Cui Dongmei. Atlas of Histology: with functional and clinical correlations. 1st ed

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J. Naftel

1. Spermatogonium

2. Prepachytene primary

spermatocyte

3. Pachytene primary

spermatocyte

4. Metaphase primary or

secondary spermatocyte

5. Early spermatid

6. Intermediate

spermatocyte

7. Late spermatid

8. Detaching spermatozoan

Figure 18-9. Overview of readily identiﬁ able spermatogenic cells in the seminiferous epithelium. H&E, 1,496

Spermatogenesis involves an orderly sequence of changes as cells proceed through mitosis (spermatogonia), meiosis (spermatocytes),

and spermiogenesis (spermatids). Only the eight most readily identiﬁ able stages are illustrated here owing to their distinctiveness

and adequate abundance in ordinary sections. Spermatogonia can be identiﬁ ed by their position (in contact with the basement mem-

brane) and their oval interphase nuclei with the long axis parallel to the basement membrane. Primary spermatocytes undergo

several substages of prophase I, but, here, the earlier substages are denoted as prepachytene. The condensing chromosomes in

prepachytene primary spermatocytes tend to be clumped at one edge of the nuclear envelope. By contrast, the paired chromosomes

of pachytene primary spermatocytes form broad bands that ﬁ ll the nucleus. Pachytene primary spermatocytes are abundant in

sections, because this is the phase of meiosis with the longest duration. After a primary spermatocyte completes pachytene, the

remaining steps of meiosis I and meiosis II (by the daughter secondary spermatocytes) are completed very rapidly, so examples of

cells in these stages of meiosis are more difﬁ cult to ﬁ nd in sections. Cells in either metaphase I or metaphase II are most conspicuous

and easiest to locate. The products of meiosis II are spermatids. These haploid cells begin as early spermatids, recognizable by their

small spherical interphase nuclei. The ﬁ rst clear evidence that spermiogenesis is underway is a change in shape of the nucleus from

spherical to a broad diamond shape; a cell with such a nucleus can be designated an intermediate spermatid. When the nucleus has

assumed the sharply pointed shape and dense appearance of a spermatozoan but remains inserted deeply into the epithelium, the

cell can be denoted a late spermatid. Finally, nuclei of detaching spermatozoa can readily be recognized, because they form a row at

the surface of the epithelium and overlie a layer of residual bodies.

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Figure 18-10. Overview of spermatogenesis and the stages of the seminiferous epithelium.

If small patches of seminiferous epithelium are examined, it can be seen that there are six recurring groupings of stages of developing

gametes that populate the epithelium. These groupings (associations) represent recurring stages that a patch of epithelium cycles

through over time, and their existence indicates that the many steps in spermatogenesis proceed with a very rigid timetable. If the

composition of a bit of epithelium could be monitored over time, it would be seen that, as cohorts of germ cells begin and complete

spermatogenesis within the epithelium, the epithelium itself will change in appearance and contain the six different groupings of

developing germ cells. The ability to recognize the stages in the cycle of the epithelium has made it possible to undertake simple

experiments that have revealed some important dynamics of spermatogenesis. Therefore, the time required for a patch of epithelium

to complete the six stages of one cycle is 16 days, and it can be inferred that with each 16-day cycle a single patch of epithelium will

release a group of new spermatozoa for only a brief period when it reaches the end of stage II. Likewise, the end of stage II is the

only time during the 16-day cycle that a new cohort or generation of primary spermatocytes will enter the adluminal compartment

to begin meiosis I. The time required for a new type B spermatogonium to generate completed spermatozoa is 56 days.

IIII III

IV V VI

J. Naftel

AAA

Interphase primary

spermatocyte

Interphase primary

spermatocyte

Prepachytene

primary spermatocyte

Pachytene primary

spermatocyte

Meiotic metaphase

spermatocyte

Early spermatid

Intermediate

spermatid

Late spermatid

Detaching

spermatozoan

with residual

body

4.8 days’

duration

3.1 days’

duration

1.0 days’

duration

1.2 days’

duration

5.0 days’

duration

0.8 days’

duration

type B

spermatogonium

type A

spermatogonium

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Figure 18-11A. Stage I seminiferous epithelium. H&E, left 207; right 747

Stage I seminiferous epithelium is shown at low magniﬁ cation (left), and a detailed representation of the region is indicated by the

box (right). Stage I seminiferous epithelium is characterized by the following: (1) Spermatogonia are located at the basement mem-

brane; both type A and B spermatogonia are present, although the two types are not easily distinguished in H&E stained sections.

