phase
endometrium prepares for implantation
- blood supply inc
- glands enlarge and secrete glycogen-rich fluids
- cervical secretions more sticky forming a plug
hormonal control: progesterone (and estrogen)
125
gestation
the whole process of pregnancy
- the length of time of intrauterine fetal development (9 months)
126
embryo
an organism during the early stages of development
in humans first 2 months
127
fetus
describes a developing human from 2 months until birth
128
site of fertilization
the female uterine tube or fallopian tube or oviduct
129
why do only several hundred sperm make it to the uterine tubes
damage due to the acidic environment in the female tract
loss of sperm from the female reproductive tract due to leakage from the cervix
loss of energy
130
capacitation
the process by which the previously regular wavelike action of the sperm's tail is replaced by a more whiplike action that propels the sperm forward in stronger surges and the sperm's plasma membrane becomes altered, or slightly unstable, so that it will be capable of fusing with the surface membrane of the egg
131
zone pellucida
a thick protein layer suurounding the ovum
132
polyspermy
an egg that has been fertilized by more than one sperm
- not favored and is prevented to maintain the diploid chromosome number
133
pronuclues
either of a pair of gametic nuclei before their fusion leads to the formation of the nucleus of the zygote
- female pronucleus: female chromosome content surrounded by a distinct membrane
- male pronucleus: male chromosome content surrounded by a distinct membrane
134
events of fertilization
many sperm bind to receptors (glycoproteins) on the zona pellucida -> binding to receptors triggers the acrosomal reaction -> plasma membrane of the sperm head is altered so that the acrosomal enzymes are now exposed to the outside, or to the zona pellucida -> enzymes digest a path through the zona pellucida -> first sperm to penetrate the zona pellucida and reach the egg's plasma membrane fuses with the membrane
- egg releases the contents of the secretory vesicles:
sperm binding to the zona pellucida causes a change in membrane potential which causes the release of the vesicle content into the space btw the egg plasma membrane and the zona -> enzymes enter the zone pellucida and begin hardening the entire zona pellucida -> blocks other sperm trying to get in and channel through the zona pellucida layer
following binding of sperm to egg plasma membrane -> sperm is drawn into the egg -> egg completes the second meiotic division -> nuclei of the sperm and egg unite -> fusion of the two nuclei occurs forming a zygote
enzymes from the egg are activated as soon as the sperm binds to the zona pellucida -> these enzymes are required for the cell division and embryogenesis -> zygote can start the process of mitosis
135
block of polyspermy
change in membrane potential
release of contents from cortical granules
enzymes enter and harden zona pellucida
enzymes inactivate sperm binding receptor
136
what happens to the oocyte during fertilization
fusion of sperm and oocyte stimulates second meiotic division of oocyte
oocyte converted to a fertilized ovum
sperm plasma membrane disintegrates
chromosomes from sperm and ovum migrate to center
dna replicated -> zygote
137
morula
contains many cells
zona pellucida intact
division from early cleavage to the morula is known as cell cleavage - during cleavage the number of cells inc but these is no overall inc in the size of the structure or no overall cell growth
cells at the morula stage are totipotent - have the capacity to develop into a complete individual; cells can differentiate into any structure from this point on
16-32 cells
develops into the blastocyst
138
twins
division of totipotent morula cells results in identical twins
fertilization of two oocytes (released during the same cycle) results in non-identical twins
139
blastocyst
4-5 days after fertilization
cells lose their totipotentiality and begin to differentiate
no zone pellucida
outer cell layer = trophoblast - will become fetal placenta
inner cell mass - will become embryo, when the inner cell mass is pushed to one side of the blastocyst, a fluid filled cavity called the blastocoel is formed
140
implantation
cell divisions and the formation of the morula coincides with the secretory phase of the uterine cycle - glands in uterus secrete a glycogen-rich fluid
happens 6-7 days after fertilization
- blastocyst will anchor itself to the wall of the endometrial lining with the side containing the inner cell mass positioned against the endometrium - trophoblast cells which are closer to the inner cell mass are very sticky
- this stimulates proliferation of the trophoblast cells which divide into two parts: syncytiotrophoblast, cytotrophoblast
141
syncytiotrophoblast
fused layer
some of the outer trophoblast cells enter deep into the endometrial layer and start diving and become fused; they form a syncytium (meaning there are multiple nuclei but no cell membranes)
142
cytotrophoblast
trophoblast layer which is closest to the inner cell mass becomes the cytotrophoblast; these cells release or secrete the early hormones for the growing embryo
143
decidua
the endometrium during pregnancy
144
decidual response/reaction
when the fused syncytiotrophoblast layer is forming and gradually penetration into the endometrial layer, all the blood vessels that are around the endometrial layer start branching out and move close to this blastocyst
blood vessels and gland-like structure which have glycogen provide the developing embryo with nutrition
the decidual response is a response of the endometrial tissue where there is the appearance of blood vessels and glycogen-secreting glands for the newly anchored or implanted embryo or blastocyst
145
two components of the placenta
fetal, maternal
146
fetal placenta
develops from the same blastocyst that forms the fetus
147
maternal placenta
develops from the maternal uterine tissue
