the urinary system chapter 26. the organs of the urinary system include:
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The Urinary SystemThe Urinary SystemChapter 26Chapter 26
The Urinary SystemThe Urinary SystemChapter 26Chapter 26
Functions of the urinary system (all done by kidneys):
Regulate the volume, concentration, pH and content of blood
Eliminate metabolic wastes as urine
3 processes occur within the kidneys to accomplish these goals
Blood vessels (capillaries)
Renal tubules
R
Reabsorption (R) – Movement (by passive & active means) of most fluid & many solutes from renal tubules back into the blood; approx. 99% filtate reabsorbed
F
Filtration (F) – Pressure (blood pressure) forces some fluid (plasma) and small substances from blood to renal (kidney) tubules. Results in the formation of “filtrate” in the renal tubules; approx. 180 liters filtrate/day
blood
filtrate
S
Secretion (S) – Selective movement of specific substances (e.g. H+, K+) from blood to tubules
urine
Filtered blood
Gross Anatomy of the Kidneys Retroperitoneal organs
Left kidney more superior than right (due to liver)
Notch at medial border (hilus/hilum) for renal artery & vein, ureter
Each kidney surrounded by 3 layers of CT:
renal capsule – innermost layer of dense CT
adipose capsule – middle layer protecting & insulating kidneys
renal fascia – outer layer holding kidneys in place in abdominal cavity
Internal Anatomy of the Kidneys
Cortex
Medulla
pyramids
renal papillae
renal columns
Pelvis - collecting basin
minor calyces
major calyces
renal pelvis
where urine formation occurs
Microscopic Anatomy of the KidneysFunctional unit of the kidneys is the “Nephron”
Nephron = renal corpuscle + renal tubules
Most (85%) nephrons classified as “cortical nephrons” – corpuscle & most of tubule located within cortex
Some (15%) classified as “juxtamedullary nephrons” – corpuscle at junction of cortex & medulla & loop of nephron extends into medulla
Bowman’s capsule (parietal (capsular) layer)
Visceral layer of Bowman’s capsule (podocytes)
glomerulus
capsular space
Filtration occurs across “endothelial capsular (filtration) membrane” – junction between glomerular endothelium & podocytes; results in formation of “filtrate” in capsular space
Renal corpuscle – 1st part of the nephron; site of filtration; comprised of glomerulus – capillary network Bowman’s (glomerular) capsule – double layered capsule of epithelial tissue (inner visceral layer/outer parietal layer), surrounding glomerulus
NEPHRON
proximal convoluted tubule
reabsorption
Loop of Henle
more reabsorption
distal convoluted tubule
Secretion, some reabsorption
renal corpuscle
filtration
H2O
solutes
filtrate
COLLECTING SYSTEM
collecting duct
variable secretion &/or reabsorption
papillary duct
delivery of urine to minor
calyx
Representative Nephron
Filtrate from renal corpuscle will move into proximal convoluted tubule (PCT) loop of Henle distal convoluted tubule (DCT); and then into a collecting system of tubes (connecting tubule collecting duct papillary duct minor calyx)
Connecting tubule
Efferent arteriole
Afferent arteriole
glomerulus
Blood supply to kidneys
(Cortical radiate arteries)
Efferent arterioles branch into a second capillary network, the peritubular capillaries, which surround the renal tubules. The peritubular capillaries which surround the tubules of juxtamedullary nephrons are longer & straighter, therefore known as vasa recta
Reabsorption & secretion occur between the renal tubules & peritubular capillaries
Peritubular capillaries venules interlobular veins arcuate veins interlobar veins renal vein
Juxtaglomerular Apparatus (JGA)Extremely important to regulate the rate of filtration that occurs at the glomerulus (glomerular filtration rate “GFR”)
To regulate glomerular BP, we have a feedback system – the juxtaglomerular apparatus (JGA)
JGA =
juxtaglomerular cells of the afferent arteriole – recognize if renal BP is too low & then can respond
macula densa cells of the distal convoluted tubule – recognize if decreased filtrate produced or too many solutes within filtrate & then can respond
Juxtaglomerular cells
Macula densa
Once urine is formed, it will move from the pelvis of the kidneys into the ureters
retroperitoneal, muscular tubes running from kidneys to urinary bladder
lined with transitional epithelium
transports urine primarily by peristalsis
Urinary bladder Hollow muscular organ that temporarily stores urine prior to “micturition”
Lined with mucosa of transitional epithelium with rugae
Muscularis of 3 layers of smooth muscle known as “detrussor muscle”
Internally have “trigone” – triangular area formed by openings of ureters & urethra
Micturition reflex – stretch receptors in wall of bladder stimulate smooth muscle of detrussor muscle (involuntary); stimulation of internal urethral sphincter (involuntary) & external urethral sphincter of skeletal muscle (voluntary)
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