From Canvas (Anatomy Vocabulary) - Unit 12: The Urinary System

Urology

The medical specialty that studies the anatomy and physiology of the urinary system. It uses diagnostic tests, medical and surgical procedures, and drugs to treat urinary diseases.

Urinary System

A body system located within the abdominopelvic cavity that begins with the kidneys. Its functions include removing waste products from the blood, producing and eliminating urine, and using a filtering-reabsorption process to maintain internal stability. It also produces the hormone Erythropoietin (EPO) to stimulate red blood cell production in bone marrow, and the enzyme Renin to aid in raising blood pressure.

Homeostasis

The state of equilibrium or internal stability within an organism or cell, caused by opposing equal or similar forces. It involves controlling physiological processes to create stability, sameness, or to adjust internal equilibrium. This filtering system is so vital that without it, the body becomes toxic and cannot function.

Kidneys

Reddish-brown, bean-shaped, sophisticated reprocessing organs about the size of a fist. They are located near the middle of the back, just below the rib cage, on either side of the spine between the thoracic vertebrae (T12) and the lumbar region at the back of the upper abdominal cavity. They sit in the retroperitoneal space (behind the peritoneal membrane between the back muscles and the peritoneal cavity) and are surrounded by adipose (fatty) tissue for support and protection.

Kidney Functions

Besides producing and excreting urine, the kidneys help the body maintain a normal, constant internal environment by responding if blood pressure decreases, if blood pH decreases, or if the number of red blood cells decreases. They process about 200 quarts of blood daily to sift out about 2 quarts of waste products and extra water. They also produce the hormone Erythropoietin (EPO), which stimulates red blood cell production in bone marrow, and the enzyme Renin, which helps raise blood pressure.

External Structure of Kidneys

Each kidney features a convex border and a concave border. A capsule of fibrous connective tissue surrounds the entire kidney for protection.

Hilum

An area of indentation or a notch located at the center of the concave border on the medial surface of the kidney. It serves as a port where nerves, ducts, or blood vessels enter or leave the organ, specifically allowing the renal artery to enter and the renal vein and ureter to exit.

Parenchyma

The functional or working area of any organ. In the kidney, this includes the outer cortex and the inner medulla.

Renal Cortex

The outer layer of kidney tissue located just beneath the fibrous capsule. It represents a part of the kidney's parenchyma and contains millions of microscopic functional units called nephrons.

Renal Medulla

The inner layer of the kidney's parenchyma located beneath the renal cortex. It contains the triangular-shaped structures known as renal pyramids.

Minor Calyx

A cuplike urine collection cavity into which the renal pyramids extend. Urine flows continuously into this cavity.

Major Calyx

A larger collection cavity formed by the merging of multiple minor calyces.

Renal Pelvis

The funnel-like, dilated proximal part of the ureter inside the kidney. It is formed by the merging of the major calyces and serves as the final collection area where urine gathers before entering the ureters.

Nephron

The microscopic structure that serves as the functional unit of the kidney and the primary site of urine production. Its vital functions are to regulate, control, and remove waste products of metabolism from blood plasma, and to maintain normal fluid balance by regulating the reabsorption of water and allowing selected electrolytes back into the blood. The first part of the nephron is the glomerular capsule.

Components of a Nephron

The three main structural components of a nephron are the glomerulus, Bowman’s capsule (renal capsule), and the renal tubule.

Glomerulus

A ball-shaped collection of very tiny, coiled, and intertwined capillaries within the nephron that acts as the initial filtering site.

Bowman’s Capsule (Renal Capsule)

A double-walled cup that surrounds the glomerulus. It collects the filtrate pushed out of the glomerular capillaries and directs it into the renal tubule.

Renal Tubule

The tubular portion of the nephron through which filtrate travels. It is divided into three parts: the proximal convoluted tubule, the loop of Henle (nephron loop), and the distal convoluted tubule.

Formation of Urine (Overview)

A process consisting of three distinct stages: glomerular filtration, tubular reabsorption, and tubular secretion. The blood passes through the kidneys, which determine the volume and chemical composition of the blood by adjusting the amount of water and electrolytes the body needs. Waste products like urea, uric acid, and creatinine are eliminated, while water and vital solutes (dissolved substances like electrolytes, proteins, glucose, and fats) are retained or excreted as needed. Daily urine excretion is about 2 quarts (representing 1% of the total filtrate), consisting of 95% water and 5% other substances like urea, salts, and acids.

Glomerular Filtration (Step 1)

The urine formation process begins as blood enters the kidneys via the left and right renal arteries, which enter through the hilum. The arteries branch into smaller vessels and arterioles throughout the kidney tissue until they reach the cortex, where each arteriole leads to a glomerulus.

Filtration Mechanism (Step 1 Continued)

Blood pressure forces blood, water, and materials through the thin, porous walls of the glomerular capillaries into the ball-shaped collecting area of Bowman's capsule. Water, sugar, salts, and nitrogenous waste products (urea, creatinine, uric acid) are small enough to pass through as glomerular filtrate. Large substances, such as proteins and blood cells, are too big to pass and remain in the blood. The filtrate also contains vital nutritional substances entering the nephron, including electrolytes, glucose, amino acids, and vitamins.

