Msle and female physiology of reproduction

Reproduction physiology

1. Physiology of Reproduction Prof Dr Adeela Shahid MBBS, M.PhiL, PhD SMDC

2. OBJECTIVES: At the end of Lecture students should be able to: Explain physiological anatomy of Male reproductive system Discuss spermatogenesis Elaborate Spermiogenesis Explain functions of prostate, seminal vesicles Describe Capacitation of spermatozoa Explain Acrosome reaction

3. Reproduction Reproductive System Not needed for the survival of the individual Species survival Sexual reproduction Genes from two individual Combine at random Creates new combinations Increases chances of species survival

4. Male reproductive system

5. Male reproductive system Testis made up of seminiferous tubule Epididymis Vas deferens Which enlarges into the ampulla of the vas deferens & enters into Prostate gland Prostate gland Two seminal vesicles on either side of prostate Emptying into Prostatic end of Ampulla contents from ampulla, seminal vesicles & prostate pass into an ejaculatory duct. Which empties into the internal urethra

6. Cross Section of a Seminiferous Tubules

7. Stages in the Development of Sperm from Spermatogonia

8. Spermatogenesis During formation of the embryo Primordial germ cells migrate into the testes and become immature germ cells called spermatogonia Spermatogonia lie in two or three layers of the inner surfaces of the seminiferous tubules

9. Spermatogenesis Spermatogonia: undergo mitotic division which begins at puberty due to stimulation by anterior pituitary Gonadotropic hormones (FSH, LH) Produce two cells Becomes Primary spermatocytes by Mitosis

10. Stages in the development of sperm from spermatogonia

11. Spermatogonia:

12. Primary spermatocytes formed by Mitosis

13. Primary spermatocytes undergoes meiotic division : Form two secondary spermatocytes These too divide to form spermatids Spermatids are modified to become spermatozoa 46 chromosomes in spermatocytes are divided 23 chromosomes go to one spermatid and the other 23 to the second spermatid Spermatogenesis (cont……)

14. Primary spermatocytes undergoes meiotic division

15. Sexual Reproduction Each individual produces gametes Formed in gonads (Testes / Ovaries) by meiosis Male: testes produce Sperms Testosterone Female: ovaries produce Ova Estrogens, Progesterone Gametes (Sperm & Ova) unite in the process of fertilization Restores diploid number Forms zygote

16. Sexual Determination Each zygote inherits 23 chromosomes from mother 23 chromosomes from father 23 pairs of homologous chromosomes chromosomes  having the same genes at the same loci Kinds of chromosomes 1-22 pairs of chromosomes: autosomal 23 rd pair are sex chromosomes. Male: XY Female: XX Gender of zygote is determined by fertilizing sperm.

17. Sex Chromosomes In each spermatogonium, one pair of chromosomes carries the genetic information that determines the sex It is composed of one X chromosome called the female chromosome, and one Y chromosome called the male chromosome. During meiotic division Y chromosome goes to one spermatid that then becomes a male sperm X chromosome goes to another spermatid that becomes a female sperm. The sex of the eventual offspring is determined by which of these two types of sperm fertilizes the ovum

18. Formation of Testes First 40 days after conception the gonads of males and females are similar in appearance. During this time: Spermatogonia and oogonia migrate from yolk sac to developing embryonic gonads Gonads could become either testes or ovaries depending on the presence of. TDF (testis-determining factor): promotes the conversion of embryonic gonads to testes: Gene for TDF is located on short arm of Y, called SRY (sex determining region of Y chromosome)

19. Formation of Testes First 40 days after conception the gonads of males and females are similar in appearance. Gonads could become either testes or ovaries depending on the presence or absence of TDF (testis-determining factor): TDF promotes the conversion of embryonic gonads to testes Gene for TDF is located on short arm of Y, called SRY (sex determining region of Y chromosome)

