⮚ Introduction
✔ Gametogenesis: Process of formation of gametes.
✔ Insemination: Process of transfer of the male gametes (sperm) into the female genital tract.
✔ Implantation: Process of attachment of blastocyst to the uterine walls.
✔ Gestation: The event of embryonic development.
✔ Parturition: The process of delivery of the baby.
⮚ The male reproductive system
✔ Location: Pelvis region
✔ Consists of :
o Pair of Testes: (Sing. Testis), also called testicles
o Accessory ducts: (Rete Testis, Vasa Efferentia, Epididymis, Vas Deferens)
o Glands: (Paired Seminal Vesicle, Prostate gland, Bulbourethral gland)
o External Genitalia: (Penis)
The Testis (Primary Sex Organ)
✔ Location: Inside a pouch like structure called scrotum, Present outside the abdominal cavity.
✔ Shape : Oval
✔ Size: Length 4-5 cm; Width 2-3 cm.
✔ Role of scrotum / Why are testes located outside the abdominal cavity?
o The production of the sperm requires 2-2.50 C less than the normal body cavity. To maintain this lower temperature the testes are located outside the abdominal cavity.
Structural Organisation
✔ Each of the testis has about 250 compartments called testicular lobules.
✔ Each of the testicular lobules has 1-3 highly coiled structure called seminiferous tubules.
o Sperm in developed in the seminiferous tubules.
o The seminiferous tubules are lined by two types of cells on the inside
▪ Spermatogonia – Male germ cells
● Produces sperm by meiotic cell division.
▪ Sertoli Cells
● Provides nutrition to the developing sperm cells.
▪ Immunologically competent cells
✔ Interstitial spaces: The region outside the seminiferous tubules, within the testicular lobules.
o It consists of :
▪ Small blood vessels
▪ Leydig cells or interstitial cells.
● Releases Androgen (Testicular Hormone)
Male Accessory ducts: (Secondary Sex Organ)
✔ The seminiferous tubule opens into the vasa efferentia through the rete testis.
✔ The vasa efferentia opens into the epididymis (located on the posterior side of the testis).
✔ The epididymis then opens into the vas deferens.
✔ The vas deferens then receives the duct from the seminal vesicle and opens into urethra as the ejaculatory duct.
o Role of ejaculatory duct: to store and transport the sperms from the testis to the outside through urethra.
✔ Urethra starts from the Urinary Bladder and extends through the penis.
✔ The external opening of the penis is called the urethral meatus.
The Male Accessory Glands: (Secondary Sex Organ)
✔ Consists of seminal vesicle (paired), Bulbourethral gland (paired) and a prostate gland.
✔ Together they secrete Seminal Plasma
✔ Prostate gland: Milky secretion. It nourishes and activates the spermatozoa to swim.
✔ Seminal Vesicle: Secrete mucus and alkaline fluid containing fructose.
o Only place where fructose is secreted in the body.
o It acts as the substrate for the energy production by sperm.
✔ Bulbourethral gland/ Cowper’s gland: Release mucus fluid that helps in the lubrication of the penis.
✔ Sperm + Seminal Plasma = Semen
The Penis: (External Genitalia)
✔ Consists of specialized tissue – erectile tissue.
✔ This helps in erection, which is necessary for the process of insemination.
✔ The Glans Penis (enlarged end of penis) is covered by the Foreskin (loose fold of skin)
➢ The Female reproductive system
✔ Location: Pelvis region
✔ Consists of
o Pair of Ovaries :(Sing. Ova)
o Accessory ducts 🙁Paired Fallopian Tube, Uterus, Cervix, Vagina)
o External Genitalia 🙁Vulva)
o Glands 🙁Paired Mammary gland)
Ovaries (Primary Sex Organs)
✔ Location: One on each side of lower abdomen.
✔ Size: 2 to 4 cm in length
✔ Role of Ovaries
o Production of Ovum/Egg (Female gamete)
o Secretion of steroid hormones
▪ Estrogen, Progesterone, Relaxin
✔ Each ovary is covered by epithelium, and contains the ovarian stroma.
✔ The ovarian stroma is made up of:
o Peripheral cortex
o Inner medulla
Fallopian Tube / Oviduct (Secondary Sex Organ)
✔ Tube like structure that connects the uterus to the periphery of the ovary.
✔ Length : About 10-12 cm long
✔ Oviduct is divided into 3 parts:
o Infundibulum : Funnel shaped structure closest to the ovary
▪ The edges contain finger like structure called Fimbriae that help in collection of the egg after ovulation and pass it on to the oviduct.
o Ampulla : Middle wider structure of the oviduct.
o Isthmus : Closest to the uterus and joins with it.
Uterus / Womb (Secondary Sex Organ)
✔ Shape: Inverted Pear.
