HUMAN REPRODUCTION

1. Human reproduces ➤SEXUALLY & VIVIPAROUS

2. Puberty is the time in life when a boy or girl becomes sexually mature. It is a process that usually happens between ages 10 and 14 for girls and ages 12 and 16 for boys. It causes physical changes, and affects boys and girls differently.

3. The REPRODUCTIVE EVENTS in human are :

o Gametogenesis : production of sperm and ovum.

o Insemination : It is transfer of sperm into female genital tract

o Fertilization: Fusion of male and female gamete.

o Implantation : Attachment of Blastocyst into uterine wall.

o Gestation : Embryonic development.

o Parturition : Delivery of baby.

4. THE MALE REPRODUCTIVE SYSTEM :

o It is located in pelvis region.

o It includes a pair of testes, accessory ducts, glands and external genitelia.

 5. TESTES :

o A pair of testes are located outside the abdominal cavity in a pouch called SCROTUM.

o The scrotum helps in maintaining the low temperature of the testes

2–2.5o C lower than the normal internal body temperature necessary for spermatogenesis

o In adults, each testis is oval in shape,

length of about 4 to 5 cm and

a width of about 2 to 3 cm.

o Each testis has about 250 compartments

called TESTICULAR LOBULES

o Each lobule contains one to three highly coiled seminiferous tubules in which sperms are produced.

o Each seminiferous tubule is lined on its inside by two types of cells

●Male germ cells (spermatogonia)

●Sertoli cells

o The male germ cells undergo meiotic divisions finally leading to sperm formation

o Sertoli cells provide nutrition to the germ cells.

o INTERSTITIAL SPACE is theSpace outside the seminiferous tubules

It has blood vessels and interstitial cells (Leydig cells).

Leydig cells secrete testicular hormone called androgen.

o Immunocompetent cells keeps the testes environment sterile.

6. THE MALE SEX ACCESSORY DUCTS :

o Rete testis, vasa efferentia, epididymis and vas deferens are accessory ducts.

o These duct store & transport sperms from testis to the outside through urethra.

7. The seminiferous tubules of testis open into vasa efferentia through rete testis.

8. The vasa efferentia leave the testis and open into epididymis present at the posterior side of testis.

9. Epididymis is highly coiled structure which open into vas deferens .

10. Vas deference goes up to abdomen and a duct from seminal vesicle joins  it then it joins  the urethra. 

11. Seminal vesicle contributes in seminal fluid.

12. Urethra arises from urinary bladder & run inside penis and its opening towards outside is called urethral meatus.

13. THE PENIS

●The penis is male external genitalia

●Made up of special tissues (Carpora cavernosa & Carpora spongiosum) that help in erection of penis to facilitate insemination .

GLANS PENIS  Anterior enlarged part of penis which is covered by fold of skin called FORE SKIN (Prepuce)

14. THE MALE ACCESSORY GLANDS

●a pair of seminal vesicle.

●One prostate gland

●a pair of cowper’s gland (bulbourethral gland )

●All above gland contribute in seminal plasma/semen /seminal fluid.

15. SPERMATOGENESIS :

The Production of sperm from spermatogonia (male germ cells )

Spermatogonia present inside the wall of seminiferous tubules divide mitotically and increase in number

Primary spermatocyte (2n = 46)  Some of the Spermatogonia which periodically undergo meiosis.

After meiosis I ,primary spermatocyte divide and form two haploid secondary spermatocytes.

The secondary spermatocytes (n=23) undergo meiosis II and produce four equal haploid spermatids.

16. SPERMIOGENESIS

The process which transform the spermatid into sperm.

These sperms ‘s heads become embedded in Sertoli cells.

        Secretion from Sertoli cells under the influence of FSH (follicle stimulating hormone ) help in this transformation.

17. SPERMIATION

o The process which release the sperms from seminiferous tubules.

