Male Reproductive System

Human Reproduction Overview

• Focus on the male reproductive system

Male Reproductive System Components:

• Primary sex organs are the testes
• Ducts include the epididymis, vas deferens (sperm duct), and urethra
• Accessory glands are the seminal vesicles and prostate gland
• External genitalia consist of the penis and scrotum

Scrotum Function

• The scrotum contains the testes
• It regulates temperature, keeping the testes 2-3°C lower than body temperature for fertile sperm formation
• The scrotum also houses and protects the testes

Testes

• The testes are the primary male sex organs, producing sperm and testosterone
• testis = singular, testes = plural
• Internally, the testis is divided into compartments or small lobules

Testes: Lobules and Seminiferous Tubules

• Each lobule contains tightly packed, convoluted seminiferous tubules
• Seminiferous tubules are lined with germinal epithelium
• Germinal epithelium cells divide, giving rise to sperm (male gametes) during spermatogenesis

Sertoli Cells

• Some germinal epithelium cells develop into large columnar Sertoli cells
• Sertoli cells provide nourishment for developing sperm

Leydig Cells

• Seminiferous tubules are surrounded by connective tissue containing interstitial Leydig cells
• Leydig cells produce testosterone

Functions of the Testes

• Produce sperm
• Produce testosterone

Epididymis

• Seminiferous tubules connect to the epididymis,which is a long, convuluted tubule
• These tubules are located at the back of the testes and lined with a mucous membrane
• The epididymis stores sperm
• Sperm mature and gain the ability to swim until they can fertilize an egg

Vas Deferens (Sperm Duct)

• The vas deferens is a continuation of the epididymis and opens into the urethra
• Its function is to transport sperm from the epididymis to the urethra via peristaltic movements

Urethra

• The two sperm ducts join at the urethra, which opens to the exterior
• The urethra transports both urine and sperm (in semen) to the exterior, but not at the same time

Seminal Vesicles

• Seminal vesicles are sac-like structures connected to the base of each sperm duct
• They are lined with a mucous membrane that secretes a yellowish, sticky substance

Seminal Vesicles Fluid Contribution

• Seminal vesicles secrete a thick, clear fluid that stimulates sperm movement
• The fluid contains water, enzymes, proteins, mucus (for slipperiness), vitamin C, fructose (for energy), and prostaglandins to suppress the female's immune response

Prostate Gland

• The prostate gland is a conical gland situated against the bladder
• It surrounds the urethra near where the ejaculatory ducts join

Prostate Gland Fluid Contribution

• The prostate gland secretes a white, milky fluid
• This fluid ensures sperm motility
• The secretion also protects sperm against low pH (acidity) in the urethra and vagina

Penis

• It is a copulation organ with a shaft and head region
• The shaft is divided into three columns of erectile tissue
• The cone-shaped head is the glans penis
• The glans penis is partially covered by the foreskin, which may be removed during circumcision

Erection

• Erectile tissue in the penis fills with blood during arousal due to increased blood pressure and flow
• This causes an erection, allowing the penis to be inserted into the vagina to release sperm near the cervix

Penis Functions

• Transfers semen containing sperm from the male to the female
• Excretes urine

Key Terms

• Sperm: male gametes (sex cells)
• Semen: sperm from the testes and seminal fluid from the sperm duct and accessory glands
• Erection: stiffening of the penis
• Ejaculation: expulsion of semen

Female Reproductive System Components:

• Primary sex organs are the ovaries
• Organs responsible for transportation and care of the ovum and zygote are the fallopian tubes, uterus, endometrium, cervix, vagina
• External genitalia consist of the vulva and clitoris

Ovaries

• The ovaries are the primary female sex organs, located in the pelvic cavity on either side of the uterus
• They are almond-shaped organs held in place by ligaments
• Ovaries are surrounded by germinal epithelium that produces ova by oogenesis

Ovaries Function

• Produce and release ova
• Produce estrogen and progesterone

Fallopian Tubes (Oviducts)

• Muscular tubes that are lined with cilia
• They stretch from each ovary to the uterus

Fallopian Tubes (Oviducts) Functions

• Provide a pathway between the uterus and ovary for eggs, sperm, and the zygote
• Site of fertilization and initial cell division of the zygote
• Facilitate the movement of the egg or developing zygote towards the uterus via muscle action and cilia

Ectopic Pregnancy

• An ectopic pregnancy occurs when an embryo implants somewhere other than the uterus, such as in a fallopian tube

Uterus

• The uterus (womb) is a hollow, pear-shaped organ

Uterus Composition

• The uterine wall consists of the myometrium (muscle layer enabling childbirth contractions), and the endometrium (inner lining richly supplied with blood vessels)
• Its lower part, the cervix, projects into the vagina

Endometrium

• At ovulation, progesterone causes the endometrium to thicken to prepare for blastocyst implantation

If Fertilization Does not Occur

• If fertilization does not occur, the upper endometrium layer detaches and is passed out with the unfertilized egg
• Ths occurs roughly every 28 days and is known as menstruation

Uterus Functions

• Implantation, development, and growth of the blastocyst
• Myometrium contractions facilitate the fetus expulsion during birth

Uniqueness of the Human Uterus

• Human females have a simplex uterus with no separation between the horns, resulting in a single cavity
• Early placentals have a duplex uterus with two separated uterine horns and cervices

Cervix

• Normally the opening is only millimeters in diameter allowing menstrual blood to flow and sperm to enter
• It dilates enormously during the birth process.
• The sphincter muscles of the cervix keep the uterus closed during pregnancy to prevent miscarriage

Vagina

• The vagina/birth canal is a muscular passage between the uterus and the outside of the body
• It has elastic, folded walls that stretch during intercourse and childbirth

Vagina & pH

• The pH of the vagina is normally acidic, helping to maintain its health and prevent infection

Vagina Function

• The location of sperm deposit during sexual intercourse
• Functions as birth canal during birth

Vulva

• The vulva is the external genitalia, but plays no role in the reproductive process

Clitoris

• A small mass of erectile tissue found at the anterior end of the vulva
• The clitoris is the female counterpart to the male penis and plays a role in sexual arousal.

