Human reproductive systems

State similarities between the male and female reproductive system

- both sexes have a pair of gamete producing organs = gonads

- both have a system of ducts which connects the gonads to other parts of the body and the outside world

- both are structured for copulation

Define copulation

- the act of mating, when the sperm from the male are transferred to the female

Benefit of copulation

- humans have evolved to reproduced by copulation to bring the gametes together without them having to pass through the air

- prevents them drying out

State features of the male reproductive system

- pair of testes in external sac = scrotum

- penis

- ducts connecting testes with penis

- accessory glands which secrete fluids that mix with sperm to make semens

State accessory glands in male reproductive system

- prostate gland

- seminal vesicles

- Cowper's glands

Function of scrotum

- external sac, holds the testes 2 degrees lower than body temp

Function of testes

- site of spermatogenesis

- sperm maturation + storage

- testosterone produced

Function of seminiferous tubules

- highly coiled, spermatogenesis occurs

Function of vas efferens

- coiled

- spermatozoa collect here from seminiferous tubules

What are spermatozoa

Sperm

Function of epidiymis

- Sperm become motile here

- coiled

Function of vas deferens

- tube through which sperm travel during ejaculation to reach penis

Function of seminal vesicles

- secretes mucus containing chemicals and nutrients (fructose) for sperm for energy

Function of prostate gland

- secretes an alkaline zinc containing fluid

- helps motility of sperm and neutralises acidic conditions of vagina and uterus

function of bulbourethral gland/Cowper's gland

- Secretes an alkaline lubricant

- all secretions + sperm = semen

Function of urethra

- tube: sperm + urea exit penis (not at same time)

Function of penis

- Spongy erectile tissue filled with blood = erection

- penis = intramittant organ

- delivers sperm into vagina

What is spermatogenesis

production of mature sperm

Where does spermatogenesis occur?

- seminiferous tubules of the testes

Is there mitosis or meiosis in spermatogenesis

Both

When is a males life are spermatozoa produced

Throughout the life of a sexually mature male

Which cells produce testosterone

Leydig cells in between the seminiferous tubules

Outline spermatogenesis

- primordial germ cell in embryo divides by mitosis

- produces 2 spermatogonium stem cells which divide by mitosis to produce more

- some spermatogonium undergo mitosis to produce a primary spermatocyte (2n)

- primary spermatocytes undergo meiosis 1 to produce secondary spermatocytes (n)

- these undergo meiosisII to produce early spermatids (n)

- these undergo differentiation (nutrients provided by sertoli cells) to produce sperm (n)

Define autosome

all chromosomes except sex chromosomes

State features of the female reproductive system

- pair of ovaries

- system of ducts: oviducts

- chambers: uterus & vagina - that carry gametes and house the developing embryo/fetus

Function of ovary

- abdominal cavity, site of oogenesis to produce the oocyte/egg cell/ female gamete

Function of oviduct

- to transport oocyte to uterus, cilla to move oocyte

Function of infundibulum (funnel)

Open end of oviduct by ovary

Function of fimbrae

- finger like projections

- sweep the oocyte released at ovulation into oviduct

Function of uterus

- plantation site of a fertilised ovum + development of embryo/fetus

Function of myometrium

- muscle tissue making up bulk of uterus

Function of endometrium

- surface lining of many blood vessels, shed during menstruation

Function of cervix

- neck of the uterus

- spermatozoa are deposited here during sexual intercourse

- has to widen to 10cm during labour

Function of vagina

- chamber into which sperm ejaculated

- birth canal

Function of vulva

- opening of vagina

Outline spermatogenesis (6)

- sperm development starts in outer layer of the seminiferous tubules, in the germinal epithelium

- these cells, called the spermatogonia undergo mitosis a number of times to produce primary spermatocytes

- the primary spermatocytes are diploid cells found nearer the lumen of the seminiferous tubule than the spermatogonia

- the primary spermatocytes undergoes the first division of meiosis to produce two secondary spermatocytes (haploid)

- these 2 secondary spermatocytes undergo the second division of meiosis to produce 4 spermatids (also haploid)

- the Sertoli cells in the walls of the tubule then phagocytose some of the spermatid cytoplasm (they support spermatid development). Eventually the spermatids will have undergone enough complex modelling to form spermatozoa

Describe the structure of the mature spermatozoa

- the acrosome is a thin cap over the nucleus of sperm

- acrosome vesicle contains enzymes required to digest its way though the ovum wall

- haploid nucleus (n=23) contains the paternal chromosome set

- the mid section of the sperm contains many mitochondria to provide the energy for the movement of the tails structure

- protein fibres in the tail add longitudinal rigidity and provide a mechanism of propulsion

Define oogenesis

- development of mature oocytes

How long does oogenesis take

- can take many years

- oogenesis and fertility normally end with menopause

Where does oogenesis occur?

- ovary

Describe Egg cells

- contains stored nutrients and are large cells (much larger that sperm cells)

Outline oogenesis (9)

- the outer layer of the ovary is the germinal epithelium; before birth, this has produced oogonia

- oogonia divide by mitosis to produce primary oocytes, which enters prophase1 of meiosis, and follicle cells that cluster around the oocytes

- the structures made of oocytes and follicle cells are called primary follicles

- at sexual maturity, one follicle per month starts to develop

- the primary oocyte completes meiosis 1 forming a secondary oocyte which enters meiosis 2 and the follicle cells proliferate forming a secondary follicle

- the secondary oocyte, which is arrested at metaphase 2, becomes surrounded by fluid containing growth factors; this whole structure is now known as the Graafian follicle

- at ovulation the graafian follicle ruptures, releasing the secondary oocyte surrounded by some follicle cells

- after ovulation the remaining follicle becomes corpus luteum, which secretes hormones

- this eventually degenerates, unless fertilisation takes place

Describe the mature egg

- The haploid nucleus (arrested at metaphase 2) sits inside a cell with a large volume of cytoplasm

- during follicle development unequal division of the cell during meiosis produces the 1st polar body (located outside the plasma membrane) which does not develop

- the zona pellucida surrounds the structure and is composed of glycoproteins with cortical granules (role in the acrosome reaction at fertilisation)

- around the outside are the follicular cells

Oogenesis vs spermatogenesis

- in oogenesis, one egg forms from each cycle of meiosis; in spermatogenesis 4 sperm form from each cycle of meiosis

- oogenesis stops in later life in females; spermatogenesis continues throughout the adult life of males

- oogenesis has long interruptions; spermatogenesis produces sperm form precursor cells in a continious sequence