Fig' 18'1

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Fig. 18.1
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Functions

• Excretion- main organs
• Blood volume control
• Ion concentration
• pH regulation
• RBC concentration/production
• Vitamin D synthesis

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Kidneys

• Bean-shaped, size of fist, posterior abdominal
  wall
• Renal capsule- connective tissue
• Surrounded by thick fat
• Hilum- medial side, where renal blood vessels,
  ureter, and nerves enter/exit
• Hilum opens into the renal sinus- contains blood
  vessels, urine collecting system, fat

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Kidney

• Divided into outer cortex and inner medulla,
  surround renal sinus
• Base of renal pyramids located at boundary
  between medulla and cortex
• Tips of pyramids project toward the center
• Calyx- funnel shaped, surrounds tips of pyramids
• Calyces form a large funnel called the renal
  pelvis, which forms the ureter, which connects to
  urinary bladded

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Nephron

• Functional unit of the kidney
• 4 basic parts- renal corpuscle, proximal tubule,
  loop of Henle, distal tubule
• Many distal tubules empty into a collecting duct
• Collecting ducts empty into papillary ducts,
  which empty into calyces

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Fig. 18.4
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Renal corpuscle

• Bowmans capsule is lined cells called podocytes,
  outer layer is simple squamous
• Glomerular capillaries have holes in them,
  podocytes have cell processes with gaps between
  them
• Podocytes, glomerular capillaries, basement
  membrane form a filtration membrane
• Filtrate is filtered through this membrane

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Fig. 18.5b
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Tissues

• Simple cuboidal- most of nephron, collecting duct
• Simple squamous- loop of Henle thin segments
• Numerous microvilli, mitochondria

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Arteries and Veins

• Renal artery afferent arterioles- glomerular
  capillary- efferent arteriole- peritubular
  capillary (vasa recta)- venules- Renal vein

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Fig. 18.6
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Tubes and Bladder

• Ureters- kidney to bladder
• Urinary bladder- hollow muscular container that
  stores urine, reflex controls release of urine,
  smooth muscle
• Urethra- bladder to outside
• Bladder and urethra lined with transitional
  epithelium- designed to stretch
• Urethra is rifled in males

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Sphincter says what

• Round muscle around a tube- controls opening and
  closing
• Internal sphincter- males only, prevents semen
  from entering bladder, mixing of fluids
• External sphincter- pelvic floor, controls flow
  to outside
• Urethra longer in males than females

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Urine Production

• Urine- water, organic wastes (urea, uric acid,
  creatinine), Cl, K, Na, HCO3, H
• 3 processes to formation
• Filtration- movement of materials across
  filtration membrane (filtrate)
• Reabsorption- transport of substances from
  filtrate into interstitial fluid
• Secretion- transport of substances across nephron
  into filtrate

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Filtration

• 21 of the blood pumped per minute enters kidney
• 180 L of filtrate per day
• 1 or less becomes urine
• Filtration membrane allows only water and small
  solutes through, cells and proteins cannot pass

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Filtration

• Formation of filtrate depends upon a pressure
  gradient
• Glomerular capillary pressure
• Capsular pressure
• Colloid osmotic pressure
• Filtration pressure

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Fig. 18.9
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Reabsorption

• 99 of the filtrate will be reabsorbed from renal
  tubule into peritubular capillaries
• Excess ions and metabolic wastes become highly
  concentrated in urine
• Proximal tubule- simple cuboidal with lots of
  microvilli, active transport of amino acids,
  glucose, ions, water follows the ions through
  osmosis
• 65 of filtrate is reabsorbed in proximal tube

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Reabsorption

• Descending limb- concentrates filtrate
• Interstitial fluid of medulla has a high Na,
  Cl_, and urea concentration
• Wall of descending limb is permeable to water
• Water moves out by osmosis, some substances move
  in by diffusion
• Reabsorbed filtrate enters the vasa recta

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Reabsorption

• Ascending limb- dilutes by removing solutes, not
  by adding solution
• Not permeable to water
• Active/ Cotransport of Na, Cl-, and K
• These solutes keep the interstitial fluid high in
  solute concentration so water leaves the
  descending limb
• As filtrate enters cortex, it is more dilute and
  only 205 of its original volume

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Fig. 18.12
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Fig. 18.13
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Reabsorption

• Distal tubule and collecting duct- remove water
  and additional solutes
• Similar to descending limb
• Controlled by hormones- regulate urine output
• Only 1 of original volume is sent to urinary
  bladder
• Much more concentrated than original filtrate

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Fig. 18.14
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Secretion

• Toxic metabolic wastes, drugs/molecules not
  produced by body
• From peritubular capillary to filtrate
• Active or passive
• H, K, creatinine, histamine, penicillin
• Occurs in proximal or distal tubule

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Regulation of volume, conc.

