1. The Reproductive System

2. The Two Sexes
Male and female gametes (sex cells) combine their genes to form a zygote (fertilized egg)
One gamete has motility: sperm (spermatozoon)
Parent producing sperm considered male
Parent with a Y chromosome is male
Other gamete contains nutrients for developing embryo: egg (ovum)
Parent producing eggs considered female
Anyone lacking a Y chromosome is female
In mammals, female is the parent that provides a sheltered internal environment and prenatal nutrition of the embryo

3. Overview of the Reproductive System
Male reproductive system serves to produce sperm and introduce them into the female body
Males have a copulatory organ (penis) for introducing their gametes into the female reproductive tract
Female reproductive system produces eggs, receives sperm, provides for the union of the gametes, harbors the fetus, and nourishes the offspring
Females have a copulatory organ (vagina) for receiving the sperm

4. Reproductive System
Primary sex organs (gonads) – testes in males, ovaries in females
Gonads produce sex cells called gametes and secrete sex hormones
Accessory reproductive organs – ducts, glands, and external genitalia
Sex hormones – androgens (males), and estrogens and progesterone (females)

5. Male reproductive system
Gonads – testes
Produces sperm and secretes hormones
System of ducts – transport and stores sperm, assists in their maturation, and conveys them to the exterior
Epididymis, ductus deferens, ejaculatory ducts, and urethra
Accessory sex glands – adds secretions to semen
Seminal vesicles, Prostate, and Bulbourethral glands
Supporting structures
Scrotum supports testes and penis delivers sperm into female reproductive tract

6. Male Reproductive System

7. Semen
Milky white, sticky mixture of sperm and accessory gland secretions
Provides a transport medium, nutrients and protection
Slightly alkaline (pH 7.2 – 7.7)
Prostaglandins
Decrease the viscosity of mucus in the cervix
Typical ejaculate = 2-5 ml fluid
60% seminal vesicle fluid, 30% prostatic fluid, and 10% sperm and spermatic duct secretions
Contains between 20 – 100 million spermatozoa per ml

8. Accessory Glands: Seminal Vesicles
Lie on the posterior wall of the bladder
Produces seminal fluid
secrete 60% of the volume of semen
Slightly alkaline
Seminal fluid contains
fructose, prostaglandins and fibrinogen-like protein

9. Accessory Glands: Prostate Gland
Doughnut-shaped gland that encircles part of the urethra
About 25-30% of the semen
Prostatic fluid is slightly acidic
-contains seminalplasmin, an antibiotic
-Plays a role in the activation of sperm

10. Accessory Glands: Bulbourethral Glands (Cowper’s Glands)
Pea-sized glands inferior to the prostate
Produce thick, clear mucus
Alkaline to neutralize acidic urine in the urethra; Protects the sperm by neutralizing the acidity of residual urine in the urethra
During sexual arousal, they produce a clear slippery fluid that lubricates the head of the penis in preparation for intercourse

11. The Scrotum Contains paired testicles separated by a midline septum
Its external positioning keeps the testes 2-3C lower than core body temperature (needed for sperm production)
Cremaster muscle
Dartos muscle

12. The Testes Descent of the testes
Movement of testes through inguinal canal into scrotum
Occurs during fetal development
Cryptorchidism

13. The Structure of the Testes

14. The Testes Each testis is surrounded by two tunics:
The tunica vaginalis
The tunica albuginea
Septa divide the testis into lobules, each containing 1-4 seminiferous tubules
Seminiferous tubules:
Produce the sperm
Seminiferous tubules conveys sperm to the rete testis

15. Sperm production
In seminiferous tubules
Interstitial cells between seminiferous tubules
Secrete sex hormones
Sperm pass through rete testis

16. Histology of the Testis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Blood vessel
Seminiferous
tubule
Spermatids
Sustentacular
cell nuclei
Tubule lumen
Germ cells
Connective tissue
wall of tubule
Interstitial cells
(b)
50 µm
© Ed Reschke

