Introduction to Urinary System: Organs.

 

Introduction.

  • Urine is a waste material formed by Kidneys after filtering the blood, the system involved in formation and excretion of urine is called “Urinary System”.

  • Like other systems of the body, the Urinary system also works in coordination with other systems.

  • It plays a vital role in maintaining homeostasis along with the respiratory system and cardiovascular system.

  • The branch of science that deals with the structure, function, diagnosis and treatment of diseases of Kidneys is called Nephrology.

  • The study of the Urinary system is covered in Urology.

Urinary System:

  • It consists of,

    1. Kidneys.

    2. Ureters

    3. Urinary Bladder.

    4. Urethra.

  1. Urethra.

  • It is a muscular tube that transports urine from the bladder to outside the body for disposal.

  • It's the only organ of the urinary system that differs in male and female sexes

  • It starts from the basal trigonal part of the urinary bladder.

  • Draining of urine is regulated by two types of sphincters

    • Internal Urinary Sphincter (Smooth muscle)

    • External Urinary Sphincter (Skeletal Muscle).

  • Female Urethra:

    • It is short and 4cm in length.

    • Starts from the urinary bladder and opens above the vaginal opening, medial to labia minora.

  • Male Urethra:

    • It is longer and is about 20cm in length.

    • It starts from the bladder and opens at the tip of penis.

    • It has four parts,

      • Preprostatic Urethra

      • Prostate Urethra

      • Membranous Urethra.

      • Spongy (Penile) Urethra.

    • Male urethra also serves the functions of the reproductive system i.e. carrying the sperms outside the body.

  1. Urinary Bladder.

  • It is a muscular bag made up of smooth muscle and lies in the “pelvic cavity.”

  • It is “Pear Shaped” but becomes “Ovalwhen filled with urine.

  • It is divided into,

    • Body 

    • Neck

  • It has three openings,

    • Two openings for ureters at the body.

    • One for the urethra in the neck region.

  • The three openings form a triangle called “Trigone”.

  • Histology:

    • Inner Layer: Mucosa (Transitional epithelium).

    • Middle Layer: Muscular layer (Smooth Muscles).

    • Outer Layer: Fibrous Layer (Connective Tissue).

  • It acts as a temporary reservoir for urine.

  • Internal urethral sphincter from the upper part of the urethra controls urine flow.

  • External urethral sphincter is skeletal and hence voluntary.


  1. Ureters.

  • Two in number from each kidney.

  • These are muscular tubes that transport urine from the kidney to the urinary bladder.

  • 25-30 cm long and 3mm in thickness.

  • They start from the renal pelvis and end in the posterior wall of the urinary bladder.

  • Histology:

    • Inner Layer: Mucosa (Transitional epithelium).

    • Middle Layer: Muscular layer (Smooth Muscles).

    • Outer Layer: Fibrous Layer (Connective Tissue).

  • Its function is to transport urine.

  1. Kidneys.

External Anatomy of Kidney:

  • They are “Two” in number, reddish in color and bean shaped in appearance.

  • Each lie on either side of the spine, well protected by ribs, muscles and adipose tissues.

  • Each kidney weighs around 150gm, male kidneys are slightly larger than female kidneys.

  • They are 10-15 cm in length, 5-7cm in width and 3cm thick.

  • Near the center of the concave border of the kidney there is a deep vertical fissure called “Renal Hilus” from which blood vessels, lymphatic vessels, nerves enter and exit the kidney, and ureters also come out of the kidney through it.

  • Coverings of the Kidneys:

    • Renal fascia: outermost covering. (Dense connective tissue).

    • Adipose Capsule: Middle covering of adipose tissue that acts as shock absorbant.

    • Renal Capsule: Inner covering of connective tissue.

  • On top of each kidney there is a “Suprarenal Gland” also called “Adrenal Gland” which secretes “Aldosterone” and directly affects functioning of the kidney.

Internal Anatomy of Kidney:

  • A longitudinal section of kidney shows “Two” distinct parts,

    • Renal Cortex (Outer)

    • Renal medulla (Inner).

  • Renal columns  are connective tissue extensions that come from the renal cortex to renal medulla.

  • In between renal columns there are characteristic structures of the kidney called “Renal  Pyramids” and “Renal papillae”.

  • Renal pyramids are conical areas present between two renal columns.

  • Each human kidney contains around 10-18 renal pyramids.

  • Renal papilla is the location where urine from collecting ducts is poured in renal calyx.

    • This is the area where collecting ducts merge with each other to form “papillary Duct”.

  • Renal calyx is a chamber through which urine from the papillary duct  is poured in the renal pelvis.

    • Renal calyces are of two types,

      • Major calyx (Receives two or more minor calyces)

      • Minor calyx

  • Renal pelvis is a funnel-like structure formed by merging two to three major calyces, it narrows to form the “Ureter”.

  • Renal sinus is a cavity in the kidney formed by merging renal pelvis and renal calyces.

  • Renal hilum is the area of the kidney from which nerves, lymph and blood vessels enter and exit the kidney.

Commonly Asked Questions.

  1. Write in detail about the Urinary System.

  2. Write a note on the organs of the urinary system.

  3. With a well labelled diagram describe the external and internal anatomy of the Kidneys.

Topics u may like to read