Physiology of Reproduction

Dr. Niranjan Murthy HLAsst Prof of PhysiologyESIC-MC & PGIMSRBangalore

• Preservation and perpetuation of species

• Asexual reproduction- genes from a single parent

• Sexual reproduction- fusion of male and female gametes

• Fission- invertebrates

• Budding • Fragmentation

• Parthenogenesis – fishes, amphibians and lizards• Hermaphroditism• Sequential hermaphroditism

Figure 46.3a, b

Time

Ova

rysi

zeH

orm

ones

Beha

vior

Ovulation Ovulation

ProgesteroneEstrogen

Female-like

Male-like

Female-like

Male-like

(a) Both lizards in this photograph are C. uniparensfemales. The one on top is playing the role of a male. Every two or three weeks during the breeding season, individuals switch sex roles.

(b) The sexual behavior of C. uniparens is correlated with the cycle of ovulation mediated by sex hormones. As blood levels of estrogen rise, the ovaries grow, and the lizard behaves like a female. After ovulation, the estrogen level drops abruptly, and the progesterone level rises; these hormone levels correlate with male behavior.

• External fertilization

• Internal fertilization

Figure

46.10

Erectile tissueof penis

Prostate gland

(Urinarybladder)

Bulbourethral gland

Vas deferensEpididymis

Testis

Seminalvesicle(behind bladder)

Urethra

Scrotum

Glans penis

Vagina

Uterus

Cervix

OvariesOviduct

Uterine wallEndometrium

Follicles

Corpus luteum

Physiology of Human Reproduction

• Fertilization• Parturition • Lactation • Sexual dimorphism completes at puberty

Sex determination

• Gender differences are mainly by Y chromosome and GONADS

• Gonads have dual function- gametogenic and endocrine

• Gonadal function depends on gonadotropins• Cyclic secretion in females and noncyclic in

males

• Chromosomal sex:

• Sex determination is by1. Karyotyping2. Sex chromatin

Barr bodies

Development of reproductive system

Development of gonads:• Primitive gonad arises from genital ridge• Identical in both genders till 6th week• Cortex regresses in genetic males in 7-8th week• Medulla regresses in genetic females• No hormonal effects on gonadal development

Development of genitalia: • In 7th week of gestation• Mullerian duct in females- develops into

uterus and fallopian tubes• Wolffian duct in males- develops into

epididymis and vas deferens

• External genitalia bipotential till 8th week• Urogenital slit closes in males and remain

open in females

• Testis secrete MIS and testosterone• MIS causes regression of mullerian duct on

same side• Testosterone induces development of vas

deferens and epididymis on same side• DHT induces male external genitalia and

secondary sexual characters

Brain development:• Male behavior and male pattern of

gonadotropin secretion if exposed to androgens early

Sex differentiation

1. Genetic sex:• Male genetic sex is determined by

Y chromosome• SRY gene encodes TDF• SRY is essential for maleness but not adequate• Absence of SRY causes development of ovaries

2. Gonadal sex:• Differentiation occurs around 7-8 weeks

3. Genital sex:• Testosterone and MIS in males• Absence of these factors leads to

development of female tract

Abnormalities of sex differentiation

I Chromosomal abnormalities: 1. Turner’s syndrome: • ovarian agenesis• 45 XO pattern• Dwarfism, webbing of neck, diminished sexual

development

2. Klinefelter syndrome:• Seminiferous tubule dysgenesis• 47 XXY• Female genetic sex with male gonadal and

genital sex• Tall stature• Mental retardation

3. Superfemale:• 47 XXX• No abnormalities4. True hermaphroditism:• XX/XY mosaic• Both gonads present

II Hormonal abnormalities:• Pseudohermaphroditism- Genetic sex of one

type with external genitalia of opposite sex1. Female Pseudohermaphroditism- Genetic

females exposed to androgens by 8th to 13th week

2. Male Pseudohermaphroditism- Genetic males with female genitalia due to defective testis or androgen resistance

Puberty

• Transition from the non-reproductive state to the state of reproductive functions that allows procreation

