Welcome to the lab class in histology of organs and systems. ((48))
The aim of these lab class is to provide students with the educational resources necessary to acquire the basic practical skills of each subject, i.e. to recognize, locate and describe the types of cells, tissues and structures of each organ.
Each of these practical sessions are structured around three main elements:
- Definition of learning objectives.
- Handbook: Description of structures, tissues and cell types of the system itself.
- Exercises: location of structures / cell types in virtual slides
- In the testis, find the tunica albuginia, septa of connective tissue and seminiferous tubules.
- In the seminiferous tubules identify myoid cells and Sertoli cells.
- Identify the different stages of gametogenesis: spermatogonia and spermatocytes (differentiate between primary, secondary), spermatids and spermatozoa. Identify the ultrastructural features of the spermatozoa.
- Identify the interstitial Leydig cells.
- Characterize the tubes of the rete testis
- Identify the epididymal tubule.
- Characterize the tube wall of the epididymis and differentiate it from the seminiferous tubules.
- Identify the vas deferens (ductus deferens) and characterize its wall.
- Identify and characterize the seminal vesicle structure.
- Identify the prostate and identify the prostatic urethra and its glands.
- Identify the prostate glands starch bodies (corpora amilacea).
- Identify and characterize the penis structure.
- Identify the elements of the corpus spongiosum and corpora cavernosa.
The male reproductive system is responsible to form male gametes (spermatozoa) and male sex hormones (androgens, mainly testosterone).
The male reproductive system consists of four functional parts: 1
- The testis are the organs responsible for sperm formation and androgens synthesis.
- The transport ducts (and maturation of sperm): epididymis, vas deferens, ejaculatory duct and urethra.
- Sex exocrine glands (seminal vesicles, prostate and bulbo-rectal glands or Cowper), responsible for synthesizing nutrients for sperm and other substances that forms the semen.
- The penis or copulatory apparatus which is responsible for depositing sperm in the female reproductive system.
The testes are paired organs located in the scrotal sac (scrotum). 2 The location outside the abdomen is due to the temperature suitable for the formation of sperm must be 2 or 3° C lower than body temperature.
The testes are surrounded by a thick layer of dense connective tissue, called tunica albuginia. 2 3 4 From the tunica albuginea of connective tissue emerge several septa which delimite lobules. Inside lobules are located in the seminiferous tubules (2 to 4 tubes per lobule). 2 3 The seminiferous tubules are blind at one end and on the other side, drains into a tubular network, located in the mediastinum, known as rete testis. 11 12 The rete testis drains on the epididymal tube at various levels, in the head of the epididymis. 2
The seminiferous tubules are surrounded by myoid cells (cells with contractility and connective origin), 5 6 7 over this myoid cell layer, a basal lamina can be found. This basal lamina is the support of the seminiferous epithelium of the tube (seminiferous epithelium). 7
The seminiferous epithelium is composed of two cell series:
- Spermatogenics cells series or stem cells, which, through meiosis, form male gametes (spermatozoa) 6
- Somatic cells series. It is composed by the Sertoli cells. 6 7 The Sertoli cells are supporting cells and does not perform meiosis.
The spermatogenesis is the process by which, cells of the germ line become male gametes (spermatozoa) through a process of meiosis. This meiosis process, lowers the chromosome set of the cells in half, making them haploid, ready to fertilize the female gamete (oocyte , which is also haploid). The final part of the process of spermatogenesis is spermiogenesis, in which haploid cells differentiates to the morphology of the spermatozoa. 9 10
Seminiferous tube wall is formed (in addition to myoid cell envelope) by a stratified epithelium where cells can be seen in different stages of spermatogenesis 5 6 corresponding, cells closest to the basement membrane with those belonging to earlier stages and closer to tubule lumen with more advanced stages of the process.
In the germinal epithelium can be seen: 6
- Spermatogonia: they are the stem cells spermatogenic series (diploid) that divide by mitosis. One of the daughter cells start the spermatogenesis, while the other remains as spermatogonia. These cells are located in the basal part of germinal epithelium, ie adjacent to the basal lamina. They are cuboidal shaped and have a round or slightly oval nucleus. Morphologically there are two types of these cells: - type A spermatogonia (dark mucleus) and - type B spermatogonia (clear nucleus, with small peripheral clumps of chromatin and a central nucleolus).
- Spermatocytes: The type B spermatogonia grows to form primary spermatocytes which undergo the first meiotic division giving the secondary spermatocytes qhich in turn undergo the second meiotic divisions forming the spermatids. In humans these two meiotic divisions have few different times, so while the first meiotic division takes about three weeks the second meiotic division is very fast. This means that in a section of the seminiferous tube is very easy to see primary spermatocytes while it is very difficult to observe secondary spermatocytes. The primary spermatocytes are characterized by having a large cytoplasm, in which can be seen a large nucleus which is characterized by the presence of clumps of heterochromatin / chromosomes.
- Spermatids: The spermatids are the result of meiotic divisions of spermatocytes and are, accordingly, the male gametes. Spermatids perform the spermiogenesis process, ie to acquire the differentiation of spermatozoa morphology. This process is characterized, essentially, by the compression of chromatin (so that the nucleus becomes more compact and small) and by the loss of part of the cytoplasm by the residual bodies. Considering the degree of differentiation of these cells can distinguish between early spermatids and late spermatids. Using electron microscope can see the development of structures characteristic of spermatozoa such as the acrosome, axoneme and mitochondria are arranged around it.
