REPRODUCTIVE SYSTEM

• designed to facilitate the process of human sexual reproduction

• the reproductive system is a collection of internal and external organs — in both males and females — that work together for the purpose of procreating

• due to its vital role in the survival of the species, many scientists feel that the reproductive system is among the most important systems in the entire body

• of the body’s major systems, the reproductive system is the one that differs most between sexes, and the only system that does not function until puberty

• the male reproductive system is responsible for delivering sperm to the female reproductive system

Gametogenesis

• the production of sex cells or gametes and the process of fertilization that eventually leads to the development of human embryo

MALE REPRODUCTIVE SYSTEM

• the male reproductive system performs the following functions:

1. secretion of the male sex hormones

2. production of sperm cells

3. transfer of sperm cells

• the male gonads are the testes (singular: testis) hanging in the scrotum

• sperm production requires a slightly lower temperature than the human body that is why the scrotum hangs loosely outside the body cavity

• however, when the testis fails to descend, it leads to sterility because of the inhibiting effect of normal body temperature on sperm development

• in males, the reproductive organs include the penis, the testes, a number of storage and transport ducts, and some supporting structures

• the two oval-shaped testes (also called testicles) lie outside the body in a pouch of skin called the scrotum, where they can maintain the optimum temperature for sperm production – approximately 5° F, lower than body temperature

• testes are oval-shaped glands responsible for the manufacture of sperm and the sex hormone testosterone

• from each testis, sperm pass into a coiled tube – the epididymis – for the final stages of maturation

INSIDE THE SCROTUM

• the scrotum contains two testes (testicles) where sperm are manufactured within tubes called seminiferous tubules, and the two epididymises where sperm are stored

• unlike female egg maturation, which occurs in cycles and ceases at menopause, sperm production is continuous, reducing gradually with age

• each epididymis is a tube about 20 feet long, which is tightly coiled and bunched into a length of just 2 inches

SPERMATOGENESIS

• the process of producing sperm cells

• takes place in coiled tubules called seminiferous tubules in the testes

MAKING SPERM

• each testis is a mass of more than 800 tightly looped and folded vessels known as seminiferous tubules

• inside each tubule, sperm begin as blob-like cells called spermatogonia lining the inner wall

• these pass through a larger stage, as primary spermatocytes, then become smaller as secondary spermatocytes, and begin to develop tails as spermatids

• as all of this happens, they move steadily towards the middle of the tubule

• the spermatids finally develop into ripe sperm with long tails

• thousands of sperm are produced every second, each taking about two months to mature

DIFFERENCE OF SEMEN AND SPERM

• semen, also known as seminal fluid, is much more than just sperm

• sperm is only about 5 to 10% of any given male single ejaculation and the rest is fructose (aka sugar), fatty acids, and proteins to nourish the sperm during their journey

SPERM COUNT

• a man will produce roughly 525 billion sperm during his whole lifetime and close to 1 billion per month

• there are around 200 to 500 million sperm in an average in a single male human ejaculation

SPERM CELL

• a sperm is about 1/500 inch long, but most of this is a tail

• the sperm head is only 1/5000 inch, about the same size as a red blood cell

• sperm develop in the testes and consist of a head, a midpiece, and a tail

• the head contains the nucleus with densely coiled chromatin fibers (chromosomes), with a front section – the acrosome that contains enzymes for penetrating the female egg

• the midpiece has a central filamentous core with many mitochondria spiraled around it, to give it energy to move the tail which propels it forward

PARTS OF THE MALE REPRODUCTIVE SYSTEM

• Testis (plural testes)

  • produces sperm cells

• Scrotum

  • sac of skin that holds the testis

• Seminiferous Tubules

  • highly coiled tubules where the sperm are formed

• Epididymis

  • where the sperm are temporarily stored

• Penis

  • deposits sperms into the vagina during mating

• Vas deferens (tube)

  • carries sperm from testes to urethra

• Urethra

  • carries sperm and urine out of the body

• Glands

  • provide liquid in which sperm can swim

    • Seminal vesicle – secretes a fluid that makes up most of the components of the semen

    • Prostate gland – secretes a slightly alkaline milky fluid that is discharged as part of the semen

    • Bulbourethral gland (Cowper’s gland) – secretes a thick and clear mucus that lubricates and neutralizes any trace of acidic urine in the urethra

FEMALE REPRODUCTIVE SYSTEM

• the female reproductive system has the following functions:

1. produces female sex cells

2. receives sperm cells from the male

3. nurtures the development of and provides nourishment for the new individual

• the female reproductive system includes external and internal genitalia

• the vulva and its structures form the external genitalia

• the internal genitalia includes a three-part system of ducts: the uterine tubes, the uterus, and the vagina

• this system of ducts connects to the ovaries, the primary reproductive organs

• the ovaries produce egg cells and release them for fertilization

• fertilized egg develop inside the uterus

• unlike the male, the female reproductive organs are located entirely inside the body

• from puberty, their function is to ripen and release an egg at regular intervals, and, if the egg is fertilized, to protect and nourish the embryo and fetus

• no eggs are manufactured after birth – a female is born with a full set

REPRODUCTIVE TRACT

• the female reproductive glands (ovaries) are located within the abdomen

• this release occurs roughly once a month as part of the menstrual cycle

• the ripe egg travels along the fallopian tube to the uterus, the muscular sac in which it develops into an embryo and then fetus

EGG CELLS FROM THE OVARIES MOVE THROUGH THE UTERINE TUBES

• the uterine tubes (also called fallopian tubes or oviducts) connect the ovaries to the uterus

• the walls of each tube have an external serous layer, a middle muscular layer, and an internal mucous layer that is continuous with the inner lining of the uterus

• each uterine tube can be divided into three parts:

1. infundibulum

2. isthmus connects with the uterus

3. a dilated portion, the ampulla, curves over the ovary

• egg fertilization usually occurs in the ampulla, the eggs then travel through the isthmus to the uterus

THE VAGINA: A TUNNEL WITH THREE CORE FUNCTIONS

• the vagina extends down from the cervix, the lower part of the uterus, to the vestibule, which is part of the vulva and the external genitalia

• it sits behind the bladder and in front of the rectum

• an inner mucous membrane lines the smooth muscle walls of the vagina

• this lining, like the inner layer of the uterine tubes, is continuous with the mucous lining of the uterus

• the vagina has three core functions:

1. carries menstrual flow outside the body

2. receives the male penis during sexual intercourse

3. serves as a birth canal during labor

OVULATION

• an ovary contains thousands of immature egg cells

• during each menstrual cycle, follicle-stimulating hormone (FSH) causes one egg to begin development; this takes place inside a primary follicle

• the follicle enlarges as its cells proliferate and begins to fill with fluid, becoming a secondary follicle that moves to the ovary’s surface

• it also increases its production of the hormone estrogen

• a surge of luteinizing hormone (LH) causes the follicle to rupture and release the ripe egg – this is ovulation

• the lining of the empty follicle thickens into a corpus luteum – a temporary source of hormones

PARTS OF THE FEMALE REPRODUCTIVE SYSTEM

• Ovary

  • produces egg cells

  • slightly flattened bean-shaped bodies, each about two to five cm in length and two to three cm in width

• Follicles

  • from these the female sex cells, egg cells, or ova develops

• Oviduct

  • fallopian tube or uterine tube

  • site of egg fertilization

  • passageway through which the ovum passes from the ovary to the uterine cavity

• Uterus

  • serves as the site of egg implantation

  • where the fertilized egg develops

• Vagina

  • receives the penis of the male during mating

FERTILIZATION: A SPERM AND AN EGG FORM A ZYGOTE

• union of two kinds of gametes resulting to the formation of a fertilized egg called zygote

• the sperm and the egg are called gametes

• they each contain half of the genetic information necessary for reproduction

• when a sperm cell penetrates and fertilizes an egg, that genetic information combines

• the 23 chromosomes from the sperm pair with 23 chromosomes in the egg, forming a 46-chromosome cell called a zygote

• the zygote starts to divide and multiply

• as it travels toward the uterus it divides to become a blastocyst, which will burrow into the uterine wall

EMBRYO

• refers to the earliest stage of development of an organism into which the zygote develops through a series of cell divisions

THE ZYGOTE BECOMES AN EMBRYO: DEVELOPMENT PRIOR TO AND DURING IMPLANTATION

• the blastocyst attaches to the wall of the uterus and gradually implants itself into the uterine lining

• during implantation, its cells differentiate further

• at day 15 after conception, the cells that will form the embryo become an embryonic disc, other cells begin to form support structures

• the yolk sac, on one side of the disc, will become part of the digestive tract

• on the other side, the amnion fills with fluid and will surround the embryo as it develops

• other cells groups initiate the placenta and umbilical cord, which will bring in nutrients and eliminate waste

OOGENESIS

• formation of egg cells or ova

• takes place in numerous round structures called follicles

WHAT HAPPENS WHEN THE EGG IS NOT FERTILIZED?