18. STRUCTURE OF A SPERM

o A sperm is consist of head, neck, middle piece and tail.

o The whole sperm is surrounded by plasma membrane.

o Sperm head contain elongated nucleus which is covered by a cap like structure called ACROSOME.

o ACROSOME has enzymes which help the entry of sperm into ovum through zona pellusida & plasma membrane of ovum during fertilization.

o MIDDLE PIECE posses many mitochondria which generate energy for movement of sperm tail.

19. The human male ejaculate 200 million to 300 million sperms during a coitus ; for effective fertility out of which at least 60% Sperms must have normal shape and size and At least 40% of them have vigorous motility.

20. Secretion of epididymis, vas deferens, seminal vesicle & prostrate is required for maturation and motility of sperms.

21. Function of all these ducts and glands are maintained by androgen hormone which is secreted by Leydig cells

22. Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing hormone (GnRH). (hypothalamic hormone)

●The increased levels of GnRH then acts at the anterior pituitary gland and stimulates secretion of two gonadotropins – luteinising hormone (LH) and follicle stimulating hormone (FSH).

●LH acts at the Leydig cells and stimulates synthesis and secretion of androgens.

●Androgens, in turn, stimulate the process of spermatogenesis.

●FSH acts on the Sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis.

23. THE FEMALE REPRODUCTIVE SYSTEM :

o It consists of a –

●A pair of ovary.

●An Uterus (womb)

●Cervix.

●Vagina.

●The external genitalia.

●A pair of mammary gland.

24. OVARY

●They produce female gametes called ova.

●They are located at one on each side of the lower abdomen.

●Length : 2 – 4 cm.

●Ligament connect the ovaries to pelvic wall & uterus.

●Thin epithelium cover the ovarian stroma

●Stroma is divided into peripheral cortex and inner medulla.

●Ovaries produce several steroid hormones (ovarian hormones )

25. THE FEMALE ACCESSORY DUCTS :

Oviduct, uterus, vagina constitute the accessory duct.

26. OVIDUCT

It is also called fallopian tube.

oviduct is 10-12 cm long tube which has three part :

Funnel shape Infundibulum towards ovary side.

• It has minute finger like projections called FIMBRIAE on the edge to collect the ovum from ovary.

    AMPULLA is wider part between infundibulum and isthmus.

• Fertilization takes place here.

o Isthmus is narrow part ,which joins the oviduct to uterus

 27. UTERUS

o A single uterus is present between two oviduct .

o Ligament attaches uterus to pelvic wall.

o uterus open into vagina through cervical canal of cervix.

o Vagina and cervix make the birth canal.

o Uterus wall has three layer:

PERIMETRIUM : external thin layer.

MYOMETRIUM : middle thick layer of smooth muscle

• Exhibits strong contraction during child birth.

ENDOMETRIUM :It is inner glandular layer

• It lines the uterine cavity and goes cyclical changes during menstrual cycle

28. THE EXTERNAL GENITALIA IN FEMALE

o MONS PUBIS : It is cushion of thick fatty tissue covered with skin & pubic hairs.

o THE LABIA MAJOR : It is fleshy fold of tissue which surrounds the vaginal opening.

o THE LABIA MINORA : It is paired folds of tissue present under Labia majora.

o HYMEN : It is a membrane which partially cover the opening of vagina.

●It can be torn during first coitus/sudden fall /insertion of tampoon /active sports.

o THE CLITORIS : It is a tiny finger like structure present at the joint of two Labia minora.

29. MAMMARY GLAND (Breasts)

o A pair of functional mammary gland

o Characteristic of all female mammals.

o Consists of glandular tissue and variable amount of fat.

 o 15 to 20 mammary lobes are present in glandular tissue of each breast.

o Each lobes has cluster of cells called alveoli which secretes milk and store it in alveoli cavity .

o Alveoli open into tubule & tubules of each mammary lobe join to form mammary duct then this duct join to form wider ampulla & this ampulla is connected to lactiferous duct through which milk is sucked out.

30. MENSTRUATION CYCLE:

o It is reproductive cycle of female primates

e.g. monkey,apes and human beings

o It is repeated at an average of 28 to 29 days.

o The cycle of events from one menstruation till the next one is called menstruation cycle. 

o This cycle has

●MENSTRUAL PHASE :

●FOLLICULAR  PHASE.

