Human Reproduction Flashcards
What are the structures of the male reproductive system?
Testes
Scrotum
Penis
Seminiferous tubules
Epididymis
Vas deferens
Seminal vesicle
Prostate gland
Urethra
Ureter
bladder
rectum
What are testes?
a pair of organs that contain the seminiferous tubules and epididymis, crucial for sperm production. (site of spermatogenesis)
What is the scrotum?
an external sac that protects the testes and maintains them at a temperature lower than the body’s core temperature(37 °C).
What is the penis?
This intromittent organ is responsible for delivering sperm into the female reproductive system.
What are the seminiferous tubules?
structures within the testes where spermatozoa are produced
What is the epididymis?
where spermatozoa mature and are stored until ejaculation.
What is the vas deferens?
Spermatozoa travel along this tube from the epididymis to the urethra during ejaculation.
what is the seminal vesicle?
produces a mucus secretion that enhances sperm motility.
what does the prostate gland do?
produce an alkaline fluid that neutralises urine and vaginal acidity and supports sperm motility.
what does the urethra do?
This tube carries urine from the bladder to the outside of the body.
What does the ureter do?
These tubes connect the kidneys to the bladder.
What are the features of the female reproductive system?
Ovary
Fallopian tubes (oviducts)
Uterus
Endometrium
Cervix
Vagina
What are the ovaries?
a pair of organs where both mitosis and meiosis occur to produce primary and secondary oocytes. (FSH and LH regulate the development and release of secondary oocytes.)
what are the oviducts (fallopian tubes)?
the pathways through which ova travel to reach the uterus. They are lined with ciliated epithelial cells and are the site of fertilisation.
what does the cilia do?
move to waft the oocyte towards the uterus in case there is any spermatozoa for fertilisation
What is the uterus?
Commonly referred to as the womb, this organ has muscular walls (the myometrium) and is lined with the endometrium.
During childbirth, oxytocin induces contractions through a positive feedback mechanism.
What is the endometrium?
the mucus membrane lining of the uterus, with a rich supply of blood. The embryo implants here during pregnancy or is shed during menstruation. Its maintenance is regulated by the hormones progesterone and oestrogen.
what is the cervix?
the ring of muscle and connective tissue at the entrance to the uterus.
what is the vagina?
a canal that provides a passageway for menstrual blood and mucosal tissue from the uterus. It also receives the penis during sex and serves as the birth canal during childbirth.
what is gametogenesis?
the process of producing game area which occurs in specialised glands called gonads
What is spermatogenesis?
formation of sperm in the testes
what is oogenesis?
the formation of ova in the ovaries
What happens to the germinal epithelium cells in the gonads gametogenesis?
both mitosis and meiosis to produce genetically different haploid gametes
why is it important that the gametes are haploid?
so that when fertilisation occurs, the diploid number is restored, and the zygote has a full set of homologous chromosomes.
What leads to the genetic variation in the gametes?
-crossing over (chiasmata formation) of non sister chromatids between homologous chromosomes during prophase I
-independent assortment of bivalents during metaphase one
-Independent assortment of sister chromatids during metaphase two
where are spermatozoa produced?
within the seminiferous tubules of the testes and germinal epithelial cells in these tubules give rise to approximately 120 million viable spermatozoa daily.
What does the development of spermatozoa require?
FSH and testosterone
what is the process of spermatogenesis?
Germinal epithelial cell
|
spermatogonium (2n)
|
(mitotic division)
Primary spermatocytes (2n)
|
(meiotic division I)
Secondary spermatocytes 2n)
|
(meiotic division II)
spermatids (n)
| (differentiate and mature)
spermatozoa (n)
What is the process of spermatogenesis?
-Diploid spermatogonia divide many times by mitosis to produce diploid primary spermatocytes.
-These then undergo meiosis I to form haploid secondary spermatocytes.
-These then undergo meiosis II to form spermatids which then differentiate and mature to form spermatozoa
How does spermatogenesis occur at the seminiferous tubules?
outside in
what are sertoli cells?
type of somatic cell that spermatids develop around
Located in the seminiferous tubules
what cells do the seminiferous tubules contain?
sertoli cells and interstitial cells (cells of Leydig)
what is the role of sertoli cells?
•To secrete a fluid which nourishes the spermatids and protects them from the immune system of the male.
•To provide oxygen and remove waste products.
What are interstitial cells?
A type of somatic cell that is stimulated by the hormone LH. Located outside the seminiferous tubules
what is the role of the interstitial cells?
to secrete testosterone
what does testosterone do?
stimulates spermatogenesis and causes male secondary sexual characteristics to develop
what is the summary of spermatogenesis?
