[OS 206] E03-LAB01-Anatomy Laboratory Mini LEAP_compressed

• Kidneys lie retroperitoneally on the posterior abdominal wall (PAW)
• Kidneys sit on either side of the vertebral column from T12-L3
• Kidneys description:
  • Reddish-brown in color during life
  • Approximately 10 cm long
  • Approximately 5 cm wide
  • Approximately 5.5 cm thick
• The left kidney's hilum is located near the transpyloric plane
• Kidneys are bean-shaped, each featuring:
  • Anterior and posterior surfaces
  • Medial and lateral margins
    • Lateral margins are convex
    • Medial margins are concave, housing the renal hilum, renal sinus and renal pelvis
  • Superior and inferior poles

Renal Hilum

• The point where structures serving the kidneys enter and exit the renal sinus
  • Includes vessels, nerves, and urine-draining structures
• Structures within the renal hilum, anterior to posterior:
  • Renal vein: Bigger and wider than artery
  • Renal artery
  • Renal pelvis: A flattened, funnel-shaped expansion at the ureter's superior end, continuous with the ureter

Laterality of the Kidneys

• To determine kidney laterality, note that the renal pelvis or ureter sits on the hilum's posterior aspect

Vasculature

• Length difference: The right renal artery is longer because the aorta is on the left
• Branching pattern: The renal artery gives off five segmental end arteries (one posterior, four anterior)
• Veins: The left renal vein is longer, about 6-10 cm in length, because the inferior vena cava (IVC) is on the right side, the left renal vein receives three tributaries: inferior phrenic vein, gonadal vein, and lumbar vein
• Collateral circulation: Segmental arteries lack collateral circulation, thus tissue dies if one is blocked and Extensive collateral circulation exists around the infundibula and perinephric area
• Blood flow pathway: Renal artery to segmental end arteries to lobar to interlobar to arcuate to interlobular to afferent arteriole to glomerulus to efferent arteriole to vasa recta and then secondary capillary networks to interlobular veins to arcuate veins to interlobar veins to lobar veins to segmental veins to renal vein

Arteries

• The longer, right renal artery runs posterior to the IVC
• Kidneys have five vascular (renal) segments, each supplied by an end artery
  • Renal segments are independent and surgically removable
  • End arteries mean no collateral circulation, and blockage leads to ischemia
• Renal arteries split into five segmental end arteries

Five Segmental End Arteries

• Posterior: Arises as a continuation of renal artery's posterior branch, supplying the posterior segment
• Apical: Comes from the superior segmental artery, supplying the superior (apical) segment
• Anterosuperior: Originates from renal artery's anterior branch, supplying the anterosuperior area
• Anteroinferior: Originates from renal artery's anterior branch, supplying the anteroinferior area
• Inferior: Originates from the renal artery, supplying the inferior segment

Superior Polar Artery

• Superior polar renal artery often displays unusual branching patterns with varying origins:
  • Abdominal aorta as an accessory renal artery
  • Direct branch from the main renal artery
  • Superior hilar renal artery
  • Segmental branch of the renal artery
• Superior polar artery as an accessory renal artery rising from the abdominal aorta occurring because the kidneys originally develop in the pelvic cavity, and as the embryo develops, they ascend to the lumbar region, and during development, blood supply shifts from branches of iliac arteries to the abdominal aorta:
  • Accessory arteries due to the persistence of embryonic vessels formed during the ascent of the kidneys

Internal Anatomy of the Kidney

• Coverings of the kidney
  • Perinephric Fat: A fat pad that surrounds the kidneys extending into their hollow centers, the renal sinuses
  • Renal Capsule: Made of tough, fibrous connective tissue closely enveloping each kidney, providing support to the soft tissues inside
• Spaces/Areas surrounding the kidney
  • Renal Sinus: the space within the kidney
  • Renal Hilum: The entrance to the renal sinus

Parenchyma of the Kidney

• Renal Cortex: The outer region of the kidney located inner to the capsule, surrounding the medulla
• Renal Columns: also known as Columns of Bertin, extensions of parenchyma that extend between and separate the renal pyramids
  • Renal columns permit blood vessels to pass throughout the cortex towards the pyramids
  • Renal columns also contain fibrous connective tissue contributing to the stroma
• Renal Medulla: Composed of striated renal pyramids containing tubular structures and blood vessels
• Renal Pyramids: Triangular structures comprised of collecting ducts that condense at the apex forming the renal papilla and also form the lobes of the kidneys, which are only visible on the external surface

Drainage of Urine From Parenchyma

• Renal Papilla: The apex of the renal pyramid, where urine is excreted and drained into the ureter
• Calyces: Two or three major calyces receive urine from the renal pelvis
  • Each major calyx splits into two or three minor calyces
  • Each minor calyx is indented by a renal papilla
  • In living people, the renal pelvis and calyces are normally collapsed or empty
• Renal Pelvis: A flattened, funnel-shaped expansion of the ureter's superior end, with its apex continuous with the ureter
• Ureter: The two narrow tubes that carry urine from the kidneys to the bladder in the pelvis

