Urinary System Anatomy

• This lecture covers the anatomy of the urinary system, including its structure, arterial supply, and venous drainage.

The Urinary System

• A main excretory system of the body.
• Organs include kidneys, ureters, urinary bladder, and urethra.
• Kidneys: Two organs which excrete urine.
• Ureters: Two tubes that carry urine from the kidneys to the urinary bladder.
• Urinary Bladder: Collects urine.
• Urethra: Passes urine to the outside of the body.

Kidney Functions

• Carries out 4 primary function
• Filters nitrogenous wastes, toxins, ions, etc. from the blood which are then excreted as urine.
• Regulates blood volume and chemical composition through balancing water, salts, acids, and bases.
• Kidney produces regulatory enzymes such as renin, which regulates blood pressure and kidney function, and erythropoietin, which stimulates red blood cell production from marrow.
• Kidney helps the metabolism of Vitamin D into its active form.

Kidney Location

• Kidneys are reddish-brown organs located behind the peritoneum.
• Lie high up on the superior lumbar region of the posterior abdominal wall on either side of the vertebral column
• Kidneys are retroperitoneal
• They extend from the T12 to L3 vertebrae.
• The right kidney is slightly lower because of the presence of the liver.
• Lateral surface: Convex
• Medial surface: Concave
• Two poles: Superior and inferior
• Two surfaces: Anterior and posterior
• Lateral border: Convex
• Medial border: Concave
• Renal hilum: area where blood vessels, nerves, and ureters enter and exit the kidneys.
• Adrenal glands: Situated superior to each kidney.

Anatomical Relations

• Right kidney: related to the right adrenal gland, right lobe of the liver, duodenum, and right colic flexure
• Left kidney: related to the left adrenal gland, stomach, spleen, body of the pancreas, left colic flexure, descending colon, and jejunum

Hilum of the Kidney

• Found on the medial border of the kidney.
• Serves as a passage for structures from anterior to posterior: the renal vein (anterior), the renal artery (intermediate), and the pelvis of the ureter which leaves the hilum posterior to the renal vessels.

Internal Anatomy of the Kidney

• Cortex: Superficial region of the kidney.
  • Light and granular
• Medulla: Deep, central region of the kidney.
  • It consists of a deep layer and is darker in color.
• Renal pyramids: Cone-shaped structures found within the renal medulla with the base against cortex and the apex as the papilla
• Renal columns: Extensions of cortex that separate the renal pyramids within the medulla.
• Collecting parts: Renal papillae, minor calyces, major calyces, and the renal pelvis.

Urine Collection

• Urine flows through ducts inside each renal papilla.
• The urine is then released into a minor calyx, then to major calyx, then the renal pelvis, and finally into the ureter.

Blood Supply

• The kidneys receive a direct blood supply from the aorta via the renal arteries.
• Blood is returned to the inferior vena cava via the renal veins.

Blood Flow to Kidney - Arteries

• Renal arteries provide blood to the kidneys.
• Segmental arteries are a branch of renal arteries.
• Lobar arteries are a branch of segmental arteries.
• Interlobar arteries: A branch of Lobar arteries
• Arcuate arteries: A branch of Interlobar arteries
• Interlobular arteries: A branch of arcuate arteries
• Afferent arterioles: feed blood into the glomerulus

Blood Flow from Kidney – Veins

• Blood flows from the nephron to the interlobular veins, then to the arcuate veins, then interlobar veins, and finally to the renal vein.

The Nephron

• A structural and functional unit that forms urine.
• Consists of the glomerular (Bowman's) capsule, glomerulus, and renal tubules.
• Glomerular (Bowman’s) Capsule: Blind, cup-shaped end of a renal tubule that completely surrounds the glomerulus.
• Glomerulus: A tuft of capillaries associated with a renal tubule.
• Renal Tubules: divided into three main parts - proximal convoluted tubule, loop of Henle, and distal convoluted tubules.

Layers of Tissue Supporting the Kidney

• Renal Capsule: fibrous capsule, prevents kidney infection.
• Adipose Capsule: Fatty mass that cushions the kidney and helps attach it to the body wall.
• Renal Fascia: Outer layer of dense fibrous connective tissue that anchors the kidney.

Ureters

• Narrow, thick-walled tubes, that are a continuation of the renal pelvis.
• Transport urine from the kidneys to the urinary bladder.
• Retroperitoneal, running behind the peritoneum.
• Length: typically 25 cm.
• Diameter: typically 3 mm.
• Has two parts - abdominal and pelvic.
• Course medially within the posterior bladder wall before opening into the interior.
• Extend inferiorly to enter the posterolateral wall of the base of the urinary bladder.
• Oblique entry helps prevent the backflow of urine.

Ureter Characteristics

• Narrows can be found on the ureter
• At its starting point ( the junction with the renal pelvis) renal calculi (stones) can get stuck
• At pelvic brim
• Entering the bladder at the trigone in an angle, this helps prevent backflow of urine up the ureter and act as a sphincter

Trigone

• Triangular region of the internal urinary bladder.
• Formed from two ureteric orifices and the internal urethral orifice.
• Sensitive to expansion and signals when the bladder needs to be emptied.

Urinary Bladder

• A bag that collects urine and stores it until micturition (passing urine).

• Position: superior and posterior to the pubic symphysis.

• In females, the urinary bladder is in contact with the uterus posterosuperiorly and with the vagina posteroinferiorly.

• Males: Posterior surface related to the rectovesical pouch

• Lower part is related to the seminal vesicle and vas deferens

• Inferiorly, it is related to the prostate gland.

• When empty, the bladder exhibits an upside-down pyramidal shape.

How Urine Passes

• During micturition, the urethral sphincter at the base of the bladder relaxes.
• The detrusor muscle contracts.
• Urine is voided via the urethra.

Urethra

• A fibromuscular tube that conducts urine to the exterior of the body.
• Exits the urinary bladder through the urethral opening at anteroinferior surface.
• Contains two urethral sphincters:
  • The internal urethral sphincter restricts the release of urine until the pressure within the urinary bladder is high enough.
  • The external urethral sphincter and voluntary activities are needed to release the urine.
• Approximately 18 to 20 centimeters long.

Male Urethra

• Serves for both urinary and reproductive functions.
• Has three segments, the prostatic urethra, the membranous urethra, and the spongy urethra.
• Prostatic urethra is approximately 3 to 4 centimeters long and is the most dilatable portion.
  • It extends through the prostate gland, immediately inferior to the male bladder, where multiple small prostatic ducts enter it.
• Membranous urethra is the shortest and least dilatable portion.
  • Extends from the inferior surface of the prostate gland through the urogenital diaphragm.
• Spongy urethra is the longest part, at 15 centimeters.
  • Encased within a cylinder of erectile tissue in the penis called the corpus spongiosum.
  • extends to the external urethral orifice

Female Urethra

• Serves for a single function- urine
• Transports urine from the urinary bladder to the vestibule, an external space immediately internal to the labia minora
• 3 to 5 centimeters long, it opens to the outside of the body at the external urethral orifice located in the female perineum.

Lecture on the anatomy of the urinary system. Covers the organs of the urinary system (kidneys, ureters, bladder, urethra) and their functions. Also discusses kidney location, structure, blood supply and venous drainage.