PHYSL REPRODUCTIVE SYSTEM

function of reproductive system

• provides gametes for procreation of the species

• mating

• fertilization

organs of reproductive system

• gonads

• pathway for gamete transport

• accesssory organs and glands

functions of gonads

• organs which produce the gametes

• source of / secrete sex steroid hormones

gonads of male reproductive system

testis = sperm production

order of male reproductive tract

1. testis

2. Epidydimys

3.Vas deferens

4. Connects to seminal vesicle, prostate gland, and bulboretheral gland

prostate gland

penetrated as vas deferens descends downwards below the urinary bladder

urethra

• leads from the urinary bladder to the outside of the body

• where the common urogenital (organs for reproduction and urinary excretion) tract is formed

• genital tract forms a junction with the urinary tract

Scrotum

• also known as the scrotal sac

• External sac that contains the testes, blood vessels, and nerves

blood vessels in scrotum

• allow for countercurrent blood flow

• regulate temperature in this region

countercurrent blood flow

• testis are housed outside the body maintained at the temp of at least 2°C

• necessary for optimal spermatogenesis (sperm production)

• Blood flows in opposite directions very close in vessels, so that heat from

  warm arterial blood is passed to cooler venous blood

Spermatic cord

• cord-like structure which passes through a slit in the abdomen down into the scrotal sac

• combination of the vas deferens, blood vessels, and nerves

• The slit opening is in the inguinal canal and this continues down into the scrotal sac

Descent of the testes

• Start in abdomen near kidneys (8 weeks)

• Phase 1 (8–12 wks): move toward inguinal canal

• Phase 2 (7–9 months): pass through inguinal canal → scrotum

• At birth: should be in scrotum

• Failure to descend = corrected with surgery

Inguinal canal

the channel through which the testis descends into the scrotum in the male

Semeniferous tubules

• sites of sperm production

• spermatogenic cells (spermatogenesis begins at puberty)

• tiny coiled tubes within the testes in which sperm are produced

Leydig Cells

• found in the connective tissues surrounding the seminiferous tubules

• interstitial cells

• produce testosterone

Sertoli cells

• epithelial cells lining the circular seminiferous tubule

• helps in the process of sperm development

myoid cells

• smooth muscle cells

• outside the basement membrane

• Contract to move sperm through perastalsis

Blood testis barrier

• This is provided by the sertoli cells (epithelial cells)

• They create a tight junction which prevent blood from making antibodies to destroy developing sperm.

Luminal vs Basolateral compartment

Luminal: from the tight junction to the lumen (inner part)

Basolateral: from the basement membrane up to the tight junction (outer part)

Sertoli cells function

1. support sperm development (trophic role) and secretes luminal fluid for sperm housing

2. Secrete androgen-binding protein to maintain steady androgens in the lumen and androgen buffer

3. Target cells for FSH and testosterone (paracrine stimulates spermatogenesis)

4. Secretes inhibin (feedback for FSH)

5. Phagocytosis of old and damaged sperm

6. site of immunosuppression (blood-testis barrier)

Testosterone & FSH in Spermatogenesis

• Leydig cells → Testosterone

• Testosterone diffuses into seminiferous tubules

• Sertoli cells = target of FSH & Testosterone

• FSH and testosterone regulate spermatogenesis

Corticosteroid synthesis

Cholesterol → Progesterone → Aldosterone, cortisol, and adrenal androgens

How are androgens made in leydig cells

Cholesterol → pregnenolone → progesterone → androgens

What happens when testosterone enters into the blood stream

• Remains as testosterone

• Becomes DHT by 5 alpha reductase

• Is made inactive

• Is converted to estrogen by aromatase

DHT

• maintains other tissues or sexual characteristics

• maintenance of the prostate gland

• secondary male sexual characteristics

adolesences (10-14 years)

inability to reproduce

puberty (starts at 10-14 years, later in boys)

• sexual maturation

• reproductive organs mature (can produce gametes)

• secondary sexual characteristics develop

ex. hair growth, deepening of voice

Testosterone levels throughout a male lifespan

Peak before birth, peak after birth, remains low during childhood and then increases throughout puberty

Hypothalamic Pituitary Leydig Cell Axis

• Hypothalamus signals secretion of GnRH in a pulsatile manner

• Anterior pituitary releases LH and FSH

• FSH goes to leydig cells and FSH goes to sertoli cells

Why is pulsatile secretion necessary?