●OVULATORY PHASE.

●LUTEAL PHASE.

31. Menstrual cycle starts with menstrual phase

 32. OOGENESIS :

o The process of formation of female gamete is called oogenesis.

o It is started during embryonic development.

o During this stage millions of oogonia (gamete mother cell is formed in foetus ovary.(multiplication phase ).

o Total number of oogonia is decided in a female during her embryonic development.

33. PRIMARY OOCYTES :

o Oogonial cells start cell division and enter in prophase of meiosis I and arrested in this stage is called PRIMARY OOCYTES.

o Primary oocyte are arrested in this stage till puberty.

o When female reaches at puberty, the following changes start in primary oocyte. which we will study under FOLLICULAR PHASE OF MENSTRUAL CYCLE.

34. FOLLICULAR PHASE:

o It is the development of primary follicle to mature Graafian follicle in the ovary. 

o PRIMARY FOLLICLE

●It is primary oocyte which is surrounded by a granulosa cells.

●A large number of primary follicles are degenerated during the phase from birth to puberty

●Only 60,000 to 80,000 primary follicle are present at time of puberty in female. (In each ovary)

o SECONDARY FOLLICLES :

●When primary follicle get surrounded by one more layer of granulosa cells and a new theca.

o TERTIARY FOLLICLE :

●A fluid filled cavity called antrum is develop in secondary follicle and theca is organised into outer externa and internal theca interna then it is called tertiary follicle.

●In this stage primary oocyte present inside the tertiary follicle completed the MEIOSIS I which is a unequal division resulted into one large haploid secondary oocyte and a small polar body.

o GRAAFIAN FOLLICLE :

  ● Tertiary follicle then changes into Graafian follicle (mature follicle).

●The secondary oocyte form a new membrane called ZONA PELLUCIDA.

o The transformation of Primary follicle to graafian follicle is termed as FOLLICULAR PHASE OF MENSTRUAL CYCLE.

35. The development of follicles and regeneration of endometrium take place together under the stimulation of LH and FSH

o The level of LH and FSH (gonadotropins) increases gradually during follicular phase (just after menses or menstrual phase of menstruation cycle).

o These gonadotropin also induce the growing follicles to secrete Oestrogen hormone. 

o Both LH and FSH attain a peak level in the middle of cycle (about 14th day).

o LH SURGE-

●Responsible for ovulation i.e. rupture of Graafian follicle and release of ovum or secondary oocyte.

●Only one ovum is released in an ovulation.

36. Secondary oocyte is a haploid cell , It is formed after meiosis I.

●Meiosis II will take place when sperm enter in secondary oocyte

37. OVULATORY PHASE :

o It is release of ovum from Graafian oocyte

o Ovum released inside the ampulla of oviduct.

o The ovulation (ovulatory phase) is followed by the luteal phase

38. LUTEAL PHASE

o After ovulation remaining parts of the Graafian follicle transform as the corpus luteum

o The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium.

o Such an endometrium is necessary for implantation of the fertilised ovum and other events of pregnancy.

o During pregnancy all events of the menstrual cycle stop and there is no menstruation. 

o In the absence of fertilisation, the corpus luteum degenerates.

o This causes disintegration of the endometrium leading to menstruation, marking a new cycle.

39. MENARCHE It is the first menstruation which starts at puberty.

40. MENSTRUATION PHASE :

o Menstruation (menses) is menstrual flow which lasts for 3 to 5 days

o it occurs if there is no pregnancy.

o In the absence of fertilization, the corpus luteum degenerates which result into disintegration of endometrium.

o Menstrual flow has endometrium ( inner lining of uterus) and blood vessels (liquid) which comes out from vagina.

41. MENOPAUSE is the ceasing of menstrual /reproductive cycle .

o It is ceases around the age of 50 years in female whereas in male spermatogenesis is continue till whole life.

