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By Matthew M. Green and Carlos Krumpach


By Matthew M. Green and Carlos Krumpach – PowerPoint PPT presentation

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Title: By Matthew M. Green and Carlos Krumpach

The Urinary System
  • By Matthew M. Green and Carlos Krumpach

  • The purpose of the urinary system is to
  • remove certain salts and nitrogenous wastes from
    the body,
  • maintain normal concentrations of water and
    electrolytes within body fluids,
  • regulate the pH and volume of body fluids,
  • and help control red blood cell production and
    blood volume.
  • The Urinary System consists of
  • a pair of kidneys,
  • a pair of tubular ureters,
  • a saclike urinary bladder,
  • and a tubular urethra

Introduction to the Kidneys
  • A kidney is a reddish-brown, bean-shaped organ,
    with a smooth surface. (Adult kidneys are 12
    centimeters long, 6 centimeters wide, and 3
    centimeters thick.) They are enclosed in a
    strong, fibrous capsule.

Location of the Kidneys
  • The kidneys lie on either side of the vertebral
    column in a depression high on the posterior wall
    of the abdominal cavity. The upper and lower
    borders of the kidneys are usually at the levels
    of the twelfth thoracic and third lumbar
    vertebrae. (The left kidney is 1.5-2.0
    centimeters higher than the right kidney.) The
    kidneys are positioned retroperitoneally, or
    behind the parietal peritoneum and against the
    deep muscles of the back. (The kidneys are held
    in place by connective tissue and adipose tissue.)

Kidney Structure
  • The kidneys later surface is convex, while its
    medial side is concave. The resulting medial
    depression leads to the renal sinus, a hallow
    chamber. The entrance to the renal sinus is
    called the hilium, this where blood vessels,
    nerves, lymphatic vessels and the ureter enter
    the kidney. The superior end of the ureter
    expands and forms a funnel-shaped sac called the
    renal pelvis. The renal pelvis subdivides into
    two or three major calyces, which subdivide into
    several minor calyces. Renal papillae project
    into the renal sinus from its wall, and contain
    openings that lead into a minor calyx. The inside
    of the kidney is the renal medulla, which is
    composed of renal pyramids and appears striated.
    The renal cortex forms a shell around the medulla
    and dips in between renal pyramids, forming
    renal columns. Within in the renal cortex are
    nephrons, or the kidneys functional units.

Kidney Functions
  • The kidneys help maintain homeostasis by
    regulating the composition, volume, and pH of
    extracellular fluid. They do this by forming, and
    excreting urine, a combination of metabolic
    wastes, (from the blood), water, and
    electrolytes. The kidneys also secrete the
    hormone erythropoietin, which helps control red
    blood cell production, they help activate vitamin
    D, and they help maintain blood volume and
    pressure by releasing the enzyme renin.

Renal Blood Vessels
  • Renal arteries supply blood to the kidneys. When
    a person is at rest these arteries usually carry
    15-30 of the total cardiac out put into the
    kidneys. Renal arteries give off several branches
    called interlobar arteries, which pass between
    renal pyramids. Arcuate arteries at the junction
    between the medulla and cortex give rise to
    interlobular arteries. Afferent arterioles, the
    final branches of interlobular arteries, lead to
    nephrons. Venous blood returns in vessels that
    correspond to arterial pathways, which then lead
    to the renal vein. The renal vein leads the blood
    back to the inferior vena cava.

Nephrons and their Structure
  • Nephrons consist of a renal corpuscle and a renal
    tubule. Fluid flows through the tubules on its
    way out of the body. Renal corpuscles are made of
    tangled clusters of blood capillaries called
    glomerulus. Glomerular capillaries filter fluid,
    which is the first step in urine formation. The
    glomerular capsule, a thin-walled, saclike
    structure surrounds the glomerulus. The
    glomerular capsule, an expansion at the proximal
    end of a renal tubule, receives the fluid the
    glomerulus filters. The renal tubule leads away
    from the capsule and becomes tightly coiled, this
    coiled portion is the proximal convoluted tubule.
    This tubule dips towards the renal pelvis, and
    becomes the descending limb of the nephron loop.
    The tubule then curves back towards the renal
    corpuscle and forms the ascending limb of the
    nephron loop. This tubule returns to the region
    of the renal corpuscle, where it is tightly
    coiled and is called the distal convoluted
    tubule. These tubules merge in the renal cortex
    to form collecting ducts, which passes through
    the renal medulla and is joined by other tubules.
    The resulting tube empties into a minor calyx
    through an opening in a renal papilla.