20. Development of Accessory Sex Organs & Genitalia Presence or absence of testes determines the accessory sex organs and external genitalia. Female accessory organs derived from mullerian ducts (Paramesonephritic ) Fetal Sertoli cells secrete MIF (mullerian inhibition factor) MIF inhibits development of female accessory organs in male baby. Male accessory organs derived from wolffian ducts ( Mesonephric )

21. MIS continues to be secreted by the Sertoli cells, and it reaches mean values of 48 ng/mL in plasma in 1- to 2-year-old boys. Thereafter, it declines to low levels by the time of puberty and persists at low levels throughout life. Testosterone is secretion starts at 8 th week of IUL and peak levels are achieved at 12- 14 th week of IUL secreted for the 10 weeks after birth then the levels decline and increases after puberty in males

22. MIS and testosterone act unilaterally. MIS causes regression of the mullerian ducts by apoptosis on the side on which it is secreted Testosterone stimulates the development of the vas deferens and Epididymis from the wolffian ducts . The testosterone metabolite dihydrotestosterone (DHT) induces the formation of male external genitalia and male secondary sex characteristics

23. Testes Structures in the testes: Seminiferous tubules: 900 coiled seminiferous tubules are present in testes. more than one half meter long, in which the sperm are formed. Site where spermatogenesis occurs. Germinal cells : sperm Nongerminal cells : Sertoli cells (sustentacular cells) Contain receptors for FSH Leydig cells (interstitial cells): Contain receptors for LH Secrete Testosterone, androsterone & dehydroepianrdosterone when stimulated by LH

24. Formation & Structure of a Sperm When the spermatids are first formed, they are like epithelioid cells They differentiate and elongate into spermatozoa. Head and a tail is formed. The head is a condensed nucleus with a thin cytoplasmic and cell membrane layer around it On the anterior two thirds of the head is a thick cap called acrosome formed by the Golgi apparatus

25. Structure of sperm Acrosome contains Hyaluronidase It is an enzyme that depolymerizes the mucopolysaccharide hyaluronic acid, which is a component of the ground substance or tissue cement (digest proteoglycan filaments of tissues) Proteolytic enzymes (digest proteins) These enzymes allow the sperm to enter the ovum and fertilize it.

26. Flagellum Tail / flagellum has three major components: Central skeleton (axoneme) made up of 11 microtubules Thin cell membrane covering the axoneme Collection of mitochondria surrounding the axoneme in the proximal portion/body of the tail).

27. Cross Section of a Seminiferous Tubules

28. Sertoli Cells Form Blood-testes barrier : Prevents autoimmune destruction of sperm. Contain aromatase (CYP19) enzyme that converts testosterone to estrogen Sertoli cells secrete Inhibin , mullerian inhibiting substance (MIS) MIS causes regression of the mullerian ducts by apoptosis Inhibin inhibits FSH secretion Phagocytize residual bodies Secrete androgen-binding protein (ABP): Binds to testosterone and concentrates testosterone in the tubules.

29. Testes Leydig cells secrete testosterone Begins at 8 th week of IUL and peaks at 12-14 th week Testosterone masculinizes embryonic structures Testes descend into scrotum shortly before birth Temp in scrotum is about 3 0C below internal temp.

30. Formation of Ovaries Absence of Y chromosome and TDF (testis-determining factor) results in development of ovaries. Ovarian follicles do not appear until 3 nd trimester.

31. In both sexes gonads secrete other polypeptides, including inhibin B, a polypeptide that inhibits follicle stimulating hormone (FSH) secretion

32. Formation of Sperm /Spermiogenesis Maturation of spermatozoa. Cytoplasm is pinched off and ingested by the Sertoli cell cytoplasm.