17. Seminiferous tubule

18. Interstitial Cells & Sertoli Cells
Interstitial Cells (Leydig cells): responsible for the production of androgens- testosterone
Steroli Cells (Sustentacular or Nurse cells): cells that extend from the basal lamina to surrounds developing cells
Functions
-Maintain Blood-Testis Barrier
-Support Mitosis and Meiosis
-Support spermiogenesis
-Secrets inhibin
-Secrets Androgen-binding Protein (ABP)

19. Epididymis
Nonmotile sperm enter, pass through its tubes and become motile
Upon ejaculation the epididymis contracts, expelling sperm into the ductus deferens

20. Ductus Deferens and Ejaculatory Duct
Propels sperm from the epididymis to the urethra
Vasectomy – cutting and ligating the ductus deferens, which is a nearly 100% effective form of birth control

21. Urethra
Conveys both urine and semen (at different times)
Three regions:
Prostatic urethra
Membranous urethra
Penile or spongy urethra

22. The Penis
A copulatory organ designed to deliver sperm into the female reproductive tract
Corpus spongiosum
Corpora cavernosa
Prepuce, or foreskin – cuff of skin covering the distal end of the penis
Circumcision – surgical removal of the foreskin after birth

23. Spermatogenesis Primordial germ cells form in yolk sac of embryo
Colonize gonadal ridges and become spermatogonia
Puberty brings on spermatogenesis
Spermatogonia lie along periphery of seminiferous tubules and divide by mitosis
One daughter cell of each division remains in tubule wall as stem cell: type A spermatogonium
Other daughter cell migrates slightly away from wall and is on its way to producing sperm: type B spermatogonium

24. Spermatogenesis contd.
Type B spermatogonium enlarges and becomes a primary spermatocyte
Sustentacular cells protect it from the body’s immune system: blood–testis barrier (BTB)
Primary spermatocyte undergoes meiosis I which gives rise to two equal-size, haploid, genetically unique secondary spermatocytes
Each secondary spermatocyte undergoes meiosis II dividing into two spermatids—a total of four for each spermatogonium
Spermiogenesis—four spermatids divide no further, but undergo a transformation in which it differentiates into a spermatozoon

25. Spermatogenesis

26. Spermatogenesis
The sequence of events that produces sperm in the seminiferous tubules of the testes
Each cell has two sets of chromosomes (one maternal, one paternal) and is said to be diploid (2n chromosomal number)
Humans have 23 pairs of homologous chromosomes
Gametes only have 23 chromosomes and are said to be haploid (n chromosomal number)
Gamete formation is by meiosis, in which the number of chromosomes is halved (from 2n to n)

27. Spermatocytes to Spermatids

28. Spermatogenesis
Once the primary spermatocyte undergoes meiosis, it becomes genetically different and needs to be protected from the immune system.
The primary spermatocyte moves toward the lumen of the seminiferous tubule and a new tight junction between sustentacular cells forms behind it.
Now protected by the blood–testis barrier closing behind it.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cross section of
seminiferous tubules
Lumen of
seminiferous tubule
Sperm 5
Spermiogenesis
Spermatid n n n n 4
Meiosis II
Secondary spermatocyte n n 3
Meiosis I
Blood–testis barrier
Primary
spermatocyte 2n
Sustentacular cell 2
Type B spermatogonium 2n
Tight junction
Type A spermatogonium 1 2n
Basement membrane
of seminiferous tubule

29. Spermiogenesis: Spermatids to Sperm

30. Anatomy of spermatozoon
Each spermatozoon has:
Head
Nucleus and densely packed chromosomes
Middle piece
Mitochondria that produce the ATP needed to move the tail
Tail
The only flagellum in the human body

31. The Mature Spermatozoon
Acrosome
Head
Nucleus
Basal body
Mitochondrion
Midpiece
of tail
Axoneme
Principal
piece of
tail
Endpiece
of tail
2 µm
(a)
(b)

32. Hormonal Feedback and the Regulation of the Male Reproductive Function