Y11 Ch 11 and 12 - Human Reproductive Systems and Pregnancy

Gametes

sex cells produced in specialised sex organs

Gonads

specialised sex organ that produces gametes (testis and ovaries)

Zygote

single cell as a result of fusion of a male and female gamete at fertilisation

Primary Sex Organ

produces gametes (gonads)

Secondary Sex Organs

stores gametes, brings them together for fertilisation and supports developing baby

Male Reproductive System

Consists of:
- Penis: erectile tissue, urethra and foreskin
- Two Testicles/testis: produces spermatazoa
- Scrotum: Supports/protects the testis
- Epididymis (x2): stores sperm
- Bulbo-urethral gland (x2): secretes fluid found in semen
- Prostate Gland: secretes alkaline fluid to activate sperm
- seminal vesicles (x2): secretes sugar rich fluid found in semen
- Vas Deferens (x2): Carries sperm to urethra

Scrotum

- located outside the body because sperm production requires a cooler temperature then body temperature
- muscle fibres contract/relax to regulate the temperature of the testes (closer to the body when cold and lowered when its hot)

Testes (singular testis)

• oval shaped

• internally divided into 200-300 lobules which are fulled with seminiferous tubules

• lined with cells that produce gametes

• ducts carry gametes and leave the testis to the epididymis

Vas Deferens

- carries sperm away from the testes, around the back of the bladder
- join to form the urethra after passing around the bladder

Inside of Testis

- Interstitial Cells: between the seminiferous tubules, secrete testosterone
- Epididymis: stores sperm, sperm can be stored here for a month to mature, approx 6m in length

Seminal Fluid

- semen (seminal fluid) nourishes and aids the transport of sperm.
- mixture of secretions from 3 glands: 1. Seminal Vesicles - sugary fluid, 2. Prostate Gland - thin milky alkaline fluid, 3. Bulbo-urethral gland - clear, lubricating fluid

Female Reproductive System

Primary Sex Organs:

• Ovaries: produces gametes (ova) and hormones

• Fimbriae: finger-like projections that guide the egg to the fallopian tube

• Fallopian Tube (x2): carries eggs to the uterus by cillia

• Uterus: houses embryo during pregnancy

• Cervix: neck of the uterus, keeps uterus during pregnancy

• Vagina: forms birth canal (only the birth canal, not the whole system)

• Clitoris: contains erectile tissue

• Labia minora/majora: forms opening of vagina

Ovaries

- either side of the abdominal cavity
- supported by ligaments
- composed of a mass of connective tissue (stroma)
- stroma are surrounded by germ cells
- each germ cell is enclosed in a follicle
- at any one time, numerous follicles are at different stages of development
- mature eggs rupture from the follicle
- enter the fallopian tube which carries eggs from the ovary to the uterus

Uterus

- situated behind the bladder and in front of the rectum
- held in place by ligaments
- outer wall - smooth muscles
- inner wall (endometrium) - soft inner mucous lining

Vagina

- muscular, capable of stretching
- opening may or may not be partially covered by the hymen
- lined with mucous membranes

Vulva

external genital organs:
- labia majora: fat and fibrous tissue, produces oily secretions
- labia minora: two smaller folds of skin, not fat tissue, lack hair, surrounded by clitoris
- clitoris: contains erectile tissue and nerves, fills with blood when stimulated

Spermatogenesis

• occurs inside the seminiferous tubules of the testes

• spermatogonia (diploid) - immature cells which line the seminiferous tubules

• spermatogonia begin to divide at puberty to provide continuous source of new cells

• some spermatogonia are pushed to the centre of the tubule where they grow, now called primary spermatocytes (diploid)

• First Meiotic Division:

• primary spermatocytes (diploid) divide to produce secondary spermatocytes (haploid)

• Second Meiotic Division:

• secondary spermatocyte (haploid) divides into 2 spermatids

• four haploid spermatids are formed from one spermatogonium Final Stage:

• spermatids mature into spermatozoa (sperm)

• much of the cytoplasm of the cell is lost

• tail forms which contains contractile Maturing spermatozoa are nourished by special cells that extend from the outer portion of the seminiferous tubule into the centre

• this entire process (from spermatogonium to spermatozoa) takes about 72 days and occurs continuously after puberty