• Constant GnRH → receptor desensitization (no LH/FSH release)

• Pulsatile GnRH required to activate anterior pituitary

• LH stimulates Leydig cells → Testosterone

• Testosterone = negative feedback

  • ↓ GnRH amplitude (hypothalamus)

  • ↓ LH release (↓ pituitary sensitivity)

What pulse causes LH release

High frequency

What pulse causes FSH release

Low frequency

effects of androgens

• Stimulate spermatogenesis

• Promote development of secondary sex characteristics during puberty and maintenance of these characteristics in adult life

• Increase sex drive

• Promote protein synthesis in skeletal muscle → Anabolic effect– Stimulate growth hormone secretion, which permits bone growth during adolescence

• Promote development of male reproductive structures during embryonic life

spermatogenesis

• formation of the male gamete (sperm)

Spermatogenesis steps

1. Spermatagonium

MITOSIS

2. Primary Spermatocyte

Meiosis 1

3. Secondary spermatocyte

Meiosis 2

4. Spermatid

how long is spermiogenesis

~24 days

Purpose of mitosis in spermatogenesis

• enlarge and split a cell into 2 identical daughter cells that are genetically identical to the original cell

• Ensures a continuous supply of spermatogonia

Purpose of meiosis in spermatogenesis

• each daughter cell receives half of the chromosomes

• 46 (diploid) —> 23 (haploid)

differentiation and packaging

• specialization for transport and delivery of proper genetic material

spermatogenesis in seminiferous tubule

• Formation of sperm begins close to the basement membrane in the seminiferous tubule (from basement to lumen)

• occurs in the space between adjacent sertoli cells

• germ cells are found close to the basement membrane

What occurs in the basal compartment?

Spermatagonium to primary spermatocyte

What occurs in the luminal compartment?

Primary spermatocyte secondary spermatocyte to spermatids to sperm cells

Time to produce sperm

64 days

Spermiogenesis

Spermatids mature into motile spermatazoa

Parts of spermiogenesis

• A flagella forms

• Spermatid gains the shape of sperm

• Some cytoplasm is shed and mitochondria line up in the middle to form the neck

nucleus of sperm

• contains the chromosomes / genetic material (haploid number)

Acrosome of sperm

• vesicle positioned close to the plasma membrane at the tip of the sperm’s head

• Contains enzymes needed for the fertilization of an egg

Midpiece of a sperm

• Contains mitochondra as a source of energy (ATP) which is needed for the movement of the tail

Tail of sperm

• Has whip like movements to propel sperm

sperm maturation

• Seminiferous tubules: sperm released immature & immotile

• Sertoli cell fluid pushes sperm → epididymis

• Epididymis (6–12 days): maturation → motility & fertilization ability; fluid reabsorbed → sperm concentrated

• Move to vas deferens (peristalsis) → temporary storage until ejaculation

• Fertility depends on sperm number & structure

• Most of the fluid is reabsorbed and the sperm is concentrated

Where does sperm remain until ejaculation?

Vas deferens

What does FSH do for men?

• gonadotropins

• Stimulate spermatogenesis

What does LH do for men?

• gonadotropins

• Stimulate androgen secretion

negative feedback control of gonadotropins

Pulse generator (GnRH) → anterior pituitary to release FSH → Sertoli cells → secrete androgen binding protein and inhibin

Inhibin

• peptide hormone

• Secreted by setoli cells in response to FSH to the anterior pituitary

• does not act at the hypothalamic level

Testosterone vs inhibin feedback

• Testosterone acts on both the hypothalamus and the pituitary

• Inhibin acts on only the anterior pituitary

FSH vs LH in men

• LH acts on Leydig cells: secrete testosterone, inhibiting secretion of LH at the level of the anterior pituitary and hypothalamus

• FSH acts on the sertoli cells: release of FSH from the anterior pituitary is inhibited by inhibin released from the sertoli cells

• FSH stimulates the relaese of inhibin and androgen binding protein

androgen binding proteins

• binds to testosterone to keep conc. of the testosterone high in the lumen of the seminiferous tubule

accesory sex organs

• secrete seminal fluid

• semen = sperm + seminal fluid

seminal fluid

• comes from seminal vesicle, prostate gland, and bulbourethral gland

• dilution of sperm, provides energy (fructose), formation of semen clot (fibrin-like protein that helos in tge formation of the semen plug)

