Urinary System: Anatomy and Function

• The urinary system consists of two kidneys, two ureters, one urinary bladder, and one urethra

Functions of the Urinary System

• Filters the blood, eliminating waste
• Maintains homeostasis by regulating blood pressure/volume and acid balance
• Secretes hormones like Erythropoietin, which stimulates red blood cell formation in bone marrow, and Calcitriol including Vitamin D
• Urine is initially produced by the kidneys, then passes through the ureters, into the urinary bladder, and exits the body through the urethra

The Kidney

• A pair of bean-shaped, reddish-brown, parenchymatous organs
• Dimensions are approximately 10-13cm in length, 5-7cm in breadth, and 4cm in thickness, weighing 120-150g
• The left kidney is generally more slender, while the right kidney tends to be broader and shorter
• Kidneys feature two borders, two extremities, and two surfaces

Renal Hilum

• Located on the medial border of each kidney
• Serves as a point of entry/exit for renal vessels, nerves, and a part of the pelvis

Renal Sinus

• A central recess extending from the renal hilum
• Contains branches of the renal artery and vein, nerves, lymphatic vessels, minor and major renal calices, renal pelvis, and adipose tissue

Renal Pedicle

• Structures within the renal hilum are enclosed by connective tissue, forming the renal pedicle
• Orientation of structures within the renal pedicle from front to back: renal vein, renal artery, renal pelvis
• From top to bottom, the arrangement is: renal artery, renal vein, renal pelvis
• The right kidney sits lower than the left
• The renal hilum is around the first lumbar vertebra level
• The renal region is clinically defined as the area between the twelfth rib and the lateral border of the erector spinae muscle

The Adjacencies of Kidneys

• Adrenal glands are positioned above both kidneys, separated by loose connective tissue

Kidney Variations

• Location, number, and shape can vary between individuals

Kidney Transplant

• The need for kidney replacement

Structure of the Kidney

• Renal Tissue: Consisting of the cortex and medulla
• Conveing Duct: Consisting of minor renal calices, major renal calices, and the renal pelvis

Renal Cortex

• Contains renal corpuscles and renal tubules

Renal Medulla

• Features renal pyramids (15-20) and renal columns

Renal Papilla

• Characteristics; 7-12 papillary foramina

Coverings of the Kidneys

• Kidneys have three layers of coverings
• From inner to outer: fibrous capsule (firm, strong), adipose capsule, renal fascia
• Fibrous Capsule: A tough, dense membrane with elastic fibers that can be easily peeled off
• Adipose Capsule: It is a fatty layer which offers elastic buffer protection
• Renal Fascia: Includes anterior and posterior layers plus connective tissue trabeculae connecting to the fibrous capsule for fixation

Kidney Fixation

• Primarily depends on the renal capsules
• Secondarily depends on abdominal pressure, vessels, the peritoneum, and nearby organs

The Ureters

• Muscular tubes carrying urine from the kidney's renal pelvis to the urinary bladder for storage
• The course of each ureter can be divided into three parts: the abdominal part, the pelvic part, which occurs at the superior pelvic aperture, and the intramural part
• Male: ductus deferens. They run beside the Ureter
• Female: uterine vessels. They also run beside the Ureter

Ureter Orifice

• Opens into the superolateral angle of the bladder
• The intramural part acts as a valve to stop urine backflow when the bladder is full
• There are three constricted parts within the ureters
• The junction where the ureter meets the renal pelvis
• The point where the ureter crosses the superior aperture of the lesser pelvis
• The intramural segment

The Urinary Bladder

• Is a hollow, muscular organ that stores urine
• Size, shape, position, and relations change with urine volume
• An empty urinary bladder resembles a triangular pyramid, split into apex, body, fundus, and neck sections
• The neck of the bladder, which is the lowest and most fixed portion, with the internal urethral orifice

Trigone of Bladder

• A smooth triangular region located on the fundus of the bladder
• Formed by the internal urethral orifice and two ureteric orifices
• This area is prone to disease
• Notable Structures: interureteric ridge, cystoscope
• In males, the bladder neck is attached to the prostate gland
• In females, it's secured to the urogenital diaphragm

The adjacencies of The Fundus of The Bladder

• In males: seminal vesicles, ampullae of the ductus deferens, and rectum
• In females: uterus and vagina

The Urethra

• The urethra extends from the urinary bladder to the exterior opening
• The female urethra differs significantly from the male urethra
• The female urethra is short (3-5cm), wide (0.6cm), and straight, surrounded by the urethrovaginal sphincter, with its external orifice located just anterior to the vaginal orifice

Summary of Urine Pathway:

• Urine produced by renal tissue flows through minor renal calices to major renal calices, then to the renal pelvis, through the ureters, into the urinary bladder, and finally exits the body via the urethra