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Biology Unit 4 > 📚4.1- Sexual Reproduction In Humans > Flashcards

📚4.1- Sexual Reproduction In Humans Flashcards

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1
Q

What are the parts of the male reproductive system that you need to know how to label

A

-Testis
-in testis there’s the:
Seminiferous tubules, epididymis and vas efferens
-vas deferens
-prostate gland
-seminal vesicle
-ejaculatory duct
-urethra

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2
Q

What is the name of the external sac in which the testes are contained?

A

The scrotum

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3
Q

What glands are present in the male reproductive system and what is their general function?

A

Accessory glands such as the seminal vesicles, pair of Cowper’s glands and the prostate gland which secret fluids that mix with the sperm to make semen.

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4
Q

Where does sperm formation occur?

A

In the cells lining the seminiferous tubules in the testis

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5
Q

Describe the process of sperm formation in the seminiferous tubules of the testis

A

Cells lining the seminiferous tubules move towards the lumen running through the middle of the tubule. When spermatozoa reach the lumen they move through the tubule and collect in the vasa efferentia. The sperm remain in the epididymis for a short time while they become motile and then pass into the vas deferens during ejaculation

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6
Q

What is the vasa efferentia?

A

Coiled tubes that carry sperm to the head of the epididymis.

(The word ‘vas’ means container and ‘efferens’ means to carry away’)

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7
Q

Describe the passage of sperm from the vas deferens to the exit from the male body

A
  • Vas deferens carries sperm from the epididymis towards the penis.
  • On the way the seminal vesicles secret mucus into the vas deferens.
  • the mucus contains a mixture of chemicals including fructose, respired by the sperm for energy
  • the spermatozoa and seminal fluid move through the ejaculatory duct which passes through the prostate gland, where zinc containing prostate fluid is secreted.
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8
Q

What is the purpose of the seminal fluid (mucus) secreted by the seminal vesicles?

A

-the mucus contains a mixture of chemicals including fructose, respired by the sperm for energy

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9
Q

Are secretions of accessory glands in the male reproductive system acid or alkali? (Accessory glands include prostate gland and seminal vesicles)

A

Alkali

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10
Q

What is the function of the secretions from accessory glands in the male reproductive system? (Accessory glands include prostate gland and seminal vesicles)

A

1) Maintain sperm mobility
2) provide nutrients for the sperm (including fructose their main energy source, amino acids and zinc ions)
3) naturalise the acidity if urine reminding in the urethra
4) neutralise then acidity of the vaginal tract

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11
Q

What is the fluid emerging from the prostate gland called?

What is it comprised of

A

It is called semen, it is a mixture of spermatozoa, seminal and prostate fluids.

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12
Q

How is the semen carried through the penis?

A

It is carried through the penis in the urethra

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13
Q

What cells form the outer margin of of the seminiferous tubules?

A

Germinal epithelium cells

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14
Q

What is directly inwards of the germinal epithelium cells?

A

Primary spermatocytes

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15
Q

Why are secondary spermatocytes rarely seen in a TS examination of the testis?

A

Rarely seen because they progress rapidly to spermatids

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16
Q

What is adjacent to the lumen of the testis?

How do you identify these?

A

Spermatozoa, their tails can be seen on the inside of the lumen

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17
Q

Where are Sertoli cells found in the testis? What are they needed for?

A

Sertoli cells are found between strands of developing spermatids, in the seminiferous tubules.
They secrete a fluid which nourishes the spermatids and protects them against the males immune system.

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18
Q

What are the groups of cells between the seminiferous tubules in the testis called?

A

They are called interstitial cells or Leydig cells.

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19
Q

What is the function of interstitial cells?

A

They secret testosterone, the Male sex hormone which has roles in sperm formation and maturation, as well as the development of male secondary sexual characteristics.

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20
Q

List the main parts of the female reproductive system in which we have to label?

A 
Ovary 
Oviducal funnel 
Oviduct 
Ureter 
Uterus
Cervix 
Vagina 
Bladder
Urethra 
Vulva
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21
Q

Why do oocytes mature?

