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Urinary System: Functions, Anatomy, and Physiology, Study notes of Anatomy

Central Philippine University (CPU)Anatomy

A comprehensive overview of the urinary system, covering its functions, anatomy, and physiology. It delves into the roles of the kidneys, ureters, bladder, and urethra in waste elimination, fluid balance, and electrolyte regulation. The document also explores the processes of urine formation, including filtration, reabsorption, and secretion, and discusses the characteristics of urine. Additionally, it examines age-related changes in the urinary system and common urinary issues.

Typology: Study notes

2024/2025

Available from 01/11/2025

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charles-andrew-martin 🇵🇭

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C.A.B.M. | 2024
1
Urinary System
Functions of the Urinary System
1. Waste Elimination:
o Kidneys remove waste products through
urine, including:
▪ Nitrogenous wastes
▪ Toxins
▪ Drugs
▪ Excess ions
2. Regulation:
o Produces renin to maintain blood
pressure.
o Produces erythropoietin to stimulate red
blood cell production.
o Converts vitamin D to its active form.
Organs of the Urinary System
1. Kidneys
2. Ureters
3. Urinary Bladder
4. Urethra
Kidneys
Location and Structure
• Position: Retroperitoneal (behind the parietal
peritoneum).
o Located at T12 to L3 vertebral level.
o Right kidney is slightly lower than the
left due to liver placement.
• Size: 12 cm (5 in) long, 6 cm (2.5 in) wide.
• Renal Hilum: Medial indentation where ureters,
renal blood vessels, and nerves enter/exit.
• Adrenal Gland: Positioned atop each kidney.
Protective Layers
1. Fibrous Capsule: Directly encloses the kidney.
2. Perirenal Fat Capsule: Cushions against
trauma.
3. Renal Fascia: Anchors kidney to surrounding
structures.
Internal Anatomy
1. Renal Cortex: Outer region.
2. Renal Medulla:
o Contains Renal Pyramids: Triangular
regions of tissue.
o Renal Columns: Separate the pyramids,
made of cortical tissue.
3. Renal Pelvis:
o Funnel-shaped structure leading to the
ureter.
o Calyces: Cup-shaped structures
collecting urine from pyramids.
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Urinary System Functions of the Urinary System

  1. Waste Elimination : o Kidneys remove waste products through urine, including: ▪ Nitrogenous wastes ▪ Toxins ▪ Drugs ▪ Excess ions
  2. Regulation : o Produces renin to maintain blood pressure. o Produces erythropoietin to stimulate red blood cell production. o Converts vitamin D to its active form. Organs of the Urinary System
  3. Kidneys
  4. Ureters
  5. Urinary Bladder
  6. Urethra Kidneys Location and Structure
  • Position : Retroperitoneal (behind the parietal peritoneum). o Located at T 12 to L 3 vertebral level. o Right kidney is slightly lower than the left due to liver placement.
  • Size : 12 cm (5 in) long, 6 cm (2.5 in) wide.
  • Renal Hilum : Medial indentation where ureters, renal blood vessels, and nerves enter/exit.
  • Adrenal Gland : Positioned atop each kidney. Protective Layers
  1. Fibrous Capsule : Directly encloses the kidney.
  2. Perirenal Fat Capsule : Cushions against trauma.
  3. Renal Fascia : Anchors kidney to surrounding structures. Internal Anatomy
  4. Renal Cortex : Outer region.
  5. Renal Medulla : o Contains Renal Pyramids : Triangular regions of tissue. o Renal Columns : Separate the pyramids, made of cortical tissue.
  6. Renal Pelvis : o Funnel-shaped structure leading to the ureter. o Calyces : Cup-shaped structures collecting urine from pyramids.

Blood Supply

  • One-quarter of the total blood supply of the body passes through the kidneys each minute
  • Renal artery provides each kidney with arterial blood supply
  • Arterial Flow : o Renal artery → Segmental arteries → Interlobar arteries → Arcuate arteries → Cortical radiate arteries.
  • Venous Flow : o Cortical radiate veins → Arcuate veins → Interlobar veins → Renal vein → Inferior vena cava. o No segmental veins Nephrons
  • Functional units of the kidneys (>1 million per kidney).
  • Consist of:
  1. Renal Corpuscle : ▪ Glomerulus : Network of capillaries with filtration slits formed by podocytes. ▪ Glomerular (Bowman’s) Capsule : Surrounds the glomerulus and collects filtrate; first part of renal tubule.
  2. Renal Tubule : Extends from glomerular capsule and ends when it empties into the collecting duct ▪ Subdivisions: ➢ Proximal Convoluted Tubule (PCT) : Major site of reabsorption. ➢ Nephron Loop (Loop of Henle) : Maintains concentration gradients. ➢ Distal Convoluted Tubule (DCT) : Involved in secretion and fine-tuning reabsorption.
  • Types of Nephrons:
  1. Cortical Nephrons : Located mostly in the cortex; include most nephrons
  2. Juxtamedullary Nephrons : Nephron loops dip deep into the medulla for concentrated urine production.
  • Capillary Beds :
  1. Glomerulus : Specialized for filtration. ▪ Fed and drained by arterioles ➢ Afferent arteriole — arises from a cortical radiate artery and feeds the glomerulus ➢ Efferent arteriole — receives blood that has passed through the glomerulus ▪ High pressure forces fluid and solutes out of blood and into the glomerular capsule
  2. Peritubular Capillaries : Adapted for absorption and secretion. ▪ Arise from the efferent arteriole of the glomerulus