• Activation of gonads and development of reproductive tract

• Period of maturation is called ADOLESCENCE

Events of puberty:• Thelarche• Pubarche• Menarche • Adrenarche

• Control of onset of puberty• Pulsatile secretion of gonadotropins• Role of leptin

Sexual precocity

Male Reproductive System

• Gonads- Testes• Reproductive tract- internal and external

genitalia• Accessory sex glands- prostate, seminal

vesicle, bulbourethral glands• Lifelong spermatogenesis

• Testes formed in abdomen• Descend into scrotum in 7th month of

intrauterine life• Requires MIS and other factors• Cryptorchidism • Slightly lower body temperature [2⁰ C]• Gametogenesis and hormonal secretion

Scrotum

• Sac of skin and superficial fascia that hangs outside the abdomino-pelvic cavity at the root of the penis

• Role or cremaster and dartos??• Contains paired testicles separated by a

midline septum• Its external positioning keeps the testes 2C

lower than core body temperature

Testis

• Covered by tunica vaginalis and albuginia• 300 lobules with 2-4 Seminiferous tubules• Each lobule has intratubular compartment

(Seminiferous epithelium) and peritubular compartment (neurovascular elements)

• Seminiferous epithelium- sperm cells and sertoli cells

TESTIS

MALE REPRODUCTIVE SYSTEM

EPIDIDYMIS

TUNICA ALBUGINEA

Mediastinum containing

RETE TESTIS

LOBULES

TESTIS H&ETESTIS H&E

SEMINIFEROUS TUBULESSEMINIFEROUS TUBULES

SEMINIFEROUS TUBULESSEMINIFEROUS TUBULES

INTERSTITIAL CONN. TISSUEINTERSTITIAL CONN. TISSUE

TESTIS H&ETESTIS H&E

SEMINIFEROUS TUBULESSEMINIFEROUS TUBULES

• Cells of testis:1. Germ cells2. Sertoli cells3. Leydig cells

Spermatogenesis

• Spermatogonia• Primary spermatocyte• Secondary spermatocyte• Spermatid• Mature sperm

• Spermatogonia- stem cells- enter meiosis• Incomplete cytokinesis

• Primary spermatocyte- prophase of 1st meiotic division

• Secondary spermatocyte- completion of 1st meiotic division

• Spermatids- completion of 2nd meiotic division• Spermatozoa- spermiogenesis

• Duration of 72 days• Recruitment of adjacent spermatogonia every

16 days• Spermiogenesis- maturation of spermatids

into spermatozoa• Spermiation- release of spermatozoa• Further maturation occurs as it passes through

the genital tract

Spermiogenesis

Sertoli cells

• True epithelium• Extend from basal lamina to the lumen• From gap junction with each sperm cell stage• Tight junction between adjacent sertoli cells

forms blood-testis barrier

Functions of sertoli cells

1. Forms blood-testis barrier2. Provide nutrition to sperm cells3. Expresses FSH and androgen receptor4. Express CYP19/aromatase, which converts androgens

to estradiol5. Express ABP6. Phagocytose residual body7. Secretes large amount of fluid as a bathing medium

for sperms8. Production of AMH9. Production of Inhibin

Peritubular compartment

• Loose connective tissue• Peritubular capillary net work• Leydig cells

Leydig cells

• Steroidogenic • Cholesterol is synthesized de novo, or

acquired through LDL and HDL receptors• Synthesizes testosterone from

androstenedione

Androgens- Fate and Actions

• Significant amounts diffuse into seminiferous tubules and get concentrated by ABP

• 100 times more concentrated than blood• Converted to 17β estradiol in sertoli cells• Sperm cells have estrogen receptors• Aromatase deficiency lead to tall stature• Conversion to 5α-dihydrotestosterone by

5α-reductase

Functions of DHT: • Masculinization of external genitalia in utero• Growth and activity of prostate• Growth of penis• Darkening and folding of scrotum• Growth of pubic and axillary hair• Growth of facial and body hair• Increased muscle mass• 5α-reductase inhibitors- prostatic hypertrophy

