Kidney Development and Anatomy: Embryology, Structure, and Function

The kidneys develop from the ___ (also called the metanephrogenic blastema).

Paramesonephric tissue

Which embryonic kidney appears first during development?

Pronephros

When do the pronephros appear?

4th week of gestation

When do the pronephros regress?

By week 5

Where do the pronephros begin?

Cervical region of the embryo

Segmented divisions of mesoderm form tubules called ___.

Nephrotomes

Tubules of the pronephros join to form the ___.

Pronephric duct

The pronephric duct extends from the cervical region to the ___.

Cloaca

Are the pronephros functional?

No - they are non-functional

The mesonephros develop ___ to the pronephros.

Caudally

The mesonephros form the ___.

Mesonephric duct (Wolffian duct)

What serves as the interim kidney during the first trimester?

Mesonephros

Which structure sprouts the ureteric bud?

Mesonephros

The ureteric bud induces development of the ___.

Definitive kidney (metanephros)

The metanephros forms the ___.

Definitive kidney

When does the metanephros appear?

5th week of development

When does the kidney become functional?

About 10-12 weeks

The ureteric bud contacts the metanephric blastema to form the ___.

Metanephric system

The collecting system develops from the ___.

Ureteric bud

The collecting system forms which structures?

Ureter, renal pelvis, major and minor calyces, collecting tubules

The excretory system develops from the ___.

Metanephric blastema

The excretory system forms the kidney's functional units called ___.

Nephrons

The proximal end of each nephron forms the ___.

Bowman's capsule around a glomerulus

The distal end of the nephron elongates to form the ___, ___, and ___.

Proximal convoluted tubule, loop of Henle, distal convoluted tubule

The kidneys develop in the pelvic region before ___.

Ascending into the abdomen

Kidneys are paired, ___-shaped organs.

Bean

The kidneys lie in which body cavity?

Retroperitoneal cavity

The kidneys lie anterior to the ___.

Psoas muscles

Which kidney sits slightly lower and why?

Right kidney - due to the right lobe of the liver

Each kidney moves inferiorly up to ≈ ___ cm with inspiration.

2.5 cm

Each kidney has a vertical slit on its medial surface called the ___.

Hilum

The hilum leads into the ___.

Renal sinus

The outer functional area of the kidney is the ___.

Renal parenchyma (cortex and medulla)

The central cavity area of the kidney is the ___.

Renal sinus

The renal cortex extends from the capsule to the base of the ___.

Pyramids

The renal medulla consists of the ___.

Medullary pyramids

The tip (apex) of each pyramid sits within the ___.

Minor calyx

The cortical tissue separating pyramids is called ___.

Columns of Bertin

Urine is produced in the ___ and collected in the ___.

Cortex; medulla

The renal sinus houses the ___, ___, ___, and ___.

Renal artery, renal vein, nerves, lymphatics and fat

The collecting system of the sinus consists of the ___ and ___.

Infundibulum and renal pelvis

Minor calyces unite to form ___.

Major calyces

The renal pelvis receives urine from the ___.

Major calyces

The renal pelvis is continuous with the ___.

Ureter

The functional unit of the kidney is the ___.

Nephron

Each kidney contains about how many nephrons?

≈ 1 million

The nephron's vascular component begins with the ___.

Afferent arteriole → glomerulus → efferent arteriole

The glomerulus is surrounded by the ___.

Bowman's capsule

The renal tubule sequence is: proximal → loop of Henle → distal → ___.

Collecting duct

The kidneys play a role in the production of ___.

Red blood cells (erythropoietin)

The kidneys produce urine and filter blood to remove ___.

Toxic wastes such as ammonia and nitrogen

The kidneys maintain ___ and ___ homeostasis.

Salt and water

The kidneys help regulate blood ___ levels.

pH (around 7)

The kidneys regulate endocrine functions such as ___.

Erythropoietin, renin, and vitamin D metabolism

Renin secretion by the kidneys helps regulate ___.

Blood pressure

Vitamin D metabolism by the kidneys affects ___.

Skeletal development and calcium absorption

Urine secretion starts at the ___ and ends at the ___.

