Chapter 28

The Reproductive Systems

 

Lecture Outline

INTRODUCTION

•      Sexual reproduction is a process in which organisms produce offspring by means of germ cells called gametes.

•      The organs of reproduction are grouped as gonads (produce gametes and secrete hormones), ducts (transport, receive, and store gametes), and accessory sex glands (produce materials that support gametes).

•      Gynecology is the specialized branch of medicine concerned with the diagnosis and treatment of diseases of the female reproductive system. Urology is the study of the urinary system but also includes diagnosis and treatment of diseases and disorders of the male reproductive system.

Chapter 28
The Reproductive Systems

•      Sexual reproduction produces new individuals

–   germ cells called gametes (sperm & 2nd oocyte)

–   fertilization produces one cell with one set of chromosomes from each parent

•      Gonads produce gametes & secrete sex hormones

•      Reproductive systems

–   gonads, ducts, glands & supporting structures

–   Gynecology is study of female reproductive system

–   Urology is study of urinary system & male reproductive system

MALE REPRODUCTIVE SYSTEM

•      The male structures of reproduction include the testes, a system of ducts (ductus epididymis, ductus deferens, ejaculatory duct, urethra), accessory sex glands (seminal vesicles, prostate gland, bulbourethral glands), and several supporting structures, including the penis (Figure 28.1).

Male Reproductive System

•       Gonads, ducts, sex glands & supporting structures

•       Semen contains sperm plus glandular secretions

Scrotum

•      The scrotum is a cutaneous outpouching of the abdomen that supports the testes; internally, a vertical septum divides it into two sacs, each containing a single testis (Figures 28.2).

•      Skin contains dartos muscle causes wrinkling

•      Temperature regulation of testes

–   sperm survival requires 3 degrees lower temperature than core body temperature

–   cremaster muscle in spermatic cord

•   elevates testes on exposure to cold & during arousal

•   warmth reverses the process

Scrotal Sacs, Dartos & Cremaster Mm

Testes

•      The testes, or testicles, are paired oval-shaped glands (gonads) in the scrotum (Figure 28.3).

 

•      The testes contain seminiferous tubules (in which sperm cells are made) (figure 28.5).

•      Embedded among the spermatogenic cells in the tubules are large Sertoli cells or sustentacular cells (Figure 28.4).

–   The tight junctions of these cells form the blood-testis barrier that prevents an immune response against the surface antigens on the spermatogenic cells.

Testes

•      Paired oval glands measuring 2 in. by 1in.

•      Surrounded by dense white capsule called tunica albuginea

–   septa form 200 - 300 compartments called lobules

•      Each is filled with 2 or 3 seminiferous tubules where sperm are formed

Tunica Vaginalis

•      Piece of peritoneum that descended with testes into scrotal sac.

•      Facilitates movement of testes within scrotum

Descent of Testes

•      Develop near kidney on posterior abdominal wall

•      Descends into scrotum by passing through inguinal canal

–   during 7th month of fetal development

•      Failure of  the testes to descend is called cryptorchidism; it may  involve one or both testes.

 

Cryptorchidism

•      Testes do not descend into the scrotum

•      3% of full-term & 30% of premature infants

•      Untreated bilateral cryptorchidism results in sterility & a greater risk of testicular cancer

•      Descend spontaneously 80% of time during the first year of life

–   surgical treatment necessary before 18 months

 

Testes - cells

•      The sustentacular cells

–   nourish spermatocytes, spermatids, and spermatozoa

–   mediate the effects of testosterone and follicle stimulating hormone on spermatogenesis

–   phagocytose excess spermatids cytoplasm as development proceeds

–   control movements of spermatogenic cells and the release of spermatozoa into the lumen of the seminiferous tubule

–   secrete fluid for sperm transport and the hormone inhibin.

•      The Leydig cells or interstitial endocrinocytes found in the spaces between adjacent seminiferous tubules secrete testosterone (Figure 28.4).

Spermatogenesis - Introduction

•      Spermatogenesis is the process by which the seminiferous tubules of the testes produce haploid sperm. (Review the discussion of reproductive cell division in Chapter 3.  Take special note of Figures 3.33 and 3.34)

•      It begins in the diploid spermatogia (stem cells). They undergo mitosis to reserve future stem cells and to develop cells (2n primary spermatocytes) for sperm production.

