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A level Biology > Unit 4.1 - Reproducton in Humans > Flashcards

Unit 4.1 - Reproducton in Humans Flashcards

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1
Q

Is sexual reproduction different in different mammals?

A

No, it’s pretty much the same in all mammals

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2
Q

What is the main purpose of sexual reproduction?

A

To promote genetic variation

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3
Q

How does sexual reproduction promote genetic variation?

A

The offspring are not genetically identical or genetically identical to the parents

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4
Q

Advantage of genetic variation in a species + give examples

A

Increases the chances of survival of the species (not the individuals)
e.g - disease: some will be more resistant
Climate change: some will be more able to survive

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5
Q

Describe the offspring of asexual reproduction

A

Genetically identical to the parents (clones)

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6
Q

Why is sexual reproduction troublesome compared with asexual reproduction?

A

Due to the need to produce gametes and to find a partner in order to combine gametes to form a zygote

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7
Q

What forms when gametes combine?

A

A zygote

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8
Q

Why is sexual reproduction costly?

A

Individuals can become vulnerable to predators

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9
Q

How do we know that the risks taken during sexual reproduction are justified?

A

After evolution, the process still exists

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10
Q

Scrotum function (male reproductive system)

A

External sac or skin containing the testes

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11
Q

Testis/testes function in the male reproductive system

A
  • produce gametes (sperm formed by spermatogenesis) and the sperm is used in reproduction when mature
  • produce testosterone
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12
Q

Where are both sperm and testosterone produces?

A

Testes

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13
Q

Seminiferous tubules and epididymis function

A

Sperm are stored here and mature to become fully mobile

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14
Q

Vas deferens function

A

Carries sperm towards the penis during ejaculation

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15
Q

Semincal vesicle function

A

Secretes a fluid into the vas deferens that contains a mixture of chemicals which make up approximately 60% of semen

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16
Q

Name all of the functions of seminal fluid, produced by the seminal vesicle

A

Provides nutrients for sperm such as fructose for respiration and amino acids
When sperm are released from the body, the seminal fluid helps to provide a source of nutrients
Seminal fluid is also alkaline which helps to neutralise the acidity of any urine remaining in the urethra and the acidity of the vaginal tract. Sperm would otherwise be killed by the acidity.

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17
Q

Prostate function

A

Secretes a fluid into the vas deferens that contains a mixture of chemicals that make up approximately 30% of semen.

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18
Q

What does prostate fluid do?

A

Contains zinc ions and is also alkaline which helps to neutralise the acidity of any urine remaining in the urethra and the acidity of the vaginal tract

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19
Q

Urethra functions

A

Carries semen through the penis and out of the body
Carries urine from the bladder through the penis and out of the body

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20
Q

Semen contents

A

Spermatozoa
Seminal fluids
Prostate fluids

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21
Q

Penis function

A

Specialised organ adapted to transfer semen to the vagina during sexual intercourse

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22
Q

Ovaries function

A

Production of gametes (secondary oocytes produced during oogenesis)
Produce oestrogen and progesterone

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23
Q

What do we call female gametes and what don’t be call them?

A

Secondary oocytes, not “eggs”

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24
Q

What are oestrogen and progesterone?

A

Hormones involved in the menstrual cycle and changes during pregnancy

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25
Q

Oviducts (fallopian tube) function

A

They have a lining of ciliated epithelial cells which move the secondary oocyte to the uterus

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26
Q

What adaptation do the oviducts (fallopian tubes) have in order to move the secondary oocytes to the uterus and why?

A

Lining of ciliated epithelial cell
The oocyte can’t propel itself like sperm can

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27
Q

Uterus function

A

Holds the developing foetus until birth

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28
Q

Endometrium function

A

Important in the early stages of pregnancy. The inner most later of the uterus wall. It has a good blood supply and builds up every month during the menstrual cycle (every month, a new endometrium is produced). If implantation of an embryo does not happen (no pregnancy), the endometrium is broken down and shed during menstruation

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29
Q

What is broken down and shed during menstruation if implantation of an embryo does not happen?

