Human Reproduction - ALL

SRY Gene - What is it’s significance

• human sex is determined by the presence/absence of the SRY gene found on the Y- chromosome

• if the SRY gene is present, primordial germ cells (PGC’S) migrate to the medullary region of urogenital region and become spermatogonia

• in the SRY gene is absent, PGC’s migrate to the cortical region of the urogenital region and become oogonia

Male Primary and Secondary Sexual Organs

• Primary Sexual Organs - testes (produce gamete)

• Secondary Sexual Organs - penis, sperm ducts and glands (help gametes to fuse)

Testes

• produce sperm

• produce testosterone

Scrotum

• sac of skin which holds the testes

• sperm need a temperature of 2/3 degrees lower then the body temperature to develop

• being situated of the abdominal cavity allows this temperature to be achieved

  • when cold - muscles in the scrotum contract to bring the testes closer to warmth of the body, heat they relax

Seminiferous Tubules

• they produce spermatozoa/sperm through spermatogenesis

• Leydig cells in between the tubules produce testosterone

• sertoli cells are also located in the testes - nourish developing sperm

List the Sperm Ducts

• vasa efferentia (vas efferens sing.)

• epididymis

• vas deferens

• urethra

Vasa Efferentia

carry sperm from the testis to the epididymis

Epididymis

• coiled tube where sperm are concentrated

• this is because of the reabsorption of fluid secreted by the seminiferous tubule

• sperm mature and aquire the ability to swim - do not yet

Vas Deferens

• sperm is stored here

  • passed to urethra

Urethra

• connected to the bladder - pass urine

• passes sperm from the vasa differentia through the penis

The Glands

• seminal vesicles

• prostate glands

• cowper’s glands - bulbourethral glands

Seminal Vesicles

• secrete a thick yellowish alkaline fluid which nourishes the sperm and helps to neutralize acidity of urethra

• contains fructose - energy source, along with amino acids, enzymes and flavin (vitamin which provides nutrients to sperm and suppresses the female immune system so it doesn’t attack sperm)

• empty into the ejaculatory duct during ejaculation

• other chemicals may help sperm penetrate cervical mucus and cause peristaltic movement of the lining of uterus/fallopian tubes which help move sperm toward the ovaries

Prostate Gland

• secrete a thin milky white alkaline fluid into urethra during ejaculation which helps to neutralize acidity

Cowper’s or Bulbourethral Glands

• clear slightly alkaline fluid which helps to neutralize any acidity of remaining urine in the urethra

• produce mucus which acts as a lubricant

• produces prostate specific antigen → dissolve cervical mucus

• PRODUCES ZN → STABILIZE SPERM DNA

Semen

mixture of sperm and gland secretions discharged during ejaculation

The Penis

• contains erectile tissue which becomes engorged with blood when sexually excited - causing penis to become erect

• this is bcs the arterioles dilate and accommodate more blood, thus compressing the venules meaning the blood moves into erectile tissue but cannot escape

• this raises bp and erects the penis

this is closely related with the excretory system - urogenital system

Ovaries

• primary sexual organs - female gametes are made

• secrete estrogen and progesterone

• outermost layer of the ovaries are made of germinal epithelial cells - produce gamete

• middle is made of stroma - contains connective tissue, blood vessels and mature follicles

Oviducts - fallopian tubes

• carry ova from ovaries to uterus

• end of the tubes closest to the ovary have feathery projections - fimbriae

• these move closer to the ovaries during ovulation

• cilia lining fimbriae beat and cause a current which draws in the ovum after it is released from the ovary

• cilia lining the oviduct beat and smooth muscle contracts causing peristaltic movements moving the ovum down the oviduct to the uterus

• site of fertilization

Uterus

• size/shape of an inverted pear

• embryo implants itself into the wall of the uterus where it will grow during the duration of pregnancy

• myometrium - outermost wall of uterus, smooth muscle, contracts strongly during birth

• endometrium - many glands and highly vascularized - efficiently exchange nutrients with the placenta