33. Structure of spermatozoon

34. Hormonal Factors That Stimulate Spermatogenesis Testosterone Luteinizing hormone Follicle-stimulating hormone Estrogens Growth hormone

35. Testosterone Causes growth and division of the testicular germinal cells Luteinizing hormone stimulates the Leydig cells to secrete testosterone Follicle-stimulating hormone stimulates the Sertoli cells ,without this stimulation, the conversion of the spermatids to sperm will not occur

36. Estrogens FSH stimulate Sertoli cells which convert testosterone to estrogen, it is essential for Spermiogenesis Growth hormone controls background metabolic functions of the testes promotes early division of the Spermatogonia

37. Maturation of Sperm in the Epididymis Sperms are nonmotile in the seminiferous tubules and in the early portions of the Epididymis After 18 to 24 hours in the Epididymis they become motile There are several inhibitory proteins in the epididymal fluid which still prevent final motility

38. Storage of Sperm in the Testes 120 million sperm are formed by testes each day sperm are stored in the Epididymis small quantity is also stored in the vas deferens Sperms are kept in inactive state by multiple inhibitory substances in the secretions of the ducts

39. FUNCTION OF THE SEMINAL VESICLES Each seminal vesicle is a tortuous, loculated tube with a secretory epithelium Secretes a mucoid secretion Contains fructose, citric acid, prostaglandins, fibrinogen, and other nutrient substances Seminal vesicle empties its contents into the ejaculatory duct Prostaglandins help the fertilization in two ways: React with cervical mucus to make it more receptive for sperm movement Cause reverse peristaltic contractions in uterus & fallopian tubes to move the sperm toward the ovaries

40. FUNCTIONS OF THE PROSTATE GLAND Prostatic fluid is Alkaline in nature It contains calcium, citrate ion, phosphate ion, a clotting enzyme, and a profibrinolysin. Alkaline fluid is important for fertilization of the ovum Fluid of the vas deferens is acidic due to the presence of citric acid and metabolic end products of the sperm which inhibit sperm fertility Vaginal secretions are also acidic (with a pH of 3.5 to 4.0) Sperm do not become motile until the pH rises to about 6.0 to 6.5 Prostatic fluid helps neutralize the acidity and enhances the motility and fertility of the sperm

41. OBJECTIVES: At the end of Lecture students should be able to: Describe Capacitation of spermatozoa Explain Acrosome reaction Explain the development of testes Describe blood tests barrier Discuss male infertility Elaborate metabolism, secretion, mechanism and functions of testosterone

42. CAPACITATION OF SPERMATOZOA

43. Obstacles

44. Capacitation of Spermatozoa Sperm Capacitation  refers to the physiological changes  spermatozoa  must undergo in order to have the ability to penetrate and fertilize an egg. It is the preparation of spermatozoa to penetrate ovum

45. Spermatozoa are unable to fertilize the ovum when secreted Multiple changes occur when sperm comes in contact with the fluids of the female genital tract, these changes activate the sperm for fertilization. These collective changes are called Capacitation of the spermatozoa Importance of Capacitation : Capacitation is required for fertilization of the Ovum Capacitation of Spermatozoa (cont….)

46. Capacitation of Spermatozoa

47. Following changes occur in Capacitation: It requires from 1 to 10 hours. 1. Inhibitory factors that suppress sperm activity are washed away by uterine and fallopian tube fluids 2. Spermatozoa are continually exposed to cholesterol in floating vesicles coming from the seminiferous tubules. Cholesterol is continually added to the cell membrane of acrosome, toughening this membrane and preventing release of its enzymes. In female genital tract sperms are deprived of the cholesterol vesicles move into the uterine cavity They gradually lose excess cholesterol during the next few hours. Membrane of the acrosome becomes weak

48. Capacitation of Spermatozoa 3. The membrane becomes permeable to calcium ions Calcium enters the sperm in abundance Activity of the flagellum increases Flagellum achieves powerful whiplash motion Calcium ions cause changes in the cell membrane of the acrosome to release its enzymes rapidly and easily, when the sperm penetrates the granulosa cell mass and the zona pellucida of the ovum

49. ACROSOME REACTION REACTION THAT OCCURS IN THE ACROSOME OF THE SPERM AS IT APPROACHES THE EGG IS CALLED ACROSOME REACTION