A

The endometrium

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30
Q

Cervix functions

A

A narrow ring of connective tissue and muscle
Acts as a barrier between the uterus and the outside environment during pregnancy
During pregnancy, a mucous plug forms in the cervix which helps prevent entry of pathogens.
It’s also what a baby exits the body through.

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31
Q

Vagina function

A

It has muscular walls and opens at the vulva
Semen is deposited in the vagina during sexual intercourse and the foetus is able to pass out from the uterus through the vagina during birth

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32
Q

What is the production of the male gametes in mammals known as?

A

Spermatogenesis

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33
Q

What does spermatogenesis lead to and how?

A

The formation of spermatozoa after a series of cell divisions in the testis

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34
Q

What the name of the thousands of tubules that make up the tissues of the testis?

A

Seminiferous tubules

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35
Q

Where does spermatogenesis occur?

A

In the walls of the seminiferous tubules

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36
Q

Between what type of cells does spermatogenesis occur?

A

Sertoli cells

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37
Q

Explain briefly what spermatogenesis is

A

The production of male gametes by the process of mitosis and meiosis and a version of gametogenesis

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38
Q

Where does spermatogenesis occur?

A

In the seminiferous tubules of the testes

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39
Q

How many seminiferous tubules does each of the testes contain and what is their total length?

A

About 1000
600m

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40
Q

What is there a layer of in each seminiferous tubule and what does this give rise to?

A

Layer of germinal epithelium which gives rise to the spermtogonia by a seres of mitotic divisions

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41
Q

When does spermatogenesis start and end?

A

Begins at puberty and continues throughout the life of the male

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42
Q

Describe spermatogenesis

A

The 1st cells are spermatogonia, which are constantly dividing through mitosis
After dividing, the cells undergo differentiation
This forms primary spermtocytes, which are still diploid cells
These undergo first meiotic division to form 2 haploid cells (homologous chromosome pairs separate during 1st meiotic division) —> secondary spermatocytes
2nd meiotic division occurs and spermatids are formed (are also haploid)
Spermatids undergo differentiation to form spermatozoa (these have a more complex structure)

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43
Q

Where exactly in the seminiferous tubule does spermatogenesis occur?

A

When cells divide, they are pushed down towards the lumen of the seminiferous tubule. The spermatozoa are produced at the bottom.

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44
Q

Sertoli cells

A

Specialised cells that share the same basement membrane as the germinal epithelial cells in the testis

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45
Q

Name the functions of Sertoli cells

A

Believed to support the developing spermatozoa and provide nutrients to these cells as they develop by secreting a nutritive solution
Also provide protection from the male’s immune system
Spermatogenesis occurs between these cells
The heads of the spermatozoa are in these cells

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46
Q

Order of the main things to label in a seminiferous tubule

A

Germinal epithelium
Spermatogonia
Spermatocyte
Spermatids
Spermatozoa

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47
Q

Where are leydig cells found?

A

Between the seminiferous tubules

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48
Q

What do leydig cells do?

A

Secrete testosterone

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49
Q

Testosterone

A

The hormone responsible for developing male characteristics and developing spermatozoa

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50
Q

Length of spermatozoa

A

About 50 micrometres (small cell)

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51
Q

3 main parts of the spermatozoa

A

Head
Mid-section
Tail

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52
Q

What are the 2 things to label on a Spermatozoa?

A

Nucleus
Acrosome

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53
Q

Where is the nucleus of spermatozoa found and what is its function?

A

Haploid nucleus formed during meiosis
Holds the DNA of the cell and so contains genetic material

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54
Q

Where is acrosome in spermatozoa and what is its function?

A

In the head
Contains hydrolytic enzymes that help the sperm break through the corona radiata and zona pellucida surrounding the secondary oocyte. This helps their sperm fuse with the nucleus of the female gametes.

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55
Q

What do the hydrolytic enzymes of acrosome hep sperm do?