Cervix

• narrow entrance to uterus from vagina

• plug of mucus blocks it - prevent infection

• ring of muscle can close it

Vagina

• muscular tube - contains elastic tissue

• stretches during childbirth and during sexual intercourse

• two folds of skin surround opening of it labia majora and labia minora

Clitoris

• can become erect in response to sexual stimulation

• equivalent to male penis

is there a urogenital system in women

• no there are separate openings to the excretory and reproductive system

Gametogenesis

• production of sperm/ova in the testes and ovaries

• involve meiosis which occur from spore mother cells - spermatocyte or oocytes

• 1. multiplication stage - mitosis to produce many spermatogonia and oogonia

• 2. period of growth in preparation for first meiotic division

• 3. maturation stage which the first and second meiotic divisions occur

brief outline of spermatogenesis and oogenesis

germ cell —mitosis—> spermatogonia /oogonia

—growth to prepare for meiosis—→ 1* spermatocyte/oocyte

—meiosis 1——> 2 spermatocyte/oocyte

—meiosis 2—→ spermatid and ootid → sperm and ova

Secondary oocyte must be fertilized to form ova

Describe the process of spermatogenesis

• seminiferous tubule has a wall with an outer layer of germinal epithelial cells - aka PGC!

• pgc’s undergo mitotic divisions to form the spermatogonia - this occurs in the embryo

• spermatogonia undergo more mitotic divisions to produce more spermatogonia - occurs during puberty

• spermatogonia increase in size to form primary spermatocytes - these become embedded in the sertoli cells

• 1 spermatocytes undergo the first meiotic division forming 2 spermatocyte

• 2 spermatocyte undergo the second meiotic division forming 4 haploid spermatids

• spermatids then develop into mature sperm

• this takes around 2 months

Sertoli cells

• infoldings of the surface membrane seminiferous tubules

• carry out the remolding of spermatids → sperm

• exchange of nutrients, oxygen and waste substance between developing sperm and blood vessels acting as a barrier between them and any harmful substance in the blood

• secrete fluid to carry the sperm through seminiferous tubules - this is then later absorbed in the epididymis where sperm is concentrated and matures and become motile

Sperm

• head contains the

  • nucleus with a haploid number of chromosomes

  • acrosome - contains hydrolytic enzymes which are involved in the penetration of the layers surrounding ovum

• short neck has 2 centrioles, microtubule of one of the centrioles elongate during development and form the axial filament of the flagellum in a 9+2 microtubule arrangement

• midpiece - many mitochondria to produce lots of atp needed to bring about beating movement of the tail

• tail - activation of tail takes place in vagina, needed to orient spermatozoa and help penetrate oocyte, enable sperm to group up around oocyte

• tail movements are insufficient to cover distance from vag to site of fertilization

• streamlined → good for locomotion

Hormonal Control of Spermatogenesis

• controlled by the hypothalamus and anterior pituitary

• Hypothalamus secretes gonadotrophin-releasing hormone (GnRH)

• this stimulates the anterior pituitary to secrete gonadotrophins - FSH and LH

• Follicle Stimulating Hormone: this stimulates the sertoli cells to convert spermatids → sperm

• Luteinizing Hormone: synthesis of testosterone by the Leydig Cells

  • FSH and LH use a second messenger cyclic AMP - goes to nucleus to stimulate the synthesis of enzymes

• Testosterone: stimulates sperm production, stimulates Sertoli cells, affects primary and secondary sexual characteristics

• Testosterone - negative feedback, inhibits GnRH (decreasing FSH/LH - decreasing sperm production). It also acts directly on ant pit to reduce LH further

• Inhibin; released from the Sertoli cells and reduces secretion of FSH and reduces GnRH

  • inhibin is released in amounts proportional to sperm count, high sperm count, high inhibin, to inhibit spermatogenesis

Secondary Sexual Characteristics - Males

• deeper voice due to thickening of the larynx caused by testosterone

• enlargement of the penis, testes and glands

• increased muscle development

• growth of pubic hair

Describe the process of Oogenesis

• oogonia are produced during fetal development

• oogonia undergo mitosis and form primary oocytes which enter prophase I

• primary oocyte grows large due to the development of ribosomes, rna, energy stores