Blood Supply of a Nephron
  • The capillaries that form a glomerulus all come
    from arterioles. Blood, after passing through the
    glomerular capillaries, enters an efferent
    arteriole, (that is smaller than the afferent
    vessel). The arteriole resists blood flow, which
    raises blood pressure in the glomular capillary.
    The efferent arteriole branches off into a freely
    interconnecting network of capillaries called the
    peritubular capillary system, that surrounds the
    renal tubule. After flowing through the
    peritubular capillary system, the blood rejoins
    from other branches and enters the venous system
    of the kidney.

Juxtaglomerular Apparatus
  • The structure of densely packed epithelial cells
    at the point of contact between the distal
    convoluted tubule and efferent and afferent
    arterioles makes up the macula densa. Within the
    walls of arterioles are juxtaglomerular cells,
    that with the cells of the macula densa form the
    juxtaglomerular apparatus. This apparatus
    controls the secretion of renin.

Urine Formation
  • Urine formation begins with glomerular
    filtration, which is the process of the
    glomerular capillaries filtrating plasma. Tubular
    reabsorption, which moves substances from tubular
    fluid back into the blood within the peritubular
    capillary, and tubular secretion, which is the
    reverse process of tubular absorption, also aid
    in forming urine.

Glomerular Filtration
  • Urine formation begins with water and certain
    dissolved substances being filtered out. The
    resulting glomerular filtrate is sent into
    glomerular capsules.

Filtration Pressure and Filtration Rate
  • The hydrostatic pressure of blood and the osmotic
    pressure of plasma influence the pressure of
    glomerular capillaries, and capsules. The net
    filtration pressure is the net pressure for
    forcing substances out of the glomerulus. The net
    filtration pressure is responsible for the
    kidneys filtration rate.

Regulation of Filtration Rate
  • The glomerular filtration rate is an example of a
    negative feedback mechanism. The filtration rate
    can also be regulated by sympathetic nervous
    system reflexes. Juxtaglomerular cells also
    control the rate by releasing renin, which reacts
    with the plasma protein angiotensinogen to form
    angiotensin I. A second enzyme called angiotensin
    converting enzyme, converts angiotensin I to
    angiotensin II. Angiotensin II is a plasma
    protein that helps maintain sodium balance, water
    balance, and blood pressure in the body.

Tubular reabsorption and Secretion
  • Tubular reabsorption is the process in which
    filtered substances are returned to the blood
    stream. Sodium and water can be reabsorbed
    multiple times making them more concentrated.
    Tubular secretion is when substances move from
    the bloods plasma in the peritubular capillary to
    fluid in the renal tubule.

Regulation of Urine Concentration and Volume
  • Aldosterone and antidiuretic hormone may
    stimulate the additional reabsorption of sodium
    and water. These changes in sodium and water
    excretion in response to these hormones are the
    final adjustments the kidney makes before

Urea, Uric Acid Excretion, and Urine Composition
  • Urea is a by-product of amino acid catabolism,
    uric acid is a result of the metabolism of
    organic bases in nucleic acids. Both of these
    by-products are excreted in urine. Urine
    composition reflects the amount of water and
    solutes that the kidney must eliminate or retain.

Urine Elimination
  • From the kidneys, urine passes through the renal
    pelvis, and a ureter conveys it to the urinary
    bladder and reference plate. The urethra then
    excretes urine to the outside.

The Ureters, The Urinary bladder, Micturition and
The Urethra
  • The ureters are 25 centimeters long, they begin
    as the renal pelvis, and connect to the urinary
    bladder. The urinary bladder is a hollow,
    distensible, muscular organ that stores urine and
    forces it out into the urethra. The detrusor
    muscle is a muscle that prevents the bladder from
    emptying until a certain pressure is reached.
    Micturition is the process that conveys urine
    from the urinary bladder to the outside of the

Medical Conditions
  • Dysuria is a condition that causes painful
  • Nephrolithiasis, which is a kidney stone.
  • Cystis, which is an inflammation of the urinary

Work Cited
  • Butler, Jackie. Lewis, Ricki. Shier, David, ed.
    Holes Essentials of Human Anatomy and
    Physiology. New York McGraw- Hill.2006. 454-471.
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