(2) A layer of pachytene primary spermatocytes is present. Although some of these cells are near the basement membrane, they are

not in direct contact with it. (3) A prominent layer of round, undifferentiated early spermatids has moved toward the surface of the

epithelium. (4) The late spermatids have their heads inserted deep into the epithelium.

Late spermatid

in the epithelium

Early spermatid

Pachytene

spermatocytes

Late spermatid

in the epithelium

Early spermatid

Pachytene

spermatocytes

Basement

membrane

Spermatogonia

Basement

membrane

Spermatogonia

Sertoli cell

Late spermatid

on the surface

of theepithelium

Detaching

spermatozoa

on the surface

of the epithelium

Residual

bodies

Residual

bodies

Pachytene

primary spermatocyte

Pachytene

primary spermatocyte

Spermatogonium

Early spermatid

Sertoli

cell

Sertoli

cell

Figure 18-11B. Stage II seminiferous epithelium. H&E, left 207; right 747

Stage II seminiferous epithelium is shown at low magniﬁ cation (left), and a detailed representation of the region is indicated by the

box (right). The composition of the spermatogenic cell in stage II seminiferous epithelium is similar to that of stage I. The most

characteristic features of this stage are the following: (1) Detaching spermatozoa (very late spermatids) have completed differentia-

tion and are in the process of shedding their excess cytoplasm. (2) The small leftover cytoplasmic masses that have been shed are

called residual bodies and are present in the luminal border of the epithelium, beneath the heads of the detaching spermatozoa.

(3) These detaching spermatozoa are positioned in a row on the surface of the epithelium ready to be released from the epithelium

into the lumen. (4) Early spermatids with round nuclei and pachytene primary spermatocytes are present. (5) Both type A and B

spermatogonia are present.

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Figure 18-12B. Stage IV seminiferous epithelium. H&E, left 207; right 747

Stage IV seminiferous epithelium is shown at low magniﬁ cation (left), and a detailed representation of the region is indicated by the

box (right). Stage IV differs from stage III mainly in the progression of the generation of early spermatids (in stage III) to intermediate

spermatids (in stage IV). Stage IV has the following composition: (1) Intermediate spermatids with diamond-shaped or irregular nuclei;

(2) one generation of primary spermatocytes in pachytene of prophase I; (3) a separate generation of primary spermatocytes at an

early (prepachytene) stage of prophase I; and (4) Type A spermatogonia in the basal compartment.

Figure 18-12A. Stage III seminiferous epithelium. H&E, left 207; right 747

Stage III seminiferous epithelium is shown at low magniﬁ cation (left), and a detailed representation of the region is indicated by

the box (right). Stage III has a similar composition of spermatogenic cells as that of stage II, except for the absence of the detaching

spermatozoa at the surface and the added presence of a new generation of primary spermatocytes near the basement membrane

(not readily apparent). This stage is characterized by the following: (1) There is an absence of detaching spermatozoa, which have

been released into the lumen to be suspended in testicular ﬂ uid and transported along the genital ducts. (2) Early spermatids with

round nuclei have moved to the surface of the epithelium. (3) There is the continued presence of a generation (cohort) of primary

spermatocytes in the pachytene stage of prophase I. (4) A new generation of primary spermatocytes has moved from the basal com-

partment into the adluminal compartment, although they are difﬁ cult to distinguish. Compartments are created by tight junctions of

neighboring Sertoli cells. The basal compartment is situated on the basement membrane side of the tight junctions between Sertoli

cells, and it contains spermatogonia. The adluminal compartment is situated above the junctions and toward the lumen and contains

spermatocytes and spermatids. The tight junctions establish a blood-testis barrier that prevents immunoglobulins from entering the

adluminal compartment. Newly formed primary spermatocytes are lifted from the basal compartment and into the adluminal com-

partment by outgrowth of processes extended from the local Sertoli cells.

Early

spermatids

Early

spermatid

Pachytene

primary

spermatocytes

Pachytene

primary

spermatocyte

Sertoli cell

Lumen

Spermatogonium

Basal

compartment

Basal

compartment

Basement

membrane

Basement

membrane

Adluminal

compartment

Adluminal

compartment

Prepachytene

primary

spermatocyte

Prepachytene

primary

spermatocyte

Lumen

Intermediate

spermatids

Intermediate

spermatids

Pachytene

primary

spermatocytes

Pachytene

primary

spermatocytes

Spermatogonium

Sertoli cell

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Figure 18-13A. Stage V seminiferous epithelium. H&E, left 207; right 747

Stage V seminiferous epithelium is shown at low magniﬁ cation (left), and a detailed representation of the region is indicated by

the box (right). In this example, stage V has newly developed late spermatids and two generations of primary spermatocytes. Stage

V is characterized by the following: (1) There are no early or intermediate spermatids; only late spermatids are present. The cyto-

plasm of each late spermatid extends from the sharply pointed nucleus toward the lumen. (2) Two generations (both pachytene and

p repachytene) of primary spermatocytes are present. (3) Type A spermatogonia are present, as always, in the basal compartment.

