PHYS EXAM #4

-occurs due to the pressure gradient in the glomerulus -125 mL/min - increased BV & BP will increase GFR -is the measure that describes the total amount of filtrate formed by all the renal corpuscles in both kidneys per minute - if too high, needed substances cannot be reabsorbed quickly enough and are lost in the urine - if too low, everything is reabsorbed, including wastes that are normally disposed of

The most important function of the kidney is the homeostatic regulation of the water and ion content of the blood, also called salt and water balance or fluid and electrolyte balance

Regulation of extracellular fluid volume and blood pressure, regulation of osmolarity, maintenance of ion balance, Homeostatic regulation of pH, Excretion of wastes, and production of hormones.

nephron

-80% of nephrons - almost completely contained within the cortex

-20% Nephrons near the medulla. Responsible for the development of osmotic gradients in the renal medulla, which are used to concentrate urine Composed of: macula dense cells that secrete paracrine that vasoconstrictor the afferent artiole/ act as chemoreceptors or osmoreceptors and also afferent arteriole smooth muscle cells and act as mechanoreceptors

the movement of fluid from blood into the lumen of the nephron; takes place only in the renal corpuscle, where the walls of glomerular capillaries and Bowman's capsule are modified to allow bulk flow of fluid. Once the filtered fluid, called filtrate, passes into the lumen of the nephron, it becomes part of the body's external environment. For this reason, anything that filters into the nephron is destined for excretion, removal in the urine, unless it is reabsorbed into the body.

the process of moving substances in the filtrate from the lumen of the tubule back into the blood flowing through peritubular capillaries.

reabsorption of isosmotic fluid, organic nutrients, ions & water

The loop of Henle is the primary site for creating dilute urine

1.5 L/ day

Filtration takes place in the renal corpuscle, which consist of the glomerular capillaries surrounded by Bowman's capsule. Substances leaving the plasma must pass through three filtration barriers before entering the tubule lumen: the glomerular capillary endothelium, a basal lamina, and the epithelium of Bowman's capsule.

fenestrated, blood cells

Glomerular mesangial cells lie between and around the glomerular capillaries. Mesangial cells have cytoplasmic bundles of actin-like filaments that enable them to contract and alter blood flow through the capillaries. In addition, mesangial cells secrete cytokines associated with immune and inflammatory processes.

The basal lamina (basement membrane) is an acellular layer of extracellular matrix that separates the capillary endothelium from the epithelial lining of Bowman's capsule. The basal lamina consists of negatively charged glycoproteins, collagen, and other proteins. The lamina acts like a coarse sieve, excluding most plasma proteins from the fluid that filters through it.

The portion of the capsule epithelium that surrounds each glomerular capillary consists of specialized cells called podocytes. Podocytes have long cytoplasmic extensions called foot processes that extend from the main cell body. Foot processes wrap around the glomerular capillaries and interlace with one another, leaving narrow filtration slits closed by a semiporous membrane.

a net driving force of 10 mm Hg in the direction favoring filtration

Average glomerular filtration rate is 180 L/day or 125 mL/min.

GFR is controlled primarily by regulation of blood flow through the renal arterioles. If the overall resistance of the renal arterioles increases, renal blood flow decreases, and blood is diverted to other organs. The effect of increased resistance on GFR, however, depends on where the resistance change takes place. If resistance increases in the afferent arteriole, hydrostatic pressure decreases on the glomerular side of the constriction. This translates into a decrease in GFR. If resistance increases in the efferent arteriole, blood "dams up" in front of the constriction, and hydrostatic pressure in the glomerular capillaries increases. Increased glomerular pressure increases GFR. The opposite changes occur with decreased resistance in the afferent or efferent arterioles. Most regulation occurs at the afferent arteriole.

Afferent arteriole, glomerulus, efferent arteriole, particular capillaries. The vasa recta capillaries dip into the medulla.

The outer cortex and inner medulla.

Autoregulation of glomerular filtration rate is a local control process in which kidney maintains a relatively constant GFR in the face of normal fluctuations in blood pressure. One important function of GFR autoregulation is to protect the filtration barriers from high blood pressures that might damage them. We do not completely understand the autoregulation process, but several mechanisms are at work. The myogenic response is the intrinsic ability of vascular smooth muscle to respond to pressure changes. Tubuloglomerular feedback is a paracrine signaling mechanism through which changes in fluid flow through the loop of Henle influence GFR.

They receive filtrate from more than 1 nephron They run through the pyramids, then fuse & deliver urine to calyces Intercalated (cuboidal cells with microvilli) & principal cells (cuboidal cells without microvilli invoked in body's water & salt balance)

Vasodilation of the afferent arteriole ( meaning resistance increases) Vasoconstriction of the efferent arteriole ( resistance increases, blood dams up in front of the constriction, and hydrostatic pressure int he glomerular capillaries increases.