Sperm

• short survival period due to small amount of cytoplasm

• receives nourishment from seminal fluid

  Consists of:

1. Head: Mostly nuclear material, contains a fluid filled vesicle called acrosome that contains enzymes capable of dissolving in the membrane of the egg (ova)

2. Neck

3. Middle: contains mitochondria, produces energy for tail

4. Tail: capable of contractile motions for movement/swimming

Oogenesis

- like spermatogenesis involves both meiosis and maturation
- production of ova in the ovaries
- very similar to spermatogenesis
- as a foetus (before birth) millions of oogonia (diploid) develop in the ovaries (born with all oogonia you will ever have)
By Birth:
- Oogonia have grown to become primary oocytes
- Primary oocytes begin prophase 1 and then stop
- each primary oocyte is surrounded by a single layer of cells to form a primary follicle.

Oogenesis at Puberty

At puberty:

• Primary Oocyte (diploid) completes meiosis and produces 2 haploid cells of unequal size

• secondary oocyte (larger) - receives half the chromosomes but nearly all the cytoplasm

• first polar body (smaller) - receieves half the chromosomes but very little cytoplasm (may undergo second meiotic division to produce two more polar bodies

• secondary oocyte commences second division of meiosis

• stops at metaphase

• Ovulation occurs: follicle ruptures, secondary oocyte and polar body is expelled.

Reproductive Hormones

- The menstrual and ovarian cycles depend on endocrine glands for their regulation and control
- the pituitary gland secretes hormones that stimulate parts of the reproductive system.
- main target organs are the testes and ovaries

Gonadotropins

1. Follicle Stimulating Hormone (FSH):

• Female: development and maturation of the ovarian follicle

• Male: stimulates epithelial tissue of seminiferous tubules for Production of sperm

2. Luteinising Hormone (LH):

• Female: final maturation of the ovarian follicle, ovulation, formation of the corpus luteum, stimulates secretion of oestrogen and progesterone

• Male: secretion of testosterone

3. Prolactin/lactogeic hormone:

• Female: pregnant women: prepares breasts for milk production

4. Oxytocin:

• Female: Uterine contractions and movement of milk in breast tissue

• Male: plays a role in sperm production and testosterone

5. Testosterone:

• Male: body development (sexual maturity)

• development of immature sperm cells to mature spermatozoa

• maintenance of reproductive organs

• sex drive

The Ovarian Cycle (explanation, no steps)

- A sequence of events that includes the maturation of an egg and its release into a uterine tube
- length of the cycle is typically 28 days (can be 20-40 days)
- at birth, ovaries contain around 400,000 immature eggs
- cells undergo a number of divisions but stop dividing before any eggs are formed
- immature eggs remain in the restine phase for many years

The Ovarian Cycle - Steps

At puberty, some of the primary follicles undergo further development. During the first half of the cycle:
- Follicle stimulating hormone and Luteinising Hormone (FSH and LH) levels increase
- prompts the growth and maturation of follicles over 10-14 days
- each follicle that develops goes through the following steps:
1. Cells forming the wall of the primary follicle enlarge and divide - creates a layer of cells around the developing oocyte
2. Secretions from the cells form a fluid filled space
3. Fluid inside the follicle forces the egg to the edge of the follicle, now the secondary follicle
4. The follicle moves to the edge fo the ovary to become a mature/Graafian follicle
5. The mature follicle bursts to release an egg (ovulation)
6. Secondary follicles may develop in each cycle, but usually only one completes development
7. The ones that do not complete development break down and are reabsorbed.
8. As they grow, they release oestrogen and progesterone at at approximately day 14, the level of oestrogen becomes high enough to stimulate a spike in LH and FSH, which causes ovulation of the most mature follicle
9. It is a matter of chance as to which ovary eventually releases an egg each month.
10. The open end of the fallopian tube is like a funnel over the ovary
11. Beating cillia create a current that sweeps the egg into the fallopian tube towards the uterus.
- after ovulation, the ruptured follicle collapses and forms a blood clot
- the clot is reabsorbed and enlarges to form the corpus luteum.

