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Kidneys & Homeostasis
K1 Anatomy Urinary system
Essential functions of the kidneys
1. Conserve body fluid and electrolytes and remove metabolic waste
2. Regulate water- and electrolyte balance, tissue osmolality, blood pressure and acid-base balance
3. Function also as endocrine organ: synthesis and secretion of erythropoietin (bone marrow erythropoiesis) and renin (blood
pressure) and activation of vitamin D (Ca2+ metabolism)
Topography
Primary retroperitoneal organs surrounded by fat:
1. Perinephric fat: perirenal fat capsule (structural adipose tissue)
2. Renal fascia: enclosing membranous layer open inferiorly
3. Paranephric fat: pararenal fat body (retroperitoneal adipose tissue)
The kidneys are surrounded by a fibrous capsule that consists of two layers that aid in resisting volume and pressure variations
(Due to the stiffness of this capsule high hydrostatic pressure may be generated within the renal tissue):
1. Fibroblasts and collagen fibers (outer)
2. Myofibroblasts (inner)
Real hilum = entrance:
Kidneys & Homeostasis 1
, Marcoscopic anatomy
Parenchyma:
1. Cortex (outer part): cortical labyrinths and renal columns
2. Medulla (inner part): medullary pyramids, renal papilla, medullary rays
Cavity:
1. There is also a central cavity within the kidney that is called the renal sinus surrounded by fat: minor renal calyces – major
renal calyces – renal pelvis.
Lobule: physiological unit of kidney - all the nephrons which drain their urine on the same collecting duct (not visible)
Lobe: anatomical seperated cortex and medullary pyramid
Anatomy nephron
Nephron: smallest structural and functional unit of the kindey (located in cortex as well as medulla). The general organization of
the nephron is as follows:
Renal corpuscle (of Malpaghi)
Function = ultrafiltration
Subcapsular
Intermediate
Juxtamedullary > long loops of Henle
Filtration apparatus of the kidney
Glomerulus
Vascular element
Capillary tuft with large open fenestrations
afferent and efferent arteriole (vascular pole)
Kidneys & Homeostasis 2
, Bowman’s capsule
Epithelial element
visceral layer (podocytes) and parietal layer (squamous epithelial cells) with in between Bouwman’s space
Urinary pole
1. endothelium glomerular capillaries with fenestrations
2. glomerular basement membrane which is the product of glomerular endothelium and podocytes which acts as
physical barrier and ion-selective filter
a. Lamina rara interna (adjacent to capillary enthodelium) = ion-selective filter composed of negeatively charged
molecules
b. lamina densa = physical filter composed of collagen
c. lamina rara externa (adjacent to podocytes) = ion-selective filter composed of negeatively charged molecules
3. Bowman’s capsule podocytes: in-between podocyte filtration slits with slit dhiagram made up of nephrin for size-
selective filtration
Mesangium
Consists of mesangial cells which phagocytose and endocytose of residues from GBM and filtration slit diaphgram
(keep it clean).
other functions: structural support, production and secretion of inflammatory substances, modulation of glomerular
distension and regulation of blood pressure (?)
derived from smooth muscle cells
Juxtaglomerular apparatus (IN DISTAL TUBULE)
Regulates blood pressure by activating the renin-angiotensin-aldosterone system (RAAS)
Kidneys & Homeostasis 3
Kidneys & Homeostasis
K1 Anatomy Urinary system
Essential functions of the kidneys
1. Conserve body fluid and electrolytes and remove metabolic waste
2. Regulate water- and electrolyte balance, tissue osmolality, blood pressure and acid-base balance
3. Function also as endocrine organ: synthesis and secretion of erythropoietin (bone marrow erythropoiesis) and renin (blood
pressure) and activation of vitamin D (Ca2+ metabolism)
Topography
Primary retroperitoneal organs surrounded by fat:
1. Perinephric fat: perirenal fat capsule (structural adipose tissue)
2. Renal fascia: enclosing membranous layer open inferiorly
3. Paranephric fat: pararenal fat body (retroperitoneal adipose tissue)
The kidneys are surrounded by a fibrous capsule that consists of two layers that aid in resisting volume and pressure variations
(Due to the stiffness of this capsule high hydrostatic pressure may be generated within the renal tissue):
1. Fibroblasts and collagen fibers (outer)
2. Myofibroblasts (inner)
Real hilum = entrance:
Kidneys & Homeostasis 1
, Marcoscopic anatomy
Parenchyma:
1. Cortex (outer part): cortical labyrinths and renal columns
2. Medulla (inner part): medullary pyramids, renal papilla, medullary rays
Cavity:
1. There is also a central cavity within the kidney that is called the renal sinus surrounded by fat: minor renal calyces – major
renal calyces – renal pelvis.
Lobule: physiological unit of kidney - all the nephrons which drain their urine on the same collecting duct (not visible)
Lobe: anatomical seperated cortex and medullary pyramid
Anatomy nephron
Nephron: smallest structural and functional unit of the kindey (located in cortex as well as medulla). The general organization of
the nephron is as follows:
Renal corpuscle (of Malpaghi)
Function = ultrafiltration
Subcapsular
Intermediate
Juxtamedullary > long loops of Henle
Filtration apparatus of the kidney
Glomerulus
Vascular element
Capillary tuft with large open fenestrations
afferent and efferent arteriole (vascular pole)
Kidneys & Homeostasis 2
, Bowman’s capsule
Epithelial element
visceral layer (podocytes) and parietal layer (squamous epithelial cells) with in between Bouwman’s space
Urinary pole
1. endothelium glomerular capillaries with fenestrations
2. glomerular basement membrane which is the product of glomerular endothelium and podocytes which acts as
physical barrier and ion-selective filter
a. Lamina rara interna (adjacent to capillary enthodelium) = ion-selective filter composed of negeatively charged
molecules
b. lamina densa = physical filter composed of collagen
c. lamina rara externa (adjacent to podocytes) = ion-selective filter composed of negeatively charged molecules
3. Bowman’s capsule podocytes: in-between podocyte filtration slits with slit dhiagram made up of nephrin for size-
selective filtration
Mesangium
Consists of mesangial cells which phagocytose and endocytose of residues from GBM and filtration slit diaphgram
(keep it clean).
other functions: structural support, production and secretion of inflammatory substances, modulation of glomerular
distension and regulation of blood pressure (?)
derived from smooth muscle cells
Juxtaglomerular apparatus (IN DISTAL TUBULE)
Regulates blood pressure by activating the renin-angiotensin-aldosterone system (RAAS)
Kidneys & Homeostasis 3
