Physiology Renal System

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Nephron

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functional unit of kidney, the smallest structure that can carry out all of the function o the organ. The blood processing unit.

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How many nephorns are the approximately in each kidney

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There are about 1,000,000

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List 6 Major functions of a nephron

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1.Regulation of extracellular fluid volume
2. Regulation of extracellular fluid osmolarity
3. Maintenance of ion balance
4. Homeostatic Regulation of pH
5. Excretion of wastes and foreign substances (xenobiotics)
6. Production of hormone

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Major Constituents of the Nephron

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Renal Corpuscle and the Renal tubule

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Renal Corpuscle

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the vascular element and performs the function of filtration

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Renal Tubule

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the tubular element that performs the function of secretion and re absorption

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Major Components of the Renal Corpuscle

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Glomerulus and the Glomerular Capsule

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Glomerulus

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is a knot of capillaries which resembles a tangled ball of yarn, in fact the term means a ball of yarn. Serves as the site of production of the protein free filtrate that eventually becomes urine. It is made of simple squamous epithelial cell with fenestrations

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Glomerular Capsule

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a blind ended , double walled cup that completely surrounds the glomerulus

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Parietal Layer of the Glomerular Capsule

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outer wall is made of highly branching epithelial cells called podocytes

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Visceral Layer of G.C

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inner walls is made of highly branching epithelial cells

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Capsular Space of G.C

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the area between the two layers of the glomerular capsule.

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Podocytes

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rest on the slit membrance and give rise to terminal branches called pedicels

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Pedicels

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"little feet" of the docytes intertwin with each other and connect to the basement membrane of the glomeruls. The clefts between the pedicels are called filtration slits

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Filtration Slits

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allow filtrate to pass through to the interior of the chamber called capsular space

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Slit Membranes

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prevent filtration of medium sized proteins

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Filtration Membrane

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name often given to the collective structures that allows the free passage of water and solutes smalles that the plasma protein fromt he blood to capsular space. it is made up of the G.Capilary and its fenestration, the podocytes of the visceral layer of the G. Capilary and the slit membranes which also posses an electrical charge.

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Proximal Convoluted Tubule

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the tubule leading from the glomerular capsule, while it contains cells for reabsorption and secretion, its primary function is reabsorption. It is made up of simple cubical cells that have any microvilli and a large amount of mitochondria for a greater surface area for reabsorption and greater energy production.

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Nephron Loop (Loop of Henle)

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this segment can be divided into three regions. The descending limb, the hairpin turn or the loop itself and the ascending limb. It is important for concentrating and diluting urine.

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Descending limb

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the proximal portion of the descending limb is continuous and resembles the proximal convoluted tubule. The rest of it is made up of simple squamous epithelium. It is freely permeable to water and only permeable to water.

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Loop of Henle

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this is the hairpin turn that the thin segment takes to begin the ascending limb.

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Ascending limb

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depending on the nephron, the thin segment may or may not be present. The thick ascending limb is due to the presence of cuboidal cells as well. This section is impermeable to water, but solutes can go across cells.

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Distal Convoluted Tubule

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the cells in the initial part of this segment are similar to those in the proximal convoluted tubule except that they are thinner and lack microvilli. This hints at their function to primarily secrete substances. As one moves farther down the tubule, the cells begin to differentiate. The two most important cell types here are the intercalated cells and the principal cells.

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Intercalated cells

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these are important in the maintenance of acid-base balance of the blood as the secrete H+.

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Principal cells

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these help maintain the body water balance and have aquaporins that are sensitive to ADH.

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Arterioles

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there is a larger diameter afferent arteriole which brings blood to the glomerulus and a smaller diameter efferent arteriole which takes blood away. While not part of the glomerulus, these structures are important in dictating the initial filtered volumes. The efferent arteriole in turn leads to another capillary bed called the peritubular capillary network. This capillary network surrounds the tubules and plays an important role in secretion and reabsorption, plus it delivers oxygen to kidney cells.

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Juxtaglomerular Apparatus (JGA)

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is an area where all structures have been modified and it occurs at the initial portion of the distal tubule where it contacts the afferent and efferent arterioles. The enlarged smooth muscle cells of the afferent arteriole are the juxtaglomerular cells (JG cells) which secrete renin. These cells act as mechanoreceptors which directly sense the blood pressure in the afferent arteriole. The enlarged cells in the distal convoluted tubule make up the macula densa. These cells are osmoreceptors mechanoreceptors, chemoreceptors that respond to changes in the solute concentration of the tubular lumen.

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Nephron Physiology

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180 liters 47 gallons of filtrate per day
99% reabsorbed so urine volume is about 1.5 L/day
Kidneys consume 20-25% of oxygen when at rest

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Urine Formation Depends on Three Factors

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Glomerular filtration
Tubular reabsorption
Tubular secretion

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Glomerular filtration

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filtration of plasma through glomerular capillaries which then becomes ultrafiltrate.