The Corpus Luteum

Secretes:
- Progesterone: development and maintenance of the endometrium to prepare for implanation, inhibits the release of LH and FSH so no other follicles can develop
- Oestrogen
- reaches maximum development 8-10 days after ovulation
- If there is no fertilisation: the corpus luteum breaks down into scar tissue (fibrous mass) called corpus albicans which will eventually disappear
- If fertilisation does occur: the corpus luteum continues to develop, ovarian cycle ceases, maintained by HCG (human chorionic gonadotropin) produced by placenta in pregnant women
- the corpus luteum peaks in the 3rd month of pregnancy and then degenerates
- slow process and still present in the ovary at child birth.

The Menstrual Cycle

- changes in the lining of the uterus (endometrium)
- this happens at the same time as the ovarian cycle
- these changes are in preparation for a developing embryo in the case the egg is fertilised.
- when the embryo reaches the uterus, it needs to implant into the endometrium
- Phase 1 (proliferative phase): during the follicular phase of the ovarian cycle, progesterone causes the endometrium to become thicker and softer, increase in the number of blood vessels and mucus-secreting glands.
- Phase 2 (secretory phase): after ovulation, endometrium continues to thicken, thickest around day 16-24, glands secrete watery mucus rich in glycogen.

No Fertilisation

- corpus luteum degenerates
- reduces hormones buildings the endometrium
- menstruation: endometrium breaks down and is lost through the vagina. The onset of menstruation is day 1 of the menstrual cycle.

Menstrual Cycle starting and ending times

Menarche: when menstruation first begins (beginning of puberty)

• Lasts until menopause (usually age 45-55)

• menopause takes place over a number of years - menstruation becomes sporadic and eventually ceases

Secondary Sexual Characteristics

- All hormones released at puberty cause the development of secondary sexual characteristics (characteristics associated with person's sex but not directly involved in sexual reproduction
- Female: development of breasts, broadening of hips, deposition of fats, growth of pubic hair, change in voice
- Male: growth of pubic hair, change in voice

Summary of Reproductive Hormones

Need to know all hormones, target organs and effect of hormones for extended response on page 290

Sexual Intercourse

• the act in which gametes are passed from male to female: penis becomes enlarged and firm (erection), caused by blood rushing into the tissues

• male reproductive: rhythmic contractions of the epididymis, vas deferens, seminal vesicles and prostate gland occur. The contractions propel the contents of the ducts and gland into the urethra and out of the body (ejaculation).

Fertilisation occuring

Insemination: when the semen is released into the vagina. Semen travel up the vagina, through the cervix, up the uterus and along one of the fallopian tubes

• muscular secretions of the uterus and the sperm swimming move the sperm to the waiting ova.

Sperm Mortality

- death rate of sperm is very high
- hundreds of millions of sperm are released
- only a few thousand will reach the fallopian tube

Fertilisation - structure of a secondary oocyte

Secondary Oocyte: released during ovulation and paused in Metaphase 2. Surrounded by 2 layers: Corona radiata (outermost layer), which supplies proteins for growth and development and Zona Pellucida: inner layer (protection and communication between sperm and ovum)

Fertilisation (sperm penetration)

• mature egg is surrounded by corona radiata (layer of cells)

• acid holds eggs together

• tips of sperm contains an enzyme capable of breaking down the acid in the corona radiata

• one sperm doesn't have enough enzyme to break it down

• thousands of sperm contains enough to loosen cells to allow one sperm in

• once the sperm has entered it stimulates the formation of a fertilisation membrane which prevents the entrance of any more sperm.

Zona Pellucida

Inner Layer
- protection and communication between sperm and ovum

Fertilisation (after zona pellucida)

- once sperm has entered the corona radiata, it encounters the zona pellucida, which initiates:
- the tail is absorbed
- head begins to move through the cytoplasm in the form of male pronucleus (haploid)
- egg is stimulated (secondary oocyte) to complete second meiotic division
- female pronucleus (haploid) fuses with male pronucleus to form a single nucleus (diploid)
- fertilisation is complete (zygote)

Embryonic Development and Implantation

1. After fertilisation, the zygote travels down the fallopian tube and begins to develop and divide by mitosis (called cleavage). divides into 2 cells exactly the same, then 4, then 8 and so on

2. after around 6 days, the zygote reaches the uterus and has developed into a blastocyst

3. Blastocyst remains free within the cavity of the uterus for 2-3 days

4. Blastocyst implants into the endometrium (gains nourishment for growth and development)

Blastocyst Parts

• Blastocyst: a hollow ball of cells that surrounds a cavity filled with fluid

• Inner Cell Mass (embryoblast): group of stem cells at one side of the cavity which develop into the embryo

• Trophoblast: group of stem cells that will become the placenta

Hormone Production

• In order for the blastocyst to continue developing, the endometrium must be maintained

• High levels of oestrogen and progesterone in the blood stop the endometrium from breaking down, ceasing the menstrual cycle

• corpus luteum produces these hormones until the placenta takes over at approx 8-12 weeks.

