TLDR;
Alright, so this video gives a basic rundown of kidney function, glomerular filtration, and nephrotic syndrome. It covers the kidney's role in maintaining fluid balance, excreting waste, and secreting hormones. It also explains what gets filtered in the glomerulus, what doesn't, and why. Plus, it touches on nephrotic syndrome, GFR, and what happens to the filtrate as it moves through the nephron.
- Kidneys maintain fluid balance, excrete waste, and secrete hormones.
- Glomerular filtration involves filtering plasma into Bowman's capsule, with certain substances being reabsorbed or secreted along the nephron.
- Nephrotic syndrome involves excessive protein excretion due to altered glomerular membrane permeability.
Kidney Functions [0:05]
The main job of the kidney is to keep the volume, osmolality, and composition of extracellular fluid within a normal range. Kidneys also excrete metabolic waste like urea, uric acid, creatinine, hormones, and drugs. They maintain pH balance and retain vital substances like glucose and amino acids. Plus, kidneys have endocrine functions, like regulating red blood cell production via erythropoietin, calcium levels via active vitamin D, and long-term blood pressure by managing fluid balance and secreting renin.
Renal Blood Flow and Glomerular Filtration [1:16]
About 20% of the heart's output goes to the kidneys, which is about one liter of blood per minute. Of that, 20% gets filtered as glomerular filtrate. During pregnancy, this filtration increases because of increased blood volume. Glomerular filtration happens when plasma filters into Bowman's capsule as blood passes through the glomerulus. Plasma proteins and stuff bound to them, like bilirubin and fatty acids, don't get filtered, but water, electrolytes (sodium, potassium, calcium, magnesium, chloride, bicarbonate), metabolic waste (urea, creatinine), and metabolites (glucose, amino acids) do. Some drugs and small proteins also get filtered.
Filtration of Specific Proteins [2:38]
Insulin and hemoglobin are examples of small proteins that can be filtered. Insulin gets taken up by proximal tubular cells, and its carbon skeletons are used to make glucose if needed. Free hemoglobin in the blood gets filtered and broken down in proximal tubular cells, which can cause kidney damage. Albumin, even though it's a small molecule, doesn't usually get filtered because the glomerular basement membrane has negatively charged sialoproteins that repel the negatively charged albumin.
Nephrotic Syndrome Explained [3:29]
Nephrotic syndrome is a kidney problem where there's too much protein in the urine because the glomerular basement membrane is messed up. The negative charge on the glomerular capillary membrane is lost, so albumin and other proteins aren't repelled and end up in Bowman's capsule. This loss of plasma proteins, especially albumin, leads to decreased capillary oncotic pressure. Because of this, fluid leaves the capillaries and goes into the interstitial fluid, causing edema.
Glomerular Filtration Rate (GFR) and Factors Affecting It [4:32]
Glomerular filtration rate (GFR) is the amount of plasma ultrafiltrate formed in the glomeruli each minute, and the normal value is about 125 milliliters per minute. Factors that affect GFR include changes in renal blood flow, systemic blood pressure, glomerular capillary hydrostatic pressure, afferent and efferent arteriolar tone, glomerular capillary membrane permeability, effective filtration surface area, and the concentration of plasma proteins. Mesangial cells in the glomerulus can change the surface area. Angiotensin II, vasopressin, norepinephrine, histamine, endothelin, leukotrienes, and thromboxane A2 increase mesangial cell contraction.
Reabsorption and Secretion in the Nephron [5:30]
As the glomerular filtrate moves along the nephron, most of the fluid and substances are reabsorbed. Some substances are secreted into the filtrate by the renal tubular cells. Glucose, amino acids, water, urea, sodium, potassium, and bicarbonate are reabsorbed. Potassium, hydrogen ions, creatinine, and some drugs are secreted.
Urine Output and Its Significance [6:09]
Normal urine output is about 500 milliliters to 3500 milliliters, with 1.5 liters being an average. The lower limit is 500 milliliters because you need at least that much water to dissolve the metabolic waste produced by a healthy adult. For patients with severe trauma, burns, sepsis, or after surgery, the lower limit should be more than 500 milliliters per day because they have higher metabolic rates and produce more waste.