Renal Physiology Basic Questions

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What are the three hormones that the Kidney's secrete?

Renin, Erythropoietin, and 1,25-dihydroxycholecalciferol.

What is the papilla?

It is the innermost tip of the inner medulla that empties into the minor and major calyces.

What are the Calyces?

The Calyces are extensions of the ureter.

What constitutes a "nephron?"

A Nephron consists of a glomerulus and a renal tubule.

What is the glomerulus?

The glomerulus is a glomerular capillary network which emerges from an afferent arteriole.

What surrounds the glomerular capillaries?

Bowman's Capsule which is continuous with the first portion of the nephron.

What are the segments of the renal tubule?

Proximal Convoluted Tubule, the proximal straight tubule, the loop of henle (containing the thin descending limb, thin ascending limb, and thick ascending limb), the distal convoluted tubule, and the collecting duct.

What is structurally unique about the Proximal Convoluted Tubule that adds to its absorption amounts?

The Brush Border

What are the two types of Nephrons and how are they different?

Superficial Cortical Nephrons and Juxtamedullary Nephrons which are distinguished by location of their glomeruli. The Superficial Cortical Nephrons These nephrons have short loops of Henle that only descend into the outer medulla. The Juxtamedullar Nephron have their Glomeruli near the corticomedullar border, these nephrons are larger and higher filtration rates.

Explain the general path of blood flow into the Kidney:

Blood enters each Kidney via a renal artery which branches into interlobar arteriers to arcuate arteries to cortical radial arteries. The smallest arteries divide into afferent arterioles which deliver blood to the glomerulus. Blood leaves the capillaries via the Efferent Arterioles. The Efferent Arterioles deliver blood to the peritubular capillaries that surround the nephron.

How is blood flow different in the Superficial Nephrons than the Juxtamedullary Nephrons?

Superficial Nephrons have peritubular capillaries that branch off the efferent arterioles to deliver nutrients to the epithelial cells. The Juxtamedullary Nephrons has the peritubular capillaries have a specialization called the Vasa Recta that follow allong the loops of Henle.

What is the function of the Vasa Recta?

To serve as osmotic exchangers for the production of concentrated urine.

What is the 60-40-20 rule?

Water is 60% of total body weight. ICF is 40% of total body weight. ECF is 20% of total body weight.

ECF and ICF are what fractions of total body water?

ECF is 2/3 total body water. ICF is 1/3 of total body water.

Water content of the body correlates inversely to what content?

Water correlates inversely with fat content. Women have lower percentages of water because they have higher percentages of adipose tissue.

What contents make up the ECF component of total body water?

ECF is divided into Interstitial Fluid (3/4 ECF) and Plasma (1/4 ECF)

What are the major cations and anions of the ICF?

Potassium and Magnesium are the main cations in the ICF while proteins and organic phosphates serve as the major anions of the ICF.

What are the major cations and anions of the ECF?

Sodium is the major cation of the ECF while Cl and Bicarb are the major anions.

What is hematocrit?

Hematocrit is the persentage of blood volume occupied by red blood cells. It should average around 45% (48% in males and 42% in females).

What is the Gibbs Donnan effect?

This effect predicts that the plasma cation levels will be higher than that of interstitial fluid.

What kind of shift in body fluid compartments would you see in Diarrhea?

Diarrhea leads to isosmotic volume contraction because the fluid that is lost to diarrhea is relatively the same as ECF fluid. Since its Isosmotic, ICF levels would not change, only ECF would decrease.

Relative to ECF, how does the osmolarity of sweat differ? How would someone who is sweating a lot change their body fluid compartments.

Sweat is Hyposmotic. That means you are losing more water than solute. This is causing the ECF to lose water but hold on to its sodium ions. Thus fluid will fall from ICF into ECF to follow the solute. Overall there will be a Hypertonic Volume Contraction.

What kind of shift in body fluid compartments would you see with Aldosterone or Renal Deficiency?

In this situation, excess NaCl will be excreted in the Urine, therefore ECF would lose both volume and osmolarity. Since ECF osmolarity will not be lower than ICF's, fluid from ECF will expand the ICF compartment and further lower the ECF fluid volume.

How does SIADH shift the body fluid compartments?

SIADH means there is excess of ADH in which there is an overabundance of water reabsorption in the collecting ducts. The osmolarities.

What is renal clearance?

Renal Clearance is the volume of plasma completely cleared of a substance by the kidneys per unit time.

Discuss what happens when clearance gets higher or lower.

The higher the clearance, the more plasma is cleared of the substance. Substances with the highest renal clearances may be completely removed on a single pass of blood through the kidneys.

What is the equation for clearance?

(Urine Concentration of a substance X Urine Flow Rate) / Plasma Concentration

What is the clearance of albumin and glucose? Why?

The clearance of Albumin is 0 because albumin is not filtered across the glomerular capillaries. The clearance of Glucose is 0 because it is filtered and then completely reabsorbed.

What is so special about Inulin's clearance?

Inulin is freely filtered across the glomerular capillaries, but it is neither reabsorbed nor secreted. Therefore its clearance measures the GFR.

Why does PAH and organic acids have the highest clearance?

Because PAH is both secreted and filtered that means it is filtered out of the plasma and secreted into what is filtered to add what is cleared.

What is the clearance ratio?

The clearance ratio compares the clearance of a substance to the clearance of inulin. Cx/Cin. If this ratio is equal to 1 then it is filtered but neither reabsorbed or secreted. If it is less than one, then the substance is either not filtered or reabsorbed. If the ratio is greater than 1 then the substance is filtered and secreted.