A

Break through the corona radiata and zona pellucida surrounding the secondary oocyte, helping it fuse with the nucleus of the female gametes

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56
Q

Surrounding of secondary oocyte that a sperm needs to break through the fuse with the nucleus of female gametes

A

Corona radiata and zona pellucida

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57
Q

What happens to the cell membrane of the spermatozoa during capacitation?

A

Becomes more permeable

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58
Q

How are the mitochondria present in the mid-section of spermatozoa?

A

Spiralled around microtubules

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59
Q

Describe the mid-section of spermatozoa

A

Packed with mitochondria. Sperm use the ATP produced by the mitochondria to move.
Contains microtubules that responsible for movement of the tail (these use the ATP).

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60
Q

What do the sperm use the mitochondria in the mid-section for?

A

Use the ATP produced to move

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61
Q

What is the tail of spermatozoa?

A

A long flagellum that pushes the sperm forward

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62
Q

Why are spermatozoa described as being motile?

A

They can move (swim) towards the egg cell

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63
Q

Describe the tail of spermatozoa

A

Microtubules from mid-section extend into axial filament in the tail

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64
Q

What propels spermatozoa forward?

A

The whiplash movement of the tail

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65
Q

What does the whiplash movement of the tail of spermatozoa help propel the spermatozoa through?

A

The seminal fluid to the female gametes

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66
Q

What in spermatozoa indicates that mammals evolved from aquatic organisms?

A

The presence of a flagellum

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67
Q

Due to the presence of a flagellum in spermatozoa, what must be done?

A

Sperm must be kept in a liquid environment and be transmitted directly from inside the male mammal to inside the female —> internal fertilisation

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68
Q

Internal fertilisation

A

Sperm is transmitted directly from inside the male mammal to inside the female

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69
Q

What does internal fertilisation ensure?

A

That the spermatozoa are kept in an aquatic environment even though the majority of mammal live on land

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70
Q

Explain how internal fertilisation with spermatozoa is different to plants

A

In plants, the pollen grains (male gametes) have a waterproof outer coat so that they don’t dry out. They can therefore be released into the atmosphere and can survive outside of the organism.

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71
Q

Function of spermatozoa

A

To deliver male gametes to female gametes to fuse and form a zygote during fertilisation

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72
Q

What is formed when male and female gametes fuse?

A

A zygote

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73
Q

How many spermatozoa are produced in a male’s life?

A

In heir millions, constantly, throughout the adult life

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74
Q

Why are spermatozoa produced in their millions, constantly, throughout the adult life?

A

Increases the probability of fertilising the egg

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75
Q

Do spermatozoa know where to go to fertilise the egg? How?

A

Yes, they follow a chemical rail released by the oocyte

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76
Q

How does meiosis promote genetic variation?

A

Crossing over
Random assortment

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77
Q

When does crossing over occur during meiosis?

A

During prophase I

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78
Q

When does random assortment occur during meiosis?

A

During metaphase I and II

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79
Q

What occurs during crossing over (meiosis)?

A

Parts of homologous pairs of chromosomes are swapped over
Homologous pairs form bivalents during Synapsis and parts swap over. New combinations of alleles are formed on the chromatids (same genes as homologous chromosomes, different alleles)

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80
Q

Random assortment

A

How the homologous chromosomes arrange themselves along the spindle

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81
Q

Describe random assortment during metaphase II

A

The chromatids are no longer homologous, so this can lead to even more genetic variation

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82
Q

Chromosome number of cells after meiosis I and why

A

2 haploid nuclei (number of chromosomes per cell has halved)

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83
Q

Chromosome number throughout meiosis II + why

A

Haploid throughout (4 haploid cells with non-duplicated chromosomes are made)

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84
Q

Oogenesis

A

The production of female gametes

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85
Q

Oogenium

A

Stem cells in the ovaries of a foetus in the womb

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86
Q

When is there no further developments of oocytes?

