Deeper regions of the medulla, closer to the pelvis, reach very high salt concentrations
Water easily diffuses by osmosis out of the tubular filtrate and into the medulla
NaCl is removed from the filtrate both by active transport and by passive diffusion
At the tip of the loop, the tubular filtrate concentration is increased and its volume is decreased
The descending limb of the loop of Henle is seemingly impermeable to salt diffusion but is permeable to water, forming a hypertonic filtrate.
Interaction between ascending and descending tubular flow in the loop of Henle where the more salt is extruded, the more concentrated the tissue fluid will be, is an example of negative feedback.
Salt becomes recirculated and trapped in the medullary tissue fluid, increasing in "saltiness" as it accumulates toward the lower tip of the pyramids.
Water is removed from the medulla by the higher colloid osmotic pressure of the blood in the vasa recta capillaries.
The walls of the collecting ducts become less permeable to dissolved solutes and water.
Water channels, or aquaporins, appear in the cell membranes of the collecting duct epithelial cells promoting the reabsorption of water from the filtrate.
The ultrafiltrate flowing through the collecting duct becomes more hypotonic.
A greater volume of dilute urine is excreted
ADH is synthesized by neurons of the hypothalamus and released from the posterior pituitary gland.
ADH binds to receptors on the collecting duct cells and activates a cAMP second messenger system.
ADH is released during body dehydration conditions to place water channels, or aquaporins, that reabsorb water along the collecting duct
ADH is released when osmoreceptors in the hypothalamus sense a decrease in the blood osmolality (blood becomes more hypotonic).
Is associated with the inadequate secretion or action of antidiuretic hormone (ADH).
Results from overeating and hypersecretion of hormones by the pancreas.
Is characterized by an abnormal increase in glucose concentrations in the blood and urine.
Can be cured by injections of the hormone, insulin.
Inulin is a polymer of fructose, a simple sugar or monosaccharide found in some plants.
Inulin is easily filtered by the glomerulus of the nephron and is measurable in the urine.
Inulin is easily reabsorbed by the walls of the nephron and returned to the blood.
Inulin is not removed from capillary blood and secreted by walls of the nephron into the filtrate - thereby permitting an estimate of the glomerular filtration rate (GFR).
Para-aminohippuric acid (PAH)
Potassium ion (K+)
They are easily filtered by the glomeruli into the renal tubules of the nephrons.
They are normally not found in the urine
They are reabsorbed into the nephron tubule cells by primary rather than secondary active transport mechanisms.
They are reabsorbed completely until their concentrations in the blood and in the filtrate exceed their transport maximum (Tm).
It is a major steroid (mineralocorticoid) hormone secreted by the kidney.
It promotes the reabsorption of Na+ in the late distal tubule and the cortical region of the collecting duct.
It stimulates the secretion of K+ from the peritubular blood into the distal tubule.
Without it, no K+ is ever excreted in the urine.
It is a location in each nephron where the afferent arteriole and the distal convoluted tubule contact each other.
The role of the macula densa region of the distal tubule is to secrete the enzyme renin.
The granular cells within the afferent arteriole are sensitive to renal blood flow (perhaps acting as baroreceptors).
High Na+ concentrations in the filtrate can inhibit the secretion of renin.
A decrease in renin secretion
A decrease in aldosterone secretion
A decrease in atrial natriuretic peptide (ANP) secretion
An increase in Na+ excretion in the urine
The kidneys excrete bicarbonate ion and reabsorb hydrogen ion.
Hydrogen ion (H+) enters the filtrate in two ways: by glomerular filtration and by secretion into the nephron tubule.
Most of the hydrogen ion secretion occurs across the wall of the proximal tubule in exchange for the reabsorption of sodium ion.
Buffers like bicarbonate ion can bind and release free H+ and thus can stabilize pH.
The apical membranes of the tubule cells are impermeable to bicarbonate ion.
Bicarbonate in the filtrate is converted to carbon dioxide and water by the action of carbonic anhydrase.
The enzyme carbonic anhydrase is located both in the apical cell membrane and in the tubule cell cytoplasm.
During alkalosis, more bicarbonate is reabsorbed and less bicarbonate is excreted to help stabilize the pH.
Heart and kidneys
Liver and lungs
Kidneys and lungs
Lungs and heart
The kidneys can filter and secrete H+ into the tubular filtrate.
The kidneys normally reabsorb all bicarbonate ions that are filtered at the glomerulus.
Normally some H+ is excreted each day in the urine, thereby raising the urine pH value above that of the blood, which is normally 7.4.
Filtered bicarbonate present in the filtrate is reabsorbed into the blood indirectly as CO2 gas.
Carbonic anhydrase inhibitors
Carbonic anhydrase inhibitors
Separate molecules on the basis of size
Prevent the diffusion of plasma proteins
Reabsorb Na+, K+, glucose, and other molecules
Allow the free movement of water (solvent)
Here's an interesting quiz for you.