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21.2: Kidneys

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    Kidneys

    There are two kidneys, one right and one left. They are retroperitoneal (posterior to peritoneum) and encased in protective layers of adipose tissue along the posterior body wall of the abdomen.

    Location of the kidneys

    Above: Position of the kidneys. The kidneys are surrounded by perinephric fat and surrounded by an anterior renal fascia and posterior renal fascia.

    The kidneys filter dissolved materials from the blood, including metabolic wastes, regulate electrolytes, regulate fluid volume (thereby influencing blood pressure), concentrates and stores waste products in the form of urine, and reabsorbs metabolically important substances back into the circulatory system. The following are specific functions of the kidneys:

    1. Remove waste: The kidneys filter waste products and excess fluid out of the blood and remove them from the body in the form of urine. (nitrogenous wastes such as urea and ammonium)
    2. Maintain the right balance of chemicals in the body: The kidneys keep the right balance of chemicals, such as sodium, potassium, calcium, magnesium, and other substances your body needs to function properly. They filter excess amounts of these chemicals from the blood and get rid of them in the urine.
    3. Synthesize several regulatory chemicals: The kidneys produce and secrete three important chemicals: renin, erythropoietin, and the active form of vitamin D (Calcitriol).

    Anatomy of the kidney. Hilum, Renal artery, Renal vein, Renal pelvis, Ureter, Major calyx, Minor calyx, Renal cortex, Renal medulla, Renal papilla, Renal pyramids, Renal columns, Fibrous capsule

    Above: Anatomy of a kidney. Left kidney shown with frontal section.

    Kidney Structure

    Location

    Function

    columns (renal)

    tissue-filled areas between the pyramids

    anchor the medulla to the cortex and provide a place for blood vessels to travel

    cortex (renal)

    a region of the kidney where nephrons are mostly located

    region of the kidney where blood is filtered and urine is formed; contain nephrons

    fibrous capsule

    fibrous layer on the lining the outside of the kidney

    Protects and supports the kidney

    glomerulus

    microscopic bundle of capillaries in the cortex of the kidney; part of a nephron

    high-pressure leaky capillaries create raw filtrate (fluid that will become urine); fluid and solutes are pushed out of these capillaries from the blood and into the Bowman's capsule / glomerular capsule

    hilum

    a central, medial fissure in the kidney

    location where ureters, blood vessels, and nerves enter the kidney

    major calyx

    large divisions of the renal pelvis; where minor calyces fuse together

    collects urine from the minor calyces and transfer it to the renal pelvis

    minor calyx

    smaller divisions of the major calyces; between major calyces and renal papillae

    collects urine from the renal papillae and transfers it to the major calyces

    medulla (renal)

    a region of the kidney between the cortex and the minor calyces

    contain nephron loops of juxtamedullary nephrons; balancing water and salt concentrations in the blood

    nephron

    microscopic structures mostly found in the renal cortex, but some components found in the medulla; composed of kidney tubules

    filters the blood to remove wastes and fluid; produces urine

    papilla (renal)

    between the pyramids and the minor calyces

    collects urine from the collecting ducts and transfers to the minor calyces

    pyramids (renal)

    triangular-shaped regions of the medulla

    transfer of urine from nephrons to the calyces

    renal pelvis

    between the major calyces and the ureter

    collects urine from the major calyces and transfers it to the ureter

    Cadaver images of a kidney. Capsule, Renal papilla, Renal sinus, Renal a., Column, Pyramid, Renal v., Cortex, Ureter, Medulla, Minor calyces, Major calyx, Renal pelvis, Capsule

    Above: Cadaver kidney (left) right kidney, unsectioned and (right) kidney, frontal sectioned.

    Microscopic image of kidney section. Medulla, cortex, pyramid, renal column.

    Above: Microscopic image of kidney tissue, magnified by 10x.

    In order for the kidney to work properly, blood vessels must carry blood to the glomerulus for filtration, then to the peritubular capillaries to drop off oxygen (and pick up carbon dioxide and reabsorb water and electrolytes), and then to the renal vein to head back to the heart. Below are the vessels that make this special circulation happen. They are listed in the order that blood flows through them.

    1. descending abdominal aorta
    2. renal artery
    3. segmental artery
    4. interlobar artery
    5. arcuate artery
    6. cortical radiate artery
    7. afferent arteriole
    8. glomerulus
    9. efferent arteriole
    10. peritubular capillary
    11. cortical radiate vein
    12. arcuate vein
    13. interlobar vein
    14. segmental vein
    15. renal vein
    16. inferior vena cava

    Blood vessels of the kidney. Capsule, Renal a. & v., Renal pelvis, Major calyx, Minor calyces, Renal papilla, pyramid, Ureter, Cortical radiate, Arcuate, Interlobar, Renal sinus, Typical location of nephrons, Column, Medulla

    Above: Blood vessel network of the kidney.

    This page titled 21.2: Kidneys is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline.

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