- Sertoli cells: 6 7 are the cells of the somatic series, they provide support for spermatogenic cells. Sertoli cells shows irregular shape, rest on the basal lamina and its extensions surround the cells of the spermatogenic series and reach the lumen. Lateral projections of adjacent Sertoli cells are joined by tight junctions, which defines two compartments in the tubular wall. the basal compartment (in which are located the spermatogonia) and adluminal compartment (in which are located spermatocytes and spermatids). This compartmentalization perform the blood-testis barrier, which prevents haploid cells contact with the immune system and cause autoimmune reactions. Besides the formation of the blood-testis barrier, Sertoli cells are responsible for nutrition of the cells of spermatogenic series, the removal of residual bodies by phagocytosis. This cells have endocrine activity, they are stimulated by FSH from the adenohypophysis and produce ABP, inhibin and activin. Under the microscope, Sertoli cells can be easily recognized, mainly due to the shape and location of its nucleus, which is placed perpendicular to the basal lamina and it shows a deep indentation very characteristic.
Rete testis 11 12
In its final section, the wall of the seminiferous tube is simplified, the cells of spermatogenic series disappear leaving only Sertoli cells, which give way to a cuboidal epithelium. This area is known as straight tubule and it drains into the rete testis.
The rete testis is located in the mediastinum and is a network of anastomosing tubes lined with cuboidal epithelium which receive the sperm produced in the seminiferous tubules and carry them to the epididymis via the efferent ductules.
Interstitial space 8
The interstitial space is the space located between the seminiferous tubules. It consists of connective tissue in which can locate blood vessels, fibroblasts and immune system cells, as well as cells of large cytoplasm containing large numbers of lipid droplets and elongated crystalline structures (Reinke crystals), with oval nucleus and a prominent nucleolus, these cells are known as Leydig cells. Leydig cells are endocrine cells that respond to LH stimulation of the adenohypophysis, producing testosterone.
The epididymis is an organ adjacent to the testis. It consists of a single tube very convoluted, immersed in a matrix of connective tissue and surrounded by a tunica albuginea (dense connective tissue) 13
Epididymal tube is lined by ciliated pseudostratified columnar epithelium. 14 15 Spermatozoa are transported by peristalsis from head to tail of the epididymis where they are stored until ejaculation. In its passage through the epididymis, spermatozoa performs a process of maturation (stabilization of the chromatin, changes the surface charges, acquisition of anterograde motility).
VAS DEFERENS (Ductus DEFERENS) 16 17
The vas deferens carries sperm from the epididymis to the urethra at the prostate level.
The vas deferens is lined by pseudostratified ciliated columnar epithelium immersed in a lamina propria of connective tissue, this set is covered by three concentric layers of smooth muscle (the middle layer shows circular orientation but the other two layers show longitudinal orientation).
The vas deferens is included in a structure of highly vascularized connective tissue, known as the spermatic cord.
SEMINAL VESICLES 18
The seminal vesicles are exocrine glands that discharge their secretions (mainly proteins and fructose) in the vas deferens.
The secretory mucosa is highly folded and it is lined by cubic to pseudostratified cylindrical epithelium. The mucosa is surrounded by a layer of smooth muscle. The entire organ is surrounded by a connective tissue capsule.
PROSTATE 19 20
The prostate gland is the largest gland of the male reproductive system. On it converge the vas deferens (which in this area are called ejaculatory ducts) which drain into the prostatic urethra.
The prostate is an endocrine gland that secretes to the prostatic urethra: alkaline phosphatase, PSA, amylase and fibrinolysin. Prostatic glands are tubule-alveolar glands and are divided into three regions:
- Periurethral mucous glands (located in the mucosa, adjacent to the urethra).
- Submucosal glands (located in the submucosa).
- Major glands (located furthest from the urethra).
A specific structure of the prostate are the amylaceous bodies (corpora amylacea), calcareous concretions which are located in the lumen of the prostate glands, which develop with age.
The penis is copulatory apparatus that can deposit sperm in the vagina.
To perform its function penis has a complex structure in that they emphasize the corpora cavernosa (paired structures located in the dorsal position, which join at the front of the penis) and the corpus spongiosum (unique structure that is surrounding the penile urethra). 21 These structures form the erectile tissue, elastic connective tissue with a large number of sinusoids, 22 23 which, when filled with blood, causes penile erection.
The corpora cavernosa and corpus spongiosum are surrounded by two concentric circular layers of elastic connective tissue (not as vascularized as the erectile tissue), known as fascias (fascia fascia internal and external). The whole structure is surrounded by skin.
- Locate in the testis: the tunica albuginea, seminiferous tubules and interstitial space ((24.1))
- Identify the different cell types of the seminiferous tube:spermatogonia (A and B), spermatocytes I, spermatids (early and late) and Sertoli cells ((24.2)) ((24.3))
- Identifies the seminiferous tube wall and its components ((24.2)) ((24.3))
- Locate the interstitial space and Leydig cells. Identifies Reinke crystals ((24.2)) ((24.3))
- Identifies and characterizes the epididymal tube wall 25
- Identify the layers of the vas deferens 26
- Identify the layers of the seminal vesicles 27
- Identifies the glands of the prostate and locate the corpora amylacea 28
- Characterize the components of the erectile tissue and penile urethra ((29.1))
- Characterizes the external fascia tissue of the penis and compare it to the erectile tissue ((29.2))
|Species / Animal group||Mammal|
|Microscopy Method||Light field optical microscopy|
|Section thickness||5-10 um|
This digital sample shows several sections of the epididymary tubule (epididymis) in a paraffin section stained with hematoxylin-eosin.
Tissues & Structures:
- Epididymary tubule (pseudostratified columnar epithelium and smooth muscle cells)
- Intertubular space
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