Hymen

• A membrane that surrounds or partially covers the external vaginal opening, forming part of the vulva
• May be considered as an example of external genitalia
• Appears to lack a specific physiological purpose

Puberty

• The time during which sex organs develop and gametes are produced
• Many physical and physiological changes take place
• By the end of puberty, an immature individual (child) should be capable of reproduction

Female Puberty Timeline

• Typically occurs between ages 11 and 14

Female Puberty Process

• The pituitary gland releases follicle-stimulating hormone (FSH)
• FSH then stimulates the follicles in the ovaries to develop and produce estrogen

Estrogen Initiates Change

• Estrogen initiates changes - development of the gonads (primary sexual characteristics), and other parts of the body (secondary sexual characteristics)

Male Puberty Timeline

• Typically occurs between ages 14 and 16

Male Puberty Process

• The pituitary gland releases luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
• LH stimulates the cells of Leydig in the testes to secrete testosterone

Testosterone/FSH Initiates Change

• FSH together with testosterone stimulates sperm formation
• Testosterone then initiates changes to the gonads (primary sexual characteristics), and other parts of the body (secondary sexual characteristics)

Initiating Puberty:

• In females, the pituitary gland releases follicle-stimulating hormone (FSH), stimulating the follicles in the ovaries to produce estrogen
• In males, the pituitary gland releases luteinizing hormone (LH) that stimulates the cells of Leydig to secrete testosterone

Further Process of Initiation of Puberty:

• Furthermore, in males the pituitary gland also releases follicle stimulating hormone (FSH), which, combined with testosterone, will stimulate sperm formation
• Testosterone and estrogen then initiate changes the gonads (primary sexual characteristics) and other parts of the body (secondary sexual characteristics)

Haploid Gametes Formation

• A diploid individual is produced with its own genetic combination from both parents, two haploid gametes must fuse
• The gametes from the male and female are produced in the gonads

Spermatogenesis

• Sperm are formed from the germinal epithelial cells lining the seminiferous tubules of the testes
• This starts during puberty and continues throughout male's lifetime
• This process is controlled by hormones.

Oogenesis

• Ova are formed from the germinal epithelial cells forming the ovaries outer layer
• This process is controlled by hormones
• The first stages of development occur before birth in ovaries of the female fetus
• Oogenesis starts in the fetus, continues via puberty and ends in menopause

Menstrual Cycle Overview

• It includes the uterine and ovarian cycles
• These cycles happen from puberty until menopause
• The endocrine system controls both cycles
• These cycles last approximately 28 days in a human female

Initiating Ovarian Cycles

• The release of FSH from the pituitary gland triggers the cycles, starting on day 2 of the cycle

Components of Ovarian Cylces:

• Development of Graafian follicle occurs from day 1-14

Development of the Graafian Follicle

• FSH stimulates development of a primary follicle into a Graafian follicle from the ovaries

Estrogen Release

• The developed follicle will release estrogen till ovulation

Functions of Estrogen

• The secretion of estrogen starting is initiated from day 6
• It inhibits FSH production so that no more follicles mature
• Promotes development of the female secondary sexual characteristics (ex: mammary glands, curves, skin etc;)
• It stimulates the fluid and blood of the uterus wall
• Therefore its function is preparing endometrium for embedding

Ovulation Details

• Day 14 is ovulation. The mature Graffian follicle starts to grows and bursts at the ovary surface.
• Next, the matured follicle releases the ovum
• The high levels of Luteinizing Hormone (LH) from the pituitary gland will trigger ovulation
• The hormone, produced from the pituitary around days 12-13, because of high estrogen levels is called lutenizing hormone
• LH's function is to trigger Ovulation and develop the corpus luteum

Ovum Lifespan

• The ovum only lives for between 24 to 36 hours
• If the ovum isn't fertilized during this period it will disintegrate

Formation of the Corpus Luteum

• This lasts for about 10 to 12 days
• The corpus luteum will degenerate if fertilization has not taken place, this will lead to the production of progesterone ceasing
• Next, FSH production will begin leading to the process starting again

Importance of Corpus Luteum and Progesterone for Pregnancy

• Corpus luteum will still degenerate for the first three months of pregnancy and then the placenta takes over the role of progesterone secretion
• Progesterone: production is initiated in corpus luteum, functions include: inhibiting of FSH production, preparing the uterus, controlling implementation, maintenance of endometrium and preventing miscarriage

Uterine Cycle

• Endometrium undergoes hormone regulated changes
• The endometrium is vessels and glands
• After ovulation the uterus must be prepared for implantation
• Hence, maintaining and thickening of estrogen and progesterone is maintained

Endometrial and Uterine function

• in the event of not fertilization = the endometrial will breakdown and discards the egg
• Menstruations is the process of endometrial break down and egg discardal
• Normally it takes about 4-6 days to complete
• After this the endometrium will start to thicken again