-Spermatozoa are produced in the seminiferous tubules of the testes by a process called spermatogenesis.
-Spermatogonia divide many times to produce primary diploid spermatocytes
-These undergo meiosis and the products of the first meiotic division are haploid secondary spermatocytes
-These undergo the second half of the meiotic division producing spermatids which differentiate and mature into spermatozoa.
-The spermatozoa are protected and nourished by the sertoli cells.
What are the features of a spermatozoon?
-cell membrane
-acrosome (contains hydrolytic enzymes)
-nucleus (haploid 2n)
-centriole
-mitochondrion
-Axial filament
what is the function and contents of the head of a spermatozoon?
Contains a haploid nucleus and is covered at the end by a structure called the acrosome, a large lysosome which contains enzymes used in fertilisation.
what is the function of the mid piece of a spermatozoon?
Packed with mitochondria which provide ATP for movement.
What is the function of the tail of a spermatozoon?
Also known as the flagellum, this structure makes lashing movements that propel the sperm, enabling its motility
Why are both mitosis and meiosis important in spermatozoon production?
•Mitosis produces large numbers of primary spermatocytes- leads to large numbers of spermatocytes, which increases the chances of fertilisation.
•Meiosis produces haploid spermatozoa and leads to genetic variation.
What is the process of oogenesis?
Primary germ cell (2n)
(mitotic division)
|
oogonium
(mitotic division)
|
primary oocyte arrested in prophase I (present at birth)
(completion of meiosis I, onset of meiosis II) |
1st polar body secondary oocyte arrested metaphase II
(ovulation)
|
2nd polar body, ovum
What do polar bodies contain and why is this a benefit?
-The polar bodies contain much less cytoplasm than the oocyte.
-This is a benefit as at fertilisation the resulting zygote will have sufficient cytoplasm to provide nutrients for rapid cell division.
What does the second polar body do?
serves DNA content so that of the ovum is haploid with a full set of sister chromosomes- the sperm nucleus and the ovum nucleus then fuse inside the ovum- diploid zygote
what is the process of oogenesis? (2)
-Before birth, as female foetus develops, cells of the germinal epithelium divide by mitosis to make diploid oogonia (and more germinal epithelial cells).
-The oogonia undergo mitosis many times and enlarge to form diploid primary oocytes (and more oogonia).
-The primary oocytes begin meiosis I but stop during prophase I. )baby girl is born with millions of primary oocytes arrested at prophase I in her ovaries)
-Before each ovulation, a primary oocyte matures, completing the first meiotic division to form a haploid secondary oocyte and a polar body (a smaller cell with less cytoplasm that often degenerates).
-The secondary oocyte is released from the ovary during ovulation and begins meiosis II. It pauses at metaphase II until fertilisation takes place.
-On fertilisation, meiosis II completes, resulting in the formation of a large ovum and a second polar body.
What is the process of the ovarian cycle?
-During oogenesis, the germinal epithelial cells also divide to form follicle cells, which surround the primary oocytes to form primary follicles.
-At puberty, hormones stimulate these follicles to develop further. -Each month, one or more follicles will mature into a Graafian follicle containing a secondary oocyte.
-The mature Graafian follicle migrates to the surface of the ovary where it bursts to release the secondary oocyte – this is ovulation.
-After ovulation, the Graafian follicle becomes the corpus luteum which (if fertilisation occurs) secretes hormones for pregnancy.
-If fertilisation does not occur, the corpus luteum degenerates into the corpus albicans.
What is fertilisation?
Sperm nucleus (haploid) fuses with ovum nucleus (haploid) inside the ovum= diploid zygote
What is a structure of a secondary oocyte after ovulation?
-A clear glycoprotein layer called the zona pellucida surrounds the cell membrane of the secondary oocyte. The chromosomes of the secondary oocyte are at metaphase II.
-Corona radiata cells surround the secondary oocyte and provide nutrients.
what do theca cells do?
secrete oestrogen
What are the stages of the woman’s life? (oogenesis)
before birth, puberty, fertilisation
what happens before birth?
-Germinal epithelial cells (2n) divide by mitosis to form oogonia (2n). -Oogonia undergo mitosis to form primary oocytes (2n). These commence meiosis I but stop at prophase I.
-This primary oocyte is contained within a primary follicle.
what happens at puberty?
-The primary oocyte completes meiosis I to form a secondary oocyte (n). This commences meiosis II but stops at metaphase II.