Formation of Sperm

Spermatogenesis - Introduction

•      The diploid primary spermatocytes undergo meiosis I forming haploid secondary spermatocytes.

•      Meiosis II è haploid spermatids.

–   The spermatids are connected by cytoplasmic bridges.

•      The final stage of spermatogenesis is spermiogenesis which is the maturation of the spermatids into sperm.

•      The release of a sperm from its connection to a Sertoli cell is known as spermiation.

Review

•      Review of Meiosis

Chromosomes in Somatic Cells & Gametes

•      Somatic cells (diploid cells)

–   23 pairs of chromosomes for a total of 46

•   each pair is homologous since contain similar genes in same order

•   one member of each pair is from each parent

–   22 autosomes & 1 pair of sex chromosomes

•   sex chromosomes are either X or Y

•   females have two X chromosomes

•   males have an X and a smaller Y chromosome

•      Gametes (haploid cells)

–   single set of chromosomes for a total of 23

–   produced by special type of division: meiosis

 

 

Meiosis I -- Prophase I

•       Chromosomes become visible, mitotic spindle appears, nuclear membrane & nucleoli disappear

•       Events not seen in prophase of Metaphase or Meiosis II

–    synapsis

•    all copies of homologous chromosomes pair off forming a tetrad

–    crossing-over

•    portions of chromatids are exchanged between any members of the tetrad

•    parts of maternal chromosomes may be exchanged with paternal ones

–    genetic recombination produces gametes unlike either parent

Exchange of Genetic Material

•       Chromosomes are exchanged between chromatids on homologous chromosomes

Meiosis I -- Metaphase I, Anaphase I & Telophase I

•       In metaphase I, homologous pairs of chromosomes line up along metaphase plate with attached microtubules

•       In anaphase I, each set of homologous chromatids held together by a centromere are pulled to opposite ends of the dividing cell

•       Telophase I and cytokinesis are similar to mitotic division

•       Result is 2 cells with haploid number of chromosomes

 

 

Meiosis II

•       Consists of 4 phases : prophase II, metaphase II, anaphase II and telophase II

•       Similar steps in this cellular process as in mitosis

–    centromeres split

–    sister chromatids separate and move toward opposite poles of the cell

•       Each of the daughter cells produced by meiosis I divides during meiosis II and the net result is 4 genetically unique haploid cells or gametes.

Spermatagonium

Location of Stages of Sperm Formation

•       Seminiferous tubules contain

–    all stages of sperm development: spermatogonia, primary spermatocyte, secondary spermatocyte, spermatid, spermatozoa

–    supporting cells called sertoli cells

•       Leydig cells in between tubules secrete testosterone

Supporting Cells of Sperm Formation

•       Sertoli cells -- extend from basement membrane to lumen

–    form blood-testis barrier

–    support developing sperm cells

–    produce fluid & control release of sperm into lumen

–    secrete inhibin which slows sperm production by inhibiting FSH

Spermatogenesis

•      Spermatogonium (stem cells) give rise to 2 daughter cells by mitosis

•      One daughter cell kept in reserve -- other becomes primary spermatocyte

•      Primary spermatocyte goes through meiosis I

–   DNA replication

–   tetrad formation

–   crossing over

 

Spermatogenesis

•       Secondary spermatocytes are formed

–    23 chromosomes of which each is 2 chromatids joined by centromere

–    goes through meiosis II

•       4 spermatids are formed

–    each is haploid & unique

–    all 4 remain in contact with cytoplasmic bridge

–    accounts for synchronized release of sperm that are 50% X chromosome & 50% Y chromosome

Spermiogenesis & Spermiation

•      Spermiogenesis = maturation of spermatids into sperm cells

•      Spermiation = release of a sperm cell from a sertoli (sustentacular) cell

Sperm Morphology (Figure 28.8)

•      Adapted for reaching & penetrating a secondary oocyte

•      Head contains DNA & acrosome (hyaluronidase and proteinase enzymes)

•      Midpiece contains mitochondria to form ATP

•      Tail is flagellum used for locomotion

 

•      They are produced at the rate of about 300 million per day and, once ejaculated, have a life expectancy of 48 hours within the female reproductive tract.

 

Hormonal Control of the Testes

•      GnRH (gonadotropin releasing hormone) stimulates anterior pituitary secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

–   LH assists spermatogenesis and stimulates production of testosterone.

