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B - Embryology for EoY4 > Determination of Sex > Flashcards

Determination of Sex Flashcards

1
Q

What is a germ cell?

A

​A biological cell that gives rise to the gametes of an organism to reproduce sexually

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2
Q

What is a gamete?

A

A mature haploid male or female germ cell, which is able to unite with another of the opposite sex in sexual reproduction to form a zygote

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3
Q

What does the female gamete always contain?

A

X chromosome

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4
Q

What does the male gamete contain?

A

Either X or Y chromosome

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5
Q

What is the result of the male gamete containing either an X or Y chromosome?

A

Sperm decides the sex of offspring

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6
Q

What is found on the Y chromosome?

A

A gene known as SRY gene

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7
Q

What does the SRY gene code for?

A

Transcription factors that are members of the SOX family

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8
Q

What do the SOX transcription factors do?

A

Induces expression of another family of transcription factors

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9
Q

What does the action of male derived transcription factors do?

A

Determines that the gonad that develops will be a testis

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10
Q

What are primordial germ cells?

A

A special population that are the ‘seed’ for the next generation

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11
Q

When are the primordial germ cells allocated?

A

Shortly after gastrulation

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12
Q

What is the significance of the primordial germ cells being allocated shortly after initiation of the current generation?

A

They are recruited and specialise very early

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13
Q

Where do primordial germ cells arise?

A

In the yolk sac, near a structure called the allantois

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14
Q

What happens to the primordial germ cells once they have arisen?

A

They migrate

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15
Q

What course to the primordial germ cells take during migration?

A

They migrate into the retroperitoneum, in through the umbilicus, move up through the dorsal mesentery, and populate the gonads

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16
Q

What is the problem with the migration of primordial germ cells?

A

They have to migrate widely along the posterior abdominal wall, which may cause them to get lost or die

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17
Q

What can sometimes occur due to errors in primordial germ cell migration?

A

Get germ cell tumours along pathway of migration

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18
Q

What is true of the gonad at the point of migration of primordial germ cells?

A

It is indistinguishable between male and female

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19
Q

Where do male germ cells (XY) colonise the gonad?

A

The medulla

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20
Q

Where do female germ cells (XX) colonise the gonad?

A

The cortex

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21
Q

What is the ‘default’ position of the gonad?

A

Female

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22
Q

What happens to germ cells after they have colonised the gonad?

A
  • Proliferate by mitosis
  • Reshuffle genetically and reduce to haploid
  • Cytodifferentiate into mature gametes
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23
Q

How do germ cells reshuffle genetically and reduce to haploid once they have colonised the gonad?

A

By meiosis

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24
Q

What are the functions of meiosis in the gonad?

A
  • Reduces the chromosome number in the gamete to 23, giving a haploid gamete
  • Ensures every gamete is genetically unique
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25
Q

When is meiosis used?

A

Only in the production of sperm and eggs

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26
Q

What happens in meiosis?

A

There are two successive divisions, meiosis 1 and 2

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27
Q

What do the divisions in meiosis 1 and 2 produce?

A

4 daughter cells

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28
Q

What happens to the daughter cells from meiosis in the females?

A

Only one develops into mature oocyte, others from polar bodies

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29
Q

What does genetic variation arise from in meisois?

A
  • Crossing over
  • Random segregation
  • Independant assortment
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30
Q

What happens in crossing over?

A

Exchange of regions of DNA between 2 homologous chromosomes

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31
Q

When does crossing over occur?

A

Prophase 1 of meiosis 1

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32
Q

When is crossing over visible?

A

Not until metaphase 1

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33
Q

What happens in random segregation?

A

Distribution of chromosomes among four gametes

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34
Q

What happens in independent assortment?

A

Two homologous chromosomes of a pair must go into seperate gametes

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35
Q

How does cytodifferentiation into mature gametes differ between the sexes?

A

Timing and scale varies

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36
Q

What produces the ovum?

A

Oogenesis

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37
Q

What produces the sperm?

A

Spermatogenesis

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38
Q

How do oogenesis and spermatogenesis differ?

A
  • In oogenesis, there are very few gametes. In spermatogenesis, there are a huge number of gametes
  • In oogenesis there is intermittent production. In spermatogenesis, production is constant
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39
Q

How many gametes are produced from oogenesis?

A

About 400 in a lifetime

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40
Q

What does each ovum have?

