excretory system tony serino, ph.d. clinical anatomy misericordia univ
TRANSCRIPT
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Excretory System
Tony Serino, Ph.D.
Clinical AnatomyMisericordia Univ.
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Excretory System
• Remove wastes from internal environment• Wastes: water, heat, salts, urea, etc.• Excretory organs include: Lungs, Skin, Liver, GI
tract, and Kidneys• Urinary system account for bulk of excretion
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Fluid Input & Output
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Urinary System
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Ureter Histolgy
Mucosa
Muscularis
Adventitia
-about 25 cm long, retroperitoneal, moves urine by peristalsis; volume of urine moved is called a jet (1-5 jets/min)-ureters enter the bladder wall obliquely, allowing them to remain closed except during peristalsis
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Urinary Bladder(Remanent of Allantois)
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Urinary Bladder Histology
Mucosa
Submucosa
Muscularis
(Serosa)
(Detrusor Muscle)
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Urinary Bladder Filling
• Highly distensible• 10-600ml normally• Capable of 2-3X that
volume• Under normal
conditions, the pressure does not significantly increase until at least 300 ml volume is reached
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Urethra
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Urethra Histology
-epithelium changes from transitional to stratified squamous along its length-large numbers of mucous glands present
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Bladder (Storage) Reflex
Voluntary control
• As urine accumulates, the bladder wall thins and rugae disappear
• Innervation (sympathetic) to the sphincter muscles (particularly the internal sphincter) keeps the bladder closed and depresses bladder contraction
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Micturition Reflex (Voiding)• Urine volume increases, and
the smooth muscle increases pressure in bladder
• Stretch receptors in detrusor muscle, increase parasympathetic activity in the splanchnic nerve cause increase bladder contraction and internal sphincter relaxation
• Voluntary relaxation of external sphincter by a decrease in firing of the pudendal nerve
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Kidney Location (x.s.)(Retroperitoneal)
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Cortex vs. Medulla
Capsule
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Anatomy of Kidney
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Major and Minor Calyx
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Arterial Supply
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Venous Drainage
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Renal Circulation
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Nephron (two types)
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Urine Formation Overveiw
a. Pressure Filtration
b. Reabsorption
c. Secretion
d. Reabsorption of water
d
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GlomerulusBowman’s Capsule
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Podocytes
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Filtration in GlomerulusCapillary Lumen Endothelium
Fenestration
Basement Mem.Pedicels
Slit pores
Glomerular Filtrate
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Glomerular Filtration• A pressure filtration produced by the BP, fenestrated
capillaries of glomerulus, and the podocytes creates the glomerular filtrate
• Slit size allows filtration of any substance smaller than a protein
• Blood proteins create an osmotic gradient to prevent complete loss of water in blood,
• Pressure in Bowman’s capsule also works against filtration
• Volume of filtrate produced per minute is the Glomerular Filtration Rate (GFR)
• Average GFR = 120-125 ml/min
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Tubular Reabsorption• 75-85% of glomerular filtrate reabsorbed in PCT
• Some of the reabsorption is by passive diffusion– Example: Na+
• Much of the reabsorption is active, most linked to the transport of Na+; known as co-transport
• The amount of transporter proteins is limited; so most actively transported substances have a maximum tubular transport rate (Tm)
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Loop of Henle and CD
• Provides mechanism where water can be conserved; capable of producing a low volume, concentrated urine
• Loop of Henle acts as a counter-current multiplier to maintain a high salt concentration in medulla
• CD has variable water permeability and must pass through the medulla
• Allows for the passive absorption of water
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Counter-current Multiplier• Descending is permeable to
water but not salt; loss of water concentrates urine in tube
• Ascending is permeable to NaCl but not water; Salt now higher in tube than interstitium; first passively diffuses out then near top is actively transported out
• Results in a self-perpetuating mechanism; maintaining a high salt concentration in center of kidney
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Vasa Recta• Supply long loops of
Henle• Provide mechanism to
prevent accumulation of water in interstitial space
• Passive diffusion allows the blood to equilibrate with osmotic gradient in extracellular space
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Counter-current Exchange
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Tubular Secretion
• PCT and DCT both actively involved in secretion (active transport of substances from the blood to the urine)
• Both ducts play important roles in controlling amount of H+/HCO3
- lost in urine and therefore blood pH
• DCT actively controls Na+ reabsorption upon stimulation by aldosterone (controls final 2% of Na+ in urine)
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Summary
Re-absorption
Loses water
Loses NaCl Selective Secretion & Re-absorption
Water Re-absorptionwith ADH present