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Eye The eyeball is formed by three distinct layers. The outermost fibrous corneoscleral layer comprises the translucent cornea and the nontransparent sclera. The middle layer is the uvea, a vascular layer that also includes the choroid (choroidea) as well as the stroma of the ciliary body and the iris. The innermost coat is the retina that surrounds the vitreous chamber. Cornea is composed of a corneal…

Nervous tissue Nervous tissue forms the parenchyma of the nervous system, and it is composed of neurons and glial cells. The major glial cell types of the central nervous system (CNS) are the astrocytes (astroglia), oligodendrocytes (oligodendroglia) microglia and ependymal cells, while peripheral nervous system (PNS) contains Schwann cells and satellite cells. Detailed description of the cells populating the nervous system is given in Chapter I…

Hypophysis (pituitary gland) Hypophysis, together with the hypothalamus is considered to be the master organ of the endocrine system influencing all the endocrine functions of the body. It is composed of an anterior lobe (adenohypophysis) that derives from the ectoderm of the oropharynx (Rathke’s pouch) and the posterior lobe (neurohypophysis) that is developing from the neuroectoderm, and thus it is part of the central nervous system.…

Ovary Ovary is covered by a single layer of low cuboidal cells (germinal epithelium) that transitions into a mesothelial cell lining near the mesovarium. The epithelium is attached to a dense connective tissue tunica albuginea that is thinner than the one in the testis. The parenchyma of the ovary is composed of the outer cortex, containing the ovarian follicles embedded into a cell rich stroma, and…

Testis and epididymis Most of the testis and the epididymis are covered with a thin serous membrane layer, the tunica vaginalis, which is formed by mesothelial cells and the underlying loose connective tissue lamina propria serosae. Under the tunica vaginalis, testis is enclosed by a thick dense connective tissue capsule, the tunica albuginea that rests on a thin, vascular, loose connective tissue tunica vasculosa. Tunica albuginea…

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Nasal cavity The initial part of the airways are the nasal cavities that – apart from the vestibule, the cavity of the external nose that is lined with stratified squamous keratinized epithelium – are covered with kinociliated pseudostratified columnar epithelium with goblet cells and occasional sensory brush cells. The lamina propria under the epithelium is attached to the periosteum of the underlying bone and contains scattered…

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Esophagus The mucous membrane of the esophagus (oesophagus) is covered by stratified squamous nonkeratinized epithelium. The lamina propria is composed of loose connective tissue with lymphatic elements that form occasional lymphatic follicles. The muscularis mucosae is remarkably thick and it is formed by longitudinally arranged smooth muscle bundles. The underlying submucosa is composed of dense irregular connective tissue with occasional ganglion cells and nerve fibers (Meissner’s…

Layers of the gastrointestinal tract The wall structure of the tubular (hollow) organs follows a general organization that is uniform along the gastrointestinal tract. The lumen of the organs is covered with tunica mucosa (mucous membrane) that is composed of the superficial epithelial lining , the underlying lamina propria mucosae and the tunica muscularis mucosae . Lamina propria is composed of loose connective tissue that often…

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Heart The primary component of the heart is the myocardium composed of cardiac muscle that has been described previously with the basic tissues. Briefly, cardiac muscle cells are elongated branched cells with centrally located, round or oval nuclei, many cells are binucleated. Cytoplasm is eosinophilic and features cross striation; cell boundaries are prominent lines identified as intercalated discs. The innermost surface of the cardiac wall is…

Lymphatic follicles Lymphatic follicles (lymphatic nodules) are spherical or ovoid structures composed of aggregated lymphocytes and a meshwork of reticular cells. Lymphatic follicles lack capsule, and they typically populate the lamina propria of the mucous membranes in the alimentary (gut-associated lymphoid tissue, GALT) and respiratory tracts (bronchus-associated lymphoid tissue, BALT). Primary follicles are mostly composed of small lymphocytes, while secondary follicles contain a central light zone,…

Epithelium Functionally, epithelium can be subdivided into two main types: covering (surface) epithelium and glandular epithelium. Surface epithelium covers mucous and serous membranes of tubular (hollow) organs as well as the outer surface of the body as epidermis. Structurally, surface epithelium can be composed of a single layer of epithelial cells (simple epithelium) or multiple layers of cells (stratified epithelium). Epithelial cells forming the simple epithelium…