✔ The uterus opens into the vagina via a narrow opening called the cervix.
✔ The cavity of the cervix is called cervical canal.
✔ Cervical Canal + Vagina = Birth Canal
✔ Uterine wall has 3 tissue layer:
o Perimetrium: Outer most layer; thin membrane.
o Myometrium: Middle Layer; Thick muscular (Smooth muscle)
▪ Exhibits strong contraction during the process of child birth.
o Endometrium: Innermost layer; Glandular
▪ Undergoes cyclic change and play important role in the menstruation.
External Genitalia
✔ Consists of :
o Mons Pubis
▪ A cushion of fatty tissue covered by skin and pubic hair
o Labia Majora
▪ Fleshy folds of tissue, which extend down from the mons pubis and surround the vaginal opening.
o Labia Minora
▪ Paired folds of tissue under the labia majora.
o Hymen
▪ Membrane covering the opening of the vagina.
▪ It is often torn during the first coitus (intercourse).
▪ It can also be broken by a sudden fall or jolt, insertion of a vaginal tampon, active participation in some sports like horseback riding, cycling, etc.
▪ In some women the hymen persists even after coitus.
● Therefore, the presence or absence of hymen is not a reliable indicator of virginity or sexual experience.
o Clitoris
▪ Tiny finger like structure
▪ Present at the upper junction of the two labia minora above the urethral opening.
Mammary Gland (Secondary Sex Organ)
✔ Paired structure consists of glandular tissue and variable amount of fat.
✔ The glandular tissue is divided into 15-20 mammary lobes.
✔ The mammary lobes contain cluster of cells called alveoli.
o The cells of alveoli secrets Milk.
o It is stored in the lumens (cavities) of alveoli.
✔ The alveoli open into mammary tubules.
✔ The mammary tubules join to form a mammary duct.
✔ Several mammary ducts join to form a wider mammary ampulla
✔ The ampulla is connected to lactiferous duct through which milk is sucked out.
➢ Gametogenesis
✔ It refers to the process of development of sperm and ovum in the testis and ovaries respectively.
✔ Spermatogenesis is the process of gametogenesis in males while Oogenesis is the process of gametogenesis in females.
Spermatogenesis
✔ Process begins at the age of puberty.
✔ The process of Spermatogonium (Pl.– Spermatogonia) developing into the spermatozoa.
✔ Location of spermatogonia: inside wall of seminiferous tubules.
✔ Step #1 : Mitotic division of spermatogonia to increase in number.
o Ploidy level : Diploid (46 chromosomes)
✔ Step #2 : Some of the spermatogonia undergoes meiosis. These are called the primary spermatocytes.
o Ploidy level : Diploid (46 chromosomes)
✔ Step #3 : At the end of Meiosis-1, two cells are formed called the secondary spermatocytes.
o Ploidy level : Haploid (23 chromosomes)
✔ Step #4 : The secondary spermatocytes undergoes meiosis-2 and produces four cells, called the spermatids.
o Ploidy level : Haploid (23 chromosomes)
✔ Step #5 : Spermatids are transformed into the spermatozoa (sperms) by the process of spermiogenesis.
✔ Step #6 : The sperms cells heads then gets embedded into the Sertoli cells to complete the development process.
✔ Spermiation : The process of release of fully developed sperms from the seminiferous tubules.
Hormonal Regulation:
✔ The process is regulated by gonadotropin releasing hormone (GnRH) secreted from the hypothalamus.
✔ The GnRH stimulates the anterior pituitary and secrets two gonadotropins: luteinising hormone (LH) and follicle stimulating hormone (FSH).
|
Gonadotropin |
Acts on |
Secretions |
Role |
|
LH |
Leydig Cells |
Secretion of Androgen |
stimulate the process of spermatogenesis |
|
FSH |
Sertoli Cells |
Various Factors |
help in the process of spermiogenesis |
Structure of Sperm
✔ Single celled structure.
✔ Consists of a head, neck, a middle piece and a tail.
✔ A single plasma membrane covers the entire sperm.
✔ Sperm Head : Contains nucleus with haploid set of chromosomes
o Acrosome– cap like structure on the anterior portion of head.
▪ Filled with enzymes that is essential for the process of fertilization/
✔ Middle Piece : Contains numerous mitochondria.
o It is essential for the energy production which is needed for the sperm movement (motility).
✔ Tail : Helps in the sperm motility.
✔ A single human male ejaculation consists of about 200 to 300 million sperms.
o at least 60 per cent sperms must have normal shape and size and at least 40 per cent of them must show vigorous motility.
✔ The testicular hormones or androgens maintain the functions of male sex accessory ducts and glands.
Oogenesis
✔ The process of formation of the female gamete that starts during the embryonic development stage.
