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BSC NURSING SEM1 APPLIED ANATOMY UNIT 8 The Renal System

  • Structure of kidney,

Structure of the Kidney

The kidneys are bean-shaped organs located on either side of the vertebral column in the retroperitoneal space. They play a critical role in filtering blood, maintaining fluid and electrolyte balance, and excreting waste products in the form of urine.

1. External Structure of the Kidney

A. Shape and Size:

  • Shape: Bean-shaped.
  • Dimensions:
    • Length: ~10–12 cm.
    • Width: ~5–7 cm.
    • Thickness: ~2–3 cm.
  • Weight: Approximately 120–150 grams in adults.

B. Location:

  • Positioned retroperitoneally (behind the peritoneum).
  • Right kidney is slightly lower than the left due to the liver’s position.

C. Coverings:

  1. Renal Capsule:
    • Thin, fibrous membrane that encloses the kidney.
  2. Adipose Capsule:
    • Fat layer providing cushioning and protection.
  3. Renal Fascia:
    • Dense connective tissue anchoring the kidney to surrounding structures.
  4. Pararenal Fat:
    • Outer layer of fat acting as additional protection.

2. Internal Structure of the Kidney

A. Regions of the Kidney:

  1. Cortex:
    • Outer region of the kidney.
    • Contains renal corpuscles (glomeruli and Bowman’s capsules) and proximal and distal convoluted tubules.
    • Functions in filtering blood and initial urine formation.
  2. Medulla:
    • Inner region consisting of renal pyramids.
    • Each pyramid is cone-shaped and composed of collecting ducts and loops of Henle.
    • Functions in concentrating urine.
  3. Renal Pelvis:
    • Funnel-shaped structure located in the kidney’s hilum.
    • Collects urine from the major calyces and drains it into the ureter.

B. Microscopic Structure:

  1. Nephron:
    • Functional unit of the kidney.
    • Each kidney contains ~1 million nephrons.
    • Parts of the Nephron:
      • Renal Corpuscle:
        • Glomerulus: Network of capillaries where filtration occurs.
        • Bowman’s Capsule: Surrounds the glomerulus and collects filtrate.
      • Renal Tubule:
        • Proximal Convoluted Tubule (PCT): Reabsorbs water, ions, and nutrients.
        • Loop of Henle: Concentrates urine by reabsorbing water and salts.
        • Distal Convoluted Tubule (DCT): Regulates ion balance and pH.
      • Collecting Duct:
        • Drains urine from multiple nephrons into the renal pelvis.
  2. Blood Supply of the Nephron:
    • Afferent Arterioles: Deliver blood to the glomerulus.
    • Efferent Arterioles: Carry blood away from the glomerulus.
    • Peritubular Capillaries: Surround the tubules for reabsorption and secretion.

C. Hilum:

  • Indentation on the medial side of the kidney.
  • Entry and exit point for:
    • Renal Artery: Supplies oxygenated blood.
    • Renal Vein: Drains deoxygenated blood.
    • Ureter: Transports urine to the bladder.

3. Blood Supply to the Kidney

  1. Renal Artery:
    • Branches from the abdominal aorta.
    • Divides into smaller arteries:
      • Segmental Arteries → Interlobar Arteries → Arcuate Arteries → Interlobular Arteries.
  2. Glomerular Capillaries:
    • Facilitate filtration in the nephron.
  3. Renal Vein:
    • Drains filtered blood into the inferior vena cava.

4. Functions of the Kidney

  1. Filtration:
    • Removes waste products like urea and creatinine from the blood.
  2. Reabsorption:
    • Reabsorbs essential substances like glucose, water, and ions back into the bloodstream.
  3. Secretion:
    • Excretes excess ions and toxins into the urine.
  4. Regulation:
    • Maintains fluid, electrolyte, and pH balance.
    • Regulates blood pressure via the renin-angiotensin-aldosterone system (RAAS).
  5. Erythropoiesis:
    • Produces erythropoietin, a hormone stimulating red blood cell production.

