Lecture 32 - Intro to Urinary System

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Urinary System

-Kidneys, Ureters, Urinary Bladder, Urethra
-Urine flows from each kidney, down its ureter to the bladder and to the outside via the urethra
-Kidneys filter the blood and return most of water and solutes to the bloodstream

Kidney Functions

-Regulation of blood ionic composition (Na+, K+, Ca2+, Cl-)
-Regulation of blood pH, osmolarity & glucose
-Regulation of blood volume (conserving or eliminating water)
-Regulation of blood pressure (secreting the enzyme renin, adjusting renal resistance)
-Release of erythropoietin & calcitriol
-Excretion of wastes & foreign substances

Nephron

-Kidney has over 1 million nephrons composed of a corpuscle and tubule
-Renal corpuscle = site of plasma filtration occurs
-Glomerular (bowman's) capsule is double-walled epithelial cup that collects filtrate
-Renal tubule: proximal convoluted tubule; loop of Henle dips down into medulla; distal convoluted tubule
-Collecting ducts and papillary ducts drain urine to the renal pelvis and ureter

Blood vessels around the nephron

-Glomerular capillaries are formed between the afferent & efferent arterioles
-Efferent arterioles give rise to the peritubular capillaries and vasa recta

Cortical Nephron

Flow of fluid through a --- ---
Glomerular (Bowman's) Capsule > Proximal convoluted tubule > Descending limb of the loop of Henle > Ascending limb of the loop of Henle > Distal convoluted tubule (drains into collecting duct)

Cortical Nephrons

-80-85% of nephrons are cortical nephrons
-Renal corpuscles are in outer cortex and loops of Henle lie mainly in cortex but can dip into the medulla

Juxtamedullary Nephron

Flow of fluid through a --- ---
Glomerular (Bowman's) capsule > Proximal convoluted tubule > Descending limb of the loop of Henle > Thin ascending limb of the loop of Henle > Thick ascending limb of the loop of Henle > Distal convoluted tubule (drains into collecting duct)

Juxtamedullary Nephron

-15-20% of nephrons are juxtamedullary nephrons
-Renal corpuscles close to medulla and long loops of Henle extend into deepest medulla enabling excretion of dilute or concentrated urine

Blood and Nerve

--- Supply of Kidney
-Abundantly supplied with blood vessels: receive 25% of resting cardiac output via renal arteries
-Functions of different capillary beds:
Glomerular capillaries where filtration of blood occurs: vasoconstriction & vasodilation of afferent & efferent arterioles produce large changes in renal filtration
Peritubular capillaries carry away reabsorbed substances from filtrate
-Sympathetic vasomotor nerves regulate blood flow & renal resistance by altering diameter of arterioles

Histology

--- of the Nephron & Collecting Duct
-Single layer of epithelial cells forms walls of entire tube
-Distinctinve features due to function of each region
-microvilli
-cuboidal versus simple
-hormone receptors

Renal Corpuscle

Structure of ---
-Bowman's capsule surrounds capsular space
-Podocytes cover capillaries to form visceral layer
-Simple squamous cells form parietal layer of capsule
-Glomerular capillaries arise from afferent arteriole & form a ball before emptying into efferent arteriole

Filtration Barrier

1) Fenestration (pore) of glomerular endothelial cell: prevents filtration of blood cells but allows all components of blood plasma to pass through
2) Basal lamina of glomerulus: prevents filtration of larger proteins
3) Slit membrane between pedicels: prevents filtration of medium-sized proteins

Juxtaglomerular Apparatus

-Structure where afferent arteriole makes contact with ascending limb of loop of Henle
-macula densa is thickened part of ascending limb
-Juxtaglomerular cells are modified muscle cells in arteriole

Nephrons

Number of ---
-Remains constant from birth: any increase in size of kidney is size increase of individual nephrons
-If injured, no replacement occurs
-Dysfunction is not evident until function declines to less than 25% of normal (other nephrons handle the extra work)
-Removal of one kidney causes enlargement of the remaining until it can filter at 80% of normal rate of 2 kidneys

Fenestration of glomerular endothelial cell

prevents filtration of blood cells but allows all components of blood plasma to pass through

Basal lamina of glomerulus

prevents filtration of larger proteins

Slit membrane between pedicels

prevents filtration of medium-sized proteins

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