-The primary follicle develops into a Graafian follicle containing the secondary oocyte.
What happens at fertilisation?
The secondary oocyte completes meiosis II to form an ovum.
what happens in the absence of an implanted embryo?
the endometrium is shed through menstruation. This occurs monthly from the start of puberty (menarche) to the menopause (menstrual cycle)
what is the menstrual cycle?
a system of positive and negative feedback, operating between events involving the brain, the ovaries and the uterus.
What is the process of the menstrual cycle?
at the start (day 0) the anterior pituitary gland secretes follicle-stimulating hormone (FSH) which triggers the development of a follicle in the ovary (this will mature into a Graafian follicle). FSH also stimulates the production of oestrogen. Following menstruation, the level of ostrogen (secreted by the developing follicle) increases in the blood resulting in
•Inhibition of further production of FSH by negative feedback so no new follicles develop.
•Stimulation of the anterior pituitary gland to secrete luteinising hormone (LH) by positive feedback.
•Growth and repair of the endometrium
-A high level of LH, secreted by the anterior pituitary gland, initiates ovulation This also causes the Graafian follicle to develop into the corpus luteum which secretes progesterone which causes further development of the endometrium. -Progesterone also inhibits further production and release of LH and increases the level of mucus in the cervix to block the entry of sperm.
-If implantation does not occur:
•FSH is no longer inhibited, and another menstrual cycle is initiated.
•Falling FSH and LH levels cause the corpus luteum to degenerate
•Progesterone levels fall
•The endometrium breaks down and is lost during menstruation
What is the summary of the menstrual cycle?
-FSH secreted by the anterior pituitary gland, stimulates the maturation of a follicle, stimulating the production of
oestrogen
-As a result, ostrogen (secreted by the developing follicle) increases in the blood which triggers the repair of the endometrium, inhibits
FSH production, and stimulates LH
production.
-A high level of LH, secreted by the anterior pituitary, initiates ovulation and causes the graafian follicle to develop into a corpus luteum
-Progesterone secreted by the corpus luteum, causes further development of the endometrium prior to menstruation,
-if implantation does not occur, falling FSH levels cause the corpus luteum to degenerate, progesterone levels fall, the endometrium breaks down and is lost during menstruation
how can oestrogen be used as a contraceptive pill?
-Oestrogen inhibits secretion of FSH from the apg
-Without FSH the primary follicles do not develop
-So without a mature/ Graafian follicle, ovulation and fertilisation cannot take place
How can progesterone be used as a contraceptive pill?
-progesterone inhibits LH secretion + so no ovulation
progesterone increases level of mucus in cervix + so blocks entry of sperm
-No ovulation or no sperm means no fertilisation can take place
IVF involves the maturation of a large number of follicles which can then be retrieved from the ovary. Suggest the hormone that would be provided to patients and explain your answer. (2)
FSH- high levels of FSH injected means many primary follicles develop into graafian follicles- Many secondary oocytes are extracted from the ovary which increases the chances of more fertilisation.
what is copulation?
sexual intercourse
What is the process of sexual intercourse?
•Arterioles entering the penis dilate while the venules leaving the penis constrict.
•This leads to a build-up of blood in spaces in the penis, causing it to become erect.
•The penis is then inserted into the vagina, and movements result in the ejaculation of semen
•The force of ejaculation is sufficient to propel some sperm through the cervix into the uterus, with the remainder being deposited at the top of the vagina.
•The sperm respond to chemoattractants released by the secondary oocyte and swim to the oviduct.
•The sperm can remain viable for 2-5 days but are most fertile 12-24 hours after ejaculation. If ovulation has recently occurred, a secondary oocyte will be present in the oviduct, although it will only remain viable for 24 hours unless fertilised.
What are the stages of fertilisation?
Capaciation
Acrosome reaction
Cortical reaction
when can spermatozoa only fertilise a secondary oocyte?
after undergoing a process called capacitation, which takes several hours
what is the process of capacitation?
-Spermatozoa swim through oviduct and become hyper-mobile
-cholesterol and glycoprotein is shed from cell membrane of sperm head (some membrane becomes more fluid)
-Acrosome fully forms containing hydrolytic enzymes a.k.a. acrosome cap
what is the process of the acrosome reaction?
-Spermatozoa swim through the Corona radiata
-when’s the spermatozoa contact the Zona pellucida the acrosome fuses with the sperm cell membrane releasing hydrolytic enzymes by exocytosis
-Endopeptidases hydrolyse non-terminal peptide bonds in glycoproteins of the zona pellucida
-Digesting a path through the Zona pellucida sperm inject nucleus into secondary oocyte cytoplasm
what is the zona pellucida?
