Renal Class 2, Glomerular Filtration and Renal Blood Flow

how can hormones and ANS alter glomerular filtration rate?

1. changing resistance to the arterioles 2. altering the filtration coefficient

Reasons for high GFR

1. many foreign substances are filtered into the tubule but not reabsorbed in the blood 2. filtering ions and water into the tubule simplifies their regulation (if water reaches and isn't needed it will be sent as urine, otherwise it will be reabsorbed)

Filtration Fraction Equation

Filtration Fraction = (Glomerular Filtration Rate) / (Renal Plasma Flow) = 0.20

Selective changes in arteriolar resistance alters ____ and ____ in the following ways: How?

GFR and RBF c. resistance changes in renal arterioles alter renal blood flow and GFR d. vasoconstriction of the afferent arteriole increases resistance and decreases renal blood flow, capillary blood pressure and GFR e. increased resistance of efferent arteriole decrease renal blood flow but increase Ph and GFR

Review Starling Forces of Capillary Exchange:

Hydrostatic pressure (Pcapillary - Pinterstitial ) Oncotic (colloid osmotic) pressure (Pπ capillary - Pπ interstitial )

Reabsorption: Sodium linked reabsorption

Na + enters the tubule cells by cotransport, then is actively pumped out the basolateral side by the Na/K/AtPase pump. Solutes that are absorbed by Na linked cotransport include glucose, amino acids and other organic solutes, and some ions such as phosphate and sulfate 1. Na+ moving down its electrochemical gradient yses the SGLT protein to pull glucose into the cell against its concentration gradient 2.

Most of the Filtrate is Reabsorbed by the _____________

Nephron-Collecting Duct

Starling Forces in the Glomerulus: What gives us a constant hydrostatic pressure within the glomerular capillaries,

Pnet = (PGC - PBS) - pGC the serial combination of the afferent and the efferent arterials that give us a constant hydrostatic pressure within the glomerular capillaries,

Glomerular Filtration Rate is Determined by

Pnet and Kf 1.Net filtration pressure (Pnet) 2.Forces favoring filtration are the hydrostatic pressure in the glomerular capillary (PGC) and the oncotic pressure in Bowman's space (pBS). 3.Forces opposing filtration are the oncotic pressure in the glomerular capillary (pGC) and the hydrostatic pressure in Bowman's space (PBS) Pnet = Pgc (hydrostatic pressure in glomerular capillaries) + Pie s (oncotic pressure of bowmans space) - PBS (hydrostatic pressure in bowman's sapce)- pGC (oncotic pressure in glomerular capillaries)

Comparison of Glomerular capillaries to Systemic capillaries

Systemic: arteriole (sit of resistance that changes flow rate) venule Portal System: 2 sites of resistance (affarent & efferent)- So they're affecting not only blood flow through the whole circuit, they're affecting the hydrostatic pressure profile, which is a powerful determinant of filtration

What is the "filter"

The Glomerulus, (renal corpuscle) contains

Autoregulation of Renal Blood Flow (RBF) and Glomerular Filtration Rate (GFR)

Two mechanisms, intrinsic to the each nephron, are responsible. 1.Myogenic (Bayless) -Activated by changes in arterial blood pressure -Stretch of vascular smooth muscle (essentially takes the bumps out of the road) 2.Tubuloglomerular feedback (TGF) -Activated by an increase in tubular fluid NaCl flowing past macula densa -Adenosine increases resistance of afferent arteriole (built into every nephron)

tubuloglomerular feedback-

a paracrine signaling mechanism through which changes in fluid flow through the loop of Henle influence GFR

_______ is vasoconstrictor & _______ are vasodilators

angiotension II; prostaglandins

basal lamina fixed negative charge does what?

anything with a negative charge is going to be repelled by that negativity. And there's negative fixed negative charges on the surface of the parasites as well. -removal of this layer can cause leakage of proteins in

if resistance increases in the effarent arteriole, what happens to glomerular filtration rate (GFR)?