A

Between birth and puberty

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87
Q

Describe the process of oogenesis

A

Before birth:
Oogenium are stem cells in the ovaries of a foetus in the womb
These undergo mitosis in order to increase in number
These grow to form the primary oocyte
Therefore, before birth there’s lots of primary oocytes

Between birth and puberty, there’s no further development of oocytes

From puberty through the menopause:
One primary oocyte develops into a secondary oocyte and is released during ovulation every month
During the first meiotic division, the secondary oocyte and the 1st polar body are formed
Both of these are haploid
The polar body is small and non-functional, whereas the secondary oocyte is functional -> the female gamete
Meiosis is then stopped and the second meiotic division doesn’t happen until a sperm cell penetrates into the egg cell
If and when this happens, the second meiotic division occurs. This forms the ovum (mature egg cell) and the 2nd polar body
The 1st polar body can divide to form more polar bodies (not always + not impotent in fertilisation anyway)

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88
Q

What is the functional female gamete?

A

Secondary oocyte

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89
Q

Under which circumstance does the second meiotic division occur during oogenesis?

A

When a sperm cell penetrates into the egg cell

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90
Q

Where do oocytes develop?

A

Within follicles

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91
Q

Follicles

A

Fluid-filled spaces that provide protection and nutrition for the developing oocyte

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92
Q

When are primary follicles formed?

A

Before the birth of the female child

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93
Q

What does a primary follicle contain?

A

A primary oocyte

94
Q

What causes a primary follicle to mature?

A

When the level of follicle stimulating hormone - FSH increases

95
Q

FSH

A

Follicle stimulating hormone

96
Q

What do secondary follicles develop from?

A

Primary follicles

97
Q

What do secondary follicles contain?

A

Secondary oocytes

98
Q

What happens to each secondary follicle as it matures?

A

It becomes fluid-filled (the fluid filled area is called the antrum) and the secondary oocyte becomes surrounded by small follicular cells known as the corona radiata

99
Q

Antrum

A

Fluid filled area of a secondary follicle

100
Q

Corona radiata

A

Small follicular cells surrounding the secondary oocyte

101
Q

Small follicular cells surrounding the secondary oocyte

A

Corona radiata

102
Q

Fluid-filled space of a secondary follicle

A

Antrum

103
Q

What is a fully mature follicle called?

A

A Graafian follicle

104
Q

Graafian follicle

A

Fully mature follicle

105
Q

When is the Graafian follicle formed?

A

When the secondary oocyte is ready to be released at ovulation

106
Q

Where do all of the processes of oogenesis occur?

A

In the ovary

107
Q

What does the Graafian follicle stay in the ovary as after ovulation and why?

A

As the corpus luteum
Helps control hormone levels during pregnancy

108
Q

What does the corpus luteum do?

A

Controls hormone levels during pregnancy

109
Q

Other word for Graafian follicle

A

Ovarian follicle

110
Q

What are the different things to label on a Graafian follicle?

A

Theca
Antrum
Secondary oocyte
Cumulus cells (cells of corona radiata)

111
Q

When are cumulus cells released (present in a Graafian follicle)?

A

With the oocyte from the Graafian follicle

112
Q

1epu at 40x magnification

A

0.025mm

113
Q

1epu at 100x magnification

A

0.01mm

114
Q

1 epu at 400x magnification

A

0.0025mm

115
Q

Things to label on a secondary oocyte

A

Corona radiata
Plasma membrane
Nucleus (haploid)
Cytoplasm
Zona pellucida

116
Q

Zona pellucida of a secondary oocyte

A

Protective layer

117
Q

Protective layer of a seondary oocyte

A

Zona pellucida

118
Q

Type of nucleus of a secondary oocyte

A

Haploid

119
Q

Why is the cytoplasm of a secondary oocyte very large?

A

Contains nutrients that will feed the embryo in the early stages of developments

120
Q

Why would one secondary follicles have different appearances under the microscope to others?

A

May have been cut in a different plane or is in an earlier stage of development

121
Q

Fertilisation definition

A

The fusion of the male and female gametes

122
Q

What is fertilisation the same for?

A

All organisms that undergo sexual reproduction

123
Q

What is not fertilisation?

A

The penetration of the sperm into the egg

124
Q

When exactly is fertilisation occurring?