Tubular Reabsorption (Step 2)

As the glomerular filtrate passes through the renal tubules, water, sugar, salts, and other essential nutritional substances are returned to the bloodstream. This movement occurs through a network of capillaries that closely surround the tubules.

Tubular Secretion (Step 3)

A process where certain materials bypass the initial filtration system of the glomerulus altogether. Instead, these materials are selectively transferred directly from the surrounding blood capillaries into the renal tubules to be excreted in the urine. Examples of substances directly excreted this way include potassium, hydrogen, and certain drugs.

Nephron Loop & Distal Tubule (Step 4 / Continuation)

The proximal convoluted tubule narrows into a U-shaped tubule known as the nephron loop (loop of Henle), where more water and electrolytes are reabsorbed. The nephron loop then widens to become the distal convoluted tubule, where additional water, electrolytes, amino acids, and other nutritional substances are reabsorbed into the bloodstream. Urine is produced continuously by the nephrons through these tubule movements, with some substances being reabsorbed and remaining waste products being excreted.

Ureters

Two 12-inch muscular tubes lined with mucous membrane that connect the renal pelvis of each kidney to the urinary bladder, traveling through the abdominopelvic cavity. Peristalsis, which consists of wavelike muscular contractions, continuously propels urine from the renal pelvis down through the ureters. The anatomical pathways of the ureters differ between men and women based on the size and position of the female reproductive organs.

Bladder

A hollow, muscular sac located in the anterior pelvic cavity that serves as a temporary reservoir for urine, capable of holding about 1 liter or 1 quart. It is spherical when full, resembles an inverted pyramid when empty, and its mucosal lining collapses into folds called rugae when empty. Anatomically, it is located between the pubic symphysis and the rectum in men, and between the pubic symphysis and the uterus and vagina in women.

Urethra

A mucous membrane-lined tube that leads from the bladder to the exterior of the body, through which urine exits. The release of urine from the bladder is controlled by the external sphincter. The female urethra carries only urine, whereas the male urethra carries both urine and semen during ejaculation.

Urinary Meatus

The external opening of the urethra through which urine is expelled from the body.

Urination (Micturition / Voiding)

The final process of eliminating urine from the body. After urine collects in the renal pelvis, travels through the ureters, and fills the bladder, it is expelled out of the body through the urethra. This process is also referred to as micturition, voiding, or passing water.

Urine Composition

Urine consists of water and other materials that were filtered or secreted into the renal tubules but not reabsorbed back into the bloodstream. Normally, only 1% of the total glomerular filtrate is excreted as urine. The daily output is about 2 quarts, which consists of 95% water and 5% other substances, including urea, salts, and acids.

Normal Urine Color

Ranges from pale yellow to a deep golden color. The darker the urine, the greater its concentration. The yellow color is caused by a pigment called urochrome.

Normal Urine Clarity

Normal urine is clear. A cloudy or turbid appearance may indicate the presence of pus or bacteria, suggesting a bladder or kidney infection, or it may simply happen to a specimen that has been standing for more than an hour.

Normal Urine Odor

Normal urine is aromatic, meaning it has a strong but agreeable odor.

Normal Urine Specific Gravity

The normal range is 1.003 to 1.030. Specific gravity is a measurement of the amount of solids in the urine, where a lower value indicates fewer solids and a higher value indicates more solids. A lower specific gravity can indicate kidney disease (releasing too much water), while a higher specific gravity can indicate diabetes (too much glucose/sugar in the urine).

Normal Urine pH

Normal urine is slightly acidic with an average pH of 6.0, though the overall normal range is 4.5 to 8.0. A pH of 7.0 is neutral, a pH below 7.0 is acidic, and a pH above 7.0 is alkaline (base).

Normal Urine Protein

Protein is normally either completely absent or present only in insignificant amounts that are too small to be detected by a standard reagent strip. The clear presence of detectable protein could indicate kidney disease.

Normal Urine Glucose

Normal urine does not contain glucose. The presence of glucose could be an indication of diabetes (high blood sugar), occurring because the renal tubules are overloaded and unable to reabsorb all the sugar from the filtrate.

Normal Urine Ketones

Normal urine does not contain ketone bodies, which are chemical substances that result from the breakdown of fats. In uncontrolled diabetes, the body breaks down fat to use for energy, causing ketones to accumulate in large quantities in the blood and urine. Ketones can also appear in urine due to starvation, dehydration, or taking too much aspirin.

Life Span Considerations: Aging

Changes noted in the urinary system of older adults include a loss of muscle tone in the ureters, bladder, and urethra. Bladder capacity can be reduced by half, leading to frequent trips to the bathroom. Urge incontinence, which is the inability to retain urine voluntarily, is a common concern for older adults.

Life Span Considerations: Youth

Urinary tract infections (UTIs) are common in children and are mostly caused by microorganisms such as Escherichia coli, Klebsiella, and Proteus. Signs and symptoms are age-related. Older children with a UTI may experience frequent and/or painful urination (dysuria), abdominal pain, blood in the urine (hematuria), fever, chills, or new bed-wetting episodes in a previously toilet-trained child.

Life Span Considerations: Infants

Infants experiencing a urinary tract infection (UTI) show age-specific symptoms, which can include a fever, weight loss, nausea and vomiting, increased urination (micturition), foul-smelling urine, a persistent diaper rash, or failure to thrive.