Lesson 1 Chapter 27/28 – The Reproductive System

Lesson 1 Chapter 27/28 – The Reproductive System 1 Unit 11 Study Guide The Reproductive System The primary sex organs, or gonads, are the testes in the male and the ovaries in the female. The gonads produce gametes and secrete sex hormones. Other reproductive structures are accessory reproductive organs. The male manufactures sperm and delivers them to the female reproductive tract where fertilization may occur when the sperm fuses with an egg. The fertilized egg is the zygote which is the first cell of the new individual. The zygote begins the process of many rounds of mitosis and later differentiation will occur as body structures are formed. Anatomy of the Male Reproductive System The testes are housed in the scrotum which is located outside of the abdominopelvic cavity for reasons of sperm production. Sperm cannot be produced at core body temperature and the temperature in the scrotum is 3 degrees lower. The testes are divided into many wedge-shaped compartments called lobules which contain the seminiferous tubules. Sperm are produced in the seminiferous tubules. The tubules are surrounded by interstitial cells (Leydig cells) which produce testosterone. Lesson 1 Chapter 27/28 – The Reproductive System 2 Sperm leave the seminiferous tubules and travel to the epididymis. During the time in the epididymis the non-motile sperm gain the ability to swim. The sperm then pass into the ductus deferens or vas deferens which runs up through the spermatic cord and into the pelvic cavity. The end of this tubue expands and joins with the duct of the seminal vesicle to form the ejaculatory duct. This passes into the prostate gland and empties into the urethra. Accessory glands assist in the production of semen. They include the seminal vesicles, the bulbourethral glands, and the prostate gland. The seminal vesicles produce an alkaline fluid containing fructose (provides energy to sperm), coagulating enzymes, ascorbic acid, and prostaglandins (decrease viscosity of mucus at the entry of the uterus and stimulate reverse peristalsis at the uterus). Sperm and seminal fluid mix in the ejaculatory duct. The prostate gland produces an acidic fluid which contains citrate (nutrient) and several enzymes which activate the sperm. The bulbourethral glands (Cowper’s) produce a thick, clear mucus which is secreted into the urethra before ejaculation to neutralize traces of acidic urine. The urethra runs through the penis and is surrounded by a spongy network of vascular tissue. During an erection this tissue is flooded with blood which is temporarily unable to drain into the venous return. The influx of blood is stimulated by a parasympathetic reflex which promotes the release of nitric oxide locally. The NO causes the arterioles to dilate. Ejaculation of the sperm is accomplished by a sympathetic nervous system spinal reflex which causes three things: reproductive ducts and accessory glands contract and empty contents into the urethra, bladder sphincter muscle constricts preventing urine expulsion or reflux of semen, and smooth muscles of penis contract. This process is influenced by hormones. The hypothalamus stimulates the anterior pituitary to make follicle-stimulating hormone and luteinizing hormone. FSH stimulates spermatogenesis by causing sperm-producing cells to be receptive to testosterone's effects. LH binds to interstitial cells and causes them to secrete testosterone which serves as final trigger for sperm formation. Testosterone also targets the accessory reproductive organs and causes them to grow to adult size and function. Testosterone also stimulates the male secondary sex characteristics of enhanced hair growth in pubic, axillary, and facial regions, deepening of the voice, bone and skeletal muscle growth, increased basal metabolic rate, and increased sex drive. Adrenal glands also secrete testosterone (sex drive in females). Lesson 1 Chapter 27/28 – The Reproductive System 3 Outermost layer is a serous membrane called “tunica vaginalis” o Internal layer is white capsule called tunica albuginea 1. Testes: Descend at birth through inguinal canal. o Undescended testes is known as cryptorchidism, occurring in 30% of premature babies – increasing risk of cancer and infertility o Produces sperm in the seminiferous tubules in response to FSH o Sertoli cells nourish and support developing sperms that are located in the seminiferous tubules. o Produce testosterone in the interstitial cells in response to LH. 2. Scrotum: A sac that supports the testes outside the body o A slightly lower body temp is required for proper sperm production 3. Epididymis: An area of sperm storage and maturation. Sperm gain motility in this area. 4. Ductus Deferens/Vas Deferens: A tube that allows semen to pass from the epididymis to the urethra. 