50. STRUCTURE OF OVUM

51. Zona Pellucida Thick membrane Form protective coat Corona radiata 2-3 layers of cells attached cells to zona pellucida Vitteline membrane Plasma membrane of egg cell Controls entry and exit of substances STRUCTURE OF OVUM

52. Acrosome Reaction Reaction  that occurs in the  acrosome  of the sperm as it approaches the egg is called Acrosome reaction When the ovum is expelled from the ovarian follicle into the fallopian tube, it carries multiple layers of granulosa cells called corona radiata These granulosa cell layers must dissolute before a sperm can fertilize the ovum Sperm must penetrate through the zona pellucida which is a thick covering of the ovum When the sperm reaches the zona pellucida of the ovum, the membrane of the sperm binds with receptor proteins in the zona pellucida

53. Acrosome Reaction (continued) Vittilline layer

54. Acrosome Reaction (continued) Acrosome is rapidly dissolved and all the acrosomal enzymes are released Hyaluronidase depolymerizes the hyaluronic acid polymers in the intercellular cement that holds the ovarian granulosa cells together and makes pathways between the granulosa cells so that sperm can reach the ovum. The proteolytic enzymes digest proteins in the cells that still adhere to the ovum and open pathway for passage of the sperm head through the zona pellucida to the inside of the ovum Within 30 minutes, the cell membranes of the sperm head and of the oocyte fuse with each other & Genetic material of the sperm and the oocyte combine to form zygote

55. Acrosome Reaction

56. Why Does Only One Sperm Enter the Oocyte? When the first sperm penetrates the zona pellucida of the ovum Ca ions diffuse inward through the oocyte membrane After few minutes multiple cortical granules are released from the oocyte by exocytosis into the perivitelline space These granules contain substances that permeate all portions of the zona pellucida and prevent binding of additional sperm, and fall off those sperms that have already begun to bind.

57. BLOOD–TESTIS BARRIER I T IS THE PHYSICAL BARRIER BETWEEN BLOOD AND LYMPH VESSELS AND LUMEN OF THE SEMINIFEROUS TUBULES

58. Blood–Testis Barrier Blood–testis barrier is formed by tight junctions, adherens junctions and gap Junctions between the Sertoli cells near the basal lamina. The walls of the seminiferous tubules are lined by primitive germ cells and Sertoli cells which are large complex glycogen-containing cells that stretch from the basal lamina of the tubule to the lumen Germ cells must stay in contact with Sertoli cells to survive, the contact is maintained by cytoplasmic bridges.

59. Blood–Testis barrier Steroids penetrate this barrier easily Some proteins pass from the Sertoli cells to the Leydig cells and vice versa in a paracrine fashion Maturing germ cells must pass through the barrier as they move to the lumen By progressive breakdown of the tight junctions above the germ cells along with formation of new tight junctions below them

60. Functions of Blood–Testis Barrier Blood–testis barrier prevents many large molecules to pass from the interstitial fluid or blood and the basal lamina into the lumen or near the lumen of seminiferous tubules Protects the germ cells from blood borne noxious agents Prevents antigenic products of dividing germ cells from entering the circulation and generating an autoimmune response Prevents autoimmune destruction of sperm

61. Functions of blood–testis barrier (continued) Composition of fluid in seminiferous tubule is maintained by blood–testis barrier Fluid in the seminiferous tubule is: rich in androgens, estrogens, K+, inositol , and glutamic and aspartic acids Contains little protein and glucose also Help to establish an osmotic gradient that facilitates movement of fluid into the tubular lumen.

62. Sertoli Cells Form Blood-testes barrier : Prevents autoimmune destruction of sperm. Contain aromatase (CYP19) enzyme that c onverts testosterone to estrogen Sertoli cells secrete Inhibin , mullerian inhibiting substance (MIS) MIS causes regression of the mullerian ducts by apoptosis Inhibin inhibits FSH secretion Phagocytize residual bodies Secrete ABP (androgen-binding protein): Binds to testosterone and concentrates testosterone in the tubules.

