Chapter 16 The Reproductive System Intro & Male

The Reproductive System 1. Gonads – primary sex organs Testes in males Ovaries in females 2. Gonads produce gametes (sex cells) and secrete hormones Sperm – male Ova (eggs) – female

Male Reproductive System Accessory organs - Seminal vesicle - Prostate gland - Bulbourethral gland External genitalia - Penis - Scrotum Testes Duct system - Epididymis - Ductus deferens - Urethra

Testes Tunica albuginea – capsule that surrounds each testis Septa – extensions into testis; dividing it into lobules

Testes Each lobule contains 1-4 seminiferous tubules Tightly coiled Sperm-forming factories Empty sperm into the rete testis Sperm travels through the rete testis to epididymis Interstitial cells produce androgens such as testosterone

Duct System Epididymis Comma-shaped, tightly coiled tube Superior and along posterior lateral side Matures and stores sperm cells (at least 20 days) Expels sperm with the contraction of muscles in the epididymis walls to the vas deferens

Ductus Deferens Carries sperm from epididymis to ejaculatory duct Passes through inguinal canal & over bladder Moves by peristalsis Spermatic cord – ductus deferens, blood vessels, and nerves in a connective tissue Ends in the ejaculatory duct which unites with urethra Vasectomy – cutting of the ductus deferens at the level of the testes to prevent transportation of sperm

Urethra Extends from the base of bladder to the tip of penis Carries both urine and sperm Sperm enters from the ejaculatory duct Regions: Prostatic urethra –surrounded by prostate Membranous urethra – from prostatic urethra to penis Spongy (penile) urethra – runs the length of the penis

Figure 27.4 Ureter Ampulla of ductus deferens Seminal vesicle Urinary bladder Ejaculatory duct Prostate Prostatic urethra Orifices of prostatic ducts Bulbourethral gland and duct Membranous urethra Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbourethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Shaft (body) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) (a) External urethral orifice Dorsal vessels and nerves Corpora cavernosa Urethra Skin Tunica albuginea of erectile bodies Deep arteries (b) Corpus spongiosum Figure 27.4

Accessory Glands and Semen Seminal Vesicles Located at the base of the bladder Produces a thick, yellowish secretion (60% of semen) Fructose (sugar) Vitamin C Prostaglandins Substances that nourish & activate sperm

Figure 27.4 Ureter Ampulla of ductus deferens Seminal vesicle Urinary bladder Ejaculatory duct Prostate Prostatic urethra Orifices of prostatic ducts Bulbourethral gland and duct Membranous urethra Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbourethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Shaft (body) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) (a) External urethral orifice Dorsal vessels and nerves Corpora cavernosa Urethra Skin Tunica albuginea of erectile bodies Deep arteries (b) Corpus spongiosum Figure 27.4

Prostate Gland Encircles upper part of urethra Secretes a milky fluid Helps activate sperm Enters urethra through several small ducts

Figure 27.4 Ureter Ampulla of ductus deferens Seminal vesicle Urinary bladder Ejaculatory duct Prostate Prostatic urethra Orifices of prostatic ducts Bulbourethral gland and duct Membranous urethra Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbourethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Shaft (body) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) (a) External urethral orifice Dorsal vessels and nerves Corpora cavernosa Urethra Skin Tunica albuginea of erectile bodies Deep arteries (b) Corpus spongiosum Figure 27.4

Bulbourethral Glands Pea-sized gland inferior to prostate Produces a thick, clear mucus Cleanses urethra of acidic urine Lubricant during intercourse Secreted into penile urethra

Figure 27.4 Ureter Ampulla of ductus deferens Seminal vesicle Urinary bladder Ejaculatory duct Prostate Prostatic urethra Orifices of prostatic ducts Bulbourethral gland and duct Membranous urethra Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbourethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Shaft (body) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) (a) External urethral orifice Dorsal vessels and nerves Corpora cavernosa Urethra Skin Tunica albuginea of erectile bodies Deep arteries (b) Corpus spongiosum Figure 27.4

Semen Mixture of sperm & gland secretions Advantages of secretions Fructose provides energy Alkalinity neutralizes acidic vagina Semen inhibits bacterial growth Elements of semen enhance sperm motility

External Genitalia Scrotum - Divided sac of skin outside abdomen - 3°C lower than body temp to protect sperm

External Genitalia Penis- Delivers sperm into female repro tract Shaft Glans penis (enlarged tip) Prepuce (foreskin) Folded cuff of skin around proximal end Often removed by circumcision

External Genitalia 3 areas of spongy erectile tissue around the urethra

Figure 27.4 Ureter Ampulla of ductus deferens Seminal vesicle Urinary bladder Ejaculatory duct Prostate Prostatic urethra Orifices of prostatic ducts Bulbourethral gland and duct Membranous urethra Urogenital diaphragm Bulb of penis Root of penis Crus of penis Bulbourethral duct opening Ductus deferens Corpora cavernosa Epididymis Corpus spongiosum Shaft (body) of penis Testis Section of (b) Spongy urethra Glans penis Prepuce (foreskin) (a) External urethral orifice Dorsal vessels and nerves Corpora cavernosa Urethra Skin Tunica albuginea of erectile bodies Deep arteries (b) Corpus spongiosum Figure 27.4

Figure 27.4b Male reproductive structures. Section of (b) Spongy urethra Glans penis Prepuce (foreskin) External urethral orifice Dorsal vessels and nerves Corpora cavernosa Urethra Skin Tunica albuginea of erectile bodies Deep arteries (b) Corpus spongiosum

Spermatogenesis Production of sperm cells Begins at puberty and continues throughout life Occurs in the seminiferous tubules

Figure 27.7a Spermatogenesis.

