61. Physiology - Proximal Tubule Tm Mechanism

Maximum rate at which a substance can be reabsorbed by the proximal tubule.

The rate at which blood is filtered by the glomeruli in the kidneys, typically around 125 ml/min.

Tubular Transport Maximum, the maximum rate of reabsorption or secretion of a substance by the nephron.

The process of reclaiming essential substances and water from the filtered fluid in the kidneys.

The kidneys reabsorb a large volume (178-179 liters) of fluid daily to maintain balance and avoid excessive urine output

The formula to calculate the reabsorption of glucose: UgluV = (GFR * Aglu) – Rglu Where Rglu = Tmglu to determine whether glucose appears in urine

Some substances have a maximum reabsorption rate (Tm), while others do not, meaning they can be reabsorbed without a maximum point.

The total amount of water in a 70kg person's body, approximately 42 liters.

Part of the nephron where about 60-80% of filtered solutes and water are reabsorbed.

Reabsorption of substances without a maximum transport rate, such as sodium, potassium, chloride, bicarbonate, and urea.

Most water reabsorption occurs in the proximal tubule, approximately 60-80%, passively following solute reabsorption by osmosis, maintained isotonic to renal ISF.

The maximum rate at which a solute can be reabsorbed or secreted by the proximal tubule, not for a single transporter but for the entire tubule.

High water permeability in proximal tubule cells allowing water reabsorption through aquaporin 1.

Extracellular fluid volume which is about a third of total body water (TBW).

Intracellular fluid volume which is about two thirds of total body water (TBW).

Water channels specifically involved in isotonic water reabsorption in proximal tubules.

The process of removing substances from the blood into the tubular fluid in the kidneys.

80% of the kidney's energy (ATP) is used to reabsorb Na+ ions.

The maximum rate at which a substance can be reabsorbed or secreted by the nephron.

The rate at which blood is filtered by the glomeruli in the kidneys.

Higher GFR results in a lower blood glucose threshold, and vice versa.

The rate of transport reaches a maximum when all carriers are saturated.

Mechanisms reabsorbing substances at a maximum rate exhibit characteristics of 2ndary active transport.

Tm transporters only move specific molecules.

Tm transporters may compete with similar molecules for reabsorbetion.

The rate of glucose excretion, product of urine flow (V) and glucose concentration in urine (Uglucose)

A small area within or around a cell with specific properties, like higher osmolality, influencing movement of water.

The concentration of solute particles in a solution, influencing water movement.

Water movement that appears constant and balanced at a larger scale, even though tiny osmolality differences drive it.

Part of the nephron where most reabsorption occurs.

Maximum rate of reabsorption by a specific transport mechanism; usually a constant for most substances.

Plasma concentration at which a transport mechanism becomes saturated and cannot reabsorb more of a substance.

Maximum transport rate for glucose, calculated using GFR (Glomerular Filtration Rate) and threshold.

The rate at which fluid is filtered from the blood into the Bowman's capsule in the kidney

A medical condition where the blood glucose level is abnormally elevated.

The process of returning filtered substances back to the blood.

Pressure exerted by proteins in the blood plasma, drawing water toward the capillary.

Capillary network surrounding the nephron that receives reabsorbed substances.

Not defined in the provided text.

Glucose is reabsorbed from the filtered fluid in the proximal tubule primarily by a Na+-glucose co-transporter.

The sodium-glucose transporter is always saturated with sodium due to high sodium concentration, making sodium concentration not rate limiting.

Glucose transporters are specific. They only transport certain types of glucose, not all sugars.

Other sugars (like fructose) can compete with glucose for the same transport proteins, affecting glucose reabsorption.

Glucose transport utilizes the energy from sodium ions moving down their concentration gradient to move glucose up its concentration gradient.

The Na+/K+ ATPase pump located on the basolateral membrane maintains the low intracellular sodium concentration, driving sodium into the cell.

The maximum rate at which a substance like glucose can be reabsorbed by the nephron, not by a single transporter but for the entire tubule.

Glucose reabsorption has a maximum rate (Tm) because of the limited capacity of the transport proteins, while other substances like sodium might not have limited maximum reabsorption rate.

Segment of the nephron where most filtered glucose is reabsorbed.

The Na,K-ATPase in the basolateral membrane maintains a low intracellular sodium concentration ([Na+]ICF).

If poisoned, intracellular sodium concentration ([Na+]ICF) increases, reducing the driving force for secondary active transport and halting Na+-coupled transport.

In untreated diabetes mellitus, plasma glucose exceeds the renal threshold, exceeding the maximum reabsorption capacity (Tm).

A high-capacity, low-affinity transporter that carries Na+ and glucose at a 1:1 ratio, establishing a cell-to-tubular fluid glucose ratio of ~70.

A low-capacity, high-affinity transporter that carries Na+ and glucose at a 2:1 ratio, transporting at a lower maximum rate.

These new diabetes medications reduce cardiovascular risk and diabetic kidney disease by inhibiting SGLT2, resulting in glucose excretion.