63. TESTOSTERONE AND OTHER MALE SEX HORMONES

64. MALE SEX HORMONES Androgen means any steroid hormone that has masculinizing effect The testes secrete several male sex hormones Inhibin MIS Testosterone Dihydrotestosterone Androstenedione Oestradiol Insulin like factor 3

65. MALE SEX HORMONES (continued) Testosterone is secreted by the Interstitial Cells of Leydig in the Testes Leydig cells are numerous in the newborn male infant for the first few months of life and in the adult male after puberty In new born and after puberty the testes secrete large quantities of testosterone Leydig cells are almost non existent in the testes during childhood when the testes secrete almost no testosterone

66. Testosterone Testosterone is secreted in excess & considered to be the primary testicular hormone Most of the testosterone is eventually converted into the more active hormone Dihydrotestosterone (DHT) It is also converted to Estrogen by the Sertoli cells

67. Enzymes in Leydig cells 11β-hydroxylase and 21 β -hydroxylase (adrenal cortex) are absent in the Leydig cells Leydig cells contain 17α-hydroxylase Hence Pregnenolone is converted to 17 alpha hydroxypregnenolone 17 alpha hydroxypregnenolone is converted to DHEA DHEA is converted to Androstenedione DHEA and Androstenedione are then converted to Testosterone

68. Biosynthesis of Testosterone

69. Derivatives of testosterone Dehydroepiandrosterone (DHEA) Androstenedione Estrone Estriol Testosterone DHT Estradiol Estriol

70. Secretion of Androgens Elsewhere in the Body Adrenal gland Ovaries Placenta Adrenogenital syndrome Excess quantities of androgenic hormones are produced that causes male secondary sexual characteristics to occur, even in the female. Arrhenoblastoma Tumor of embryonic crest cells in the ovary, produces excessive quantities of androgens in women

71. Metabolism of Testosterone (97%) bound with plasma albumin or with a beta globulin called sex hormone–binding globulin and rest circulate in blood in free form. Testosterone fixed to the tissues in target organs is converted to Dihydrotestosterone

72. Degradation and Excretion of Testosterone The testosterone not fixed to the tissues is converted by the liver into androsterone & dehydroepiandrosterone Conjugated with glucuronides or sulfates in the liver These substances are secreted in the bile by the liver into the gut and ultimately excreted out of the gut into feces Or excreted into the urine through the kidneys

73. Production of Estrogen in the Male Sertoli cells convert testosterone to estradiol 80 % Estrogens in men are derived from circulating androgens through aromatization of testosterone and Androstenedione aromatase enzyme in liver convert testosterone to estradiol and Androstenedione to estrone

74. Production of Estrogen in the Male

75. Plasma testosterone concentrations & sperm production at different ages

76. FUNCTIONS OF TESTOSTERONE Functions of Testosterone During Fetal Development SRY protein (TDF) initiates a cascade of gene activations that cause the genital ridge cells to differentiate into cells that secrete testosterone and eventually become the testes Testes are stimulated by HCG from the placenta to produce testosterone in 7 th week of fetal life & 10 or more weeks after birth Development of the male body characteristics Development of secondary sexual characteristics Descent of Testes

77. Cryptorchidism Failure of a testis to descend from the abdomen into the scrotum at or near the time of birth of a fetus is called Cryptorchidism Testes are derived from the genital ridges in the abdomen 3 weeks to 1 month before birth of the baby, the testes normally descend through the inguinal canals into the scrotum.

78. Cryptorchidism (continued) Testes may not descent in few cases in IUL One or both testes may remain in the: Abdomen Inguinal canal Any where along the route of descent A testis that remains throughout life in the abdominal cavity because of high temperature is not capable of spermatogenesis. There is degeneration of tubular epithelium leaving only the interstitial structures of the testes.

79. Cryptorchidism (continued) Testosterone is important hormone secreted by the fetal testes It causes the testes to descend into the scrotum from the abdomen. Deficiency of Testosterone results from : Abnormally formed testes that are unable to secrete enoaugh testosterone. The surgical operation is not successful in these patietns