5. Ejaculatory duct: A tube connecting the ductus deferens to the penis. It regulates the movement of sperm into the urethra. 6. Seminal Vesicle: produces a mucous-like fluid that contains sugar fructose which provides energy for sperm Lesson 1 Chapter 27/28 – The Reproductive System 4 o Nourishes the sperm and increases their motility 7. Prostate Gland: produces an alkaline (basic) buffer to protect the sperm from the acidity of the vagina. o Increases motility 8. Cowper’s Gland: produces a fluid that cleans the urethra before ejaculation. 9. Urethra: A passage for both semen and urine Seminal Fluid: fluids from seminal vesicle + prostate gland + cowper’s gland + sperm = Semen Sperm pathway: seminiferous tubules  ejaculatory duct  prostatic urethra  membranous urethra  penile urethra Spermatozoon Mitochondria in midpiece produce ATP that generates the beating of the flagellum. Lesson 1 Chapter 27/28 – The Reproductive System The Penis Body is composed of 3 mass of tissues each surrounded by tunica albuginea. 3 cylindrical mass of tissues are: – Corpora cavernosa (dorsolateral) – Corpus spongiosum (mid ventral) 5 Lesson 1 Chapter 27/28 – The Reproductive System • contains penile urethra • ends as glans penis 6 In summary: I. In the male, the pituitary secretion of LH is controlled by negative feedback from testosterone, whereas the secretion of FSH is controlled by the secretion of inhibin from the testes. o The secretion of testosterone is relatively constant rather than cyclic, and it does not decline sharply at a particular age. II. Testosterone promotes the growth of soft tissue and bones before the epiphyseal discs have sealed; thus, testosterone and related androgens are anabolic steroids. o Testosterone is secreted by the interstitial cells of Leydig under stimulation of LH. o LH receptor proteins are located in the interstitial tissue. FSH receptors are located in the Sertoli cells within the seminiferous tubules. o The Leydig cells of the interstitial compartment and the Sertoli cells of the tubular compartment of the testes secrete autocrine regulatory molecules which allow these compartments to interact. III. Diploid spermatogonia in the seminiferous tubules undergo meiotic cell division to produce haploid sperm. o At the end of meiosis, four spermatids are formed. They develop into spermatozoa by a maturational process called spermiogenesis. o Sertoli cells in the seminiferous tubules are required for spermatogenesis. o At puberty, testosterone is required for the completion of meiosis, and FSH is required for spermiogenesis. Lesson 1 Chapter 27/28 – The Reproductive System 7 IV. Spermatozoa in the seminiferous tubules are conducted to the epididymis and drained from the epididymis into the ductus deferens. The prostate and seminal vesicles add fluid to the semen. V. Penile erection is produced by parasympathetic-induced vasodilation. Ejaculation is produced by sympathetic nerve stimulation of peristaltic contraction of the male sex accessory organs. Anatomy of the Female Reproductive System     Primary organ o Ovaries Accessory ducts and organs o Uterine tubes o Uterus  Cervix o Vagina External genitalia o Vulva  Vestibule o Clitoris Mammary glands Lesson 1 Chapter 27/28 – The Reproductive System 8 The ovaries produce the eggs and also the female sex hormones, estrogen and progesterone. The accessory ducts (uterine tubes, uterus, and vagina) transport or otherwise serve the needs of the reproductive cells and a developing fetus. Ovaries are held in place by ligaments. Embedded in the ovarian tissue are saclike follicles each of which consists of an immature egg (oocyte) surrounded by other cells. Each month a follicle undergoes development to produce a viable egg cell. When ovulation occurs the egg is cast into the peritoneal cavity. The uterine tubes distally branch out into fingerlike projections called fimbriae. They drape over the ovary and their cilia create currents in the peritoneal fluid which carries the oocyte toward the uterine tube. As the oocyte reaches the curve in the tube called the ampulla, fertilization may take place there if a sperm is present. The oocyte or the fertilized ovum (zygote) makes its way to the uterus. An unfertilized oocyte will eventually degenerate. The uterus functions to receive, retain, and nourish a fertilized ovum. The unfertilized ovum will degenerate. A fertilized ovum burrows into the endometrium (inner most layer of uterus). The middle layer, myometrium, contains smooth muscle cells, the outer perimetrium is the visceral peritoneum. If implantation does not occur part of the endometrium is shed during the monthly menstrual cycle. The cervix is the inferior opening of the uterus between uterus