5. Clinical Relevance

  1. Chronic Kidney Disease (CKD):
    • Progressive loss of kidney function affecting filtration and homeostasis.
  2. Kidney Stones:
    • Crystallized minerals or salts obstructing the renal pelvis or ureter.
  3. Urinary Tract Infections (UTIs):
    • Bacterial infections affecting the kidneys, bladder, or urethra.
  4. Acute Kidney Injury (AKI):
    • Sudden decline in kidney function due to injury or illness.
  5. Hypertension:
    • Poor kidney function can lead to high blood pressure.
  • ureters,

Ureters: Anatomy and Function

The ureters are paired muscular tubes that transport urine from the kidneys to the urinary bladder. They are a vital component of the urinary system, ensuring the continuous flow of urine for excretion.

1. Structure of the Ureters

A. Dimensions:

  • Length: ~25–30 cm.
  • Diameter: ~3–4 mm (varies along the course; narrows at specific points).

B. Location:

  • Retroperitoneal structures running vertically along the posterior abdominal wall.

2. Parts of the Ureters

The ureters are divided into three parts based on their course:

  1. Abdominal Part:
    • Extends from the renal pelvis to the pelvic brim.
    • Located anterior to the psoas major muscle.
  2. Pelvic Part:
    • Descends into the pelvis and crosses over the iliac vessels.
  3. Intramural Part:
    • Passes through the wall of the urinary bladder at an oblique angle.
    • This oblique entry prevents urine backflow (vesicoureteral reflux).

3. Layers of the Ureter Wall

  1. Mucosa (Inner Layer):
    • Lined with transitional epithelium (urothelium).
    • Allows stretching as urine flows.
  2. Muscularis (Middle Layer):
    • Composed of smooth muscle fibers arranged in:
      • Inner longitudinal layer.
      • Outer circular layer.
    • Facilitates peristalsis to move urine.
  3. Adventitia (Outer Layer):
    • Connective tissue layer anchoring the ureter to surrounding structures.
    • Contains blood vessels, lymphatics, and nerves.

4. Blood Supply

  1. Arterial Supply:
    • Upper Ureter: Renal arteries.
    • Middle Ureter: Gonadal arteries (testicular/ovarian arteries) and abdominal aorta branches.
    • Lower Ureter: Superior and inferior vesical arteries.
  2. Venous Drainage:
    • Follows the arterial supply:
      • Renal, gonadal, and vesical veins.

5. Nerve Supply

  • Sympathetic Innervation:
    • Derived from the renal, aortic, and hypogastric plexuses.
  • Parasympathetic Innervation:
    • Pelvic splanchnic nerves (S2-S4).

Pain from the ureters is often referred to the lower abdomen, groin, or genitalia.

6. Points of Ureteric Constriction

The ureter has three natural narrowings where kidney stones are likely to get lodged:

  1. Ureteropelvic Junction (UPJ):
    • Where the renal pelvis narrows into the ureter.
  2. Pelvic Brim:
    • Where the ureter crosses over the iliac vessels.
  3. Ureterovesical Junction (UVJ):
    • Where the ureter enters the urinary bladder.

7. Function of the Ureters

  1. Transport of Urine:
    • Ureters use peristaltic waves to move urine from the renal pelvis to the bladder.
  2. Prevention of Reflux:
    • The oblique entry into the bladder ensures one-way flow and prevents backflow.

8. Clinical Relevance

  1. Ureteric Stones (Urolithiasis):
    • Stones can obstruct urine flow, causing severe pain (renal colic).
    • Common sites: UPJ, pelvic brim, UVJ.
  2. Hydroureter:
    • Dilation of the ureter due to obstruction, often accompanied by hydronephrosis (kidney swelling).
  3. Ureteral Stricture:
    • Narrowing of the ureter due to scar tissue, congenital defects, or trauma.
  4. Vesicoureteral Reflux:
    • Backward flow of urine from the bladder into the ureters, often due to an abnormal UVJ.
  5. Infections:
    • Ureteritis (inflammation of the ureters) can occur as part of a urinary tract infection (UTI).
  6. Ectopic Ureter:
    • A congenital condition where the ureter does not properly connect to the bladder.

9. Diagnostic Tools

  1. Ultrasound:
    • Detects ureteric stones or dilation.
  2. CT Scan:
    • High-resolution imaging to identify stones, strictures, or tumors.
  3. Intravenous Pyelogram (IVP):
    • Uses contrast dye to visualize the urinary tract.
  4. Cystoscopy:
    • Allows direct visualization of the ureteral openings in the bladder.
  • bladder,

Urinary Bladder: Anatomy and Function

The urinary bladder is a hollow, muscular organ that temporarily stores urine before it is excreted from the body. It is an essential component of the urinary system.

