The gonads 1 Flashcards
What enzyme converts Adrostenedione into oestrone?
AROMATASE
What are the names of the Sex Steriods produced in Men by the Gonads?
Sate the name of the sex steriods produced in large amounts and the sex hormones produced in much smaller amounts in the gonads?
Androgens- Large
Oestrogen , Progestogens- Small
In response to … stimulation, the Thecal Cells will start steroid hormone synthesis and produce the ……………….
In response to LH stimulation, the Thecal Cells will start steroid hormone synthesis and produce the Androgens
What does inhibin do?
INHIBIN - feeds back on the axis and inhibits FSH secretion
What is the main hormone during the luteal phase?
LUTEAL PHASE - PROGESTERONE is the dominant hormone
The spermatozoa produced travel down to the collection in the …………. …………. where they are concentrated and drained by the …………. …………… into the …………… where they are stored
The spermatozoa produced travel down to the collection in the Rete Testis where they are concentrated and drained by the Vasa efferentia into the epididymis where they are stored
What enzyme converts progesterone to 17-OH Progesterone to Androstenedione?
The same enzyme is used for both reactions
17,20-lyase
17α-hydroxylase
They are both the same enzyme
What converts 17-OH progesterone to 11-deoxycortisol?
21α-Hydroxylase
When event signifies the start of the menstral cycle?
Historically taken to begin on the first day of menstruation
Describe the embryogenesis of gonads?
Name the cells present in the undifferentiated structure which forms into the gonad and state what cells they become in the testes?
Ovaries and Testes develop from the same undifferentiated gonad. By about 6 weeks of embryogenesis this undifferentiated structure consists of primordial germ cells, support cells and laydic cells and it is a gene on the Y chromosome- the SRY gene that triggers the differentiation into the testes. So it triggers the these primordial germ cells to differentiate into spermatogonia, the support cells differentiate into sertoli cells and the steriodigenic cells differentiate into leydig cells. In the abscence of the Y chromosome the Ovaries will form
Cross section of a seminiferous tubule
Under the influence of FSH, the follicles will get bigger until they eventually get to their maximum size which is the …………. Follicle which is ready for ovulation
Under the influence of FSH, the follicles will get bigger until they eventually get to their maximum size which is the Graffian Follicle which is ready for ovulation
Postaglandins help with the expulsion of menses
NB: The follicle most sensitive to FSH do not undergo ATRESIA
The endometrium is the lining of the uterus and contains a ……………. ……………… layer and a …………… …………… layer
The endometrium is the lining of the uterus and contains a superficial epithelial layer and a deeper stromal layer
How much cooler is the scrotom to the core body temperatureand why is this important?
The scrotum is 2-3 degrees cooler than core temperature - which is critical for spermatogenesis
Overview
Proliferative - Oestradiol is the dominant influence - causes proliferation of the endometrium
Endometrium thickens - it stimulates mitosis and the glands which are initially straight becomes enlarged and they coil - increased blood supply
Secretory - Progesterone is the dominant influence
In the secretory phase, oestrogen and progesterone are secreted
The glands become secretory, they dilate and produce large amounts of glycogen and mucopolysaccharides and other things
The mucosa is engorged with blood
If fertilisation doesn’t take place, oestrogen and progesterone levels fall so they no longer stimulate the epithelium
You get spasm of the blood vessels, tissue becomes necrotic and the blood is shed
Progesterone reverses the effects of oestrogen - it reduces the proliferation that oestrogen causes by reducing oestrogen receptors
Progesterone also increases the secretory activity of the cells in the myometrium (middle layer of the uterus lining) - glands become wider and produce various substances which make the environment suitable for implantation to occur
What is Spermatogonia?
A spermatogonium (plural: spermatogonia) is an undifferentiated male germ cell. Spermatogoniaundergo spermatogenesis to form mature spermatozoa in the seminiferous tubules of the testis.
Where in the testes does spermatogenesis occur?
Spermatogenesis takes place in the SEMINIFEROUS TUBULES of the testes
The dominant follicle will produce large amounts of ……………….