Peripheral actions of testosterone:• Regulation of sertoli cell function• Induces development of male tract• Increase LDL and VLDL levels• Increased RBC production• Promote bone growth• Anabolic effect• Maintenance of erectile function and libido

Mechanism of action

• Cytoplasmic androgen receptors (AR) bound to chaperone proteins

• ARE- Androgen Response Element• Both testosterone and DHT act through AR

Regulation of testicular functions

• Male contraceptive• Steroid abuse

Male Reproductive Tract

• Epididymis• Vas deferens• Ejaculatory duct

Accessory structures:• Seminal vesicles• Prostate• Bulbourethral glands• Scrotum• Penis

Epididymis

Epididymis

• Posterior border of testis• Coiled and 7mtr long• Head, body and tail• Sperms spend a month in epididymis and

acquire motility• Sperm can be stored for several months in tail

of the epididymis• Decapacitation

Vas deferens

Vas deferens

• 40-45cm long• Ascend as part of spermatic cord• Stores sperms• Vasectomy

Ejaculatory duct

• 2cms in length• Empties into prostatic urethra

Seminal fluid

• Milky white sticky mixture of sperms and glandular secretions

• Mixture of secretions from glands like prostate, seminal vesicle and bulbourethral glands

• Provide nutrition to sperms• Propulsion of sperm• Buffering

Seminal vesicle secretion:• Primary source of fructose• 60% of seminal fluid• Seminogelins- coagulation of semen after

ejaculationProstatic fluid:• 30% of volume• High in citrate, zinc, spermine and acid phosphatase• PSA- liquefies coagulated semen after a few

minutesBulbourethral glands:• Rich in mucus• Lubrication , cleansing and buffering of urethra

Spermiogenesis

• Spermatids lose excess cytoplasm, acquire tail• Parts of sperm;• Head- contains DNA; covered by acrosomal

cap containing enzymes required for penetration of ovum

• Body- plenty of mitochondriae• Tail- flagellum

Journey of spermatozoa

• Stays for one month in epididymis and undergoes maturation

• Decapacitation • Stored for several months in tail of epididymis

and vas deferens• Acquire motility in epididymis by activation of

CatSper protein• Undergoes capacitation when exposed to

female reproductive tract environment

The penis

• Copulatory organ designed to deliver sperms deep into vagina

• Corpora cavernosa and corpus spongiosum• Vascular spaces• Circumcision

Erection Psychic stimuli and impulses

from genitalia

Efferent parasympathetic nerves: Nervi erigentis

Nonadrenergic noncholinergic fibers

Nitric oxide

Guanylyl cyclase

cGMP

Dilation of arterioles

Erectile tissue gets engorged with blood

Veins get compressed

Sympathetic vasoconstrictors to renal arteries

• Erectile dysfunction• Sildenafil citrate• Phosphodiesterase inhibitor• Achromatopsia

• Emission: propulsion of semen into urethra• Ejaculation: ejection of semen out of urethra• Afferents- Internal pudendal nerves• Emission- Sympathetic response- upper

lumbar segments- contraction of smooth muscles of vas deferens and seminal vesicles

• Ejaculation- contraction of bulbocavernosus- S1,2,3 motor

Female Reproductive System

• Ovaries• Oviducts, Uterus, Cervix, Vagina• External genitalia

The Ovary

• Bilateral• Located in broad ligament• Cortex- cellular• Medulla- neurovascular elements• Ovarian follicles- oocyte surrounded by

follicular cells• Cortex covered by tunica albuginea and

surface epithelial cells

• Functions:1. Gametogenesis2. Secretion of female sex hormones3. Production of Inhibin

Uterus

• Provide mechanical support, protection and nutrition to developing conceptus

• Parts- Fundus, Body and Isthmus

Uterine wall

• Endometrium• Myometrium• Perimetrium

Endometrium- • 10% of wall thickness• Glands and blood vessels• Functional and Basilar zoneMyometrium-• 90%• Longitudinal, circular and oblique muscles

