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160 Cards in this Set
- Front
- Back
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The Male & Female Reproductive System
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Reproduction is to ensure continuity of the species by producing offspring
Hormones play a vital role in development & functioning of reproductive organs in both the male and the female as well as contributing to sexual behaviour & drives |
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Males
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Reproductive role of the male is to manufacture sperm & deliver them to the female reproductive tract
In the male reproductive organs & certain hormones play a role in producing sperm to inseminate the oocyte (egg) in the female |
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The Male Reproductive Structures:
The Testes: |
produces sperm & secretes hormones
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The Male Reproductive Structures:
The duct system: |
is a passageway for the transport & storage of sperm & place for the maturation process of sperm
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The Male Reproductive Structures:
The accessory glands: |
(prostate gland, bulbourethral gland and Seminal Vesicles) secrete secretions into the male reproductive tract to assist with sperm viability & motility
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The Male Reproductive Structures:
The supporting structures: |
the penis delivers the sperm & the scrotum houses the testes
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Female
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The reproductive role of the female is production of the oocyte & receiving the male sperm and if the time is suitable to create a fertilised ovum
This is the first cell of a new individual |
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The Female Reproductive Structures:
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These structures are situated within the pelvis between the urinary bladder & rectum
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The Female Reproductive Structures: consists of:
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2 Ovaries
2 Fallopian tubes Uterus Vagina (internal genitalia) Vulva (external genitalia) |
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Uterus
Vagina (internal genitalia) |
The uterus & vagina are midline with an ovary to either side of uterus
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Chromosomes
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Stem cells divide in process of production of the male sperm and the female oocyte. Firstly in order to understand the process of cell division in the male and female it is necessary to understand the make up of the chromosomes in the body's DNA
Chromosomes carry portions of the hereditary information of an organism and is formed from a single DNA molecule containing many genes |
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All human cells contain
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46 Chromosomes
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They are grouped into
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23 pairs termed diploid (2n)
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autosomes
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22 pairs are identical in the male & female and are called autosomes
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The 23rd pair are termed
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sex chromosomes
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Males have a pair of
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X,Y sex chromosomes
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Females have a pair of
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X,X sex chromosomes
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Cell Division:
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When cells divide during the production of the sperm and oocyte the chromosomes also divide.
During cell division all of the chromosomes split, one half are contained within one cell and the other half in another cell. Along with the other chromosomes the 23rd chromosome will split also. |
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In the female producing 2 separate cells
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with a single X (1n) sex chromosome in each
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In the male
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producing a single X (1n) sex chromosome in one cell and a single Y (1n) sex chromosome in the another cell
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1. Mitosis:
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Mitosis is a process where a Stem Cell (parent cell) divides into 2 identical cells (daughter cells) each containing 23 pairs of chromosomes. These are also called diploid cells (2n)
So this process is for replication of cells (not dividing) Note: the chromosomes have not been separated in the process of mitosis but an identical set of cells have been created |
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Meiosis
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The next step is Meiosis and it's purpose is for sexual reproduction. It is a process whereby cell division produces cells but with only half of the number of chromosomes as the parent cell 23(1n).
There are 2 cell divisions during meiosis creating 4 daughter cells |
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Meiosis 1.
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The first division causes the 46 pairs of chromosomes in the parent cell to be divided between 2 daughter cells 23(n). These are termed haploid cells (1n)
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Meiosis 2.
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The second cell division is a bit like mitosis where identical daughter cells are created from the 2 daughter cells with 23(n)
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Oogenesis
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is the term used for the formation of reproductive cells (gametes) in the female.
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Oocyte Production
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Unlike the male in which spem production begins at the onset of puberty, in the female oogenesis begins before birth during foetal development. The male and female both have similar steps in the production of their gametes.