A

When the nuclei of both the sperm and the egg fuse in the oocyte

125
Q

When can the second meiotic division of the oocyte occur?

A

After the sperm cell penetrates into the oocyte

126
Q

Describe the size different between the oocyte and spermatozoa

A

Oocyte is much bigger

127
Q

How many male gametes should fuse with the male gamete in the oocyte?

A

Only 1

128
Q

Why does it have to be ensured that only 1 male gamete fuses with the female gamete in the oocyte?

A

If not, will lead to mutations and the embryo won’t develop

129
Q

Explain the stages of fertilisation

A
  1. Following sexual intercourse, spermatozoa move into the oviducts and approach the secondary oocyte
  2. Capacitation increases the permeability of he cell membrane in the head of the sperm above the acrosome. When the sperm approached the egg, an acrosome reaction occurs. This is where hydrolase enzymes from the acrosome are released from the head of the sperm. These enzymes digest through the zona pellucida. This enables the membrane of the sperm cell to reach the membrane of the oocyte.
  3. When the sperm cell reaches the oocyte membrane, there are receptor proteins on the oocyte membrane and the proteins on the sperm’s head attract to these receptors
  4. Fusion of sperm and secondary oocyte membranes. The sperm now moves into the cytoplasm of the oocyte and now fertilisation can occur. Genetic material of sperm cell enters the secondary oocyte triggering completion of meiosis II and formation of ovum and second polar body.
  5. Only one male nucleus can fertilise the female nucleus. The cortical reaction ensures this. During this reaction, cortical granules fuse with the cell membrane and modify the zone pellucida to form the fertilisation membrane. This ensues that only 1 sperm can fertilise and prevents polyspermy.
  6. Nuclei of the sperm and ovum fuse to form a zygotic nucleus. 2 haploid nuclei form a diploid zygote nucleus.
130
Q

Capacitation

A

How the enzymes are released from the acrosome

131
Q

Describe the acrosome reaction during fertilisation

A

Hydrolase enzymes from the acrosome are released from the head of the sperm. These enzymes digest through the zona pellucida.

132
Q

Describe the cortical reaction during fertilisation

A

Cortical granules fuse with the cell membrane and modify the zona pellucida to form the fertilisation membrane. This ensures that only 1 sperm can fertilise and prevents polyspermy

133
Q

Where does fertilisation happen?

A

In the oviduct (Fallopian tube)

134
Q

What has to be true for fertilisation to lead to a pregnancy?

A

Has to happen early after ovulation

135
Q

At which stage would it be unlikely that fertilisation will occur?

A

If fertilisation happens later on after ovulation

136
Q

List the stages before, including and after fertilisation

A

Ovulation
Fertilisation
Cleavage
Morula
Early blastocyst
Late blastocyst

137
Q

Explain how everything is still contained within the same structure after fertilisation

A

Still a zona pellucida
The same oocyte

138
Q

What type of divisions does the zygote undergo as it moves down the oviduct?

A

Mitotic

139
Q

When does the zygote undergo repeated mitotic divisions?

A

As it moves down the oviduct

140
Q

What can a blastocyst be described as?

A

A hollow ball of cells

141
Q

List the stages from the zygote to the blastocyst

A

Zygote
2 cell stage
4 cell stage
8 cell stage
Morula
Blastocyst

142
Q

How long does a morula last?

A

72 hours

143
Q

How long does a blastocyst last?

A

4 days

144
Q

What is the morula?

A

A solid ball of cells

145
Q

Which part of the oocyte undergoes divisions to room more cells in the oocyte?

A

The cytoplasm

146
Q

What is the morula?

A

A cluster of undifferentiated cells

147
Q

Which stage of development of the zygote are embryonic stem cells?

A

Morula

148
Q

Why are the cells of the morula used as embryonic stem cells?

A

No differentiation has occurred so the cells are genetically identical

149
Q

How can we use the cells of the morula as embryonic stem cells?

A

We’ able to remove one of these cells and all of the others can form a new embryo. The cell can be used for embryo splitting for cloning.

