Reproduction Flashcards
What is the male reproductive tract?
The male reproductive tract is external and consists of a penis and a pair of testes enclosed within the scrotum.
What are the testes?
The testes are gonads i.e. the structures responsible for the production of sperm - a process called spermatogenesis.
They are also the primary source of the male sex hormones known collectively as androgens.
The best known example of an androgen is testosterone.
The testes are composed of a series of coiled tubes called what?
Seminiferous tubules
What are the 2 important cell types in the seminiferous tubules?
- Sertoli cells which are responsible for sperm production
- Leydig cells which are responsible for testosterone production and release
Leydig cells are sometimes called interstitial cells.
Where do individual seminiferous tubules drain into?
Structures called the rete testes
What do the rete testes drain into?
The rete testes drain into a highly coiled tube called the epididymis, which in turn drains into the vas deferens.
The vas deferens from each testicle dilates and forms a structure called the ampulla of the vas deferens.
The ampulla merges with the outflow from the seminal vesicle to form a structure called the ejaculatory duct.
What is the general organisation of the male reproductive tract?
Figure 9.1 PG 133
What is the cross section through a testicle?
Figure 9.2 PG 134
What is the process of ejaculation?
The ejaculatory ducts enter the prostate gland, merge together, and enter the urethra which allows sperm and the secretions of various glands to be released from the penis.
What is ejaculated from the penis?
Whilst sperm are produced in the testes and mature as they move through to the epididymis, it is semen which is ejaculated.
What is semen?
Semen is a mixture of sperm and secretions of the seminal vesicle and prostate gland.
These secretions provide nutrients for the sperm cells, are alkaline ( to buffer the acidic secretions of the female reproductive tract) and contain anticoagulants.
What is a typical ejaculatory volume?
2 - 5 ml, 80% of which is made up from glandular secretions.
What is the production of functional sperm known as?
It is known as spermatogenesis.
This begins at puberty and continues, although at a reduced efficiency, until death
Once spermatogenesis is initiated how much sperm does a male produce each day?
Once spermatogenesis is initiated a male may produce 200 -250 million sperm a day.
What is the first step of spermatogenesis?
It is the production from diploid germ cells of cells called spermatogonia.
Diploid means that the cells have a full complement of chromosomes, i.e. 23 pairs comprising 22 pairs of autosomes and one each of the X and Y chromosomes (the so called sex chromosomes)
What does haploid mean?
Haploid
A cell that contains a single set of chromosomes. For example, human egg and sperm cells are haploid, containing 23 chromosomes.
What does diploid mean?
Diploid
A cell that contains two complete sets of chromosomes. For example, most cells in humans are diploid, containing 46 chromosomes in total.
How are primary and secondary spermatocytes formed?
Spermatogonia undertake 2 further mitotic cell divisions to form primary spermatocytes which are still diploid.
They then begin to undergo meiotic cell divisions to form structures called secondary spermatocytes.
How are spermatids formed?
Secondary spermatocytes undergo a further meiotic cell division to form spermatids. These are now haploid cells.
They contain one of each pair of autosomes and one of the sex chromosomes - making 23 chromosomes in total
What are autosomes?
any chromosome that is not a sex chromosome.
What is the final stage in the production of sperm?
Maturation and formation of sperm cells from the spermatids - a process called spermiogenesis
What is the cross section through a seminiferous tubule?
Figure 9.3 PG 135
What happens as the development from spermatogonia to sperm occurs?
As the development from spermatogonia to sperm occurs, the cells move through the Sertoli cells towards the lumen of the seminiferous tubules.
How long does it take to produce sperm cells from spermatagonia?
about 70 days
What is the structure of a typical sperm cell?
Figure 9.4 PG 136
What are the 3 regions of sperm?
- Head
- Mid-piece
- Tail
What does the head of the sperm cell contain?
The head contains the nucleus (which contains half the full chromosome number.)
Within the head is the acrosome. This contains hydrolytic enzymes whose function is to allow the sperm to penetrate the egg at fertilization.