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The sequence to produce oocytes in the female includes:
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1. Mitosis
2. Meiosis I 3. Meiosis II 4. Maturation |
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1. Mitosis
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In the female stem cells migrate to ovaries during early fetal development. This is where these stem cells divide through the process of Mitosis (cell replication) which in turn produces millions of oogonia (immature oocytes)
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oogonia
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immature oocytes
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By the 4th month of fetal development each ovary contains approx
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5 million oogonia
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By birth the oocytes have decreased to
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2 million in each ovary
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2. Meiosis I
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In the female Meiosis I begins before birth
At the time of birth the oogonia have either begun Meiosis I & become primary oocytes or have degenerated (atresia) Even though Meiosis I begins prior to birth the process is arrested here and does not go through the complete process and ceases before birth |
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The daughter cells created by meiosis are called
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primary oocytes
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atresia
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degenerated oogonia
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follicle
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At this stage a follicle also develops around the oocyte which is a layer of cells encasing the oocyte
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At puberty,
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during the development of the ovarian follicle, the primary oocyte restarts Meiosis I and divides into two cells within the follicle:
1. A secondary oocyte 2. A polar body The chromosomes also divide with 23 unpaired chromosomes (1n) in each of these cells Because these cells have divided each cell has only a single sex chromosomes X |
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The secondary oocyte is
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the larger of the 2 cells and receives most of the cytoplasm
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The polar body is
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a smaller cell & receives little (hence it disintergrates later)
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3. Meiosis II
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The secondary oocyte begins Meiosis II before fertilisation but requires fertilisation to occur in order to complete the process of Meiosis II
The begining of Meiosis II causes the secondary oocyte to split again into two more cells each also containing 23 (1n) single chromosomes One is a large cell: the ovum, & the other is a small cell: a secondary polar body When fertilisation occurs the Nuclei in the ovum and in the sperm unite forming a zygote. The beginning of a human life All polar bodies have degenerated |
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Sperm Production
Spermatogenesis |
Prior to puberty testes remain relatively unchanged and no sperm production occurs. At puberty (12-14 years) sperm cell production then begins which takes approximately 65 – 75 days
The testes are able to produce about 300 million sperm a day Spermatogenesis is the term used for the process when stem cells divide and develop into mature sperm cells (gametes) which are called Spermatoza in the male |
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There are 4 phases of spermatogenesis:
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1. Mitosis
2. Meiosis I 3. Meiosis II 4. Spermiogenesis |
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spermatogenesis:
1. Mitosis |
Spermatogonia is a stem cell that undergoes mitosis (replication) into 2 cells termed daughter cells
Half of the daughter cells differentiate into primary spermatocytes that go on to become sperm cells and the other half of daughter cells remain as spermatogonia which continue the process of producing additional spermatogonia and spermatocytes The spermatocytes are called primary spermatocytes as they still have 23 pairs of X & Y sex chromosomes (2n) In the male the 23rd sex chromosome on 2 of the daughter cells will have 1 X(n) sex chromosome and the other 2 will have the Y(n) sex chromosome |
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spermatogenesis:
2. Meiosis I |
The primary spermatocyte divides by Meiosis I into 2 Secondary Spermatocytes
The paired chromosomes from the Primary Spermatocytes split: one set into each Secondary Spermatocyte One secondary spermatocyte carries the Y sex chromosome & the other carries the X sex chromosome |
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spermatogenesis:
3. Meiosis II |
Meiosis II then occurs & the 2 Secondary Spermatocytes divide again each into 2 smaller cells called spermatids
This makes 4 spermatids in total from one Primary Spermatocyte They contain the same 23(n) chromosomes, X or Y, from the secondary spermatocyte they came from These are now called spermatids and 2 spermatids have the X chromosome & the other 2 have the Y chromosome |
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spermatogenesis:
4. Spermatogenesis |
Further development of spermatids into sperm needs to occur
As spermatids develop, a head & tail (flagellum) form At this stage the sperm cell is called spermatozoa Sperm cells then separate from sertoli cell & dispose of excess cytoplasm (spermiation) During spermatogenesis the stem cells divide at the basement membrane of the seminiferous tubule As the spermatocytes divide and mature into spematids they progress in layers from the basement membrane to the centre of the lumen of the seminiferous tubules Synchronized release of the developed sperm ensures that 50% are X chromosome & 50% are Y chromosome |
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Testes
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Are a set of paired oval glands which are housed suspended in the scrotal sac outside the pelvic cavity
The testes originally develop in the retroperitoneal cavity and are connected to the testes by a fibromuscular cord The testes begin their descent into scrotum through inguinal canal in later half of the 7th month of fetal development Connective tissue forms a septa which divides each testis into compartments of 200-300 lobules Each lobule contains Seminiferous tubules: 1-3 tightly coiled tubules Leydig cells: endocrine cells |
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Testes have two functions:
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1. Exocrine cells which produce sperm
2. Endocrine cells which produce testosterone The testes contains a system of ducts which is where sperm production and maturation occur and it is the pathway for sperm to travel to the outside world |
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1. Exocrine cells
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which produce sperm
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Leydig cells:
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endocrine cells
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2. Endocrine cells
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which produce testosterone
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The system of ducts includes:
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Seminiferous tubules
Straight tubules Rete testis Efferent ducts Ductus epididymis Ductus vas deferens |
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1. Seminiferous tubules
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The seminiferous tubules are a set of tightly coiled tubules
They are found in the 200-300 lobule compartments of the testes Sperm are produced & nourished in the seminiferous tubules |
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2. Straight tubules
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Sperm & fluid flows from the seminiferous tubules through short ducts called straight tubules
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3. Rete testis
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The Rete Testes are the next section of the tubules that follow on from the straight tubules. These are a network of ducts that branch.
