Reproduction in Humans Flashcards
Describe sexual reproduction
- Gametes (sperm and ova) are produced
- The male gamete is transferred to the female gamete
- Fertilisation must occur, the sperm fuses with the ovum
- The zygote formed develops into a new individual
Describe the function of the ovary
Contains follicles which develop the ova and produce oestrogen and progesterone
Describe the function of the cervix
The neck of the uterus, it is a hole where the sperm can reach the eggs
Describe the function of the oviduct (or Fallopian tube)
A muscular tube that carries the ovum from the ovary to the uterus. Fertilisation usually occurs it the first third of the oviduct
Describe the function of the uterus
The organ where the embryo grows (womb)
Describe the function of the funnel of oviduct
It collects ovum released from the ovary at
Describe the function of the vagina
It receives the penis during intercourse and is the “way out” for the baby at birth
Describe the function of the penis
It becomes erect when spaces around its structure fill with blood
Describe the function of the glands
Produce the liquid that is added to sperm to make it semen
Describe the function of the urethra
A tube which carries sperm through the penis during ejaculation. Urine also passes through the urethra to exit the body
Describe the function of the testis
It is made up of many coiled tubes which produce sperm.
Describe the function of the sperm duct
Muscular tube that carries sperm from the testis to the urethra
Describe the function of the Endometrium (lining of the uterus)
Has good blood supply for implantation of the embryo
What is a gene?
Is a section of DNA that codes for one protein
What is an allele?
It is alternate versions of a gene
Why do we need to make new copies of cells?
Mitosis: -Development -Growth and repair Meiosis: -Produce gametes
What happens in mitosis?
Is when a cell reproduces itself by splitting to form two cells with identical sets of chromosomes (1 split of into two genetically identical ‘daughter cells’)
How many chromosomes does a human have?
46 (diploid) (2 sets of 23)
Where is DNA stored?
In the chromosomes
Explain Mitosis
- In a cell that is not dividing the DNA is all spread out in long strings
1. If a cell gets a signal to divide, it needs to duplicate its DNA so there is one copy for each new cell. The DNA forms X-shaped chromosomes. Each ‘arm’ of the chromosome is an exact duplicate of the other (the left arm has the same DNA as the right arm of the chromosome)
2. The chromosomes then line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell
3. Membranes from around each of the sets of chromosomes. These become the nuclei of the two new cells
4. Lastly the cytoplasm divides
5. You now have two new cells containing exactly the same DNA, they are genetically identical
Where and when does mitosis happen? What is it controlled by?
- Happens all the time all around your body and occurs:
- During growth, repair, cloning and asexual reproduction - Controlled by your genes (oncogenes)
- If damage to oncogenes they cannot control mitosis can from tumour malign of benign
Where does meiosis happen?
- In testes (after puberty)
- In ovaries (before birth)
What are gametes?
They are haploid which means they have half the number of chromosomes in a normal cell, in humans each gamete contains 23 chromosomes so the haploid number is 23
What happens in meiosis?
Meiosis produces four haploid cells whose chromosomes are not identical
Explain meiosis
Division 1:
1. Before the cell starts to divide it duplicates its DNA (so there is enough for each new cell). One arm of each chromosome is an exact copy of the other arm
2. In the first division in meiosis (there are two divisions) the chromosomes line up in pairs in the centre of the cell
3. The pairs are then pulled apart so each new cell only has one copy of each chromosome. Some of the father’s chromosomes and some of the mother’s chromosomes go into each new cell
4. Each new cell will have a mixture of the mother’s and father’s chromosomes, mixing up the genes like this creates variation in the offspring
Division 2:
1. In the second division the chromosomes line up again in the centre of the cell. It is a lot like mitosis. The arms of the chromosomes are pulled apart
6. You get four haploid gametes each only has a single set of chromosomes. The gametes are all genetically different
Describe the Follicle Stimulating Hormone (FSH)
-Made in the pituitary gland
Function:
-Stimulate one egg cell to develop (become follicle)
-Stimulate oestrogen secretion in females and sperm production in males
Describe Oestrogen
-Made in the follicle (ovary)
Function:
-Controls development of female secondary sexual characteristics
-Stimulate rebuilding of the uterus wall
Describe Luteinising Hormone (LH)
-Made in the pituitary gland
Function:
-Stimulates follicle to burst and release the ovum (ovulation) in women
-Stimulates testosterone production in males
Describe Progesterone
-Made in the corpus lutem (ovary) Function: -Completes development of uterus walls -Promotes glycogen storage -Regulates menstrual cycle
Describe the first half of the menstrual cycle (until LH released)
- During the first week of the menstrual cycle the pituitary gland is stimulated and releases FSH
- FSH stimulates a potential egg cell in ovary and the cells around the ovum also develop. This is called a follicle
- The follicle secrete oestrogen and oestrogen stimulates rebuilding of the uterus wall (More FSH, more oestrogen)
- The initial concentration of oestrogen are low
- The low concentration has a negative feedback effect on the secretion of FSH
- However as the follicle grows it produces larger concentration of oestrogen and at a certain threshold its effect reverses
- It now has a positive feedback effect on the secretion of FSH from pituitary. The higher concentration of oestrogen also stimulates pituitary gland to release LH
Describe the second half of the menstrual cycle
- Peak of LH causes the follicle to burst and release ovum (ovulation), this happens of day 14 of the cycle
- The follicle reforms to become structure called corpus lutem (‘yellow body’)
- LH stimulates corpus lutem to produce progesterone
- The progesterone completes the uterus wall and increases blood supply to the uterus and promotes glycogen storage
- The rising concentration of progesterone and oestrogen have a negative feedback effect of the levels of FSH and LH
- This prevents new follicles forming as it stops other eggs maturing before this cycle ends
Describe the third half of the menstrual cycle (after levels of FSH and LH go down)
- Fertilisation must occur within two days of ovulation
- Embryo takes 3 days to reach the uterus and implant
- If no embryo implants within a week the corpus lutem starts to break down
- Progesterone and oestrogen levels begin to fall. Uterus wall begins to break down
- FSH is no longer inhibited so begins to rise
- The cycle starts again
What happens if the fertilised ovum implants in the uterus?
