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Sexual reproduction is the process by which organism produce offspring by making germ cells called gametes
After the male gamete (sperm cell) unites with the female gamete (secondary oocyte) an event called fertilization-the resulting cell contains one set of chromosomes from each parents.
The male and female reproductive system organs can be grouped by function
- gonads testes in males and females produce gametes and secrete sex hormones
- Ducts store and transport the gametes
- accessory sex glands produce substance that protect the gamets and facilitate their movementSupporting structure, such as penis in males and the uterus in females, assist the delivery of gametes. Uterus is also the site for the growth of the embryo and fetus during pregnancy
Gynecology is study of female reproductive system
Urology is study of urinary system & male reproductive system
Somatic cells – any cell of the body other than a germ cell
Germ cell is a gamete (sperm or oocyte) or any precursor cell intended to become a gamete.
Homologous chromosomes. The two chromosomes that make up each pair are called homologous chromosomes or homologs.They contain similar genes arranged in the same order.
Diploid cells. Because somatic cells contain two sets of chromosomes, they are called diploid cells.
in 22 of the pairs, the homologous chromosomes look alike and have the same appearance in both males and females; these 22 pairs are called autosomes
The two members of the 23rd pair are termed the sex chromosomes. In females, the pair consist of two chromosomes called X chromosomes. (XX).In males have an X and a smaller Y chromosome(XY)
The reproductive cell division that occurs in the gonads (ovaries and testes), produces gamets in which the number of chromosomes is reduced by half. As result gametes contain a single set of 23 chromosomes and thus haploid cells. Fertilization restores the diploid number of chromosomes.
Meiosis , the reproductive cell division that occurs in the gonald (ovaries and testes), produces gametes in which the number of chromosomes is reduced by half. Meiosis occurs in two successive stages: meiosis I and meiosis II
organs of the male reproductive system include
- The testes: produce sperm and secrete hormone
- A system of ducts including the epididymis, ductus deferns, ejaculatory ducts, and urethra; duct system transport and stores sperm, assist in their maturation, and conveys them to the exterior
- accessory sex glands (seminal vesicles, prostate and bulbourethral glands)
The scrotum, the supporting structure for the testes consist of loose skin and underlying subcutaneous layer that hangs from the root of the penis
externally scrotum separated into lateral portion by a median ridge called the raphe
Internally, the scrotal septum divides the scrotum into two sacs, each contains a single testis
Septum is made up of a subcutaneous layer and muscle tissue called the dartos muscle. The dartos muscle is also found in the subcutaneous layer of the scrotum.Dartos muscle causes wrinkles and relaxes the skin of the scrotum
A series of small bands of skeletal muscle that descends through the spermatic cord.
regulation the temperature of the testes
Normal sperm production required a temperature about 2-3 0 below core body.(core temperature 37). In response to cold temperature, the cremaster and dartos muscle contract. Two muscles regulate temp:Contraction of cremaster muscle moves the testes closer to the body, where they can absorb heat. Contraction of the dartos muscle causes the scrotum to become tight (wrinkled in appearance), which reduces heat loss.
The testes or testicles are paired oval glands in the scrotum measuring about 5 cm (2in) long and 2.5 cm(1in) in diameter. Each testis 10 -15grams.The testes develop near the kidney, in the posterior portion of abdomen
Testes are surrounded by two tunics
- Outer tunic – tunica vaginalis
- Inner tunic – tunica albuginea
A serous membrane called the tunica vaginalis partially (outer) covers the testes. A collection of serous fluid in the tunica vaginalis is called a hydrocele. It may caused by injury to the testes
Inner tunic – tunica albuginea divides the testis into lobules. Each of the 200-300 lobules contains 1 to 4 tightly coiled seminiferous tubules – site of sperm production. (spermatogenesis).
Two types of cells in the seminiferous tubules:
- spermatogenic cells-the sperm forming
- cellsertoli cells have several function in supporting spermatogenesis
Spermatogonia – the stem cells, divide via mitosis, diploid chromosome number (46 chromosomes)
Sertoli cells which extend from the basement membrane to the lumen of the tubule. They form blood-testis barrier. By isolating the developing gametes from the blood, the blood-testis barrier prevents an immune response againts the spermatogenic cell's surface antigens, which are recognized as "foreign" by the immune system.
sertoli cells support
- They nourish spermatocytes, spermatids, and sperm
- Phagocytize excess spermatid cytoplasm as development proceeds
- Control movements of spermatogenic cells and the release of sperm into the lumen of the seminiferous tubule.
