Function of the Urinary System Flashcards
Function of the Urinary System
Removal of metabolic wastes (nitrogenous and acidic)
Removal of hormones, drugs, and other foreign material from the body
Regulation of water, electrolytes and acid-base balance
Secretion of erythropoietin
Activation of vitamin D
Regulation of blood pressure through renin-angiotensin-aldosterone system
Kidneys
Superior portion protected by lower ribs
Cortex (outer layer) contains glomeruli
Medulla (inner section) contains tubules and collecting ducts. Inside the medulla is the renal pelvis and calyces through which urine flows into ureter.
Filtration
A large volume of fluid including wastes, nutrients, electrolytes and other dissolve substances, passes from the blood into the tubule, cells and protein remain in the blood. When pressure is increased, more filtrate forms, more urine is produced.
Three parts of the tubule
Proximal convoluted tubule, loop of Henle, and the distal convoluted tubule
Function of tubule
Reabsorption of essential nutrients, water and electrolytes and secretion of certain wastes and electrolytes.
Main action of proximal tubule
Most water is reabsorbed into blood along with glucose and other nutrients and some electrolytes.
Glucosuria
Limit on reabsorption of glucose (transport or tubular maximum), hyperglycemia associated with diabetes mellitus.
What is the function of hormones in the renal system?
Control the reabsorption of fluid and electrolytes.
ADA
Antidiuretic hormone - from the posterior pituitary, controls reabsorption of water by altering the permeability of the distal convoluted tubule and collecting duct
Aldosterone
Adrenal cortex, control sodium reabsorption and water by exchanging sodium ions for potassium or hydrogen ions in the distal convoluted tubule.
Atrial natriuretic hormone
From the heart, also controls fluid balance by reducing sodium and fluid reabsorption in the kidneys
How much of the cardiac output enters the rental arteries from the aorta?
20-25%
Peritubular capillaries or vasa recta
Flow blood vessels to kidney: afferent arteriole, glomerular capillaries, efferent arteriole, then peritubular capillaries or vasa recta
How many sets of arterioles and capillaries are included in each nephron?
Two arterioles: afferent and efferent
Two capillaries: glomerular and peritubular
Summary of blood flow through kidney
Renal artery, interlobar artery, arcuate artery, interlobal artery, afferent arteriole, glomerular capillaries, efferent arteriole, peritubular capillaries, interlobular vein, arcuate vein, interlobar vein, renal vein.
What is the purpose of dual arterioles (afferent and efferent?)
To control the pressure in the glomerular capillaries and consequently the glomerular filtration pressure. This pressure determines the glomerular filtration rate (GFR)
What three factors control constriction in the arterioles
Local autoregulation - small, local reflex adjustments in the diameter of the arterioles made in response to minor changes in blood flow in the kidneys
Sympathetic nervous system - increases vasoconstriction in both arterioles when stimulated
Renin angiotensin mechanism - Renin is secreted by the juxtaglomerular cells in the kidney when blood flow in the afferent arteriole is reduced for any reason. Renin acts on the plasma protein angiotensinogen to produce angiotensin 1 and as the blood passes through the lung, angiotensin converting enzyme converts angiotensin 1 to angiotensin 2, a powerful systemic vasoconstrictor.
What happens if blood flow to the kidney is seriously impaired? E.g. blood pressure drop
Both the SNS and the renin-angiotensin mechanism are activated to restore blood pressure and flow to vital areas.
The renin-angiotensin-aldosterone
When blood flow decreases for any reason, angiotensin causes systemic vasoconstriction and stimulates production of aldosterone which increased reabsorption of sodium and water to increase blood volume
Location of bladder
Retroperitoneally
What can obstruct urine flow in men?
Prostate gland, hypertrophied in older men.
What facilitates kidney infection?
The mucosa lining the urinary tract is continuous through the urethra, bladder, and ureter to the pelvis of the kidney
Micturition
Urination, occurs when a reflex is stimulated by increased pressure as the bladder distends.
Enuresis
Involuntary urination by a child after age 4-5 - associated with developmental delay, sleep pattern, or psychosocial aspects rather than a physical defect
Stress incontinence
Increased intra-abdominal pressure forces urine through the sphincter - coughing, lifting, laughing women after urogenital diaphragm weakend by multiple pregnancies and age.
Overflow incontinence
Incompetent bladder sphincter - elderly, weakened detrusor muscle may prevent complete emptying leading to frequent emptying and incontinence.
Neurogenic bladder
Spastic or flaccid due to interference with CNS
Retention
Inability to empty the bladder, may be accompanied by overflow incontinence - a spinal cord injury at the sacral level can block the micturition reflex
Retention can occur after anesthesia
Catheter
Tube inserted in the urethra that drains urine from the bladder to a collecting bag - irritating to the tissue, can be a means of introducing bacteria however prevent kidney damage due to backup of urine
Urine pH range
4.5-8.0
Urinalysis - cloudy
Indicates presence of large amount of protein, blood cells, or bacteria and pus
Urinalysis - dark colour
May be hematuria, excessive bilirubin, or highly concentrated
Urinalysis - Unusual odor
Infections or certain dietary components or medications
Abnormal constituents of urine
Blood - hematuria -infection, inflammation, tumors in urinary tract, increased glomerular permeability or hemorrhage in the tract
Protein - Leakage of albumin or mixed plasma proteins into the filtrate, inflammation, increased glomerular permeability
Bacteria (bacteriuria) and pus (puyuria) infection in urinary tract
Urinary casts - microscopic sized molds of tubules - inflammation of kidney tubules.
