Human Reproduction

• Human beings are viviparous. The reproduction always involves sexual method.

• Sexual reproduction: It is the reproduction takes place by formation and fusion of gametes.

• The gametes are develops in primary sex organ testes and ovaries.

THE MALE REPRODUCTIVE SYSTEM.

• The Male reproductive system includes

• A pair of testes.• Accessory ducts.• Accessory glands.• External genitalia

• Testes:• Pair of testis are present in scrotal sac outside the

abdominal cavity . Before birth testes descend to the sac called scrotum.

• The scrotum provides low temperature about 2 to 3 0C required for spermatogenesis.

• If testes donot descend, it leads to sterility. Because normal sperm production is inhibited by internal body temperature.

• The failure of testes to descend down into scortal sac is called cryptorchidism.

• Each testis has about 250 compartments called testicular lobules.. Each lobule contains coiled seminiferous tubules.

• The inner wall of seminiferous tubules lined by male germ cells and Sertoli cells.

• Male germ cell undergoes meiosis and produce sperm.

• Sertoli cells provide nutrition to the developing sperm.

• In between the seminiferous tubule interstitial cell or Leydig cell are present.

• Leydig cells produce male hormones called androgen (testosterone).

• Accessory ducts:• Accessory ducts includes

rete testis, vasa efferentia, epididymis and vas deferens.

• Seminiferous tubules open into vasa efferentia through rete testis. The vasa efferentia leaves the testis and open into epididymis.

• In epididymis sperms stores and further maturation takes place.

• The epididymis leads to vas deferens. Vas deferens opens into the urethra as the ejaculatory duct.

• Urethra originates from the urinary bladder and extends through the penis to its external opening

• Accessory glands:• Accessory glands

Includes • Paired seminal

vesicle• A prostate gland• Paired

bulbourethral gland.

• These glands secretes the secretion called seminal plasma.

• It rich in fructose, calcium, and certain enzyme. Seminal plasma with sperm forms semen.

• After puberty millions of sperms matures every day. Each ejaculation contains 300 million sperms.

• External genitalia:• Penis is the external genitalia.• It is made of special tissue that helps in erection

of the penis to facilitate insemination.

Spermatogenesis:• The process of formation of haploid male

gamete sperm in seminiferous tubules of testis is called spermatogenesis.

• The inner wall of the seminiferous tubule contains two types of cells as germ cells (spermatogonial cells) and sertoli cells.

• germl cells divides and develops into sperms. The sertoli cell nourishes the developing sperms.

• The spermatogenesis takes place in two stages as spermatidogenesis and spermiogenesis

• Spermatidogenesis: It is the process of formation of spermatids. It involves 3 sub stages

• Multiplication phase: The spermatogonial cells undergoes repeated mitotic division and forms large number of diploid spermatogonial cells.

• Growth phase: The spermatogonial cells grow in size by increasing cytoplasm and gets ready for maturation. Now the spermatogonial cells are called primary spermatocytes

• Maturation phase: The diploid primary spermatocyte undergoes first meiosis resulting in the formation of two haploid cells called secondary spermatocyte. This later undergoes second meiotic division to produce four haploid spermatids.

• Spermiogenesis: It is The process of formation of inactive non-motile spermatid into active motile spermatozoa .

• The spermatid undergoes following structural changes. 1. The small vesicles of Golgi complex fuse to form a large cup

like acrosome anterior to the nucleus.2. The two centrioles of spermatid moves towards the nucleus

and arrange beneath the nucleus as a proximal and distal centriole.

3. The distal centriole elongates to form a tail.4. The mitochondria forms a large mass at neck region.5. The nucleus becomes elongated and forms a spherical shape.

Structure of human sperm:• Sperm is a male haploid gamete.

It measures about 60 μ in length. It contains three regions as head, middle piece and tail.

• Head: The head of the sperm is arrow shaped contains a large haploid nucleus.

• anteriorly nucleus is covered by a cap like structure called acrosome. It is formed by Golgi complex. It contains the lytic enzymes to dissolve the egg membrane during fertilization

• Neck: Below the head a small neck is present. It contains a proximal and distal centriole.

• Middle piece: The distal centriole gives rice to axial filament and becomes basal bodies.

• The axial filament is surrounded spirally by mitochondria and forms middle piece. The mitochondria provides energy for motility of sperm.

• Tail: The tail is divided into principal piece and end piece.

• The principal piece has axial filament surrounded by plasma membrane.

• The end piece lacks the protoplasmic sheath.

