Sexual reproduction Flashcards
Importance of reproduction?
Ensure continuity and survival of a species
Sexual reproduction involves the
production of male and female gametes by individuals who have reached sexual maturity
Fallopian tube?
thin muscular duct lined with cilia. the beating of cilia and peristaltic action of Fallopian tubes help move zygote to uterus
Uterus is
a thick-walled and muscular organ
- Uterine wall is lined with tissues
- Uterus is the place for embryonic development. The embryo implants itself onto the endometrium
- The thick layer of tissues rich in blood vessels supply nutrients and oxygen to the embryo
Cervix secretes….
mucus to make it easier for the sperm to swim towards the Fallopian tube
Vagina is the
entryway of the sperm, the place where menstrual blood flows out and a baby’s passage at birth
Sperm are produced in the
seminiferous tubules and channelled through the sperm duct (vas deferens), epididymis and finally collect in the seminal vesicle
The seminal vesicle secretes
fluids containing nutrients for the sperm
Prostate glands secretes
fluids that help in the movement of the sperm
Process of gamete formation is known as
gametogenesis
Gonads?
testes for males and the ovaries for females
Spermatogenesis is
process of sperm formation
Spermatogenesis takes place in
seminiferous tubules
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Each seminiferous tubule consists of
primordial germ cells
Primordial germ cells undergo cell division to
form sperm
Sertoli cells found in the walls of seminiferous tubules…..
supply nutrients throughout the process of spermatogenesis
Spermatogenesis is stimulated by
FSH and Testosterone. This process is also assisted by LH that stimulates testosterone in the testis
Primordial germ cells divide by mitosis repeatedly to produce many
spermatogenia that are diploid
Spermatogenia develops into
primary spermatocytes (2n)
Each primary spermatocytes undergoes
meiosis I to form two secondary spermatocytes that are haploid
Each secondary spermatocyte divides during
meiosis II to produce two haploid spermatids. Thus each primary spermatocyte produces four spermatids
Spermatids undergo
differentiation and specialisation to form sperms
Oogenesis is the process of
forming the ova or female gametes
At birth, a female baby already has almost…..
two million primary oocytes that remain in the prophase I stage of meiosis I in her ovaries. This number is reduced to about 400000 at puberty
(Before birth) Oogenesis begins when primordial germ cells undergo
repeated mitosis to form oogenia that are diploid
(Before birth) The oogonia then develop into
primary oocytes (2n).
Each primary oocyte is surrounded by one or more layers of
follicular cells and this entire structure is called a primary follicle. The growth of the follicle is stimulated by the FSH. As the foetus develops, primary oocytes undergo meiosis but stop at the prophase I stage of meiosis I
Primary oocytes remain at
prophase I of meiosis I during foetal development
Secondary oocytes are large round cells surrounded by
layers of jelly and follicular cells
Menstruation is the
disintegration of the endometrium on the uterine wall accompanied by bleeding
Placenta is the site for
exchange of nutrients between foetus and mother
- glucose, amino acids, hormones, antibodies, and oxygen diffuse from the mother’s blood through thin placental membrane into the mothers blood surrounding the placenta
- Carbon dioxide and waste substances such as urea diffuse from the foetal blood capillaries through the membrane into the mother’s blood surrounding the placenta
Placenta acts as ______ that takes over function of corpus luteum which declines after third month of pregnancy
endocrine organ
In 4th month, placenta replaces corpus luteum to secrete
progesterone and oestrogen that are needed to maintain the thickness of the endometrium
Umbilical cord is a tube that
contains umbilical vein and umbilical arteries that connect the foetus to the placenta
Umbilical vein transports blood rich in
oxygen and nutrients from placenta to the foetus
Umbilical arteries transport blood rich in
carbon dioxide and nitrogenous waste products such as urea from the foetus to the placenta
In placenta, there are many blood capillaries that
increase the surface area to facilitate diffusion of substances between mother and the foetus
Both maternal and foetal circulation do not mix because they are separated by a thin membrane. This is important to
- protect the foetus from some harmful chemicals such as toxins and bacteria from diffusing into the foetal circulation
- prevent the fine blood vessels of the foetus from bursting as a result of the mother’s higher blood pressure. This prevents agglutination or blood clots from happening in the foetus because the foetal blood group may differ from the mother’s blood group
The thin membrane layer of placenta cannot stop diffusion of substances such as
drugs or medication, alcohol and cigarette smoke. Viruses such as HIV and rubella can pass through the placenta and diffuse into the foetal bloodstream and disrupt the development of the foetus
Identical twins
- One ovum is fertilised by one sperm
- Embryo divides into two
- Two identical foetuses share one placenta
- The sex of the twins is the same
- The genetic makeup and physical traits are the same because they are formed from one zygote
Fraternal twins
- Two ova are fertilised by two different sperms
- Division of embryo doesn’t happen
- Each foetus has its own placenta
- The sex of the twins may be same or different
- The genetic makeup and physical traits differ because they are formed from two different zygotes
Impotency occurs when a married couple
is unable to have children
Causes of impotency?
- Women : blocked Fallopian tubes, failure of embryo to implant on the endometrium, the inability to produce secondary oocytes, tumours in the uterus or and abnormal uterus.
- Men : low sperm count, low sperm quality, blocked sperm ducts, and testes do not produce sperm or abnormal sperm are produced
How are conjoined twins formed?
When embryonic division that happens in identical twins is incomplete.
Conjoined twins can be separated surgically if they do not share
major internal organs like the heart, brain or lungs
Insects undergo two types of growth
complete metamorphosis (butterfly) and incomplete metamorphosis (grasshopper)
Ecdysis is the process of
shedding an insect’s external skeleton by replacing the old skeleton with a new bigger skeleton to allow for growth and development
Process of ecdysis is regulated by
hormones