Renal pyramid; ureter

Average kidney length = ___ cm.

9-12 cm

Average kidney width = ___ cm.

4-5 cm

Average kidney AP (depth) = ___ cm.

2.5-3 cm

The arterial blood supply to the kidneys arises from the ___.

Main renal arteries

Renal arteries usually branch from the aorta just below the ___.

Superior mesenteric artery (SMA)

Renal arteries divide into which branches?

Segmental → Interlobar → Arcuate → Interlobular → Afferent arterioles

List the full renal arterial flow.

Aorta → Main Renal → Segmental → Interlobar → Arcuate → Interlobular → Afferent arteriole

The right renal artery is longer and runs ___.

Posterior to the IVC

Arcuate arteries are located at the ___.

Base of the pyramids (junction between cortex and medulla)

Venous drainage begins with the ___.

Efferent vessel

Renal veins lie ___ to renal arteries.

Anterior

The renal veins drain directly into the ___.

IVC (inferior vena cava)

The left renal vein is ___ than the right and courses ___.

Longer; posterior to SMA and anterior to aorta

At the renal hilum, which structures lie from anterior to posterior?

Vein (anterior) → Artery (middle) → Ureter (posterior)

Right kidney relations: superomedial = ___, superolateral = ___, medial = ___ (duodenum), inferior = ___.

Right adrenal gland; liver; 2nd part of duodenum; colon

Left kidney relations: superior = ___, anterior/superior = ___, anterior/medial = ___, anterior to upper pole = ___, inferior = ___.

Left adrenal gland; spleen; stomach; pancreatic tail; left colic flexure

Posterior to both kidneys are the ___, ___, ___, and ___.

Diaphragm; psoas; quadratus lumborum; transversus abdominis muscles

Which muscle can mimic kidney pain?

Psoas muscle

A Column of Bertin is a ___ that extends into the ___.

Prominent invagination of cortex; medulla

A Hypertrophied Column of Bertin may be mistaken for a ___.

Renal mass

A Dromedary hump appears as a ___ on the ___ surface of the ___.

Bulge of cortical tissue; lateral; left kidney

A Junctional Parenchymal Defect is an embryonic remnant of ___.

Fusion site between upper and lower kidney segments

Sonographic appearance of JPD (Junctional Parenchymal Defect): ___.

Triangular, echogenic area (anterior/superior pole)

A Fetal Lobulation is a ___ variation present until ≈ age 5.

Developmental (surface lobes on kidney)

A Duplex Collecting System occurs when ___.

Renal sinus is divided and may have two pelves or ureters

Incomplete duplication means ___.

Two collecting systems with a single ureter entering the bladder

Complete duplication means ___.

Two separate ureters entering the bladder

An Extrarenal Pelvis is a renal pelvis that ___.

Extends outside the renal border and can mimic hydronephrosis

A Horseshoe Kidney occurs when ___.

Lower poles of kidneys are fused across midline

The isthmus of a horseshoe kidney lies ___.

Anterior to the spine

A Renal Ectopia occurs when ___.

A kidney fails to ascend from the pelvis during development

Common locations for renal ectopia include ___.

Lower abdomen and pelvic regions

The shape, position, and size of the urinary bladder vary with ___ and ___.

Age and the amount of urine it contains

The bladder wall measures about ___ mm when distended and ___ mm when empty in adults.

3 mm; 5 mm

On ultrasound, a distended bladder appears ___ on transverse and ___ on longitudinal scans.

Square; triangular

The base of the bladder where ureters enter is called the ___.

Trigone

If the bladder is collapsed, the lumen appears ___.

Not visible

The bladder lumen is ___ and the walls are ___.

Anechoic; hyperechoic

Why is a full bladder useful in ultrasound?

It acts as an acoustic window and displaces bowel for better pelvic imaging

Cystitis refers to ___.

Inflammation of the bladder

The ureters are approximately ___ cm long.

25 cm

The ureters drain urine from the ___ to the ___.

Kidneys; bladder

The ureters begin at the ___.

Ureteropelvic junction (UPJ)