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4. Efferent ducts/tubules
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The efferent ducts pass outside of the testes and are a series of coiled ducts called the epididymis
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5. Epididymis
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Encases the outside of the testes in the shape of a C. It runs down posterior side of testes & is about 4 cm long
The sperm cells go through final process of maturation here over a 10-14 day period and they become motile & fertile. It also provides temporary storage for immature sperm up to a month or more |
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The epididymis consists of
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a head, body and a tail
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The head
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Contains several coiled efferent ductules
They lead into a single duct called the ductus epididymis |
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The body
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Contains the ductus epididymis
Ductus epididymis is quite long & if straightened out it would be about 6 metres long |
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The tail
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Ductus epididymis ends at the tail
Continues as ductus Vas deferens |
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6. Ductus vas deferens
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Emerges from tail of epididymis & ascends posterior side of testes
Vas deferens becomes connected with blood vessels & nerves that supply testes including the testicular artery, autonomic nerves, veins, lymphatic vessels & cremaster muscle (which contacts and brings the testes closer to the body) The Vas Deferens contains smooth muscle which contracts & conveys sperm along by peristalsis Vas deferens passes out of the scrotum through spermatic cord, along inguinal canal & enters abdominal cavity |
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The spermatic cord
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is a supportive structure that ascends out of the scrotum
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Pelvic & Accessory Muscles
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In the last page you learnt about the structures held within the testes. The Vas deferens passes out of the epididymis through spermatic cord, along inguinal canal & enters abdominal cavity, travels over back of bladder & behind the ureters & approaches the prostrate gland
Just before the vas deferens reaches the prostrate the vas deferens enlarges to form the ampulla Just near the ampulla is a pair of glands called the seminal vesicles (which are an accessory sex glands) The vas deferens and the seminal vessicles lead into short ducts called the ejaculatory duct (approx 2cm long) The ejaculatory ducts project into the prostate gland pass through it & opens into the prostatic urethra These ducts eject sperm into the urethra and transport secretions from the seminal vesicles |
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Accessory Sex Glands
Seminal Vesicles |
A pair of vesicles that lie either side of the bladder inferiorly
Empties into the ejaculatory duct Produces 60% of the volume of semen They secrete a thick yellowish alkaline secretion rich in sugar, vitamins and prostaglandins which nourishes & activates sperm The prostaglandins stimulate muscular contraction in the female reproductive tract |
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Accessory Sex Glands
Prostrate Gland |
This gland is the size of a golf ball & surrounds the prostate urethra
It secretes a milky, slightly acidic fluid that makes up 25% of semen & contributes to sperm motility and viability Prostatic urethra passes through prostate Secretions enter the prostatic urethra through a the ejaculatory duct at ejaculation Enlarges with age |
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Accessory Sex Glands
Bulbourethral Glands |
Also called Cowper's Gland
Pair of pea-sized mucous glands that lie inferior to the prostrate gland either side of the membranous urethra The ducts of each gland unite to form a single duct & enters the spongy urethra at base of penis They produce a thick, clear mucus which drains into the penile urethra when a man is sexually excited This cleanses the urethra of acidic urine & lubricates the end of the penis |
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Accessory Sex Glands
The Urethra |
e Urethra
Passageway for sperm and urine Male Urethra is 15 to 20cm long The Urethra is divided into three regions |
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Prostatic urethra:
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2-3cm long section of urethra passing through the prostrate
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Membranous urethra:
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1 cm long section of urethra passing through the perineum
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Spongy urethra:
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15cm long section of urethra passing through the penis
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Secretions of the accessory sex glands
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Semen is made up of sperm cells & secretions from accessory sex glands & testes in the male reproductive system
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Seminal vesicles produce
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60% of secretions
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Prostrate gland produce
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30% of secretions
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Testes produce
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5% of secretions
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Bulbourethral glands produce
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5% of secretions
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Semen
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Semen is a milky white, sticky secretion of sperm & accessory gland secretions
Alkaline (pH 7.2-7.6) Neutralises the acidic environment of the vagina (pH 3.5-4) Sperm are sluggish in acid conditions 2-6mls are ejaculated Each ml of semen contains 50-100 million sperm |
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Male Supportive structures
The scrotum |
is a pouch of skin supporting the testes
The skin of the Scrotum consists of |
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1. a layer of loose connective tissue (superficial fascia)
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The loose connective tissue divides scrotum by a septum into two sacs each containing a single testis
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2. smooth muscle: called dartos muscle
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The dartos muscle contracts with cold elevating the testes & relaxes with heat descending the testes away from the body
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Temperature regulation of testes
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The dartos muscle is important in controlling the temperature within the testes as viable sperm cannot be produced at body T˚.
For sperm survival T˚ needs to be 3˚ lower than core body T˚ The cremaster muscle in spermatic cord & dartos muscle elevates testes closer to body on exposure to cold & during arousal Warmth relaxes the muscles and the testes move away from the body so they don’t overheat |
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Core body T˚= 38˚ scrotal T˚=
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scrotal T˚= 35˚
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Penis
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The penis is a supporting structure of the male reproductive system and contains spongy urethra & is passageway for urine & ejaculation of semen
The penis consists of |
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1. Root
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is the portion attached to the body & consists of the bulb of the penis, which is attached to the deep muscles of perineum and the crura of the penis is attached to coxae muscle which when contracted aid ejaculation.
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2. Body (shaft)
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of the penis is composed of three cylindrical masses of spongy tissue that surround the penile (spongy) urethra
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a. corpora cavernosa:
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Two columns forming the dorsum (back) & sides of penis
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b. corpus spongiosum
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Forms a cap over the distal end of the penis (glans penis)
Expands to form bulb of penis |
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b. Spongy Urethra
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Passes through corpus spongiosum
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tunica albuginea
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Each of these cylindrical masses is surrounded by fibrous tissue called tunica albuginea
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3. Glans penis that includes the prepuce or foreskin
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Is acorn shaped and forms the distal enlarged end of spongy corpus spongiosum
The distal urethra enlarges within glans penis & forms an opening called external urethral orifice The foreskin or prepuce covers the glans penis The transport of semen through the penis occurs as a result of erection of the penis and ejaculation of the semen |
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Male Hormonal Influences
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There are 5 hormones that influence the reproductive system in the male. Some of these hormones function in both the male and female but obviously have different roles in each.