Stem Cells + Differentiation

Stem cells can: divide, create more stem cells, develop into specialised cells

Stem Cells (Definitions)

• Cell Differentiation: process where unspecialised cells (stem cells) develop into specialised cells (blood cells, muscle cells, etc)

• Proliferation: cells replicating to make new cells

• Tissue: a group of cells that have a similar structure and work together to perform a common function

• Potency: potential capacity of a stem cell to differentiate into different specialised cells

1. Totipotent Stem Cells

- egg at the point of fertilisation
- able to create any type of cell needed for embryonic development (embryo, placenta, membranes)

2. Pluripotent Stem Cells

- cells of inner cell mass
- form all tissues of human body except cells that make up embryonic membrane and placenta

Multipotent Stem Cells

- give rise to cells that have a particular function e.g blood stem cells give rise to red or white blood cells or platelets while skin stem cells give rise to many types of skin cells.
- for example, blood stem cells give rise to blood cells
- exists in both embryos and adults.

Primary Germ Cells

• As implantation occurs, the inner cell mass forms 3 primary germ layers

• these will differentiate into all the tissues and organs of the body

• Mesoderm (middle), Endoderm (innermost layer), Ectoderm (outermost layer)

Endoderm

- epithelium of alimentary canal and its glands (liver and pancreas)
- epithelium of urinary bladder, urethra and gall bladder
- epithelium of pharynx, auditory canal, larynx, trachea, bronchi and lungs
- epithelium of tonsils, thyroid, parathyroid, thymus glands
- Epithelium of vagina and associated glands

Mesoderm

- skeletal, smooth and cardiac muscles
- cartilage, bone, blood, and other connective tissue
- lymphoid tissue
- endothelium of blood vessels and lymphatics
- epithelium of the body cavity and joint cavities
- epithelium of kidneys and ureters
- epithelium of ovaries, testes and reproductive tracts
- epithelium of adrenal cortex
- dermis of skin

Ectoderm

- epidermis of skin
- hair, nails, glands of skin
- lens, cornea and muscles of the eye
- receptor cells of the sense organs
- epithelium of mouth, nostrils, sinuses, glands of mouth and anal canal
- enamel of teeth
- entire nervous system
- anterior lobe of the pituitary gland
- adrenal medulla

Embryonic Membranes

• early in the embryonic period (first two months of pregnancy), 4 membranes form.

• these lie outside the embryo and protect and nourish through development

• includes: amnion, chorion, yolk sac and allantois

Amnion

- first membrane to develop
- surrounds the embryo
- maintains constant temperature
- allows foetus to move freely
- secretes amniotic fluid
- shock absorber for the embryo
- expands as the foetus grows
- ruptures just before childbirth (water breaking)

Chorion

- formed from the outer cells of the blastocyst and layer of mesodermal cells
- surrounds the embryo and other embryonic membranes
- becomes main part of the foetal portion of the placenta

Yolk Sac and the allantois

Form outer structure of umbilical cord

Development of the Placenta

- Chorionic Villi: finger like projections that increase SA for exchange of nutrients and wastes. Develop from outer layer of cells. grow into endometrium and become surrounded by mother's blood (doesn't mix)
- Placenta is attached to the foetus by the umbilical cord
- Umbilical cord contains: 2 umbilical arteries (carry blood to the capillaries of the chorionic villi) and 1 umbilical vein (carries blood from placenta to foetus)
- blood from the mother enters the placenta through the uterine arteries and leaves through uterine tubes.