✔ Step #1: The ovary of the foetus develops a couple of million gamete mother cells (oogonia).
o No more oogonia are added later.
✔ Step #2: The oogonia undergoes meiosis, but the processes temporarily arrested at the Prophase-I stage. These are called primary oocytes.
o Step #3: The primary oocyte gets surrounded by a layer of granulosa cells and is called the primary follicle.
▪ At puberty only 60,000-80,000 primary follicles are left in each ovary, while the remaining degenerate.
o Step #4: The primary follicle then turns into the secondary follicle as it gets surrounded by more layers of granulosa cells and a new theca.
o Step #5: The secondary follicle develops into the tertiary follicle and it develops a fluid filled cavity called the antrum.
▪ The primary oocyte within the tertiary follicle grows in size and completes its first meiotic division at this stage.
✔ Step #6: The primary oocyte after the first meiotic division forms two unequal cells.
o Large Cell – Haploid Secondary Oocyte
▪ Contains most of the nutrient rich cytoplasm of the primary oocyte.
o Smaller Cell – First Polar Body
✔ Step #7: The tertiary follicle then develops into the mature follicle or graafian follicle.
o Step #8: The secondary oocyte gets a new membrane called the Zona Pellucida.
✔ Step #9 : Ovulation– The graafian follicle ruptures to release the secondary oocyte (ovum) under the influence of LH.
➢ Menstrual Cycle
✔ It refers to the reproductive cycle (Cyclic ovarian and uterine changes) in the female primates.
✔ Menarche – The first menstruation during puberty.
✔ Menopause – The stoppage of the menstruation at around 50 years of age.
✔ Menstrual Cycle – Events between two menstruation that repeats about every 28/29 days.
✔ Consists of 4 phases: Menstruation, Follicular, Ovulatory, Luteal phase.
✔ During pregnancy there is no menstruation or menstrual cycle.
Menstrual Phase
✔ First phase lasts for 3-5 days
✔ The endometrium lining of the uterus breaks down.
✔ The blood vessels and other tissues come out via the vagina.
✔ It occurs only if there is no fertilization.
o The absence is an indication of pregnancy.
✔ Menstruation does not occur in some of the following situations also
o Stress
o Poor Health condition.
Follicular Phase (Proliferative Phase)
✔ Follicular development occurs
✔ Hormones: The level of LH and FSH (gonadotropin) gradually increases.
o Stimulates follicular development.
o Stimulates the secretion of estrogen by developing follicle.
✔ Ovarian Change: The primary follicle develops into the mature follicle or graafian follicle.
✔ Uterine Change: The broken endometrium regenerated via cell proliferation.
Ovulatory Phase (Ovulation)
✔ The level of the LH and FSH is highest during the middle of the cycle (14th day).
✔ The LH surge induces the rupture of the graafian follicle and releases the ovum.
Luteal Phase (Secretory Phase)
✔ The graafian follicle changes into corpus luteum.
o It secretes the hormone progesterone.
o Progesterone is required to maintain the thick endometrium.
o It is essential in case of fertilization for the implantation to occur.
✔ In the absence of fertilisation, the corpus luteum degenerates.
o It forms corpus albicans.
o Disintegration of the endometrium occurs that leads to the menstruation.
o A new cycle begins
➢ Fertilization
✔ The process of fusion of the male and the female gamete is known as fertilization.
✔ Sexual intercourse / coitus/ copulation leads to the release of semen into the vagina of female (process is referred to as insemination).
✔ The sperm swims through the cervix, uterus and finally reaches to the ampullary region of the fallopian tube.
✔ If ovulation has occurred and the egg is present in the ampullary region then the fertilization occurs.
✔ This is why all the copulation need not lead to pregnancy.
✔ Process of fertilization
o The ovum is surrounded by the plasma membrane and the zona pellucida
o The acrosome present at the tip of the sperm helps the sperm to enter into the cytoplasm of the ovum.
o At this time the Meiosis-II division of the secondary oocyte is completed.
▪ The division is unequal
● Larger cell: Haploid Ovum (ootid)
● Smaller cell: Second Polar Body
o The haploid nucleus of the sperm and the ovum fuses together to form the diploid cell called the Zygote.
✔ What ensures that only one sperm can fertilise an ovum?
o When the first sperm comes in contact with the zona pellucida, there is a change in the membranes. This change prevents additional sperm from fertilizing the ovum.
➢ Sex-determination
✔ Genetically determined at the zygote stage.
✔ Human male has a chromosomal arrangement of 44 Autosome + XY Sex Chromosome.
✔ Human female has a chromosomal arrangement of 44 Autosome + XX Sex Chromosome.
✔ The haploid gametes in females consists of only X type of sex chromosome.
✔ The haploid gametes in males can contain either the X type or the Y type of sex chromosome.
