Human Anatomy
urinary system
Filtration of the blood and the production of urine are the primary functions of the urinary system. This system also regulates blood volume, pressure, and pH.
The urinary tract
The human urinary system includes the kidneys, renal pelvis, ureters, bladder, and urethra. The kidneys produce urine by filtering waste and fluid from the blood. The urine is then stored in the bladder and eventually expelled through the urethra. Male and female urinary systems are very similar, sharing many of the same structures, but they are not identical.
The urinary system’s function is to filter blood and excrete the waste as urine and regulate blood volume, pressure, and pH. The system consists of two kidneys, two uterus, one urinary bladder, and one urethra.
The upper part of the urinary system comprises the kidneys and ureters, while the lower p[art consists of the pelvic urinary organs, including a short portion of the ureters, the urinary bladder, and the urethra.
Urine production is continuous process in the kidneys. Urine drains through the kidneys as it is produced and is stored in the bladder until micturition (i.e., the act of urinating).
Each ureter connects a kidney to the urinary bladder. The ureters are muscular ducts with a narrow lumen (i.e., a tubular cavity) that carries urine to the bladder by means of peristaltic muscle contractions, which are wavelike contractions. When contracted, the musculature of the urinary bladder acts as a sphincter, preventing the reflux of urine into the ureters. This musculature also increases internal pressure in the bladder during micturition.
The urinary tract receives blood mainly through the renal arteries, and the renal veins carry blood out of it. It is innervated by the renal plexus, aortic plexus, hypogastric plexus, and pelvic plexus.
The urinary bladder is a hollow organ lined with strong, distensible muscular walls. It serves as a temporary reservoir for urine. The bladder is attached to the subcutaneous fatty tissues of the peritoneal cavity by its lateral ligaments. The internal iliac arteries provide blood to the bladder, and it is drained by the internal iliac veins.
The urethra is the duct from the urinary bladder through which urine is evacuated. In males, the urethra, the also provides an exit for semen. The male urethra can be divided into four parts: the intramural (or prostatic) urethra, the prostatic urethra, the membranous urethra, and the spongy urethra. The ejaculatory ducts open into the prostatic urethra, at which point the male urinary and reproductive tracts merge.
The female urethra begins at the internal urethral orifice of the urinary bladder and ends at the external urethral orifice. Unlike the male system, the musculature of the female internal urethral orifice does not incorporate an internal sphincter. The external urethral orifice is located in front of the vaginal orifice. The female urethral receives blood via the internal pudendal and vaginal arteries.
In both men and women, the reflexes that govern the storage and release of urine are controlled by spinal reflexes and the pontine micturition center (also called the Barrington’s nucleus), which is located in the brain stem.
The importance of water and hydration. Approximately 60 percent of the body is made up of water. Water helps transport nutrients and assists with thermoregulation. Drinking enough water is essential to maintain the body’s fluid balance. Adequate water is also required to flush the kidneys and keep them healthy. The kidneys regulate the amount of water that is reabsorbed in their tubules. A decrease in the concentration of water in the blood is detected by osomoreceptors in the hypothalamus. This stimulates the pituitary gland to release the antidiuretic hormone. This makes the walls of the collecting ducts and tubules in the kidneys more permeable, which facilitates the reabsorption of fluids, preventing much of the water from being excreted.
The urinary system
The kidneys
The kidneys are a par of fist-sized, bean-shaped organs located behind the peritoneum, which is a membrane that lines the abdominal cavity. The kidneys’ main function is to filter the blood in order to eliminate excess bodily fluids, salts, and the by-products of metabolism, such as creatinine, while retaining plasma proteins.
The kindeyse regulate three key functions: blood pressure, hormone production, and the acid/base balance. The kidneys control the amount of fluid in the body by increasing or decreasing urine production, which maintains healthy blood pressure. The kidneys are also involved in the secretion of two hormones: They form calcitriol, the active form of vitamin D, and also secrete erythropoietin, which stimulates bone marrow to produce blood cells. In addition, they maintain the pH of blood at 7.4 by regulating hydrogen ion excretion.
Three layers protect the kidneys: the renal capsule, a tough fibrous layer surrounding each kidney; the perirenal fat capsule, which provides some protection from trauma and damage; and the renal fascia, which is a layer of connective tissue that covers the kidneys and also encloses each adrenal gland and its surrounding fat.
Each kidney receives blood through a single renal artery, which are direct lateral branches of the abdominal aorta. The kidneys are innervated by the renal plexus, which connects with both the sympathetic and parasympathetic nervous systems.