148
contents of the placenta
amniotic cavity filled with amniotic fluid
amnion - inner most membrane that encloses the embryo - fused with the chorion - outer layer
149
chorion
the embryonic derived portion of the placenta
made of trophoblasts
invades the maternal endometrium and develops finger-like projections called chorionic villi
on the maternal side the endometrial tissue immediately surrounds the chorionic villi; space develop right around the chorionic villi which are filled with maternal blood
chorionic villi allow the transfer of materials btw the maternal blood and the fetal blood
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umbilical artery carries
deoxygenated, nutrient-depleted blood from the fetus to the placenta
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umbilical vein carries
oxygenated, nutrient-rich blood from the placenta to the fetus
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functions of the placenta
a temporary endocrine gland
an exchange tissue - respiratory gases, nutrients, waste products
a filter/immunological barrier
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human chorionic gonadotropic hormone (hCG)
at about 2 months there us a very sharp peak of hCG which then decreases
- low constant level throughout pregnancy
released from the chorionic layer in the placenta
stimulates the female gonads to secrete hormones
helps maintain the corpus luteum in the early part - corpus luteum survives if conception occurs
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human placental lactogen (hPL)
profile is similar to what is seen with estrogen
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major hormones of the placenta
hCG: released from the chorionic layer, maintains the corpus luteum in the early parts of pregnancy (first 2-2.5 months)
hPL: growth hormone-like and anti-insulin like actions in the mother, insulin stimulates glucose uptake from the blood by cells in the body (lower plasma levels of glucose); will not allow glucose to be taken up into the tissues to keep levels of glucose and nutrients in the mother's plasma high; helps the fetus take up more glucose
progesterone: released from placenta after corpus luteum degenerates; decreases uterine contractions; inhibits secretion of the gonadotropins LH and FSH from the anterior pituitary (no selection of follicles, no menstrual cycles); stimulates growth of the alveolar ducts; causes cervical glands to secrete a sperm-unfriendly mucus
estrogen: released from placenta after corpus luteum degenerates; causes growth of the myometrium; causes growth of mammary ducts; inhibits LH and FSH at the level of the anterior pituitary
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steroid hormones
cholesterol -> progesterone -> androgens -> estrogen
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parturition
during childbirth, weak uterine contractions develop slowly -> occur infrequently and push the fetus forwards to the cervix -> pressure of the fetus against the cervix sends a positive message to the posterior pituitary to release oxytocin -> oxytocin acts in the uterine myometrial layer, binding to the tissue and casuing more contractions
- positive feedback loop
- this continues until the contractions are strong enough to cause the fetus' head to come out and the process of parturition takes place
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hormones involved in parturition
myometrial contractions: inc by estrogen, prostaglandins, oxytocin, and stretch from the fetus' head pushing down on the cervix
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cervical ripening
process that prepares the tissue in such a way that the cervix becomes soft, making it easier for expansion
- due to prostaglandins and relaxin
- relaxin relaxes the cervix
- relaxin comes from corpus luteum in the earlier months of pregnancy and later the placenta
- progesterone inhibits cervical ripening
- progesterone and relaxin inhibit contraction in the mother's body during pregnancy when it is not yet time to deliver
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mammary glands
contain mammary alveoli - site of milk production and storage in the mammary gland; clustered into groups called lobules and a group of lobules is called a lobe
birth to puberty: breast tissue has rudimentary ducts, few if any alveoli
puberty: estrogen causes ducts to start growing and branch out; progesterone causes growth of the alveolar tissues; fat is deposited around alveolar space
pregnancy and lactation: estrogen, progesterone, prolactin and hPL, are required; prolactin released from the anterior pituitary. promotes lactation; oxytocin required for milk ejection or milk let-down from the breast tissue
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lactogenesis
process by which cells in the breast tissue start making milk
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galactopoiesis
process of maintenance of lactation while the mother is breast feeding; requires prolactin
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alveolar epithelial cells
synthesize milk but they cannot release the milk protein into the space outside, or the lumen, to be carried away in the duct
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myoepithelial cells
muscle-like; have contractile properties; contract to expel the milk
- have receptors for oxytocin: at the time of breast feeding or hearing the cries of the baby, oxytocin leaves the posterior pituitary, acts on its receptors on the myoepithelial cells and causes contraction; milk that is already synthesized in the epithelial cells is released into the lumen and then into the duct
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suckling
activates tactile receptors (mechanoreceptors) in the mother's breast tissue -> activates the hypothalamus -> stimulates the neurosecretory cells of the posterior pituitary to secrete oxytocin -> oxytocin causes contraction of the myoepithelial cells of the breasts and milk is ejected