and vagina. Cervical glands produce mucus to protect the uterus from bacterial infections and also keep sperm out Lesson 1 Chapter 27/28 – The Reproductive System 9 unless it is in midcycle, when it becomes less viscous. After implantation of a zygote more mucus is produced to keep other sperm out of the uterus. The vagina is inferior to the cervix and opens to the exterior of the body between the urethra and rectum. The epithelial cells secrete glycogen which is metabolized to lactic acid, making the vagina normally have an acidic pH. This keeps the vagina free from infection but is also hostile to sperm. However, the sperm contain substances that allow them to resist the acidity of the vagina and to neutralize some of the mucus at the cervical opening in order for them to swim through the uterus, into the uterine tube and there potentially fertilize an oocyte. Males produce sperm throughout life beginning in puberty. A female's total supply of eggs is already in place when she is born. Each egg is suspended in the first part of meiosis (the series of divisions to make a gamete). At puberty each month one of these eggs is stimulated to finish the process and be released by ovulation. As estrogen levels rise during puberty it promotes oogenesis and follicle growth and development of the female reproductive tract. It causes a temporary growth spurt and development of secondary female sex characteristics such as breast growth, increase in subcutaneous fat, widening and lightening of the pelvis, growth of axillary and pubic hair, and other metabolic effects. Ovulation Lesson 1 Chapter 27/28 – The Reproductive System 10 Fallopian Tubes The fallopian tubes are a pair of muscular tubes that extend from the left and right superior corners of the uterus to the edge of the ovaries. The fallopian tubes end in a funnel-shaped structure called the infundibulum, which is covered with small finger-like projections called fimbriae. The fimbriae swipe over the outside of the ovaries to pick up released ova and carry them into the infundibulum for transport to the uterus. The inside of each fallopian tube is covered in cilia that work with the smooth muscle of the tube to carry the ovum to the uterus. – Infundibulum is open, funnel-shaped portion near the ovary • fimbriae are finger-like processes – Ampulla is central region of tube -widest – Isthmus is narrowest portion joins uterus Has 3 layers: – Mucosa = ciliated columnar epithelium with secretory cells provide nutrients & cilia move along ovum – Muscularis = circular & longitudinal smooth muscle • peristalsis helps move ovum down to the uterus – Serosa = outer serous membrane Lesson 1 Chapter 27/28 – The Reproductive System 11 Uterus The uterus is a hollow, muscular, pear-shaped organ located posterior and superior to the urinary bladder. Connected to the two fallopian tubes on its superior end and to the vagina (via the cervix) on its inferior end, the uterus is also known as the womb, as it surrounds and supports the developing fetus during pregnancy. The inner lining of the uterus, known as the endometrium, provides support to the embryo during early development. The visceral muscles of the uterus contract during childbirth to push the fetus through the birth canal. • • • Endometrium (innermost) – simple columnar epithelium – connective tissue and endometrial glands Myometrium (middle layer) – 3 layers of smooth muscle Perimetrium (outer layer) – part of the visceral peritoneum Lesson 1 Chapter 27/28 – The Reproductive System 12 Vagina The vagina is an elastic, muscular tube that connects the cervix of the uterus to the exterior of the body. It is located inferior to the uterus and posterior to the urinary bladder. The vagina functions as the receptacle for the penis during sexual intercourse and carries sperm to the uterus and fallopian tubes. It also serves as the birth canal by stretching to allow delivery of the fetus during childbirth. During menstruation, the menstrual flow exits the body via the vagina. • • • mucosal layer – stratified squamous epithelium muscularis layer is smooth muscle lies between urinary bladder and rectum Lesson 1 Chapter 27/28 – The Reproductive System 13 External Genitalia – Labia majora – folds of skin - equivalent to scrotum – Labia minora – smaller folds of skin encircling vestibule - urethral and vaginal openings – equivalent to penile urethra – Clitoris -- small mass of erectile tissue Perineum The region between the scrotum and the anus in males, and between the posterior vulva junction and the anus in females. • Diamond-shaped area between the thighs in both sexes – bounded by pubic symphysis anteriorly and coccyx posteriorly – Laterally – ischial tuberosities Mammary Gland Lesson 1 Chapter 27/28 – The Reproductive System 14