Functions of the Placenta (Role and then Function)

- Endocrine: secretes hormones for maintaining pregnancy
- Excretory: transports wastes from foetal blood to mother's blood for excretion
- Immune: transports antibodies from mother to foetal blood supply
- Nutritional: transports nutrients from mother's blood to foetal blood
- Respiratory: transports oxygen (by diffusion) from mother to foetus and CO2 from foetus to mother
- transfer occurs by active transport and diffusion

After 1 month

- embryo is 4mm long
- brain is beginning to form
- tail is evident
- development of muscle segments (become brain and spinal cord)
- heart and liver begin to develop
- cleffs in throat

During 5th week

- arm and leg buds start to appear

End of 8 weeks (embryonic period)

- all organs are present but may not be fully functional
- considerable growth (3cm in length)
- head almost half the size of the embryo
- jaw and nose almost fully developed
- hands and feet formed with fingers and toes
- external sexual organs now evident
- now called foetus

During the 4th month

- uterus expands (women's abdomen bulges)
- foetus is around 18cm in length and around 100g in weight
- posture of the foetus is more erect
- fingerprints appear
- foetus movement

End of Week 20 (5th month):

- foetus should be around 25cm long and around 300g
- foetal movements felt clearly

End of Week 24 (6th month)

- 27-35cm long
- 565-680g in weight

28 Weeks

- around 38cm
- around 1kg
- brain has enlarged
- if male, testes descend into the scrotum

32 Weeks

- around 45cm long
- 1.8-2.2kg in weight

40 Weeks (full term)

- less movement (baby has no room)
- around 50cm long
- around 3.5kg
- foetus changes position so that it lies with head inside pelvis
- placenta begins to fail and become fibrous
- antibodies from mother diffuse into babies blood (temporary immunity)

Changes in the Pregnant Mother

- growing abdomen: due to the growth of the uterus and internal organs that are forced upwards and outwards
- enlarged breasts: hormones released result in the development of milk secreting tissues
- increased heart size
- increased blood volume (around 40% extra), which caters for the extra blood flow through placenta
- increased urine production (due to increased blood flow to kidneys)
- increase in urination (pressure on bladder bu uterus in the first 3 months and final stages)

Gestation

- the time that embryo/foetus is carried in the uterus (around 280 days)

Parturition

process of expelling the foetus from mother's body at the end of gestation

Labour

the sequence of events leading up to parturition

Puerperium

the period (around 8 weeks) where a woman's body returns to its prepregnant state (uterus contracts, organs return to its normal position)

Preparation for Birth

Hormonal changes, which cause:
- ligaments of the pelvis to soften
- increase uterus response to stimuli
- increase strength of uterine contractions
Before labour, the cervix shortens in length and the baby positions itself with head in mother's pelvis

Final Months of gestation

- uterus undergoes weak, irregular contractions
- contractions become stronger and more frequent during the final weeks
- when contractions occur every 30 minutes, said to be the beginning of the birth process

First Stage of Labour (dilation)

• dilation of the cervix: the time from onset of labour to complete dilation of the cervix (10cm)

• variable in length (8-9 hours and for subsequent children average is 4)

• waves of contractions travel from the upper uterus downward towards the cervix (similar to peristalsis)

• cervix shortens as muscle fibes pull on the cervix

• cervix no longer projects down the vagina

• cervix is opened

• allows the foetus to move deep into the pelvis

• head of foetus is pushed more forcefully against the cervix

• eventually, cervix is completely dilated (10cm)

• uterus, cervix and vagina form a single, curved passage called birth canal

• complete dilation of the cervix marks the end of the first stage.

Second Stage of Labour (expulsion)

• delivery of the foetus (expulsion)

• begins with bursting of membrane (amnion) that surrounds foetus (water breaking)

• Lasts from 20 min - 2 hours

• As the foetus moves through the fully dilated cervix, its head stretches the vagina

• the distension of the vagina stimulates the woman to contract her abdominal muscles

• abdominal and uterine contractions push the foetus through the vagina

• baby's head turns to face the mother's back

• once the head has emerged, it turns sideways to face the mother's hips

• this allows the shoulders and body to move easily through birth canal

• pressure on head may cause it to be pushed out of shape (bones of skull are pliable and will resume its normal shape a few days after birth)

Third Stage of Labour

• Baby is still connected to the placenta via umbilical cord

• Once born, the baby will begin to breathe with its own lungs

• the amnion, chorion and placenta are still inside the uterus

• Umbilical cord is clamped, tied in two places and then cut

• the arteries and vein within the umbilical cord dries up and falls away (the navel (umbilicus) remains)

• the baby is covered in a waxy material (vernix) which is a protective layer that protects baby from skin infections

• uterus continues to contract

• around 5 min after delivery, the baby, the placenta, other membranes and remains of the umbilical cord are expelled (after childbirth)

• little blood is lost as the placental blood vessels constrict and contractions of the uterus squeeze shut the uterine vessels that supply blood to the placenta.

