Urinary System and Excretion

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Chapter 10

• Urinary System and Excretion

• What is going on?
• What is meant by compatibility and rejection?

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Outline

• Excretory substances / Organs of excretion
• Urinary System
• Organs of the Urinary System
• Functions of the Urinary System
• Kidney Structure
• Anatomy of a Nephron
• Urine Formation
• Regulatory Functions of the Kidneys
• Water-Salt Balance
• Acid-Base Balance of Body Fluids
• Disorders with Kidney Function
• Homeostasis

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Excretory Substances

• 1. Nitrogenous end products?
• ammonia (deamination, highly toxic)
• urea (liver)
• uric acid (gout)
• creatinine (muscles)
• 2. Other excretory substances
• bile pigments (RBCs)
• carbon dioxide

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• ions (salts K, Na, Ca, Mg)
• water (blood pressure).

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Organs of Excretion

• is the elimination on metabolic wastes from the
  body.
• Kidneys (primary organ of excretion) excretes
  urine . . . .
• Skin (sweat glands)
• Liver (bile pigments, urochrome)
• Lungs (carbon dioxide, water)
• Large intestines (iron and calcium salts in
  feces)
• Transp. 88

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Urinary System - Organs

• Kidneys are primary organs of the urinary system
  (and of excretion).
• The concave side of a kidney has depression
  called the hilum where the renal artery enters
  and the renal vein and ureters exit the kidney.
• Urinary bladder gradually expands as urine enters
  (holds about 600 ml, 3/5 quart).
• Urethra extends from the urinary bladder to an
  exterior opening (20 cm vs. 4 cm).

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Functions of the Urinary System

• Function of the urinary system is to produce
  urine and conduct it outside the body.
• Excretion is the removal of metabolic wastes from
  the body.
• Defecation refers to the elimination of feces
  (non-digestable matter) from the body.

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Functions of the Urinary System

• As urine is being produced, the kidneys
• Carry out excretion of metabolic wastes.
• Urea is the primary nitrogenous end product, but
  ammonium, creatinine, and uric acid are also
  excreted.
• Maintain water-salt balance of blood and thus
  blood volume and blood pressure.
• Maintain acid-base balance of the blood (by
  secreting H ions, reabsorbing Na and
  bicarbonate ions blood pH 7.4).
• Secretion of hormones (erythropoietin).

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Urination ( micturition)
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Urinary Tract Infections Require Attention. (4 cm
vs. 20 cm)
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HEALTH FOCUS

• Urinary Difficulties Due to an Enlarged Prostate

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Kidney Structure

• The kidney contains three major regions
• Renal cortex.
• Renal medulla.
• Renal pelvis.
• Microscopically, the kidney is composed of over
  one-million nephrons that produce urine (renal
  tubules or kidney tubules).
• Nephron is the functional unit of excretion
• Kidney Gross Anatomy. . . . . .

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Kidney Gross Anatomy
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Anatomy of a Nephron (Microscopic Structure)

• Each nephron has its own blood supply.
• From the renal artery, afferent (at or to)
  arteriole leads to the glomerulus, then to the
  efferent (exit or away) arteriole and then to
  the peritubular capillary network which surrounds
  the nephron.
• From there blood goes into a venule that joins
  the renal vein.

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Nephron Anatomy
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Parts of a Nephron

• Each nephron is composed of several parts.
• Glomerular capsule (Glomerulus and Bowmans
  capsule).
• Proximal convoluted tubule.
• Loop of the nephron (loop of Henle).
• Distal convoluted tubule.
• Collecting duct.

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Urine Formation

• Urine is 95 water and 5 solids (urea, salts,
  bicarbonate ions).
• Urine formation is divided into three steps.
• Glomerular filtration
• (Pressure filtration).
• Tubular reabsorption
• (Selective reabsorption).
• Tubular secretion
• (Tubular excretion).

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Health Focus

• Urine Analysis

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Regulatory Functions of the KidneysWater-Salt
Balance

• Remember the kidneys maintain the water-salt
  balance of the blood and, thus, maintain blood
  volume and pressure. They are also involved in
  maintaining the acid-base balance of the blood so
  as to maintain the blood at a pH of 7.4
• Reabsorption of Water.
• Excretion of hypertonic urine is dependent upon
  reabsorption of water from the loop of the
  nephron and the collecting duct.
• This is through water channels (aquaporins)
  within a plasma membrane protein.
• An osmotic gradient exists within the tissues of
  the renal medulla.

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• The hormone involved in this regulation of water
  and the processes associated with it are
• Antidiuretic hormone (ADH) - released by the
  posterior pituitary lobe, causes more water to be
  reabsorbed into the blood and less urine to form.
• Diuresis increases urine (but more dilute), so
  less water reabsorbed by the blood from the
  kidney.
• Diuretic is a chemical that increases the flow
  of urine, such as alcohol and caffeine.

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Reabsorption of Water
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Maintaining Water-Salt Balance

• Reabsorption of Salt.
• Kidneys regulate bloods salt balance by
  controlling excretion and reabsorption of various
  salt ions (sodium, potassium, bicarbonate,
  magnesium).
• Usually more than 99 of sodium filtered at the
  glomerulus is returned to the blood.
• Most is reabsorbed at the proximal convoluted
  tube, while a sizeable amount is reabsorbed from
  the convoluted tubule and collecting duct.

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Hormones involved in reabsorption of salt are

• Aldosterone regulates sodium reabsorption.
• Renin is an enzyme that converts angiotensinogen.
• Atrial natriuretic hormone (ANH) secreted by
  the atria of the heart when its cells are
  stretched due to too much blood volume which
  promotes the excretion of sodium (natriuresis) in
  the kidneys, resulting in less water being
  reabsorbed back into the blood so as to decrease
  blood volume.

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Acid-Base Balance of Body Fluids

• Kidneys reabsorb bicarbonate ions and excrete
  hydrogen ions as needed to maintain normal blood
  pH.
• In doing this, they work with the lungs to buffer
  the bloods pH.
• Alkalosis is when blood pH rises above 7.4
• Acidosis is when blood pH drops below 7.4
• Either are abnormal and may require medical
  attention.

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Disorders with Kidney Function

• Urinary Infections
• Nephritis (Pyelonephritis).
• Cystitis.
• Urethritis.
• Uremia is when urea / other wastes accumulate in
  the blood due to due to excessive kidney
  disfunction.
• Urinalysis?
• Many types of illness cause progressive renal
  disease and ultimate renal failure.
• Diabetes.
• Hypertension.
• Inherited conditions.

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Disorders with Kidney Function

• Treatment of renal failure can include
  hemodialysis
• Artificial kidney machine ( 6 hrs/ 2X / week)
• or
• Continuous Ambulatory Peritoneal Dialysis (CAPD)
• Collect each 4 8 hours.
• kidney replacement?
• One year survival rate is 97, 90
• Tissue match and rejection.
• Immunosuppressive drugs?

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Homeostasis

• Dont forget to read Section 10.6 Homeostasis
  
• Also examine Figure 10.11, Human Systems Work
  Together.

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Bioethical Focus

• The Right to Die
• ? !

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Outline

• Excretory substances / Organs of excretion
• Urinary System
• Organs of the Urinary System
• Functions of the Urinary System
• Kidney Structure
• Anatomy of a Nephron
• Urine Formation
• Regulatory Functions of the Kidneys
• Water-Salt Balance
• Acid-Base Balance of Body Fluids
• Disorders with Kidney Function
• Homeostasis

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