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1. Gonadotropin-Releasing Hormone (GnRH)
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Produced by neuro secretory cells in Hypothalamus and stimulates LH and FSH release from the anterior pituitary gland
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2. Luteinising Hormone (LH)
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Produced by Anterior Pituitary and the release is stimulated by GnRH released from the hypothalamus
Low levels of testosterone influence GnRH release which in turn stimulates LH release. LH stimulates Leydig cells in seminiferous tubules to produce testosterone When testosterone levels rise this shuts off & inhibits further release of LH |
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3. Testosterone
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As mentioned above testosterone inhibits secretion of LH and GnRH
Before birth, testosterone stimulates the development of male sex organs & descent of testes. At puberty, it promotes development of reproductive organs to reach adult size & underlies sex drive It is responsible for development of secondary male sex characteristics: Muscular and skeletal growth – leading to wide shoulders and narrow hips Pubic, axillary, facial and chest hair Thickening of skin Increased sebaceous glands secretion Enlargement of the larynx – deepening of voice A Negative feedback system controls blood levels of testosterone Receptors in hypothalamus detect ↑ blood levels of testosterone ↓ Secretion of GnRH occurs Anterior pituitary ↓ release of FSH & LH Leydig cells ↓ release of testosterone Blood level returns normal |
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4. Follicle Stimulating Hormone (FSH)
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FSH release is initially stimulated by GnRH in the hypothalamus which influences secretion of FSH by the Anterior Pituitary Gland
Secretion is inhibited by a hormone called Inhibin which is secreted by Sertoli cells of the testes FSH acts synergistically with Testosterone to stimulate Sertoli Cells to promote sperm production |
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5. Inhibin
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When the sertoli cells detect an increase in sperm production it releases the hormone inhibin which stops FSH release and therefore sperm production
If sperm production is proceeding too slowly then less inhibin is released by the sertoli cells and more FSH will be secreted so that sperm production will be increased |
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The anatomy of the female reproductive system consists of
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1. 2 Ovaries
2. 2 Fallopian tubes 3. Uterus 4. Vagina (internal genitalia) 5. Vulva (external genitalia) 6. Mammary glands |
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The organs 1-5 are situated
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within the pelvis between the urinary bladder & rectum
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The uterus & vagina are
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midline with an ovary to either side of uterus
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1. Two Ovaries
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The ovaries are a paired set of glands one sitting either side of uterus.
they are size & shape of almonds which are held in position by a series of ligaments Internally the ovaries have numerous small sac-like structures distributed throughout called ovarian follicles. Each of these ovarian follicles has an oocyte surrounded by a layer of follicular cells |
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The Broad ligament
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is a double fold of peritoneum that spreads over uterus & attaches to the ovaries & fallopian tubes
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The Ovarian ligament
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anchors ovaries to superior margin of the uterus
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The Suspensory ligament
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attaches ovaries to the pelvic wall
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2. Two Fallopian tubes
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The fallopian tubes are two hollow tubes 10 cm long that extends out laterally from the uterus toward the ovaries
They do not actually connect with the ovaries but open to a funnel-shaped end close to the ovaries The funnel shaped end is called the infundibulum which has a fringe of finger-like projections called fimbriae The fallopian tubes role is to transport the secondary oocyte (and if fertilised the ovum) from the ovaries to uterus The fimbriae assist with this process and beat in a wave-like motion creating a fluid current carrying the secondary oocyte into the fallopian tube Once inside movement of the cilia lining fallopian tubes & peristalsis of the tubes encourage movement of the oocyte toward the uterus Sperm have to enter the fallopian tubes & swim against the current created by the cilia in order to reach the oocyte for fertilisation to take place. Fertilisation must occur within 24 hours and in the fallopian tubes Some oocytes are lost in the pelvic cavity and never enter the fallopian tubes |
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3. Uterus
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The uterus lies in pelvic cavity between the bladder & rectum
It is a pear shaped, hollow muscular organ In a female who has never been pregnant the uterus is about 7.5 cm long & 5cm wide and larger in women who have been pregnant Atrophies (shrinks) when sex hormones are low (menopause & oral contraceptives) The role of the Uterus is to receive & nourish a fertilised ovum The Uterus is divided into 3 anatomical regions: |
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Fundus:
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dome shaped upper portion superior to the uterine (fallopian) tubes
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Body:
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central portion that tapers
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Cervix:
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inferior narrow portion opening into the vagina