-The women becomes pregnant and then the level of progesterone will stay high to maintain the lining of the uterus during pregnancy
(If a fertilised ovum arrives in the uterus, progesterones helps to keep the pregnancy going)
-If a sperm fertilises an ovum and dorms a zygote in the Fallopian tube, a pregnancy begins and the developing embryo moves into the uterus
-It needs to be implanted in the lining of the uterus for pregnancy to continue
What is the function of the amniotic fluid?
The amnion membrane forms and this surrounds the embryo and is full of amniotic fluid which protects the embryo against knocks and bumps
What is the function of the placenta?
- Once the embryo has implanted the placenta develops, this lets the blood of the mrbyo an dmother get very close to allow the exchange of food oxygen and waste
- The embryo’s deoxygenated blood, and waste will go via the umbilical artery away from the embryo and the embryo’s oxygenated blood and food will travel go to the embryo via the umbilical vein
- The mother and baby’s blood never touch and this is important as they might not be the same blood which could kill potentially both if mixed
- The placenta passes food and oxygen from the mother to the developing fetus and it takes urea and carbon dioxide from the fetus and passes them into the mothers’s blood and secretes the hormone progesterone which maintains the pregnancy
- The fetus is connected to the placenta by the umbilical cord
How is the placenta adapted to its function?
- High surface area for effective diffusion
2. Counter current multiplier (two vessels running in opposite direction so there is always a concentration gradient)
Describe the function of testosterone
- Controls development of male secondary sexual characteristics
1. Growth and development of male sexual organs
2. Growth of armpit and pubic hair, and chest and facial hair
3. Increase in body mass; growth of muscles
4. Voice breaks (deepens)
5. Sperm production starts
Describe the function of oestrogen
- Controls development of female secondary sexual characteristics
1. The menstrual cycle begins and eggs are released by the ovaries every month
2. Breasts develop
3. Growth of armpit and pubic hair
4. Increase in body mass; development of ‘rounded’ shape to hips (hips widen)
5. Growth and development of female sexual organs
What are the stages of a baby?
- Gametes
- Zygote
- Embryo
- Foetus
- Baby
- ONLY CALL BABY WHEN OUT OF WOMAN
How long is the gestation period for a human?
9 months
What are the sex cells in plants? What are the sex cells in humans?
- Plants: ovules and pollen
- Animals: ova and sperm
- Female gametes in plants are made in the ovule, and in mammals it is made in the ovary
- Male gametes are made in the anther in plants and the testes in mammals
- Gametes are brought together by pollination in flowering plants and copulation in mammals
- Embryos develop in the seed of flowering plants but in the uterus in mammals
- Fertilisation takes place in the ovule of flowering plants and in the fallopian tube in mammals
What is the role of oestrogen in the menstrual cycle?
- Causes the lining of the uterus to thicken and grow
- (Actually LH. but oestrogen stimulates production of LH in the first place) Stimulates the release of an ovum at day 14
- Reduces levels of FSH produced by the pituitary gland and increases the levels of LH
What is the role of progesterone in the menstrual cycle?
- Maintains the lining of the uterus, when the level of progesterone falls, the lining breaks down
- By stimulating the growth of blood vessels in the lining of the uterus getting ready for pregnancy
What is the role of the Follicle Stimulating Hormone (FSH) in the menstrual cycle?
- Stimulates the ova in the follicles of the ovary to develop
- Stimulates the ovary to make oestrogen
What is the role of the Luteinising Hormone (LH) in the menstrual cycle?
- Stimulates the release of a mature egg from the ovary
2. Stimulates the ovary to make progesterone
What does the division of a diploid cell in mitosis produce?
Two cells which contain identical sets of chromosomes
What does the division of a cell by meiosis produce?
Four cells, each with half the number of chromosomes, and that results in the formation of genetically different haploid gametes
What does random fertilisation produce?
- Genetic variation of offspring
- Sexual reproduction produces genetic variation in other species too, e.g. plants
- The exceptions to the rule are identical twins, because their genes are exactly the same
What is the diploid and haploid number in human cells?
- The diploid number of chromosomes in is 46
2. The haploid number is 23