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dopamine
inhibits prolactin secretion by the anterior pituitary cells
- activation of the hypothalamus by suckling decreases dopamine secretion (this removes the inhibition on prolactin secretion)
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how is the sex of a person determined
male characteristics must be imposed on the fetus by the testicular hormones testosterone and AMH (antimullerian hormone) and that in the absence or inactivity of these hormones, the fetus becomes phenotypically female
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gonadal sex
whether the gonads are female or male
determined by chromosomal sex
the male and female gonads develop from the same site, called the urogenital ridge or the gonadal ridge
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klinefelter's syndrome
male XXY
infertile - spermatogenesis does not occur
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turner's syndrome
XO
streaked ovaries - do not look round but are a flattened structure
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sexual differentiation
the process of development of the differences between males and females from an undifferentiated zygote
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double genital duct system
in males -> Wolffian ducts persist and the Mullerian ducts regress
in females -> Mullerian ducts persist and the Wolffian ducts regress
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mullerian-inhibiting hormone (MIH)
testes secrete mih from sertoli cells
in males -> mih causes regression of the mullerian duct; the wolffian duct persists (due to the presence of testosterone)
in females -> do not have mih so the mullerian duct persists and wolffian ducts regress (due to lack of testosterone)
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what are the male internal organs or genitalia
all the tracts (epididymis, vas deferens, seminal vesicles and ejaculatory ducts) and the testes
- testosterone secreted from leydig cells causes development of the male internal genitalia
- testosterone is converted to dihydrotestosterone (DHT) which causes masculinization of the male external genitalia (penile structure and prostate)
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what are the female internal genitalia
mullerian duct will grow to become the female internal genitalia - uterine structures, fallopian tubes, the cervix, the vaginal space
- as DHT is not present, all the external tissue structures do not develop into a male structure by default
- all the differentiation occurs by default with some modulation due to the presence of ovarian factors, such as estrogen
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congenital adrenal hyperplasia
genetically female (XX) but phenotype is male
- problem with adrenal steroid secretory pathway
- too much androgen production in the fetal stage causes the development of the male external appearance
- dec cortisol -> inc ACTH -> adrenal androgens -> muscularization of external genitalia
- infertile
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androgen insensitivity syndrome
genetically male (XY) but phenotype is female
- tissues in the body were unresponsive to the male hormone testosterone during development
- the testes developed correctly and the sertoli cells secreted mih
- mih caused regression of the mullerian duct and no female internal structures develop
- leydig cells of the testes secrete testosterone but the wolffian ducts are not responsive to testosterone
- develop female external genitalia
- no internal male or female structures, therefore infertile
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puberty
a period of time, lasting a few years, when a child becomes sexually mature
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what triggers the onset of puberty
increased secretion of GnRH results in more LH and FSH secreted from the anterior pituitary, which causes more sex steroids to be released from the gonads
- genetic influences and environmental influences alter GnRH levels
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hypothalmic-pituitary-gonadal axis in the young child
in a child who has not reached puberty, the axis is normally dormant because centres in the hypothalamus are suppressed (central suppression; low levels of GnRH, LH, FSH)
at this stage, low levels of sex steroids provide a strong negative feedback to keep the higher centres suppressed
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hypothalamic-pituitary-gonadal axis at the time of puberty
during puberty the hypothalamic area begins to come out of the central suppression
- the hypothalamus begins to generate high frequency, pulsatile secretion of GnRH
- kisspeptin: a neuropeptide which acts in the cells that release GnRH in the hypothalamus; a cue triggers changes in the cells that cause the production of kisspeptin at the time of puberty
- adipose tissue: a source of the hormone leptin; leptin acts in the hypothalamus on the cells which release kisspeptin; important for regulating the pulse generator
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andropause
in males, start anywhere from age 40 onwards
lowering of the male hormone
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menopause
in females
reproductive status comes to a halt
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hormonal changes in menopause
- follicular depletion occurs throughout life by apoptosis
- dec follicle numbers and dec responsiveness to gonadotrophs -> dec estrogen and dec inhibin
- ovulation becomes irregular then cease
- dec estrogen, inhibin, and progesterone removes negative feedback inhibition: FSH and LH levels inc, inc FSH:LH ratio
- many menopausal problems die to dec estrogen