What is the major mechanism for changing blood flow to the kidneys?

Changing arteriolar resistance.

Explain Sympathetic Action on RBF and GFR

Sympathetic Nervous System and circulation catecholamines innervate BOTH the afferent and efferent arterioles an produce vasoconstriction via alpha1 receptors. Because there are far MORE receptors on the Afferent Arterioles, sympathetic action will decrease Renal Blood Flow (RBF) and the Glomerular FIltration Rate (GFR).

Explain how the heart will direct blood flow during hemorrhage in regards to the Kidney:

During hemorrhage, the baroreceptors sense a fall i arterial pressure and will send out the signal to increase sympathetic outflow to the heart and blood vessels. Thus the Alpha 1 Receptors are activated. This will decrease the normal 25% Cardiac Output going to the kidney so the heart will be able to pull more blood towards it and shunt from the kidney.

Explain how Angiotensin II will effect RBF and GFR:

Angiotensin II is a potent vasocontrictor of both afferent and efferent arterioles, but the EFFERENT arterioles are more sensitive to its actions. Thus the consequence is to raise the GFR at LOWER levels while lowering the GFR at higher levels. In hemorrhage, the sympathetic action and HIGH angiotensin II will lower GFR.

Explain how Prostaglandins effect RBF

Several prostaglandins are produced locally in the kidneys and cause vasodialation of both afferent and efferent arterioles.

Explain the unusual relationship between Prostaglandins and the Sympathetic Activity on the Arterioles

Sympathetic Activity causes vasoconstriction via A1 receptors on both afferent and efferent arterioles (more so on Afferent) causing a decrease in GFR and RBF. Sympathetic activty will also stimulate the release of Prostaglandins that act on the arterioles to cause vasodialation. These two actions seem contradictory, but the Prostaglandins act to preserve the integrity of the vasoconstriction and prevent renal failure in the event of Sympathetic activation such as with hemorrhage.

Explain Dopamine usage in treating hemorrhage

Dopamine can dialate cerebral, cardiac, splanchnic, and renal arterioles while constricting arterioles in skeletal muscles and skin. This action occurs with low levels of dopamine administration. This is useful in treating hemorrhage in order to protect from renal failure.

Explain the basic principle behind autoregulation of renal blood flow.

Renal Arterial Pressure can vary from 80 to 200, but RBF will be kept constant in this bracket. The pressure s accommodated for by the resistances in the arterioles, particularly the afferent arteriole. The mechanism is not completely understood but there are two major theories behind it.

What is the Myogenic Hypothesis of Autoregulation of RBF?

This hypothesis states that autoregulation of RBF occurs because the arterial pressure build up causes a reflex contraction of the smooth muscle in the blood vessel walls due to stretch-activated calcium channels.

What is the Tubuloglomerular Feedback hypothesis of Autoregulation of RBF?

This hypothesis states that when renal pressure increases, both RBF and GFR increase. The increase in GFR results in more solute and water into the macula densa of the early distal tubule. The Macula Dnse is a part of the Juxtaglomerular Apparatus that will respond by secreting a mysterious constricting substance that will work on the afferent arteriole.

The clearance of which substance can be used to estimate Renal Plasma Flow?

Para-Aminohippuric Acid (PAH)

What is the Fick Principle?

Assuming that a substance is neither synthesized or degraded by the organ it's passing through, the amount of the substance entering the organ will equal the amount leaving the organ.

Why is PAH used to measure RPF?

PAH is neither metabolized or synthesized by the Kidney. It does not alter RPF. Most importantly, the Kidney's extract most of the PAH from renal arterial blood by filtration and secretion. Essentially, all of the PAH entering the Kidney via the renal artery is excreted in urine, and the concentration in the Renal Vein is nearly zero. Also to add to the calculation, only the Kidney extracts PAH. The infusion of PAH is used to measure Renal Plasma Flow since it is almost impossible to get a blood sample from renal blood vessels.

How do you calculate the RBF from RPF?

RBF is equal to the RPF / (1-Hct)

What is ultrafiltrate?

As the renal blood flow enters the glomerular capillaries, a portion of that blood is filtered in Bowman's space, the first part of the nephron. This is ultrafiltrate in that it has only water and small solutes of blood, it contains no protein or blood.

What are the three layers that constitute the glomerular capillary wall?

Endothelium, Basement Membrane, and Epithelium

What is the function of the Endothelium of the Glomerular Capillary Wall?

It contains pore that are big enough for solutes, fluids, and proteins to pass, but this particular layer filters out the blood cells.

What is the function of the Basement Membrane of the Glomerular Capillary Wall?

This contains the Lamina Rara Interna which is fused to the endothelium. It contains the Lamina Dense or middle of the basement membrane. It contains the Lamina Rara Externa which is fused to the epithelial cell layer. The entire 3 layers prevent the passage of plasma proteins and constitute the most significant barrier of the glomerular capillary.

What is the function of the Epithelium of the Glomerular Capillary Wall?

The Epithelium consists of Podocytes that are connected to the basement membrane by foot processes. This is important because between the feet are filtration slits that are bridged by a think diaphragm. It functions as another barrier to filtration.

Why is the charge of the Glomerular Capillary Wall important?

The Glomerular Capillary Barrier is negatively charged (all layers) and this is important to keep large solutes such as proteins repelled. This makes sure that things are filtered by size AND charge.

Explain how a loss in glycoproteins of the Glomerular Capillary Barrier can lead to proteinuria:

The Glycoproteins of the Barrier give each layer of the Glomerular Capillary Barrier its negative charge. Without that, proteins that can make it through and be filtered.

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