1. Structure of the Bladder

A. Shape and Location

  • Shape:
    • Empty: Pyramid-shaped.
    • Full: Oval or balloon-shaped.
  • Location:
    • In males: Lies anterior to the rectum and superior to the prostate gland.
    • In females: Lies anterior to the vagina and inferior to the uterus.
  • Position:
    • Lies in the pelvic cavity when empty but extends into the abdominal cavity when full.

B. Parts of the Bladder

  1. Apex:
    • The anterior, pointed part connected to the umbilicus by the median umbilical ligament (a remnant of the urachus).
  2. Base (Fundus):
    • The posterior part of the bladder that faces backward.
    • In females, it is in contact with the vagina.
    • In males, it is in contact with the rectum.
  3. Body:
    • The main, central part of the bladder.
  4. Neck:
    • Narrow, inferior portion leading to the urethra.
  5. Trigone:
    • A triangular area on the bladder’s interior floor.
    • Bounded by:
      • Two ureteral openings (where urine enters from the ureters).
      • The internal urethral orifice (where urine exits into the urethra).
    • Unlike the rest of the bladder, the trigone is smooth and does not expand.

C. Layers of the Bladder Wall

  1. Mucosa (Inner Layer):
    • Lined with transitional epithelium (urothelium), allowing expansion.
    • Contains rugae (folds) that disappear when the bladder is full.
  2. Submucosa:
    • Connective tissue supporting the mucosa.
  3. Detrusor Muscle (Middle Layer):
    • Thick layer of smooth muscle arranged in three layers (longitudinal, circular, longitudinal).
    • Contracts during urination to expel urine.
  4. Adventitia/Serosa (Outer Layer):
    • Adventitia: Covers the bladder’s posterior and inferior parts.
    • Serosa: Covers the bladder’s superior surface (peritoneal covering).

2. Blood Supply

Arterial Supply:

  1. Superior Vesical Arteries: Supply the upper part of the bladder.
  2. Inferior Vesical Arteries (Males): Supply the lower bladder and prostate.
  3. Vaginal Arteries (Females): Supply the lower bladder.

Venous Drainage:

  • Vesical Venous Plexus: Drains into the internal iliac veins.

3. Nerve Supply

  1. Sympathetic Nerves:
    • From the hypogastric plexus.
    • Facilitate bladder relaxation and storage of urine.
  2. Parasympathetic Nerves:
    • From the pelvic splanchnic nerves (S2-S4).
    • Cause contraction of the detrusor muscle for urination.
  3. Somatic Nerves:
    • Pudendal Nerve (S2-S4):
      • Controls the external urethral sphincter for voluntary urination.

4. Lymphatic Drainage

  • Drains into the external iliac lymph nodes.

5. Functions of the Bladder

  1. Urine Storage:
    • Temporarily holds urine (400–600 mL in adults).
  2. Urine Expulsion (Micturition):
    • Contracts to release urine through the urethra.
  3. Protection:
    • Mucosa and detrusor muscle protect against infection and mechanical injury.

6. Mechanism of Urination (Micturition Reflex)

  1. Filling Phase:
    • Bladder fills with urine.
    • Stretch receptors in the bladder wall send signals to the brain, signaling the need to urinate.
  2. Voiding Phase:
    • Parasympathetic stimulation contracts the detrusor muscle.
    • Internal urethral sphincter relaxes involuntarily.
    • External urethral sphincter relaxes voluntarily, allowing urine to exit.

7. Clinical Relevance

  1. Urinary Tract Infections (UTIs):
    • Common in the bladder (cystitis), causing pain and frequent urination.
  2. Bladder Stones:
    • Crystallized minerals that can obstruct urine flow and cause pain.
  3. Overactive Bladder:
    • Increased urgency and frequency of urination due to involuntary detrusor muscle contractions.
  4. Neurogenic Bladder:
    • Dysfunction caused by nerve damage, leading to loss of bladder control.
  5. Bladder Cancer:
    • Commonly arises from the urothelium; presents with hematuria (blood in urine).
  6. Vesicoureteral Reflux:
    • Backflow of urine from the bladder into the ureters, often due to an abnormal trigone.
  7. Urinary Retention:
    • Inability to empty the bladder completely, often due to prostate enlargement in men.
  • urethra

Urethra: Anatomy and Function

The urethra is a tube-like structure that allows urine to exit the body from the urinary bladder. In males, it also serves as a passage for semen, making it part of both the urinary and reproductive systems.

