02 泌尿系统生理功能1

泌尿系统生理：肾小球的功能

Renal Physiology主讲教师：许文燮

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泌尿系统生理：肾小球的功能

Renal Function

泌尿系统生理：肾小球的功能

Functions of the kidneys Regulation of body fluid osmolality& volume:Excretion of water and NaCl is regulated in conjunction with cardiovascular, endocrine,& central nervous systems

Regulation of electrolyte balance:– Daily intake of inorganic ions (Na+, K+, Cl-, HCO3-, H+, Ca2+, Mg2+& PO43-)– Should be matched by daily excretion through kidneys. Regulation of acid-base balance: Kidneys work in concert with lungs to regulate the pH in a narrow limits of buffers within body fluids.

泌尿系统生理：肾小球的功能

Functions of the kidneys Excretion of metabolic products& foreign substances:– Urea from amino acid metabolism– Uric acid from nucleic acids– Creatinine from muscles– End products of hemoglobin metabolism– Hormone metabolites– Foreign substances (e.g., Drugs, pesticides,& other chemicals ingested in the food)

泌尿系统生理：肾小球的功能

Functions of the kidneys Production and secretion of hormones:– Renin -activates the renin-angiotensinaldosterone system, thus regulating blood pressure& Na+, K+ balance– Prostaglandins/kinins - bradykinin= vasoactive, leading to modulation of renal blood flow& along with angiotensin II affect the systemic blood flow– Erythropoietin -stimulates red blood cell formation by bone marrow

泌尿系统生理：肾小球的功能

Glomerular filtration

泌尿系统生理：肾小球的功能

Glomerular filtrationGlomerular filtration; Tubular reabsorption Tubular secretion

泌尿系统生理：肾小球的功能

Glomerular filtration Glomerular filtrate is produced from blood plasma Must pass through:– Pores between endothelial cells of the glomerular capillary– Basement membrane acellular gelatinous membrane made of collagen and glycoprotein– Filtration slits formed by podocytes

泌尿系统生理：肾小球的功能

Filtrate CompositionFiltrate is similar to plasma in terms of concentrations of salts and of organic molecules (e.g., glucose, amino acids) except it is essentially proteinfree

泌尿系统生理：肾小球的功能

Glomerular filtration Glomerular filtration barrier:restricts the filtration of molecules on the basis of size and electrical charge

Neutral solutes:– Solutes smaller than 2 nanometers in radius are freely filtered– Solutes greater than 4.2 nanometers do not filter– Solutes between 2 and 4.2 nm are filtered to various degrees

泌尿系统生理：肾小球的功能

Filtrate Composition Serum albumin is anionic and has a 3.6 nmradius, only~7 g is filtered per day.

In a number of glomerular diseases, thenegative charge on various barriers for filtration is lost due to immunologic damage and inflammation, resulting in proteinuria (i.e.increased filtration of serum proteins that are mostly negatively charged).

泌尿系统生理：肾小球的功能

Filtrate Composition Principles of fluid dynamics that account for tissue fluid in the capillary beds apply to the glomerulus as well

Filtration is driven by Starling forces across the glomerular capillaries, and changes in these forces and in renal plasma flow alter the glomerular filtration rate (GFR)

泌尿系统生理：肾小球的功能

Glomerular filtration T

he glomerulus is more efficient than other capillary beds because:

– Its filtration membrane is significantly more permeable– Glomerular blood pressure is higher– It has a higher net filtration pressure

Plasma proteins are not filtered and are used to maintain oncotic (colloid osmotic) pressure of the blood

泌尿系统生理：肾小球的功能

Forces Involved in Glomerular Filtration

Mechanism: Bulk flow Direction of movement: From glomerular capillaries to capsule space Driving force: Pressure gradient (net or efficient filtration pressure, NFP or EFP) Types of pressure: Favoring Force: Capillary Blood Pressure (BP), Opposing Force: Blood colloid osmoticpressure(COP) and Capsule Pressure (CP)

泌尿系统生理：肾小球的功能

泌尿系统生理：肾小球的功能

Glomerular Filtration Rate (GFR) The total amount of filtrate formed per minute by the kidneys Filtration rate factors:– Total surface area available for filtration and membrane permeability (filtration coefficient= Kf)– Net filtration pressure (NFP) EFP– GFR= Kf x NFP GFR is directly proportional to the NFP Changes in GFR normally result from changes in glomerular capillary blood pressure

泌尿系统生理：肾小球的功能

Factors affecting GFR Changes in renal blood flow Changes in glomerular capillary hydrostatic p - changes in systemic BP - afferent or efferent arteriolar constriction Changes in hydrostatic p in Bowman’s capsule - ureteral obstruction, renal edema Changes in plasma protein concentration Reduction in effective filtration surface area Changes in glomerular capillary permeability

泌尿系统生理：肾小球的功能

泌尿系统生理：肾小球的功能

Regulation of Glomerular Filtration If the GFR is too high, needed substancescannot be reabsorbed quickly enough and are lost in the urine If the GFR is too low -everything is reabsorbed, including wastes that are normally disposed of Control of GFR normally result from adjusting glomerular capillary blood pressure

Three mechanisms control the GFR– Renal autoregulation (intrinsic system)– Neural controls– Hormonal mechanism (the renin-angiotensin system)

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