Male Reproductive System
Testis Structure
- Oval shape; each testis has ~250 compartments called testicular lobules
- Each lobule contains 1 to 3 highly coiled seminiferous tubules
Seminiferous Tubules
Lined on inside by two types of cells:
- Male germ cells (Spermatogonia): Undergo meiotic divisions to form sperms
- Sertoli cells: Provide nutrition to germ cells 2010. Regulated by pituitary hormone FSH 2006, 2024
Interstitial Spaces
Regions outside seminiferous tubules containing blood vessels and Leydig cells (Interstitial cells)
- Key Function: Leydig cells synthesise and secrete testicular hormones called androgens (mainly testosterone) 1993, 1991, 2024
Accessory Ducts and Transport Pathway
NEET 2019, NEET-II 2016
Pathway: Seminiferous tubules → Rete testis → Vasa efferentia → Epididymis → Vas deferens → joins seminal vesicle duct to form Ejaculatory duct → Urethra → Urethral meatus
Blockage of vasa efferentia stops gamete transport from testis to epididymis 2011
Male Accessory Glands
Paired seminal vesicles, a prostate, and paired bulbourethral glands
- Secretions constitute seminal plasma, rich in fructose, calcium, and certain enzymes 2010, 2009, 2020
- Bulbourethral gland secretions help in penis lubrication
External Genitalia
The penis: Enlarged end is glans penis, covered by loose fold of skin called foreskin
Female Reproductive System
Ovaries
Primary female sex organs producing ovum and steroid ovarian hormones. Covered by thin epithelium enclosing ovarian stroma (peripheral cortex and inner medulla)
Accessory Ducts
Oviducts (Fallopian tubes), uterus, and vagina
Fallopian Tube Parts
- Infundibulum: Funnel-shaped part closest to ovary 2010. Edges possess finger-like projections called fimbriae (collect ovum after ovulation)
- Ampulla: Wider part of oviduct
- Isthmus: Last part with narrow lumen; joins uterus
Uterus (Womb)
Inverted pear shape. Opens into vagina through narrow cervix
Wall Layers
- Perimetrium: External thin membranous layer
- Myometrium: Middle thick layer of smooth muscle. Exhibits strong contraction during baby delivery
- Endometrium: Inner glandular layer. Undergoes cyclical changes during menstrual cycle
Female External Genitalia
- Mons pubis: Cushion of fatty tissue covered by skin and pubic hair 2024 Re
- Labia majora & Labia minora: Fleshy tissue folds surrounding vaginal opening
- Clitoris: Tiny finger-like structure at upper junction of two labia minora above urethral opening
- Hymen: Membrane partially covering vaginal opening
Mammary Glands
Contains glandular tissue divided into 15-20 mammary lobes containing clusters of cells called alveoli (secrete milk)
Milk Transport Pathway
2024 Re
Alveoli lumen → Mammary tubule → Mammary duct → Mammary ampulla → Lactiferous duct → Nipple
Gametogenesis
Spermatogenesis
Begins at puberty due to significant increase in GnRH secretion
| Cell Stage | Process / Action | Ploidy & Chromosome No. |
|---|---|---|
| Spermatogonia | Multiply by mitosis on inside wall of tubules | Diploid (46) 2015 |
| Primary Spermatocytes | Undergo 1st meiotic division (reductional) | Diploid (46) |
| Secondary Spermatocytes | Undergo 2nd meiotic division (1 makes 2 sperms) 1990 | Haploid (23) |
| Spermatids | Transformed into spermatozoa | Haploid (23) |
| Spermatozoa (Sperms) | Heads embed in Sertoli cells, then released | Haploid (23) |
Spermiogenesis vs Spermiation
NEET 2018, 2022
- Spermiogenesis: Transformation of spermatids into spermatozoa (sperms)
- Spermiation: Release of mature sperms from Sertoli cells into seminiferous tubule cavity
Structure of a Sperm
- Enveloped by plasma membrane
- Head: Contains haploid nucleus. Anterior portion covered by acrosome, filled with enzymes that help in fertilisation of ovum 2010
- Middle Piece: Possesses numerous mitochondria that produce energy for tail movement and sperm motility 1999
Oogenesis
Primary Oocyte
- Oogonia enter prophase-I of meiosis and get temporarily arrested
- Surrounded by granulosa cells to form Primary follicle
- At puberty, only 60,000-80,000 primary follicles remain per ovary
Follicular Maturation
Primary → Secondary → Tertiary follicle
