Glomerulus (kidney)

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The glomerular ( ), plural glomeruli , is a capillary network known as tuft , located at the beginning of the nephron in the kidney. Tuft is structurally supported by intraglomerular mesangial cells. Blood is filtered through this capillary wall through a glomerular filtration barrier, which produces a water filtrate and a soluble substance to a sac like a cup known as the Bowman capsule. The filtrate then enters the renal tubule, from the nephron.

The glomerulus receives its blood supply from the afferent arterioles from the circulation of the renal arteries. Unlike most bed capillaries, the glomerular capillaries go into the efferent arterioles rather than the venules. Efficient arteriolar resistance causes considerable hydrostatic pressure in the glomerulus to provide strength for ultrafiltration.

The glomerulus and the surrounding Bowman capsule form the renal corpuscus, the renal base filtration unit. The rate at which blood is filtered through all the glomeruli, and thus the overall size of the kidney function, is the glomerular filtration rate (GFR).

Video Glomerulus (kidney)

Structure

Glomerulus is a small blood vessel sheath called capillaries located inside Bowman's capsule inside the kidney. Glomerular mesangial cells structurally support fiber bundles. Blood enters the glomerular capillaries by a single arteriole called afferent arterioles and leaves by the efferent arterioles. Capillaries consist of tubes coated by endothelial cells with central lumen. The walls have a unique structure: there are pores between the cells that allow water and solutes to come out, and after passing through the glomerular basement membrane, and between the process of the podocyte foot, enter the capsule as ultrafiltration.

Blood supply

Lining

Glomerular capillaries are enclosed by endothelial cells. It contains many pores - also called fenestrae - 50-100Ã, nm in diameter. Unlike other capillaries with fenestration, this fenestration is not stretched by the diaphragm. They allow for the filtering of fluids, blood plasma solutes and proteins, at the same time preventing the filtering of red blood cells, white blood cells, and platelets.

The glomerulus has a glomerular basement membrane (GBM) consisting primarily of laminin, type IV collagen, agrin and nidogen, which is synthesized and secreted by endothelial cells and podocytes: thus GBM is sandwiched between glomerular capillaries and podocytes. GBM has a thickness of 250-400Ã,m, which is thicker than other base network membranes. This is a barrier to blood proteins such as albumin and globulin.

The part of the podocyte in contact with GBM is called the podocyte foot process or pedicle (Fig 3): there is a gap between the foot processes through which the filtrate flows into the Bowman capsule chamber.. The space between adjacent podocyte foot processes is laid out by a gap diaphragm consisting of a protein mat, including podocin and nephrin. In addition, the foot process has a negatively charged mantle (glikokaliks) that reject negatively charged molecules such as serum albumin.

Maps Glomerulus (kidney)

intraclomerular mesangial cells

The space between the glomerular capillaries is occupied by intraglomerular mesangial cells. They are not part of the filtration barrier but are specific pericytes that participate in regulating filtration levels by contracting or expanding: they contain actin filaments and myosin to achieve this. Some mesangial cels are in physical contact with capillaries, others are in physical contact with podocytes. There is a two-way chemical cross-talk between mesangial cells, capillaries, and podocytes to perfect GFR.

Intrahenal circulation

Blood out of the glomerular capillaries by eferent arteriol rather than venule , as seen in most capillary systems (Figure 4). This gives tighter control over the blood flow through the glomerulus, because the arteriole widens and narrows more easily than the venules, due to the thick layer of smooth muscle (tunica media). The blood coming out of the efferent arterioles enters the renal venule, which in turn enters the interlobular vein of the kidney and then enters the renal vein.

The cortical nephrons near the corticomedulla junction (15% of all nephrons) are called nephron juxtamedullary. The blood coming out of the efferent arterioles of the nephron enters the rectal vasa, which is a straight capillary branch that delivers blood to the renal medulla. This recta vasa runs adjacent to the downward and rising loop of Henle, and participates in the maintenance of the medullary opposite system of medullary currents.

Drainage filtration

The filtrate that has passed through a three-layer filtration unit enters the Bowman chamber. From there, it flows into the kidney tubule - the nephron - which follows the U-shaped path to the collecting ducts, eventually coming out into the kidneys of the kidneys as urine.