• The tail is used for swimming movement in the liquid media.

• Hormonal control of spermatogenesis:

• This process is initiated at puberty due to secretion of gonadotrophin releasing hormone (GnRH)

• GnRH secreted form hypothalamus stimulates anterior pituitary to secrete two gonadotrophin.

• Luteinizing hormone (LH) and Follicle stimulating Hormone (FSH)

• LH acts on Leydig cells (Interstitial calls) to stimulates synthesis of androgens.

• Androgen stimulates spermatogenesis.

• FSH acts on Sertoli cells and stimulates spermatogenesis.

THE FEMALE REPRODUCTIVE SYSTEM

• The female reproduction system is located in the pelvic region.

• It includes: 1. A pair of ovaries2. A pair of oviduct.3. Uterus4. Cervix5. Vagina6. External genitalia.

Female gonads: Ovaries.• Ovaries are the primary female sex organs

that produce the female gamete (ovum). It also produces several female steroid hormones.

• The ovaries located in the lower abdomen.• Each ovary is about 2-4 cm in length. These

are Connected to the pelvic wall and uterus by ligaments.

• Each ovary is covered by thin epithelium. With in this covering small sac like structures called ovarian follicles.

• The ovarian stroma or folicle has two zones• A peripheral cortex.• An inner medulla.

• Oviduct :• Each fallopian tube is about 10-12

cm long and extends from the of each ovary to the uterus.

• Close to the ovary the oviduct has a funnel shaped structure called infundibulum.

• The infundibulum leads to a wider part of the oviduct called ampulla.

• The edges of the infundibulum possess finger-like projections called fimbriae, which helps in collection of the ovum after ovulation.

• The last part of the oviduct is called isthmus which joined to uterus.

• Uterus:• It is a hallow pear shaped muscular

organ. Single uterus is present in lower abdomen region is also called womb.

• Inside the uterus fertilized ovum grows and develops in to embryo.

• The wall of the uterus has three layers of tissues

• Perimetrium: external thin membranous.

• Myometrium: middle thick layer of smooth muscles

• Endometrium: inner glandular layer.• Endometrium undergoes cyclical

changes during menstrual cycle.

• Myometrium exhibits strong contraction during delivery of the baby

• The uterus opens into vagina through a narrow cervix.• The lumen of cervix is called cervical canal.• Cervical canal along with vagina form the birth canal..

• External genitalia:• It includes following structure: • Mons Pubis: cushion of fatty tissue covered by skin.• Labia majora: fleshy folds of tissue that surrounds the

vaginal opening.• Labia minora: are paired folds of tissue under the labia

majora.

• Hymen: the opening of vagina is covered partially by a membrane called hymen.

• Clitoris: It is a tiny finger-like structure lies at the upper junction of two labia minora above the urethral opening.

Mammary glands:• The mammals has

mammary gland that secretes milk to feed young ones. Human beings are mammals. The pair of mammary glands in females are active.

• Each mammary gland consists of glandular tissue and fat.

• Glandular tissue of each breast divided into 15-20 mammary lobes.

• Mammary lobes contain cluster of cells called alveoli. The cells of alveoli secrete milk, stored in the lumen of alveoli.

• The alveoli open into mammary tubules.

• The tubules of each lobe join to form a mammary duct. Several mammary ducts join to form a wider mammary ampulla.

• Mammary ampulla connected to lactiferous duct that opens at nipple. Through this milk is sucked out by baby.

Section of ovary.• The ovary contains

number of ovarian follicle with immature oocytes.

• After puberty primary follicles get surrounded by more layers of granulosa cells and a new theca to form secondary follicles.

• The secondary follicle transformed into tertiary follicle, characterized by a fluid filled cavity called antrum.

• As one of the oocyte matures the ovarian follicle develops into graafine follicle.

• The wall of the graafine follicle is made up of outer fibrous theca externa and inner vascular theca interna. Inner to the theca interna 10-15 layers of follicle cells forms the membrana granulosa.

• The graafine follicle encloses the cavity called antrum. The matured haploid ovum is present inside the graafine follicle.

• The plasma membrane of the ovum is externally covered by a thick and transparent primary membrane called zona pellucid.

• On the outer side of zona pellucid, the ovum is covered by a layer of follicle cells forming corona radiata.

• Corona radiata attaches to any one side of the membrana granulose.

• The C-shaped antrum is filled by fluid secreted by follicle cells. It is rich with F.S.H, L.H and estrogen.

• During ovulation graafine follicle releases the ovum and changes into corpus luteum. It secrets progesterone hormone to maintain the pregnancy.

