Anatomy and Histology

1. Receive 20‐25% of cardiac output = ca. 1.2 L min‐1

2. Renal artery from aorta abdominalis

3. After entering the kidney at the hilum

4. Venous system is the same in reverse, ending in the renal vein 

Als Nierenhilus bezeichnet man die am konkaven medialen Rand der Niere befindliche Einziehung, die als Ein- und Austrittsstelle sämtlicher Leistungsstrukturen der Niere dient. 

Der Nierenhilus bildet den Zugang zum Sinus renalis.

The Functional Unit /  Glomerular filtrate is protein‐free solution 

1. Human kidney: about 1 Million nephrons

2. Two major components:

   1. renal corpuscle (responsible for the filtration of plasma) = Bowman’s capsule + glomerulus (capillary network)

      • Filtration of water and low molecular weight constituents of plasma are filtered from the glomerular capillaries into Bowman’s space to form the glomerular ultra filtrate, which then passes into the renal tubule.

      • Glomerular filtrate is protein‐free solution (120mL/min, all but 1mL reabsorbed)

      • The afferent arteriole, which supplies the glomerulus, and the efferent arteriole, which drains it, enter and leave the corpuscle at the vascular pole that is usually situated opposite the entrance to the renal tubule, the urinary pole.

   2. and renal tubule: extends from Bowman’s capsule to its junction with a collecting duct

      • Renal tubule begins at the renal corpuscle (cup‐shaped chamber) ca. 0.2 mm diameter

      • Up to 55 mm long and is lined by a single layer of epithelial cells

      • selective reabsorption of water, inorganic ions and other molecules

        from the glomerular filtrate 

1. Proximal convolute tubule (PCT), reabsorbs ca. 65% of ions and water, confined to the renal cortex and make up the greater part of its bulk.

2. Nephron loop (loop of Henle) = distal straight part of the proximal tubule, the pars recta, the thin descending and ascending limbs and the thick ascending limb.

3. Distal convoluted tubule (DCT)a continuation of the thick limb of the loop of Henle after its return to the cortex. Shorter and less convoluted than the PCT, the DCT is responsible for reabsorption of sodium ions, an active process controlled by the adrenocortical hormone aldosterone.

4. Collecting tubule: straight terminal portion of the nephron, several collecting tubules converging to form a collecting duct. The collecting ducts descend through the cortex in parallel bundles called medullary raysmerge in the medulla to form ducts of Bellini open at the tips of the renal papillae to discharge urine into the pelvicalyceal system. The collecting tubules and ducts are not normally permeable to water. 

Proximal convolute tubule (PCT), reabsorbs ca. 65% of ions and water, confined to the renal cortex and make up the greater part of its bulk.

1. renal corpuscle (responsible for the filtration of plasma) = Bowman’s capsule + glomerulus (capillary network)

   • Filtration of water and low molecular weight constituents of plasma are filtered from the glomerular capillaries into Bowman’s space to form the glomerular ultra filtrate, which then passes into the renal tubule.

   • Glomerular filtrate is protein‐free solution (120mL/min, all but 1mL reabsorbed)

   • The afferent arteriole, which supplies the glomerulus, and the efferent arteriole, which drains it, enter and leave the corpuscle at the vascular pole that is usually situated opposite the entrance to the renal tubule, the urinary pole. 

1. Nephron loop (loop of Henle) = distal straight part of the proximal tubule, the pars recta, the thin descending and ascending limbs and the thick ascending limb.

Distal convoluted tubule (DCT)a continuation of the thick limb of the loop of Henle after its return to the cortex. Shorter and less convoluted than the PCT, the DCT is responsible for reabsorption of sodium ions, an active process controlled by the adrenocortical hormone aldosterone.

