4.1 sexual reproduction in humans Flashcards
1
Q
what does the male reproductive system include?
A
- seminal vesicle
- prostate gland
- epididymis
- vas deferens
- testis
- urethra
- seminiferous tubules
2
Q
what does the seminal vesicle do in the male reproductive system?
A
produces secretion, to aid sperm mobility
3
Q
what does the prostate gland do in the male reproductive system?
A
produces alkaline secretion to neutralise acidity of urine
4
Q
what does the seminiferous tubules do in the male reproductive system?
A
produces spermatozoa
5
Q
each testi contains around one thousand _______ _____ where spermatozoa are formed
A
seminiferous tubules
6
Q
spermatozoa collect in the _____ where their mobility improves
A
epididymis
7
Q
- seminal vesicles secrete mucus and prostate fluid mixes with spermatozoa during ejaculation
- these fluids maintain:
A
- sperm mobility
- provide nutrients e.g fructose
- and are alkaline which neutralises acidity found in urine and the vagina
- (the resultant fluid containing sperm is called semen, and leaves by the urethra)
8
Q
it’s prostate gland NOT prostrate
A
9
Q
what does the female reproductive system include?
A
- ureter
- uterus
- oviduct/fallopian tube
- ovary
- cervix
- bladder
- urethra
- vagina
- vulva
10
Q
how many ovaries are there in the female reproductive system?
A
2
11
Q
where do oocytes mature from germinal epithelial cells in the female reproductive system?
A
in the ovaries
12
Q
each month, one secondary oocyte is released during _____ from the surface of one of the ovaries
A
ovulation
13
Q
- cillia lining the _____ ____ waft the secondary oocyte along
A
- fallopian tube (oviduct)
14
Q
what does the uterus consist of?
A
- a thin outer layer called the perimetrium
- inside this is the muscle layer or myometrium
- the endometrium is the innermost layer consisting of a mucous membrane which is well supplied with blood (this layer is shed each month during the menstrual cycle if an embryo fails to implant)
15
Q
what is gametogenesis?
A
the production of gametes through a series of mitotic and meiotic divisions in the testis and ovaries
16
Q
sperm is produced by _____
A
spermatogenesis
17
Q
eggs are produces by ______
A
oogenesis
18
Q
as you move from the outside towards the centre of the seminiferous tubule, the cells become (more/less) mature?
A
more
19
Q
germinal epithelium cell —>
spermatogonium —>
primary spermatocyte —>
secondary spermatocytes —>
spermatids —>
spermatozoa
A
20
Q
diploid germinal epithelial cells divide by means of (mitosis/meiosis) to produce diploid ____
A
- mitosis
- spermatogonia
21
Q
primary spermatocytes (2n) divide by means of (meiosis I/ meiosis II /mitosis) to produce _____
A
- meiosis I
- secondary spermatocytes (n)
22
Q
secondary spermatocytes (n) undergo (mitosis / meiosis I / meiosis II) to make ____
A
- meiosis II
- spermatids (n)
23
Q
spermatids (n) differentiate and mature into _____
A
spermatozoa (n)
24
Q
what cells provide spermatozoa with nutrients and protect them from the male’s immune system?
A
sertoli cells
25
what cells secrete testosterone?
interstitial cells
26
diploid = 2n
haploid = n
(where n is number of chromosomes)
27
ovulation is the release of a secondary oocyte NOT an ovum
28
what does an ovary contain?
- primary follicle
- developing secondary follicle
- stroma
- Graafian follicle
- secondary oocyte released at ovulation
- corpus luteum
- degenerating corpus luteum
29
before birth, germinal epithelial cells divide by means of mitosis to produce _____ and then _____
- oogonia (2n)
- primary oocytes (2n)
30
primary oocytes are surrounded by germinal epithelial cells which form the _______
primary follicle
31
primary oocytes begin (mitosis/meiosis) but stop at what stage?
- meiosis I
but stop at prophase I
(division resumes from puberty)
32
each month, a primary oocyte continues meiosis I to produce :
- a secondary oocyte
- and a polar body
(both of which are haploid)
33
the primary follicle also develops into a secondary follicle, which matures into a ______?
Graafian follicle
34
what does the Graafian follicle do?