1. Structure of the Urethra

A. Location:

  • The urethra originates from the bladder neck and ends at the external urethral orifice.

B. Gender Differences:

  • The urethra is shorter in females (~4 cm) compared to males (~18–20 cm).

2. Parts of the Urethra

In Males:

The male urethra is divided into four regions:

  1. Preprostatic Urethra:
    • Length: ~1–1.5 cm.
    • Location: Between the bladder neck and prostate.
    • Function: Internal urethral sphincter here prevents retrograde ejaculation.
  2. Prostatic Urethra:
    • Length: ~3 cm.
    • Location: Passes through the prostate gland.
    • Features:
      • Urethral Crest: Raised ridge on the posterior wall.
      • Prostatic Sinus: Openings for prostatic ducts.
      • Ejaculatory Ducts: Drain into the prostatic urethra, allowing semen to mix with urine.
  3. Membranous Urethra:
    • Length: ~1–2 cm.
    • Location: Passes through the deep perineal pouch.
    • Surrounded by the external urethral sphincter, which is under voluntary control.
  4. Spongy (Penile) Urethra:
    • Length: ~15 cm.
    • Location: Runs through the corpus spongiosum of the penis.
    • Features:
      • Bulbourethral Glands (of Cowper): Open into this segment, secreting lubricating mucus.

In Females:

The female urethra is shorter and simpler, divided into:

  1. Proximal Part:
    • Located near the bladder neck.
    • Contains the internal urethral sphincter.
  2. Distal Part:
    • Opens to the external urethral orifice, located anterior to the vaginal opening.

3. Layers of the Urethra Wall

  1. Mucosa (Inner Layer):
    • Lined with epithelium:
      • Transitional epithelium near the bladder.
      • Stratified squamous epithelium near the external opening.
    • Contains glands secreting protective mucus.
  2. Muscularis (Middle Layer):
    • Inner longitudinal and outer circular smooth muscle.
    • Helps propel urine.
  3. Adventitia (Outer Layer):
    • Connective tissue anchoring the urethra to surrounding structures.

4. Functions of the Urethra

  1. Urine Excretion:
    • Transports urine from the bladder to the exterior of the body.
  2. Reproductive Function (Males Only):
    • Conveys semen during ejaculation.

5. Blood Supply

  1. Arterial Supply:
    • Males:
      • Prostatic branch of the inferior vesical artery.
      • Branches of the internal pudendal artery.
    • Females:
      • Internal pudendal and vaginal arteries.
  2. Venous Drainage:
    • Corresponds to arterial supply, draining into the internal pudendal vein.

6. Nerve Supply

  1. Autonomic Innervation:
    • Sympathetic: From the hypogastric plexus, controlling internal urethral sphincter.
    • Parasympathetic: From pelvic splanchnic nerves (S2-S4), relaxing the sphincter for urination.
  2. Somatic Innervation:
    • Pudendal nerve (S2-S4): Controls the external urethral sphincter.

7. Clinical Relevance

  1. Urinary Tract Infections (UTIs):
    • More common in females due to the short urethra.
    • Symptoms: Dysuria (painful urination) and increased frequency.
  2. Urethral Stricture:
    • Narrowing of the urethra due to scarring or trauma, causing obstructed urine flow.
  3. Urethritis:
    • Inflammation of the urethra, often due to infection (e.g., gonorrhea or chlamydia).
  4. Incontinence:
    • Weakness of the external urethral sphincter leads to involuntary urine leakage.
  5. Prostatic Enlargement (Males):
    • Benign prostatic hyperplasia (BPH) compresses the prostatic urethra, causing difficulty in urination.
  6. Fistulas:
    • Abnormal connections between the urethra and adjacent organs (e.g., rectum or vagina).
  7. Catheterization:
    • Insertion of a catheter into the urethra for draining urine in medical procedures.

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