- Produce fluid for sperm transport,
- Secrete inhibin which slows sperm production by inhibiting FSH
Leydig cells in between tubules secrete testosterone –androgen. An androgen is a hormone that promotes development of masculine characteristics. Testosterone also promotes a man’s sexual drive.
The condition in which testes do not move down into the scrotum.it occurs in about 3% of full-term infants and about 30% of premature infants. 80% descend spontaneously during the first year of life.Surgical treatment necessary if descent does not occur before 18 months.Untreated bilateral cryptorchidism results in sterility & a greater risk of testicular cancer
Spermatogenesis is formation of sperm cells from spermatogonia. It begins with spermatogonia – the stem cells, which contains the diploid (2n) (diploid chromosome number 46 chromosomes), divide via mitosis, some spermatogonia remain near the basement membrane of the seminiferous tubule in an undifferentiated state. The rest of the spermatogonia lose contact with the basement membrane, squeeze through the tight junction of the blood-testis barrier, undergo development changes, and differentiate into primary spermatocytes. Primary spermatocytes like spermatogonia are diploid (2N); that is they have 46 chromosomes.
Each Primary spermatocytes replicates its DNA and then meiosis begins. Meiosis I, homologous pairs of chromosomes line up at the metaphase plate and crossing over occurs. Then the meiotic spindle pulls one (duplicated) chromosome of each pair to an opposite pole of the dividing cell. The two cells formed by meiosis I are called secondary spermatocytes. Secondary spermatocytes – daughter cells formed by meiosis I, have a haploid chromosome number (n) (23 chromosomes). However each chromosome within a secondary spermatocyte is made up of two chromatids(two copies of DNA) still attached by a centromere
Meiosis II, the chromosomes line up in single file along the metaphase plate, and two chromotids of each chromosome separate. The four haploid cells resulting from meiosis II are called spermatids. A single primary spermatocyte therefore produces four spermatids via two round of cell division (meiosis I and meisosi II)
process occur during spermatogenesis
As spermatogenic cells proliferate, they fail to complete cytoplasmic separation (cytokinesis). The cell remains in contact via cytoplasmic bridges through their entire development
The final stage of spermatogenesis, spermiogenesis, is the development of haploid spermatids into sperm.No cell division occurs in spermiogenesis. Each spermatid becomes a single sperm cell. Finally, sperm are released from their connections to Sertoli cells, an event known as spermiation. Sperm then enter the lumen of the seminiferous tubule. Fluid secreted by Sertoli cells pushes sperm along their way, toward the ducts of the testes. (AT this point, sperm are not yet able to swim).
Complete the process of spermatogenesis
Head of the sperm
The head contains a nucleus with 23 highly condensed chromosomes. Covering the head is an acrosome which contains enzymes that are needed to penetrate the egg. (enzymes are hyaluronidase and proteases)
Tail of the sperm
The tail of a sperm is subdivided into 4 pieces:1) neck just behind the head that contains centrioles. 2) middle piece contains mitochondria arranged in a spiral, which provides energy (ATP) for locomotion of sperm to the site of fertilization.3) principal piece longest portion of the tail is flagellum used for locomotion.4) End piece is the terminal
gonadotropin-releasing hormone (GnRH)
hypothalamic neurosecretory cells increase of gonadotropin-releasing hormone (GnRH).Gonadotropin-releasing hormone (GnRH) stimulates in the anterior pituitary to increase secretion of the two gonadotropins. 1) luteiniing hormone (LH) 2) follicle-stimulating hormone (FSH)
luteiniing hormone (LH)
luteiniing hormone (LH) stimulates Leyding cells, which are located between seminiferous tubules, to secrete the hormone testosterone. In some target cells, such as those in the external genitals and prostate, the enzyme 5 alpha-reductase converts testosterone to another androgen called dihydrotestosterone (DHT).
follicle-stimulating hormone (FSH)
FSH stimulates spermatogenesis, but acts indirectly to stimulate spermatogenesis. FSH with testosterone stimulates sertoli cells to secrete androgen-binding protein into lumen of the seminiferous cells. ABP binds to testosterone, keeping its concentration high.Testosterone stimulates the final steps of spermatogenesis in the seminiferous tubules. Once the degree of spermatogenesis required for male reproductive function has been achieved, sertoli cells release inhibin, a protein hormone that inhibiting FSH secretion by the anterior pituitary. If spermatogenesis is proceeding slowly, less inhibin is released, which permits more FSH secretion and an increased rate of spermatogenesis
Testosterone & DHT
- Testosterone & DHT bind to androgen receptors in cell nucleus & change genetic activity in developing embryo. Because of these changes, the androgen produce several effects:
- 1. Prenatal development. Before birth, testosterone stimulates the male pattern of development of reproductive system ducts. Testosterone also is converted in the brain to estrogen, which play role in the development of certain regions of the brain in males.