How is the mid piece of the sperm characterized?
The mid piece is characterized by spirally arranged mitochondria
What is the tail of the sperm?
The tail of the sperm is motile, powered by the ATP produced in the mitochondria of the mid-piece.
The tail is a single flagellum and is identical to the 9 + 2 flagella seen in other organisms.
What do sperm cells lack?
Other intracellular organelles.
What is one of the roles of the testes?
Produce the male sex hormones (androgens) - primarily testosterone.
What are the multiple functions of testosterone?
Testosterone has a number of important functions:
- It stimulates sperm production
- It promotes the development of male secondary sexual characteristics at puberty
- Its anabolic effects include increased protein synthesis and muscle growth hence its use as a banned substance in sport
- Via its effect on the CNS, it increases libido.
What produces testosterone?
Leydig cells in the testes.
Where does the vast majority of testosterone go?
The vast majority enters the plasma however some enters the seminiferous tubules where it binds to androgen-binding protein and stimulates sperm production.
Why is it important that the levels of testosterone are regulated?
To ensure the male reproductive function is optimized
How is hormonal control of testicular function achieved?
By the hypothalamo - pituitary axis
Where is Gonadotrophin releasing hormone (GnRH) released from?
Gonadotrophin releasing hormone (GnRH) is synthesized and released from neurons in the hypothalamus.
What does Gonadotrophin releasing hormone promote?
It enters the portal blood vessels and travels to the anterior pituitary gland where it promotes the release of follicle stimulating hormone (FSH) and luteinizing hormone (LH)
What does LH do?
LH targets Leydig cells, where it promotes the release of testosterone.
What does FSH do?
FSH targets Sertoli cells, where it promotes the release of androgen-binding protein.
It also promotes the release of inhibin and the enzyme aromatase, which promotes the conversion of testosterone to the female sex hormone oestradiol (oestrogen.)
How does the released testosterone inhibit the release of further LH?
By reducing activity in both the hypothalamus and the anterior pituitary gland.
What does increased levels of inhibin and aromatase result in?
They inhibit activity in the hypothalamus and anterior pituitary gland and reduce FSH secretion.
What is the female reproductive tract responsible for?
The production of ova and the development of the foetus.
Following birth there is a variable period when the mother is the sole source of nutrients for the baby.
Is the female reproductive system internal or external?
The female reproductive system is internal in contrast with the male reproductive system.
What is the general organisation of the female reproductive tract?
Fig 9.5 PG 138
What are the paired ovaries?
The paired ovaries lie within the pelvis these are the gonads of the female reproductive tract.
They are responsible for ensuring that on a cyclical basis, an ovum (egg) is prepared for fertilisation.
Where do the fallopian tubes originate from?
Functioning with the ovaries are a pair of fallopian tubes, which originate from the uterus.
Where does sperm deposited in the vagina travel to?
The distal regions of the fallopian tubes where fertilization of the ovum occurs.
They then allow the fertilized egg to travel back to the uterus where it will initially implant in the uterus prior to the formation of the placenta.
What does distal mean?
Distal refers to sites located away from a specific area, most often the centre of the body
What are the 2 important regions of the uterus?
- The innermost lining called the endometrium which undergoes cyclical changes to ensure that a fertilized egg has an initial location for development to proceed prior to the formation of the placenta.
- The uterus also contains smooth muscle the myometrium. Activity in this muscle expels the foetus at the end of pregnancy.
What is the cervix?
The cervix is the start of the birth canal.
It is linked to the vagina, allowing deposition of sperm during sexual intercourse and also forms the birth canal during childbirth.
What is the opening of the vagina protected by?
The opening to the vagina is protected by the vulva, which consists of folds of tissue called the labia majora and the labia minora.
How long does ovum production occur from?
Puberty until the onset of menopause unlike males where sperm is produced from puberty until death.
When does ovum (egg) production occur?
Cyclical i.e. monthly fashion unlike males where sperm is produces continually.
What is the ova?
The ovary at birth contains all the ova a woman will ever possess.