Basement

membrane

Basement

membrane

Prepachytene

primary

spermatocyte

Prepachytene

primary

spermatocyte

Late

spermatids

Late

spermatids

Pachytene

primary

spermatocyte

Pachytene

primary

spermatocyte

Spermatogonium

Secondary

spermatocytes

Primary

spermatocytes

Primary

spermatocytes

Lumen

(in metaphases)

Figure 18-13B. Stage VI seminiferous epithelium. H&E, left 207; right 747

Stage VI seminiferous epithelium is shown at low magniﬁ cation (left), and a detailed representation of the region is indicated by the

box (right). The most characteristic feature of stage VI is the presence of metaphases of either primary or secondary spermatocytes,

which are present only in this stage. Interphase secondary spermatocytes also occur in stage VI, but these are rarely apparent. The

characteristics at this stage are as follows: (1) Late spermatids are present at the epithelium near the lumen. (2) Dividing sperma-

tocytes with their chromosomes clumped in the center of the cytoplasm. (3) A separate generation of primary spermatocytes in

prophase is present, although they are not easily distinguished. (4) Type A spermatogonia are present. This is a very active stage

during which each member of the older cohort of primary spermatocytes completes the ﬁ rst meiotic division to produce two second-

ary spermatocytes, and, in a very short time, each secondary spermatocyte completes the second meiotic division to produce two

spermatids.

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Intratesticular Genital Ducts

Fig. 18-14B

Fig. 18-15A,B

Ductus

epididymis

Mediastinum

Ductus

deferens

Ductus

epididymis

Ductuli

efferente

Rete testis

Tubuli recti

Seminiferous

tubule

Intratesticula

genital

ducts

Fig. 18-14C

Tes t i s

Lumens of

seminiferous

tubules

Lumens of

seminiferous

tubules

Seminiferous

tubule

Seminiferous

tubule

Lumens of the

tubulus rectus

Lumens of the

tubulus rectus

Tubulus rectus

Rete testis

Mediastinum

Lumen of

rete testis

Lumen of

rete testis

Figure 18-14A. Intratesticular genital ducts. H&E, 6

The series of ducts which transport spermatozoa from the seminiferous tubules to the outside of the male body are called genital

ducts. They include intratesticular genital ducts and extratesticular genital ducts. The intratesticular genital ducts refer to ducts

within the testis. They are composed of the tubuli recti, rete testis, and ductuli efferentes. The extratesticular genital ducts include

the ductus epididymis, ductus deferens, ejaculatory ducts, and urethra.

Figure 18-14B. Tubuli recti. H&E, 71; inset 210

The tubuli recti are short (about 1 mm), straight tubules that

carry the spermatozoa from the seminiferous tubules into the

rete testis. Rectus means “straight.” Each tubulus rectus is

lined by a single layer of cuboidal epithelial cells and is sup-

ported by a layer of dense connective tissue. It is located in

the septum (connective tissue) and opens into the rete testis

in the mediastinum. The terminal portion of the seminiferous

tubules is lined by Sertoli cells. The germinal cells in the sem-

iniferous tubules are gradually reduced in number near the

tubuli recti and disappear at the terminal portion. The sper-

matozoa are pushed forward by the ﬂ ow of the testicular ﬂ uid

through the tubuli recti and into the rete testis. An example

here shows two segments of a tubulus rectus.

Figure 18-14C. Rete testis. H&E, 35; inset 163

The rete testis is an interconnecting network of tubules

located in the mediastinum. These tubules have an irregu-

lar lumen and are lined by simple cuboidal epithelium and

supported by a dense connective tissue. This example shows

the terminal portion of the tubulus rectus opening into the

tubule of the rete testis.

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Figure 18-15A. Ductuli efferentes. H&E, 68; inset 234

There are 15 to 20 tubules of ductuli efferentes leading from the

rete testis in the mediastinum to the head of the epididymis. They

are also called efferent ducts. The ductuli efferentes are lined by two

types of epithelial cells: nonciliated cuboidal cells with microvilli

(absorptive cells) and ciliated columnar cells. They are alternately

distributed on the luminal surface of the ductuli efferentes. The epi-

thelium of the ductuli efferentes is supported by a thin layer of con-

nective tissue; beneath it is a thin layer of circular smooth muscle

that contracts to move testicular ﬂ uid and spermatozoa toward the

ductus epididymis (inset). Smooth muscle cells are interspersed with

some elastic ﬁ bers. The muscle layer becomes thicker as it nears the

ductus epididymis.

