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Primary cell types

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Primary cell types
Within the seminiferous tubules
Here, germ cells develop into spermatogonia, spermatocytes, spermatids and spermatozoon through the process of spermatogenesis.

The gametes contain DNA for fertilization of an ovum[10]
Sertoli cells – the true epithelium of the seminiferous epithelium, critical for the support of germ cell development into spermatozoa. Sertoli cells secrete inhibin.[11]
Peritubular myoid cells surround the seminiferous tubules.[12]
Between tubules (interstitial cells)
Leydig cells – cells localized between seminiferous tubules that produce and secrete testosterone and other androgens important for sexual development and puberty, secondary sexual characteristics like facial hair, sexual behavior and libido, supporting spermatogenesis and erectile function. Testosterone also controls testicular volume.
Also present are:
Immature Leydig cells
Interstitial macrophages and epithelial cells.

Spermatogonium. A spermatogonium (plural: spermatogonia) is an undifferentiated male germ cell, originating in a seminiferous tubule and dividing into two primary spermatocytes (a kind of germ cell) in the production of spermatozoa.

Spermatogonium

There are three subtypes: Type A(d) cells, with dark nuclei. These cells replicate to ensure a constant supply of spermatogonia to fuel spermatogenesis.Type A(p) cells, with pale nuclei. These cells divide by mitosis to produce Type B cells.Type B cells, which divide to give rise to primary spermatocytes. Each primary spermatocyte duplicates its DNA and subsequently undergoes meiosis I to produce two haploid secondary spermatocytes. The spermatids then undergo spermiogenesis to produce spermatozoa. Additional images[edit] Spermatocyte. Spermatocytes are a type of male gametocyte in animals.

Spermatocyte

They derive from immature germ cells called spermatogonia. They are found in the testis, in a structure known as the seminiferous tubules.[1] There are two types of spermatocytes, primary and secondary spermatocytes (Figure 1). Primary and secondary spermatocytes are formed through the process of spermatocytogenesis (Figure 3).[2] Primary spermatocytes are diploid (2N) cells containing 46 chromosomes. After Meiosis I, two secondary spermatocytes are formed. All male animals produce spermatocytes, even hermaphrodites such as C. elegans, which exist as a male or hermaphrodite. Spermatid. The spermatid is the haploid male gametid that results from division of secondary spermatocytes.

Spermatid

As a result of meiosis, each spermatid contains only half of the genetic material present in the original primary spermatocyte. Spermatids are connected by cytoplasmic material and have superfluous cytoplasmic material around their nuclei. When formed, early round spermatids must undergo further maturational events to develop into spermatozoa, a process termed spermiogenesis (also termed spermeteliosis). The spermatids begin to grow a living thread, develop a thickened mid-piece where the mitochondria become localised, and form an acrosome. Spermatid DNA also undergoes packaging, becoming highly condensed. Additional images[edit] External links[edit] Spermatozoon. Sperm cells contribute approximately half of the nuclear genetic information to the diploid offspring (excluding, in most cases, mitochondrial DNA).

Spermatozoon

In mammals, the sex of the offspring is determined by the sperm cell: a spermatozoon bearing a Y chromosome will lead to a male (XY) offspring, while one bearing an X chromosome will lead to a female (XX) offspring. Sperm cells were first observed by Anton van Leeuwenhoek in 1677.[1] Mammalian spermatozoan structure, function, and size[edit] Humans[edit] The human sperm cell is the reproductive cell in males and will only survive in warm environments; once it leaves the male body the sperm's survival likelihood is reduced and it may die, thereby decreasing the total sperm quality.

The spermatozoon is characterized by a minimum of cytoplasm and the most densely packed DNA known in eukaryotes. Sertoli cell. It is activated by follicle-stimulating hormone and has FSH-receptor on its membranes.

Sertoli cell

It is specifically located in the convoluted seminiferous tubules (since this is the only place in the testes where the spermatozoa are produced). Development of Sertoli cells is directed by the testis-determining factor protein. Leydig cell. Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle.

Leydig cell

They produce testosterone in the presence of luteinizing hormone (LH). Leydig cells are polyhedral in shape, display a large prominent nucleus, an eosinophilic cytoplasm and numerous lipid-filled vesicles. Macrophage. Life cycle[edit] When a monocyte enters damaged tissue through the endothelium of a blood vessel, a process known as the leukocyte extravasation, it undergoes a series of changes to become a macrophage.

Macrophage

Monocytes are attracted to a damaged site by chemical substances through chemotaxis, triggered by a range of stimuli including damaged cells, pathogens and cytokines released by macrophages already at the site. At some sites such as the testis, macrophages have been shown to populate the organ through proliferation. Unlike short-lived neutrophils, macrophages survive longer in the body up to a maximum of several months. Epithelium. Epithelial layers are avascular, so they must receive nourishment via diffusion of substances from the underlying connective tissue, through the basement membrane.[2][3] Epithelia can also be organised into clusters of cells that function as exocrine and endocrine glands.

Epithelium

Classification[edit] Summary showing different epithelial cells/tissues and their characteristics.