• primary oocyte is enclosed by a single layer of granulosa cells → PRIMORDIAL FOLLICLE

• primordial follicle → Graafian follicle

• as the follicle changes the primary oocyte must become an ovum through;

• primordial follicle → primary follicle ( granulosa cells multiply around primary oocyte + theca develops over these layer of granulosa cells from stroma)

• primary oocyte undergoes meiosis I producing a haploid secondary oocyte and a polar body

• antrum develops inside the follicle - now this is a secondary follicle (secondary ooctye inside)

• growth of follicle+ secondary oocyte + fully formed antrum → Graafian Follicle

• second meiotic division proceeds as far as metaphase II but doesnt continue unless fertilization occurs

• FERTILIZATION; secondary oocyte + polar body —→ meiosis II producing the OVUM and a second polar body

• 1st polar body makes a 3rd polar body - these all disintegrate

Functions of Oestrogen

• brings about female secondary sexual characteristics

  • enlargement of breast

  • growth of pubic hair

  • widening of hips

Hormonal Control of the menstrual cycle - preovulatory or follicular phase

• hypothalamus secretes GnRH which stimulates the anterior pituitary to release FSH and LH

• FSH stimulate primordial follicles to develop - however only one follicle will complete development

• as the primary follicle develops the granulosa cells on the follicle being to secrete oestrogen

  • stimulates thickening of the endometrium lining

  • inhibits FSH (prevents more follicles from developing)

  • stimulates secretion of LH at high concentrations toward the midpoint of the cycle

• LH stimulates the graafian follicle to rupture - triggering ovulation

→ at this stage oestrogen has an inhibitory effect on the hypothalamus

Hormonal Control During ovulation

• occurs during the midpoint of the cycle

• graafian follicle at this point is secreting lots of oestrogen

• FSH and LH are released in a surge once oestrogen exceeds a threshold limit

• LH; causes ovulation release of the secondary oocyte from the graafian follicle - this surge ensures precise timing of ovulation

• stimulates remaining graafian follicle to develop into the corpus luteum

• ovulated oocyte consists of a secondary oocyte arrested in metaphase II

  • zona pellucida - glycoproteins secreted by follicle cells

  • corona radiata - layer of granulosa cells protecting and nourishing the oocyte

→ oestrogen has a stimulatory effect on the hypothalamus

Hormonal Control in the postovulatory or Luteal Phase

• Corpus luteum continues to secrete oestrogen and progesterone - these make sure that the lining of the uterus is ready for implantation of a fertilized ovum

• oestrogen inhibits FSH and maintains the endometrium

• progesterone

  • stimulates the uterus to maintain its thickening

  • inhibits LH and FSH

  • associated with a rise in body temperature just after ovulation

• if fertilization DOESNT OCCUR corpus luteum degenerates, hence oestrogen and progesterone levels drop

  • endometrium lining breaks down - menstruation (prostaglandins help by causing contraction of uterine muscles)

  • release of fsh and lh is no longer inhibited

  • ovum dies after the 36hrs of being shed in the oviduct

What happens if fertilization occurs

• ovum forms - meiosis II completes

• oestrogen and progesterone continue to be produced maintaining the endometrium lining

• the ovum then implants itself into the endometrium lining - abundance of nutrients and rich blood supply

How do birth control pills work

• contain hormones which resemble progesterone and oestrogen

• negative feedback on hypothalamus and anterior pituitary

Copulation

• sexual stimulation involves stimulation of the parasympathetic nervous system

• penis becomes erect

• inserted into the vagina, rhythmic movements produced during sexual intercourse cause friction increase stimulation of cells at the tip of the penis