The dominant follicle will produce large amounts of oestrogen
Thecal cells do NOT have the ……………….enzymes to convert ………………….. to oestrogen
The Granulosa cells have …….. Receptors and stimulation of these cells will stimulate the ………………. enzyme which convert these ……………..into oestradiol
Thecal cells do NOT have the aromatase enzymes to convert androgens to oestrogen
The Granulosa cells have FSH Receptors and stimulation of these cells will stimulate the aromatase enzyme which convert these androgens into oestradiol
As these cells develop they towards the lumen and are released into the lumen
What effect does oestrogen have on the endometrial cycle?
It is the oestrogens (produced in the follicular phase) which cause the effects that we see in the proliferative phase in the endometrial cycle
Oestrogen causes proliferation of the endometrium - there is an increase in mitosis and an increase in the progesterone receptors (which acts later in the cycle) and an increase in oestrogen receptors
The endometrium gets thicker, the glands get bigger and the blood vessels get longer
What effect does progesterone have on the menstral cycle?
We have follicles with the oocyte that is stuck in the early stage of meiosis
The follicle will develop over embryonic life and will develop to this pre-antral stage
Up until the pre-antral stage, gonadotrophins are NOT needed
To develop any further requires FSH (to get to early-antral stage)
What happens if the FSH levels are not at a high enough level?
If FSH isn’t at a high enough level to continue the development they will undergo atresia
Why is the FSH level slightly raised at the beginning?
FSH levels are slightly raised at the beginning - this small increase is enough to rescue the dormant follicles so they continue their development
Lable the diagram below
The seminiferous tubules are lined by layers of …………… and layers of ………………. ………
The seminiferous tubules are lined by layers of spermatogonia and layers of Sertoli cells
What is spermatogenesis?
production of mature spermatozoa
What type of receptors do sertoli cells synthesise?
Synthesise FSH and androgen receptors
Aproximately how many days does the menstral cycle last? (give a range as well)
Lasts approximates 28 days (can last from 20 to 35+)
As soon as the Primary Oocytes are formed they enter the first meiotic division
As soon as they get to the first stage in meiosis (PROPHASE) the development is HALTED so they stay in that stage of development
List the type of hormones produced by the gonads and state their carbon numbers?
What do sertoli cells respond to?
What hormones?
SERTOLI - respond to FSH + Androgen
Where does spermatogenesis occur in the seminiferous tubule?
How does spematogonia get past the blood-testes barrier?
The spermatogonia have a special mechanism by which they can get through the barrier
The spermatogonia move into the Sertoli cells and they are enclosed in the cytoplasm of the Sertoli cells where spermatogenesis actually takes place
What enzyme converts corticosterone to aldosterone?
Aldosterone Synthase
The cycle can be divided into the………….. ………. (1st half) and the ………… …………. (2nd half) - it lasts about 28 days and ovulation occurs mid-cycle
Menstruation occurs in the first … days of the cycle
FSH levels are slightly raised at the beginning - this small increase in enough to rescue the dormant follicles so they continue their development
These follicles start growing and as they grow they start producing …………………….
The 17b-oestradiol has a negative feedback effect on …………………………. secretion
As these follicles grow, one of them is selected as the …………….. follicle and the others will undergo …………..
The cycle can be divided into the follicular phase (1st half) and the luteal phase (2nd half) - it lasts about 28 days and ovulation occurs mid-cycle
Menstruation occurs in the first 5 days of the cycle
FSH levels are slightly raised at the beginning - this small increase in enough to rescue the dormant follicles so they continue their development
These follicles start growing and as they grow they start producing 17b-oestradiol
The 17b-oestradiol has a negative feedback effect on gonadotrophin secretion
As these follicles grow, one of them is selected as the DOMINANT follicle and the others will undergo atresia
What is the name of the enzyme that converts Cholesterol to pregnenolone
p450 side chain cleavage enzyme
What cells produces inhibin?
What is Inhibin produced in response to?
Sertoli cells
FSH
What enzyme converts testosterone into 17 beta-Oestradiol?
