URINARY SYSTEM :beer_mugs: (Filtration (Occurs primarily in the glomerulus…
Occurs primarily in the glomerulus.
Water and dissolved solutes are passively separated from the blood plasma within the glomerular capillaries.
Water and solutes enter the capsular space of the renal corpuscle due to pressure gradient.
This separated fluid is called filtrate, which is essentially protein-free plasma.
Glomerular Hydrostatic Blood Pressure
Pressure that promotes filtration.
Blood pressure in the glomerulus.
Higher value than the blood pressure of other systemic capillaries.
This higher pressure is required for filtration to occur.
Blood Colloid Osmotic Pressure and Capsular Hydrostatic Pressure
Lower value than glomerular hydrostatic pressure, even combined.
Blood colloid osmotic pressure is the pressure exerted by the blood due to the dissolved solutes it contains.
Capsular hydrostatic pressure is the pressure in glomerular capsule due to the amount of filtrate already within capsular space.
Water, glucose, amino acids, ions, urea, some hormones, water-soluble vitamins, and ketones.
Formed elements and large proteins cannot normally pass through the filtration membrane.
Intermediate sized proteins are generally not filtered. Their size or their negative charge repels them from the membrane.
Only limited amounts of these substances would become part of the filtrate.
Regulation of blood pressure
One of the kidney's most important functions.
Contraction and relaxation of the afferent arteriole.
Contracts when systemic blood pressure is high.
Dilates when systemic blood pressure is too low.
Tubuloglomerular feedback mechanism
Supplemental response to an increase in blood pressure.
Accomplished by the juxtaglomerular apparatus based on the detection of NaCl levels.
As glomerular blood pressure increases, so does the amount of NaCl found in tubular fluid.
Increased NaCl levels cause the macula densa to respond by releasing paracrine molecules.
Causing vasoconstriction of afferent capillaries.
Mesangial cells also contract, decreasing filtration membrane surface.
As a result, GFR and blood pressure return to normal levels.
Prevent drastic decrease of blood pressure.
Regulation of blood and urine pH.
Regulation occurs in the collecting tubules via intercalated cells.
Secrete hydrogen ions and reabsorb bicarbonate.
Secrete bicarbonate and reabsorb hydrogen ions.
As kidneys filter blood, they measure blood oxygen levels.
If too low, the kidneys secrete EPO hormone.
Stimulating red bone marrow to increase its rate of erythrocyte formation.
The increased number of erythrocytes transport additional oxygen.
Occurs throughout tubules
When components within the tubular fluid move by diffusion, osmosis, or active transport.
All vital solutes and most water in filtrate are reabsorbed.
Involves the movement of filtrate from the tubules to the capillaries.
Simple cuboidal epithelium facilitates absorption of solutes.
Proximal Convoluted Tubule
Most water is reabsorbed throughout tubule unless the transport maximum is exceeded.
Nutrients are reabsorbed completely here via specific transport protein.
Glucose is also reabsorbed completely here unless renal threshold is exceeded. Glucose in urine is indicative of diabetes mellitus.
Majority of ions are reabsorbed here, some reabsorption also occurs in the loop of Henle.
98-100% of sodium is reabsorbed throughout tubule.
Agents affecting reabsorption
Steroid hormone that stimulates protein synthesis of Na channels and Na/K pumps. Increases reabsorption of Na.
Increases water reabsorption as well via obligatory water reabsorption. Water follows sodium.
Atrial natriuretic peptide
Released by the heart. Inhibits both the reabsorption of Na and the release of aldosterone. Increases GFR.
Released from the posterior pituitary when we are dehydrated. Promotes water reabsorption.
Inhibits reabsorption of phosphate in the PCT and promotes the absorption of calcium in the DCT. Increasing blood calcium levels.
Secretion and Excretion
Occurs throughout tubules
Movement of solutes out of the blood within the peritubular and vasa recta capillaries into tubular fluid.
Movement usually occurs via active transport.
What is secreted?
Re-absorbable substances that exceed the transport maximum.
Only secreted, no reabsorption of any kind.
Prevents the accumulation of...
Various hormones and their metabolites.
Foreign substances like drugs and chemicals.
Where it leads?
Filtrate that is secreted flows from the nephron tubule to collecting tubules.
Continues to collecting duct, then papillary duct.
Once filtrate leaves collecting duct, it becomes urine to be excreted from the body.