Cervix

• Considered separately from uterus• Internal os, cervical canal, external os• Extends from isthmus to vagina and projects

into it

Fallopian tube

• 13 cm long• Transport gametes• Site of fertilization• Infundibulum, Ampulla, Isthmus

Vagina

• 7.5 to 9cm• Highly distensible• Fornix is a shallow recess surrounding cervical

protrusion• Hymen- elastic epithelial fold

External genitalia• Vulva or Pudendum• Vestibule- area surrounded by labia minora;

has urethral and vaginal openings• Clitoris- equivalent of penis• Labia majora

Menstrual cycle

• Ovarian cycle• Endometrial cycle• Cervical changes• Vaginal changes• Hormonal changes• Usually around 28 days • Start from the first day of menstruation

Oogenesis

1. Resting primordial follicle2. Growing preantral follicle3. Growing antral follicle4. Dominant follicle5. Dominant follicle within periovulatory period6. Corpus luteum7. Atretic follicle

Resting primordial follicle

• Appear during mid-gestation• Made of oogonia and somatocytes• Ovarian reserve• 7 million ooogonia enter process of 1st meiotic

division at 5th month- primary oocytes• Primary oocytes get surrounded by follicle cellsFollicular reserve:• 3lakh at maturity• <1000 at menopause

• Small subset of follicles enter growth phase in waves

• Independent of gonadotropins• Gamete- primary oocyte- maturational

incompetence- arrest in diplotene stage of 1st meiotic division

Growing preantral follicle

• Appearance of cuboidal granulosa cells- primary follicle

• Granulosa cells become stratified- secondary follicle

• Formation of thecal cells- mature preantral follicle

• Move inwards and release angiogenic factors

• Gametes secrete ZP1, ZP2 & ZP3. • Form zona pellucida- species specific• Granulosa cells express FSH receptor• Thecal cells secrete small amounts of

androstenidione and express LH receptor

Growing antral follicles

• 25 days to grow into early antral follicle• Granulosa cell become 6-7 layered• Formation of antrum• Reach 2-5mm in 45days• Recruitable follicle• Stratum granulosa- steroidogenic• Cumulus oophorus• Highly dependent on FSH

• Oocyte acquires maturation competence but still maintains meiotic arrest

• Maintenance of high levels of cAMP• Thecal cells produce increased amounts of

androgens• FSH stimulates expression of aromatase in

granulosa cells• Inhibin B formation by granulosa cells

Dominant follicle

• About 20 follicles are recruited• Prolifera quota• Dominant follicle• 20mm in preovulatory phase• Oocyte becomes 140µ in diameter• Dominant follicle- significantly steroidogenic• FSH induces LH receptors In mural granulosa

cells

Dominant follicle during periovulatory period

• From onset LH surge to ovulation 32-36hrs• Luteinization process

Ovulation

• LH surge• Oocyte progresses to metaphase of meiosis II• Formation of stigma• Release of cytokines and hydrolytic enzymes• Breakdown at stigma• Cumulus-oocyte complex released into

peritoneum

Ovulation

• Cumulus expansion- hyaluronic acid and matrix components

• Granulosa cells secrete angiogenic factors

Corpus luteum

• Corpus hemorhagicum• Enlargement of granulosa lutein cells• 14 days life• Needs hCG• PGF2α cause regression of lutein cells• Corpus albicans• Peaking of progesterone production• Inhibin A repress FSH

• Fall in hormones during 2nd half of luteal phase• Luteal phase deficiency

Atretic follicles

• Apoptosis • Thecal cells persist

Ovarian cycle

• Follicular phase: preovulatory phase• Luteal phase: postovulatory phase• Luteal phase is fixed- 14 days

Uterine cycle

• Proliferatory phase: follicular phase• Secretory phase: luteal phase• Proliferatory phase begins at day 1 of

menstruation• Menstruation: process of endometrial

(stratum functionale) sloughing; lasts 1-5 days; loss of upto 80ml (average 35ml) of blood; withdrawal of progesterone