AROMATASE
What effects does progesterone have?
the second half of the menstrual cycle after ovulation; the corpus luteum secretes progesterone which prepares the endometrium for the implantation of an embryo
Progesterone reverses the effects of oestrogen - it reduces the proliferation that oestrogen causes by reducing oestrogen receptors
Progesterone also increases the secretory activity of the cells in the myometrium (middle layer of the uterus lining) - glands become wider and produce various substances which make the environment suitable for implantation to occur
How are primordial follicals formed?
Germ cells multiply up to produce oogonia - at this point they are all DIPLOID
The oogonia then multiply again to produce Primary Oocytes
As soon as the Primary Oocytes are formed they enter the first meiotic division
As soon as they get to the first stage in meiosis (PROPHASE) the development is HALTED so they stay in that stage of development
At this time, the oocytes form a layer of cells around them (primordial follicles - the oocytes are in a follicle)
This all occurs before birth - you have your primordial follicles with your oocytes in it before birth
The primordial follicle consists of an oocyte surrounded by a single layer of flat, supporting granulosa cells.
What is the function of leydig cells?
Leydig cells contain enzymes so that they can make and secrete testosterone
It is important that the Leydig cells are nearby because testosterone is needed for spermatogenesis to take place
What enzyme converts Deoxycorticosterone to Corticosterone?
11 Beta hydroxylase
State the names of the cells and the chromosome numbers of cells during the process of oogenesis?
Germ cells multiply up to produce oogonia - at this point they are all DIPLOID
The oogonia then multiply again to produce Primary Oocytes
As soon as the Primary Oocytes are formed they enter the first meiotic division
As soon as they get to the first stage in meiosis (PROPHASE) the development is HALTED so they stay in that stage of development
At this time, the oocytes form a layer of cells around them (primordial follicles - the oocytes are in a follicle)
This all occurs before birth - you have your primordial follicles with your oocytes in it before birth
The oocytes are dormant for the next 12-50 years (stuck in that phase of meiosis)
After 12 years (at puberty) some of the oocytes will be rescued - the last lot won’t be rescued until around menopause
While they’re in this stage there is a process of ATRESIA -some of the cells are degenerating and start to die
When puberty starts, under the influence of FSH - the FSH will rescue a group of these cells and they can continue the development
It isn’t until around the time of ovulation that they complete the first meiotic division to produce the Secondary Oocyte and a Polar Body
REMEMBER: in females in meiosis, there is an unequal distribution of the cytoplasm - one cell retains all the cytoplasm and the cells resources and the other daughter cells (the polar body) contains just the chromosomes and these cells will eventually die off
The secondary oocyte enters the second meiotic division and it won’t complete that division until FERTILISATION
If fertilised, it will produce the Ovum and the Second Polar Body
Ovum and Second Polar Body - again there is unequal distribution of cytoplasm - the ovum retains all the cells resources (and so becomes one of the largest cells in the body) - the Second Polar Body will eventually disintegrate
We have follicles with the oocyte that is stuck in the early stage of meiosis- prophase
The follicle will develop over embryonic life and will develop to this …………………. stage
Up until the …………….. stage, ……………. are NOT needed
We have follicles with the oocyte that is stuck in the early stage of meiosis
The follicle will develop over embryonic life and will develop to this pre-antral stage
Up until the pre-antral stage, gonadotrophins are NOT neede
What happens when the Oestrogen and Progesterone levels fall?
When oestrogen and progesterone levels fall, it means that it is NOT supporting the endometrium any more
You get changes the endometrium - vasospasm in some blood vessels, necrosis of the tissue and contraction of the muscle and loss of the tissue with the blood - MENSTRUATION
As a result of the decrease in progesterone and oestrogen, the negative feedback is reduced so FSH levels start to rise again so you get back to the start of the cycle
What is the name of the process which involves the production of a ripe ova?
OOGENESIS
ova. [oh-vuh] (Show IPA) 1. Cell Biology. the female reproductive cell or gamete of animals, which is capable of developing, usually only after fertilization, into a new individual.
Lable the diagram below
The Sertoli cells provide ………….. support for spermatogonia and provide ……………. support as well
The Sertoli cells provide structural support for spermatogonia and provide metabolic support as well
What type of follicle is the follicle below?
