Situated in the retroperitoneum on either side of the vertebral column at the level of the lower thoracic spine and upper lumbar vertebrae.

The right kidney is a little lower than the left because of the liver.

Weighs about 150 gm and is about 12 x 6 x 3 cm.

The inner aspect of the kidney contains 6-15 conical structures, the pyramids, the bases of which are situated at the corticomedullary junction and the apex extends into the hilum of the kidney at the papilla.

The ureter enters the kidney at the hilum and it dilates into a funnel shaped cavity, the renal pelvis.

The renal pelvis is the upper expanded section of the urinary tract and it extends outward to form three major calyces, each of which branches into eight or more minor calyces.

Funnel shaped minor calyces extend toward the pyramid and encompass each papilla, draining the urine formed by the pyramidal unit.

Urine from several minor calyces drain into a major calyx and then into the renal pelvis which leads the ureter.

Cortex 1.2-1.5 cm in thickness.

The medulla consists or renal pyramids, the apices of which are call papillae, each related the a calyx.

The cortex extends between the pyramids associated the renal columns of Bertin.

Blood supply comes from the renal artery branching from the aorta at the level of the first lumbar vertebra.

Although the kidneys make up only 0.5% of total body weight they receive about 25% of cardiac output.

With 90% of renal blood flow, the cortex is the most vascularized part of the kidney.

Kidneys filter blood at a rate of 120 cc per minute.

Kidneys filter 45 gallons of blood in a 24 hour day.

In adults the renal glomerulus selective filtration produces more than I50 L of ultrafiltrate every day, 99% of which must be reabsorbed byp renal tubule segments.

Kidney filters all the blood in the body over 30 times each day.

The kidneys extract the soluble wastes from the bloodstream, as well as excess water, sugars, and a variety of other compounds. 

Functions as an endocrine function of producing erythropoeitin and 1,25-hydroxy vitamin D.

The renal artery enters the hilum of the kidney and divides into 2 main segmental branches, which subdivide into lobar arteries supplying the upper, middle and lower regions of the kidney.

The lobar arteries branch as they enter the kidney to interlobar arteries toward the renal cortex along the lateral margins of the pyramids, they then provide small perpendicular archlike branches, arcuate arteries, at the corticomedullary junction.

The arcuate arteries provide interlobular arteries and branch radially within the renal cortex.

The terminal interlobular arteries provide afferent arterioles to the glomerular capillaries.

The efferent arteriole leaves the glomerular capillary bed and supplies the blood vessels that surround the tubular structures.

The efferent arterioles from the superficial nephrons form the peritubular vascular network, while the deeper juxtaglomerular vessels give rise to the vasa recta and then supplies the inner and outer medulla.

Efferent arterioles of the juxtamedullary glomeruli form vasa recta, hairpin loops, that extend in the medulla.

The arterial vasa recta then ascend as the venous vasa recta.

The arterial blood supply is largely end-arterial, meaning that occlusions of any branch leads to infarction of the specific area that it supplies.

Glomerular disease that impairs blood flow in the glomerular capillaries effects the tubules in the cortex and the medulla because all tubular capillary beds are derived from the efferent arterioles.

The GFR is generally accepted as the best index of kidney function in health and disease and albuminuria is a marker of kidney damage are the principal kidney measures define and stage and acute and chronic kidney disease.

The renal medulla blood supply is vulnerable to ischemia because its blood supply emanates from the glomerular efferent arterioles, and the blood in the capillary loops in the medulla have a low level of oxygenation.

Innervated by the autonomic nervous system with sympathetic nerve endings in the renal vasculature, renal tubules, and juxtaglomerular apparatus.

Stimulation of the sympathetic system enhances the release of renin from the juxtaglomerular cells with an increase in angiotensin and aldosterone production.

Each kidney has about 1 million nephrons, its functional unit.

The nephron is composed of a filtering element enclosed in a capillary network and its attached tubule.

The first post glomerular segment, the proximal tubule can cause losses of fluid and electrolytes and low molecular weight nutrients when it’s function is impaired.

The tubule includes the proximal tubule, the loop of Henle, the distal tubule and the connecting segment.

The loop of Henle is composed of the straight part of the proximal tubule, the thin descending limb and the thick ascending limb.

The tubules drain into the collecting duct system that contains the cortical collecting ducts and the outer and inner medullary collecting segments.

Short looped nephrons usually originate from superficial and midcortical regions and their loops of Henle bend within the outer medulla.

Long looped nephrons originate from the juxtamedullary region of the kidney and their loops of Henle extend in to the inner medulla.

The glomerulus is a network of capillaries suspended between afferent and efferent arterioles enclosed within an epithelial structure, the Bowman’s capsule.

Capillaries of the glomerulus are lined by a thin layer of endothelial cells.

The core of the glomerulus consists of mesangial matrix with mesangial cells.

The glomerulus has a basement membrane, visceral and parietal epithelial cells.

The glomerulus capillary wall is the filtering membrane and has a thin layered fenestrated endothelium with 70-100 nm fenestrations, a basement membrane with a dense central layer, the lamina densa and a thinner electron lucent peripheral layers, the lamina rara interna and lamina rara externa.

Glomeruli ensures selective ultrafiltration of plasma, by which proteins are retained in the blood.