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Tissue Layers of the Uterus
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The wall of the uterus has 3 layers:
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Perimetrium:
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outer serous layer of visceral peritoneum
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Myometrium:
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bulky middle layer consisting of 3 layers of smooth muscle
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Endometrium:
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inner highly vascular layer consisting of simple columnar epithelium lying on a region of lamina propria & endometrial glands
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4. Vagina (internal genitalia)
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The vagina is highly elastic muscular tube lying between urethra & rectum and is 8-10 cm long
It provides a passage way for delivery of a baby, menstrual flow & semen during sexual intercourse The distal end of the Vagina is partially closed by a hymen It has a first line of defense mechanism: an acidic environment which retards microbial growth |
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5. Vulva (external genitalia)
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The Vulva is the external genitalia & comprises of:
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Mons pubis:
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is a round cushion of fat over the symphysis pubis covered with skin & hair
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Labia:
Labia majora – |
two outer folds of skin from the mons pubis to the perineum consisting of adipose & connective tissue covered with hair
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Labia:
Labia minora – |
inner hair free delicate folds of mucosal tissue containing sebaceous glands
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Clitoris:
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Is located in front of the labia minora & contains sensitive erectile tissue & nerves
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Vestibule:
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Is a region found between the labia minora and contains:
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The hymen
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The distal end of the Vagina is partially closed by a hymen
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Vaginal orifice
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is an opening of the vagina into the vulva
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External urethral orifice
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is an opening of the urethra into the vulva
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Paraurethral Glands,
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found in the walls of the urethra, Ducts open either side of the urethral orifice
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Bartholin’s glands,
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either side of vaginal orifice, Flank the vagina and lubricate the distal end of the vagina during intercourse
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Perineum:
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Perineum:
The perineum is a diamond shaped region located between the thighs The area contains the external genitalia & anus and extends from mons pubis to the coccyx It is further divided into anal & urogenital triangles and the area is found in both males & females |
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6. Mammary glands
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Are located in each breast and consists of modified sweat glands that produce milk
Each nipple contains closely spaced openings lactiferous ducts that open externally of which milk emerges from these ducts Within the mammary gland are 15-20 lobes divided into smaller compartments called lobules. These lobules contain milk-secreting glands (alveoli) embedded in connective tissue that produce milk The pigmented area surrounding the nipple is the areola The function of the mammary glands is lactation which includes synthesis, secretion & ejection of milk Milk production is stimulated by the hormone prolactin Milk ejection is stimulated by the hormone oxytocin & is influenced by the infant suckling on the mother’s breast |
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There are 7 hormones that influence the female reproductive system.
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These hormones influence the female ovarian and uterine cycles
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1. Gonadotropin –Releasing Hormone (GnRH)
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Is released by Hypothalamus in response to low levels of oestrogen & progesterone
GnRH assists in controlling both the uterine & ovarian cycles by stimulating the Anterior Pituitary Gland to release FSH & LH |
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2. Follicle Stimulating Hormone (FSH)
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Initiates development of primary follicles in stimulating follicular growth so it can nourish and prepare the oocyte for release at ovulation
It also stimulates secretion of oestrogen from ovarian follicles |
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3. Luteinizing Hormone (LH)
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Assists with further development of ovarian follicles and together with FSH stimulates secretion of oestrogen from ovarian follicles
A surge in LH at day 14 of the ovarian cycle triggers ovulation & continues to influence production of the corpus luteum (the follicle left after ovulation) post ovulation |
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4. Oestrogen
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Is secreted by ovarian follicles and promotes development & maintenance of female reproductive structures
It increase protein anabolism including building strong bones and lowers blood cholesterol (so it is a protective factor for heart disease until post menopause) Moderate levels inhibit release of GnRH, FSH & LH as they all influence the secretion of oestrogen Oestrogen is responsible for secondary sexual characteristics of the female. |