(jelly coat made from glycoprotein) = becomes fertilisation membrane
What is the corona radiata?
follicle cells
What is the process of the cortical reaction?
-injection of the sperm nucleus cause the release of Ca2+ ions into cytoplasm secondary oocyte (from smooth endoplasmic reticulum)
-Higher Ca2+ conc stimulates migration of cortical granules to fuse with the cell membrane
-Chemicals released by exocytosis cause the zona pellucida to thicken and harden forming the fertilisation membrane preventing polyspermy
why is it important that the cortical reaction occurs?
if polyspermy occurred the oocyte could receive too many chromosomes resulting in an unviable zygote
what does the entry of the spermatozoon’s genetic material also trigger? (cortical reaction)
meiosis II to continue forming the ovum and the second polar body.
The nuclei of the sperm and ovum fuse to form a zygotic nucleus (DIPLOID)
what is the summary of fertilisation?
-Sperm enter oviduct and swim towards the secondary oocyte.
-Spermatozoa are attracted to oocyte due to chemo-attractants.
-On contact with the zona pellucida, the spermatozoon’s acrosome ruptures releasing hydrolase enzymes
-The enzymes digest a pathway through the zona pellucida (endo)
-Membranes of secondary oocyte and sperm fuse together and the haploid nucleus of the sperm enters the secondary oocyte.
-Cortical reaction occurs releasing cortical granules. (increase ca2+)
-The nucleus of secondary oocyte completes meiosis II. (increase ca2+)
-Zona pellucida hardens and fertilisation membrane forms to prevent polyspermy.
-haploid nuclei of the sperm and secondary oocyte fuse to form a diploid zygote
what is the process of implantation?
-The zygote undergoes repeated mitotic divisions, forming a ball of cells. This process is known as cleavage
•By day seven, cleavage has resulted in the production of a hollow ball of cells called a blastocyst.
•The blastocyst moves into the uterus, where it attaches and embeds into the endometrium, a process known as implantation.
What happens to the endometrium lining during implantation?
Endometrium lining continues to thicken due to progesterone in the corpus Luteum (in the ovary)
The corpus luteumdoes not degrade due to HCG Secreted from the chorion
What is pregnancy?
the period from the first day of the last menstrual cycle until birth. This lasts approximately 39 weeks in humans
what happens in the amniotic fluid?
The embryo, which later becomes the foetus, develops and grows in the uterus, enclosed by the amnion, a membrane derived from the blastocyst
What are the roles of amniotic fluid?
-Maintains the foetal temperature
-Acts as a shock absorber, protecting the foetus from injury from outside the uterus.
pre natal diagnosis can take place to identify foetal chromosomal abnormalities. Suggest two concerns that some people may have about the ethics of prenatal diagnosis.
•Selective abortion may become more common
•Moral status of foetus/right to live
•May cause harm to foetus
•Could result in false positive/negative results
What is the percent of form and what is it connected to the foetus by?
The placenta forms between the maternal and foetal tissues and is connected to the foetus by the umbilical cord.
What does the umbilical cord contain?
two blood vessels; an umbilical artery and an umbilical vein
What does the umbilical vein do?
carries oxygenated blood and nutrients, such as glucose, to the foetus
What does the umbilical artery do?
carries deoxygenated blood and waste products, such as carbon dioxide, away from the foetus.
where are the capillaries located in the placenta?
within chorionic villi, which form the boundary between maternal and foetal blood
Why does the blood from maternal arterioles go in the placenta?
Blood from maternal arterioles empties into an intervillous space. There absence of maternal capillaries between the maternal arteriole and maternal venule reduces the number of cell layers to be crossed, providing a shorter diffusion pathway for materials.
what is immersed in this intervillous space? (placenta)
Foetal capillaries are immersed in this intervillous space, allowing the exchange of materials to occur. Blood containing waste materials then returns to maternal venules from the intervillous space.
How do maternal and foetal blood flow in the placenta?
in opposite directions to maintain a concentration gradient. (cc flow)
what are the roles of the placenta?
Facilitates the exchange of materials across a thin barrier which separates maternal and foetal blood:
•into foetal blood: glucose, oxygen, amino acids, salts
•out of foetal blood: carbon dioxide and nitrogenous waste
2. Provides protection from the immune system of the mother.
3. Protects the foetus from the differences in maternal and foetal blood pressures (the mother’s blood pressure is much higher than that of the foetus, and could cause damage)
4. Allows the passage of maternal antibodies into the foetus to provide short term immunity.
Describe and explain the position of the foetal oxygen dissociation curve and how this benefits the foetus.