Seminal vesicles function

• Secretes an alkaline fluid with fructose, enzymes and prostaglandins

• enzymes necessary to produce semen clot

• alkaline to balance the highly acidic female genital tract, fructose to give energy

• prostaglandins causes contraction of the female tract for sperm to move forward

prostate gland function

• Secrete citrate and PSA enzymes

Citrate purpose sperm

gives the sperm energy

PSA purpose

• enzyme (protease) that breaks down proteins to make the semen more fluid

• biomarker for detection of abnormal growth of prostate tissue

Bulberitheral glands purpose

Secrete a viscous mucous

neural control of the male sexual response

• controlled by ANS

• involves spinal reflexes

Erection phase

1. Parasympathetic response increases

2. Relaxes artery smooth muscle

4. Blood Flow to penis increases

5. Erection

Emission phase

• Sympathetic nervous system causes contraction on the muscular tissue of the seminal vesical, prostate gland, and vas deferents to mix the contents of the sperm

Ejaculation phase

• skeletal muscle rapid contraction that allows for the movement of sperm to the outside of the body (somatic control)

Control of erection

• Activation of parasympathetic stimulation is caused by release of nitric oxide (NO), NO release

• NO stimulates guanylate cyclase to convert GTP to cGMP

• Causes vasodilation

• Broken down by phosphodiesterase

Phosphodiesterase

Breaks down cGMP, stopping erection

erectile dysfunction

• can’t have an erection

• treated with viagra which acts as an ihibitor of the enzyme phosphodiesterase

Three things involved in erections

1. NO

2. cGMP

3. Phosphodiesterase

Capacitation

• a process that sperm undergo while traveling through the woman's reproductive tract

• Receptors made available through the removal of the glycoprotein layer

• area altered

• Tail moves to a wave like movement to a whip like movement

Zona pellucuda

Triggers acrosomal reaction surrounds the egg, acrosomal enzymes released by exocytosis

female cyclic changes in activity

menstrual cycle

female restricted period of fertility

Ovulation

How do the amount of gametes for females differ than males?

Female gamete pools are established at birth

Menarche

onset of menstruation (puberty)

Menstruation

Female reproductive cycles

Menopause

When females lose the ability to reproduce around 45-50

Ovaries

• female gonads

• Site of ova maturation

• are suspended by ligamentous tissue in the peritoneal cavity, and are not directly linked to the uterine tubes

female reproductive tract and organs

• uterus, uterine tubes, vaginal canal

• consists of connective tissue with follicles

• organs are separate from reproductive tract

Uterine tubes

• fallopian tubes/oviducts, openings are the maturation sites for gametes

• transports ova from the ovaries to the uterus

infundibulum and fimbriae

• Pick up the released ovum from the ovary

What moves the ovum through the uterine tube

• initially peristaltic contractions

• mostly ciliary actions

• duration of 4 days to uterus

ectopic pregnancy

• problems in the oviduct/fallopian tube when the cilia do not move properly can result in a fertilized egg in the uterine tube

perimetrium

• outer layer of the uterus

• epithelial cells and connective tissues, providing a protective covering

Myometrium

• Middle layer of the uterus

• thickest layer of smooth muscle (myo = muscle)

endometrium

• inner layer

• layer of epithelial cells and connective tissue

• numerous glands which contain things such as glycogen

• this layer sheds during a cyclic change every month under the influence of hormones (period)

Birth canal

cervix and vagina

Primordial folliocles

Small tiny follicles

Primary follicles

In the medium stage of growth

Mature follicles

• larger stage of growth with a fluid-filled cavity

• releases the egg

Corpus leuteum

• Follicles in which the eggs have been released from (mature follicles)

• remians for a while and acts as an endocrine gland

What forms after the corpus luteum

corpus albicans

Parts of the ovarian cycle

1. Follicular phase

2. Ovulation

3. Luteal Phase

follicular phase

• first phase (first 14 days)

• associated with development of the follicles in which the eggs are growing

ovulation

• release of the egg

• occurs on the 14th day

luteal phase

• next 14 days of the cycle

• The egg is released, and it is related to the corpus leuteum