Collecting tubule: straight terminal portion of the nephron, several collecting tubules converging to form a collecting duct. The collecting ducts descend through the cortex in parallel bundles called medullary raysmerge in the medulla to form ducts of Bellini open at the tips of the renal papillae to discharge urine into the pelvicalyceal system. The collecting tubules and ducts are not normally permeable to water.

1. Capillary knot, initial portion of tubule (glomerular capsule/Bowman’s capsule) ‐ single layer of flattened cells resting on a basement membrane; it is derived from the distended blind end of the renal tubule

2. Renal corpuscle has a vascular pole

3. Glomerulus sits in a capsule analogous to the heart in the pericardial cavity, i.e. outer wall of simple squamous (parietal) epithelium continuous with the inner (visceral) epithelium ‐ globular network of anastomosing capillaries which invaginates Bowman’s capsule

4. Visceral epithelium (podocytes) wraps around the glomerular capillaries with special process

5. Blood pressure forces fluid and solutes out of the capillaries into capsular space (120mL/min, all but 1mL reabsorbed)

6. Initial passive filtration based on molecular size, i.e. both “good” and “bad” molecules in filtrate

7. Distal segments actively reabsorb useful organic substances, and water, while secreting substances initially missed

8. The visceral layer is reflected around the vascular stalk of the glomerulus to become continuous with the parietal layer that constitutes Bowman’s capsule proper.

9. The space between the two layers is known as Bowman’s space and is continuous with the lumen of the renal tubule;

10. parietalepitheliumofBowman’scapsuleiscontinuouswiththeepitheliumlining the renal tubule. 

1. Muscular tubes that carry urine from the kidneys to the bladder

2. 3‐4mm diameter

3. Wall:

   1. Two layers of smooth muscle: longitudinal and circular

   2. A third outer longitudinal layer of smooth muscle cells present in the lower third of the ureter

4. Lumen: lined by transitional epithelium (urothelium), i.e. cuboidal cells that stretch

   and thus become squamous

5. Lamina propria: beneath the epithelium.

6. Surrounding the muscular wall – loose collagenous adventitia layer containing blood

   vessels, lymphatics and nerves.

7. Outer connective tissue, continuous with the fibrous peritoneum

8. Peristaltic contractions every 30 sec “milk” the kidneys 

Storage of urine until it can be discarded

1) Three layer:

1. 1)  Mucosa with distensible transitional epithelium and lamina propria. Mucosal lining highly folded-- rugae: stretch and distend

2. 2)  Thick muscularis = detrusor muscle
   Loosely arranged layers of smooth muscle and elastic fibres that contract during micturition: inner longitudinal + outer circular + outermost longitudinal

3. Adventitia: fibrous layer, rich in blood and lymphatic vessesl 

1. 1)  In females, it extends 3‐5 cm from the (external) urethral sphincter muscle at the neck of the urinary bladder to the external urethral orifice, anterior to the vaginal orifice

2. 2)  In males, it extends 18‐20 cm from the neck to the tip of the penis, with three portions with functional differences

   1. 1)  Prostatic urethra passes through the prostate gland

   2. 2)  Membranous urethra penetrates the urogenital diaphragm

   3. 3)  Spongy urethra extends from the base to the tip of the penis 

1. 1)  Initially transitional cells as it exits the bladderthen there are pseudostratified columnar and stratified columnar epitheliathen stratified squamous cells near the external urethral orifice.

2. 2)  There are small mucus‐secreting urethral glands, that help protect the epithelium from the corrosive urine.

3. 3)  Lamina propria is thick and elastic, well vascularised

4. 4)  Surrounded by concentric layers of smooth muscle: muscularis 

•  Endocrine glands

•  Ca. 7.5g, yellow-ish, sit atop the kidneys, i.e. also retroperitoneal

•  Function: Production of adrenaline, aldosterone and cortisol

•  Dense fibrous capsule

•  Highly vascularised

•  Secretes over 24 different hormones (adrenocortical steroids/corticosteroids)

•  Affect metabolic operations primarily by influencing gene transcription