• deterioration of corpus luteum

• maturation of a new follicle for the next reproductive cycle of the female

• breaking down of the uterus lining which is discharged as menstrual flow

MENSTRUATION

• a discharging of blood, secretions, and tissue debris from the uterus that occurs in non-pregnant females

GONAD

• primary male and female reproductive organs

MALE ANATOMY

MALE REPRODUCTIVE HORMONES

CELLS OF THE TESTES

• Leydig (interstitial) cells

  • synthesize hormones and produce testosterone in the presence of LH

• Sertoli cells

  • synthesize sperm (spermatogenesis)

  • nurse cell of the testicles that is part of seminiferous tubules

ANDROGEN

• male sexual and reproductive function

• secondary male characteristics

• bone and muscle development and metabolism

• released from testes

TESTOSTERONE

• primary sex hormone and anabolic steroids in male

• development of male reproductive tissues (testes and prostate)

• released from testes

PRIMARY SEXUAL CHARACTERISTICS

• associated with the reproductive system

• development of vas deferens, external reproductive structures

• stimulate spermatogenesis: sperm production in sertoli cells (lifetime process)

SECONDARY SEX CHARACTERISTICS

• not directly related to the reproductive system

• develops characteristics at puberty

  • deepening of voice

  • facial and pubic hair

  • muscle growth

  • increased secretion of body oils (associated with body odor)

MALE REPRODUCTIVE HORMONES

1. Hypothalamus: Gonadotropin-releasing hormone (GnRH)

2. Anterior Pituitary: Gonadotropic hormones FSH and LH

3. Sertoli cells: FSH stimulates spermatogenesis

4. Leydig cells: LH stimulates hormone secretion

5. Androgen and Testosterone: affects primary and secondary sexual characteristics

GONADOTROPIC HORMONES

• two types:

  • Follicle-stimulating hormone (FSH)

  • Luteinizing hormone (LH)

• peptide hormones

• present in both male and female

• plays an important role for reproduction

GONADOTROPINS IN MALES

• FSH

  • act on Sertoli cells to increase spermatogenesis (nontropic)

• LH

  • stimulate Leydig cells to make androgens (tropic)

MALE REPRODUCTIVE HORMONE: NEUROENDOCRINE PATHWAY – NONTROPIC

MALE REPRODUCTIVE HORMONE: NEUROENDOCRINE PATHWAY – TROPIC

MALE REPRODUCTIVE HORMONAL CONTROL

NEGATIVE FEEDBACK

• testosterone negatively feedback to the hypothalamus and pituitary to decrease the production of GnRH and LH

FEMALE REPRODUCTIVE HORMONES

ESTROGEN

• female sex hormones

• three compounds

  • Estriol

  • Estradiol – predominant

  • Estrone

• develops secondary sexual characteristics

  • breast development

  • wider hips

  • fat deposition

OVARY FOLLICLE CELLS

• primary oocyte

  • egg that can be fertilized by sperm

• granulosa cells

  • provide nutrients for primary oocyte

OVARIAN CYCLE REGULATION: NEUROENDOCRINE PATHWAY

GONADOTROPIN-RELEASING HORMONE (GnRH)

• GnRH levels not shown in graph or right but correlates to the rise in LH/FSH levels

• released in slow waves during follicular phase

• rate of release is increased (peaked) when approaching ovulation

• rate decreases greatly during luteal phase

GONADOTROPINS IN FEMALES

• FSH

  • stimulates growth of follicle (maturation) in follicular phase

• LH

  • luteinizes the follicle into the corpus luteum

  • induces ovulation

  • matures the corpus luteum in luteal phase

OVARIAN CYCLE

• Follicular phase

  • growth of several follicles but only one matures while others disintegrate

  • egg in follicle enlarges

  • coat of follicle thickens

  • fluid-filled cavity inside follicle develops and bulges

• Ovulation

  • follicle and wall of ovary rupture

  • egg is released

• Luteal phase

  • follicular tissue develops into corpus luteum

  • corpus luteum secretes female hormones

OVULATION

FEMALE REPRODUCTIVE HORMONE

PROGESTERONE

• corpus luteum secretes progesterone (and some estrogens)

• correlates to thickening of endometrium

  • in order to accept fertilized egg and enable implantation and growth

• if no implantation then corpus luteum disintegrates

  • progesterone isn’t secreted

• decreased progesterone levels leads to:

  • stop of endometrium growth

  • endometrium breaks down (menstruation)

