Reproduction Flashcards Preview

HH2 > Reproduction > Flashcards

Flashcards in Reproduction Deck (17)
Loading flashcards...
1

REPRODUCTION

- Asexual→ 2 identical copies made from 1 cell (e.g. bacteria)
- Sexual→ female gamete (ovum) fertilised by male gamete (sperm) to form first cell (zygote) of new organism

2

WHY SEXUAL REPRODUCTION?

- Maintains genetic material
- Genetic material of ovum is combined with genetic material of sperm

3

MAKING GAMETES

- Gamete (either ova or sperm) production→ process of meiosis
- Several genetic modifications occur during meiosis including halving number of chromosomes

4

SPERM PRODUCTION

- Occurs in the testes
- Continuous process starting in puberty through to old age
- Process is regulated by lutenising hormone, follicle-stimulating hormone and testosterone

5

REPRODUCTIVE FUNCTION IN FEMALES

- Several interconnected processes occurring at the same time
- Production of ova and the development of the ovarian follicle (the ovarian cycle)
- Changes in the lining of uterus
- Fertilisation→ cell division→ embryonic development→ fetal development

6

OOGENESIS

- Process of making ova and is a more complicated process linked with process of ova release (ovulation)
- Process occurs in the ovaries
- Outer region of each ovary contains thousands of ovarian follicles at different stages of development
- Each follicle contains the cell that will give rise to an ovum (an oocyte) surrounded by supporting follicle cells
- Process of ovum production and ovulation is tied up with changes in the follicle
- The process starts when in utero and becomes a cyclical process during the period that a woman remains fertile

7

OOGENESIS (process)

- It is a process that starts before birth
- Meiosis begins but it halts at a very early age
- At birth a female will have about 1,500,000 follicles in each ovary each with an oocyte halted at this early stage of meiosis
- With the onset of puberty the process begins again
- At onset there are about 400,000 follicles left
- Puberty sees the onset of the ovarian cycle which runs for around 28 days/cycle

8

THE OVARIAN CYCLE

- From puberty to menopause a woman undergoes cycle after cycle of ocum production and ovum release from the ovaries
- In each cycle around 20 follicles are stimulated to mature but typically only one reaches full maturity
- Meiosis restarts but is only completed in the ovum that gets fertilised
- At around 14 of the 28 day cycle (usually) a single ovum is released from its follicle in one of the ovaries; process known as ovulation
- The ruptured follicle undergoes further changes and becomes an endocrine gland
- Hormones from this gland help sustain the modified lining of the uterus
- If there is no fertilisation and/or implantation doesn’t occur, then the follicle degenerates
The endocrine activity of the follicle ends

9

HORMONAL REGULATION OF THE OVARIAN CYCLE

- The gonadotropic hormones (lutenising hormone and follicle stimulation hormone) oestrogen and progesterone regulate ovarian cycle
- Their blood levels vary during the cycle and that is linked to the steps in the process they stimulate

10

CHANGES IN THE ENDOMETRIUM DURING THE OVARIAN CYCLE

- In preparation for implantation and maintenance of the future embryos, the lining of the uterus (the endometrium) undergoes extensive changes including substantial thickening and an increased vascular supply
- If there is no implantation and the follicle degenerates; this layer is sloughed up during menstruation

11

FERTILISATION/CELL DIVISION/ IMPLANTATION

- Fertilisation is the process by which the sperm and the ovum unite to form the first cell of the future embryo (first cell called zygote 0
- Fertilisation usually occurs in the widest part of the uterine tube
After fertilisation: the zygote commences cell division to give rise to a mass of cells
- Within about a week of fertilisation this mass of cells will have reached the lumen of the uterus
- It can become lodged into the endometrium and if it does it then burrows into it
- Successful implantation leads to changes in the implanted mass of cells then it begins producing and secreting the hormone human chorionic gonadotropin (hCG)
hCG keeps the follicle active
- It continues to produce the needed hormones for several months
- In doing so the wall of uterus is maintained in a state that keeps the embryo/fetus alive and developing normally
- Detection of hCG in the urine is the basis of most tests to confirm pregnancy

12

SEXUAL INTERCOURSE
The Penis

- The penis and scrotum are the external genitalia in the male
- The penis is suspended anteriorly at the inferior part of the torso
- The penis serves both the urinary and reproductive systems
- The penis is made up of the cylindrical shaft and a bulbous tip: the glans
- In the penis there are 3 erectile bodies (corpora)
- Within these erectile bodies there are venous spaces that can fill with blood

13

The male sexual response

- In the early part of this, the blood vessels that supply the penis dilate and blood fills the venous spaces
- As the erectile bodies fill they will close off venous flow and so the penis stays filled with blood
- The penis becomes erect which aids in insertion
- Stimulation to the erect penis during intercourse leads to heightened sexual pleasure and generally orgasm and expulsion of semen (ejaculation)
- In this case the PSNS (erection) and SNS (ejaculation) work together in the sexual response

14

THE VAGINA AND CLITORIS
Between the labia minoria of the vulva there is;

The clitoris
The urethral orifice
The vaginal orifice

15

The clitoris

- There are structural similarities between the clitoris and penis in that both contain erectile bodies each has a glans
- During the sexual response the clitoris becomes engorged with blood as do several other organs

16

The vagina

- The vagina is a thick walled muscular tube
It runs from the vulva to the uterus
- So in addition to the role in intercourse, it serves as the birth canal

17

THE FIRST SEXUAL RESPONSE

- At the onset of the sexual response: the breasts, the clitoris, the labia and the all of the vagina become engorged with blood
- Glands within the wall of the vagina will secrete a lubricant
- The uterus shifts towards a more upright position
- The increasing sexual pleasure brought on by persistent stimulation of her body can culminate in the woman coming to orgasm
- This is most clearly manifested in the rhythmic contractions of the vagina and the uterus
- The urethral orifice may also constrict
- Again both the PSNS and SNS work together in the female sexual response