Excretory System Tony Serino, Ph.D. Clinical Anatomy Renal: Topic Objectives Be able to describe and identify bladder and urethra anatomy and function, including differences between male and female.
Be able to describe micturition reflex. Be able to describe and identify kidney anatomy, histology and function. Be able to describe and identify circulation pattern to, from and within the kidney. Be able to identify parts of the nephron and their functions. Be able to describe urine formation and predict changes to output with
changes in BP, ion pumps, and hydration status. Be able to describe kidney contribution to acid/base balance and be able to predict kidney response to blood pH changes Be able to describe hormonal BP control and predict response to low and high BP 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
Fluid Input & Output Urinary System Ureter Histolgy -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 Adventitia Mucosa
Muscularis Urinary Bladder (Remanent of Allantois) Urinary Bladder Histology
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 Urethra
Urethra Histology -epithelium changes from transitional to stratified squamous along its length -large numbers of mucous glands present 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 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
Kidney Location (x.s.) (Retroperitoneal) Cortex vs. Medulla Capsule Anatomy of
Kidney Major and Minor Calyx Arterial Supply Venous Drainage
Renal Circulation BP in Renal Vessels Nephron (two types)
Epithelium of Nephron Urine Formation Overveiw a. b. c.
d. d Pressure Filtration Reabsorption Secretion
Reabsorption of water Glomerulus Bowmans Capsule Podocytes
Filtration in Glomerulus Capillary Lumen Endothelium Basement Mem. Pedicels
Slit pores Glomerular Filtrate Fenestration 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 Bowmans capsule also works against
filtration Volume of filtrate produced per minute is the Glomerular Filtration Rate (GFR) Average GFR = 120-125 ml/min Forces controlling Glomerular Filtration
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 (T m) Reabsorption
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 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 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 Counter-current Exchange 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) Summary Re-absorption Water Re-absorption
with ADH present Loses water Loses NaCl Selective Secretion & Re-absorption
Dehydration & Water Intoxication Thirst ADH release Reabsorption of Water in CD
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