• If the ovum is unfertilized corpus luteum generates into a mass of fibrous tissue called corpus albicans

Oogenisis.• The process of formation of

haploid female gamete ovum in the follicles of ovary is called oogenesis.

• Oogenesis starts during embryonic stage.

• Germinal epithelium of ovary divided mitotically to produce millions of gamete mother cell or oogonia.

• No oogonia formed or added after birth.

• Oogonia enters into meiosis-I. It proceeds Prophase-I , get suspended and forms primary Oocytes.

• during puberty, the primary oocyte restarts its first meiotic division.

• Oogenesis takes place by three stages as follows.

1. Multiplication phase: The ovary is lined by germinal epithelium. These cells undergo mitotic cell division to form large number of diploid oogonia and follicle cells.

2. Growth phase: One of the diploid oogonia undergoes growth increasing in cytoplasm and accumulation of yolk. This enlarged oogonia is called primary oocyte.

3. Maturation phase: A fully-grown primary oocyte undergoes I meiotic division results in the formation of two unequaled sized haploid cells.

• The large secondary oocyte and a small sterile polocyte (polar body). The secondary oocyte undergoes II meiotic division to form a large ootid and a small sterile 2ed polar body.

• The 1st polar body also undergoes equal division to produce two cells.

• Thus during oogenesis four cells are produced. Among them one is functional ootid and three are non-functional polar bodies. The ootid with very little change becomes an ovum.

Menstrual cycle:• Reproductive cycle of female primates is called menstrual

cycle. • The menstrual cycle begins when a female reaches the age

of puberty. The first menstruation begins at puberty is called Menarche.

• During the menstrual cycle the uterus endometrium prepares itself for implantation of a fertilized egg. If fertilization does not occur the uterus lining is shed from the body. This is known as menstruation .

• Menstrual cycle repeated at an average interval of 28 days.• One ovum is released in the middle usually 14th day of each

menstrual cycle.

Menstrual cycle has following phases:The cycle can be divided into four phases1. Menstrual phase

(bleeding period).2. follicular (before the

egg is released).3. ovulatory (egg is

released)4. luteal (after release of

the egg).

• Menstrual phase (bleeding period).

• It is the 1st phase of menstrual cycle lasts for 3-5 days.

• Breakdown of endometrial lining and blood vessel occurs. It leads to bleeding comes out through vagina.

• It occurs only when ovum released and fertilization does not occurs.

• Lack of menstruation is the indication of pregnancy.

Follicular phase: • Menstrual phase

followed by follicular phase.

• During this phase the pituitary gland increases the production of follicle-stimulating hormone (FSH).

• This hormone stimulates the growth of primary follicle to becomes Graafian follicle.

• The levels of FSH hormone decreases and the graafian follicles begin to secrete oestrogen. Level of estrogen increases.

• This helps regeneration and proliferation of uterine endometrium.

• It lasts for 5-13 days.

• Ovulatory Phase• Usually this phase occurs

at 14th day.• This phase begins with the

luteinizing hormone surge (LH surge). The level of FSH increases to a lesser extent.

• LH stimulates enzymes in the graafin follicle to follicle rupture and release of egg (ovulation).

• The egg travels into the fallopian tube, ready for fertilisation. The egg can survive for 12 to 24 hours after ovulation.

• The ovulatory phase usually lasts 16 to 32 hours and ends when the egg is released.

• Luteal phase: • This phase begins after

ovulation.• Ruptured Graafian follicle

transformed into corpus luteum. It produces large amount of progesterone.

• LH and FSH levels fall back to low and steady levels.

• Progesterone maintains the uterine endometrium and prepares it for implantation.

• Thickness of uterine endometrium increase in many folds, due to proliferation.

• If fertilization occurs corpus luteum grows further and pregnancy continues. Menstrual cycle stops up.

• In the absence of fertilization corpus luteum degenerates into corpus albicans.

• Decrease in progesterone hormone leads to mensuration.

• Menstrual cycle stops around 50 years of age. The condition is called menopause.

FERTILIZATION.• During copulation (coitus or

sexual activity) semen is released by the penis into the vagina is called insemination.

• The motile sperm swim rapidly, pass through cervix, uterus and finally reach the junction of isthmus and ampulla (ammpullary-isthmic junction).

• The ovum released from the ovary also transported to ampullary isthmic junction. The fertilization takes place in that place.

• Fertilization only takes place if both sperm and ovum reach ampullary – isthmic junction simultaneously.

