Microscope Types

.. own as the corpus hemorrhagicum. Cells of the membrane granulosa are transformed into large granulosa lutein cells. Moreover, the cells of the theca interna also increase in size to become theca lutein cells, although they remain smaller than the granulosa lutein cells. Corpus Albicans (D) The corpus albicans is a corpus luteum that is in the process of involution a hyalinization.

It becomes fibrotic with few fibroblasts among the intercellular materials. Eventually, the corpus albicans will become scar tissue on the ovarian surface. TESTES Capsule The fibromuscular connective tissue capsule of the testes is known as the tunica albuginea, whose inner vascular layer is the tunica vasculosa. The capsule is thickened at the mediastinum testis from which septa emanate subdividing the testis into approximately 250 incomplete lobuli testis, with each containing one to four seminiferous tubules embedded in a connective tissue stroma. Seminiferous Tubules Each highly convoluted seminiferous tubule is composed of a fibromuscular tunica propria, which is separated from the seminiferous epithelium by a basal membrane. Seminiferous Epithelium The seminiferous epithelium is a composed of sustentacular sertoli cells and a stratified layer of developing male gametes. Sertoli cells establish a blood testis barrier by forming occluding junctions with each other, thus subdividing the seminiferous tubule into adluminal and basal compartments.

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The basal compartments house spermatogonia A (both light and dark), spermatogonia B, and the basal aspects of sertoli cells. The adluminal compartment contains the apical portions of sertoli cells primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa. Tunica Propria The tunica propria consist of loose collagenous connective tissue, fibroblasts, and myoid cells. Stroma loose, vascular, connective tissue stroma surrounding seminiferous tubules houses small clusters of large, vacuolated appearing endocrine cells, in the interstitial cells (of leydig). COLON, APPENDIX Mucosa the mucosa presents no specialised folds. It is thicker than that of the small intestine. Epithelium (A) The simple columnar epithelium has goblet cells and columnar cells.

Lamina Propria (B) The crypts of lieberkhn of the lamina propria are longer than those of the small intestine. They are composed of numerous goblet cells, a few APUD cells, and stem cells. Lymphatic nodules are frequently present. Muscularis Mucosae (C) The muscularis mucosae consist of inner circular and outer longitudinal smooth muscle layers. Submucosa The submucosa resembles that of the jejunum or ileum. Muscularis Externa The muscularis externa is composed of inner circular and outer longitudinal smooth muscle layers. The outer longitudinal muscle is modified into teniae coli, three flat ribbons of longitudinally arranged smooth muscle.

These are responsible for the formation of haustra coli (sacculation). Auerbachs plexus occupies its position between the two layers. Serosa (A) The colon possesses both serosa and adventitia. The serosa presents small, fat filled pouches, the appendices epiploicae. Appendix (B) The lumen of the appendix is usually stellate shaped, and it may be obliterated.

The simple columnar epithelium covers a lamina propria rich in lymphatic nodules and some crypts of lieberkhn. The muscularis mucosae, submucosa, and muscularis externa conform to the general plan of the digestive tract. It is covered by serosa. Anal Canal (C) The anal canal presents longitudinal folds, anal columns, that become jointed at the orifice of the anus to form anal valves and intervening anal sinuses. The epithelium changes from the simple columnar of the rectum, to simple cuboidal at the anal valves, to epidermis at the orifice of the anus.

Circumanal glands, hair follicles, and sebaceous glands are present here. The submucosa is rich in vascular supply, while the muscularis externa forms the internal anal sphincter muscle. An adventitia connects the anus to the surrounding structures. STRIATED MUSCLES Longitudinal Section (A) Connective tissue elements are clearly identifiable because of the presence of the nuclei that are considerably smaller than those of cardiac muscle cells. The connective tissue is rich in vascular components, especially capillaries. The endomysium is present but indistinct.

Longitudinal Section (B) Cardiac muscle cells from long, branching, and anastomosing muscle fibers Bluntly oval nuclei are large, are centrally located within the cell, and appearing somewhat vesicular. A and I bands are present but are not as clearly defined as in skeletal muscle. Intercalated discs, marking the boundaries of contiguous cardiac muscle cell, may be indistinct unless special staining techniques are used. Purkinje fibers are occasionally evident. ROOT TIP As root tissues differentiate behind the growing tip, they form a pattern of cylinders (tubes) within the cylinders.

Each cylinder is composed of tissue that has a specific role to play for the plant. Epidermis The outermost cylinder is only cell in thickness and is called the epidermis. This encloses and protects the underlying tissues. Some epidermis cells differentiate into hair cells. These stick out into surrounding soil spaces and absorb water and selected mineral ions.

Cortex Parenchyma A very thick cylinder is found just under the epidermis. This called the cortex or cortex parenchyma. Parenchyma cells store excess nutrients, usually in the form of starch. These cells are loosely packed so that the spaces between them can direct water and mineral ions coming from root hairs and cortex spaces and directs them into the central vascular core. Pericycle Another thin cylinder is found under the endodermis, the pericycle. Pericycle cells can function like meristem and mitotically produce secondary or branch roots.

The pericycle also constitutes the outer boundary of the vascular core, a structure that contains the internal, liquid transport highways of the plant in the form of highly specialised tube like or conducting tissues. Vascular Cylinder The vascular cylinder is comprised of tissues that transport nutrients. Water and mineral ions taken in by root hairs and concentrated into the core by the endodermis are transported up into the plant shoot by xylem tubes. Sugar rich fluid, sucrose, made in the leaves as glucose is transported by phloem sieve tubes into the root core, where it is distributed to root cells for energy production or storage as starch in the cortex parenchyma. Xylem and phloem tissues are excellent examples of how cell structure dictates function. Xylem Cells (A) Xylem cells have to die before they can serve the transport needs of the plant.

Dead xylem cells leave behind a thick, hollow, tubular wall, which joins end to end with other xylem walls to form a microscopic but strong and fixable tube, which extends from root to leaf. Xylem walls have slit like openings or pits, which provide for the sideways transfer of water and mineral ions into surrounding tissue. Close examination of these wall shows that their thickness is due to cellulose and a cement like substance call lignin. Lignin creates the wood in woody plants some walls are reinforced with internal rings or spirals. These rings of lignin help to support the plant. Xylem tubes are sometimes called vessels, i.e. composed of vessel cells, or elements. Primitive plants such as pines and firs have tracheid xylem which thinner walls and tapered ends. Phloem (B) Phloem is made up of two basic cell types, both of which are living when they serve the transport needs of the plant.

The lager cell type is a sieve tube member; the small is a companion cell. The sieve tubes member, though living, does not have a nucleus and therefore does not control its own metabolism. What the needs it has are apparently provide for by the tiny companion cell that is attached to the sieve tube member. Sieve tubes members are very much smaller and have thinner walls than xylem, but like xylem, they join end to end to form sieve tubes that extend leaves to roots. These take their name from the tiny, sieve like pores in their walls and the larger pores called sieve plates that separate one member from another.

Pores provide for the horizontal and vertical movement of the sugar rich sap that slowly moves down from the leaves, supplying energy, and elements to all plant tissues. Large parenchymal cells called pith may also be associated with the vascular cylinder phloem.


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