A

In follicles which develop from cells in the germinal epithelium of the periphery of the ovary

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22
Q

Where do mature follicles go in the ovaries?

A

They migrate to the surface of the ovary from where a secondary oocyte is released during ovulation.

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23
Q

What is important to note about the ovaries and ovulation.

A

The ovaries alternate each month in releasing the oocyte

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24
Q

What is the function of the cilia at the entrance of the oviducal funnel?

A

They sweep the secondary oocyte into the oviduct (fallopian tube).

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25
Q

What conveys the secondary oocyte to the uterus of the women?

A

Ciliates epithelium cells lining the oviduct.

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26
Q

What are the 3 walls of the uterus?

A

1) the perimetrium (thin layer around the outside)
2) the myometrium (the muscle layer)
3) the endometrium (the innermost layer)

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27
Q

Describe the endometrium (inner most layer of the uterus)

A

It is a mucous membrane which is well supplied with blood. It is the layer which builds and is shed in a monthly cycle, unless an oocyte is fertilised, in which case the embryo implants in the endometrium establishing a pregnancy.

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28
Q

What is the cervix?

A

A narrow ring of connective tissue and muscle which opens the uterus wall into the vagina.

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29
Q

Describe the walls of the vagina

A

Muscular and open at the vulva.

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30
Q

What happens if there is a blockage in an oviduct?

A

The passage of a secondary oocyte to the site of fertilisation is prevented.
Treatment normally includes microsurgery.

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31
Q

What do you need to label on the diagram of the TS section of an ovary?

A

1) germinal epithelium
2) primary follicle
3) stroma
4) secondary follicle

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32
Q

What parts do you need to label on a diagram of a developing secondary follicle?

A

1) theca
2) antrum
3) cumulus cells of corona radiata
4) secondary oocyte
5) zona pellucida

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33
Q

Where is the Graffian follicle located in the ovary if a person is not ovulating?
What if the TS section was taken soon after ovulation?

A

The Graafian follicle is towards the centre of the ovary normally, but if the image is take soon after ovulation it is located at the edge of the ovary where the follicle has ruptured.

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34
Q

How do you identify a maturing Graffian follicle on a histological examination?

A

It has a block coloured fluid filled antrum

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35
Q

What forms the outer edge of an ovary?

A

A germinal epithelium layer of cells

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36
Q

How do you distinguish an oocyte inside of a Graffian follicle?

A
  • it will only be seen in a histological examination if the plane of the sections passes through it.
  • if present the dark staining zona pellucida can be distinguished (if the first neurotic division has taken place it is a secondary oocyte, if not it is a primary oocyte)
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37
Q

What is the secondary oocyte surrounded by in a Graffian follicle?
What does this contribute towards?

A

The secondary oocyte is surrounded by cumulus cells which contribute to the corona radiata

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38
Q

Why may the antrum of the Graffian follice look opaque under a histological examination?

A

It may appear opaque because solutes tend to crystalline out during the preparation of the slide

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39
Q

What is the name for the matrix of the ovary?

A

Stroma

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40
Q

Define the term gametogenesis

A

The production of gametes in the sex organs

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41
Q

Define spermatogenesis

A

The formation of sperm in the testis

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42
Q

Define the term oogenesis

A

The formation of the secondary oocyte in the ovary

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43
Q

What cells undergo the series of division to form haploid gametes in both the ovaries and the testis?

A

Germinal epithelium cells

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44
Q

Why is it important that meiosis occurs to from the haploid gametes during gametogenesis?

A

1) at fertilisation the diploid number is restored
2) the chromosome number does not double in every generation
3) to produce genetic variation amongst the population

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45
Q

Describe the process of spermatogenesis

A

1) cells of the germinal epithelium are diploid. They divide by mitosis to make diploid spermatogonia and germinal epithelium cells.
2) The spermatogonia divide many times by mitosis and enlarge, making diploid primary spermatocytes and more spermatogonia.
3) Primary spermatocytes undergo mitosis (I) making secondary spermatocytes which are haploid.
4) Secondary spermatocytes undergo meiosis (II) making haploid spermatids.
5) spermatids mature into spermatozoa or sperm.