A

1/400 of the potential to pass on gene to next generation

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41
Q

What is the result of each ovum having 1/400 of the potential to pass on genes to next generation?

A

Only the best cells are selected to survive

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42
Q

How often are ovums produced?

A

˜1 per month

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43
Q

How many sperm are produced per day?

A

˜200million

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44
Q

Where does spermatogenesis occur?

A

In seminiferous tubules

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45
Q

What happens once spermatogenesis has occured in the seminiferous tubules?

A

They coalesece in the rete testis

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46
Q

What happens to sperm in the rete testis?

A

They are concentrated

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47
Q

When does the initial development of gonads occur?

A

In the indifferent stage

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48
Q

What causes development of a male or female gonad following the indifferent stage?

A

Y influence, or lack of it

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49
Q

What happens to the indifferent gonad in males?

A
  • Medually cords develop
  • No corticol cords
  • Thick outer covering, called the tunica albuginea
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50
Q

What does the tunica albuginea do?

A

Encloses the gonad quite tightly

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51
Q

What happens to the indifferent gonad in females?

A
  • Medually cords don’t develop
  • Corticol cords develop
  • No tunica albuginea
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52
Q

Why is there no tunica albuginea in females?

A

Facilitates ovulation

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53
Q

What is the urogenital ridge?

A

A region of intermediate mesoderm

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54
Q

What does the urogenital ridge give rise to?

A

Both embyonic kidney and gonad

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55
Q

What is the gonad derived from?

A

Both intermediate mesoderm and primordial germ cells (extragonadal)

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56
Q

What is meant by the primordial germ cells being extragonadal?

A

They have to move into supporting tissues

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57
Q

What does the gonad start off as?

A

An indifferent stage gonad

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58
Q

What is the indifferent stage gonad?

A

Just supporting tissue

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59
Q

What is the purpose of the indifferent stage gonad?

A

Provides environment for gametogenesis to occur

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60
Q

What embryonic tissues does the vagina have contributions from?

A

The endoderm and mesoderm

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61
Q

What does the internal genitalia of the male consist of?

A
  • Testis
  • Duct system
  • Seminal vesicles
  • Prostate gland
  • Bulbo-urethral glands
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62
Q

What does the duct system consist of in the male?

A
  • Epididymis
  • Vas deferens
  • Urethra
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63
Q

What is the purpose of the epididymis?

A

Main storage of sperm

64
Q

What does the external genitalia of the male consist of?

A
  • Penis
  • Scrotum
65
Q

What does the internal genitalia of the female consist of?

A
  • Ovaries
  • Duct system
66
Q

What does the duct system of the female consist of?

A
  • Fallopian tube
  • Uterus
  • Cervix
  • Vagina
67
Q

What does the external genitalia of the female consist of?

A
  • Vagina
  • Vestibule
  • Labia minora
  • Labia majora
  • Clitoris
68
Q

Why is development of the reproductive tracts complex?

A

Because at some point, you have to choose a path

69
Q

What is the path chosen by development of the reproductive tract regulated by?

A

The karyotype of embyro (XX or XY)

70
Q

What does the karyotype of the embryo (XX or XY) do?

A

Sets chain of events that leads to development of specific genitalia

71
Q

What does the indifferent stage of the gonad encompass?

A

Development of the gonad and duct system

72
Q

Where does structural development of the reproductive system occur?

A

In utero

73
Q

What does functional develoment and maturation of the reproductive system occur?

A

After birth

74
Q

Describe the reproductive system in babies and childhood

A
  • Human babies are born physically immature
  • Childhood is a period of complete immaturity, with no sexual reproduction possible
75
Q

When does sexual maturation and puberty occur?

A

In adolesence

76
Q

What develops in sexual maturation and puberty?

A

Systems are activated that cause secondary sexual characteristics to develop

77
Q

What is the purpose of secondary sexual characteristics?

A
  • Allows function of system
  • Behavioural characteristics
78
Q

What are the male sexual secondary characteristics?

A
  • Larger body size
  • Body composition and fat distribution
  • Hair and skin
  • Facial hair, male pattern baldness
  • Central nervous effects
  • Skin
79
Q

What are the female sexual secondary characteristics?

A
  • Smaller body size
  • Subcutaneous fat distribution
  • Hair and skin
  • Breast development
  • Central nervous effects
80
Q

What does the secondary sexual characteristic of subcutaneous fat distribution relate to?

