Understanding Excretory Organs - High School Biology

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 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.

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).