Blood flows to kidney, in middle-trunk back wall, where filtration removes waste products {excretion, kidney}.
Kidneys have adjacent nephrons, in which water flows in opposite directions {countercurrent mechanism}|, that exchange water to regulate blood acidity, blood salt concentrations, blood volume, and total body water.
processing
First, in kidney cortex, blood pressure forces urea, creatinine, uric acid, ammonia, ions, and water to diffuse through capillary membranes into Bowman's capsule.
Below Bowman's capsule, nephron convolutes, and active-transport reabsorption returns glucose, amino acids, and salts from proximal convoluted tubule to blood, along with water.
Proximal convoluted tubule then goes down into kidney medulla, becomes loop of Henle, turns around, and comes back up to kidney cortex.
Loop then convolutes and becomes distal convoluted tubule, which secretes non-diffusible waste substances from blood into urine in augmentation.
Distal convoluted tubule then goes into kidney medulla, becomes collecting tubule, which is adjacent to loop of Henle, and absorbs or desorbs water to regulate blood and urine water concentrations.
countercurrent
Loop of Henle and collecting tubule form a countercurrent structure. See Figure 1.
The first downward loop-of-Henle part contains liquid that has received blood waste and nutrients, in Bowman's capsule, and returned nutrients and water to blood, in proximal convoluted tubule. It has moderate waste concentration and low nutrient concentration. Collecting tubule has received waste from blood that cannot diffuse out. If collecting tubule has too little water and downward loop has too much water, downward loop diffuses water to collecting tubule, causing upward loop to receive moderate water from downward loop and send it into collecting tubule. If collecting tubule has too much water and downward loop has too little water, collecting tubule diffuses water to downward loop, causing upward loop to receive moderate water from downward loop and send it into collecting tubule.
The second upward loop-of-Henle part can diffuse water into, or receive diffuse water from, downward loop and collecting tubule to exactly balance water concentrations.
Water typically flows from loop of Henle into collecting tubule, because collecting tubule has high waste concentrations and therefore has low water concentration. Loop of Henle has low diffusible-waste concentrations, has no non-diffusible wastes, and has higher water concentration, as blood excretes water into Bowman's capsule.
changes
If you drink water, blood water increases and blood pressure increases. Blood puts much water into Bowman's capsule with little waste and nutrients. Proximal convoluted tubule puts water and most nutrients back into blood. Loop of Henle carries water to distal convoluted tubule, where urine receives little non-diffusible waste. Collecting tubule has almost same concentrations as loop of Henle, so little water diffuses. Extra water in your body then excretes.
If you do not drink enough water, blood water decreases and blood pressure decreases. Blood puts little water into Bowman's capsule, with high waste and nutrient concentrations. Proximal convoluted tubule puts all water and nutrients back into blood. Loop of Henle carries little water but high waste concentration to distal convoluted tubule, where urine receives little non-diffusible waste. Collecting tubule has almost same concentrations as loop of Henle, so water diffuses back into loop of Henle. Little water excretes.
pressure
Water-diffusion countercurrent process determines water, salt-ion, and hydrogen-ion concentrations at downward-loop top and so in proximal convoluted tubule. The liquid at proximal-convoluted-tubule end can put more or less back pressure on proximal-convoluted-tubule liquid, which then diffuses more or less water back into blood, controlling blood volume and total body water.
The liquid at proximal-convoluted-tubule end can have higher or lower salt-ion concentrations, which push more or less salt ion back into blood, controlling blood salt. The liquid at proximal-convoluted-tubule end can have higher or lower hydrogen-ion concentration, which pushes more or less hydrogen ion back into blood, controlling blood acidity.
Bladder distension stimulates contraction, and urine flows through urethra to outside {urination, excretion}|.
Kidneys secrete fluid {urine}| with ions and urea. Hemoglobin breakdown products cause urine color.
Renal pelvis becomes a muscular tube {ureter} to bladder. Urine moves by peristalsis.
Bladder distension stimulates contraction, and urine flows through a tube {urethra}| to outside.
kidney {renal}|.
Excretory system has organs {kidney}| in middle-trunk back wall. Kidney regulates blood pH, blood salt, blood volume, and total body water. Increasing blood water increases blood pressure. Increasing blood pressure increases water filtration into kidney, reducing water in blood and reducing blood pressure. Kidney problems can cause edema. Kidney makes aldosterone, which controls blood pressure.
Kidneys have outer layers {cortex, kidney}.
Kidneys have inner layers {medulla, kidney}.
In kidney cortex, blood capillaries {glomerulus, kidney} {glomeruli, kidney} surround nephrons.
In kidney cortex, glomeruli surround small tubules {nephron}.
In kidney cortex, sacs {Bowman's capsule} {Bowman capsule} surround capillaries. Urea, creatinine, uric acid, ammonia, and ions diffuse under pressure into Bowman's capsule.
Below Bowman's capsule, tubules loop {proximal convoluted tubule}, and active transport returns glucose, amino acids, salts, and water by reabsorption to blood.
Proximal convoluted tubules dip down into kidney medulla and then back up to kidney cortex {Henle loop} {loop of Henle}.
In kidney cortex, looped regions {distal convoluted tubule} secrete selected substances back into urine from blood for augmentation.
Distal convoluted tubules go into kidney medulla {collecting tubule}, where countercurrent processes regulate water concentration, as low-concentration fluid passes by high-concentration fluid in opposite direction and diffusion balances water in blood and urine.
Collecting tubules can become funnel-shaped chambers {renal pelvis}.
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Date Modified: 2022.0225