Urinary system

Function of the Urinary System is to Maintain Homeostasis

-Storage and excretion of urine

-Filtration of blood

-Release hormones

-Regulation of erythrocyte production

»»»Erythropoietin (EPO) → stimulates RBC production

-Regulation of ions and acid/base levels

F-E-H-I-A = Filtration, Excretion, Hormones, Ions, Acid-base.

Kidney disease

kidney is unable to filter toxins

Chronic kidney disease ↓ EPO → ↓ RBCs → anemia → low oxygen → organ failure

Tissue of origin

intermediate mesoderm (IM)

Pronephros

4-5 tubules

• First to appear

• Vestigial, non-functional

• Degenerates quickly

• duct develops alongside
  pronephros

• Its degeneration triggers mesonephros to form

Mesonephros

• Temporary functional kidney

• Contains small nephrons that filter blood

• Drains via mesonephric duct → cloaca

• Eventually degenerates

Metanephros

• Adult kidney

• Formed from:

  • Ureteric bud → urine collecting system
    (ureter, renal pelvis, calyces, collecting ducts)

  • bud=collecter

  • Metanephric blastema → urine-producing system
    (nephrons

blasetema>builder>proudcing

Ureteric buds will develop into the structure

that collect urine

Metanephric blastema will develop into
the structures

that produce urine

AT WEEK 7…

urorectal septum divides
the cloaca into the …

1.urogenital sinus (The urogenital sinus will develop into the
future urinary bladder and urether)
2. anorectal canal

Renal agenesis

>Rare congenital disease….

>a kidney does not form during development.

A baby normally forms two kidneys, but sometimes one or both fail to develop.
>Results from failure of metanephric
blastema to develop

Unilateral Renal Agenesis

👉 Unilateral = one side
If a person is born with one kidney missing, they usually have zero symptoms

>Because one kidney can fully take over the work of two.
The remaining kidney grows larger (compensatory hypertrophy) and handles filtration on its own

3. Bilateral Renal Agenesis

👉 Bilateral = both sides

(BOTH kidneys missing)

This is very serious because no kidneys develop at all.

Key problems it causes

• Low amniotic fluid
  Because fetal urine normally contributes to amniotic fluid. With no kidneys → no urine → low fluid.

• Underdeveloped lungs

• Clubbed feet

• Respiratory problems at birth
  Because lungs never developed well due to low fluid.

Weeks 6–9

Kidney migration

• Kidneys ascend (superiorly)from pelvis → lumbar region

• Receive temporary arteries during ascent

• Final position at L1–L2 region with permanent renal arteries FROM ABDOMINAL AROTA

Indifferent duct system

• Testosterone present → mesonephric duct kept (male structures)

• No testosterone → paramesonephric duct kept (female structures)

• Paired Kidneys →

• filter blood & produce urine

• convert filtrate to blood

• Ureters, Urinary bladder,
  Urethra:

(collectively referred to as the
urinary tract) transport the urine
out of the body)

Kidney location & appearance

• Retroperitonea l(located behind the peritoneum.)

• Superior border at T12, inferior at L3

• Right kidney lower/inferior (liver pushes it down)

• Reddish-brown

• Adrenal gland/Suprarenal sits on top of each kidney

Kidney has 2 surrounding fat layers

• Perirenal fat + pararenal fat
  → Cushion and protect kidney.

black arrow is

Concave medial border: hilum

• Hilum = entry/exit for vessels + ureter

Renal capsule

Dense irregular CT:

• Maintains shape

• Protects from trauma

• Prevents infection spread

The kidney is divided into…

1.the cortex (outer)
2.medulla (inner) and the
renal pelvis

• Contains medullary pyramids

• Renal columns (cortex tissue between pyramids)

Where is urine produced?

renal (medullary pyramid) via the nephrons

Renal pelvis

Renal papilla

Minor calyx

Major calyx

Ureter- urinary bladder

Urine collection system pathway

Renal papilla → Minor calyx → Major calyx → Renal pelvis → Ureter

"Pee Makes My Red Ureter" = Papilla → Minor → Major → Ureter.

KIDNEY MAIN FUNC IS

TO FILTER BLOOD

⭐ Arterial Blood Flow Into the Kidney

• Blood reaches the kidneys through the renal arteries.

• These branch directly off the abdominal aorta.
  → This provides a high-pressure, high-volume blood supply needed for filtration.

⭐ Venous Drainage From the Kidney

• Renal veins return deoxygenated, filtered blood back to the inferior vena cava (IVC).