• activates sympathetic nervous system - ejaculation

• lubrication - mucus secreted by copwer glands and glands in vag and vulva

• clitoris also becomes erect

• female orgasm - muscular contractions of both the vagina and uterus

Passage of Sperm to ovum

• sperm are deposited at the top of the vagina close to the cervix

• cervix is normally blocked by a thick mucus

  • thins during the first part of the menstrual cycle

  • release of progesterone after ovulation causes it to thicken once more

• contractions of uterus and oviducts - caused by prostoglandins in the semen and hormones such as oxytocin released during copulation + action of cilia lining uterus and oviducts allow the sperm to travel to the oviducts

• it takes about 4/8 hours for most sperm to reach oviduct

• can survive for 1-3 days - most fertile for 12-24 hours

Capacitation

• when sperm undergo a series of physiological changes making it capable of fusing w oocyte

1. removal of plasma proteins and glycoproteins from outer surface of the sperm by enzymes in the uterus

2. loss of cholesterol from the membrane - weaking it

3. increased permeability to Ca2+ ions - increasing beating of the tail and promotes the acrosome reaction

Acrosome reaction

• sperm makes contact zona pellucida and the cell surface membrane of the sperm next to the acrosome and membrane of acrosome rupture

• hydrolytic enzymes - hyaluronidase and proteases are released from acrosome

• allows sperm to digest w zona pellucida

Fertilization

Fusion of the sperm nucleus with the ovum Nucleus to form a diploid cell - zygote

Explain in detail the stages of fertilization

1. hyaluronidase is released by the acrosome’s and digest a path through hyaluronic acid which holds the follicle/granulosa cells together.

2. Sperm reach the outer surface of zone pellucida where it binds to specific receptors - these receptors are species specific

3. Proteins are then released and digest through the zona pellucida

4. Head of sperm reaches membrane of oocyte, other proteins cause adhesion of sperm to oocyte and fuses with microvilli on oocyte and penetrates cytoplasm

5. Sperm binding induces Ca2+ to be released and this induces a fertilization membrane to form - zona pellucida thickens and harden through the release of enzymes. - cortical reaction, prevents other sperm from fusing. Furthermore enzymes destroy sperm receptor sites

6. Ca2+ activates oocyte metabolism and the second meiotic division is completed

7. Nucleus of sperm swells as chromatin unravels

8. Male and female pronucleus form - fertilization. New nucleus is diploid and known as a zygote. Undergoes mitosis

Define implantation

• the embedding of a blastocyst into the endometrium usually done through protein digesting enzymes

Describe implantation

1. As the zygote passes down oviduct it undergoes cleavage - mitosis division w out an increase in size due to zona pellucida

2. Morula is formed

3. blastocoel forms - cavity filled with liquid from oviduct, at this point the embryo is called a blastula, individual cells are blastomeres and the outer layer of cells is called the trophoblast

4. In a part of the blastula the trophoblast forms an inner cell mass

5. Blastula arrives in uterus and the zona pellucida disappears.

6. Trophoblast cells make contact with endometrium and begin absorbing nutrients

7. Due to presence of nutrients trophoblast cells multiply and 6-9 days after fertilization a protein digesting enzyme is secreted by blastula to embed itself in the endometrium - this is implantation

What happens after implantation

1. Trophoblast cells secrete human chorionic gonadotrophin - HCG and this prevents breakdown of corpus luteum

2. Corpus luteum continues to secrete progesterone and oestrogen leading to increased growth of the endometrium

3. Cells of trophoblast differentiate into an inner and outer layer

4. Outer layer: chorion - chorionic villi, increase SA of contact w maternal blood

5. Hydrolytic enzymes released by trophoblast cause blood vessels in endometrium to break down and fill spaces between chorionic villi

6. Exchange of substances occurs through chorionic villi until

7. Placenta takes over

Describe the development of the extra-embryonic membranes

1. Trophoblast cells develop into chorion

2. inner cell mass develops into the amnion and the yolk sac

3. Amnion - thin protective layer contains amniotic fluid protecting embryo from physical damage

4. Yolk sac has no function in humans

5. other cells of the inner cell mass give rise to the embryo- differentiation into endoderm and ectoderm and later on mesoderm - gastrulation