–   FHS initiates spermatogenesis

 

•      Figure 28.7 summarizes the hormonal relationships of the hypothalamus, pituitary gland, and testes.

Hormonal Control of Spermatogenesis

•      Puberty

–   hypothalamus increases its stimulation of anterior pituitary with releasing hormones (GnRH)

–   anterior pituitary increases secretion LH & FSH

•      LH stimulates Leydig cells to secrete testosterone

–   an enzyme in prostate & seminal vesicles converts testosterone into dihydrotestosterone (DHT is more potent.)

•      FSH stimulates spermatogenesis

–   with testosterone, stimulates sertoli cells to secrete androgen-binding protein (keeps hormones levels high)

–   testosterone stimulates final steps spermatogenesis

 

Hormonal Control of Spermatogenesis

•      Testosterone

–   controls the growth, development, functioning, and maintenance of sex organs

–   stimulates bone growth, protein anabolism, and sperm maturation

–   stimulates development of male secondary sex characteristics.

–   Negative feedback systems regulate testosterone production (Figure 28.8).

•      Inhibin is produced by sustentacular (Sertoli) cells. Inhibition of FSH by inhibin helps to regulate the rate of spermatogenesis.

 

Hormonal Effects of Testosterone

•      Testosterone & DHT bind to receptors in cell nucleus & change genetic activity

•      Prenatal effects è male genitalia

•      At puberty, final development of 2nd sexual characteristics and adult reproductive system

–   sexual behavior & libido

–   male metabolism (bone & muscle mass heavier)

–   deepening of the voice

Control of Testosterone Production

•      Negative feedback system controls blood levels of testosterone

•      Receptors in hypothalamus detect increase in blood level

•      Secretion of GnRH slowed

•      Anterior pituitary (FSH & LH hormones) slowed

•      Leydig cells of testes slowed

•      Blood level returns normal

Effect of Inhibin Hormone

•      Sperm production is sufficient

–   sertoli cells release inhibin

–   inhibits FSH secretion by the anterior pituitary

–   decreases sperm production

•      Sperm production is proceeding too slowly

–   less inhibin is released by the sertoli cells

–   more FSH will be secreted

–   sperm production will be increased

Reproductive System Ducts in Testes

•      The duct system of the testes includes the seminiferous tubules, straight tubules, rete testis, efferent ducts,  and ductus epididymis.

Pathway of Sperm Flow through the Ducts of the Testis

•       Seminiferous tubules

•       Straight tubules

•       Rete testis

•       Efferent ducts

•       Ductus epididymis

•       Ductus (vas) deferens

 

Epididymis

•      The epididymis is a comma-shaped organ that lies along the posterior border of the testis (Figures 28.3a).

•      Sperm are transported out of the testes through the efferent ducts in the epididymis which empty into a single tube called the ductus epididymis.

•      The ductus epididymis is lined by stereocilia and is the site of sperm maturation and storage; sperm may remain in storage here for at least a month, after which they are either expelled or degenerated and reabsorbed.

Epididymis

•      1.5in long along posterior border of each testis

–   Head, body and tail region

–   Multiple efferent ducts become a single ductus epididymis in the head region

•   20 foot tube if uncoiled

–   Tail region continues as ductus deferens

Histology of the Epididymis

•      Ductus epididymis

–   lined with pseudostratified ciliated columnar epithelium

–   layer of smooth muscle

•      Site of sperm maturation

–   motility increases over 2 week period

•      Storage for 1-2 months

•      Propels sperm onward

Anatomy

•      The ductus (vas) deferens, or seminal duct, stores sperm and propels them toward the urethra during ejaculation (Figures 28.3a).

•      The spermatic cord is a supporting structure of the male reproductive system, consisting

–   ductus deferens

–   testicular artery

–   autonomic nerves

–   veins and lymphatic vessels

–   cremaster muscle (Figure 28.2).

Spermatic Cord

•       All structures passing to and from the testes

–    testicular artery

–    pampiniform plexus of veins

–    autonomic nerves

–    lymphatic vessels

–    ductus (vas) deferens

–    cremaster muscle

 

Anatomy

•      The ejaculatory ducts are formed by the union of the ducts from the seminal vesicles and ducti deferens; their function is to eject spermatozoa into the prostatic urethra (Figure 28.9).