Important relationship:

• Renal veins lie superior to renal arteries at the hilum
  

Asymmetry Between Left and Right Renal Veins

Because the IVC sits on the right side of the body:

Right renal vein

• Very short

• Drains directly into the nearby IVC

Left renal vein

• Much longer because it must cross the midline to reach the IVC

• The left renal vein collects blood from the left gonadal
  vein

• Passes under the superior mesenteric artery (SMA)
  → This anatomical relationship explains Nutcracker syndrome

“Renal Vein is on Top!”
Renal vein sits superior to artery at the kidney hilum.

⭐ Left Gonadal Vein Drainage

• The left gonadal vein (ovarian/testicular) drains into the left renal vein

• The right gonadal vein drains directly into the IVC

Why this matters:
This is why varicoceles are more common on the left side—because drainage is more easily compressed.

“L→L→IVC”
Left gonadal → Left renal vein → IVC

Nutcracker syndrome

Left renal vein compressed between SMA + aorta → varicocele, blood pooling in gonads.

happens when the left renal vein gets squeezed between two arteries,(superior mesenteric artery and the abdominal aorta)

blocking blood flow and causing backed-up blood in the gonads.

>Causes varicocele and toxic pooling of blood in the gonad

Arterial flow into kidney

Renal artery → Segmental → Interlobar (between pyramids) →
Arcuate (arch over pyramids) → Cortical radiate/interlobular →
Afferent arteriole → Glomerulus → Efferent arteriole

Really Smart Intelligent Anatomy Class Always Gets Easy

• Interlobar = between pyramids

• Arcuate = arches over pyramids

• Cortical radiate = radiates into cortex

Arteries =

carry blood AWAY from heart (oxygen-rich)

veins =

carry blood TOWARD the heart (oxygen-poor)

V-A-U = “Veins Always Up”

At the kidney hilum → Vein on top, artery in middle, ureter on bottom.

Kidneys →

Ureters →

carry urine to bladder

Urinary bladder →

store urine

Urethra →

excrete urine

Q: What vessels bring blood into the glomerulus?

A: Afferent arterioles. - are the
smallest branches which
create capillary balls called
glomeruli

Q: What vessel drains blood away from the glomerulus?

A: Efferent arteriole.

Q: What are the 5 parts of the nephron?

A: Corpuscle, PCT, Loop of Henle, DCT, Collecting duct.

Q: What are the three processes of urine formation?

A: Filtration, reabsorption, secretion.

Q: Which layer of the glomerular capsule contains podocytes?

A: Visceral layer.

Q: Which nephron segment has tall microvilli?

A: PCT.

Q: What capillaries surround the loop of Henle?

A: Vasa recta.

Q: What hormones act on the collecting duct?

A: ADH and aldosterone.

Q: What type of epithelium lines the ureter and bladder?

A: Transitional epithelium.

Q: Why do ureters enter the bladder at an angle?

A: To form a one-way valve preventing urine reflux.

Q: What carries urine from kidney to bladder?

A: Ureters.

Q: List the path of urine from collecting duct to outside body.

A: Papilla → Minor calyx → Major calyx → Renal pelvis → Ureter → Bladder → Urethra → Out.

Q: What structure collects filtrate in the renal corpuscle?

A: Capsular space.

Q: What epithelium type allows the bladder to stretch?

A: Transitional epithelium.

The glomerulus

ball” of capillaries for filtration.

a tangle of
capillaries that originate from
the afferent arteriole

Cortical arteries

branch from arcuate arteries and enter the cortex.

Blood Supply to the Glomerulus Key Points

• Cortical arteries branch from arcuate arteries and enter the cortex.

• They give rise to afferent arterioles → the vessels that bring blood into the glomerulus.

• The glomerulus is a “ball” of capillaries for filtration.

• Efferent arterioles carry blood out of the glomerulus.

Big idea:

Afferent = Arrive, Efferent = Exit

Nephron Func.

Modify filtrate → create final urine.

Processes of Urine Formation

Three key processes:

1. Filtration — blood → filtrate

2. Reabsorption — filtrate → blood

3. Secretion — blood → filtrate

Why?
Filtration alone is NOT selective → body must reabsorb what it needs and secrete what it doesn’t.