- migrates to the surface (of the ovary) and bursts releasing the secondary oocyte (ovulation)
35
the secondary oocyte undergoes (mitosis / meiosis I / meiosis II), stopping at what stage?
meiosis II
- stopping at metaphase II
36
if a sperm meets the secondary oocyte and enters, meiosis II is completed resulting in the production of:
- the ovum (n)
- and second polar body (n)
37
the sperm pronucleus can now fuse with the ovum pronucleus to produce a diploid ____
zygote
38
following fertilisation, the Graafian follicle becomes the ______ ____ and produces progesterone
corpus luteum
(if no fertilisation occurs it regresses)
39
germinal epithelium (2n) —mitosis-> spermatogonium (2n) —mitosis-> primary spermatocyte (2n) —meiosis I-> secondary spermatocytes (n) —meiosis II-> spermatids (n) —maturation-> spermatozoa (n)
40
germinal epithelium (2n) —mitosis-> oogonium (2n) —mitosis-> primary oocyte (2n) —meiosis I-> (first polar body) + secondary oocyte (n) —meiosis II-> (secondary polar body) + ovum (n)
41
what does a spermatozoon (single spermatozoa) include?
- acrosome
- nucleus
- mid piece (with mitochondria)
- tail
42
each sperm head is approximately 5 µm long with a 50 µm tail
43
within the head is a haploid nucleus and the acrosome
44
what does the acrosome contain/do?
- contains proteases to digest the cells of the corona radiata and zona pellucida (on female secondary oocyte)
45
why does the mid piece of a spermatozoon contain many mitochondria?
as they provide ATP for movement
46
how does the tail of a spermatozoon move?
- in a circular wave motion to propel itself forwards
47
what does a secondary oocyte include?
- cytoplasm
- pronucleus
- zona pellucida
- corona radiata
48
a typical ovum measures 120 µm in diameter, and is one of the largest cells in the human body
49
what is the function of the fats and albumins contained within the cytoplasm of a secondary oocyte?
- provide nutrition for the developing embryo until it implants in the wall of the uterus and the placenta can provide nutrients
50
what prevents polyspermy (entry of additional sperm)?
changes to the zona pellucida following entry of a single spermatozoon
51
what is the process of the human menstrual cycle controlled by?
- gonadotrophic hormones
- from the anterior pituitary
- and hormones from the ovary itself
52
what does FSH stand for?
follicle-stimulating hormone
53
where is FSH released from?
the anterior pituitary gland
54
what does the release of FSH promote?
- maturation of the Graafian follicle (bc binds to follicle cells, stimulating them to mature)
- stimulating the production of the hormone oestrogen by the ovary
55
what is the hormone oestrogen produced by?
the ovaries
56
what effect does oestrogen have?
- increasing the thickness and vascularity of the uterus lining, the endometrium, in preparation for the implantation of a fertilised ovum
- stimulate secretion of LH
- inhibit secretion of FSH
57
- from about day 5 of the cycle, FSH is released, which then stimulates oestrogen to be produced
58
what happens once oestrogen levels are high enough?
- it inhibits further production of FSH by negative feedback
- and stimulate the release of LH
59
what does LH stand for?
luteinising hormone
60
what does the sudden release of LH lead to?
- it induces ovulation (causes graafian follicle to release a secondary oocyte)
- and also promotes the formation of a corpus luteum (from the graafian follicle)
- and stimulates the release from it of the hormone progesterone
61
by about day 14, oestrogen levels are high enough to inhibit further production of FSH and stimulate the release of LH
62
the high levels of progesterone that builds up from about the 14 day of the cycle to the 24th day, leads to what?
- it inhibits both FSH and LH
63
what happens once the oestrogen and progesterone levels drop?