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Function

Filtration

The main function of the glomerulus is to filter the plasma to produce a glomerular filtrate, which passes through the length of the nephron tubules to form urine. The rate at which the glomerulus produces the filtrate of the plasma (glomerular filtration rate) is much higher than the systemic capillaries due to certain anatomic characteristics of the glomerulus. Unlike systemic capillaries, which receive blood from high-resistance arterioles and flow into the low-resistance venules, glomerular capillaries connect at both ends to high-resistance arterioles: afferent arterioles, and efferent arterioles. This arrangement of the two arterioles in the series determines the high hydrostatic pressure in the glomerular capillaries, which is one of the forces that supports filtration into the Bowman capsule.

If a substance has passed glomerular capillary endothelial cells, glomerular basement membranes, and podocytes, it enters the tubular lumen and is known as the glomerular filtrate. If not, it exits the glomerulus through the efferent arterioles and continues the circulation as discussed below and as shown in the figure.

Permeability

The layer structure determines their permeability-selectivity ( permselectivity ). Factors affecting permselectivity are the negative charges of the basement membrane and podocytic epithelium, and the effective pore size of the glomerular wall (8 nm). As a result, large and/or negatively charged molecules will pass far less than small and/or positively charged. For example, small ions such as sodium and potassium pass freely, while larger proteins, such as hemoglobin and albumin, practically have no permeability at all.

The oncotic pressure of the glomerular capillary is one of the forces holding the filtration. Because large and negatively charged proteins have low permeability, they can not easily filter into Bowman capsules. Therefore, the concentrations of these proteins tend to increase as glomerular capillaries of plasma filtrate, increasing the oncotic pressure along the length of the capillary glomerulus.

Starling's Equation

Tingkat leaked to give glomerulus that Capsule Bowman Ditentukan (Outside Pulling Systematic) oleh Persama Starling:

${\ displaystyle \ GFR = K _ {\ mathrm {f}} [(P _ {\ mathrm {gc}} -P _ {\ mathrm {bc }}) - (\ pi _ {mathrm {gc}} - \ pi_ {\ mathrm {bc}})}} Â Â$

• GFR adalah laju filtrasi glomerulus.
• K _f adalah koefisien filtrasi - sebuah constant proporsionalitas
• P _gc adalah tekanan hidrostatik kapiler glomerulus
• P _bc adalah tekanan hidrostatik kapsul Bowman
• ? _gc adalah tekanan onkotik capiler glomerulus
• ? _bc adalah tekanan onkotik kapsul Bowman

Pengaturan tekanan darah

Afferent arteriolar walls contain specialized smooth muscle cells that synthesize renin. These juxtaglomerular cells play a major role in the renin-angiotensin system, which helps regulate blood volume and pressure.

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Clinical interests

Glomerular damage by disease may allow passing through glomerular filtration barrier of red blood cells, white blood cells, platelets, and blood proteins such as albumin and globulin. The underlying cause for glomerular injury may be inflammatory, toxic or metabolic. This can be seen in the urine (urinalysis) on microscopic and chemical examinations (dipstick). Examples are diabetic kidney disease, glomerulonephritis, and IgA nephropathy.

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History

In 1666, the Italian biologist and anatomist Marcello Malpighi first described the glomeruli and showed its continuity with the kidney vessels (281,282). About 175 years later, surgeon and anatomist William Bowman explains in detail the glomerular capillary architecture and the continuity between the surrounding capsule and proximal tubules.

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Additional images

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References

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Source

• Hall, Arthur C. Guyton, John E. (2005). Medical physiology textbook (issue 11). Philadelphia: W.B. Saunders. p.Ã, Chapter 26. ISBNÃ, 978-0-7216-0240-0.
• Deakin, Barbara Young... [] Ã,; picture by Philip J.; et al. (2006). Wheater's functional histology: a text and color atlas (5th ed.). [Edinburgh?]: Churchill Livingstone/Elsevier. p.Ã, Chapter 16. ISBNÃ, 978-0-443068508.

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