Figure 27.5 Comparison of mitosis and meiosis in a mother cell with a diploid number (2n) of 4 (1 of 2). Mother cell (before chromosome replication) Chromosome replication MITOSIS Replicated chromosome Prophase Chromosomes align at the metaphase plate Sister chromatids separate during anaphase Metaphase Daughter cells of mitosis Tetrad formed by synapsis of replicated homologous chromosomes Tetrads align at the Homologous chromosomes separate but sister chromatids remain together during anaphase I No further chromosomal replication; sister chromatids anaphase II Daughter cells of meiosis II (usually gametes) Prophase I Metaphase I Daughter cells of meiosis I Meiosis II MEIOSIS 2n = 4 2n 2n n n n n

Figure 27.6 Meiosis (1 of 2). Interphase cell Centriole pairs Nuclear envelope Chromatin Interphase events As in mitosis, meiosis is preceded by DNA replication and other preparations for cell division. Prophase I Prophase events occur, as in mitosis. Additionally, synapsis occurs: Homologous chromosomes come together along their length to form tetrads. During synapsis, the “arms” of homologous chromatids wrap around each other, forming several crossovers. The nonsister chromatids trade segments at points of crossover. Crossover is followed through the diagrams below. Anaphase I Unlike anaphase of mitosis, the centromeres do not separate during anaphase I of meiosis, so the sister chromatids (dyads) remain firmly attached. However, the homologous chromosomes do separate from each other and the dyads move toward opposite poles of the cell. Metaphase I The tetrads align randomly on the spindle equator in preparation for anaphase. Crossover Spindle Sister chromatids Nuclear envelope fragments late in prophase I Tetrad Dyad Centromere MEIOSIS I Telophase I The nuclear envelopes re-form around the chromosomal masses, the spindle breaks down, and the chromatin reappears as telophase and cytokinesis are completed. The 2 daughter cells (now haploid) enter a second interphase-like period, called interkinesis, before meiosis II occurs. There is no second replication of DNA before meiosis II. Chromosomes uncoil envelopes re-form Cleavage furrow 2n = 4

Figure 27.6 Meiosis (2 of 2). MEIOSIS II Prophase II Meiosis II begins with the products of meiosis I (2 haploid daughter cells) and undergoes a mitosis-like nuclear division process referred to as the equational division of meiosis. Prophase II Metaphase II After progressing through the phases of meiosis and cytokinesis, the product is 4 haploid cells, each genetically different from the original mother cell. (During human spermatogenesis, the daughter cells remain interconnected by cytoplasmic extensions during the meiotic phases.) Anaphase II Telophase II and cytokinesis Products of meiosis: haploid daughter cells

Processes of Spermatogenesis Follicle stimulating hormone (FSH) regulates Spermatogonia (stem cells) - rapid mitosis to produce more stem cells before puberty First division of a stem cell becomes 1 stem cell & 1 primary spermatocyte Primary spermatocytes undergo meiosis Haploid spermatids

Figure 27.7b Spermatogenesis.

Figure 27.7c Spermatogenesis. Basal lamina Spermatogonium (stem cell) Cytoplasm of adjacent sustentacular cells Sustentacular cell nucleus Tight junction between Lumen of seminifer- ous tubule Late spermatids Early spermatids Secondary spermatocytes Cytoplasmic bridge Primary spermatocyte Spermatozoa Type B daughter cell Type A daughter cell remains at basal lamina as a stem cell (c) A portion of the seminiferous tublule wall, showing the spermato- genic cells surrounded by sustentacular cells (colored gold)

Spermiogenesis Approximately 24 days Golgi apparatus Acrosomal vesicle Mitochondria Acrosome Nucleus 1 2 Centrioles Spermatid nucleus Microtubules Midpiece Head (a) 3 Flagellum Excess cytoplasm 4 Tail 5 6 7 (b) Figure 27.8a, b

Anatomy of a Mature Sperm Cell Late spermatids - distinct regions Head –DNA covered by acrosome Midpiece Tail Sperm cells = mature spermatids Spermatogenesis takes 64 to 72 days Only human flagellated cell

Testosterone Production - Most important hormone of testes - Produced in interstitial cells - Functions Organ development Sex drive Secondary sex characteristics Deepening of voice Increased hair growth Larger skeletal muscles Thicker bones

Regulation of Male Androgens (Sex Hormones)