- 2. Development of male sexual characteristics. At puberty, testosterone and dihydrotestosterone bring about development and enlargement of the male sex organs and the development of masculine secondary sexual characteristics.
- 3. Development of sexual function. Androgens contribute to male sexual behavior and spermatogenesis and to sex drive (libido) in both males and females
- 4. Stimulation of anabolism. Adrogen are anabolic hormones; that is , they stimulate protein synthesis. This effect is obvious in the heavier muscle and bone mass of most men as compared to women.
Effect of Inhibin Hormone
When sperm production is sufficient,sertoli cells release inhibin that inhibits FSH secretion by the anterior pituitary that in turn decreases sperm production. When sperm production is proceeding too slowly,less inhibin is released by the sertoli cells-more FSH will be secreted-sperm production will be increased
ducts of testis
Pressure generates by the fluid secreted by Sertoli cells pushes sperm and fluid along the lumen of seminiferous tubules and then into short ducts called straight tubules. Then into rete testis, from rete testis to efferent ducts in the epididymis that empty into a single tube called the ductus epididymis.
Comma-shaped organ, 1.5in long along posterior border of each testis, 20 foot tube if uncoiled,epididymis consist Head, body and tail region.The efferent ducts from testis join the ductus epididymis at superior portion called head.Body is the midportion of the epididymis. At the distal end, the tail of the epididymis continues as the ductus ( vas) deferns
Histology of the Epididymis
epididymis is lined with pseudostratified ciliated columnar epithelium and encircled by layer of smooth muscle. Columnar cells contain stereocilia, that increase are for the reabsorption of generated sperm
Function of epididymis
Functionally, the epididymis is the site of sperm maturation; that mean sperm move through the epididymis, they gain the ability to swim and the ability to fertilize an ovum. Motility increases over 2 week period. Also helps propel sperm into the ductus (vas) deferens during sexual arousal by peristaltic contraction of its muscle. Epididymis stores sperm for 1-2 months; any sperm that are not ejaculated by that time are eventually reabsorbed.
Ductus (Vas) Deferens
Pathway of 18 inch muscular tube. Passes up through spermatic cord and inguinal ligament and reaches posterior surface of urinary bladder.Empties into prostatic urethra with seminal vesicle.The dilated terminal portion of the ducts deferens is the ampulla.
Histolgy of Ductus (Vas) Deferens
Ductus (Vas) Deferens is a muscular tube lined with pseudostratified columnar epithelium.The musclaris is composed of three layers of smooth muscle:The inner and outer are longitudinal, the middle layer is circular
Function Ductus (Vas) Deferens
Functionally, the ductus deferns conveys sperm during sexual arousal from the epididymis toward the urethra by peristaltic contraction of its muscular coat. like the epididymis, the ductus deferns can store sperm for several month.
All structures passing to and from the testes:testicular artery, veins, autonomic nerves, lymphatic vessels,ductus (vas) deferens,cremaster muscle
Varicocele refers to a swelling in the scrotum due to a dilation of the veins that drains the testes.
The spermatic cord and ilioinguinal nerve pass through the inguinal canal, an oblique passageway in the anterior abdominal wall just superior and parallel to the medial half of the inguinal ligament. The canal, which is about 4-5 cm originates at the deep (abdominal) inguinal ring and ends at superficial inguinal ring
About 1 inch long. Formed from union of duct of seminal vesicle & ampulla of vas deferens. They end in the prostatic urethra, where they eject sperm and seminal vesicle secretion just before the release of semen from the uretra to the exterior. Seminal vesicle adds fluid to prostatic urethra just before ejaculation.
Urethra is a 8 inch long passageway for urine & semen.Prostatic urethra (1 inch long) passes through the prostatic urethra.Membranous urethra (0.5 in passes through urogenital diaphragm).Penile (spongy) urethra ( 6-8 in passes through corpus spongiosum).