✔ There is a 50% chance of the male gamete with X sex chromosome to fuse with the female gamete with X chromosome.
o This leads to the formation of the zygote with chromosomal arrangement of 44 autosomes + XX sex chromosomes.
o The child born will be a female child.
✔ There is also a 50% chance of the male gamete with Y sex chromosome to fuse with the female gamete with X chromosome.
o This leads to the formation of the zygote with chromosomal arrangement of 44 autosomes + XY sex chromosomes.
o The child born will be a male child.
➢ Events leading to Implantation
✔ Post fertilization the zygote moves through the isthmus to reach the uterus.
✔ Mitotic division leads to the formation of 2, 4, 8, 16 cell stage embryos.
o Each of the cells are called the blastomere.
✔ Embryo with 8 to 16 blastomeres is called Morula.
✔ The morula transforms into a Blastocyst due to rapid cleavage.
o It consists of around 70-100 cells.
o The blastocysts are well organized.
▪ Outer later – Trophoblast
● Gets attached to the endometrium
▪ Inner group of cells attached to trophoblast- Inner Cell Mass (ICM)
● Differentiates as embryo
▪ Fluid filled cavity – Blastocoel (Blastocyst cavity)
✔ Post the attachment of the trophoblast to the endometrium, the uterine cells divide rapidly and covers the blastocyst.
o The blastocyst gets embedded in the endometrium of the uterus.
o This process is called Implantation.
➢ Pregnancy And Embryonic Development
Placenta
✔ It is a structural and functional unit between developing embryo (foetus) and maternal body.
Development of Placenta
o Post implantation, chorionic villi are formed that are surrounded by uterine tissue and maternal blood.
▪ Chorionic villi are finger like projections on trophoblast.
o Interdigitation of the chorionic villi and the uterine tissue takes place and together they form the placenta.
✔ Role of Placenta
o Supply of oxygen to the developing embryo.
o Supply of necessary nutrients.
o Removal of CO2 and other excretory/waste materials.
o Acts as endocrine tissue and releases hormones like
▪ human chorionic gonadotropin (hCG)
▪ human placental lactogen (hPL)
▪ estrogens
▪ progestogen
✔ Placenta is connected to the embryo through the umbilical cord.
Hormones during Pregnancy
✔ hCG, hPL and relaxin are released only during pregnancy, hence are the pregnancy hormone.
✔ Relaxin is released by the ovary.
✔ The levels of estrogen, progesterone, cortisol, prolactin, thyroxine, etc., increases many folds during pregnancy.
o It is essential for supporting the fetal growth, metabolic changes in the mother and maintenance of pregnancy.
Embryonic Development
✔ The ICM contains the stem cells.
o They have the ability to develop into all the tissues and organs.
✔ After implantation the ICM differentiates into ectoderm (outer germ layer) and endoderm (inner germ layer).
✔ Mesoderm (middle germ layer) appears in between the ectoderm and endoderm.
✔ The ectoderm, mesoderm and the endoderm together give rise to all the tissues and organs.
Events during the gestation period (development period of 9 months)
✔ End of One Month
o the embryo’s heart is formed.
✔ End of Second Month
o the foetus develops limbs and digits (fingers/toes)
✔ End of Third month / 12 weeks (First Trimester)
o most of the major organ systems are formed
o the limbs and external genital organs are well developed.
✔ End of Fifth Month
o first movements of the foetus.
o appearance of hair on the head.
✔ End of Six Month / 24 weeks (Second Trimester)
o body is covered with fine hair
o eye-lids separate
o eyelashes are formed
✔ End of Nine Month / 36 weeks (Third Trimester)
o the foetus is fully developed and is ready for delivery.
➢ Parturition
✔ It refers to the process of child birth.
o A complex neuro endocrine event.
✔ Signal for parturition originates from the fully developed foetus and the placenta.
o It induces mild contraction of the uterine muscles.
o It is referred to as the foetal ejection reflex.
✔ The foetal ejection reflex induced the release of the pituitary hormone- Oxytocin.
✔ Oxytocin acts on the uterine muscle and induces stronger uterine contraction.
o It further stimulates the secretion of more oxytocin.
✔ The stimulatory reflex between the uterine contraction and oxytocin secretion continues.
✔ This results in stronger and stronger contractions.
✔ This leads to expulsion of the baby out of the uterus through the birth canal.
o The placenta is also expelled out of the uterus.
➢ Lactation
✔ It refers to the process of secretion of milk by the mammary glands.
✔ The mammary glands of the female undergo differentiation during pregnancy and start producing milk towards the end of pregnancy.
✔ The milk produced during the initial few days of lactation is called colostrum.
o It contains various antibodies (IgA) absolutely essential to develop resistance.
✔ Breast-feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby.
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