ch 27 male reproduction lecture presentation fall%2c 2011-1

8/4/2019 Ch 27 Male Reproduction Lecture Presentation Fall%2c 2011-1

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Chapter 27

The Reproductive System


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Reproductive System

Primary sex organs (gonads)testes in males,ovaries in females

Gonads produce sex cells called gametes andsecrete sex hormones

Accessory reproductive organsducts, glands,and external genitalia

Sex hormonesandrogens (males), and estrogenand progesterone (females)


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Reproductive System

Sex hormones play roles in:

The development and function of the reproductiveorgans

Sexual behavior and drives

The growth and development of many other organsand tissues


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Male Reproductive System

The male gonads (testes) produce testosterone and liewithin the scrotum

Sperm are delivered to the exterior through a system of

ducts: epididymis, ductus deferens, ejaculatory duct,and the urethra

Accessory sex glands:

Empty their secretions into the ducts during ejaculation

Include the ______ vesicles, _______ gland, and ________glands


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Male Reproductive System

Figure 27.1


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testis

Epididymis

Vas deferens

Ejaculatory duct

Testis and ducts

urethra


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Seminal vesicle

prostate

Bulbourethral gland

Accessory glands


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The Scrotum

Sac of skin and superficial fascia that hangsoutside the abdominopelvic cavity at the root ofthe penis

Contains paired testicles separated by a midlineseptum

Its external positioning keeps the testes 3C______ than core body temperature (needed forsperm production)


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Testes protection - Testicular Thermoregulation

Sperms are not produced at core body temperature

In the scrotum, the testes are kept 2-3

C cooler than in the pelvic cavity.This is essential for sperm production.

Cooling mechanisms

The cremaster muscle contains strips of the internal abdominal

oblique muscle (skeletal muscle) around the spermatic cord.

It can elevate or lower the testes.

The dartos muscle is a subcutaneous layer of smooth muscle thatwrinkles skin reducing surface area of scrotum. Can lifts testis upwards

The pampiniform plexus is an extensive network of veins thatsurround the testicular artery in the spermatic cord, keeping the testescooler countercurrent heat exchange that cools arterial blood enteringtestis


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The Scrotum

Figure 27.2


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Cremaster muscle


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Countercurrent Heat Exchanger


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Pampiniformplexus

C ti b t t ti d th


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Connection between testis and the

body The structures that connect

the testis with the body areenclosed within a connectivetissue sheath called thespermatic cord

Blood vessels Nerve fibers PNS and SNS

Vas deferens

Cremaster muscle


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The Testes

Each testis is surrounded by two tunics:

The tunica vaginalis, derived from peritoneum

The tunica albuginea, the fibrous capsule of thetestis

Septa divide the testis into 250-300 lobules, eachcontaining 1-4 seminiferous tubules

Seminiferous tubules- where ____ is produced


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The Testes

The sperm:

Leave the testis via efferent ductules

Enter the ______

Surrounding the seminiferous tubules areinterstitial cells that produce androgens liketestosterone


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The Testes

Figure 27.3a


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Testis histology - Seminiferous tubules


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Cells in the testes Seminiferous tubule

lumen lined with germinal epithelium consisting ofseveral layers ofgerm cells in the process of becomingsperm

Sustentacular (Sertoli)cells.

Between the seminiferous tubules are clusters ofinterstitial (Leydig) cells, the source oftestosterone.