Proliferative phase: • begins on 1st day of menses• Till ovulation• Increase in endometrial thickness• Endometrial glands are drawn out• Influence of estrogen• Estrogen induces progesterone receptor

expression

Secretory phase:• Glands get coiled & tortuous and

secrete clear fluid• Under the influence of

progesterone• Change in adhesivity of surface

epithelium• Differentiation of stromal cells

into predecidual cells

Menopause

• 45-55yrs• Decline in number of follicles• Reduced estrogen and progesterone• High gonadotropin levels• Climacteric• Hot flushes coincide with LH surge

Disorders of menstruation

• Menorrhagia: excessive bleeding• Metrorrhagia: irregular and intermenstrual

bleeding• Dysmenorrhoea: painful bleeding• Oligomenorrhoea:• Amenorrhoea: • Anovulatory cycle:• Endometriosis: cause of infertility

Cyclic changes in uterine cervix

• Estrogen makes cervical mucus thinner and alkaline

• Progesterone makes it thick, tenaceous, acidic and cellular

• Spinnbarkeit and fern pattern in ovulatory phase

Vaginal cycle

• Estrogens cornify vaginal epithelium• Progesterone causes proliferation of vaginal

epithelium and infilteration with leucocytes• Thick mucus secretion due to progesterone• Cornification- increased glycogen

accumulation

Hormonal regulation of menstrual cycle

Ovarian hormones

• Estrogens• progesterone

Estrogens

• LH acts on theca interna to increase androgen secretion

• FSH induces aromatase in granulosa cells• Androgens are converted to 17β estradiol• 2% of circulating estrogen is free; 60% bound

to albumin; rest to SHBG• Metabolized in liver

Actions of estrogens

1. Facilitate growth of follicles2. Increase motility of fallopian tubes3. Support endometrial growth4. Increase myometrial excitability5. Feedback inhibition of FSH6. Dual effect on LH regulation7. Increase libido8. Increased dendrites and synaptic knobs in rat

neurons

8. Reported to slow progression of alzheimer’s9. Growth hormone of breast10. Secondary sexual character development11. Salt and water retention12. Lowers plasma cholesterol13. Anti-atherogenic 14. Avoids osteoporosis

Mechanism of action:• Nuclear receptors• ERα and Erβ• Evidence of surface receptors

Progesterone

• Produced by granulosa cells• Stimulated by LH

• 2% is freely circulating; 80% bound to albumin and remaining to CBG

• Converted to pregnenidiol and conjugated

Actions of progesterone

1. Secretory changes in endometrium. Prepares it for maintenance of conceptus

2. Decreases the excitability of myometrium3. Decrease estrogen receptors and increase

conversion of active estrogens to less active ones

4. Stimulate development of lobules and alveoli of breast

5. Thermogenic6. Stimulate respiration7. Natriuresis in large doses

Mechanism of action:• Nuclear receptor bound to HSP• Mifepristone

Control of ovarian function

• GnRH secreted in episodic bursts• Continuous infusion of GnRH causes

downregulation of receptors in pituitary• GnRH frequency increases by estrogen and

decreases by progesterone• Self priming of GnRH in mid-cycle• Constantly elevated levels of GnRH will down-

regulate its receptors in pituitary: treatment of precocious puberty and prostatic cancer

• Constant elevation of estrogen to 300% (200pg/mL) for 36hrs induces LH surge

• PGF2α luteolysin• ET-1 and oxytocin

Tests for ovulation

1. Increase in BBT2. Ultrasonography3. Cervical smear4. Spinnbarkeit

Changes during intercourse

• VIP- vasodilation- increased blood supply• Stimulation of labia, clitoris, nipples• Increased vaginal secretion• Orgasm

Fertilization

• Recombination of genetic material• Initiation of embryonic development• Ampulla or junction of ampulla and isthmus

