JC HBHD 2 Week 9 Chapter 20 The Urinary System

Urinary System Overview

• The urinary system is vital for homeostasis, balancing blood components and forming urine.
• Kidneys lie beneath the back muscles, behind the parietal peritoneum, just above the waistline.
• The right kidney is typically slightly lower than the left.
• The kidney has a renal cortex (outer layer) and a renal medulla (inner portion).
• The kidneys are composed of over 1 million microscopic nephrons which are essential to maintaining body function.
• The nephron has unique components: Renal corpuscle (glomerulus and Bowman's capsule), and renal tubule (PCT, Henle Loop, DCT, and collecting duct).
• The kidney's internal structure includes renal pyramids, renal columns, renal papillae, renal pelvis, and renal calyces.
• The renal pelvis is an expanded upper end of the ureter and extends inside the kidney.

Kidney Function

• Kidneys excrete toxins and nitrogenous wastes.
• They regulate the levels of many chemicals in the blood.
• They maintain water balance.
• They help regulate blood pressure and volume.
• They regulate red blood cell production through erythropoietin (EPO) secretion.

Formation of Urine

• Filtration occurs constantly in renal corpuscles.
• High glomerular blood pressure forces water and dissolved substances into Bowman's capsule from the glomerulus.
• Typical glomerular filtration rate is 125 mL/minute.
• Filtration, reabsorption, and secretion are involved in urine formation.

Reabsorption

• Reabsorption is the movement of substances from renal tubules back into the peritubular capillaries.
• Water, nutrients, and ions are reabsorbed.
• Water is reabsorbed through osmosis, mainly from proximal tubules.
• Sodium reabsorption happens in the Henle loop via countercurrent flow.
• Countercurrent mechanisms maintain the medulla's hypertonicity for efficient water reabsorption.
• Chloride ions passively move into the blood due to their negative charge.
• In reabsorption, substances from the filtrate are returned to the blood.

Reabsorption of Glucose

• Glucose is reabsorbed from proximal tubules into the blood for energy.
• The renal threshold is the blood glucose level where reabsorption capacity is exceeded.
• Excess glucose is left in the urine, a sign of possible diabetes.
• Glucose transport is active and requires energy.

Secretion

• Secretion is the movement of substances from the peritubular capillaries into the renal tubules.
• Various substances including hydrogen ions, potassium ions, urea, uric acid, creatinine, and certain drugs are secreted through active transport.
• Ammonia is secreted via diffusion; this process maintains electrolyte balance.

Control of Urine Volume

• Antidiuretic Hormone (ADH) from the posterior pituitary promotes water reabsorption in collecting ducts, thereby reducing urine volume.
• Aldosterone, secreted by the adrenal gland, triggers the RAAS process and promotes sodium and water reabsorption reducing urine volume.
• Atrial Natriuretic Hormone (ANH) from atrial cells promotes the loss of sodium and water into kidney tubules to increase urine volume.

Renin-Angiotensin-Aldosterone System (RAAS)

• The RAAS is a crucial system for regulating blood pressure and fluid balance.
• It's triggered by low blood pressure or low plasma volume.
• The process involves renin release, angiotensin I and II conversion, and aldosterone secretion for water and sodium reabsorption; this hormone process enhances sodium retention and thus water balance.

Atypical Amounts of Urine

• Anuria: Absence of urine
• Oliguria: Scanty amounts of urine
• Polyuria: Unusually large amount of urine

Ureters

• Narrow tubes with an expanded upper end (renal pelvis), located within the kidney.
• Lined with mucous membrane and muscular layer.
• Drain urine from renal pelvis to urinary bladder.
• Urinalysis examines urine characteristics to identify potential health issues, including specific gravity.

Urinary Bladder

• Elastic muscular organ capable of expansion.
• Lined with mucous membrane arranged in rugae.
• Stores urine before voiding; this capability allows for storage of urine so that frequent urination is not required.

Urethra

• Narrow tube from urinary bladder to the exterior.
• Lined with mucous membrane.
• Opening of urethra to the exterior is called the urinary meatus.
• Transports urine from the bladder to the exterior.
• Transports semen from the male reproductive system; this process is essential for reproduction.

Micturition

• Passage of urine from the bladder (urination or voiding).
• The process involves regulatory sphincters (internal and external).
• Bladder wall permits urine storage with minimal pressure increase.
• Emptying reflex is initiated by bladder wall stretch, internal sphincter relaxation, external sphincter relaxation.

Retention and Suppression

• Urinary retention: Urine is produced but not voided.
• Urinary suppression: No urine is produced, but the bladder functions normally.

Urinary Incontinence

• Urine is involuntarily voided.
• Urge incontinence: Associated with smooth muscle overactivity in the bladder wall.
• Stress incontinence: Associated with weakened pelvic floor muscles.
• Overflow incontinence: Associated with urinary retention and overdistended bladder.
• Reflex incontinence: Occurs when there's a lack of warning signals.
• Nocturnal enuresis (bedwetting): Involves nighttime involuntary urination.
• Neurogenic bladder: Issues with voiding due to nerve and muscle problems.

Urinalysis

• Physical, chemical, and microsopic examination of urine.
• Color, turbidity, odor, and specific gravity are diagnostic clues.
• Chemical analysis provides details about pH, urea, abnormal substances, and glucose levels.
• Centrifugation reveals cell types and casts as pointers toward possible issues; this technique aids in diagnosis.

Renal and Urinary Conditions

• Obstructive conditions interfere with normal urine flow and potentially cause backflow causing hydronephrosis.
• Hydronephrosis: Enlargement of the renal pelvis and calyces due to blockage; this condition may necessitate intervention.
• Renal calculi (kidney stones): Crystallized minerals that can block ureters, causing renal colic; treatment strategies vary.
• Tumors: Renal cell carcinoma (kidney cancer) and bladder cancer often feature hematuria in the urine; early detection and intervention are crucial.

Glomerular Disorders

• Result from damage to the glomerular-capsular membrane of the renal corpuscles.
• Nephrotic syndrome arises from various glomerular conditions.
• Proteinuria: Protein in the urine.
• Hypoalbuminemia: Low plasma protein levels due to protein loss in urine.
• Edema: Swelling caused by water loss from plasma.
• Acute glomerulonephritis: Inflammatory condition triggered by a delayed immune response to streptococcal infection; this is a significant concern.
• Chronic glomerulonephritis: A slow inflammatory condition from immune mechanisms often resulting in renal failure; prompt diagnosis and treatment are vital.

Kidney Failure

• Kidney failure occurs when kidneys are unable to function properly.
• Acute renal failure involves a sudden decline in kidney function.
• Chronic renal failure involves a slow and progressive loss of nephrons caused by diverse underlying diseases.
• Polycystic Kidney Disease (PKD): Hereditary disorder causing numerous cysts to form that destroy kidney tissue.

Progression of Kidney Failure

• Stage 1: Healthy nephrons compensate for damaged ones.
• Stage 2: Renal insufficiency where function slowly diminishes and uremia occurs (high BUN).
• Stage 3: Uremia or uremic syndrome; complete kidney failure, treated with transplant or artificial kidney.

Chronic Renal Failure

• Decline in glomerular filtration rate (GFR) and increase in BUN levels characterize chronic renal failure.
• This decline in GFR is a crucial indicator of the progression of the condition.