42. Cyclic menstruation is indicator of normal reproductive phase which extends from MENARCH to MENOPAUSE.

43. FERTILIZATION AND IMPLANTATION:

o During coitus (copulation) semen is released by penis into vagina

o Motile sperm swims and reaches to ampulla region of oviduct via cervix and uterus. 

o Fertilization takes place at ampulla of oviduct if sperm and ovum reaches simultaneously in this region.

44. During fertilization, sperm comes in contact with zona pellucida layer of ovum & induces some change in this membrane so this membrane allow the entry of sperm.

45. The secretion of acrosome of sperm helps in entry of sperm in ovum cytoplasm through zona pellucida and plasma membrane of ovum.

46. Entry of sperm also induce completion of MEOSIS II in secondary oocyte which result into formation of ootid (ovum) and second polar body.

47. The haploid sperm is fused with haploid ovum and form diploid zygote (2n=46)

48. CLEAVAGE

o It is mitotic division in zygote and it starts when zygote reaches in isthmus of oviduct during its movement towards uterus.

o Blastomeres are daughter cells of zygote; result of cleavage

49. MORULA

o 8 to 16 blastomeres stage of embryo .

o Morula continues to divide and changed into blastocyst during embryo’s movement towards uterus.

50. BLASTOCYST

o The blastomeres in the blastocyst are arranged into two layers

 Outer trophoblast layer which get attach to endometrium.

 the inner blastomere form INNER CELL MASS which get differentiated as EMBRYO.

51. After attachment in uterus ,uterine cells divide rapidly and cover the blastocyst completely. this is called IMPLANTATION.

52. Implantation leads to pregnancy.

53. PLACENTA

o Chorionic villi is finger like projection from outer trophoblast.

o Chorionic villi are surrounded by uterine tissue and maternal blood .

o Uterine tissue and chorionic villi interdigited and form PLACENTA

o Placenta is a functional unit between embryo and maternal body which supply oxygen ,nutrients to the embryo and also remove CO2 ,waste from embryo.

54. UMBLICAL CoRD connects the placenta to embryo.

55. Placenta is also an endocrine tissue which produce

o human chorionic gonadotropin (hCG),

o human placental lactogen (hPL),

o Oestrogen and progesteron etc.

56. During pregnancy ,ovary also secrete RELAXIN harmone.

57. Relaxin, hCG, hPL are secreted by during pregnancy.

58. Several other hormones level like oestrogen ,progestogen, cortisol, prolactin thyroxin in body are increased many fold to support the foetal growth, and pregnancy.

59. Germinal Layers / Embryonic Layers :

o Initially there are two layer differentiated from embryo (inner cell mass) outer ECTODERM and inner ENDODERM.

o MESODERM appear between ectoderm and endoderm.

o These three layers give rise to all tissue and organ system in body.

60. STEM CELLS are cell from inner cell mass which has capability to give rise to all tissue and organs.

61. GESTATION PERIOD is average pregnancy period (about 9 months).

62. Heart is developed in one month old embryo.

63. Limbs and digits are developed in foetus by the end of second month of pregnancy.

64. After first trimester ,most of the organ system is developed.

65. Limbs and external genital opening are well develop in 3 month old foetus.

66. Movement of foetus and hair on head can be seen in fifth month.

67. At the end of second trimester (24 weeks) body hairs, eye lid separation, eyelashes are clearly visible.

68. PARTURITION is delivery of the baby is called parturition.

o It is a complex neuroendocrine mechanism.

69. FOETAL EJECTION REFLEX :

o It is mild uterine contraction induced by placenta when fully developed foetus send signal for parturition.

o First signal of parturition is send by foetus itself.

70. OXYTOCIN :

o Foetal ejection reflex trigger the secretion of oxytocin from pituitary gland

o Oxytocin work on uterine muscle (myometrium) and induce more strong contractions

o Finally result into expulsion of the baby through the birth canal i.e. cervix and vagina.

71. After parturition, placenta is also expelled out.

72. LACTATION:

o Towards the end of pregnancy mammary glands start producing milk to feed the new-born. 

73. COLOSTRUM:

o the milk produced during the few initial days contains several antibodies which provide resistance to new born baby.

o Breast feed is must for healthy growth of baby.

