Biolgoy 4.1 Sexual Reproduction in Humans

Scrotum

External sac of skin containing the testes

Testes

Produce gametes and testosterone

Epididymis

Sperm are stored here and mature to become fully mobile

Vas deferens

Carries sperm towards the penis during ejaculation

Seminal vesicle

Secretes seminal fluid into the vas deferens

Seminal fluid

makes up approximately 60% of semen

provides nutrients for sperm such as amino acids

Why is seminal fluid alkaline

Helps to neutralise the acidity of any urine remaining in the urethra and the acidity of the vaginal tract

Prostate gland

Secretes prostate fluid into the vas deferens

Prostate fluid

makes up approximately 30% of semen

Prostate fluid 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

Urethra

Carries semen through the penis and out of the body

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

Penis

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

Ovary

Production of gametes

Produce oestrogen and progesterone

Fallopian tubes

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

Uterus

Holds the developing foetus until birth

Endometrium

The inner most layer of the uterus wall. It has a good blood supply and builds up every month during the menstrual cycle. If implantation of an embryo does not happen then the endometrium is shed during menstruation

Cervix

A narrow ring of connective tissue and muscle

It 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

Vagina

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

Where does spermatogenesis take place

Seminiferous tubules

Process of spermatogenesis

Germinal epithelium cells divide by mitosis to produce spermatogonia

Spermatagonia divide many times by mitosis and increase in size to form primary spermatocytes

Primary spermatocytes undergo meiosis to form secondary spermatocytes

Secondary spermatocytes undergo meiosis to form spermatids

Spermatids mature and differentiate into spermatozoa

Sertoli cells

provide nourishment for spermatids and

protection against the male's immune

system

What surrounds the seminiferous tubule

Basement membrane of connective tissue

Interstitial cells

Secrete testosterone which

stimulates spermatogenesis

Acrosome

Contains protease enzymes

Mitochondria of sperm

Spiraled around microtubules

Mid section of sperm

Contains microtubules that are responsible for movement of tail.

Contains large numbers of mitochondria, spiraled around microtubules, to provide ATP for microtubules

Where is the axial filament

In the tail

Tail

Whiplash movement of tail propel the spermatozoa

Oogenesis

Production of ovum

Process of oogeneis

Germinal epithelium divide by mitosis to produce oogonia

Oogonia divide many times and enlarge to produce large number of primary oocytes

Primary oocytes present at birth, but development delayed at prophase I

Primary oocytes undergoes meiosis I to produce secondary oocytes just before ovulation

Meiosis II stops at metaphase II

Meiosis II completed in fertiliation occurs to produce an ovum

Follicle

A ball of diploid cells surrounding Graafian folliclean oocyte.

The cells of the follicle develop and increase in numbers as the oocyte develops

Graafian follicle

Contains secondary oocyte ready for ovulation

Primary follicle

Contains primary oocyte

Corpus luteum

If fertilisation occurs, it starts secreting progesterone and oestrogen

Ovulation

Secondary oocyte being released

Process of fertilisation

Following sexual intercourse, spermatozoa move into the fallopian tubes

Capacitation increases the permeability of the cell membrane in the head of the sperm

Acrosome reaction releases hydrolase enzymes which digest the zona pellucida

Fusion of sperm and secondary oocyte membranes

Genetic material of sperm cell enters the secondary oocyte triggering completion of meiosis II and formation of ovum and second polar body

Cortical reaction in which cortical granules fuse with the cell membrane and modify the zona pellucida to form the fertilisation membrane; this prevents polyspermy

Nuclei of the sperm and ovum fuse to form a zygotic nucleus

Cleavage

The zygote undergoes repeated mitotic divisions as it moves down the oviduct to form a ball of cells called the blastocyst

Implantation

The blastocyst moves into the uterus where it attaches and sinks into the endometrium. Cells on the outside of the blastocyst, the trophoblast cells, form trophoblastic villi that penetrate the endometrium. The villi increase the surface area for the absorption of nutrients from the endometrium

Formation of the placenta

The placenta begins to develop from the trophoblast cells

Role of the placenta in exchange of gases and nutrients

nutrients

waste products

oxygen and carbon dioxide

Role of the placenta in providing a barrier between maternal and foetal blood

Protects foetal capillaries from higher blood pressure and changes in blood pressure of the mother

Cells of the chorionic villi fuse together preventing the mother's phagocytes from passing into the foetus.

The mother's antibodies are small enough to cross into the foetal blood and provide passive immunity to the foetus

Role of the placenta in secretion of hormones

Following implantation the placenta takes over secretions of HCG from the blastocyst

This maintains the corpus luteum and its secretions of progesterone and oestrogen

As the placenta develops it takes over secretions of progesterone and oestrogen from the corpus luteum

Amniotic fluid

Acts as shock absorber protecting the

foetus from injury during development

Adaptations of chorionic villi

Microvilli that increase surface area

Thin walls therefore distance for diffusion is short

A counter-current flow of blood between foetal and maternal blood that maintains the concentration gradient

Role of umbilical arteries and veins

Transport materials between the foetus and mother

Intervillious spaces

Contain mother's blood surrounding chorionic villi

Maternal and foetal blood do not mix