CHAPTER 25 Control of the Internal Environment

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CHAPTER 25Control of the Internal Environment
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internal homeostatic mechanisms

• Thermoregulation maintains the body temperature
  within a tolerable range
• Osmoregulation controls the gain and loss of
  water and dissolved solutes
• Excretion is the disposal of metabolic wastes

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Excretion

• Function Maintain homeostasis
• Nitrogenous wastes
• 1. ammonia (most toxic)
• 2. urea
• 3.uric acid (least toxic)

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Human Excretion

• Must remove cellular metabolic wastes because at
  high concentration they are toxic.
• Organs of excretion
• 1. Lungs
• a. Carbon dioxide and water from aerobic
  cellular respiration diffuse from blood into
  lungs. Excreted when you exhale
• 2. Skin
• a. sweat glands- water, salts, some urea
  diffuse from the blood into sweat glands are
  subsequently excreted as perspiration
• b. major function of skin is to excrete excess
  heat (help maintain body temperature)

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Human Excretion

• Organs of excretion
• 3. Liver
• a. breakdown of red blood cells excreted in
  bile
• b. detoxification of blood (removal of harmful
  substances)
• c. urea formation -gt nitrogenous wastes are
  made of ammonia carbon dioxide
• Urea is formed by process called deamination

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Human Excretion

• Organs of excretion
• 4. Kidney main excretory organ main organ of
  urinary system
• a. located just above waist behind stomach
• b. main function filter blood to expel
  wastes , regulate salt water balance maintain
  blood pH
• c. urine formation
• Thus kidneys play a major role in maintaining
  homeostasis

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Urinary sytem

• Urine pathway
• Kidney-gtUreter-gtUrinary bladder-gtUrethra
• Ureters Tubes that carry urine from kidneys to
  urinary bladder
• Urinary bladder smooth muscle bag that stores
  urine
• Urethra urine passes out of the body through
  this tube

Kidney
Ureter
Bladder
Urethra
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Closer look at Kidney

• 3 parts
• 1. cortex-outer portion
• 2. medulla-middle layer
• 3. renal pelvis- inner area

Renalmedulla
Renal pelvis
Ureter
Renalcortex
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Nephrons

• Microscopic functional unit of kidney (approx.
  1million per kidney)
• Each nephron consists of a folded tubule and
  associated blood vessels
• extract a filtrate from the blood
• refine the filtrate into a much smaller amount
  of urine

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Overview The key functions of the excretory
system are filtration, reabsorption, secretion,
and excretion

• Filtration
• Blood pressure forces water and many solutes from
  the blood (glomerulus) into the nephron (Bowman's
  capsule) filtrate
• Reabsorption
• The nephron tubule reclaims valuable solutes

Bowmans capsule
Proximal tubule
Glomerulus
Distaltubule
Loop of Henlewith capillary network
Collectingduct
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Overview The key functions of the excretory
system are filtration, reabsorption, secretion,
and excretion

• Secretion
• The nephron removes substances and adds them to
  the filtrate
• The product of all of the above processes is
  urine, which is excreted

Nephron tubule
FILTRATION
REABSORPTION
EXCRETION
SECRETION
H2O, other small molecules
Urine
Capillary
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From blood to filtrate to urine A closer look

• The proximal tubule reabsorbs
• nutrients
• salts
• water
• Antidiuretic hormone and other hormones regulate
  the amount of salt and water the kidneys excrete
• How do caffeine and ethyl alcohol effect urine
  output?
• Diuretic chemicals that inhibit antidiuretic
  hormone

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From blood to filtrate to urine A closer look

• Controlled secretion of H and reabsorption of
  bicarbonate ions help regulate blood pH
• Secretion also includes the active transport of
  drugs and poisons
• Reabsorption of salts and urea promote the
  osmotic reabsorption of water

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Kidney malfunction

• Kidney disease
• various conditions in which kidneys are unable
  to function effectively in excreting nitrogenous
  wastes
• may lead to
• Dialysis( artificial kidney)
• Kidney transplant