Disorders of female reproductive system

• Sterility  :  Inability  of  the  female  to  conceive,  due  to  inadequacy  in structure or function of the genital organs.

• Menstrual irregularity

Amenorrhoea  :  Absence  of  menstruation.

Hypermenorrhoea  :  Excessive  or  prolonged  bleeding  of  uterus.

Dysmenorrhoea  :  Painful  menstruation.

Pregnancy test :

During  pregnancy,  hCG  may  be  detected  in  the  urine,  and  this  forms  the basis  of  pregnancy  test.

Types  of eggs

(1) On the basis of amount and distribution of yolk

(i) Alecithal or Microlecithal or Oligolecithal or Meolecithal and Isolecithal or Homolecithal : The amount of yolk is very small in these types of eggs. (Oligolecithal or Microlecithal or Alecithal) and yolk is evenly distributed in these eggs (Isolecithal or Homolecithal). Examples – Egg of Amphioxus,

Eutheria (Human egg), Metatheria and Sea-urchin.

(ii) Mesolecithal or Telolecithal eggs : In this type of egg the amount of yolk is moderate and yolk is concentrated in the basal part of egg (telolecithal egg). Examples – Egg of Amphibia, Petromyzon and Lung fishes.

(iii) Polylecithal or Macrolecithal or Megalecithal eggs : Eggs are with large amount of yolk e.g., eggs of shark, bony fish, Reptiles, birds, prototherian, concentrated mainly in vegetal pole.

In discoidal or highly telolecithal eggs, the yolk is enormous in amount and cytoplasm is confined to a disc like area on yolk. This disc of cytoplasm is called germinal disc. Example – Eggs of reptiles, birds, protherian mammals. 

(iv) Centrolecithal : Yolk concentrate in centre e.g., Insects egg.

• Smallest eggs are of 50 in the polychaeta and the largest eggs are of an ostrich.

(2) On the basis of fate

(i) Determinate / Mosaic eggs : Every part of fertilize egg has a definite fate, so that fate of every blastomere is determined from the beginning. It is found in invertebrates except echinoderms.

(ii) Indeterminate / Regulative eggs : The fate of different parts of egg or its blastomeres is not predetermined. Example – Echinoderms, Vertebrates.

(3) On the basis of shell

(i) Cleidoic eggs :

Eggs surrounded by a hard shell are known as cleidoic eggs. These eggs are found in those animals which have a terrestrial mode of life of which lay eggs on land. These eggs have more amount of yolk. These are adaptations to terrestrial mode of life. Shell prevents the egg from dessication. e.g., – Eggs of “Reptiles”. “Birds”. “Insects” and “Prototherians”. 

(ii) Non – Cleidoic eggs :

Eggs which are not surrounded by a hard shell are called Non-cleidoic eggs.

These eggs are found in alloviperous animals which lay eggs in water and all viviperous animals. e.g., – All viviperous animals (Mammals) and all oviperous animals which lay eggs in water (Amphibians).

CLEAVAGE

The term cleavage refers to a series of rapid mitotic division of the zygote following fertilization.

The cleavage follows fertilization and ends with the formation of a characteristic development stage called blastula. The cleavage is initiated by the appearance of a constriction or groove called cleavage furrow.

The cleavage furrows may divided the egg from different angles or plane

Bilateral cleavage seen in mammals.

In this pattern of cleavage, the blastomeres are so arranged that the right and left sides becomes distinct. In this case, two of the first four blastomeres may be larger than the other two, thus establishing a plane of bilateral symmetry in the developing embryo.

CLEAVAGE IN HUMAN ZYGOTE

1. Cleavage in the human zygote occurs during its passage through the fallopian tube to the uterus as in other mammals.

2. It is holoblastic.

3. The first cleavage takes place about 30 hours after fertilization.

4. It is meridional, coinciding with the animal-vegetal pole axis.

5. It produces two blastomeres, one slightly larger than the other.

6. The two blastomeres remain adhered to each other.

7. The second cleavage occurs within 60 hours after fertilization.

8. Third cleavage takes place about 72 hours after fertilization.

9. FORMATION OF MORULA :

o After 4th cleavage solid ball consist of 16 to 32 cells are formed which looks as a little mulberry called morula.

o Due to holoblastic and unequal cleavage, two types of blastomere are formed.

o There is an outer layer of smaller (micromere) transparent cells around on inner mass of larger cells (macromere).

o The morula reaches the uterus about 4 to 6 days after fertilization.

o It is still surrounded by the zona pellucida, that prevents its sticking to the uterine wall.