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46
Q

How long does sperm production take?

A

Sperm production takes about 70 days

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47
Q

What are the labels of the diagram if a human sperm cell that you need to know?

A
  • Cell membrane
  • acrosome
  • nucleus
  • centriole
  • mitochondrion
  • axial filament
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48
Q

What does the head of a sperm cell contain?

A

The head contains a haploid nucleus, covered at the anterior end by a lysosome called the acrosome, which contains enzymes used at fertilisation.

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49
Q

What does the middle piece of a sperm contain?

A

The middle piece of the sperm cell is packed with mitochondria, which provides ATP for movement. They spiral around the microtubules, which extend from the centriole into the axial filaments in the tail.

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50
Q

What is the function of the sperm cells flagellum (tail)?

A

The tail or flagellum makes lashing movements that move the sperm.

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51
Q

When do the sperm become motile?

A

When they have been modified in the epididymis.

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52
Q

What labels do you need to know for the diagram of the Graffian follicle?

A
  • germinal epithelium
  • theca (GF)
  • antrum (GF)
  • zona pellucida (GF)
  • secondary oocyte (GF)
  • cells of corona radiata (GF)
  • stroma of ovary
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53
Q

Describe the steps of oogenesis that occur before birth of a female

A
  • In the developing fetus, cells of the germinal epithelium of the ovary, which are diploid, divide by mitosis to make diploid oogonia, and more germinal epithelial cells.
  • The oogonia divides many times by mitosis and enlarge, making diploid primary oocytes and more Oogonia.
  • the primary oocytes begin meiosis 1 but stop; a girls is born with millions of primary oocytes in her ovaries
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54
Q

At what stage does meiosis stop when the girl is born?

A

At prophase 1

55
Q

What happens in oogenesis between when the girl is born and puberty

A

-The germinal epithelium cells divide to form diploid follicle cells which surround the primary oocytes making primary follicles.

56
Q

Describe the process of oogenesis between puberty and fertilisation (8)

A

1) hormones stimulate the primary follicles to develop further
2) just before ovulation, a primary oocyte completes meiosis (1), making a secondary oocyte, which contains most of the cytoplasm.
3) a first polar body (significantly smaller is also formed)
4) the secondary oocyte and polar body are both haploid
5) the primary follicle develops into a secondary follicle (called a Graafian follicle) when it’s mature.
6) The GF migrates to the surface of the ovary where it bursts and releases the secondary oocyte, in a process called ovulation.
7) each month several primary follicles start to develop normally but only one matures into GF
8) The secondary oocyte begins meiosis (II) but stops unless fertilisation takes place

57
Q

At what stage in meiosis (II) does the secondary oocyte stop diving unless fertilisation takes place?

A

Metaphase (II)

58
Q

Describe the process of oogenesis after fertilisation

A

1) Meiosis (II) is completed, making an ovum containing most of the cytoplasm and a smaller second polar body
2) after ovulation the GF become the corpus luteum (yellow body).
3) If fertilisation occurs the corpus luteum produces hormones, but if not it regresses.

59
Q

What is the zona pellucida made out of?

A

A clear glycoprotein layer

60
Q

Describe the chromosomes in the secondary oocyte

A

They are at metaphase (II). They are at the equator of the cell, attached to microtubules that make the spindle apparatus.

61
Q

What does the periphery of the cytoplasm of a secondary oocyte contain?

A

Cortical granules?

They are secretory organelles that prevent the entry of more than one sperm (polyspermy)

62
Q

What did the corona radiata do?

A

It surrounds the secondary oocyte and provide nutrients

63
Q

How many gametes does a primary spermatocyte produce vs a primary oocyte.