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The Penis

Internal penisthe urethra and three cylindricalbodies of erectile tissue

Erectile tissuespongy network of connectivetissue and smooth muscle riddled with vascularspaces


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The Penis Erectionduring sexual excitement, the erectile

tissue fills with ______ causing the penis toenlarge and become rigid

Corpus spongiosumsurrounds the urethra andexpands to form the glans and bulb of the penis

Corpora cavernosapaired dorsal erectilebodies bound by fibrous tunica albuginea


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The Penis

Figure 27.4


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Figure 28.11

The Penis


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Corpus spongiosum

Corpuscavernous


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Spermatic Ducts Epididymis (head, body and tail)

6 m long coiled duct adhering to posterior of testis site of sperm maturation and storage (fertile for 60 days)

Ductus deferens/vas deferens (peristalsis during orgasm)

muscular tube 45 cm long passing up from scrotum through

inguinal canal to posterior surface of bladder Ejaculatory duct

2 cm duct formed from ductus deferens and seminal vesicleand passing through prostate to empty into urethra


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Epididymis

Nonmotile sperm enter, pass through its tubesand become motile

Upon ejaculation the epididymis contracts,expelling sperm into the __________


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Epididymis

Vas deferens Ejaculatoryduct


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The Epididymus and vas deferense

Figure 28.9


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https://reader009.{domain}/reader009/html5/0513/5af84ee10a7d2/5af84ef6b2ada.j

The Epididymis

E idid i f ti


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Epididymis functions The epididymis functions:

The duct of the epididymis has stereocilia that:Absorb testicular fluid

Pass nutrients to the sperm

Recycling center for damaged spermatozoa

Storage place for spermatozoa

Facilitate functional maturation preparing them forfertilization:

Plasma membrane changes, alterations inacrosomal membrane


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Ductus Deferens and Ejaculatory

Duct Runs from epididymis through the inguinal canal

into the pelvic cavity

terminus expands= ampulla, then joins the duct

of the seminal vesicle to form the _________ Propels sperm from the epididymis to thevas

deferens

________cutting and ligating the ductusdeferens, which is a nearly 100% effective formof birth control


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Male Reproductive System Gross

AnatomyVasectomy


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Urethra

Conveys both _______ and ________ (atdifferent times)

Consists of three regions

_____portion surrounded by the prostate

______lies in the urogenital diaphragm

_______runs through the penis and opens to the

outside at the external urethral orifice


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Prostatic

Membranous

penile

A Gl d S i l


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Accessory Glands: Seminal

Vesicles Lie on the posterior wall of the bladder and

secrete 60% of the volume of semen Semenalkaline fluid containing fructose, ascorbic

acid, coagulating enzyme (vesiculase), andprostaglandins

Join the ductus deferens to form the ejaculatoryduct

Sperm and seminal fluid mix in the ejaculatoryduct and enter the prostatic urethra duringejaculation

Accessory Glands: Seminal Vesicles


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Accessory Glands: Seminal Vesicles

Lie on the posterior wall of the bladder and secrete 60% of the volume ofsemen

Join the ductus deferens to form the ejaculatory duct

The composition of the gland secretions include:

High concentration of fructose that is easily metabolized byspermatozoa

Prostaglandins that stimulate smooth muscle contractions in both male

and female reproductive tract Fibrinogen that forms temporary clot within the vagina after ejaculation

When the inactive sperms mix with the seminal fluid they undergo the firststep of activation and the flagella start moving (in some book this is doneby the help of the prostate)

The secretion of the seminal gland are discharged into the ejaculatory ductunder the control of the sympathetic system


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SeminalVesicle


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Accessory Glands: Prostate Gland

Doughnut-shaped gland that encircles part ofthe ______ inferior to the bladder

Milky, slightly acid fluid, accounts for one-thirdof the semen volume

Plays a role in the activation of sperm

Enters the prostatic urethra during ejaculation


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http://www.mastersmensclinic.com/prostate.htm


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prostate


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Accessory Glands: Bulbourethral Glands

(Cowpers Glands)

Pea-sized glands inferior to the prostate

Produce thick, clear mucus prior toejaculation that neutralizes traces of acidicurine in the urethra


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Bulbourethral Gland


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Bulbourethralgland


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Semen Milky white, sticky mixture of sperm and

accessory gland secretions Provides a transport medium and nutrients

(_____), protects and activates sperm, and

facilitates their movement Prostaglandins in semen:

Decrease the viscosity of mucus in the cervix

Stimulate reverse ________ in the uterus

Facilitate the movement of sperm through thefemale reproductive tract


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Semen The hormone relaxinenhances sperm motility

The relative alkalinity of semen neutralizes the acidenvironment found in the male urethra and female

vagina

Clotting factors coagulate semen immediately afterejaculation, then fibrinolysin liquefies the sticky mass

Only 2-5 ml of semen are ejaculated, but it contains 50-130 million sperm/ml


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Male Sexual Response: Erection

During sexual arousal, a PNS reflex promotes therelease of nitric oxide

Nitric oxide causes erectile tissue to fill with blood Expansion of the corpora cavernosa:

Compresses their drainage veins

Retards blood outflow and maintains engorgement

The corpus spongiosum functions in keeping theurethra open during ejaculation


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Ejaculation

At ejaculation, sympathetic nerves serving thegenital organs cause: Reproductive ducts and accessory organs to contract

and empty their contentsThe bladder sphincter muscle to close, preventing

the expulsion of urine

Bulbospongiosus muscles to undergo a rapid seriesof contractions

Propulsion of semen from the urethra

Human Life Cycle


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Human Life Cycle

Figure 27.5


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Spermatogenesis

The sequence of events that produces sperm in theseminiferous tubules of the testes

Each cell has two sets of chromosomes (one maternal,one paternal) and is said to be diploid (2nchromosomal

number)

Humans have 23 pairs of homologous chromosomes

Gametes only have 23 chromosomes and are said to be

haploid (nchromosomal number) Gamete formation is by meiosis, in which the number

of chromosomes is halved (from 2nto n)


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Figure 27.8b, c


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Figure 27.6


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MeiosisInterphase

Two nuclear divisionshalve the number ofchromosomes

Chromosomesreplicate prior tomeiosis I

Figure 27.7.1


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MeiosisProphase I

Homologouschromosomes undergosynapsis

Tetrads are formedwith homologouspartners

Crossing over takesplace during prophase I

Figure 27.7.2.1


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MeiosisMetaphase I

Tetrads line up at thespindle equator duringmetaphase I

Figure 27.7.2.2


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MeiosisAnaphase I

Homologouschromosomescomposed of joined

sister chromatids aredistributed to oppositeends of the cell

Figure 27.7.2.3


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MeiosisTelophase I

Nuclear membraneforms aroundchromosomal masses

Spindle break down

Chromatin reappears

With telophase andcytokinesis completed,

two haploid daughtercells are formed (with2namount of DNA)

Figure 27.7.2.4


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Meiosis II

Mirrors mitosis except that chromosomes are not_________ before it begins

Meiosis accomplishes two tasks: It reduces the chromosome number by ____ (2nto n)

It introduces genetic variability


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Meiotic Cell Division: Meiosis II

Figure 27.7.3


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Spermatogenesis

Cells making up the walls of seminiferoustubules are in various stages of cell division

These spermatogenic cells give rise to sperm in a

series of events Mitosis of spermatogonia, forming spermatocytes

Meiosis forms spermatids from spermatocytes

Spermiogenesisspermatids form sperm


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Mitosis of Spermatogonia

Spermatogoniaoutermost cells in contact withthe epithelial basal lamina

Spermatogenesis begins at puberty as each

mitotic division of spermatogonia results in typeA or type B daughter cells

Type A cells remain at the basement membraneand maintain the germ line (aka _____ cells)

Type B cells move toward the lumen andbecome primary spermatocytes


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Spermatocytes to Spermatids

Primary spermatocytes undergo meiosis I,forming two haploid cells called secondaryspermatocytes

Secondary spermatocytes undergo meiosis IIand their daughter cells are called spermatids

Spermatids are small round cells seen close to

the lumen of the tubule


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Figure 27.8b, c

Spermatogenesis


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p gSpermatogonium (2n)

Primary spermatocyte (2n)

Primary spermatocyteDivision1st meiosis

secondary spermatocyte (n)

Spermatid (n)

differentiation

2nd meiosis

Spermiogenesis: Spermatids to


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Sperm Late in spermatogenesis, spermatids are haploid

but nonmotile

Spermiogenesisspermatids lose excess

cytoplasm and form a tail, becoming sperm



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Sperm Sperm have 3 major regions:

Headcontains DNA and has a helmetlikeacrosome containing hydrolytic ______ that allow

the sperm to penetrate the egg Midpiececontains mitochondria spiraled around

the tail filaments-- What are the mitochondriafor?

