Human Physiology: Urinary System Quiz

The Urinary System

• The urinary system comprises paired kidneys, paired ureters, urinary bladder, and urethra
• Functions include: excretion (removing metabolic waste), elimination (discharging waste products), and homeostasis (regulating blood volume and solute concentration)
• Kidneys perform excretory functions, producing urine containing water, ions, and small soluble compounds
• Urine travels from kidneys through ureters to bladder for temporary storage, then through urethra to the exterior
• Urination (micturition) is the process of eliminating urine from the bladder

Learning Outcomes

• Identify the organs of the urinary system
• Understand the major functions of the urinary system
• Understand the processes involved in urine formation
• Understand factors influencing glomerular filtration pressure and glomerular filtration rate (GFR)
• Understand conditions associated with the renal system

Kidney Structure

• Kidneys are located on either side of the vertebral column
• The right kidney is slightly lower than the left
• Each kidney is capped by an adrenal gland
• Kidneys and adrenal glands lie between muscles of the dorsal body wall and peritoneal lining
• An adult kidney is approximately 12 cm long
• The renal hilum is a medial indentation where structures (ureters, blood vessels, nerves) enter or exit the kidney

Kidney Structure (Further details)

• Renal cortex is the outer layer, contacting the fibrous capsule
• Renal medulla contains renal pyramids
• A kidney lobe comprises a renal pyramid and overlying renal cortex
• Urine is produced in the kidney lobes
• Urine drains from renal papilla into cup-shaped calyces
• Renal pelvis connects to ureters, draining urine from the kidney

Blood Supply

• Kidneys have a rich blood supply
• Blood is supplied by renal artery, segmental arteries, interlobar arteries, arcuate arteries, and cortical radiate arteries

Functions of the Urinary System

• The urinary system removes metabolic wastes (urea and uric acid)
• It regulates blood volume and blood pressure by adjusting water lost in urine and secreting hormones (erythropoietin and renin)
• Regulates plasma concentrations of sodium, potassium, chloride, and other ions by regulating loss in urine; controls calcium levels through calcitriol synthesis
• Helps stabilize blood pH by controlling loss of hydrogen and bicarbonate ions in urine
• Conserves nutrients (glucose and amino acids) by preventing their loss in urine

Regulation of Blood Ion Composition

• Kidneys play a role in regulating sodium, potassium, calcium, and chloride concentrations in blood

Excretion of Waste and Toxins

• Urine removes unwanted waste products
• The main waste product is urea, formed from amino acid breakdown
• Other waste products include ammonia and bilirubin, and uric acid

Maintenance of Blood Osmolarity

• Kidneys maintain constant blood osmolarity (total dissolved particles per liter of solution)
• Normal osmolarity in a healthy human is approximately 275 to 300 milliosmoles per liter (mOsm/l)
• Kidneys control this range through independent regulation of solutes and water

Regulation of Blood pH

• Kidneys assist in regulating blood pH by controlling hydrogen ion excretion and bicarbonate ion concentration
• Normal blood pH is 7.35-7.45

Regulation of Blood Pressure

• Kidneys regulate blood pressure via the renin-angiotensin-aldosterone system
• Renin concentration changes blood pressure
• Aldosterone secretion is mainly controlled by the renin-angiotensin-aldosterone mechanism and blood potassium concentration

Hormone Production

• Kidneys secrete renin (blood pressure), erythropoietin (red blood cell production), and calcitriol (active vitamin D), enhancing calcium and phosphorus absorption

Regulation of Blood Glucose

• Kidneys help regulate blood glucose levels
• When blood glucose falls, kidneys metabolize glutamine to synthesize glucose via gluconeogenesis, restoring blood sugar levels

The Nephrons

• Nephrons are the structural and functional units of the kidney
• Each kidney contains millions of nephrons
• Nephrons filter blood, and form urine

Tubular Reabsorption

• The body needs to retain water and vital substances during urine formation
• Active and passive transport mechanisms reabsorb substances from the filtrate back into the blood. This process takes place in the renal tubule cells

Tubular Secretion

• Tubules secrete substances (e.g., hydrogen ions, creatinine, and other waste products) that are not effectively filtered by the glomerulus or that the body no longer needs

Urine Formation

• Glomerular filtration—nonselective, passive process from high glomerular pressure into lower glomerular capsule (filtrate)
• If glomerular pressure is too low (oliguria/anuria) filtration is not adequate
• Tubular reabsorption— reclaiming needed substances (glucose, water, amino acids) from filtrate
• Tubular secretion—secretion of unwanted/excess substances into the filtrate

Glomerular Pressure

• Hydrostatic pressure, from the smaller efferent arteriole size and glomerular capillaries, aids filtration
• Juxtaglomerular apparatus (autoregulation) controls glomerular blood pressure relative to systemic pressure
• Dilation/constriction in afferent/efferent arterioles ensures adequate blood flow and prevents extreme changes in blood flow

Renin-Angiotensin-Aldosterone System (RAAS)

• Regulates blood flow through the kidneys
• Response to changes in blood pressure and plasma sodium content:
• Low sodium leads to decreased water retention, decreased blood volume, and decreased blood pressure.
• Low blood pressure leads to renin release from Juxtaglomerular cells --> renin converts angiotensinogen into angiotensin I --> lungs convert into angiotensin II --> triggering aldosterone release, increasing Na+ reabsorption

Active and Passive Transport

• Active transport: Requires energy to move substances across a membrane, from tubule to blood
• Passive transport: Does not involve energy; depends on concentration gradients. This process assists water movement

Urine Volume

• Factors influencing urine volume: Fluid intake, fluid loss, hormone levels, and excretion of solids (like glucose)
• Normal output is generally 1200-1500 mL, but a range of 600-2000 mL is considered normal.
• Decreased urine output (oliguria) can be due to dehydration, increased urination (polyuria) and its causes
• Cessation of urine output (anuria) is often due to significant kidney damage

Physical Examination of Urine

• Physical examination involves assessing color, clarity, and specific gravity of urine.
• Common colors include pale yellow, yellow, dark yellow, and amber.

Urinalysis—Abnormal Urinary Constituents

• The table shows substances that might be present in abnormal levels or amounts (in urine) due to various causes

Urinalysis Report Form

• This is a form used to record the results of urinalysis
• Variables/characteristics of urine are measured and analyzed

Types of Urine Specimens

• Different types of urine specimens are collected for various purposes, for routine screening or testing

Urine Odor

• Common causes of unusual urine odor include presence of bacteria, ketones, and various metabolic disorders

pH

• Normal urine pH is typically slightly acidic (5.0-6.0) but can vary depending on meals
• Range of normal pH is 4.5-8.0
• High pH could indicate metabolic issues/conditions

Causes of Acid & Alkaline Urine

• The list details various causes, ranging from respiratory problems/diet to conditions like dehydration or infection

Clinical Significance

• Precipitation of inorganic chemicals in urine forms urinary crystals, leading to kidney stones (renal calculi), depending on urinary pH

Summary of Clinical Significance (regarding Urine pH)

• Conditions like respiratory/metabolic acidosis/ketosis, alkalosis, renal tube deficits, renal calculi, etc., impact urine pH

Urinary Tract Infection (UTI)

• Symptoms of UTI include urinary urgency and frequency, dysuria, and cloudy/blood-tinged urine.
• Back pain and fever may accompany kidney infections

Renal Failure

• Key factors include diabetes and hypertension
• Common in older adults and certain racial/ethnic groups
• Simple tests for proteinuria and creatinine can aid early kidney disease diagnosis

Self-Assessment Quiz

• A series of questions covering various aspects of the urinary system and its functions