- (and the endometrial lining breaks down)
- resulting in menstruation
64
if fertilisation had occurred, progesterone levels will remain (low/high) and this will inhibit the release of FSH and LH by the pituitary
high
65
capacitation definition
changes in the sperm membranes that increase its fluidity and allow the acrosome reaction to occur
66
acrosome reaction definition
acrosome enzymes digest the zona pellucida allowing the sperm and oocyte cell membranes to fuse
67
cortical reaction definition
- occurs when the cortical granule membranes fuse with the oocyte cell membrane
- the zona pellucida is converted into fertilisation membrane
68
sperm responds to chemicals produced by the oocyte and begin to swim through the uterus and into the _____
oviduct
69
- once in the oviduct, sperm can remain viable for a few days, but are most fertile in the 12-24 hours following intercourse
- the oocyte remains viable for only ____ hours following ovulation
24
- so needs to be fertilised relatively quickly after ovulation
70
what are the events that lead to fertilisation? summary
1. capacitation
2. acrosome reaction
3. cortical reaction
4. second meiotic division completes + ovum is formed
71
what are the events that lead to fertilisation? detailed
1. cholesterol and glycoproteins are removed from the cell membrane covering the sperm’a acrosome making the membrane more fluid. this is called capacitation and occur several hours after sperm are deposited
2. the acrosome releases protease enzymes which digest cells forming the corona radiate surrounding the oocyte allowing the sperm head to contact the zona pellucida. now acrosin (another protease) hydrolyses the zona pellucida, allowing the head to enter the oocyte. this is called the acrosome reaction
3. the cell membranes of the sperm and oocyte fuse, the male nucleus can begin to enter the oocyte cytoplasm. this triggers the cortical reaction, where cortical granule membranes fuse with the oocyte cell membrane causing it to expand and harden forming the fertilisation membrane which prevents polyspermy - the further entry of sperm
4. meanwhile, the second meiotic division completes, and the ovum is formed containing the female nucleus and a second polar body
5. fertilisation is the sequence of events from the point where the sperm and oocyte make contact until the male and female chromosomes join on the mitotic equator. the first mitotic division produces two cells, and the resulting cell is referred to as an embryo
72
the embryo continues to divide by mitosis as it passes down the oviduct, forming a ball of cells (by day 3 it’s) called a _____
morula
- by a process called cleavage
73
by day 7, what does a morula become?
- a hollow ball of cells called a blastocyst forms
74
a blastocyst has an outer layer of cells referred to as a _____
trophoblast
75
what does the trophoblast do?
develops protrusion called the trophoblastic villi
76
the endometrium thickens allowing ____ of the blastocyst to occur by day 8-10
implantation
77
trophoblast definition
cells forming the outer layer of blastocyte
78
implantation definition
the sinking of the blastocyst into the endometrium
79
what develops from the trophoblast?
- chorion + placenta
- forming the larger chorionic villi which acquire capillaries and embed into the endometrium
- they are supplied by the developing umbilical artery and vein, and form the placenta
80
as the embryo develops into a foetus, the placenta takes on a number of roles. these include:
- allows exchange of oxygen, co2, nutrients and waste between mother’s and foetus’s blood. the blood is never in direct contact, but is separated by just a few mm, and a counter current blood flow ensures that concentration gradients are maintained across the entire length of the placenta
- it produces hormones to support pregnancy
- acts as a physical barrier between the two circulations. this is important as maternal blood pressure is much higher and would ruptured delicate capillaries in the foetus, and it separates the maternal immune system from the foetus preventing an immune response
- antibodies can cross the placenta giving the foetus some passive immunity to diseases however, some microorganisms can cross the placenta e.g Rubella virus and many drugs e.g nicotine and heroin
81
what does the umbilical artery do?
carrying deoxygenated blood containing waste (including carbon dioxide) from the foetus to the placenta
82
what does the umbilical vein do?
carries oxygenated blood rich in nutrients e.g glucose and amino acids, from the placenta to the foetus
83
how many weeks does pregnancy last for?
around 39 weeks
84
- pregnancy is divided into three trimesters
- and runs from the first day of the last period until birth
85
as the foetus develops, it is enclosed by a membrane called the ____
amnion
86
what does the membrane surrounding the foetus called the amnion do?
produces amniotic fluid
(by the fifth week)
87
what are some importance functions that amniotic fluid has?
- acts as a shock absorber protecting the developing foetus
- helps to maintain the foetus’ body temperature
- provides lubricant
- allows movement
88
what does hCG stand for?
human chorionic gonadotrophin
89
where is the hormone hCG secreted by?
- the blastocyst
- and later the chorion
90
what is the hormone hCG responsible for?
- maintaining the corpus luteum which secretes progesterone (maintains endometrium) during early pregnancy until progesterone is produced directly by the placenta
91
during pregnancy, what happens to the secretion of oxytocin?
progesterone inhibits oxytocin preventing contraction of the myometrium
(and oestrogen stimulates the growth of the uterus and mammary glands)
92
to initiate birth, what happens to the production of oxytocin?