Flow of Urine

• Renal Pyramid/Medulla → Renal Papilla → Minor Calyces (2 or 3) Infundibula → Major Calyces → Renal Pelvis

Urine Formation

• Begins as protein-free fluid is filtered from glomerular capillaries into Bowman's capsule
• Filtered fluid travels through tubules, modified by reabsorption of water and solutes back into blood
• Secretion of other substances happens from peritubular capillaries into the tubules
• Urine excretion is a result of glomerular filtration, tubular reabsorption and tubular secretion
• Urinary excretion rate can be expressed as: Filtration rate - Reabsorption rate + Secretion Rate

Renal handling of substances

• Substance A: Freely filtered by glomerular capillaries, neither reabsorbed nor secreted
  • Excretion rate = filtration rate
  • Example: creatinine
• Substance B: Freely filtered, partly reabsorbed from tubules back into blood
  • Urinary excretion < filtration rate
  • Example: sodium and chloride ions (electrolytes)
• Substance C: Freely filtered at glomerulus, entirely reabsorbed
  • No excretion in urine
  • Example: amino acids and glucose (nutritional substances)
• Substance D: Freely filtered, not reabsorbed, with additional secretion from peritubular capillaries into tubules
  • Excretion rate = filtration rate + tubular secretion rate
  • Example: organic acids and bases

Anatomy of the Bladder

Related spaces of the Bladder

• Utero-vesical pouch: Located between the uterus' anterior surface and bladder's superior wall, a pelvic cavity is formed by a peritoneal fold covering both
• Recto-uterine space: Space between the posterior uterus and anterior rectum named posterior cul-de-sac
  • Potential space for fluid accumulation (peritoneal fluids, blood from menstruation, secretions)
• Retropubic space: Also known as the Space of Retzius or Perivesical space, the space between the bladder and pubic bone

Median Umbilical Ligament

• A fibrous remnant of the urachus
• Structure extends cranially/superiorly from the urinary bladder's apex toward the umbilicus
• Covered by the medial umbilical fold

Urachus

• A fibrous structure and embryonic remnant of the allantois
• Runs as fibrous cord from fetal bladder apex to the umbilicus
• Functions as an extraembryonic membrane that stores urinary wastes and helps in gas exchange
• Connects to the yolk sac within the body stalk, transforming into umbilical cord
• The junction of the allantois to the embryo forms part of the hindgut, developing into the bladder
• Allantois to urachus to median umbilical ligament

Clinical correlate

• Patent Urachus results from persistent urachal remnants
• Can present as periumbilical discharge, umbilical mass, abdominal or periumbilical pain, or dysuria with presentation based more on remnant size/location rather than embryologic origin
• Pathologic variants: Umbilical polyps, sinuses, fistulae, cysts, and bands (may occur independently or combined)

Parts of the Urinary Bladder

• Apex: Points toward the superior edge of the pubic symphysis when the bladder is empty, opposite the fundus
• Body: Major part of the bladder between apex and fundus
• Fundus: Located opposite the apex, formed by convex posterior part
• Neck: Located inferiorly, below the internal urethral orifice and emerges at junction of inferolateral surfaces, connecting to urethra
• Bladder bed: In contact with structures, laterally the pubic bone and fascia of the levator ani and superior obturator internus muscle border inferolateral surfaces
• The bladder's superior surface is covered with peritoneum
• In males: the fundus is separated from rectum by the fascial rectovesical septum (centrally) and seminal glands/ampullae (laterally)
• In females: The fundus relates directly to vagina's superior anterior wall, and the Bladder is enveloped by visceral fascia (LCT)

Detrusor Muscle

• Primary component of bladder walls and consists of smooth muscle under autonomic control
  • Parasympathetic causes contraction and relaxation of internal urethral sphincter and thus bladder emptying
  • Sympathetic causes contraction of the internal urethral sphincter and ejaculation prevents semen reflux into bladder
• Internal Urethral Sphincter (Involuntary): Muscle fibers of detrusor muscle that contracts during ejaculation to prevent retrograde ejaculation of semen
• Internal Urethral Orifice: Opening assisted by fibers that run radially in the bladder
  • In males: the muscle fibers in the neck merge with prostate fibromuscular tissue
  • In females: the muscle fibers are continuous with muscle fibers in the urethral wall
• Trigone: Smooth, triangular area with three openings inside the bladder fundus, its angles formed by the two ureteric orifices and the internal urethral orifice
  • Ureteric orifices are encircled by detrusor muscle loops to prevent reflux of urine into the ureters during bladder contraction
  • Interureteric ridge/crest/bar (bar of Mercier): A sub-mucosal ridge running across between the two ureteric orifices
• Uvula: A slight elevation of the trigone more prominent in men because of prostate enlargement

Anatomy of the kidneys, including their retroperitoneal location on the posterior abdominal wall between T12 and L3. This section describes the kidneys' size, shape, and key features such as the hilum, renal sinus, and renal pelvis. It also details the arrangement of structures within the renal hilum.