10. FORMATION OF BLASTULA (BLASTOCYST) :

The outer layer of cell becomes that and form trophoblast or trophoectoderm which draws the nutritive material secreted by the uterine endometrial glands.

The fluids absorbed by the trophoblast collects in a new central cavity called blastocoel.

As the amount of nutritive fluid increases in blastocoel, morula enlarges and takes the form of a cyst and is now called blastocyst or blastodermic vesicle.

The cells of trophoblast do not participate in the formation of embryo proper.

Inner cell mass of macromeres forms a knob at one side of trophoblast and forms an embryonal knob and is primarily determined to form the body of developing embryo so is called precursor of the embryo.

IMPLANTATION

1. The process of attachment of the blastocyst on the endometrium of the uterus

2. Though the implantation may occur at any period between 6th and 10th day after the fertilization but generally it occurs on seventh day after fertilization.

GASTRULATION

1. Gastrulation is a dynamic process involving critical changes in the embryo

o differentiation of cells,

o establishment of the three primary germ layers

o transformation of the single walled blastula into a double walled gastrula.

EXTRA EMBRYONIC MEMBRANE

These membranes are formed outside the embryo from the trophoblast only in amniotes and perform specific function

(1) Yolk sac :

It is formed below the embryo. It contains fluid, not yolk. The yolk sac is a vestigeal organ inherited from the oviparous reptilian ancestors. Yolk sac encloses by outer mesoderm and inner endodermal layer. In human beings, it is vestigial. In human embryo it act as the site of blood cell formation until about the 6th week, when the liver takes over this role.

(2) Amnion :

It is formed above the embryo.

It consist of outer mesoderm and inner ectoderm.

The amnion and the fluid filled amniotic cavity it encloses, enlarge and nearly surround the embryo.

Amniotic fluid secreted by both embryo and amnion.

(i) The amniotic fluid cushions the embryo.

(ii) It protects the embryo from jerk, injury and shocks.

(iii) It prevents desiccation of the embryo.

(3) Allantois :

It is a fold of splanchnopleur developed from the hind gut of the embryo. It consist of outer mesoderm and inner endoderm.

The cavity of the allantois serves as a urinary bladder.

It stores the protein breakdown product in the form of water-insoluble crystals of uric acid and inside the egg upto the time of hatching.

The vascular “chorioallantoic membrane” lies in a close proximity to the inner surface of the porous shell.

It acts as an extraembryonic lung by supplying the embryo with oxygen.

(4) Chorion :

It is outermost fold of somatopleur (outer ectoderm and somatic mesoderm) and surrounds the embryo.

In human beings, only chorion forms the placenta (chorionic placenta).

It protects the embryo and forms placenta for metabolic exchange between the foetus and the mother.

PLACENTA

Placenta is defined as a temporary intimate mechanical and physiological connection between foetal and maternal tissues for the nutrition, respiration and excretion of the foetus.

Human placenta consist of chorion only. Hence, it is called a chorionic placenta.

The placenta is fully formed by the end of the third month and it lasts throughout pregnancy. The placenta serves as the nutritive, respiratory and excretory organ of the foetus.

The maternal and foetal blood are not in direct contact in the placenta.

GESTATION PERIOD :

Gestation period is the duration between fertilization and parturition.

S.No.Animal           Days

1. Mouse (Minimum) 19-20

2. Rat 20-22

3. Rabbit 28-32

4. Cat 52-65

5. Dog 60-65

6. Pig 112-120

7. Goat 145-155

8. Man 270-290

9. Cow 275-290 (36 weeks)

10. Horse 330-345

11. Elephant (Maximum) 607-641

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