Characteristics of Urine

  • Color : Pale to deep yellow (due to urochrome from hemoglobin breakdown) (dilute is a pale, straw color).
  • pH : Slightly acidic (around 6).
  • Specific Gravity : 1.001 to 1.035.
  • Normal Solutes : Sodium, potassium, urea, uric acid, creatinine, ammonia, bicarbonate.
  • Abnormal Solutes : Glucose, blood proteins, hemoglobin, WBCs (pus), bile.
  • Sterile at the time of formation
  • Slightly aromatic, but smells like ammonia with time Ureters
  • Slender tubes (25-30 cm) transporting urine from kidneys to bladder.
  • Utilize peristalsis and gravity. Urinary Bladder
  • Smooth, collapsible muscular sac for temporary urine storage.
  • Trigone : Triangular area at the base defined by:
  1. Two ureteral openings.
  2. One internal urethral orifice.
  • In males, the prostate surrounds the neck of the urinary bladder.
  • Wall Composition : o Three layers of smooth muscle ( Detrusor Muscle ). o Lined with transitional epithelium. o Can expand significantly without increasing internal pressure.
  • Capacity : o Moderately full: 500 ml. o Max capacity: ~1 liter. Urethra
  • Thin-walled tube that carries urine from the bladder to the body exterior.
  • Sphincters :
  1. Internal Urethral Sphincter : Involuntary smooth muscle.
  2. External Urethral Sphincter : Voluntary skeletal muscle.
  • Length : o Females: 3-4 cm. o Males: ~20 cm, divided into prostatic, membranous, and spongy urethra. Micturition (Urination)
  • The process of voiding urine.
  • Controlled by two sphincters: o Internal: Involuntary. o External: Voluntary.
  • Reflex initiated when ~200 ml of urine collects in the bladder, activating stretch receptors. Fluid, Electrolyte, and Acid-Base Balance Blood composition depends on three factors
  1. Diet
  2. Cellular metabolism
  3. Urine output Kidneys have four roles in maintaining blood composition
  4. Excreting nitrogen-containing wastes
  5. Maintaining water balance of the blood
  6. Maintaining electrolyte balance of the blood
  7. Ensuring proper blood pH

Water Balance

  • Body Water Content : o Females: ~50%. o Males: ~60%. o Babies: ~75%. o Elderly: ~45%.
  • Fluid Compartments :
    1. Intracellular Fluid (ICF): Inside cells, ~2/3 of total body water.
    2. Extracellular Fluid (ECF): Outside cells, includes plasma, interstitial fluid, lymph, transcellular fluid. Electrolyte Balance
  • Electrolytes (e.g., sodium, potassium, calcium) regulate water movement between compartments; charged particles (ions) that conduct electrical current in an aqueous solution
  • Regulation of water intake and output o Water intake must equal water output if the body is to remain properly hydrated o Sources for water intake o Ingested foods and fluids o Water produced from metabolic processes (10%)
  • Thirst mechanism is the driving force for water intake
  • Thirst mechanism o Osmoreceptors are sensitive cells in the hypothalamus that become more active in reaction to small changes in plasma solute concentration o When activated, the thirst center in the hypothalamus is notified o A dry mouth due to decreased saliva also promotes the thirst mechanism o Both reinforce the drive to drink
  1. Phosphate Buffer System.
  2. Protein Buffer System.
  • Respiratory Regulation : o Respiratory rate can rise and fall depending on changing blood pH to retain CO2 (decreasing the blood pH) or remove CO2 (increasing the blood pH)
  • Renal Regulation : o When blood pH rises: ▪ Bicarbonate ions are excreted ▪ Hydrogen ions are retained by kidney tubules o When blood pH falls: ▪ Bicarbonate ions are reabsorbed ▪ Hydrogen ions are secreted o Urine pH varies from 4.5 to 8. Developmental Aspects of the Urinary System
  1. Fetal and Early Life Development : o Kidneys begin to develop in the first few weeks of embryonic life. o By the third month of fetal life, the kidneys are functional and excreting urine. o The fetal urinary system interacts with the amniotic fluid as urine contributes to its composition.
  2. Congenital Abnormalities : o Polycystic Kidney Disease : A genetic condition in which cysts form in the kidneys, disrupting their function. o Hypospadias : A condition in males where the urethral opening is on the underside of the penis instead of at the tip.
  3. Urinary Control in Children : o Control over the voluntary urethral sphincter begins around 18 months of age. o Full nighttime bladder control is typically achieved by 4 years old.
  4. Common Urinary Issues in Young and Middle-Aged Adults : o Urinary Tract Infections (UTIs) : ▪ Caused by fecal microorganisms or pathogens associated with sexually transmitted infections (STIs). ▪ Escherichia coli (E. coli) accounts for 80% of all UTIs. o Streptococcus infections can also lead to urinary complications.
  5. Age-Related Changes in the Urinary System : o Decline in Renal Function : ▪ Filtration rate decreases with age. ▪ Tubule cells become less efficient at concentrating urine. o Incontinence and Urgency : ▪ Incontinence (loss of bladder control) becomes more common. ▪ Urgency (a strong and immediate need to urinate) increases. o Frequency and Nocturia : ▪ Increased frequency of urination, especially at night (nocturia). o Urinary Retention : ▪ Common in men due to prostate gland hypertrophy, which obstructs urine flow.
  6. Serious Conditions : o Renal Failure : ▪ Occurs when kidneys can no longer filter and concentrate urine effectively. ▪ Requires dialysis to maintain chemical homeostasis in the blood. 7. Problems associated with aging: o Urgency —feeling that it is necessary to void o Frequency —frequent voiding of small amounts of urine o Nocturia —need to get up during the night to urinate o Incontinence —loss of control o Urinary retention —common in males, often the result of hypertrophy of the prostate gland Reference: Marieb, E. N., & Keller, S. (2018). Essentials of human anatomy & physiology (12th ed., pp. 537 – 559 ). Pearson Education, Inc.