Human Reproduction Flashcards
(28 cards)
Function of penis:
becomes erect when spaces in its structure fill with blood
Function of testes:
made up of many coiled tubes which produce sperm and the cells between the tubes produce testosterone
Function of urethra:
carries semen from the sperm duct to the tip of the penis
Function of sperm ducts:
carry sperm from testes to urethra
Function of prostate gland:
helps to produce the seminal fluid which makes up 99.5% of semen
Function of scrotum:
holds the testes from outside the body, at the ideal temperature for the formation of sperm
Function of oviduct:
carries ovum to uterus. Fertilization usually occurs in the first third of this.
Function of ovary:
contains follicles which develop the ova - they poduce oestrogen and progesterone
Function of uterus:
where the foetus develops. During pregnancy, it increases in volume.
Function of the cervix:
a ring of muscle which, until birth, keeps the foetus in the uterus. Relaxes to allow birth.
Function of the vagina:
receives the penis during intercourse and is the ‘way out’ for the baby during birth.
Comparison of sperm and ovum size
10µm : 100µm
Comparison of number of sperm and ovum
300 million per ejaculation : 1 per month
Comparison of sperm and ovum mobility
Sperm: motile - can swim by beating flagellum
Ovum: stationary but contains large food source
How often is a female gamete released?
About every 28 days (length of 1 menstrual cycle)
What happens during the first stage of the menstrual cycle?
Menstruation! The uterus lining is shed and blood and fragments of tissue leave the body through the vagina. Menstruation is triggered by a decrease in the concentration of progesterone.
What happens during the second stage of the menstrual cycle?
Repair phase! More blood vessels grow in the lining of the uterus, and the lining thickens and becomes more stable. These changes are triggered by an increase in oestrogen.
What happens during the third stage of the menstrual cycle?
Receptive phase! The lining of the uterus and its blood vessels are now well developed. If fertilization has occurred, the embryo can become buried or implanted in the lining. The optimum set of conditions for implantation remains 6-7 days after ovulation, and is maintained by an increasing concentration of progesterone.
What happens during the fourth stage of the menstrual cycle?
Premenstrual phase! The uterus lining degenerates as the progesterone concentration starts to decrease unless the embryo implantation has occurred, in which case progesterone keeps the lining intact to begin pregnancy.
What is fertilisation in humans?
The joining together of the sperm and ovum.
What happens after the first sperm penetrates the ovum’s membrane?
The ovum membrane alters to form a barrier to the entry of other sperm.
The head of the sperm (male nucleus) moves towards the nucleus of the ovum and the two fuse, forming a zygote.
The zygote now starts to divide - first into two, then into four, and so on - whilst continuing to move down the oviduct towards the uterus.
About 6 days after fertilization, the ball of cells, now called an embryo, becomes embedded in the thick lining of the uterus.
Once the embryo is attached to the lining of the uterus, some of its outer cells combine with some of its mother’s cells and a placenta begins to develop.
Functions of placenta:
- exchange of soluble materials such as vitamins and minerals, wastes, and oxygen between mother and foetus
- physical attachment of the foetus to the wall of the uterus
- protection of foetus from mother’s immune system
- protection against dangerous fluctuations in mother’s blood pressure
Function of umbilical cord:
connects foetus to placenta and contains blood vessels which carry materials for exchange between mother and foetus.
Function of amniotic sac and fluid:
protect the foetus against mechanical shock, drying out and temperature fluctuations.
