Animal Tissue and Anatomy

Epithelial tissue is arranged in single or multilayered sheets and covers the internal and external surfaces of the body of an organism. Epithelial tissue functions to protect underlying structures from injury abrasion or pressure, and from infection.

It is the simplest tissue and is the protective tissue of the body. The cells of the tissue are tightly packed and it forms a continuous sheet. It covers most of the organs and cavities within the body. It also forms a barrier to keep different body systems separate. The skin and lining of the buccal cavity, blood vessels, alveoli and kidney tubules are made of epithelial tissue.

 A single neck canal cell with two nuclei is found in the archegonium of dryopteris.

The liver is a large organ located in the upper right portion of the abdominal cavity, beneath the diaphragm.

Ruffini corpuscles respond to sustained pressure and show very little adaptation. Ruffinian endings are located in the deep layers of the skin, and register mechanical deformation within joints, more specifically angle change, with a specificity of up to 2.75 degrees, as well as continuous pressure states.

There is a triangular area, called the trigone, formed by three openings in the floor of the urinary bladder. Two of the openings are from the ureters and form the base of the trigone. Small flaps of mucosa cover these openings, and act as valves, that allow urine to enter the bladder, but prevent it from backing up, from the bladder into the ureters. The third opening, at the apex of the trigone, is the opening into the urethra. A band of the detrusor muscle encircles this opening, to form the internal urethral sphincter.

Malphigian body contains a tuft of capillaries, called glomerulus. The bowman's capsule and the glomerulus together constitutes the renal corpuscle or malpighian body.

Ureters are the ducts that carry urine from the renal pelvis of the kidneys to the urinary bladder for storage.

Henle's loop or loop of Henle is asociated with excretory system. It is a component of nephron in humans, which progresses from proximal straight tubule to distal convoluted tubule (DCT).

The renal capsule is the membranous covering of the kidney. It directly covers the renal cortex, which forms the outer stratum

The bowman's capsule and the glomerulus together constitutes the renal corpuscle or malpighian body. Glomerulous is a large double walled cup. It contains a tuft of capillaries called glomerulus and the outer wall is continuous with the rest of the nephron. The space between the two walls of the Bowman's capsule is continuous with the lumen of the next part of the nephron.

The respiratory, alimentary and genitourinary tracts are guarded immunologically by subepithelial accumulations of lymphoid tissues which are not constrained by a connective tissue capsule. These may occur as diffuse collections of lymphocytes, plasma cells and phagocytes throughout the body and the lamina propria of the intestinal wall, or as more clearly organized tissue with well-formed follicles as found in the Peyer's patches.

The nostrils are the two external openings of the nasal cavity. They serve as the primary entry point for air into the respiratory system.

The pharynx is the muscular tube that connects the nasal and oral cavities to the larynx and esophagus. It acts as a common passage for both air and food.

The trachea is kept open by rings of cartilage. These rings provide structural support to ensure the airway remains patent.