- oxytocin is secreted by the posterior pituitary gland resulting in contractions of the myometrium
- the contractions in turn cause an increased secretion of oxytocin and so on (positive feedback) causing more frequent and stronger contractions
93
what is prolactin secreted by?
the anterior pituitary gland
94
what does the production of prolactin lead to?
- stimulates lactation during and after birth (causing milk to be produced)
- (and is expelled from the nipples by contraction of muscles around milk ducts brought about by oxytocin)e
95
explain the function of these parts of the female reproductive system:
- ovaries
- fallopian tubes
- uterus
- cervix
- overies = produce egg cells in follicles
- fallopian tubes = transports an egg cel from ovary to uterus
- uterus = where embryo develops
- cervix = separates uterus from vagina, protects foetus
96
explain the function of these parts of the male reproductive system:
- testes
- vas deferens
- prostate gland
- urethra
- seminal vesicle
- epididymis
- scrotum
- testes = production of sperm cells and testosterone
- vas deferens = carry sperm from testes to urethra
- prostate gland = secretes alkaline fluid to counteract vaginal acidity
- urethra = allows excretion of urine and semen from the body
- seminal vesicle = secretes fluid (proteins and fructose) to nourish sperm
- epididymis = stores sperm
- scrotum = holds and maintains an optimum temperature for testes
97
how does the human body produce gametes?
via gametogenesis
98
where does spermatogenesis take place?
seminiferous tubules
99
how many spermatozoa does a germinal epithelium cell produce?
4
100
what is the germinal epithelium?
- a surface layer of cells surrounding the ovaries in females and testicles in males that is involved in gametogenesis
101
how are spermatids formed?
- primary spermatocytes divide in meiosis I to form haploid secondary spermatocytes
- secondary spermatocytes divide in meiosis II to form four haploid spermatids
102
how do spermatozoa form?
- spermatids differentiate to gain flagellum, acrosome and many mitochondria
103
name the three types of cells within testes
- spermatogonia
- sertoli cells
- interstitial cells
104
what are interstitial cells?
- cells located adjacent to the seminiferous tubules in the testes that secrete testosterone
105
what are sertoli cells?
- cells located within the seminiferous tubules in the testes that provide nourishment and protection to cells produced during spermatogenesis
106
where does oogenesis take place?
ovaries
107
what is a polar body?
- a haploid cell produced during meiosis in females that does not have the ability to be fertilised
108
when is the second meiotic division of oogenesis completed?
meiosis II initiated but pauses in metaphase II unless fertilisation takes place
109
describe the structure of a secondary oocyte:
- corona radiata - outer layer of follicle cells
- zona pellcida - coating above cytoplasm that prevents polyspermy and hardens when cortical granules release chemicals
- haploi nucleus - fertilisation restores diploid chromosome number
110
outline the stages in the development of a follicle:
primary follicle —> secondary follicle —> Graafian follicle —> ovulation —> corpus luteum
111
what is a primary follicle?
- an immature ovarian follicle surrounded by two layers of follicular cells
112
what is a secondary follicle?
- a larger follicle that has developed from a primary follicle
113
define Graafian follicle:
- a mature fluid-filled follicle in the ovary within which an egg cell develops
114
what is a corpus luteum?
- a mass of cells that forms from the Graafian follicle after ovulation
- it serves as a temporary endocrine structure during pregnancy, secreting progesterone
115
explain what happens during fertilisation?
- spermatozoa move into fallopian tubes
- acrosome binds to zona pellucida and releases hydrolase enzymes that digest the zona pellucida
- membranes of sperm and secondary oocyte fuse, allowing sperm nucleus to enter oocyte
- nuclei fuse, forming a diploid zygote
- cortical reaction causes zona pellucida to harden, preventing polyspermy
116
outline the stages of early embryo development
zygote —> blastocyst —> implantation
117
how does a blastocyst form?
- several mitotic divisions of zygote (cleavage) produces a ball of cells, the blastocyst
118
what is the placenta?
- temporary organ attached to the lining of the uterus during pregnancy
119
name the hormones involved in the functioning of the female reproductive system
- follicle stimulating hormone (FSH)
- luteinising hormone (LH)
- oestrogen
- progesterone
120
where is LH secreted from?
the anterior pituitary gland
121
what structure secretes progesterone in the menstrual cycle?
corpus luteum
122
what is the function of progesterone in the menstrual cycle?