A

Ability to support pregnancy

81
Q

What is the purpose of the secondary sexual characteristic of breast development?

A

For lactation

82
Q

What must be true for a genetic male to be created?

A

The male gamete (from the father) must carry the Y chromosome, therefore an XY male conceptus, thus primordial germ cells carry Y chromosomes

83
Q

What genes drive the development of a genetic male?

A

SRY genes

84
Q

What does the gonad become in the male?

A

Testis

85
Q

What does the internal genitalia develop into in the male?

A

The male duct system

86
Q

What is the develoment of the external genitalia of the male under the influence of?

A

Testistoride hormones

87
Q

What must happen for a genetic female to be produced?

A

The male gamete (father) must carry the X chromosome, therefore XX female conceptus, therefore primordial germ cells do not carry the Y chromosome

88
Q

What leads to the development of a female?

A

Absence of SRY chromsomes (and other factors)

89
Q

What is the gonad in the female?

A

The ovary

90
Q

What does the internal genitalia develop into in the female?

A

The female duct system, including uterine tubes and uterus

91
Q

In what gender do the mesonephric ducts and paramesonephric ducts develop in?

A

Both male and female

92
Q

What are the mesonephric ducts?

A

The ducts of the embryonic kidney

93
Q

Where do the mesonephric and paramesonephric ducts end?

A

At the cloaca

94
Q

What is the cloaca?

A

A single structure that the GI, urinary, and reproductive tract end at early in development

95
Q

How do paramesonephric ducts appear?

A

As invaginations of the epithelium of the urogenital ridge

96
Q

What do the paramesonephric ducts do caudally?

A

Make contact with the cloaca

97
Q

What do the paramesonephric ducts do cranially?

A

Opens into abdominal cavity

98
Q

What do the paramesonephric ducts do in the abdominal cavity

A

Grow into the abdominal cavity, try to meet each other in the midline

99
Q

What happens when the paramesonephric ducts try to meet in the midline of the abdominal cavity?

A

To start with, there is a septum, but this disappears and ducts fuse

100
Q

What ultimately happens to the mesonephric and paramesonephric ducts?

A

What happens to them depends on the effect of the gondal hormones

101
Q

What effect to the gondal hormones from the testis have on the mesonephric and paramesonephric ducts?

A
  • Androgen secretion supports mesonephric duct
    • This is a positive act to maintain the duct
  • Testis secrete Mullerian Inhibiting Substance, which causes the degeneration of the paramesonephric duct
102
Q

What can be said of androgen secretion maintaining the mesonephric duct?

A

It is a positive act to maintain the duct

103
Q

What does the mesonephric duct develop into?

A
  • Vas deferens
  • Epididymis
  • Seminal vesicles
104
Q

Why does the testis need to secrete Mullerian Inhibiting Substance?

A

Because you need to actively suppress the paramesonephric ducts, as its natural program is to develop

105
Q

What is Mullerian Inhibiting Substance secreted from?

A

Sertioli cells

106
Q

What happens to the mesonephric and paramesonephric ducts in the female?

A
  • No androgen means mesonephric duct degenerates
  • No testis derived Mullerian Inhibitng Substance means paramesonephric duct develops
107
Q

What does the paramesonephric duct develop into?

A
  • Fallopian tubes
  • Cervix
  • Uterus
  • Upper 1/3 of vagina
108
Q

When are the basic components of the external genitalia derived?

A

In the indifferent stage

109
Q

What are the basic components of the external genitalia?

A
  • Genital tubercle
  • Genital folds
  • Genital swellings
110
Q

What do the genital folds surround?

A

The urogenital sinus

111
Q

What do the genital folds become in males?

A

The urogenital sinus

112
Q

What do the genital folds become in females?

A

Labia minora

113
Q

What do the genital swellings become in males?

A

Scrotum

114
Q

What do the genital swellings become in females?

A

Labia majora

115
Q

What happens to the genital tubercle in males?

A

The GT elongates and genital folds fuse to form spongy urethra

116
Q

What is the elongation of the genital folds in the male under the influence of?

A

Testis-derived androgen hormones, including dihydrotestosterone

117
Q

What must be true for the genital tubercles to respond to dihydrotestosterone?

A

They must have working receptors

118
Q

What happens to the genital tubercle in the female?

A

No fusion occurs, and the urethra opens into the vestible

119
Q

Where do the testis arise in males?