Taila typical flagellum produced by a centriole--What are centrioles composed of?

Spermiogenesis: Spermatids to Sperm


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Figure 27.9a

Spermiogenesis


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p g

spermatozoa

Spermiogenesis spermatids lose excess cytoplasm and form a tail becoming sperm



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http://distance.stcc.edu/AandP/AP/AP2pages/reprod/spermato.ht

spermatogenesis

spermiogenesis

Spermiogenesisspermatids lose excess cytoplasm and form a tail, becoming sperm

Sustentacular Cells (Sertoli Cells)


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Sustentacular Cells (Sertoli Cells)

Extend from basal lamina to lumen- surroundsdeveloping cells

They are bound together with tight junctionsforming an unbroken layer with the

seminiferous tubule, dividing it into twocompartments:

Basal compartmentcontains spermatogonia and

primary spermatocytesAdluminal compartmentcontains meiotically

active cells and the tubule lumen


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Adluminal Compartment


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Adluminal Compartment

Activities Spermatocytes and spermatids are nearly

enclosed in sustentacular cells, which: Deliver nutrients to dividing cells

Move them along to the lumen Secrete testicular fluid that provides the transport

medium for sperm

Dispose of excess cytoplasm sloughed off during

maturation to sperm Produce chemical mediators that help regulate

spermatogenesis

The functions of Sertoli cells and BTB


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Sustentacular cells protect the germ cells and promote their

development. Tight junctions between adjacent sustentacular cellsform a blood-testis barrier (BTB)

The fluid inside the tubules contains high levels ofandrogens,potassium and amino acids

The BTB prevents the immune system from attacking thedeveloping spermatozoa (contain specific Ag that are notfound on any other cell)

Sertoli cell supply nutrients to the developing sperms

Phagocytize cytoplasm shed by spermatids

Secrete inhibin (we will talk about this hormone later)

Secrete androgen-binding-protein (ABP) binds testosteroneinside tubules to maintain high levels

Hormonal Regulation of


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Hormonal Regulation of

Testicular Function

The hypothalamus releases gonadotropin-releasing hormone (GnRH)

GnRH stimulates the anterior pituitary to secrete

FSH and LH FSH causes sustentacular cells to release androgen-

binding protein (ABP)

LH stimulates interstitial cells to release testosterone

ABP binding of testosterone enhancesspermatogenesis

Hormones and Brain-Testicular Axis


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Hormonal Regulation of Testicular Function


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Feedback inhibition onthe hypothalamus andpituitary results from:

Rising levels oftestosterone

Increased inhibin

Figure 27.10


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Testosterone


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estoste o e The principal androgen (male sex hormone) is

testosterone. This steroid is manufactured by the interstitial (Leydig) cells

of the testes.

Secretion of testosterone increases sharply at puberty and isresponsible for the development of the secondary sexualcharacteristics of men.

Testosterone is also essential for the production of sperm.

Male Secondary Sex


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y

Characteristics

Male hormones make their appearance at puberty andinduce changes in nonreproductive organs, including

Appearance of pubic, axillary, and facial hair

Enhanced growth of the chest and deepening of the voice

Skin thickens and becomes oily

Bones grow and increase in density

Skeletal muscles increase in size and mass Testosterone is the basis of libido in both males and

females

ch 27 male reproduction lecture presentation fall%2c 2011-1

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