150
Q

From which stage of development of the zygote can identical twins form?

A

Morula
(Get 2 genetically identical embryos)

151
Q

3 things to label on a blastocyst

A

Inner cell mass
Trophoblast
Blastocoel (fluid-filled cavity)

152
Q

Between which cells is there a difference in nature in them in the blastocyst?

A

Between the cells of the trophoblast and the inner cell mass

153
Q

What is the first stage in the zygote development where cells differentiate and specialise?

A

Blastocyst stage

154
Q

Which part of a blastocyst will form the placenta?

A

Trophoblast (outer layer)

155
Q

What does the trophoblast of a blastocyst go on to form?

A

The placenta

156
Q

What does the inner cell mass of a blastocyst form?

A

The foetus

157
Q

Which part of a blastocyst will form the foetus ?

A

The inner cell mass

158
Q

What happens during implantation?

A

The blastocyst moves into the uterus where it attaches and sinks into the endometrium (the lining of the uterus)

159
Q

What does the blastocyst attach and sink into in the uterus during implantation?

A

The endometrium (the lining of the uterus)

160
Q

What is the endometrium in the uterus?

A

A layer of tissue that develops during the menstrual cycle

161
Q

How is it ensured that implantation is successful?

A

Everything is timed so that the endometrium is in the right condition to receive the embryo in the uterus

162
Q

Describe how implantation occurs

A

The blastocyst sinks into the endometrium
Cells on the outside of the blastocyst, the trophoblast cells, form trophoblastic villi that will penetrate the endometrium
The villi increase the surface area for the absorption of nutrients from the endometrium
The embryo now realised on nutrients from the mother’s blood supply - the early embryo was completely dependent on what was inside of the cytoplasm of the oocyte for nutrition

163
Q

What does the placenta begin to develop from after implantation?

A

The trophoblast cells

164
Q

What do trophoblastic villi do?

A

Increase the surface a for the absorption of nutrients from the endometrium

165
Q

From when onwards does the embryo rely on the nutrients from the mother’s blood supply?

A

After the trophoblastic villi penetrate the endometrium

166
Q

Before the trophoblastic villi penetrate the endometrium and the embryo could rely on nutrients from the mother’s blood supply, how did the early embryo obtain nutrients?

A

Was completely dependent on what was inside of the cytoplasm of the oocyte for nutrition

167
Q

What do the trophoblast cells develop into after implantation?

A

The placenta

168
Q

How does the foetus get nutrients from its mother during pregnancy as it develops?

A

Via the placenta

169
Q

How does the uterus grow as the embryo develops?

A

Is controlled by changing hormone levels

170
Q

What is the foetus surrounded by in the womb?

A

Amniotic fluid

171
Q

Where is amniotic fluid in the womb?

A

Contained within the amniotic sack in the womb

172
Q

In which part of the womb does the placenta grow?

A

In the uterine wall

173
Q

How is the placenta connected to the foetus?

A

By the umbilical cord

174
Q

What transport materials between the foetus and the mother?

A

Umbilical arteries

175
Q

Functions of the placenta

A

Gas and nutrient exchange
Acts as a barrier between the mother’s blood and fetal blood
Protects the foetus from the mother’s immune system and the difference in blood pressure
Secretes hormones

176
Q

Why does the foetus need to be protected for the difference in blood pressure of the mother by the placenta?

A

The look pressure of the mother’s blood is much higher

177
Q

Which part of the placenta has features which aid the exchange of gases and nutrients between the blood of the mother and fetus?

A

The surface between the placenta and the lining of the uterus

178
Q

What are the placenta’s adaptations for exchange?

A

Chorionic villi
Barrier between the blood of the mother and the fetal blood is very thin
The blood of the mother and the fetal blood flow in the opposite direction (counter-current flow)

179
Q

What does fetal blood flow through?

A

Chorionic villi

180
Q

The surface area for the exchange of what is increased by the placenta having chorionic villi?

A

Gas
Nutrients
Waste products in the blood

181
Q

Why is the barrier between the blood of the mother and the fetal blood very thin in the placenta?

