CHAPTER 19 and CHAPTER 21 The ribs help protect the kidneys, as does a heavy cushion of fat (adipose tissue) encasing each organ. they extend from the level of the T12 vertebra to the L3 vertebra Nephronsthe filtration units of the kidney peritubular capillaries These capillaries pick up water and solutes reabsorbed by the renal tubules. Leading away from the glomerulus are a series of tube-like structures called the renal tubule. What is the kidneys filtering? The blood--- the urine is the bi-product The amount of(urine) fluid filtered by both kidneys (called the glomerular filtration rate [GFR]) equals about 180 L each day, or 60 times the body's total blood volume. The body reabsorbs about 99% of this filtrate, leaving 1 to 2 L to be excreted as urine. High blood pressure increases pressure within the glomerulus, causing glomerular capillaries to burst. Filtration in the glomerulus occurs because of the pressure gradient. The presence of protein in the urine (called proteinuria), is caused by damaged glomerular capillaries decline in blood pressure leads to decreased blood flow to release renin the kidneys. Juxtaglomerular cells in the afferent arterioles respond by releasing the enzyme renin. merular capillaries. Angiotensin II stimulates the adrenal glands to secrete aldosterone. Decreases urinary output The adrenal cortex secretes aldosterone when blood levels of Na+ decline or concentration of K+ increases. Proximal convoluted tubules- does