Spermatozoa

Ductuli

efferentes

Ductuli

efferentes

Artery

Ciliated

columnar cells

Ciliated

columnar cells

Spermatozoa

Nonciliated

cuboidal cells

Nonciliated

cuboidal cells

Figure 18-15B. Ductuli efferentes. H&E, 463

An example of ductuli efferentes at high magniﬁ cation is shown.

The nonciliated cuboidal cells have an absorptive function, absorbing

excess testicular ﬂ uid secreted by seminiferous tubules and increasing

the concentration of spermatozoa in the lumen of the ductuli effer-

entes. The ciliated columnar cells of the ductuli efferentes have a

motile function, sweeping spermatozoa and testicular ﬂ uid toward

the epididymis.

CLINICAL CORRELATION

Figure 18-15C.

Testis Seminoma. H&E, 192

Most tumors of the testes arise from the germinal epithelium of

the seminiferous tubules; therefore, this group is termed germ cell

tumors. These germ cell tumors can be divided into seminomas, and

all other germ cell tumors are called nonseminomatous, examples

of which include choriocarcinoma, embryonal carcinoma, yolk sac

tumor, and teratoma. Seminomas are the most common germ cell

tumor of the testis and are most likely to occur in the pure form,

because germ cell tumors commonly contain multiple tumor types

(mixed germ cell tumors). Germ cell tumors tend to arise from in situ

lesions of the germinal epithelium called intratubular germ cell neo-

plasia (IGCN). The incidence of seminoma peaks in the fourth and

ﬁ fth decades of life. Cryptorchidism and gonadal dysgenesis are risk

factors for germ cell tumors. Patients present with painless enlarge-

ment of the testis. Grossly, classic seminomas are circumscribed and

ﬂ eshy. Histologically, classic seminoma consists of sheets of large cells

with distinct cell borders and nucleoli, inﬁ ltrated with lymphocytes.

These cells are typically positive for placental alkaline phosphatase

on immunohistochemical preparations. Because of the potential for

seeding across fascial planes, biopsy is not recommended. Semino-

mas are very sensitive to radiation and chemotherapy.

Lymphocytes

Seminoma

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Organ Systems

Extratesticular Genital Ducts

Ductus

deferens

Ductus

epididymis

(tail)

Ductus

epididymis

(body)

Ductus epididymis

(head)

Seminiferous

tubule

Mediastinum

Seminiferous

tubule

Seminiferous

tubule

Lumen of ductus epididymis

Epithelium

Connective tissue (lamina propria)

Smooth muscle

Figure 18-16. Ductus epididymis. H&E, 11; inset 75

This is an example of the ductus epididymis in the head region. The ductus epididymis is a single highly convoluted tube about 4 to 5 m

in length. It connects the ductuli efferentes to the ductus deferens. The ductus epididymis is lined by pseudostratiﬁ ed columnar epithelium

with long stereocilia and is supported by connective tissue (lamina propria) and a circular smooth muscle layer in its wall. The ductus

epididymis can be divided into three regions: head, body, and tail. The head of the ductus epididymis, also called the initial region,

receives spermatozoa from the ductuli efferentes. The spermatozoa in the head of ductus epididymis are weak and unable to function

effectively in fertilization. They pass through the body region with the help of contraction of the smooth muscle in the wall of the

ductus epididymis and are stored in the tail region, where the spermatozoa undergo maturation. The maturation of the spermatozoa

is inﬂ uenced by androgenic hormones. The ﬁ nal step of maturation is called capacitation and occurs only after the spermatozoa

enter the female reproductive tract. Capacitation enables sperm to penetrate and fertilize an egg.

Epididymitis is an inﬂ ammation of the epididymis. Common causes include Chlamydia trachomatis, Escherichia coli, and Neisseria

gonorrhoeae infections. In the male, urethritis (an inﬂ ammation of the urethra) is often associated with epididymitis. Chronic

epididymitis may result in infertility, because spermatozoa are stored and mature in the tail of the ductus epididymis.