A

A primary spermatocyte produces 4 gametes (4 spermatozoa)

A primary Oocyte produces only 1 (1 ovum)

64
Q

Describe the process of sexual intercourse

A

1) Physical and psychological effects cause the arteriole entering the penis to dilate and the venues leaving to constrict
2) the build up if blood in spaces In the penis causes it to become erect
3) in sexual intercourse the penis is inserted into the vagina
4) movements of the penis result in the contraction of smooth muscle in the walls of the epididymis, vas deferens and penis, which cause the ejaculation of semen into the vagina
5) the force of ejaculation is sufficient enough to propel some sperm through the cervix into the uterus
6) the remainder of sperm is deposited at the top of the vagina

65
Q

Why is the penis considered an intromittent organ?

A

Because it is inserted into the vagina during sexual intercourse

66
Q

What is an orgasm?

A

The combination of physical and psychological events at their maximum intensity during sexual intercourse

67
Q

Why is internal fertilisation required?

A

It brings Male and female gametes together without the risk of them dehydrating.
It occurs in reptiles, birds and mammals.
It’s evolution is correlated with animals colonising land habitats.

68
Q

Define the term capacitation

A

Changes in the sperm cell membrane that increase its fluidity and allow the acrosome reaction to occur

69
Q

Define the term ‘the acrosome reaction’

A

Acrosome enzymes digest the corona radiata and the zona pellucida, allowing the sperm and oocyte cell membranes to fuse.

70
Q

Define the term cortical reaction

A

The fusion of cortical granule membranes with the oocyte cell membrane, releasing their contents, which converts the zona pellucida into a fertilisation membrane

71
Q

Describe the process of fertilisation (9)

A

1) spermatozoa enter the Fallopian tube following sexual intercourse
2) capacitation -cholesterol and glycoproteins are removed from the cell membrane over the acrosome in sperm head, over several hours the membrane becomes more fluid and more permeable to calcium ions
3) acrosome reaction -the acrosome releases proteins which digest the cells of the corona radiata
4) on contact with the zona pellucida the acrosome membrane ruptures and releases another protease (called acrosin) which hydrolyses the ZO around the secondary oocyte
5) sperm and secondary oocyte membranes fuse and the head of the spermatocyte sinks into the cytoplasm if the secondary oocyte (SO now called an ovum)
6) cortical reaction -the reaction of the oocyte that produces the fertilisation membrane preventing polyspermy
7) The entry of the sperm also stimulates the completion of meiosis (II) of the ovum nucleus. It proceeds through anaphase and telophase (II), divides and expels the second polar body
8) with 24 hours the first mitosis combines the genetic material of the parents to make the diploid cells of the embryo. The cell is now a zygote and the cells have been combined
9) the first mitotic division produced two cells, this collection of cells is called an embryo

72
Q

When does the embryo become a foetus?

A

After about week 10 when organs have developed

73
Q

Describe the cortical reaction in detail (3)

A

1) When the sperm attaches to the secondary oocyte, the oocytes smooth endoplasmic reticulum releases calcium ions into the cytoplasm.
2) They make the cortical granules fuse with the cell membrane and release their contents of enzymes by exocytosis.
3) The zona pellucida is chemically modifies and expands and hardens making a fertilisation membrane which is impossible for the sperm to penetrate.

74
Q

How long can a secondary oocyte survive in the oviduct?

How long can a sperm remain viable in the oviduct?
What does this mean?

A

Secondary oocyte= 24 hours
Sperm viable= 7 days

This means that fertilisation may not happen for many days after the sperm is deposited.

75
Q

Define the term implantation

A

The sinking of the blastocyst into the endometrium

76
Q

Define the term trophoblast

A

Cells forming the outer layer of the blastocyst

77
Q

What is cleavage?

A

As the embryo moves down the oviduct, it divides many times by mitosis in a sequence called cleavage.

78
Q

What is a morula?

How long does it take for a morula to form through cleavage?

A

A solid ball of 16 cells

3 days

79
Q

What happens to the embryo after 7 days of cleavage?

A

The ball of cells becomes hollow and is called a blastocyst.
The cells around the outside of the blastocyst are trophoblasts
Trophoblast divide to make an inner cell mass on one side.
The blastocyst moves from the oviduct into the uterus

80
Q

What happens to the endometrium after ovulation?

A

The endometrium thickens and gets an increased bloody supply to prepare it to receive an embryo.