• Kidneys function to maintain water balance
• Increase water reabsorption when body fluid
  concentration increases
• Decrease reabsorption when body fluid
  concentration decreases
• Also maintain blood volume and blood pressure

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Hormonal Mechanisms

• Antidiuretic hormone (ADH)- produced by posterior
  pituitary, travels to kidneys
• Regulates permeability of distal tubules and
  collecting ducts
• Increase in ADH increase in permeability
  decrease in urine production
• Vice versa

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Renin pathway

• Renin- enzyme produced by juxtaglomerular
  apparatus
• Renin converts angiotensinogen (protein produced
  by liver) into angiotensin I
• Angiotensin I is converted to Angiotensin II by
  angiotensin-converting enzyme (ACE)
• Angiotensin II acts on adrenal cortex to produce
  Aldosterone

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Aldosterone

• Increases rate of active transport of Na in
  distal tubules and collecting ducts
• Typically- high Na in filtrate causes water to
  remain in filtrate increase in urine
• Decrease in blood pressure, or Na is low in
  blood renin release
• Aldosterone promotes reabsorption of Na, water
  follows decrease in urine production increase
  in blood pressure

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Atrial Natriuretic hormone

• ANH secreted from cardiac cells in right atrium
  when blood pressure increases
• Acts on kidney to decrease Na reabsorption
• Increase in urine production decrease in blood
  volume decrease in blood pressure

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Sympathetic Innervation

• Sympathetic neurons innervate the blood vessels
  of the kidney
• Stimulation constricts the arteries decrease in
  blood flow and rate of filtrate formation
• Decreases in blood pressure results in
  sympathetic stimulation
• Increased blood pressure results in decreased
  stimulation

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Micturition

• Reflex activated by stretching of urinary bladder
• Stretch receptors are activated as urine fills
  bladder
• AP sent to spinal cord, integrated, and sent
  along parasympathetic nerves to urinary bladder
• Urinary bladder contracts

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Micturition

• External sphincter normally contracted
• Because of reflex, AP conducted on motor neurons
  decrease and sphincter relaxes
• Micturition reflex is automatic, but can be
  inhibited or stimulated by brain
• Prevent- brain sends AP to decrease intensity of
  AP sent to bladder, stimulate the external
  sphincter to contract
• Develops at 2-3 years of age

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Fig. 18.17
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Acid-Base Balance

• Normal pH 7.35 to 7.45, deviations are deadly
• 3 ways to control
• Buffers
• Respiratory system
• Kidneys

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Buffers

• Chemicals that resist pH change
• 3 major buffers- proteins, phosphate, and
  bicarbonate
• Proteins and phosphate combine with large numbers
  of H
• Can bind with more H if pH drops (increase in
  H), or release if pH rises (decrease in H)
• Bicarbonate system can be regulated by
  circulatory and urinary systems

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Respiratory System

• Influence of carbon dioxide levels on pH
• CO2 H2O ? H2CO3 ? H HCO3-

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Kidneys

• Nephrons can directly secrete H and reabsorb
  bicarbonate
• Rate of secretion and reabsorption can be
  controlled
• Kidneys are slower than respiratory

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Fig. 18.21
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Acidosis

• When blood pH drops below 7.35
• CNS malfunctions
• 2 types
• Respiratory acidosis- cannot eliminate carbon
  dioxide
• Metabolic acidosis- accumulation of acidic
  substances- lactic acid, ketone bodies

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Alkalosis

• Blood pH increases above 7.45
• Hyperexcitability of nervous system
• Spasms, tetany of respiratory muscles
• 2 types
• Respiratory alkalosis- hyperventilation
• Metabolic alkalosis- rapid elimination of H
  (severe vomiting, excess aldosterone)