- Tertiary follicle: Characterized by fluid-filled cavity called antrum 2023
- Inside tertiary follicle, primary oocyte grows and completes 1st meiotic division, forming:
- Large haploid Secondary oocyte (retaining nutrient-rich cytoplasm)
- Tiny first polar body Karnataka NEET 2013
Graafian Follicle
Mature tertiary follicle. Secondary oocyte forms new membrane, zona pellucida 2015
Ovulation
Graafian follicle ruptures to release secondary oocyte from ovary 1989, NEET 2020
Menstrual Cycle
Cycle in female primates lasting about 28/29 days. First menstruation is menarche; cessation around 50 years of age is menopause
Menstrual Phase (Days 1-5)
Menstrual flow occurs due to breakdown of endometrial lining of uterus and blood vessels. Immediate cause is withdrawal/lack of Progesterone 2006, NEET 2013
Follicular (Proliferative) Phase
- Primary follicles grow into Graafian follicles
- Endometrium regenerates
- LH and FSH increase, stimulating estrogen secretion
Ovulatory Phase (~Day 14)
Rapid secretion of LH leading to maximum level (LH surge) induces rupture of Graafian follicle and release of ovum 2011, NEET 2020, 2024 Re
Luteal (Secretory) Phase (~Days 15-28)
- Ruptured Graafian follicle transforms into Corpus luteum 2012 Mains
- Key Function: Corpus luteum acts as temporary endocrine gland 2017 and secretes large amounts of progesterone, essential for maintaining endometrium for implantation 1995, 2014, NEET 2018
If fertilization does NOT occur, corpus luteum degenerates, endometrium disintegrates, initiating new cycle
Fertilisation and Implantation
Capacitation
Final maturation of sperm, occurring in female reproductive tract NEET 2017, 2015
Fertilisation Site
Takes place in ampullary region of fallopian tube NEET-I 2016. Can only occur if ovum and sperms are transported simultaneously
Mechanism
- Sperm comes in contact with zona pellucida layer and induces changes in membrane that block entry of additional sperms (prevents polyspermy)
- Acrosome secretions help sperm enter ovum cytoplasm 2011
Completion of Meiosis II
Sperm entry induces secondary oocyte to complete 2nd meiotic division, resulting in second polar body and haploid ovum (ootid)
Sex Determination
Occurs at zygote formation. Depends entirely on whether X-bearing or Y-bearing sperm fertilises ovum Karnataka NEET 2013
Cleavage & Implantation
- Mitotic divisions (cleavage) as zygote moves through isthmus forming 2, 4, 8, 16 blastomeres
- Morula: Embryo with 8-16 blastomeres
- Blastocyst: Blastomeres arranged into outer trophoblast and inner cell mass
- Trophoblast attaches to endometrium, uterine cells cover it. This embedding is called implantation 2010 Mains
Pregnancy and Embryonic Development
Placenta
Formed by interdigitation of chorionic villi (from trophoblast) and uterine tissue
- Functions: Supplies oxygen/nutrients to embryo and removes carbon dioxide/excretory waste NEET 2013. Connected via umbilical cord
- Endocrine role: Placenta produces hCG, hPL, estrogens, progestogens NEET 2018, 2014, 2012
Germ Layers
Inner cell mass differentiates into:
- Ectoderm (outer)
- Mesoderm (middle)
- Endoderm (inner)
Inner cell mass contains stem cells with potency to form all tissues
Milestones of Foetal Development
- 1st Month: Foetus heart is formed
- 2nd Month: Foetus develops limbs and digits
- 12 Weeks (1st Trimester end): Most major organ systems (limbs, external genital organs) are well-developed 2020
- 5th Month: First movements of foetus and appearance of hair on head 2010
- 24 Weeks (2nd Trimester end): Body covered with fine hair, eye-lids separate, eyelashes formed
Parturition and Lactation
Parturition (Childbirth)
Induced by complex neuroendocrine mechanism
Foetal Ejection Reflex
- Signals originate from fully developed foetus and placenta, inducing mild uterine contractions 2009, 2010, 2012
- This reflex triggers release of oxytocin from maternal pituitary 2015, Karnataka NEET 2013
- Oxytocin acts on uterine muscle causing stronger contractions, expelling baby
Lactation
Mammary glands produce milk towards end of pregnancy
Colostrum
Milk produced during initial few days of lactation