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Secondary Sexual Characteristics
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Occurs during adolescence age 11 through to 14
Release of hormones cause rapid growth spurt Pelvis broadens & lightens Breast & hip enlargement (fat deposits) Reproductive organ enlargement Coarse pubic & underarm hair & fine body hair Higher pitched voice than male Menses |
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5. Progesterone
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Progesterone is secreted by the corpus luteum & placenta
It works with oestrogen to prepare the endometrium for implantation of a fertilised ovum and helps to maintain pregnancy by inhibiting contractions of the uterus and uterine tubes It also prepares the mammary glands for milk production High levels of progesterone inhibit GnRH and LH as the female body does not want to stimulate more oocytes being released during pregnancy |
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6. Relaxin
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Produced by corpus luteum during each monthly cycle
Inhibits contraction of uterine smooth muscles to allow implantation if fertilization occurs During pregnancy placenta produces more to relax the smooth muscle and lessens the risk of miscarriage During labour increases flexibility of pubic symphysis & dilates the cervix |
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7. Inhibin
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Inhibin is secreted by granulosa cells of the growing follicle and by the corpus luteum after ovulation
Inhibits release of FSH and to a lesser extent LH Hormonal changes also occur in cycles throughout the ovarian & menstrual cycles These occur through positive & negative feedback systems |
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Anterior Pituitary Hormones
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Hypothalamus secretes Gonadotrophin releasing hormone (GnRH) influencing
2 hormones secreted from the anterior pituitary gland and these influence follicular development and ovulation: FSH & LH Low levels of oestrogen & progesterone cause GnRH release from Hypothalamus This stimulates release of FSH & LH from anterior pituitary gland FSH & LH causes follicular development The follicle secretes oestrogen Oestrogen stimulates a positive feedback mechanism ↑ release of more LH A surge in LH occurs & causes ovulation |
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Ovarian Cycle Hormones
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After ovulation the corpus luteum is produced
The corpus luteum secretes higher levels of progesterone & oestrogen which ↓ FSH & LH release ↓ in FSH prevents new follicles developing during pre-ovulatory phase in case the oocyte is fertilised and a pregnancy occurs |
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Menstrual Cycle Hormones:
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There are hormones secreted from the ovarian follicle at different stages and these influence or inhibit the menstrual cycle depending on if there is fertilization of an oocyte:
The follicle secretes oestrogen & inhibin After ovulation the Corpus Luteum secretes oestrogen, progesterone, inhibin & relaxin Progesterone & oestrogen also prepares the endometrium post ovulation in preparation for a fertilised egg If fertilisation doesn’t occur the Corpus Luteum degenerates resulting in oestrogen & progesterone levels falling Causing the endometrial lining to deteriorate The lining is shed & menstruation occurs |
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The Ovarian Cycle consists of
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several phases occurring in the ovaries over an average of 28 days
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Primordial Follicle
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prior to birth the oocyte develops a protective layer around it called the Primordial Follicle
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The follicular development
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also occurs during this phase. Remember prior to birth the oocyte develops a protective layer around it called the Primordial Follicle. The rest of the follicular development occurs during the ovarian cycle
The stages of development of the follicle includes: a. Primordial follicle (which occurs before birth) b. Primary follicle c. Secondary follicle e. Mature follicle (graafian) f. Corpus Luteum (yellow body) These events occurring in the ovarian cycle and follicular development are controlled by hormones released from anterior pituitary, hypothalamus and the follicle itself |
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a. Follicular phase day 1 -14:
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Includes the Menstrual phase, Pre-ovulation & Ovulation
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b. Post-ovulatory phase day 15-28:
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Also called Luteal phase
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a. Follicular Phase:
Menstrual Phase Day 1-5 |
Day 1 is when FSH & LH is released from anterior pituitary gland and stimulates 20-25 primordial follicles to develop
At the same time Menses begins: discharging of menstrual fluid The Primary oocytes within the ovaries recommence Meiosis I The granulosa cells of the Primordial follicles start to multiply around the oocyte which then develops into primary follicles The granulosa cells around the follicles secrete follicular fluid rich in oestrogen within the follicles and the primary follicles evolve into secondary follicles The secondary follicles develop an antrum (cavity) that fills with fluid & pushes the primary oocyte to one side At this stage which is day 5 of the secondary follicular development, menstruation ceases |
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Pre Ovulation: Day 6-14
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Spans from end of menstruation to ovulation (day 14)
The secondary follicles secrete low levels of oestrogen which stimulate FSH & LH secretion On day 6 in one ovary the most dominant follicle thrives and starves the other follicles in that ovary of available FSH & they deteriorate This one follicle now matures into graafian follicle ready for ovulation The oocyte within the graafian follicle completes meiosis I & starts meiosis II |
