Urinary System Anatomy and Function

Introduction to the Urinary System

• The urinary system purifies blood by removing waste materials.
• The urinary system controls electrolyte and fluid balance, while the liver provides some purification to the body.
• Maintaining homeostasis can be achieved with the urinary system.

Overview of the Urinary System

• The urinary system consists of 2 kidneys, 2 ureters, 1 urinary bladder, and 1 urethra.

Kidneys

• Kidneys are bean-shaped organs that filter blood and produce urine and are located in the superior dorsal abdominal cavity.

Ureters

• Ureters are tubes that carry urine from each kidney to the urinary bladder (2 ureters).

Urinary Bladder

• This is an expandable sac that holds urine.

Urethra

• The urethra transports urine from the bladder to the outside of the body (1 urethra).

Main Functions of the Kidneys

• The kidneys have three main functions: filtering blood, reabsorbing and secreting ions, and producing urine.
• Without the kidney functions you would die in a few days.

External Anatomy of the Kidney

• The kidney is covered by a fibrous layer of connective tissue called the renal capsule.
• The renal hilum is the indentation that gives the kidney its bean shape.

Hilum

• Renal arteries bring blood to the kidneys for filtration.
• Renal veins take the filtered blood away from the kidney to return to the heart.
• The ureter attaches at the hilum to transport urine from the kidney to the bladder.

Urine Production

• The three processes necessary for urine production are filtration, reabsorption, and secretion.
• Filtration: Filtering the blood and what passes through the filter is called a filtrate.
• Reabsorption: Substances that stay in the body after being removed from urine.
• Secretion: Substances move from the bloodstream and are eliminated from the body in the urine.
• Nephrons are the functional units of the kidney where these three processes take place.

The Nephron

• Nephrons consist of millions of microscopic funnels and tubules.
• The two distinct parts of the nephron are the renal corpuscle (a filter) and the renal tubule (where reabsorption and secretion occur).

Internal Anatomy of Kidney

• Afferent arterioles lead to a ball of capillaries called a glomerulus.
• Efferent arterioles leave from the glomerulus.

Renal Tubule Steps

• Glomerular filtrate travels from the glomerular capsule into the first part of the renal tubule, the proximal tubule.
• The glomerular filtrate flows from the proximal tubule into the nephron loop (or the Loop of Henle).
• The nephron loop consists of the descending and ascending loop.
• Glomerular filtrate travels from the nephron loop to the distal tubule.
• The glomerular filtrate flows from the distal tubule into one of several collecting ducts.
• The collecting ducts lead to minor calyces, then to major calyces, the renal pelvis, and the ureter.
• At this point, the glomerular filtrate is urine.

Filtration

• Fluid and molecules pass from the glomerular capillaries into the glomerular capsule.
• Filtration moves fluid and chemicals into the nephron from blood.
• The filtrate flows into the renal tubule where the chemistry is controlled by reabsorption and secretion.

Control of Filtration

• Filter size determines what gets through the filter; the filter is the capillary wall.
• Substances are moved through a filter by differences in pressure and pressure pushes substances through the holes in the filter.
• Plasma and many of the substances dissolved in plasma pass through the filter.
• Blood cells, platelets, and large molecules (like protein) can't get into a healthy kidney, but stay in the blood vessel.
• Changes in blood pressure change filtration rate.
• As blood pressure increases, the afferent arterioles that lead to the glomerulus constrict, therefore decreasing the amount of blood that gets into the glomerulus.
• The kidney regulates fluid volume and works with the cardiovascular system to regulate blood pressure.
• With the sympathetic nervous system (Fight or Flight) takes over and adrenaline (epinephrine) is released, urine formation slows down.

Reabsorption and Secretion

• Substances that are reabsorbed pass from the renal tubule into the peritubular capillaries and return to the bloodstream.
• Substances that are secreted pass through the peritubular capillaries into the renal tubule (collecting duct) and eventually leave the body as urine.
• Some substances, like glucose, are completely reabsorbed.
• Substances like metabolic waste products (urea and creatinine) are almost completely secreted as urine.

Urine Formation

• The kidney controls fluid and electrolyte balance by controlling urine volume and composition.

Reabsorption and Secretion of Substances by Area of the Tubule

• Proximal tubule: water, glucose, sodium, and amino acids are reabsorbed; hydrogen ions (H+) are secreted.
• Descending loop: Water is reabsorbed; urea is secreted.
• Ascending loop: Sodium chloride (NaCl) is reabsorbed; potassium (K+) and urea are secreted.
• Distal tubule: Sodium and water are reabsorbed; potassium and urea are secreted.
• Collecting duct: Water and sodium chloride (NaCl) are reabsorbed; potassium and urea are secreted.

Homeostasis

• Hormones released from the endocrine glands assist the kidneys in maintaining the optimal internal balance.
• Some will increase the filtration rate and others will decrease the filtration rate and production of urine.
• All this maintains homeostasis.

Urinary Bladder

• The urinary bladder is a small hollow organ.
• The ability to stretch is enhanced by a series of pleats called rugae.

Urination Reflex

• As urine accumulates, the bladder fills and stretches, and this stretch triggers the urinary reflex and the need to void to empty the bladder.
• When the bladder is full, signals are sent from the bladder to the spinal cord to the brain.
• The brain sends signals down the spinal cord, causing contraction of the muscular walls of the bladder, and the bladder empties.

Urination

• Urine leaves the bladder via the urethra, a thin muscular tube lined with several different types of epithelium along its length.

Urinary Tract Infections (UTIs)

• A urinary tract infection is caused by the movement of fecal bacteria into the urinary tract.
• Symptoms may include frequent, painful urination, bloody or cloudy urine with an unusual odor, and low abdominal/pelvic pain caused by bladder spasm.
• Treatment should begin promptly to avoid kidney damage from infection traveling from the bladder to the kidney.
• UTIs are more common in women because the urethra is in close proximity to the anus (exposure to anal bacteria) and the urethra is short (closer to the bladder).

UTI Prevention

• Prevention methods include drinking plenty of water, voiding often so urine doesn't stay stagnant in the bladder, and making sure to wipe perineum from front to back.
• Once diagnosed, UTIs are treated with antibiotics and increased fluid intake.

Changes Related to Aging

• A loss of muscle tone in the bladder can lead to urinary incontinence.
• Kidney function begins to decline at age 40 and declines at a rate of about 1% per year beyond age 40.

Impact of Aging on the Urinary System

• Loss of muscle tone in the bladder can lead to urinary incontinence:This can be embarrassing for clients, cause odour issues, and lead to discomfort/feeling cold, increase the risk of falls if hurrying to the washroom, intentional decreased intake of fluids, skin irritation and breakdown, and increased risk of UTIs with incontinence/wet briefs.
• Kidney function decline with age: Elderly clients can produce lower levels of hormones in the kidney which triggers thirst leading to dehydration, low urine production, stagnant urine in bladder, and increased risk for infection along with slower excretion of medications from the body leading to medications that can build up in the body and become toxic.