1. Filtration and Secretion

— blood → filtrate

Reabsorption

— filtrate → blood

Renal Corpuscle includes:

• Glomerulus (capillary tangle)

• Glomerular capsule (Bowman’s capsule)

  • Visceral layer: podocytes

  • Parietal layer: simple squamous epithelium

  • Capsular space: where filtrate collects

• Glomerular capsule (Bowman’s capsule)

• Visceral layer: podocytes

• Parietal layer: simple squamous epithelium

• Capsular space: where filtrate collects

• Visceral layer

podocytes- forms a
leaky filtration membrane

• Parietal layer:

• simple squamous epithelium

• Capsular space:

• where filtrate collects

• also separate visceral and parietal

Renal corpuscle

glomerulus + glomerular capsule

Renal Corpuscle poles are

vascular and tubular pole

Filtration Process:
modified

1. Blood enters the glomerulus from the
afferent arteriole
2. High pressure forces blood against the
filtration membrane
3. Filtration membrane allows the
passage of smaller solutes into the
capsular space
NOTE: This method of filtration is not
selective
Filtrate must be

Filtration Process: step 1

Blood enters the glomerulus from the
afferent arteriole

Filtration Process: step 2

High pressure forces blood against the
filtration membrane

Filtrate must be

Filtration Process: step 3

Filtration membrane allows the
passage of smaller solutes into the
capsular space

PCT Function:

• Major reabsorption site

• Returns nutrients (glucose, amino acids), ions, water back to blood

• Some secretion (H⁺, drugs)

PCT Histology:

• Simple cuboidal epithelium

• Tall microvilli → increases surface area

• “Fuzzy” brush border appearance.

Nephron Loop Structure:

• Descending limb → goes into medulla (water)

• Ascending limb → goes back to cortex ( Salt)

Nephron Loop Func.

• Creates concentration gradient

• Reabsorbs water from descending limb

• Reabsorbs salts in ascending limb

Important for concentrated urine production

DCT Function:

• Fine-tunes filtrate

• Secretion (K⁺, H⁺, drugs)

• Reabsorption, especially under hormone control

DCT Histology:

• Simple cuboidal epithelium

• Sparse microvilli (clear lumen)

Types of Nephrons?

• Cortical nephrons

• Short loops

• Majority of nephrons

• Used during normal conditions

• Juxtamedullary nephrons

  • Long loops deep into medulla

  • Important in concentrated urine production

• Cortical nephrons

• Short loops

• Majority of nephrons

• Used during normal conditions

• Juxtamedullary nephrons

• Long loops deep into medulla

• Important for producing concentrated urine.

Capillary Beds

Two capillary networks:

1. Peritubular capillaries

• Surround PCT + DCT

• Involved in reabsorption + secretion

2. Vasa recta

• Surround loop of Henle

• Maintain concentration gradient

• Prevent “washout” of medulla

1. Peritubular capillaries

• Surround PCT + DCT

• Involved in reabsorption + secretion

2. Vasa recta

• Surround loop of Henle

• Maintain concentration gradient

• Prevent “washout” of medulla

Collecting ducts & tubules respond to:

• ADH → water reabsorption

• Aldosterone → sodium reabsorption

Function:

Determines final urine concentration.

Flow of Filtrate

1. Glomerulus

2. PCT

3. Loop of Henle

4. DCT

5. Collecting duct
   → Renal papilla
   → Minor calyx
   → Major calyx
   → Renal pelvis
   → Ureter
   → Bladder
   → Urethra
   → Outside bod

Ureters Function:

• Carry urine from kidneys to bladder (carry
  urine into pelvic cavity to
  empty into urinary bladder)

• Enter bladder posterolaterally

Type:

• Fibromuscular tubes

Layers of Ureter

Three tunics:

1. Mucosa (with transitional epithelium)

2. Muscularis (smooth muscle for peristalsis)

3. Adventitia (outer connective tissue)

1. Mucosa

1. (with transitional epithelium)

1. Muscularis

1. (smooth muscle for peristalsis)

1. Adventitia

1. (outer connective tissue)

One-Way Valve at Bladder Entry

• Ureter enters bladder obliquely

• Creates a passive one-way flap

• Prevents urine from traveling backward into ureters

(Prevents reflux → kidney damage)

Bladder Wall

Layers include:

• Transitional epithelium (can stretch)

• Thick smooth muscle (= detrusor muscle)

• Adventitia

Anatomy of Bladder Position

• Ureter enters posterior-lateral wall

• Bladder sits anterior to uterus (female)

• Urethra exits inferiorly

• Each ureter approaches the bladder from behind (posterior side).

• They enter the bladder at an angle on the upper side of the bladder wall.

Why this angle matters

This angled insertion forms a natural flap valve:

• When the bladder fills with urine, the expanding wall compresses the ureter opening,

• Preventing urine from flowing backwards into the ureter (vesicoureteral reflux).

If the angle is too shallow (common in infants), reflux happens → ↑ risk of kidney infections.

Trigone (MUST KNOW)

• A smooth triangular area at the base of the bladder

• Corners = 2 ureteric openings + urethral opening

• Does NOT stretch like the rest of the bladder

• Sensitive to stretch → signals “time to pee”

• Detects bladder fullness

• Common site of UTIs