A

In the upper lumbar region

120
Q

How are the testis secured in the upper lumbar regions?

A

They are tethered to the labioscrotal folds (future scrotum) by the gubernaculum

121
Q

What happens to the testis as the body grows?

A

The relative position of the testis becomes more caudal

122
Q

What happens to the scrotum as it develops?

A

A musculo-fasical layer evaginates the scrotum, together with the peritoneal membrane

123
Q

What is formed by the invagination of the scrotum with a musculo-fascial layer and the peritoneal membrane?

A

Processus vaginalis

124
Q

What happens to the testis between 25 and 28 weeks gestation?

A

The testis migrate over the pubic bone, behind the processus vaginalis

125
Q

When do the testis reach the scrotum?

A

Between 34-40 weeks

126
Q

What happens above the testis once they have reached the scrotum?

A

The fascia and peritoneum become closely apposed

127
Q

What is the spermatic cord formed by?

A
  • Fascial layers
  • Obliterated stem of processus vaginalis
  • Vas deferens
  • Testicular vessels and nerves
128
Q

Where does the spermatic cord occupy?

A

The inguinal canal

129
Q

What is the scrotal ligament?

A

The vestigial remnant of gubernaculum in males

130
Q

Where does the ovary originate?

A

On the posterior abdominal wall

131
Q

What is the ovary attached to?

A

The labio-scrotal folds, inferiorly

132
Q

What attaches the ovary to the labioscorotal folds?

A

The gubernaculum

133
Q

What happens to the ovary after it has originated on the posterior abdominal wall?

A

It descends into the pelvis

134
Q

What does the gubernaculum become in females?

A
  • Ovarian ligament
  • Round ligament of uterus
135
Q

What does the ovarian ligament do?

A

Connects ovary to uterus

136
Q

Where does the round ligament of the uterus run?

A

In the inguinal canal, the only structure occuping the inguinal canal in females

137
Q

What does the round ligament of the uterus do?

A

Connects uterus to labia

138
Q

What are the common abnormalities in genital development?

A
  • Genotype-phenotype mismatches
  • Structural defects
139
Q

What can happen if external genitalia are ambiguous at birth?

A

Investigations can be undertaken

140
Q

What investigations can be undertaken if external genitalia are ambigous at birth?

A
  • Investigate internal genitalia
  • Test for sex hormones
  • Genetic testing using cells from cheek
  • Karyotyping
  • Biopsy of glands
141
Q

How can internal genitalia be investigated?

A
  • Endoscopy
  • Abdominal X-ray
  • Pelvic ultrasound
142
Q

What sex hormones can be tested for?

A
  • Androgens
  • Oestrogens
143
Q

Give 3 genital structural defects?

A
  • Clocal partioning defects
  • Hypospodias
  • Uterine structural defects
144
Q

What structures produce reproductive hormones?

A
  • Hypothalamus
  • Posterior pituitary
  • Anterior pituitary
    Gonads (ovaries and testes)
  • Placenta
145
Q

What reproductive hormones does the hypothalamus produce?

A
  • Peptides releasing factor
  • GnRH (gonadotrophin releasing hormone)
  • PRH (prolactin releasing hormone)
  • PIH (prolactin inhibiting hormone)
146
Q

What reproductive hormones does the posterior pituitary release?

A

Posterior pituitary hormone

147
Q

What does posterior pituitary hormone do?

A

Produces oxytocin

148
Q

How does posterior pituitary hormone produce oxytocin?

A

Through neural control from hypothalamus

149
Q

What type of reproductive hormones does the anterior pituitary gland produce?

A

Gonadotrophins

150
Q

What gonadotrophins does the anterior pituitary gland produce?

A
  • FSH (follicle stimulating hormone)
  • LH (lutenizing hormone)
151
Q

What reproductive hormones to the gonads produce?

A
  • Gondal steroids
  • Inhibin
152
Q

What are the gonadal steriods in the male?

A

Testosterone

153
Q

What are the gondal steroids in the female?

A
  • Oestrogens
  • Progesterone
154
Q

What are the different types of oestrogens?

A
  • Principally oestradiol
  • Also oestrone and oestriol
155
Q

What reproductive hormones does the placenta produce?

A
  • Human chorionic gonadotrophin (hCG)
  • Human placental lactogen (hPL)
  • Oestrogens
  • Progesterone

B - Embryology for EoY4 (7 decks)

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