a. Nephrons are the functional units of the vertebrate kidneys. It is responsible for the actual purification and filtration of the blood. Each human kidney contains about a million nephrons. Each consists of a single long tubule and a ball of capillaries called the glomerulus. A cup-shaped swelling called the Bowman's capsule surrounds each glomerulus. Also, each one consists of a renal corpuscle and a renal tubule which carry out the functions of the nephron. The renal tubule consists of the convoluted tubule and the loop of Henle. The Loop of Henle is the part of the nephron that contains the basic pathway for liquid. The liquid begins at the Bowman's capsule, and then moves through the proximal convoluted tubule. It is here that sodium, water, amino acids, and glucose get reabsorbed. The liquid then flows down the descending limb and then back up. On the way it passes the Loop Of Henle. As it approaches the top again, hydrogen ions (waste) flow into the tube and down the collecting duct. This leads to the renal pelvis, which is drained by the ureter. The structure of the nephrons allows them to filter fluid and retain what is needed by the body while getting rid of waste.

a. Villi are fingerlike projections on the inner surface of the small intestine. They extend about 1 mm into the intestinal lumen. They are made of epithelial cells. Each of these cells is covered in many microvilli, which are exposed to the intestinal lumen. This covering is composed primarily of absorptive cells called enterocytes, with a few goblet cells in there. Goblet cells secrete mucous. Each villus contains a capillary bed and a lymphatic vessel. Nearly all nutrients enter the body across the epithelial covering of the villi in the small intestine. After crossing the epithelial covering, the molecules diffuse in the capillary bed, thus into the circulatory system. Some molecules, such as fructose, passively transport, while others do not. Some molecules, such as fats, do not get into the capillaries. They get into the lymphatic vessel, which is drained from the intestine flows rapidly into the blood.

units of the respiratory system. They are the places where the actual gas exchange occurs. They get oxygen to the blood and remove carbon dioxide from it. All the other parts of the respiratory system (trachea, bronchi, etc.) are merely structures used to get air to and from the alveoli, which is where all the work is done. Millions of these are ne

Some common words found in the essay are:
Alveolus Alveoli, Neuron Neurons, Capillary Capillaries, Sarcomere Sarcomeres, Villus Villi, Loop Henle, Nephron Nephrons, surface tension, epithelial tissue, loop henle, digestive system, air pressure, carbon dioxide, diffuses epithelial tissue, functional units, villi intestine, contracted relaxed, epithelial covering, nutrients digestive system, oxygen entire body,
Approximate Word count = 1668
Approximate Pages = 7 (250 words per page double spaced)