• The process of fusion of a sperm and ovum is called fertilization.

• Acrosome of sperm secretes lytic enzymes helps in penetration into the ovum.

• Once a sperm comes contact with the zona pellucida of ovum, it induces the changes in the membrane that blocks the entry of other sperms.

• Only one sperm fertilize with one ovum..

• Haploid nucleus of sperm fused with the haploid nucleus of ovum to form a diploid zygote

Sex determination:

Sex determination:• Sex of a baby is determined during fertilization and

in the zygote.• Sex is determined by the sex-chromosomes present

in zygote..• Human female contain XX chromosomes and male

contain XY chromosomes.• All the female gametes produced has 22 autosome

and only ‘X’ chromosome. Hence are homogametic.• Sperms produced by male, 50% has 22 autosome

with ‘X’ and 50 % has 22 autosome with ‘Y’ chromosome. Hence heterogametic.

• The fusion of androsperm (22+Y) with ovum results in male baby.

• The fusion of gynosperm (22+X) with ovum results in female baby.

• Zygote with XX chromosomes develop into female and with XY chromosome develops into male.

• Early embryonic development.• The development of zygote in to full embryo is

called early embryonic development.• It occurs by cleavage, blastulation, gastrulation and

organogenesis.• Cleavage:• Repeated mitotic division of the zygote without

growth resulting a multicellular ball is called cleavage.

• Cleavage starts soon after fertilization. The cells formed by cleavage are called blastomere. It results in formation of ball of cells called murula.

• The morula continues to divide and transformed into blastocyst (blastula).

• The blastomeres in blastocyst arranged into two layers. An outer layer called trophoblast and an inner cells called inner cell mass.

• Trophoblast cells attaches to the endometrium. It helps in implantation and development of placenta.

• Inner cell mass gets differentiated into the embryo.

• The complete attachment Blastocyst to the uterine endometrium is called implantation.

• Implantation requires 3 to 5days. It completes in 9 to 10th day after fertilization.

Pregnancy :• After implantation trophoblast

develops finger like projections called chorionic villi.

• It surrounded by uterine tissue and maternal blood.

• The placenta is a connecting vascularised organ develops between embryo and mothe uterus.

• The chorionic villi and maternal tissue together forms placenta.

• Function of placenta:• The embryo connected to the placenta by umbilical

cord.• It facilitate transport of oxygen and nutrient from

mother to embryo.• Removes CO2 and waste material from the embryo.• It is barrier for number of pathogens.• It acts as endocrine gland and produces several

hormones. Among them Imp are a. Human chorionic gonadotrophins (hCG)b. Human placental lactogen (hPL)c. Estrogen.d. Progesterone.

• Human chorionic gonadotrophins (hCG): Along with progesterone, HCG is also important to maintain pregnancy.

• The urine test is done to identify the presence of HCG. in urine confirms the pregnancy.

• Embryonic development:• The inner cell mass of blastula are called stem cells.

They had the potency to produce all types of cell, tissues and organs by differentiation.

• After implantation the stem cells of blastocyst differentiated into an outer layer ectoderm, inner layer endoderm and middle mesoderm.

• Organogenesis:• Formation of different organs in the embryo is called

organogenesis.• After one month of pregnancy heart is formed in the

embryo.• By the end of 2nd month the foetus develops limbs

and digits.

• By the end of 12 weeks (first trimester) most of organ system is formed (limbs and external genitalia are well developed).

• In the 5th month first movement of foetus and appearance of hairs observed.

• By the end of 24th week (6th month or 2nd trimesters) the body is covered with fine hairs, eye-lids separate, and eyelashes are formed.

• By the end of 9 months the foetus is fully developed and is ready for delivery.

• PARTURATION :• The period of pregnancy is called gestation period. It

is 9 months in human.• The delivery of foetus is called parturition. It occurs

by the contraction of uterine Myometrium.• The signal of parturition is originated from the fully

developed foetus and the placenta. It induces mild contraction of uterus called fetal ejection reflex.

• Fetal ejection reflex triggers the release of Oxytocin from pituitary.

• Oxytocin induces stronger contraction of uterine myometrium.

• After delivery the placenta is also expelled out of the uterus.

• Lactation:• Process of milk production in mammary gland is

called lactation.• The mammary gland starts producing milk

towards the end of the pregnancy.• Milk produced during initial days of lactation is

called colostrum.It contains several antibodies which provide immunity to the new born baby.

• The milk production is controlled by Lacto trophic or prolactin hormone secreted by pituitary.