The question states that the organ stores urine. Recall that bladder stores urine until excretion; therefore, the researcher must be analyzing a bladder. Smooth muscle and skeletal muscle are both muscle types found in the human body. Smooth muscle is involuntary, whereas skeletal muscle is voluntary. Recall that the muscle surrounding the bladder functions to empty the bladder. We cannot control bladder emptying; therefore, the muscle surrounding the bladder is involuntary and is classified as smooth muscle.

The excretory system for urine consists of the following components: kidneys, ureter, bladder, and urethra. These components are the same in both males and females. The urine is made in the kidneys. It exits the kidneys and travels through the ureter, bladder, and urethra, after which it is excreted.

The uterus is only found in females and the prostate is only found in males; however, these are reproductive structures and are not part of the excretory system. Age does not determine the structures of the excretory system. A teenager and an eighty-year old will have the same excretory system.

Kidneys are bilateral organs that function to filter metabolic waste products from the blood. These waste products are processed and excreted via urine. Once it is formed in the kidneys, urine exits via the ureter. The ureter carries the urine to the bladder, where it is stored until it can be excreted. Once the bladder is full, smooth muscles surrounding the bladder contract and push urine out of the bladder and into the urethra. The urethra is the last stop for urine, after which it is excreted.

The excretory system functions to remove waste from the body. This can happen via two pathways. First, kidneys filter metabolic wastes from the blood and excrete them via urine. Second, organs of the GI tract (such as the liver, small intestine, and colon) filter toxic substances and waste products from food and excrete it via feces; therefore, the excretory system functions to remove waste via urine and feces.

Another main function of the excretory system is to maintain homeostasis. To maintain homeostasis, the kidneys have the ability to sense changes in certain substances in the blood and can excrete them accordingly. For example, if there is an increase in the concentration of bicarbonate ions in the blood, the kidneys will sense this change and increase the excretion of bicarbonate ions via urine. This will bring the concentration of bicarbonate ions back to normal and will maintain homeostasis.

The word "renal" refers to the kidneys. Since it plays a huge role in excretion, kidney failure can alter excretory system functions.

Transitional epithelium consists of multiple layers of epithelial cells which can contract and expand. When the cells are not stretched they appear cuboidal with a domed apex, however once stretched the the tissue compresses and the cells appear flattened. This type of tissue is found in the urinary bladder, the ureters, the superior urethra, and gland ducts of the prostrate.  

All of these are functions of the kidney except for excretion of proteins. In fact, the kidney should never secrete protein or glucose (sugars) unless there is a disease state present. For example, in diabetics who have damaged kidneys (diabetic nephropathy), there is protein in the urine. To a degree, the amount of protein in the urine determines how bad their kidney disease is.

Glucose is initially filtered at the glomerulus but then all reabsorbed in the proximal convoluted tubule. If it appears in the urine, it is termed glucosuria and indicates that the patient has diabetes (impaired insulin secretion or sensitivity that causes elevated levels of glucose in the blood).

Antidiuretic hormone (ADH) is useful if an individual becomes dehydrated. When dehydrated, ADH will make the collecting ducts permeable to water. This allows water to be reabsorbed into the body from the filtrate in the kidneys. By moving water from the filtrate to the body, the urine becomes more concentrated and the body retains water. This process helps to prevent dehydration.

Oxytocin and antidiuretic hormone (ADH) are both produced by the hypothalamus and released from the posterior pituitary. In women, oxytocin is important during childbirth because it regulates uterine contractions. It also acts as a hormone in the brain and is important to sexual arousal, recognition, and trust. Antidiuretic hormone, also known as vasopressin, is an important hormone that induces increased water reabsorption in the kidney to increase blood volume.

Thyroid hormone (thyroxine or T4) and calcitonin are both produced in the thyroid. Thyroid hormone is extremely important in the regulation of metabolism. Calcitonin in the bones inhibits the activity of osteoclasts, which break down bone matrix. This decreases the amount of calcium in the blood. In the kidney, calcitonin inhibits the reabsorption of calcium. Thyroid-stimulating hormone is used to stimulate the thyroid to release thyroid hormone, and is produced by the anterior pituitary.

Follicle-stimulating hormone (FSH) is secreted by the anterior pituitary gland and plays an important role in reproduction, growth, and development, particularly during puberty. 

The nephrons of the kidney serve to balance and concentrate the filtrate in order to generate urine and eliminate nitrogenous wastes, while conserving valuable nutrients and ions. Filtration separates fluids from the cells of the blood in Bowman's capsule. Reabsorption refers to the process by which particulates and ions are removed from the filtrate and returned to the blood, while secretion refers to the addition of compounds from the blood into the filtrate. These processes are critical to establishing the proper urine composition.

While much of reabsorption and secretion occurs passively due to the manipulation of ion gradients, it is important to note that the generation of ion gradients usually requires active transport and the expenditure of energy. As such, the excretory system does utilize energy and involves active transport.