blood "damns" up in front of the constriction and hydrostatic pressure increases, therefor GFR increases

myogenic response-

change in vascular resistance in response to stretch of blood vessels in the absence of external factors -smooth muscle stretches due to ^ BP -depolarization opens Ca+ channels -vascular smooth muscle contracts SO.. -vasoconstriction ^ resistance, which decreases blood flow and that decreases filtration pressure in the glomerulus

By having a filtration kidney high filtration high reabsorption gives us what?

enormous flexibility and protection.

podocytes give what?

extra mechanical integrity

Fenestrated capillary:

have large pores that permit high volumes of fluid to pass between the plasma and the interstitial fluid. The glomerular capillary is a fenestrated capillary.

if resistance increases in the affarent arteriole, what happens to glomerular filtration rate (GFR)?

hydrostatic pressure decreases on glomerular side of the constriction, so GFR decreases *most regulation occurs at the affarent arteriole*

once a fluid filters into bowman's capsule, it is no longer apart of the bodies _______ environment

internal.

the juxtaglomerular apparatus consists of: Where is it located? How does tubuloglomerular feedback help GFR autoregulation?

macula densa and granular cells -where the nephron loops back onto itself so that the ascending limb of the loop of henle passes through the affarent and efferent arterioles 1. GFR ^ 2. Flow through tubules increase 3. Flow past macula densa ^ 4. Paracrine signal from macula densa to affarent arterioles 5. affarent arterioles constrict resistance in affarent arteriole increases > hydrostatic pressure decreases > GFR decreases

The afferent and efferent arterioles are major sites of :

resistance to blood flow through the glomerular capillaries.

what do the macula densa cells of the juxtaglomerular apparatus do?

sense distal tubule flow and release paracrine signals that affect affarent and efferent arteriole diameter

Reabsorption: Principles governing the tubular reabsorption of solutes:

some solutes and water move into and then out of epithelial cells (transcellular or epithelial transport); other solutes move through junctions between epithelial cells (the paracellular pathway). 1. Na+ is reabsorbed by active transport 2. electrochemical gradient drives anion reabsorption 3. Water moves by osmosis, following solute reabsorption. Concentration of other solutes increases as fluid volume in the lumen decreases 4. permeable solutes are reabsorbed by diffusion through membrane transporters or by the paracellular pathway

filtration coefficient: two components

surface area and permeability of filtration slits

what is the plasma & what does it contains?

the liquid part of the blood, (plasma proteins and RBCs cant get contains all the electrolytes, the nutrients, as well as the plasma proteins

Glomerular Filtration Rate (GFR)- what is it ____L/min ___L/day influenced by what two factors? is it constant or would it fluctuate with the hydrostatic pressure provided by blood? how is it controlled?

volume of fluid that filters into Bowman's capsule per unit time 125 180 net filtration pressure and filtration coefficient (two components are surface area and permeability of filtration slits) it remains constant controlled by regulation fo blood flow througb the renal arterioles

Blood Flow in the Kidney: where is it delivered? What is an important site of resistance to blood flow and regulation?

•All of the blood delivered to the kidney is delivered to the filter. Afferent arterioles are an important site of resistance to blood flow and regulation.

GFR is Relatively Constant: what is a major determinant?

•Blood pressure in the glomerular capillaries is a major determinate of GFR, yet GFR is relatively constant over a wide range of blood pressures. •Autoregulation of Renal Blood Flow (RBF) and GFR.

Organization of the Glomerular Filter and Selectivity of Filter: Selectivity of Filter Determined by:

•Glomerular capillary • •Capillary endothelium • •Podocyte • •Foot process • •Filtration Slit • •Basal lamina • •Mesangial cell • •Bowman's space Selectivity Determined by: •Size •Electrical Charge

Macula densa

•Modified epithelial cells •Senses composition of tubular fluid flowing past. •Na-K-2Cl symporter in luminal membrane •High NaCl ® Adenosine ® contraction afferent arteriole ® decreases GFR •High NaCl ® Adenosine ® contraction afferent arteriole ® decreases GFR •Low NaCl ® ® juxtaglomerular cells (JG cells) ® Renin ® RAAS ® decrease in sodium excretion (regulation of sodium balance)