D. Cui

Seminiferous

tubules

Ductus

epididymis

Seminal

vesicle

Prostate

gland

Bulbourethral

gland

Penile

urethra

Ductus

deferens

Urethra

Ejaculatory

ducts

Rete

testis

Tubuli

recti

Urethral

orifice

Ductuli

efferentes

Intratesticular

genital ducts

Extratesticular

genital ducts

Penis

Accessory

genital glands

Pathway for Sperm Conduction through the Genital Ducts

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Figure 18-17A. Epithelium of the ductus epidi-

dymis. H&E, 305

The epithelium of the ductus epididymis is a

pseudostratiﬁ ed columnar epithelium composed of

basal cells and principal cells. The basal cells are short

with round nuclei; they are stem cells and are capable

of differentiating into principal cells. The principal

cells are columnar cells with elongated nuclei and

apical stereocilia (long microvilli, 10 μm or more in

length, which function in absorption but have no

motile function). They absorb large volumes of tes-

ticular ﬂ uid. The principal cells also play an impor-

tant role in the secretion of glycerophosphocholine,

which inhibits capacitation of the premature sperm

in the male reproductive tract. Normally, capacita-

tion happens only after the sperm enters the female

reproductive tract.

Fig. 18-17B

Stereocilia

Pseudostratified

columnar epithelium

Basement

membrane

Basement

membrane

Connective

tissue

Connective

tissue

Head of spermatozoan

Tail of spermatozoan

Middle piece of

spermatozoan

Stereocilia

Junctional complex

Figure 18-17B. Epithelium of the ductus epididymis. EM, 5,900

The view here is limited to part of the lumen and the apical ends of the columnar epithelial cells forming the wall of the ductus

epididymis. Junctional complexes between neighboring epithelial cells seal the contents of the lumen from the interstitial compart-

ment underlying the epithelium. The extremely long microvilli (stereocilia) are a reﬂ ection of the large amount of testicular ﬂ uid

that is resorbed by the ductus epididymis. The lumen is the site of storage and ﬁ nal maturation of the spermatozoa that have been

delivered to the epididymis by the ﬂ ow of the testicular ﬂ uid. Note the randomly oriented sections through the heads, middle pieces,

and tails of spermatozoa in the lumen.

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Figure 18-18A. Ductus deferens, spermatic cord. H&E, 11

The ductus deferens (vas deferens) consists of bilateral tubes

that continue from the tails of the left and right ductus

epididymis. Each tube is about 30 to 40 cm long and is

surrounded by a thick wall of smooth muscle. Each ductus

deferens resides within a spermatic cord in its course from

the testis through the abdominal wall to the penis. The distal

portion of the ductus deferens becomes enlarged and is called

the ampulla (Fig. 18-18B). The spermatic cord contains the

ductus deferens, testicular artery, pampiniform venous plexus,

nerves, and lymphatic vessels within the connective tissue.

Pampiniform venous

plexus

Pampiniform venous

plexus

Ductus

deferens

Ductus

deferens

Testicular arteries

Epithelium

Folds (mucosa)

Lamina propria

Outer longitudinal

muscle

Outer longitudinal

muscle

Inner longitudinal

muscle

Inner longitudinal

muscle

Middle circular

muscle

Middle circular

muscle

Spermatozoa

Lumen

Epithelium

Lamina propria

scle

scl

Smooth muscle

Figure 18-18B. Ductus deferens. H&E, 69;

inset 476

The lining of the ductus deferens, like that of the

epididymis, is pseudostratiﬁ ed columnar epithe-

lium. The ductus deferens is characterized by ﬁ n-

gerlike mucosal folds extending into the lumen.

The thick muscularis contains inner longitudinal

muscle, middle circular muscle, and outer lon-

gitudinal muscle, although these muscle layers

are not easy to distinguish from one another.

The outer longitudinal muscle is covered by

an adventitia (connective tissue layer). The

smooth muscle of the ductus deferens is richly

innervated by postganglionic sympathetic nerve

ﬁ bers, which initiate ejaculation when activated.

The inset shows pseudostratiﬁ ed columnar epi-

thelium with stereocilia of the ductus deferens.

The spermatic cord is a very long vascular strand containing

the testicular vessels that provide the blood supply to the

testis. If testicular torsion (twisted spermatic cord) occurs,

acute testicular pain and necrosis of testis tissue may result

because of interrupted blood supply from arteries or, more

commonly, because of venous infarction.

A vasectomy (deferentectomy) is a surgical

procedure for sterilization of the male. In this

minor surgical procedure, both sides of the

proximal portion of the ductus deferens are

typically severed and sealed. The procedure

prevents sperm from entering the urethra of

the penis.

Figure 18-18C. Ductus deferens. van Gieson

stain, 139; inset 476

An example of the ductus deferens with van

Gieson stain is shown. The nuclei of the sper-

matozoa are brownish to black and are located

in the lumen of the ductus deferens. Smooth

muscle lies beneath the lamina propria.

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