MENSTRUAL CYCLE

• day 1 = first day of menstruation

• menstrual flow phase

  • sloughing of endometrial lining

  • menstrual bleeding

• Proliferative phase

  • endometrium regenerates and thickens

• Secretory phase

  • endometrium continues to thicken

  • becomes more vascularized (blood vessels)

  • develops glands to secrete fluid rich in glycogen

FOLLICLE

• granulosa cells of follicle secretes estrogen

ESTROGEN REGULATION: HIGH LEVELS

• high estrogen: positive feedback on LH & FSH by stimulating GnRH

• estrogen surge from follicle during day 12-14

  • LH & FSH surge

  • results in ovulation

ESTROGEN REGULATION

• also responsible for the early thickening of the endometrium in the proliferative phase

ESTROGEN REGULATION: LOW LEVELS

• estrogen secreted at low levels during most of the cycle

• negative feedback on GnRH, LH, and FSH

ESTROGEN REGULATION

• corpus luteum secretes estrogen and progesterone

• both act together to negatively feedback on GnRH, LH & FSH

• prevents ovulation

DUAL ROLE OF ESTROGEN

• low estrogen concentration negative feedback

• high estrogen concentration positive feedback

FEMALE REPRODUCTIVE HORMONE CONTROL

OVERVIEW OF FEMALE REPRODUCTIVE CYCLES

HORMONAL CONTROL IN FOLLICULAR PHASE

• immature follicles have receptors for FSH but not LH

• FSH stimulate follicular growth

• granulosa cells of the growing follicles secrete estrogen

• low levels of estrogen negatively feedbacks on LH and FSH

HORMONAL CONTROL NEAR OVULATION

• estrogen surge

  • positive feedback on LH and FSH by stimulating GnRH

• mature follicle have receptors for LH

• LH induces ovulation

• estrogen also stimulates thickening of endometrium

HORMONAL CONTROL IN LUTEAL PHASE

• LH luteinizes remaining follicular tissue into corpus luteum

• corpus luteum secretes estrogen and progesterone

• both act together to negatively feedback on GnRH, LH & FSH

• corpus luteum disintegrates

• sharp decline in estrogen and progesterone

• negative feedback removed

  • secretion of GnRH, LH & FSH begins

• disintegration of endometrium

MENOPAUSE

• the time in a woman’s life when her period stops

• occurs around age 46-54

• ovaries lose responsiveness to gonadotropins

  • decline in estrogen production

  • cessation of ovulation and menstruation

FEMALE REPRODUCTIVE SYSTEM

• comparatively more complicated than male reproductive system

• monthly cycle until menopause (~12 to 50 yrs)

• one ovum produced per germ cell

FEMALE ANATOMY

HORMONES

• chemical messengers of the body

• important to maintain homeostasis

THE ROLE OF HORMONES IN FEMALE AND MALE REPRODUCTIVE SYSTEMS

• human reproductive cycles are controlled by the interaction of hormones from the hypothalamus and anterior pituitary with hormones from reproductive organs

• when the reproductive hormone is required, the hypothalamus sends a gonadotropin-releasing hormone or GnRH to the anterior pituitary gland

• this causes the release of follicle-stimulating hormones or FSH and luteinizing hormones or LH from the anterior pituitary gland into the blood

• the body must reach puberty in order for the adrenal glands to release the hormones that must be present for GnRH to be produced

REGULATION OF REPRODUCTIVE HORMONE SECRETION IN MALES

• FSH enters the testes and stimulates the Sertoli cells to begin facilitating spermatogenesis using negative feedback

• LH also enters the testes and stimulates the interstitial cells of Leydig to make and release testosterone into the testes and the blood

• a negative feedback system occurs in the male with rising levels of testosterone acting on the hypothalamus and anterior pituitary to inhibit the release of GnRH, FSH, and LH

• the hormone inhibin stops the release of GnRH and FSH, which will cause spermatogenesis to slow down

FUNCTIONS OF TESTOSTERONE

• stimulates spermatogenesis

• these secondary sex characteristics:

  • deepening of the vice

  • growth of facial, axillary, and pubic hair

  • beginnings of the sexual urge

REGULATION OF REPRODUCTIVE HORMONE SECRETION IN FEMALES

• the follicle-stimulating hormones (FSH) stimulates development of egg cells or ova

• follicle cells produce the hormone inhibin which stops FSH production

FUNCTIONS OF ESTROGEN

• assists in endometrial regrowth

• ovulation

• calcium absorption

• secondary sexual characteristics of females:

  • breast development

  • widening of the hips

  • shorter period necessary for bone maturation

FUNCTIONS OF PROGESTERONE

• assists in endometrial regrowth

• inhibition of the release of FSH and LH