81
Q

What is the ‘implantation window’?

How long does it last?

A

The implantation window is when the endometrium is receptive

This occurs between 6-10 days after ovulation

82
Q

What happens to the blastocyst around 9 days after ovulation?

A

Protrusions from the trophoblast cells of the blastocyst (called trophoblastic villi) penetrate the endometrium.
The embedding of the blastocyst into the endometrium is implantation and 80% if blastocysts implant within 8-10 days.

83
Q

Why are the trophoblastic villi vital for implantation?

A

It increases the surface area for the absorption of nutrients from the endometrium.

84
Q

What happens during an ectopic pregnancy?

A

The blastocyst implants in the wall of the oviduct. The first sign a women may have of this is an intense pain when the growing embryo ruptured the oviduct.

85
Q

Of every 109 fertilised oocytes how many become:
A blastocyst?
Implanted?
Develop beyond 3 months?

A

50 become blastocysts
25 implant
13 develop beyond 3 months

86
Q

What enhances the blastocysts growth and ability to implant?

A

Progesterone from the corpus luteum stimulates secretions in the uterus, which degrade the remains of the zona pellucida, providing nutrients.

87
Q

What is the main cause of the blastocyst being unable to implant into the endometrium?

A

The endometrium may not be properly receptive.

Hormone treatment may help.

88
Q

How big is the placenta and what is it?

A

The placenta is tissue structure which connects the embryo and foetus to the uterus walls

It is 22cm long and 2cm thick, weighing 500g

89
Q

Describe how the placenta is made

A

1) the trophoblastic develops into the chorionic, an outer membrane surrounding the embryo.
2) cells of the chorion move into the trophoblastic villus and form the much larger chorionic villi.
3) chorionic villus acquire blood capillaries which are connected to the umbilical artery and vein.
4) these blood vessels then connect the embryo to the uterus wall through the umbilical cord
5) projections from the endometrium between chorionic villi are the maternal tissues of the placenta

90
Q

What are the major roles of the placenta?

A

1) it is an endocrine organ producing hormones to support pregnancy
2) an exchange surface between the mothers and foetus blood
3) a physical barrier between the foetal and maternal circulation
4) provides passive immunity to the foetus
5) protects the foetus from the mothers immune system

91
Q

How do the placenta support exchange between the mothers and foetus blood?

A

Inter-villous spaces, called lacunae, containing the mothers blood surround the chorionic villi (which have microvilli increasing SA for exchange).
The embryo and mothers blood do not touch, but the short distance of 5um allows exchange of nutrients, waste produces and respiratory gases etc through diffusion, facilitated diffusion, active transport, pinocytosis and osmosis.

92
Q

How is the concentration gradient between the mothers and foetal blood maintained?

A

Maintained by a counter current flow of blood, enhancing efficiency.

93
Q

Why is it important that the placenta provides a physical barrier between foetal and maternal circulation?

A
  • it protects the fragile, foetal capillaries from damage by the higher blood pressure of the mother
  • it protects the developing foetus from changes in maternal blood pressure
94
Q

Why is it important that the placenta provides passive immunity to the foetus?

A

It allows maternal antibodies to crops the placenta and attack pathogens but not foetal cells despite the fact that they carry the fathers antigens which are different from the mothers.

95
Q

Why does the mother not make an immune response against the foetus or placenta?

A

The cells of the wall of the chorionic villi fuse so there are no spaces between them making a syncitium :: migratory immune cells such as granulocytes can’t get through the foetal blood.

96
Q

In what ways does the placenta not always provide complete immunological protection?

A

1) some spontaneous abortions are equivalent to the rejection of a transplanted organ
2) in the 2nd trimester some women develop pre-eclampsia when they have low blood pressure. One cause is abnormal immune response towards the placenta.
3) Rhesus disease can occur in a foetus which is the destruction of its blood cells by antibodies made by a Rhesus negative mother against the blood cells of a Rhesus positive foetus.

97
Q

Why is a mother more susceptible to infection when pregnant?

A

Because she has an increased immune tolerance increasing the severity of infections such as influenza and malaria.