This follicle is a Graffian Follicle - this follicle has reached its maximum size and is ready for ovulation
All follicles are embedded in the ovarian stroma
You can see a remnant of the last corpus luteum
Where are thecal and granulosa cells found in the follicle and what type of receptor do they express?
In the follicle you have:
Thecal Cells - outer - LH Receptors
Granulosa Cells - inner - FSH Receptors
Lable the diagram below
After ovulation, the empty follicle is transformed into the ………….. ………… which continues to produce ———————- and produces large amounts of ……………….
After ovulation, the empty follicle is transformed into the corpus luteum which continues to produce 17b-oestradiol and produces large amounts of progesterone
The outer layers of the follicle are the ………….cells and the inner layer are the …………… cells
The outer layers of the follicle are the Thecal cells and the inner layer are the Granulosa cells
What is the importance of tight juctions between sertoli cells?
This tight connection means that it forms a blood-testis barrier which keeps out large proteins such as antibodies
Therefore, it protects spermatozoa from immune reactions
What are sertoli cells connected by?
The Sertoli cells are connected at the periphery by tight junctions
State the names of the cells and the chromosome numbers of cells during the process of spermatogenesis?
How long does spermatogenesis last for?
We start off with the germ cells in embryogenesis and they multiply and differentiate to produce spermatogonia which are DIPLOID
Around puberty - when FSH starts to be released - the spermatogonia divide by mitosis to produce either more spermatogonia or to produce primary spermatocytes
Primary spermatocytes are also DIPLOID
Primary spermatocytes enter the first meiotic division to give secondary spermatoctyes which are HAPLOID
Secondary spermatocytes enter second meiotic division to give spermatids
Spermatids then mature and differentiate into spermatozoa
This whole process takes around 70 DAYS
In the ………………., nutrients are secreted for them - they mature in here and attain their motility
In the epididymis, nutrients are secreted for them - they mature in here and attain their motility
What does a surge of gonadotrophins stimulate?
The dominant follicle will produce large amounts of oestrogen
If oestrogen levels are high enough for long enough (36 hours), instead of producing negative feedback effect it will switch to a positive feedback effect which stimulates a SURGE OF GONADOTROPHINS (LH and FSH)
This surge of gonadotrophins stimulates ovulation
FSH levels are slightly raised at the beginning - this small increase in enough to rescue the dormant follicles so they continue their development
These follicles start growing and as they grow they start producing …………………….
FSH levels are slightly raised at the beginning - this small increase in enough to rescue the dormant follicles so they continue their development
These follicles start growing and as they grow they start producing 17b-oestradiol
What happens of the oestrogen levels are high enough for long enough (36 hours)?
The dominant follicle will produce large amounts of oestrogen
If oestrogen levels are high enough for long enough (36 hours), instead of producing negative feedback effect it will switch to a positive feedback effect which stimulates a SURGE OF GONADOTROPHINS (LH and FSH)
This surge of gonadotrophins stimulates ovulation
Lable the diagram below
What type of receptors do Leydig cells produce?
LH receptors
What effect does oestrogen and progesterone have together?
Effect of oestrogen and progesterone together is a negative feedback effect on the gonadotrophins - the gonadotrophin levels become low
What enzyme converts Progesterone to Deoxycorticosterone?
21 hydroxylase enzyme
The testes develop in the …………. but descend into the …………… just before birth
The testes develop in the abdomen but descend into the scrotum just before birth
t this time, the ….. surge occurs and causes rupture of the follicle and release of the egg
After ovulation, the follicle is transformed into a ……… ………. which continues to secrete ……………. and …………….. in the …………. phase of the cycle
The surge of LH will stimulate the egg to complete the first meiosis
At this time, the LH surge occurs and causes rupture of the follicle and release of the egg
After ovulation, the follicle is transformed into a corpus luteum which continues to secrete oestrogen and progesterone in the Luteal phase of the cycle
The surge of LH will stimulate the egg to complete the first meiosis
Draw a graph showing how the numbers of Spermatogonia and Oogonia change from before birth to meopause?
