Kidney: Structure and Function

Structure and Function of the Kidney

• Six functions of the kidney need to be identified.
• Key anatomical structures include the renal artery, renal vein, urethra, bladder, kidney, ureter, and adrenal gland.
• Other important structures are the renal hilus, renal capsule, adipose capsule, renal fascia, cortex, medulla, papillae, renal pelvis, calyces, and renal pyramid.
• Key blood vessels are the segmental artery, collecting duct, lobular artery, lobular vein, arcuate artery, arcuate vein, interlobular artery, interlobular vein, afferent arteriole, efferent arteriole, peritubular capillaries, and vasa recta.
• The nephron consists of the glomerulus, Bowman's capsule, glomerular capillary, glomerular endothelium, podocytes, proximal convoluted tubule, loop of Henle, and distal convoluted tubule.
• Important to know the difference between cortical and juxtamedullary nephrons.
• Mesangial cells play a role in the glomerular capsule.
• Juxtaglomerular cells function in the glomerular capsule.
• The macula densa has a specific function.
• There is a filtration mechanism for fluid flow out of the glomerular capillaries.
• Blood flow order through the kidney starts at the interlobular artery.
• Urine flow pathway begins at the Bowman’s capsule.

Glomerular Filtration

• The rate of urine excretion is determined by three factors.
• Filtered molecules have four possible fates.
• Normal glomerular filtration rate (GFR) should be known, along with its range of variation.
• Forces either favor or oppose glomerular filtration.
• There is an approach to calculating GFR.
• Understanding what Kf represents is essential.
• Changes in glomerular capillary hydrostatic pressure impact net filtration pressure (NFP) and GFR.
• Protein loss from the blood due to renal diseases affects plasma oncotic pressure, NFP, and GFR.
• A kidney stone causing blockage in renal tubules increases renal tubular hydrostatic pressure, also impacting Bowman's capsule hydrostatic pressure, NFP, and GFR.
• Glomerulonephritis (inflammation of the glomerular capillary wall) increases capillary permeability, affecting NFP and GFR.
• Increased blood flow results in a decreased filtration fraction.
• Decreased renal plasma flow leads to a decreased GFR.
• Vasoconstriction or vasodilation of the afferent and efferent arterioles (assuming identical diameters) impacts NFP and GFR.
• Renal blood flow is determined by specific factors.
• The effect of increased arterial pressure on renal blood flow should be noted.
• Certain vessels regulate total renal vascular resistance.
• Sympathetic nervous system activation affects GFR.
• Angiotensin influences GFR.
• The juxtaglomerular apparatus regulates GFR.
• Myogenic reflexes predict vessel changes in response to sudden increases in blood flow.

Tubular Reabsorption

• Substances can be either completely reabsorbed or not reabsorbed at all after filtration.
• Diffusion across a membrane occurs in three types.
• ATP is necessary for primary active transport.
• Secondary active transport follows a specific mechanism.
• Secondary active transport ultimately uses ATP, despite not directly hydrolyzing it.
• Endocytosis allows certain substances to pass through renal tubules.
• Paracellular and transcellular movement of molecules across an epithelial cell layer differ.
• Tubular epithelium has a luminal side and a basolateral side, and the basolateral side has other names.
• Water moves based on the osmolarity inside and outside of a cell.
• Water flow direction depends on the osmolarity in a capillary next to a renal tubule versus the tubular lumen.
• Sodium reabsorption in the tubules results in water, amino acid, glucose, urea, and chloride reabsorption.
• Epithelial cells differ in structure and function in the PCT, thin descending loop of Henle, and collecting duct cells.
• The PCT has a role in reabsorption.
• Sodium, glucose, amino acid, and bicarbonate concentrations change in the PCT.
• The thin descending limb of the Loop of Henle differs from the PCT.
• Reabsorption occurs primarily in the thin descending limb, and affects lumen osmolarity.
• The thin ascending limb of the loop of Henle differs from the descending loop.
• The thick ascending limb of the loop of Henle primarily affects lumen osmolality.
• Countercurrent blood flow concentrates urine in the thin descending limb.
• Early and late portions of the distal convoluted tubule differ in their function.
• The DCT regulates GFR.
• Urine concentration occurs in the collecting duct.
• Peritubular pressure influences reabsorption.
• GFR influences reabsorption.
• Angiotensin, secreted in response to low blood flow to the kidney, impacts reabsorption.
• Vasopressin (ADH), secreted in response to low blood osmolarity, impacts reabsorption.
• Aldosterone, secreted in response to Angiotensin II, impacts reabsorption.
• Atrial natriuretic factor secretion is stimulated somehow and has an impact reabsorption.

Fluid, Electrolyte and Acid-Base Balance

• Electrolytes and nonelectrolytes differ.
• Osmolar concentration should be calculated for a solution containing 140 mM of NaCl.
• The milliequivalent value of a solution containing 3.0 g/L of sodium and chloride should be calculated.
• Dominant ions in the extracellular and intracellular fluids should be stated.
• A certain percentage loss in plasma volume and total body fluid triggers the feeling of thirst.
• Changes in blood volume and blood osmolality trigger a thirst response through a certain mechanism.
• Three factors provide negative feedback to inhibit the thirst response.
• ADH release is triggered by two mechanisms in the posterior pituitary.
• ADH influences kidney function.
• Aquaporins should be defined.
• Water transfers from a hyperosmotic lumen into the interstitial space through a certain process.
• Rennin release from the JGA is triggered by certain factors.
• Angiotensin II has an effect on kidney function.
• Increased Na-K ATPase pump activity in the basolateral membrane increases water reabsorption somehow.
• Constriction of efferent arterioles by angiotensin increases water reabsorption in a certain way.
• Aldosterone secretion is triggered by a set of factors.
• The impact of aldosterone on kidney function should be noted.
• ANP secretion is triggered by a factor.
• Three target organs for ANP exist and what impact it will have on these organs.
• Overproduction or underproduction of hormones affects body physiology.
• Hydrogen ions are produced in the body.
• Body pH is regulated in a certain way.
• Weak and strong acids differ.
• Three chemical buffer systems for acid exist in the body.
• Respiratory acidosis and alkalosis have specific causes.
• Metabolic acidosis and alkalosis have specific causes.
• Bicarbonate reabsorption and H+ secretion both occur in the kidney.
• Ammonium excretion is regulated somehow in the kidney.