Vaccines still work however.

98
Q

What can cross the placenta from the mothers blood into the foetus blood which shouldn’t.

A

Some micro-organisms such as Rubella virus as well as some drugs including nicotine and heroin.

99
Q

Where does the umbilical cord develop from? How long is it?

A

The umbilical cord develops from the placenta and is 60cm long

100
Q

What is the umbilical cords main function? Describe this?

A
  • It transfers blood between the foetus and the mother.
  • The blood of the foetus comes to the placenta through the umbilical cord in the 2 umbilical arteries. (Called arteries as blood is going away from the foetus heart)
  • the blood low in nutrients and deoxygenated exchanges materials with the mothers blood at the chorionic villi and returns to the foetus in a single umbilical vein.
  • blood returning is high in nutrients and is oxygenated.
101
Q

What cycle do most mammals (excluding humans) have?

A

An oestrus cycle which comprises of a short period when they are fertile and sexually actively or ‘on heat’.
This is followed by an ‘anoestrus’ period where the endometrium is reabsorbed.

102
Q

What cycle do most primates have (including humans)

A

Most primates have a menstrual cycle where (in the absence of an implanted embryo) the endometrium sheds through menstruation.

103
Q

How regular does the endometrium shed in the menstrual cycle?

A

From the first period (beginning of puberty) until menopause, about once a moth, the endometrium detaches is a blastocyst has not implanted.

104
Q

How does the endometrium leave the body and what does it appear as?

A

It leaves the body through the vagina

It has a good blood supply so appears as a bleed.

105
Q

What are the significant hormones involved in the menstrual cycle?

A

1) follicle stimulating hormone (FSH)
2) Oestrogen
3) Luteinising hormone (LH)
4) progesterone

106
Q

What happens at the start of the menstrual cycle, day 0?

A

The “first day of the period”.
The concentrations of all hormones in the plasma are low. GnRH is secreted by the hypothalamus (by positive feedback) and stimulates the anterior pituitary gland to secrete:
1- FSH (stimulating the development of primary follicles in the ovary, which form a fibrous outer layer called the theca. FSH also stimulates the theca cells to produce oestrogen.

107
Q

What is the role of oestrogen as it becomes more concentrated in the plasma?

A

1) it triggers the rebuilding of the endometrium that was shed during menstration
2) inhibits FSH secretion by negative feedback which brings its own concentration down again
3) stimulates LH production by positive feedback

108
Q

When does LH reach its maximum concentration?

A

Just before ovulation on about day 12.

109
Q

What is the major role of LH?

A

To induce ovulation on day 14 as it’s high concentration causes the Graffian follicle at the surface of the ovary to release the secondary oocyte. It has a positive feedback effect on FSH.

The remains of the Graffian follicle concert into the corpus Luteum which secretes progesterone.

110
Q

What is the role of the progesterone secreted by the corpus lutetium?

A

-maintains the rebuild of the endometrium so that is a secondary oocyte is fertilised there will be suitable tissue for it to implant.

111
Q

What causes the corpus luteum to degenerate?

What does this cause?

A

If there is no implantation the falling concentrations of FSH and LSH cause the corpus luteum to degenerate.

This causes the progesterone production to decline :: the endometrium is shed once again as the endometrium is no longer being rebuilt by oestrogen or progesterone.

Cycle repeats as oestrogen is low and :: FSH is no longer inhibited.

112
Q

Describe the main roles of FSL, oestrogen, LH and progesterone.

A

FSH- follicle development
Oestrogen- rebuild endometrium
LH- ovulation
Progesterone- maintain endometrium

113
Q

What may cause a fail in implantation even if the secondary oocyte is fertilised?

A

1) secondary oocyte may fail to divide
2) implant in the wrong place
3) fail to implant

Of those fertilised 20-70% fail to establish pregnancy.

114
Q

Describe the summary of hormone reactions in the menstrual cycle.

A

FSH up :: O up :: FSH down :: O down

FSH up :: O up :: LH up :: ovulation :: progesterone up

115
Q

What is pregnancy?