These ova are produced from stem cells which are called oogonia, which are diploid.
The egg cell or ovum ( plural. : ova) is the female reproductive cell, or gamete
What happens during the latter stages of foetal development?
During the latter stages foetal development, the oogonia begin the process of meiosis.
By the time of the birth this results in the formation of structures called primordial follicles
Primordial follicles consist of an ova surrounded by a layer of cells called the follicle cells.
Why does the process of meiosis not proceed to completion regarding the ova and foetal development?
This is because the ova within the primordial follicles remain suspended in the prophase stage of the first meiotic division until puberty, when on a cyclical basis an individual ovum completes its meiotic division and the formation of a haploid cell.
When is the first and final meiotic division completed?
The first meiotic division is completed after puberty under the influence of FSH, but the final meiotic division is only completed after an ovum has been fertilized.
What is the process of atresia?
At puberty, a number of primordial follicles are allowed to begin to complete the process of further meiotic division. However only one follicle will complete the process each month and the rest will degenerate - a process called atresia.
When can one follicle complete its development?
One follicle is allowed to complete its development once a month, although in most women this duration varies between 25 and 35 days.
This is the ovarian cycle, which is more commonly known as the menstrual cycle.
Theoretically the term menstrual cycle refers to cyclical changes in the endometrium.
When does a typical ovarian cycle considered to begin?
On the first day of bleeding of the menstrual cycle.
What happens during the first couple of days of the ovarian cycle?
The primordial follicles increase in size and forms the preantral follicle.
During this phase, cells of the follicle begin to express receptors for both LH and FSH.
What happens to the preantral follicle under the influence of LH and FSH?
It develops into an antral follicle.
Antral follicles are also known as Graffian follicles.
As this process proceeds, cells within the follicle begin to secrete oestrogen.
What happens towards the end of the phase of follicular development?
There is a further rise in the number of LH receptors (and also LH levels.) As a consequence, the follicle ruptures and the oocyte is released
This is known as ovulation and during this phase the ovum completes its first meiotic division and occurs after about 14 days (mid cycle)
What is the corpus luteum?
The empty follicle left behind after ovulation is called the corpus luteum.
In the event of pregnancy occurring, the corpus luteum assumes an endocrine role and maintains the endometrium in preparation for implantation by the fertilized egg.
What does the corpus luteum secrete?
Large amounts of progesterone
What happens if the ovum released at ovulation remains unfertilized?
The corpus luteum degenerates. This occurs 12 - 14 days after ovulation and marks the end of a single ovarian cycle.
What is the first and second half of the ovarian cycle known as?
The first half of the ovarian cycle is known as the follicular phase and is dominated by oestrogen
The second half is known as the luteal phase and is dominated by progesterone.
Why is it essential that as the development of the ova in the ovaries proceeds each month, there are changes in the endometrium?
This is because in the event of fertilization occurring, it will become the first ‘home’ for the fertilized egg.
What are the cyclical changes which occur in the endometrium known as?
The menstrual cycle
When does the menstrual cycle begin?
First day of bleeding
During the follicular phase of the ovarian cycle, what do the high oestrogen levels prepare the reproductive tract for?
Possible fertilization and subsequent implantation of the zygote
What are the fimbrae?
Under the influence of oestrogen, activity in the cilia of the fimbrae increase.
The fimbrae are the most distal regions of the fallopian tubes. This ensures that the ovum released from the follicle is ‘captured’ and is transferred back along the fallopian tubes towards the uterus.
What occurs at the same time the ovum is captured and transferred back along the fallopian tubes towards the uterus?
The endometrium begins to proliferate (increase rapidly) and as it does there is an increase in its vascularization (spiral artery development.) and an increase in its secretions.
During this time the endometrium also becomes primed to respond to progesterone in the latter half of the cycle.
This phase of the menstrual cycle is known as the proliferative phase
What happens in the second half of the menstrual cycle?
(which coincides with the luteal phase of the ovarian cycle)
The endometrium is fine tuned in preparation for pregnancy
The development if the spiral arteries within the endometrium continues.