The endothelial cells lining the capillary lumen form the initial defense that impedes passage of blood constituents from the capillary lumen the urinary space.

The endothelium surface is negatively charged and promotes the filtration barrier by selective charged properties.

Capillary endothelial cells release endothelin, prostacyclin and nitric oxide to regulated vasomotor tone.

The visceral epithelium is incorporated into the intrinsic part of the capillary wall, separated from the endothelial cells by the basement membrane.

The visceral epithelial cells, known as the podocytes, extend foot processes to directly contact the lamina rara externa of the basement membrane.

Sialoproteins on the surface of podocytes provide a negative surface charge and help form a filtration barrier.

The glomerular filtration barrier involves the glomerular endothelium, glomerular basement membrane, and podocytes the final barrier to urinary loss of proteins.

Podocytes contribute to synthesis and maintenance of the glomerular basement membrane.

Gap between podocytes foot processes is called the filtration slit.

Injury or loss of podocytes associated with noninflammatory glomerular disorders including focal sclerosis and diabetic nephropathy.

The podocyte is a specialized cell of the glomerulous which helps prevent proteinuria by regulating the actin cytoskeleton in their foot processes.

The parietal epithelium is situated on Bowman’s capsule, lines the urinary space where plasma filtrate first collects.

Basement membrane of the glomerulus consists of mostly type IV collagen, laminin, fibronectin, glycoproteins, entactin, and proteoglycans.

Glomerular basement membrane is a layered hydrated gel with glycoproteins containing collagen fibers of type IV and V.

Glomerular basement membrane is the principal barrier to filtration of plasma proteins.

Glomerular basement membrane thickness ranges from 315-373 nm.

Type IV collagen in the glomerular basement membrane provides a structure to which glycoproteins can attach.

The afferent and efferent arterioles of the glomerulus enter and leave at the vascular pole.

The Bowman’s capsule continues into the proximal tubule of the urinary pole.

Glomerular tufts are suspended within the Bowman’s capsule on a core, the mesangium.

Mesangial cells are enclosed in mucopolysaccharides and glycoproteins material, without a basement membrane between capillary endothelium and mesangial cells, providing easy entry of plasma products and a site for interaction with inflammatory cells.

Mesangial cells have contractile capabilities due to actin-myosin elements in the cytoplasm allowing such cells to alter surface area for filtration and can decrease glomerular filtration rate.

Mesangial cells have receptors to ADH and angiotensin II which can cause vasoconstriction and alteration in GFR.

Mesangial cells produce collagen and glycoproteins and remodel the extracellular matrix providing structural support to glomerular loops.

Mesangial cells secrete extracellular matrix in response to transforming growth factor and platelet derived growth factor and can cause glomerular disease s a result.

Mesangial cells have phagocytic properties.

The glomerulus funnels ultrafiltrate into renal tubules.

Proximal tubules begin at the urinary pole of the glomerulus.

The proximal convoluted tubule is located in the cortex.

The second segment of the proximal tubule, the straight part, is in the medullary ray, entering the medulla to deliver fluid to the loop of Henle.

The descending limb of the loop of Henle turns in the medulla and returns towards the cortex and forms the distal tubule.

The distal tubule consists of the thick ascending limb of the loop of Henle and the distal convoluted tubule.

The distal tubule leads the connecting segment, which comprises the cortical collecting duct and the outer and inner medullary collecting ducts.

The collecting ducts terminate in the papillary collecting ducts and then empty into the renal pelvis at the tips of the renal papillae.

Converts approximately 1700 liters of blood per day into approximately 1 liter of urine.

Excretes waste products of metabolism, maintains water, salt and acid balance and secretes renin, prostaglandins and erythropoietin.

The kidney plays a major role in glucose homeostasis by gluconeogenesis and glomerular filtration absorption of glucose in the proximal convoluted tubules.

The glomeruli of the normal adult kidney filters 180 g of glucose daily.

Glucose reabsorption from the tubules is virtually complete with less than 1% being excreted in the urine.

The reabsorption of glucose from kidney tubules is a multistep process and once filtered into the tubule must be transported through the tubular epithelial cells and then across the basolateral membrane into tubular capillaries.

When tubular glucose load is approximately 120 mg/minute or less, no glucose is lost in the urine.

When tubular glucose load exceeds 220 mg/minute, the glucose threshold, glucose begins to appear in the urine.

Kidney volume begins to shrink after the third or fourth decade of life, but there is preservation of the ratio of the glomerular surface area to proximal tubule volume ( 3:1).

With aging there is increased elastic fiber content of small vessels associated with medial hypertrophy and intimal proliferation as the nephron shrinks.

With aging there is progressive interstitial fibrosis and global glomerulosclerosis in a focal distribution throughout the kidney.

Some degree of focal global glomerulosclerosis is observed by the third decade of life in all people.

Aging initiates various structural and functional changes within the kidney so that renal mass progressively declines with advancing age, and glomerulosclerosis leads to a decrease in renal weight.

There is a decrease in glomerular number of as much as 30-50% by age 70 years.

GFR peaks during the third decade of life at approximately 120 mL/min/1.73 m2.

After age 30 GFR undergoes an annual mean decline of approximately 1 mL/min/y/1.73 m2, reaching a mean value of 70 mL/min/1.73 m2 at age 70 years.

Leave a Reply

Your email address will not be published. Required fields are marked *