A

The time from the first day of the last period until birth, it lasts around 39 weeks

116
Q

What is the amnion?

A

A membrane that is derived from the inner celll mass of the blastocyst.

117
Q

When is the amnion in contact with the embryo and when is it not?

A

The amnion is in contact with the embryo until weeks 4-5 where amniotic fluid accumulated and increases in volume for 6-7 months.
The fluid pushes the amnion out, eventually as far as the chorion (the inner layer of the placenta)

118
Q

Who is the amniotic fluid made by?

A

The amniotic fluid is made by the mother alone for the first 4 months, and after that the foetus contributes urine towards it.

119
Q

What is amniotic fluid made out of?

A

Amniotic fluid is 98% water.

It’s a solution of urea, salts, a little protein and a trace of sugar.

120
Q

What are the functions of the amniotic fluid?

A

1) maintains the foetus temperature
2) provides lubrication (fingers and toes can become webbed If too little amniotic fluid circulated between them)
3) contributes towards lung development
4) allows movement so muscles and bones function before birth
5) acts as a shock absorber, protecting the foetus from injury from outside the uterus

121
Q

How much amniotic fluid does the foetus swallow?

Why is this useful?

A
  • 500cm3 a day
  • The volume of amniotic fluid can be monitored to indicate that the foetus swallowing reflex is normal
  • 1dm3 remains at the end of pregnancy
122
Q

How many trimesters of pregnancy are there?

Define them.

A

3 trimesters of pregnancy.
1st trimester= conception, implantation and embryogenesis. All major organs are laid down.
2nd trimester=development
3rd trimester= growth

123
Q

When is the chance of miscarriage greatest?

A

In the first trimester where 15% of women who know they are pregnant miscarry.

124
Q

When is the embryo called a foetus?

A

After week 10 when the foetus is about 30mm long

125
Q

What happens during the third trimester?

A

Fat is laid down, the foetus’ mass increases three fold and it’s length doubled.
By 28 weeks more than 90% of premature babies survive.

126
Q

When is hCG secreted?

From where?

A

About 6 days after fertilisation from the embryo at the blastocyst stage

127
Q

Where is hCG made after implantation?

A

From the chorion (the inner layers of the placenta).

128
Q

What is hCG?

A

hCG is a glycoprotein which maintains the corpus luteum in its secretion of progesterone for the first 16 weeks of the pregnancy.
This is essential because progesterone maintains the endometrium which contributes to the structure of the placenta.

129
Q

Why is it essential that the corpus luteum secreted oestrogen and progesterone increasing the concentration of the hormones in the plasma of the placenta until the very end of pregnancy?

A

It inhibits the secretion of:

  • FSH so no more follicles mature
  • LH so ovulation is not possible
  • Prolactin, so no milk is made

It also:

  • progesterone inhibits oxytocin so the myometrium and muscles in the milk ducts don’t contract
  • oestrogen stimulates the growth of the uterus to accommodate the foetus
  • oestrogen stimulates the growth of the mammary glands, especially during the 3rd trimester and increases their blood supply
130
Q

What happens to the concentrations of oestrogen and progesterone in the immediate lead up to pregnancy

A

The increase in oestrogen is greater than the increase in progesterone, so progesterone concentration in the plasma declines.

131
Q

As progesterone is decreased at 39 weeks pregnant what is no longer inhibited?

A

1) oxytocin, and :: it is secreted by the posterior pituitary gland.
2) Prolactin, and :: it it secreted by the anterior pituitary gland.

132
Q

What role does oxytocin have in giving birth?

A

It causes contractions of the myometrium in the uterus wall, which operates by positive feedback going from mild to strong, increasing in frequency.

The myometrium contracts from the top down so that the foetus can be pushed out of the cervix

133
Q

Describe the role of prolactin in pregnancy

A

Prolactin stimulates the glandular tissue in the mammary glands to synthesise milk.
Milk is released when oxytocin causes the muscles around the milk ducts to contract.
Prolactin secretion continues after the birth as long as milk is needed.

Biology Unit 4 (3 decks)

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