Accessory Sex Glands
Accessory sex glands secrete most of the liquid portion of semen.
The accessory sex glands include
Seminal vesicles.Prostate gland.Bulbourethral glands
Seminal vesicles are pair of pouchlike organs found posterior to the base of urinary bladder. About 2in. Through the seminal vesicle ducts, seminal vesicles secrete an alkaline- viscous fluid neutralizes vaginal acid of male urethra and female reproductive tract, if not vaginal acid would kill sperm.
Alkaline of seminal vesicles contains
- fructose for ATP production
- prostaglandins stimulate sperm motility and may stimulate smooth muscle contraction within the female reproductive tract
- clotting proteins for coagulation of semen
- Prostate gland is a single organ the size of chestnut found inferior to bladder. Increase from birth to puberty, then rapidly expands until 30, remains stable about age 45, later further enlargement may occur The prostate secretes a milky, slightly fluid, pH about 6.5 that contains several substance.
- 1.Citric acid in prostatic fluid is used for ATP production
- 2.Several proteolytic enzymes such as pepsinogen, lysozyme, amylase
- 3.Acid phoshphatase is unknown
- 4.Seminalplasmin in prostatic fluid is antibiotic that can destroy bacteria.
Bulbourethral Glands are paired, pea-sized gland within the urogenital diaphragm. During sexual arousal, the bulbourethral glands secrete an alkaline fluid into the urethra that protects the passing sperm by acids from urine in the urethra.They also secrete mucus that lubricates the end of the penis and the lining of the urethra, decreasing the number of sperm damaged during ejaculation.
Seminal fluid contains:secretions of the seminiferous tubules, seminal vesicles, prostate gland, and bulbourethral gland.
Semen is a mixture of sperm and seminal fluid.Typical ejaculate is 2.5 to 5 ml in volume. Semen has a slightly alkaline pH 7.2-7.7 due to the higher and larger volume of fluid from the seminal vesicles,milky appearance, sticky.Normal sperm count is 50 to 150 million/ml. Actions of many are needed for one to enter the ovum for successful fertilization.Once ejaculated, liquid semen coagulates within 5 minutes -- reliquefies in 15 due to enzymes produced by the prostate gland
The presence of blood in semen is called hemospermia. in most cases, it is caused by inflammation of the blood vessels lining the seminal vesicles.
The penis contains the urethra that is a passageway for the ejaculation of semen and the excretion of urine.
Body, glans penis and root.
Body of penis
The body of penis is composed of three cylindrical masses of tissue, each surrounded by fibrous tissue called the tunica albuginea.The two dorsolateral masses are called the corpora cavernosa penis, surrounded by tunica albuginea of corpora cavernosum.The smaller midventral mass, the corpus spongiosum penis, contains the spongy urethra and keeps it open during ejaculation. Surrounded by tunica albuginea of corpus spongiosum penis. Skin and a subcutaneous layer enclose all three masses, which consist of erectile tissue. Erectile tissue is composed of numerous blood sinuses.
Upper paired, begins as crura of the penis attached to the ischial and pubic rami and covered by ischiocavernosus muscle
Surrounds urethra. Begins as bulb of penis covered by bulbospongiosus muscle.Ends as glans penis
Enlarged distal end of corpus spongiosum. External urethral orifice is small slit. Covered by loosely fitting prepuce or foreskin
The root of the penis
The root of the penis is the attached portion (proxinmal portion). It consists of the bulb of the penis and the crura of the penis (sing. crus). Each crus of the penis bends laterally away from the bulb of the penis to attach to the ischial and inferior pubic rami.
Circumcision. Removal of prepuce 3 - 4 days after birth,possibly lowers UTIs, cancer & sexually transmitted disease
- Prophase I: The two sister chromatids of each pair of homologous pair off an event called synapsis. The resulting four cromatids form s structure called a tetrad. Second part of the chromatids of two homologous chromosomes may exchange with one another. Such as exchange between parts of nonsister (genetically different) chromatids is termed crossing over
- metaphase I: In metaphase I, the tetrads line up along the metaphase plate of the cell
- anaphase I: homologous chromosomes separate (sister chromatids remain together)
- telophase. Each cell has one of thye replicated chromosomes from each homologous pair of chromosomes(N)