•Foetal haemoglobin has a higher affinity for oxygen than the mothers haemoglobin
•The dissociation curve shifts to the left.
•Therefore it can load oxygen from the mother’s blood at ALL PARTIAL PRESSURES of oxygen.
•Foetal haemoglobin becomes highly saturated with oxygen.
What does the developing embryo do just before and following implantation?
the developing embryo secretes hCG, which maintains the corpus luteum for the first 16 weeks of pregnancy
what does the placenta then secrete and what does this do?
placenta then secretes progesterone and oestrogen which rise to high levels in the blood plasma. These hormones supress the secretion of FSH and LH and prolactin
why do progesterone and oestrogen suppress FSH and LH and prolactin
FSH- so no more follicles mature (suppressed so no more primary follicles continue to develop during this menstrual cycle (primary oocytes do not complete meiosis II)
LH- so ovulation isn’t possible
-Prolactin- so no milk is made
What does progesterone do?
suppresses the uterine wall’s ability to contract and maintains the endometrium.
What does oestrogen do?
stimulates the growth of the uterus to accommodate the growing foetus and stimulates the growth and development of the mammary glands
just before birth, what happens to oestrogen and progesterone levels and what does this mean?
oestrogen levels increase, and progesterone levels decrease. This means the uterine wall can now contract
What two important hormones are secreted when oestrogen levels increase, and progesterone levels decrease?
oxytocin
Prolactin
What is oxytocin do secreted by and what does it do?
secreted by the posterior pituitary gland stimulates contraction of the myometrium (muscle layer in the wall of the uterus). These contractions stimulate the secretion of more oxytocin, which is an example of positive feedback. As the oxytocin levels increase, the contractions become stronger and more frequent.
What is prolactin released from and what does this do?
the anterior lobe of the pituitary gland during and after birth to stimulate the production of milk by the mammary glands
After birth, what does oxytocin do?
releases milk for the current feed and helps the baby to get the milk easily
when the endocrine gland are prolactin FSH and LH released by?
Anterior pituitary gland
what does FSH do in makes and females?
female- Stimulates development of Graafian follicle which releases ostrogen
male- Sperm development
What endocrine gland secretes oestrogen?
•Developing follicle
•Placenta
what does oestrogen do?
•Rebuilds endometrium
•Negative feedback on FSH
•Positive feedback on LH
•Secondary sexual characteristics
What endocrine glands is progesterone secreted by?
•Corpus luteum
•Placenta
What endocrine gland is oxytocin secreted by?
Posterior pituitary
what does oxytocin do?
•Contraction of smooth muscle in myometrium
•Contraction of smooth muscle the milk ducts to release milk
what does prolactin do?
Milk production
what endocrine gland is HCG produced by?
Developing embryo
what is the developing embryo do?
maintains corpus luteum
what does LH do?
female- •Stimulates ovulation
•Stimulates conversion of Graafian follicle into corpus luteum
male- Stimulates interstitial cells
What endocrine gland is testosterone secreted by?
Interstitial (Leydig) cells
What does testosterone do?
•Sperm development
•Secondary sexual characteristics
what are sertoli cells?
-Cells which secrete a fluid which nourishes the spermatids and protects them from the immune system of the male.
-They also provide oxygen and remove waste products.
What are interstitial cells/cells of leydig?
Cells which secrete testosterone which stimulates spermatogenesis and causes male secondary sexual characteristics to develop.
what is an acrosome?
A lysosome in the head of a sperm cell containing enzymes needed for fertilisation
What is capacitation?
Changes in the sperm cell membrane covering the acrosome where cholesterol and glycoproteins are removed.
what is a Zona Pellucida?
Transparent glycoprotein layer around the secondary oocyte
what is the Corona radiata?
Cells surrounding the secondary oocyte and provide nutrients
what is the cortical reaction?
Hardening of the zona pellucida to form the fertilisation membrane. This prevents other sperm from being able to penetrate the egg (polyspermy).
what is the blastocyst?
A hollow ball of cells which implants into the endometrium
what is amniotic fluid?
Fluid that maintains the foetal temperature and acts as a shock absorber
what is the placenta?
An organ that forms between the tissues of the mother and the foetus and is connected to the foetus by the umbilical cord
What does the umbilical vein do?
Carries blood containing oxygen and glucose to the foetus
what does the umbilical artery do?
Carries blood containing carbon dioxide away from the foetus
what is the chronic villi?
Finger-like projections in the placenta