- maintains the endometrium in preparation for the implantation of a blastocyte
- and inhibits the production of FSH and LH
- stimulates the secretion of oestrogen
123
what happens if implantation doesnt occur during the menstrual cycle?
- corpus luteum degenerates due to decreasing FSH and LH levels
- progesterone levels decrease
- endometrium breaks down
124
describe the role of the placenta during pregnancy: (summary)
- exchange of gases and nutrients
- barrier between foetal and maternal blood
- secretes progesterone and oestrogen
- protects the mother’s immune system
- protection from the difference between maternal and foetal blood pressure
125
what is the role of progesterone during pregnancy?
it suppresses contractions of the uterine wall
126
what is the role of oestrogen during pregnancy?
it stimulates uterine growth and the development of the mammary glands
127
why do progesterone levels decrease just before birth?
- allows the uterine wall to contract
128
where is oxytocin secreted from?
- posterior pituitary gland
129
describe the role of oxytocin:
- triggers the contraction of the uterus wall
(to force the foetus out during birth)
130
what type of feedback is the secretion of oxytocin an example of?
positive feedback
131
what is amniotic fluid?
- the liquid surrounding the embryo in the amniotic sac
132
describe how the placenta is adapted for the exchange of substances between maternal and foetal blood
- counter-current blood flow
- chorionic villi provide a large surface area for the exchange of products
- foetal capillaries lie close to the surface giving a short diffusion distance
- abundance of maternal blood vessels
133
what are intervillous spaces?
spaces between chorionic villi that contain maternal blood
134
the organs of the male reproductive system are specialised for what three primary functions?
- to produce, maintain, transport and nourish sperm
- to discharge sperm within the female reproductive tract
- to produce and secrete male sex hormones
135
the organs of the female reproductive system are specialised for what three primary functions?
- to produce female reproductive cells
- ad the site of development of a foetus
- to produce and secrete female sex hormones
136
oocytes develop within _____
follicles
- fluid-filled spaces that provide protection and nutrition for the developing oocyte
(a primary follicle contains a primary oocyte, a secondary follicle contains a secondary oocyte)
137
primary follicles are formed before the birth of the female child but only mature at ____
puberty
- when the level of follicle stimulating hormone FSH increases
138
what is the follicle called when it’s fully mature?
a Graafian follicle
- this is formed when the secondary oocyte is ready to be released at ovulation
139
at ovulation, the ______ _____ breaks open to release the secondary oocyte into a Fallopian tube?
graafian follicle
140
following the formation of the zygote, the new diploid cell must undergo repeated mitotic divisions to increase the cell number - during this period, there is no growth in size. what is this stage called?
cleavage
141
do foetal blood and maternal blood ever mix?
no
- to avoid the mother developing an immune response against the foetus and killing it
- the membrane also reduce the transfer of pathogens and the effect of the differences in blood pressure between the mother and the foetus
142
what are hormones? what are they produced by? by what are they transported?
- chemical messengers
- produced by endocrine glands
- transported by the blood
143
what happens if implantation doesnt occur?
- corpus luteum degenerates
- progesterone levels decrease
- endometrium breaks down
- FSH secretion is no longer inhibited and the cycle begins again
144
what happens is implantation does occur?
- (women becomes pregnant)
- the placenta forms, which secretes hCG which maintains the corpus luteum during early stages of pregnancy
- hCG ∴ maintains secretion of progesterone. due to progesterone’s inhibitory effect on LH (which inhibits oestrogen secretion) more oestrogen is secreted. the combined effect of progesterone and oestrogen is to maintain the endometrium
- after the 8th week of pregnancy, the placenta takes over secretion of oestrogen and progesterone
145
the human chorionic gonadotrophin is used as an indicator of pregnancy. why?
- it’s only produced by the blastocyst and placenta
- and therefore can only appear in the blood or urine of a woman if she is pregnant
(while the levels of progesterone and oestrogen increase greatly during pregnancy, this only occurs after week 8. they are present at all times, but at low levels)
146
what triggers the production of prolactin by the anterior pituitary gland?
- the levels of oestrogen and progesterone fall at the end of pregnancy
(prolactin prepares the mammary glands to produce milk)