• Steps of fertilization:1. Penetration of cumulus- hyaluronidase2. Bind to ZP3- Acrosomal reaction- ZP2 binding3. Fusion of membranes4. Ca2+ cascade- egg activation5. Exocytosis of cortical granules- modify ZP 2 & 36. Sperm enters ovum- completion of 2nd meiotic

division

Implantation

• Fertilization on day 16• Implantation after 6 days• Morula- 3days• Blastocyst 4-5 days• Inner cell mass and trophoblast• Embryonic pole• Digest ZP by proteases 5-6 days: hatched

blastocyst

• Cytotrophoblast• Syncytiotrophoblast- adhesive; invasive;

endocrine; phagocytosis; transport of substances

• Interstitial implantation• hCG and other hormones

Maternal response:• Decidualization• Tissue inhibitors of metalloproteinases

Failure to reject fetus

• Placental trophoblast express HLA-G• Fas ligand

Human chorionic gonadotropin

• Glycoprotein• Trophoblastic cells, blastocyst• Peaks in 60-90 days• Similar to LH, FSH and TSH• Luteotrophic• Marker of pregnancy

Human chorionic somatomammotropin

• Maternal GH of pregnancy• Proportional to the size of placenta• Retention of calcium, nitrogen and potassium• Lipolysis• Reduced glucose utilization

Other hormones

• Relaxin• CRH, β-endorphin, α-MSH • GnRH, Inhibin• Α subunit of hCG, Prolactin

Fetoplacental unit

• Placenta takes over in 6th week after pregnancy

• Placenta synthesize progesterone and pregnenolone

• Progesterone is converted to cortisol in fetal adrenal

• Pregnenolone forms DHEAS & 16OH-DHEAS in fetal liver

• They form estradiol and estriol respectively in placenta

Functions of estrogen in pregnancy

• Growth of uterus• Increase blood flow to fetus• Growth of breast• Increased size of maternal external genitalia

Functions of progesterone in pregnancy

• Decidualization• Reduces excitability of myometrium• Increases secretions of tubes and uterus

before implantation• Growth of alveoli of breasts

Placenta

• Formed by trophoblastic cells

• Bathed with maternal blood

• 2 umbilical arteries and one vein

Functions of placenta

• Fetal nutrition• Supply oxygen and remove CO2• Remove metabolic wastes• Hormonal production• Maintenance of pregnancy via progesterone

Maternal changes during pregnancy

• Weight gain-12-14 kgs; 3.5kg fetus; 2kg amniotic fluid; 2kg uterus; 2kg breast, 3kg ECF; 1.5kg fat

• BMR increases by 15%• Cardiac output increases by 30-40% at 27th week• Blood volume increases by 30%• Dilutional anemia• Neutrophilia, increased procoagulant activity• Increased RR and minute ventilation

• GFR increases by 50%• Increased renal reabsorption of sodium and

water• Relaxation of ligaments• Melasma gravidarum; striae gravidarum• Reduced IOP; subconjunctival hemorrhages;

corneal edema• Nasal congestion; hoarseness of voice• Increased salivation

• Endocrine and metabolic changes:• Thyroid enlargement; Increased Iodine uptake;

Increased thyroglobulin• Reduced serum Ca2+ levels; increased Vit D;

intestinal absorption of calcium• Increased pituitary size• Hyperplasia and hypertrophy of β cells of

langerhans; increased glycogen storage

Amniotic fluid

• 0.5 to 1.0 ltr• Contributed by fetal urine• Replaced every 3hrs• Amniocentesis

Parturition

• Duration of pregnancy- 284 days from LMP• Increased CRH secretion- increased cortisol-

lung maturation• Increase in estrogen & fall in progesterone• Increased PGF2α• Increase in oxytocin receptors in myometrium• Parturition reflex• Bearing down

Parturition reflex

Tests for Pregnancy

I Biological tests: 1. Ascheim Zondek test- urine of pregnant injected to female mice2. Friedman’s test- pregnant urine injected into female rabbit

II Immunologic tests:• Antibody prepared from rabbit• Urine + anti-HCG + HCG coated sheep RBCs