The renal cortex, renal medulla, and renal pelvis are the three main internal regions of the kidneys. The renal medulla is made up of cone-shaped tissues called renal pyramids, which contain the functional units of the kidneys, called nephrons. The function of each nephron is determined by the juxtaglomerular apparatus, so named because it is found next to the glomeruli, which are webs of arterioles and capillaries. Each nephron contains a renal corpuscle and a renal tubule. The renal corpuscle is the blood-filtering component of the kidneys, while the renal tubules carry the filtrate to the calyxes, which are at the beginning of the ureters.
The renal corpuscle is composed of a Bowman’s capsule (also called glomerular capsules), which encloses a glomerulus. Bowman’s capsules are cupcake sacs at the beginning of a nephron’s tubule and are where blood is first filtered to produce urine. Glomeruli and the glomerular membranes both help filter the blood. This filter is impermeable to larger molecules, such as plasma proteins, and permeable to smaller molecules and ions, such as creatinine, drug metabolites, sodium, potassium, and amino acids. If this filtered fluid were excreted, it would lead to an unnecessary loss of essential substances, including sodium, potassium, and amino acids. These essential substances are instead reabsorbed in the tubules and carried back to the blood. Creatinine and drug metabolites, meanwhile, are retained in the filtrate and sent along with urine for excretion from he body. Thus, the kidneys are essential to maintaining circulatory hemostasis, which is the process that keeps blood in a fluid state and confines it to the circulatory system.
Calcifediol, also known as calcidiol, this substance is produced in the liver from vitamin D3 through a process called hydroxylation (which is a chemical process that involves introducing a hydroxyl group into an organic compound). The calcifedisl blood test is used to determine how much vitamin D is in the body, as this blood concentration is considered to be the best indicator of vitamin D status. Calcifediol is converted in the kidneys to calcitriol, the active form of vitamin D, and to treat hyperparathyroidism in people with chronic kidney failure and low vitamin D levels.
urine
Urine is a slightly acidic liquid waste that is excreted by the kidneys. Healthy urine ranges from straw to amber in color. It is mostly water with salt and electrolytes, such as potassium and phosphorus. It also contains cellular metabolism byproducts, including creatinine, urea, and uric acid. Urine is stored in the bladder and discharged through the urethra.
Urine is one of the body’s chief means of eliminating excess salt and water. It is also a means of removing excess nitrogen and metabolic byproducts, such as creatinine, from the blood. Urine is stored in the bladder and discharged through the urethra. It is sterile while in the bladder, and it remains sterile until it reaches the urethra. Bacteria colonizing the epithelial lining of the urethra are fused out with urine.
Normal urine volume per voiding is about 81/2 to 131/2 ounces (250 to 400 ml) for a person with a normal fluid intake. Oliguria is condition characterized by an abnormally small volume of urine. It is often caused by shock or kidney damage. Conversely, polyuria is a condition characterized by an abnormally large amount of urine. It is often caused by diabetes.
Urine is typically a yellowish-amber color. The more dehydrated one is the higher the concentration of the urine will be, and the darker it will be in color. Light, straw-colored uric is a sign of good hydration. Red color in the urine is called hematuria and is indicative of the present of erythrocytes (i.e., red blood cells), which is a sign of kidney damage and disease.
The smell of urine can also inform on a person’s health status: fresh urine (which has not been in the system for very long) has mild odor, while aged urine (which may have sat for a while in the bladder( smells of ammonia. A fruity odor in urine is usually due to the presence of ketones of glucose; it is called glycosuria and is indicative of diabetes.
The pH of urine can range from 4.6 to 8. Variations in diet account for this spread. High-protein diets generally result in acidic urine, while vegetarian diets generally result in more alkaline urine.
The density (or specific gravity) of normal urine ranges from 0.001 to 0.035 and indicates how much “stuff” is dissolved in the urine - the dissolved solids. Fresh urine tends to be clear or slightly cloudy. Suspended particles in urine result in excess cloudiness. An increases number of cells in the urine, urinary tract infections, and obstructions can increase the turbidity (i.e., cloudiness) or urine.
Chemically, urine is mostly water combined with urea, chloride, sodium, potassium, and creatinine, which are dissolved in it. Urea is essentially a processed form of ammonia that is nontoxic to humans, so urine is a means of getting rid of excess nitrogen. A change in the chemical composition of urine is indicative of disease. Proteinuria, for example, is a condition in which there is protein in urine, and it is indicative of leaky or damaged glomeruli.
Changes in the physical and chemical characteristics of urine can actually be symptomatic of more serious diseases, and that’s why physical and chemical examination are an important component of urinalysis, which also includes microscopic analysis.