•      The male urethra is the shared terminal duct of the reproductive and urinary systems which serves as a passageway for semen and urine. The male urethra is subdivided into three portions: prostatic, membranous, and spongy (cavernous) (Figures 28.1 and 26.22).

Ejaculatory Ducts

•       Formed from duct of seminal vesicle & ampulla of vas deferens

•       About 1 inch long

•       Adds fluid to prostatic urethra just before ejaculation

Ductus (Vas) Deferens

•      Pathway of 18 inch muscular tube

–   ascends along posterior border of epididymis

–   passes up through spermatic cord and inguinal ligament

–   reaches posterior surface of urinary bladder

–   empties into prostatic urethra with seminal vesicle

•      Lined with pseudostratified columnar epithelium & covered with heavy coating of muscle

–   convey sperm along through peristaltic contractions

–   stored sperm remain viable for several months

 

Urethra

•       8 inch long passageway  for urine & semen

–    Prostatic urethra (1 inch long)

–    Membranous urethra (passes through UG diaphragm )

–    Penile (spongy) urethra (through corpus spongiosum)

Vasectomy

•      Male sterilization

•      Vas deferens cut & tied off

•      Sperm production continues

•      Sperm degenerate

•      100% effective

•      40% reversible

 

Inguinal Canal & Inguinal Hernias

The inguinal canal is 2 inch long tunnel through (i.e., weak spot in) the
3 muscles of the anterior abdominal wall

•       originates at deep inguinal ring and ends at superficial ring

•       Hernia: a rupture or separation of a portion of the abdominal wall resulting in the protrusion of a part of an organ (most commonly the small or large intestine).

–    Indirect hernia -- loop of intestine protruding through deep ring

–    Direct hernia -- loop of intestine pushes through posterior wall of inguinal canal

Accessory Sex Glands

•      The seminal vesicles secrete an alkaline, viscous fluid that contains fructose, prostaglandins, and clotting proteins (Figure 28.9).

•      The alkaline nature of the fluid helps to neutralize acid in the male urethra and female reproductive tract.

•      The fructose is for ATP production by sperm.

•      Prostaglandins contribute to sperm motility and viability.

•      Semenogelin is the main protein that causes coagulation of semen after ejaculation.

Accessory Sex Glands

Seminal Vesicles

 

•       Pair of pouchlike organs found posterior to the base of bladder

•       Alkaline, viscous fluid

–    neutralizes vaginal acid & male urethra

–    fructose

–    prostaglandins

–    coagulation proteins

 

The prostate gland (Figure 28.9)

•      Is a donut shaped gland about the size of a golf ball which is inferior to the urinary bladder and surrounds the prostatic urethra.

•      It secretes a milky, slightly acidic fluid that contains:

–   citric acid, which can be used by sperm for ATP production

–   acid phosphatase

–   several proteolytic enzymes, including:

•   prostate-specific antigen (PSA), pepsinogen, lysozyme, amylase, and hyaluronidase which liquefy coagulated semen.

•      Prostatitis is a common group of disorders which may be characterized by symptoms such as difficult urination, urinary frequency, and pain; or which may be asymptomatic.

Prostate Gland

•      Single organ

–   size of chestnut

–   inferior to bladder

–   pH 6.5 fluid

–   citric acid

–   enzymes for seminal liquefaction

•      Many duct openings

•      Enlarges with age

Bulbourethral or Cowper’s Glands

•      The bulbourethral (Cowper’s) glands

–    mucus for lubrication and an alkaline substance that neutralizes acid (Figure 28.9).

 

Bulbourethral or Cowper’s Glands

•      Paired, pea-sized gland within the urogenital diaphragm

•      alkaline mucous

•      connects to spongy urethra

 

 

 

Secretions - Summary

Semen (seminal fluid) is a mixture

•      spermatozoa and accessory sex gland secretions that provides the fluid in which spermatozoa are transported, provides nutrients, and neutralizes the acidity of the male urethra and female vagina

•      antibiotic, seminal plasmin, and prostatic enzymes that coagulate and then liquefy semen to aid in its movement through the uterine cervix.

 

Once ejaculated, liquid semen coagulates within 5 minutes due to the presence of clotting proteins from the seminal vesicles.  After about 10-20 minutes, semen re-liquifies because PSA and other proteolytic enzymes produced by the prostate gland break down the clot.

Semen Statistics

•       Mixture of sperm &