42. Urinary system. Embryonic development. Kidneys and renal parenchyma. Macroscopic character-istics.

URINARY SYSTEM

• Also known as the renal system is responsible for producing, storing and eliminating urine from the body.

Organs:

1. Kidneys

• the primary organs
• filters waste products and excess substances from the blood to produce urine.

2. Ureters:

• Narrow tubes carry urine from the kidneys to the bladder.

3. Bladder:

• Hollow, muscular organ located in the pelvis that stores urine until its ready to be expelled from the body.

Development:

• From intermediate mesoderm.
• Begins at the 4th week.
• There are 3 stages:

1. Pronephrons

• The pronephrons emerges around the 4th week of development.
• It begins in the cervical region of the embryo.
• Segmented divisions of intermediate mesoderm form tubules called nephrotomes.
• These nephrotomes join to create the pronephric duct, which extends from the cervical region to the cloaca (distal end) of the embryo.

2. Mesonephrons: “late in 4th week”

• The mesonephrons develops inferiorly to the pronephrons.
• They have mesonephric tubules, which are associated with capillaries.
• So they can perform filteration.
• The tubules drain into the mesonephric duct (Wolffian duct).
• opens into the cloaca.

3. Metanephrons

• The metanephros forms the definitive kidney.
• It appears around the 5th week of development and becomes functional around the 12th week.
• The ureteric bud from the mesonephric duct makes contact with a caudal region of intermediate mesoderm called the metanephric blastema.
• Collectively, these blastema form the metanephric system, which has two components:
• Collecting system: Derived from the ureteric bud, it includes the ureter, renal pelvis, major and minor calyces, and collecting tubules.
• Functional nephrons: These nephrons are responsible for urine production and filtration.