A

To provide a short diffusion pathway

182
Q

Why does the blood of the mother and fetal blood flow in the opposite direction (counter-current flow)?

A

To maintain a concentration gradient across the whole exchange surface

183
Q

How are hormones carried throughout the body?

A

In the bloodstream

184
Q

What all need to coincide with the development of the endometrium?

A

Follicle development, ovulation, fertilisation and implantation

185
Q

What do Follicle development, ovulation, fertilisation and implantation all need to coincide with? Why?

A

The development of the endometrium
Ensures that the uterus is prepared for the foetus to implant

186
Q

Can cilia move?

A

Ywa

187
Q

Where are the pituitary glands?

A

In the brain

188
Q

Explain all of hormonal control during the menstrual cycle

A
  1. Anterior pituitary gland secretes follicle stimulating hormone (FSH)
  2. FSH stimulates maturation of primary follicle to secondary follicle
  3. Maturing follicle secretes oestrogen
  4. Oestrogen:
    -stimulates lutenising hormone (LH) production by anterior pituitary gland
    -inhibits secretion of FSH (to stop another follicle from developing)
    -triggers rebuilding of endometrium
  5. LH:
    -stimulates secretion of FSH
    -induces ovulation on day 14 (this is the population average and can vary)
    -stimulates conversion of Graafian follicle into corpus luteum
  6. FSH inhibits oestrogen production (which has been rising until ovulation)
  7. Corpus luteum secretes progesterone that:
    -maintains endometrium
    -inhibits section of FSH
    -inhibits secretion of LH

(The corpus lutetum also releases oestrogen. However, during the latter half of the menstrual cycle, oestrogen does not stimulate LH sections because of the effects of progesterone)

  1. When no pregnancy occurs, falling levels of FSH and LH cause corpus luteum to degenerate
  2. Progesterone (and oestrogen) levels decrease as secretions from degenerating corpus luteum decline
  3. Low levels of progesterone and oestrogen cause endometrium to breakdown and be shed during menstruation
189
Q

List what the hormone oestrogen does

A

-stimulates lutenising hormone (LH) production by anterior pituitary gland
-inhibits section of FSH (to stop another follicle form developing)
-triggers rebuilding of endometrium

190
Q

Why does oestrogen inhibit the section of FSH?

A

To stop another follicle from developing

191
Q

What does the hormone LH do?

A

-stimulates section of FSH
-induces ovulation on day 14 (average)
-stimulates conversion of Graafian follicle into corpus luteum

192
Q

What does corpus luteum do?

A

Secretes progesterone

193
Q

What does progesterone do?

A

-maintains the endometrium
-inhibits secretion of FSH
-inhibits secretion of LH

194
Q

Trimester

A

3 months

195
Q

Explain all of the hormonal changes that occur during pregnancy

A

Just before and following implantation, the developing embryo secretes HCG (Human Chorionic Gonadotrophin) which maintains the corpus luteum for the first 16 weeks of pregnancy (so HCG levels rise before other hormone levels do)
The placenta then secretes progesterone and oestrogen which rise to high levels in he plasma
FHS and LH section are inhibits due to these high levels
Progesterone suppresses the uterine wall’s ability to contract
Oestrogen stimulates the growth of the uterus to accommodate the growing foetus and stimulates the growth and development of the mammary glands during pregnancy

196
Q

HCG

A

Human chorionic gonadotrophin

197
Q

When does the developing embryo secrete HCG and why?

A

Just before and following implantation
Maintains he corpus luteum for the first 16 weeks of pregnancy

198
Q

Which hormone suppresses the uterine wall’s ability to contract?

A

Progesterone

199
Q

What does progesterone do to the uterine wall?

A

Suppresses its ability to contract

200
Q

Which hormone stimulates the growth of the uterus?

A

Oestrogen

201
Q

What does oestrogen do the uterus?

A

Stimulates its growth to accommodate the growing foetus

202
Q

What does oestrogen stimulate the growth of?

