The Urinary System
The urinary system
The kidneys conserve body
fluid and electrolytes and
remove metabolic waste.
Kidney Organization
Kidney
Lobe
Capsule
The number of lobes in a
kidney equals the number of
medullary pyramids
Cortex
Renal
Pelvis
Ureter
Medullary
Pyramid
Cortex: outer layer, granular
appearance (due to many
corpuscles)
Medulla: darker striped appearance
(due to tubules)
 Subdivided into distinct renal
pyramids, terminating with a
papilla.
 Separated by renal columns from
the cortex.
Pelvis: Expanded
proximal ureter
The kidneys are highly vascular organs;
They receive approximately 25% of the cardiac output
Nephron = functional unit
Nephron =
1. Renal Corpuscle (Glomerulus +
Bowman’s Capsule)
2. PCT (proximal convoluted tubule)
3. LOH (loop of Henle)
4. DCT (distal convoluted tubule)
(>106/kidney)
LM – injected kidney vascular system
Renal Corpuscle
a, arteriole; b, parietal layer of BC; c, PCT; d, podocyte (visceral layer of BC)
The renal corpuscle represents the beginning of the nephron.
The glomerulus, a tuft of capillaries composed of 10 to 20 capillary loops,
surrounded by a double-layered epithelial cup, the renal or Bowman’s
capsule.
Bowman’s capsule is the initial portion of the nephron, where blood flowing
through the glomerular capillaries undergoes filtration to produce the
glomerular ultrafiltrate. The glomerular capillaries are supplied by an afferent
arteriole and are drained by an efferent arteriole
The renal corpuscle contains the filtration apparatus of the kidney:
1. glomerular endothelium,
2. underlying glomerular basement membrane (GBM),
3. and the visceral layer of Bowman’s capsule.
Filtration: Passage across three barriers
1. Capillary endothelium Fenestrated
2. Basement membrane
3. Glomerular epithelium (= visceral layer of Bowman’s
capsule) slit pores between pedicles of podocytes
Note: Capsular Epithelium is simple squamous epithelium
Albuminuria (presence of significant amounts
of albumin in the urine) or hematuria
(presence of significant amounts of red blood
cells in the urine) indicate physical
or functional damage to the GBM. In such
cases (e.g., diabetic nephropathy), the number
of anionic sites, especially in the lamina rara
externa, is significantly reduced.
The renal corpuscle contains an additional group of cells called mesangial cells.
These cells and their extracellular matrix constitute the mesangium.
Important functions of the mesangial cells follow:
• Phagocytosis. Mesangial cells remove trapped residues and aggregated
proteins from the GBM and filtration slit diaphragm, thus keeping the
glomerular filter free of debris.
• Structural support. Mesangial cells produce components of mesengial
matrix, which provide support for the podocytes.
• Secretion. Mesangial cells synthesize and secrete interleukin 1 (IL-1),
PGE2, and platelet-derived growth factor (PDGF).
• Modulation of glomerular distension. Mesangial cells have contractile
properties.
Clinically, it has been observed that mesangial cells proliferate in certain kidney
diseases, in which abnormal amounts of protein and protein complexes are
trapped in the GBM. Proliferation of mesangial cells is a prominent feature in the
immunoglobulin A (IgA) nephropathy (Berger disease), membranoproliferative
glomerulonephritis, lupus nephritis, and diabetic nephropathy
The tubular segments of the nephron are named according
to the course that they take (convoluted or straight), location
(proximal or distal), and wall thickness (thick or thin).
Kidney Cortex (a, glomerulus; c, DCT, d, PCT)
Kidney Cortex – PCT (P) & DCT (D)
P
D
D
P
The DCT passes by the afferent
and efferent arterioles to form the
JG apparatus
The juxtaglomerular apparatus
includes the macula densa, the
juxtaglomerular cells, and the
extraglomerular mesangial cells.
Renal Corpuscle and Macula Densa
Kidney Juxtaglomerular
Complex
MD = macula densa
JGC = juxtaglom cells
JG Cells
Juxtaglomerular (JG) Apparatus
The juxtaglomerular apparatus regulates blood pressure by activating the
renin–angiotensin–aldosterone system.
Macula densa monitors NaCl and flow through the DCT
JG cells produce renin
Cross section of Kidney Medulla
Kidney Medulla (Collect tubules and loops)
Kidney Medulla – Vasa Recta (VR)
VR
Two Types of Nephrons
Two types of nephrons are identified,
based on the location of their renal
corpuscles in the cortex
Cortical nephrons (85%) shorter, mostly in cortex
of kidney, produce "standard" urine
Juxtamedullary nephrons (15%), "juxta = next to"
the medulla - responsive to ADH, can produce
concentrated urine due to longer Loops of Henle
The Urinary System
Kidney Circulation
Efferent arterioles
Afferent
arterioles
Kidney Medulla – Vasa Recta (VR)
VR
The kidney also functions as an endocrine organ.
Erythropoietin (EPO), which acts on the
bone marrow and regulates red blood cell
formation in response to decreased blood
oxygen concentration.
EPO is synthesized by endothelial cells of
the peritubular capillaries in the renal
cortex.
The recombinant form of erythropoietin
(RhEPO) is used for the treatment of anemia in
patients with end-stage renal disease. It is also
used to treat anemia resulting from bone
marrow suppression that develops in AIDS
patients undergoing treatment with
antiretroviral drugs, such asazidothymidine
(AZT).
Hydroxylation of 25-OH vitamin D3.
This step is regulated primarily by parathyroid hormone (PTH), which stimulates activity
of the enzyme 1 hydroxylase and increases the production of the active hormone
The Urinary System
Ureter, Bladder, and Urethra
Urine collection:
Collecting ducts within each renal papilla release urine into
minor calyx → major calyx → renal pelvis → ureter
Ureters
From kidney to bladder
 Enter the posterior bladder at an angle «Trigone»
 Retroperitoneal
 Transitional Epithelium
 Nephrolithiasis
Ureter – folded mucus membrane
Transitional Epithelium
Nephrolithiasis (kidney stones)
Occurs when urine becomes too
concentrated and substances
crystallize. Symptoms arise when
stones begin to move down ureter
causing intense pain.
Kidney stones may form in the pelvis,
calyces, or in the ureter. (Rarely in
the bladder.)
Urinary Bladder
Retroperitoneal, behind pubis
 Internal folds - rugae - permit expansion
(max. holding capacity ~ 1L)
 Trigone - area at base delineated by
openings of ureters and urethra - without
muscle
 Internal urethral sphincter - involuntary
sphincter
Bladder – Transitional Epithelium
1. transitional epithelium from renal pelvis to neck of urethra.
2. detrusor muscle – smooth muscle
empty bladder
full bladder
Urethra
A drop of filtrate
1.Blood in the afferent arteriole goes to
2.Glomerular capillaries
3.Podocytes
4.Bowman’s Space
5.PCT
6.LOH
7.DCT
8. Collecting Duct
9.Minor calyx
10.Major calyx
11.Renal Pelvis
12.Ureter
13.Urinary Bladder
14.Urethra
15.Prostatic, membranous and penile in male
Thank you for attention
Manneken Pis Fountain Brussels, 1619