The nephrons are the smallest functional unit in the kidney. They are responsible for the filtration and concentration of urine.

Neurons are the smallest functional unit of the nervous system. The renal medulla is the region on the interior of the kidney, as opposed to the renal cortex. Renal corpuscles are used to filter blood into the nephron, and consist of the glomerulus and Bowman's capsule.

The kidneys are responsible for the excretion of urine, while the skin secretes sweat from the body. The pancreas secretes digestive enzymes into glands and ducts. Exocrine function differs from endocrine function, in that exocrine excretions involve ducts that generally lead to the body's exterior. Endocrine functions, in contrast, will enter the blood stream and be distributed throughout the body.

The overall organ systems that perform excretory functions are highly variable between animal groups. All animals, however, share some common features. Water and ion balances must be tightly regulated by reabsorption mechanisms, in order to maintain organismal homeostasis and functions. To assist in this process, the vessels for filtrate transport must have a large surface area. Proteins, pumps, and channels along this surface serve to moderate water and ion transport.

Blood is filtered from the renal artery into the kidneys, where it is processed into urine. Each of the two kidneys is connected to the bladder via a ureter. The bladder has only one exit, the urethra, which carries the urine out of the body.

In summary, there are two kidneys, two ureters, one bladder, and one urethra.

The filtrate is processed as it moves throughout the nephron prior to entering the ureters to be expelled. The glomerulus is a capillary bed that deposits filtrate from the blood into the nephron. The proximal tubule does not alter the osmolarity of the primary filtrate. The loop of Henle then concentrates the urine, only to have the concentration lowered again in the distal convoluted tubule.

The kidneys are able to help regulate blood pressure by releasing the hormone renin. Renin initiates a cascade that ends with the adrenal cortex releasing aldosterone. Aldosterone increases the reabsorption of sodium ions in the distal convoluted tubule and collecting duct. The increase in surrounding ion concentration resulting from the reabsorption pulls water out of the nephron via osmosis, concentrating the urine and promoting water retention.

A sphincter is a circular band of mucle that, when constricted, closes an orifice. For example, the pyloric sphincter prevents stomach contents from entering the small intestine before it has been properly digested.

A varix is a twisted, dilated vein, as in varicose vein. Plica refers to one of the folds of the intestinal mucosa. The cecum is a blind pouch at the end of the ascending colon. At its end is the appendix. A vilus is the singular term for "villi," and refers to the minute projections on the intestinal mucosa that function in the absorption of nutrients. 

Jellyfish possess a gastrovascular cavity, which serves as both mouth and anus. Food is captured and enters the gastrovascular cavity, where enzymes break it down and cells absorb the nutrients. The undigested remains leave through the same opening by which they entered.

A food vacule is a temporary stomach found in sponges. A crop is a storage organ that earthworms use to collect food. The gizzard receives food from the crop and, through the process of contraction, grinds the food into small particles. The crop and gizzard are parts of what is termed a "tubular digestive tract," which consists of a series of regions that process the food.

Glomerulus, Bowman's capsule, loop of Henle, ureter is the correct order. Blood is filtered from the glomerulus and becomes the filtrate as it enters the Bowman's capsule. The filtrate then passes through the loop of Henle of the nephron and exits the kidney, entering the ureter as urine where it is collected in the urinary bladder.

The liver is found on the right side of the body in the abdomen. Remember the liver is on the right side of the abdominal cavity. The liver cells (hepatocytes) function to detoxify products such as alcohols and other drugs.