A

The uterus
The mammary glands

203
Q

Which hormone is tested for in a pregnancy test?

A

HCG

204
Q

How do you know if you’re pregnant after a pregnancy test?

A

If there’s HCG in the blood, the individual is pregnant

205
Q

Describe the increase in oestrogen and progesterone during the last 3 months of a pregnancy

A

The increase in oestrogen is greater than the increase of progesterone but just prior to birth, the progesterone concentration in the plasma decreases

206
Q

What is in the mother’s interests during a pregnancy and what is in the foetus’ interest and what happens eventually?

A

It is in the mothers’ interest to give birth as soon as the foetus can live independently
Whereas, he foetus ants to delay birth as long as possible
They both release hormones supporting their conflicting needs but at 39 weeks, the mothers’ prevail

207
Q

What are foetal hormones that are transferred to the mother’s bloodstream at 39 weeks doing?

A

Transferred across the placenta and decrease decrease her plasma concentrations of progesterone

208
Q

What have the high levels of progesterone throughout a pregnancy inhibited?

A

The secretion of oxytocin and prolactin

209
Q

What are the main two hormonal increases and decreases just before birth?

A

Oestrogen levels increase
Progesterone levels decrease

210
Q

When is oxytocin secretion no longer inhibited?

A

When progesterone levels decrease

211
Q

What happens during birth when oxytocin secretion is no longer inhibited by progesterone?

A

Oxytocin is secreted by the posterior pituitary gland

212
Q

What do secretions of oxytocin during birth lead to?

A

Contractions of the myometrium in the uterus wall

213
Q

Explain how a positive feedback occurs with oxytocin during birth

A

Secretions of oxytocin causes contractions of the myometrium in the uterus wall
The contractions are mild initially but they stimulate the section of more oxytocin by positive feedback and so the oxytocin concentration in the blood increases and the contractions get stronger throughout the birth

214
Q

Why do contractions get stronger throughout a birth?

A

Secretions of oxytocin causes contractions of the myometrium in the uterus wall
The contractions are mild initially but they stimulate the section of more oxytocin by positive feedback and so the oxytocin concentration in the blood increases and the contractions get stronger throughout the birth

215
Q

How do contractions become as time passes and more oxytocin is secreted?

A

Contractions become stronger and more frequent

216
Q

How does the myometrium contract? Why?

A

From the top down so that the foetus can be pushed out through the cervix

217
Q

What is prolactin secreted by?

A

The anterior pituitary gland

218
Q

What does prolactin do?

A

Stimulates the glandular tissue in the mammary glands to synthesise milk

219
Q

Where synthesises milk when stimulated by prolactin?

A

The glandular tissue in the mammary glands

220
Q

When is milk released from the glandular tissue in the mammary glands?

A

When oxytocin causes the muscles around the milk ducts to contract

221
Q

When does prolactin section happen?

A

During and continues after birth, as long as the milk is needed

222
Q

Copuaiton

A

Sexual intercourse

223
Q

What does copulation increase production of?

A

LH and FSH and also progesterone levels

224
Q

Can humans ovulate with no copulation?

A

Yes

225
Q

Compare the differences between umbilical arteries and umbilical veins

A

(Arteries first, then veins)
Less O2, more O2
More CO2, less CO2
More urea, less urea
Less nutrients, more nutrients
Less antibodies, more antibodies

226
Q

What does a pressure difference in the placenta do?

A

It forces materials through capillaries

227
Q

Describe the rate of exchange in the placenta + explain this

A

Fast
Maintains concentration gradients

228
Q

What does the nucleus of spermatozoa do?

A

Fuses with oocyte to form 2n zygote

229
Q

Why does the placenta secrete hormones?

A

To maintain pregnancy

230
Q

Why is it important to have a higher number of of blood vessels in the ovary after ovulation?

A

The hormones can be transported

231
Q

where in a spermatozoa is the acrosone found?

A

at the very tip of the head

232
Q

What does amniotic fluid do?

A

Acts as a shock absorber to protect from physical damage

A level Biology (26 decks)

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