6. Ectoderm develops into brain and spinal cord 3rd week

7. Allantois develops - grows out toward chorion and forms an allantochorion which gives rise to placenta

8. 6 weeks - fetus and after gestation period of 38 weeks birth

what is the placenta

• composed of cells derived from fetus and mother

• Allows exchange of materials

• Develops after 12 weeks

Describe the structure of the placenta

→ fetal part

• consists of chorionic villi to increase SA

• These villi contain branches of umbilical arteries and veins

• Umbilical cord is a tough structure and it’s where the umbilical arteries and veins run through

→maternal part

• projections from the endometrium

• Between this and the chorionic villi there are spaces supplied with arterial blood

• Blood flows through spaces from arterioles to venules in the uterus wall

BLOOD NEVER MIXES

Why is it important blood doesn’t mix in the placenta

1. Relatively high blood pressure of mom isn’t exposed to baby

2. ABO groups may not be compatible -

Describe the mechanisms of uptake across the placenta

1. Chorionic villi have microvilli which increase surface area for active transport and diffusion and facilitated diffusion

2. Cells contain many mitochondria and carrier molecules for active transport

3. Numerous small vesicles are found inside cells of villi - pinocytosis

4. Water - osmosis l, glucose - facilitated diffusion, ions - active transport / diffusion , amino acids iron and vitamins - active transport

5. oxygen diffuses from mom to fetal blood as fetal blood has higher affinity for oxygen

6. Carbon dioxide and nitrogenous wastes are diffused to mother

7. Antibodies can cross the placenta from mother to fetus - passive immunity

Placenta as an endocrine organ

• takes over role of corpus luteum in secreting progesterone and oestrogen

• HCG - maintain activity of corpus luteum until placenta takes over

• Human Placental Lactogen: growth and development of breasts - needed before oestrogen and progesterone can affect the breasts

What are contractions during birth attributed to

• decrease in progesterone (progestone inhibits contractions)

• oestrogen → because it makes the uterus more sensitive to oxytocin

Describe the Hormonal Control that undergoes during contractions

• oestrogen production increases

• progesterone levels decrease - baby hypothalamus releases ACTH which stimulates release of cortiocosteroids from adrenals, crosses into mother circulation and this causes a progesterone decrease and an increase in prostaglandins

• stretching of uterus by fetus and pressure on cervix by fetal head - oxytocin release

First Stage

1. cervix starts to dilate

2. mild contractions, mucus plug is lost and amnion is burst releasing more amniotic fluid

3. contractions get stronger - POSITIVE FEEDBACK OF OXYTOCIN, more uterus contracts, more stretch receptors are stimulated, more release of oxytocin

4. contractions spread from top to bottom

5. cervix dilates

6. once baby + placenta r expelled stretch receptors arent stimulated so contractions stop

Second Stage of Birth

• baby is pushed out of uterus and down vagina - head first

  • umbilical cord is clamped and cut

Third Stage

• placenta detaches from the wall of the uterus and passes it out through the vagina

• bleeding is limited by vasoconstriction of the blood vessels of the uterus which supply placenta

Define Lactation

• production of milk

Describe the structure of the mammary glands/breasts

• special epithelial cells line cells called alveoli - secrete milk

• alveoli r surronded by smooth muscle fibers

• attached to series of ducts which lead to sinuses (store milk)

• passed through separate opening in the nipple

Hormones in development of breasts and milk

• progesterone - breasts increase in size

• ducts - oestrogen

• prolactin produces milk - secreted by ant pit

• presence of oestrogen and progesterone inhibits secretion of prolactin, however at birth when oestrogen and progesterone lvls fall - prolactin isnt inhibited

Contents of Human Milk vs Colostrum

• milk - fat, lactose, lactalbumin, casein

• colostrum - first secretion of breasts, rich in globulin, low in fat, passes antibodies IgA from mom to baby

Suckling Reflex

• milk ejection reflex

• sucking of baby on breast - nerve impulse to hypothalamus - oxytocin (post pit)

• contraction of smooth muscle around alveoli and forces milk outta nipples

• release of prolactin is also stimulated - produce milk for next feed

tanti hormone summary V imp