Urinary System-Structures and Functions What\'s in Filtrate? What\'s in Urine? R

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Urinary System-Structures and Functions What's in Filtrate? What's in Urine? Regulation of GFR RAAS, ANP, ACE, ADH (what does the hormone do?) Acid Base Balance Sensible and Insensible Water loss Urinary System-Structures and Functions What's in Filtrate? What's in Urine? Regulation of GFR RAAS, ANP, ACE, ADH (what does the hormone do?) Acid Base Balance Sensible and Insensible Water loss Urinary System-Structures and Functions What's in Filtrate? What's in Urine? Regulation of GFR RAAS, ANP, ACE, ADH (what does the hormone do?) Acid Base Balance Sensible and Insensible Water loss

Explanation / Answer

The human excretory system consists of 2 kidneys, 2 ureters, a urinary bladder and a urethra.

The kidneys are a pair of bean-shaped organs found along the posterior wall of the abdominal cavity. The left kidney is located slightly higher than the right kidney because the right side of the liver is much larger than the left side.

The ureters are a pair of tubes that carry urine from the kidneys to the urinary bladder. The ureters are about 10 to 12 inches long and run on the left and right sides of the body parallel to the vertebral column.

The urinary bladder is a sac-like hollow organ used for the storage of urine. The urinary bladder is located along the body’s midline at the inferior end of the pelvis.

The urethra is the tube through which urine passes from the bladder to the exterior of the body.

In the nephron, approximately 20 percent of the blood gets filtered under pressure through the walls of the glomerular capillaries and Bowman's capsule. The filtrate is composed of water, ions (sodium, potassium, chloride), glucose and small proteins (less than 30,000 daltons -- a dalton is a unit of molecular weight). This is done by ultrafiltration.

Urine is yellowish in color as it produces urochrome. Urine has dissolved salts, urea, waste etc.

Regulation of GFR-

In particular, low GFR is one of the variables that will activate the renin–angiotensin feedback system, a complex process that will increase blood volume, blood pressure, and GFR. This system is also activated by low blood pressure itself, and sympathetic nervous stimulation, in addition to low GFR.

The Bowman’s capsule space exerts a hydrostatic pressure of its own that pushes against the glomerulus. Increased Bowman’s capsule hydrostatic pressure will decrease GFR, while decreased Bowman’s capsule hydrostatic pressure will increase GFR.

Osmotic pressure is the force exerted by proteins and works against filtration because the proteins draw water in. The increased osmotic pressure in the glomerulus is due to increased serum albumin in the bloodstream and decreases GFR and vice versa.

RAAS-

The RAS increases blood volume and blood pressure in response to low blood pressure, blood loss, or dehydration. Renin is released into the blood where it catalyzes angiotensinogen from the liver into angiotensin I. Angiotensin I is further catalyzed by another enzyme into Angiotensin II.

Angiotensin II stimulates several processes, including stimulating the adrenal cortex to produce the hormone aldosterone. Aldosterone then changes the function of the kidneys to increase the reabsorption of water and sodium ions into the blood, increasing blood volume and raising blood pressure. Negative feedback from increased blood pressure finally turns off the RAS to maintain healthy blood pressure levels.

ADH- reabsorbs excess water from the urine.

ANP- It is produced by the heart. It dilates blood vessels when the volume of blood increases.

The kidneys maintain homeostasis through the excretion of waste products.

Acidosis causes more bicarbonate to be reabsorbed from the tubular fluid, while the collecting ducts secrete more hydrogen to generate more bicarbonate, and the more NH3 buffer is formed.

Alkalosis causes the kidney to excrete more bicarbonate as there is a reduced secretion of hydrogen ions and more ammonium is excreted.

Urine, of course is a "sensible" loss - it can be seen, felt, and measured! Respiratory loss is an insensible loss. This is water that is used to humidify inspired air and is then breathed out as water vapor.

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