Likewise the secretions in the endometrium continue. However they change from the watery secretion seen in proliferative phase to one which is rich in nutrients.
This is the secretary phase of the menstrual cycle
What if fertilization does not occur?
If fertilization does not occur the corpus luteum degenerates. Consequently the source of progesterone which is maintaining and developing the endometrium is lost.
When does the menstrual cycle begin?
The cycle begins on the first day of menses.
At this time, under the release of GnRH, FSH is released which promotes follicle development.
Shortly after this LH secretion begins to rise.
What happens during the first half of the menstrual cycle?
Cells in the follicle begin to express receptors for LH.
Plasma levels of oestrogen begin to increase as the follicle starts to synthesize and release oestrogen.
What happens as the levels of oestrogen continue to rise in the menstrual cycle?
Rather than producing a negative feedback influence on the anterior pituitary hormone, it produces a positive feedback effect - particularly on LH production.
This produces a so called LH surge which results in the occurrence of ovulation.
What happens after the LH surge ?
The follicle begins to produce progesterone and so the levels of progesterone rise while the level of oestrogen begin to reduce.
What happens to the positive feedback that oestrogen had on FSH and LH secretion?
It is removed and negative feedback is reasserted.
The result of this is that the FSH and LH levels drop.
Oestrogen levels may continue to rise but there is no second surge in LH - the secretion of progesterone appears to inhibit this.
What happens if fertilization fails to occur?
Menstruation starts and the FSH and LH levels begin to rise again as a new cycle starts.
What is fertilization?
Fertilization represents the union of a single sperm with a single ovum to produce a diploid zygote.
Where is sperm deposited?
Sperm is deposited in the vagina and must travel to the distal ends of the fallopian tube in order to fertilize the single released ovum.
What is the narrow time window for fertilization?
Fertilization has a narrow time window in which to occur- sperm only remain viable in the female tract for about 36-48 hours after ejaculation
And ova only remain viable for 12-24 hours post-ovulation.
Once deposited in the female, sperm must undergo a process called capacitation
What is capacitation?
Capacitation is a calcium dependant process- the membrane at the head fuses with the membrane that forms the acrosome.
Capacitation only occurs once the sperm has been deposited in the vagina.
What does capacitation allow?
Enzymes released via Ca2+ influx
(Acrosin and other proteases)
These enable the sperm to penetrate the egg
What is the acrosome reaction?
When a sperm meets an ovum the acrosome reaction occurs.
This results in the release of hyaluronidase from the acrosome.
What is hyaluronidase?
This is a hydrolytic enzyme, which digests the follicular cells surrounding the ovum.
The sperm will then fuse with the membrane of the ovum to form a zygote.
What happens if the second meiotic division of the ovum fails to occur?
Risk that the fertilized ovum may display triploidy i.e. 3 sets of chromosomes.
What is the final step in fertilization?
The fertilized ovum must now prevent the regression of the corpus luteum and thus the loss of the endometrium.
The fertilized egg does this by secreting a hormone called human chorionic gonadotrophin (hCG).
The zygote then implants in the endometrium and the gestation period - 9 months of growth and development - begins.
What is the period of gestation?
It is from formation of the zygote to birth is about 9 months.
In order for this to occur there must be an adequate delivery of oxygen and nutrients and removal of waste products.
This is achieve by the formation of a structure called the placenta.
What is the placenta?
The placenta allows maternal blood to exchange products with the blood supply of the developing foetus.
It allows the passage of nutrients and waste materials between the mother and the foetus.
What happens immediately after fertilization?
The zygote begins to undergo mitotic cell division - a process called cleavage, which results in the formation of a structure called a blastocyst.
This is completed about 7 days after fertilization.
What is a blastocyst?
The blastocyst is a hollow ball of cells.
The outer layer is called the trophoblast and will go on to contribute to the formation of the placenta.
There is also a collection of cells gathered at one end called the inner cell mass, which will eventually become the embryo.
How is the amniotic cavity formed?