Y axis- Number of germ cells ( x10^6)
Spermatogonia are quiescent during childhood- prepuberty
Follicular atresia is the breakdown of the ovarian follicles, which consist of an oocyte surrounded by granulosa cells and internal and external thecacells. It occurs continually throughout a woman’s life, as she is born with millions of follicles but will only ovulate around 400 times in her lifetime.[1][2]Typically around 20 follicles mature each month but only a single follicle is ovulated; the follicle from which the oocyte was released becomes the corpus luteum. The rest undergo follicular atresia
During embryogenesis - germ cells proliferate, reaching large numbers around 6-7 million
In males these germ cells are spermatogonia
In females these germ cells are called oogonia
During embryogenesis in males, this high number of spermatogonia remains throughout life
During childhood, these spermatogonia have a dormant period and they don’t become activated until puberty
Similarly, in females, the oogonia multiply up and reach maximum levels at 24 weeks - after this, no more oogonia are produced so they have a finite number of eggs
They start off with around 6-7 milion however a process of ATRESIA commences
Atresia - the cells start degenerating and dying off
Atresia is rapid at first - by birth there are only about 2 million oogonia left
By puberty there are only about 400,000 oogonia left
By menopause the ovary has been depleted of these cells
In the female reproductive life, only about 300-400 of these cells reach maturation and ovulation - very few are fertilised
After ovulation, the corpus luteum is formed
The Thecal cells and Granulosa cells will still be stimulated by LH and FSH and they will continue to produce large amounts of 17b-oestradiol and Progesterone
One of the effects of progesterone is that it has an effect on body temperature
You can measure an increase in body temperature after ovulation
What enzyme converts Androstenedione to Testosterone?
17β-Hydroxysteroid dehydrogenase
17β-HSD
What stimulates Leydig cells to produce androgens?
List the 3 stages of the ovarian cycle?
Ovarian Cycle
Follicular Phase (first half)
Ovulation (mid-cycle)
Luteal Phase (second half)
List the 2 stages of the endometrial cycle?
Endometrial Cycle
Proliferative
Secretory
If fertilisation does NOT take place - oestrogen and progesterone levels begin to ……..
If fertilisation does NOT take place - oestrogen and progesterone levels begin to FALL
What hormone converts pregnenolone to progesterone?
3 beta hydroxysteroid dehydrogenase
lable the diagram below
The 17b-oestradiol has a negative feedback effect on ………………….. secretion
The 17b-oestradiol has a negative feedback effect on gonadotrophin secretion
What enzyme converts Testosterone to Dihydrotestosterone?
5 alpha reductase
What hormones are produced in the Luteal phase?
In the luteal phase, the hormones produced are progesterone and 17b-oestradiol
Lable the diagram below
Then they are propelled via the ……. ………….(surrounded by smooth muscle) via the urethra
Then they are propelled via the vas deferens (surrounded by smooth muscle) via the urethra
What enzyme converts 11-deoxycortisol to Cortisol?
11β-hydroxylase
What is oogonia?
noun, plural oogonia. one of the undifferentiated germ cells giving rise to oocytes. 2. the one-celled female reproductive organ in certain thallophytes, usually a more or less spherical sac containing one or more eggs.
At birth, oogonia are no longer present.
We have follicles with the oocyte that is stuck in the early stage of meiosis
The follicle will develop over embryonic life and will develop to this pre-antral stage
Up until the pre-antral stage, gonadotrophins are NOT needed
To develop any further requires FSH (to get to early-antral stage)
If FSH isn’t at a high enough level to continue the development they will undergo atresia
They will develop into Early-Antral Follicle (when exposed to sufficient FSH)
What reactions in the diagram below are common to both the gonads and the adreanals?
The first four reactions in steroidogenesis are COMMON to both the gonads and the adrenals
What does a decrease in progesterone and oestrogen cause?
As a result of the decrease in progesterone and oestrogen, the negative feedback is reduced so FSH levels start to rise again so you get back to the start of the cycle
At the time of the gonadotrophin surge, there might be a small surge of 17-hydroxyprogesterone which adds to the positive feedback effect that oestrogen has
What enzyme converts Oestrone into 17 Beta Oestradiol?
17 beta HSD