• blood clots form to stop leakage of blood

Circulation before birth

- lungs of the foetus do not function
- obtains oxygen and nutrients via the placenta
- foetal blood is carried to and from the placenta by blood vessels in the umbilical cord
- as it circulates through the placenta, carbon dioxide and other wastes are exchanged for oxygen and nutrients
- blood returns to the foetus via umbilical vein
- most blood will bypass the liver by flowing through the ductus venosus and then into the inferior vena cava
- mother's liver is serving the needs of the foetus
- the blood returning to the foetal heart enters the right atrium
- From there it can go:
1. Right ventricle to the lungs: lungs are collapsed and not functioning, considerable resistance to blood flow, little blood reaches the lungs
2. right ventricle through the ductus arteriosis to the aorta: this lung bypass allows blood in the pulmonary artery (which carries blood to the lungs) to flow directly into the aorta
3. Directly into the left atrium through the foramen ovale (opening between two chambers): allows blood to flow to developing foetal tissues via aorta very quickly

Changes in the baby at birth

- newborn can no longer rely on placenta for food and oxygen
- lungs and liver must become fully functional - for this to occur, blood must flow through them
- first breath of life is usually triggered by the shock of birth
- stimulates the respiratory centre to start functioning
- the lungs dont offer same resistance to blood flow
- blood flow through the ductus arteriosus decreases (after a few weeks, all taht is left is fibrous tissue)
- the pressure in left atrium increases (increased pressure forces the flap of the foramen ovale to close)
- cutting the umbilical cord means that blood no longer flows through the umbilical vessels or ductus venosus
- the ductus venosus gradually constricts until it is permenantly closed off (the bypass around the liver is lost)

Maintaining a healthy pregnancy

• Maintain a healthy exercise program (don’t start a new one)

• levels of progesterone will rise (from the placenta) to prevent immature shedding of uterine lining (if progesterone too low, a miscarraige or early birth may occur

Supplying the foetus

• increase energy intake by around 850kj'

• increase protein intake - at least 65g a day

• increase calcium, iron and folic acid

• weight gain to 0.5kg per week during second half of pregnancy

• avoid exposure to chemical substances, alcohol, smoking and other drugs

Other Dietary Requirements

• folic acid supplements - required for normal cell division and production of protein

• calcium: bone growth, teeth, muscle, heart and nerve development

• flouride: protect foetus from future dental problems

• Vitamin A: normal growth of cells

Listeriosis

• pregnant women should avoid prepackaged salads, soft cheese and raw food

• mild illness caused by eating food contaminated by bacteria

• potential to cause miscarraiges and still births

Teratogens

substances that cause physical defects in the developing embryo

Teratonic Agent

severity of defects depends on:

• time: embryonic state more vulnerable then foetal 2. dose: greater the dose, greater the effect

Foetal Alcohol Syndrome

Term used to describe the effects of foetal exposure to alcohol. Can result in:

• low birth weight

• intellectual disabilities like hyperactivity and learning problems

• slow growth rate

• irregularities of the face

Smoking

• birth weight is significantly lower

• increased risk of miscarraige

• gastrointestinal and respiratory problems

• strong link between smoking during pregnancy and SIDs (sudden infant death)

Thalidomide

• chemical that was originally developed for use in sleeping pills

• found to be effective in the prevention of morning sickness during the first months of pregnancy

• two years after it went on sale, sharp rise in the incidence of certain limb malformations

Infections - Rubella

• highly infectious, if contracted by a pregnant women child maybe born deaf, blind or with heart malformations

• risk of damage decreases as pregnancy progresses

Infections - Influenza

• may be a link with brain damage if contracted by the mother during early pregnancy