Region of the trophoblast nearest to the inner cell mass makes contact with the endometrium
and through the release of enzymes, it burrows into the endometrium
As this happens, the inner cell mass detaches and pulls away from the trophoblasts creating a space that will ultimately forming the amniotic cavity.
What is the structure of a blastocyst?
Figure 9.6 PG 143
What is the process of gastrulation?
About 12 - 14 days after fertilization a process known as gastrulation occurs.
This results in a ‘rearrangement’ of the cells and the formation of three embryonic germ layers - endoderm, mesoderm and ectoderm
What is the endoderm?
The endoderm will eventually form structures which form parts of the reproductive, urinary and digestive systems amongst others.
What is the mesoderm?
The mesoderm will form the skin and skeletal system and all of the muscular and cardiovascular system.
What is the ectoderm?
The ectoderm forms all of the nervous system and parts of the endocrine, respiratory and digestive systems.
What is the process of embryogenesis?
The next 10 weeks sees the occurrence of a process called embryogenesis.
This sees the formation of a structure which has a definite body shape and also of the internal organs.
The period of time to the end of embryogenesis coincides with the first, third or trimester of pregnancy.
What is the second and third trimester?
Corresponds to further growth and development of the embryo which by this time is known as a foetus.
What is parturition?
Its a process which involves the expulsion of the foetus from the mother. (Give birth)
It is characterized by the dilation of the cervix and in increase of the contractility of the uterus.
It is thought that the process of parturition is triggered by an increase in what?
Production of foetal cortisol.
What does cortisol promote?
The conversion of progesterone to oestrogen in the placenta. Oestrogens increase the contractile activity of the uterus and also makes it more sensitive to other substances which increase contractile activity.
(E.g. oxytocin and some of the other prostaglandins)
The increased levels of oestrogen promote what?
The synthesis and release of prostaglandin by the placenta. This increases the contraction of the uterus.
What does increased contractility of the uterus increase?
It increases the release of oxytocin from the posterior pituitary gland, which in turn indicates further contraction.
What occurs following the expulsion of the foetus?
Contractions of the uterus continue to occur.
This results in rupture of the connections between the placenta and the endometrium and the placenta is expelled as the afterbirth.
What is lactation?
Lactation describes the production of milk in breast tissue. This is the initial source of nutrients for the new born baby.
Until birth how does the foetus obtain all its nutrients?
From the mother via the placenta
How does the baby receive nutrients following the immediate period of birth?
From breastmilk produced by its mother.
When does the development of the breasts begin?
During pregnancy to ensure that the nutrient needs are met of the baby.
What does breast tissue consist of?
Ducts known as lactiferous ducts, which terminate at their distal end in structures called alveoli.
At their proximal end the lactiferous ducts open into the nipple region allowing milk to leave the breast
How do the ducts develop and grow?
During pregnancy under the influence of hormones such as progesterone and other placental hormones.
What are the alveoli in the breast?
The sites of milk production.
What are myoepithelial cells?
Contractile cells which are responsible for moving the milk into the lactiferous ducts.
What is one of the most important hormones responsible for milk production?
Anterior pituitary hormone prolactin.
What does an infant suckling on the breast do?
Ensures more prolactin continues to be produced.
What happens following parturition and the loss of the placenta?
There is a sudden loss of steroids (progesterone and oestrogen) produced by the placenta.
This loss of steroids allows prolactin to exert its effect on breast tissue.
How long is the gestation
Gestation (pregnancy):
~ 266 days from conception to birth
What is the early sign of pregnancy
Missed menstruation
What is the blastocyte stage?
The pre-embryonic stage (0-2 weeks)
3 stages:
1. Cleavage
2. Implantation
3. Embryogenesis
What is the myometrium?
To house and support the growing fetus, placenta and membranes
* To grow and stretch to accommodate the growing fetus
The phases of parturition?
1) Dilation stage - Cervical Dilation
2) Expulsion stage
3) Placental stage (after birth placenta detached and expelled.
What modulates contraction?
Oxytocin
