1) a) kidney; b) head; c) urethra;

2) a) teeth; b) bladder; c) parenchyma;

3) a) cloaca; b) urogenital; c) nasal;

4) a) neck; b) pronephros; c) kidney;

5) a) liquid; b) cell; c) blood.

The kidneys are retroperitoneal organs that remove urea and other waste products from the blood. In addition, they regu late the chemical composition of plasma and the extracellular fluid of the body. Each kidney is composed of stroma and parenchyma. The stroma consists of a tough fibrous connective tissue capsule and a delicate interstitial connective tissue com posed of fibroblasts, wandering cells, collagen fibrils, and a hydrated proteoglycan extracellular matrix, which is collec tively called the renal interstitium. The parenchyma consists of more than one million elabo rate uriniferous tubules that represent the functional units of the kidney.

The kidney contains a hilum, a cortex, and a medula. The hilum is located medially and serves entrance as the point of entrance and exit for the renal artery, renal veins, and ureter. The renal pelvis, the expanded upper, divides into two or three entrance into the kidney. These, in turn, divide into eight minor calyces. Branches of the renal artery, vein, and nerve supply each part of the kidney.

The cortex forms the outer zone of the kidney, as well as several renal columns, which penetrate the kidney.

The medulla appears as a series of medullary pyramids. The tips of the pyramids point toward the at the hilus. The apex of each pyramid stream into a minor calyx. Two or three pyramids may unite to form a papilla. Uriniferous tubules consist of two functionally related portions called the nephron and the collecting tubule.

Urinoferous tubules consist of two functionally related portions called the nephron and collecting tubule.

Glomerulus is made up of several anastomotic capillary loops interposed between an afferent and an efferent arteriole. The endothelium of the glomerulus is thin and fenestrated. Plasma filtration (ultrafiltra-tion) occurs in the glomerulus.

Bowman's capsule consists of an inner visceral layer and an outer parietal layer. The space between these layers, the uri nary space, is continuous with the renal tubule.

Visceral layer is apposed to the glomerulus and closely fol lows the branches of the glomerular capillaries. The visceral layer is composed of a single layer of epithelial cells resting on a basal lamina, which is fused with the basal lamina of the capillary endothelium. The cells of the visceral layer, called podocytes, are large and their nuclei bulge into the capsular space.

Cytoplasmic extensions of podocytes, called pedicles, rest on the basal lamina. The pedicles of adjacent podocytes interdigitate along the basal lamina.

Between adjacent pedicles, a thin slit diaphragm assists in preventing large plasma proteins from escaping from the vascular system. Parietal layer is composed of a simple squamous epithelium that is continuous with the proximal convoluted tubule epithelial lining. Proximal convoluted tubule is the longest and most convolut ed segment of the nephron.