Glucose and ketones - when diabetes is not well controlled.
Specific gravity
Ability of tubules to concentrate the urine, very low (dilute urine) usually related to renal failure (assuming normal hydration)
Blood tests for urinary tract disorders
Elevated serum urea and serum creatinine - failure to excrete nitrogen wastes due to decreased GFR
Metabolic acidosis - decreased serum pH and decreased serum bicarbonate - decreased GFR and failure of tubules to control acid-base balance
Anemia - decreased erythropoietin secretion
Electrolytes
Antibody levels
Renin levels - indicate a cause of hypertension.
Conditions that prescribed diuretics
Renal disease, hypertension, edema, congestive heart failure, liver disease, pulmonary edema
Most common diuretic - inhibits sodium chloride resorption in the tubules
Side effect - loss of electrolytes
Dialysis
Provides an artificial kidney (an individual can function normally with half of one kidney)
Used to treat someone with acute renal failure until problem reversed or transplant
Hemodialysis
Special equipment and training - patient’s blood moves from implanted shunt or catheter in an artery through a tube to a machine where it exchanges wastes, fluid and electrolytes.
Semipermeable membrane separates patient’s blood from the dialysis fluid and the constituents move between the two compartments
Wastes move from blood to dialysate while bicarbonate ion moves into blood
Blood cells and protein remain in the blood
Movement occurs by ultrafiltration, diffusion (by a concentration gradient) and osmosis.
Heparin administered.
3 times a week 3-4 hours
Peritoneal Dialysis
May be done at night while patient sleeps or while ambulatory
The peritoneal membrane which is large in surface area, thin and highly vascular serves as the semipermeable membrane
A catheter with entry and exit points is implanted in the peritoneal cavity
Dialyzing fluid is instilled through the catheter into the cavity and remains there allowing exchange of wastes and electrolytes to occur by diffusion and osmosis, then the dialysate is drained from cavity.
Requires more time than hemodyalisis.
Can cause infection resulting in peritonitis.
Urinary Tract Infections
Urine generally provides an excellent medium for growth of microorganisms.
Common causative organism - Escherichia coli - resident flora of the intestine 85% - not washed out when bladder empties
Other various associated organisms
Why are women more vulnerable to UTIs then men?
Shortness of urethra, proximity to anus, frequent irritation from sexual activity, baths, feminine hygiene products
Causes of UTI in men
Prostatic hypertrophy and retention of urine (any infection of prostate or testes likely to spread to urinary structures)
Predisposing factors for UTIs
Incontinence with incomplete emptying of bladder
Retention of urine in bladder
Obstruction to urine flow - not flushing out organisms, pregnancy, scare tissue, kidney stones
Immunosuppression and diabetes mellitus
Catheterization
Cystitis and Urethritis
Cystitis - bladder wall - capacity usually reduced
Urethritis - urethral wall - inflamed, red, swollen and can be ulcerated
Lower abdominal pain
Dysuria (painful urination), frequency, urgency, nocturia
Systemic signs - fever, malaise, nausea, leukocytosis
Cloudy urine, unusual odor
Urinalysis - bacteriuria, pyuria, hematuria
Pyelonephritis
One or both kidneys
Infection extends from ureter into the kidney, involves renal pelvis and medullary tissue (tubules and interstitial tissue)
Purulent exudate fills the kidney pelvis and calyces, and the medulla is inflamed
Abscesses and necrosis can be seen in the medulla and may extend through the cortex to the surface of the capsule.
If severe - exudate can compress renal artery and vein and obstruct urine flow to ureter.
Recurrent infection can lead to fibrous scare tissue over calyx, leading to loss of tubule function and hydronephrosis.
Signs and symptoms of pyelonephritis
When bladder infection spreads to kidneys
Signs of cystitis like dysuria
Pain - dull aching in lower back or flank area - inflammation stretching renal capsule
Systemic signs
Urinalysis similar to cystitis except urinary casts consisting of leukocytes or renal epithelial cells are present.
Glomerulonephritis (Acute Poststreptococcal Glomerulonephritis
Many forms
APSGN - follows strep infection with certain strains. These infections usually originate as upper respiratory infections, middle ear infections or “strep throat”
Develops 10 days to 2 weeks after antecedent infection.
Antistreptococcal antibodies lodge in glomerular capillaries, causes inflammatory response in the glomeruli
Increased permeability and proliferation, results in leakage of some protein and large numbers of erythrocytes into filtrate.
Congestion and cell proliferation interfere with filtration in the kidney causing decreased GFR and retention of fluid and wastes.
Renal failure, elevated blood pressure and edema
Signs and symptoms of glomerulonephritis
Urine dark and cloudy - protein and red blood cells
Facial and periorbital edema as colloid osmotic pressure of blood drops and sodium and water retained
Blood pressure elevated due to increased renin secretion and decreased GFR
Flank or back pain develops as kidney tissue swells and stretches
General signs of inflammation - malaise, fatigue, headache, anorexia and nausea
Urine output decreases as GFR declines.