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Ovulation: Day 14
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On day 13 of pre-ovulatory phase the graafian follicle releases more oestrogen and the ↑ oestrogen levels ↓ FSH levels (-ve feed back). This also ↑ LH levels by positive feedback:
Oestrogen stimulates GnRH release & directly stimulates the anterior pituitary to release LH and these inturn stimulate the follicle to release more oestrogen & so it continues A surge of LH occurs over 24 hour period and this causes the wall of the follicle to weaken & ruptures releasing the secondary oocyte into the pelvic cavity |
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Ovulation then occurs on
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day 14 of the ovarian cycle several hours after the LH surge. It takes all of 2-3 minutes to occur
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Several things happen to prepare for the released oocyte;
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Fallopian tubes become oedematous
Fimbriae caress the ovary in time with the woman's heart beat Cilia create a current When released the primary oocyte is swept into the uterine (fallopian) tube Many oocytes are lost in the peritoneal cavity & don’t ever enter the fallopian tubes |
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B. Post Ovulatory Phase: Also called Luteal Phase
Starts after ovulation day 15-28 |
The ruptured follicle collapses & becomes the corpus luteum (yellow body)
Progesterone & oestrogen are produced by the corpus luteum which stimulates the endometrium to increase in size & secrete a fluid rich in nutrients which can sustain an embryo until implantation The corpus luteum also produces hormones relaxin preventing contraction of the uterus & inhibin Further events depend on fertilisation If the secondary oocyte is fertilised then the corpus luteum remains active for 3 months secreting oestrogen & progesterone preventing menses If no fertilization occurs the corpus luteum degenerates causing a ↓ in production of the hormones oestrogen, progesterone, inhibin & relaxin Which stimulates the hypothalamus to secrete GnRH & subsequent release of FSH & LH from anterior pituitary to begin the follicular cycle again |
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corpus luteum
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yellow body
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The Menstrual Cycle
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A series of cyclic changes occur to the endometrium that leads to menses
Hormones are released by the ovaries that control the menstrual (uterine) cycle and influence the endometrial lining of the uterus to go through cyclic changes |
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The Menstrual Cycle is divided into 4 phases
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1. Menstrual phase (day 1- 5)
2. Proliferative phase (day 6-14) 3. Secretory phase (day 15-26) 4. Premenstrual phase (day 27-28) |
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1.Menstrual phase (day 1- 5)
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Occurs for approx 1-5 days
The first day of bleeding marks day 1 of the menstrual phase Blood, serous fluid & degenerated endometrial lining discharge from uterus through the cervix & into the vagina. Approx 50-150mls each month. Menses or bleeding occurs for 3-5 days Menstrual fluid does not usually clot as it contains fibrinolysin |
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2.Proliferative phase (day 6-14)
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Rebuilding of endometral lining that was lost during last menstruation period which shrunk to 0.5mm thick
Oestrogen released by the growing follicle stimulates repair of the endometrium in case of fertilisation and preparation for implantation Progesterone causes hypertrophy (increase in cell size) of the uterine lining and blood vessels in the endometrium become thick & velvety The thickness of the endometrium ↑ up to 2-3 cm thick |
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3.Secretory phase (day 15-26)
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During the secretory phase the endometrial lining thickens further up to 12-18 mm
The corpus luteum secretes progesterone after ovulation This encourages the lining to become a moist & nutritious bed ready for an embryo if pregnancy occurs |
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4.Premenstrual phase (day 27-28)
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This is the last 2 days of the menstrual phase where there is endometrial degeneration in the absence of a pregnancy
Progesterone levels fall sharply Arteries of endometrium spasm causing ischaemia to endometrium. Necrosis occurs & pools of blood form as blood vessels, endometrial glands & stroma degenerate This forms the menstrual fluid |
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Fertilisation
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Fertilisation usually occurs in fallopian tubes 12-24 hours after ovulation
Sperm are viable for about 48 hours & the secondary oocyte is viable for about 24 hours There are only 3-4 days of each cycle when fertilization is likely to occur Sperm take 1-2 hours to swim up the reproductive tract Contraction of the uterus & fallopian tubes help to transport the sperm Many sperm loose their way & die |
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After fusion the oocyte’s 23 (n) chromosomes merge with
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the sperm’s 23 (n) chromosomes to produce a single nucleus with 46 (2n) chromosomes
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If the sperm’s 23rd sex chromosome is an X then the zygote is a
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female (X,X)
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If the sperms 23rd sex chromosome is a Y then the zygote is a
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male (X,Y)
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The fertilised ovum is now called a
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a zygote & contains all the genetic information to produce a complete individual
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