Urinary System Flashcards
Functions of Urinary System
- Removal of waste products from bloodstream
- Production of urine
- Storage and excretion of urine
- Blood volume regulation
- Regulation of erythrocyte production
- Regulation of ion balance/acid-base balance
Urinary system components
- kidneys
- ureters
- urinary bladder
- urethra
Location of kidneys
- retroperitoneal on posterior abdominal wall
- superior pole of left kidney is at level of T12 - right kidney 2 cm lower due to presence of liver
- concave medial border = hilum (where vessels, nevers and ureter connect w/ kidney)
- hilum continuous w/ renal sinus (internal space)
Kidneys
- each kidney surrounded & supported by several tissue layers (deepest to most superficial);
- Fibrous capsule (direct contact w/ outer surface - maintains shape, protects)
- Perinephric fat (Provides cushioning and insultion
- Renal fascia - anchors kidney to posterior abdominal wall
- paranephric fat: outermost layer surrounding kidney between renal fascia and peritoneum
Regions of Kidney (2)
-where regions meet
- Divided into outer renal cortex and inner renal medulla
- extensions of renal cortex (renal columns) project into renal medulla and subdivide medulla into renal pyramids
- 8-15 renal pyramids per kidney
- Wide base of renal pyramid makes contact w/ cortex = CORTICOMEDULLARY JUNCTION
- apex of renal pyramid = renal papilla
Tubing w/in renal sinus
- minor & major calyx
- renal pelvis
- Each renal papilla projects into hollow funnel-shaped structure = Minor calcyx
- Several minor calyces fuse to form major calyx
- major calyces fuse to form renal pelvis (collects total urine output from one kidney and transports it to ureter)
Arterial Supply to Kidney (to cortex)
- Blood enters kidneys via renal arteries
- w/in renal sinus, renal arteries branch into interlobar arteries (b/w renal pyramids)
- interlobar branch into arcuate arteries (follow corticomedullary junction)
- arcuate arteries branch into interlobular arteries (when in cortex)
Aorta -> Renal -> Segmental -> Interlobar -> arcuate -> interlobular
Arterial supply to Kindey (from cortex)
- as interlobular arteries enter kidney cortex, extend small branches called afferent arterioles
- enter renal corpuscle (struct.) and form a tuft of capillaries called glomerulus
- remaining blood exits glomerulus and renal corpsule as efferent arteriole
- Blood filtration occurs at glomerulus
interlobular -> afferent -> glomerulus -> efferent
Capillary supply to Kidney (2)
- efferent arterioles branch into one of two capillary networks: (where exchange of gases occur)
- Peritubular capillaries: surround convoluted tubules and reside primarily in cortex
- Vasa recta - ass. mainly w/ nephron loop and primarily reside in medulla (recta = straight)
Venous Return from the Kidney
-Peritubular capillaries & vasa recta drain into network of veins;
- smallest veins are interlobular veins
- merge to form arcuate veins (corticomedullary junction)
- merge in renal sinus to form renal vein
Interlobular -> arcuate -> interlobular -> renal vein
*all this blood is deoxygenated
Nephron
- is functional filtration unit of kidney
- approx. 1.25 million nephrons in each kidney
- Form urine in 3 processes (related);
- filtration
- tubular reabsorption
- tubular secretion
*final product is formation of urine (from filtrate)
2 types of nephrons
- Cortical nephrons: approx. 85% of all nephrons
- bulk of nephron resides in cortex - small component enters medulla (nephron loop) - Juxtamedullary nephrons: renal corpuscle lies near corticomedullary junction and their long nephron loops extend deep into medulla
-long medulla in animals in dry areas - really conc. urine
4 components of a nephron
- Renal corpuscle
- Proximal convoluted tubules
- nephron loop
- Distal convoluted tubule
Renal corpuscle
-2 structures
- composed of 2 structures;
1. Glomerulus: thick tangle of fenestrated capillaries (studded by lots of holes)
2. flomerular capsule (Bowman’s capsule): epithelial covering over glomerulus - corpuscle has vascular pole where afferent arteriole enters and efferent arteriole exits
- tubular pole = proximal convoluted tubule exits
2 layers of Glomerular Capsule
-podocytes
- Visceral layer: directly overlies and comes in contact w/ glomerulus
- composed of specialised cells called PODOCYTES (have little projections that help them wrap around capillaries)
- Parietal layer: formed from simple squamous epithelium
Podocytes - pedicels (function)
- Have long processes called pedicels that wrap around glomerular capillaries (don’t completely ensheathe)
- pedicels separated from each other by filtration slits
- filtration slits and fenestrated capillary wall makes up filtration membrane - mostly leaks indiscriminate contents from plasma
- role of remainder of nephron = adjust contents of nephron
Proximal Convoluted Tubule
- Walls of simple cuboidal epithelium w/ tall microvilli
- reabsorb almost all nutrients leaked through filtration membrane
- reabsorbed nutrients and water enter peritubular capillaries - returned to general circulation in vascular system
Nephron Loop
- AKA loop of henle
- projects into medulla
- 2 limbs (descending [from cortex] and ascending [to cortex])
- both limbs facilitate reabsorption of water and solutes
- enter vasa recta capillaries and returned to general circulation
Distal Convoluted Tubule
- Found in renal cortex
- Secretes K and H ions from peritubular capillaries into tubular fluid
- reabsorption of water also occurs
- lined w/ simple cuboidal epithelium - but smaller and sparse amounts of microvilli (doesn’t seem fuzzy like proximal)
- makes contact w/ afferent arteriole at vascular pole - gives feedback to rest of system - to either increase or decrease filtration)
Collecting tubules & ducts
- project through medulla toward renal papilla
- lined by simple epithelium (cuboidal to columnar)
- last structures to modify tubular fluid
- when tubular fluid leaves collecting duct at papilla, called urine
Juxtaglomerular Apparatus - 2 components
-function
-Is important in regulation of blood pressure
Comprised of;-
-juxtagomerular cells - modified smooth muscle cells of afferent arteriole located at vascular pole of renal corpuscle
-macula densa cells - group of modified epithelial cells in distal convoluted tubule - come into contact w/ juxtaglomerular cells
- help regulate sodium and other things in distal tubule
- both cells in contact - communicate info to each other
Urinary Tract components
- Ureters
- urinary bladder
- urethra
Ureters
-3 layers
-Fibromuscular tubes that conduct urine from kidney to urinary bladder
-originate at renal pelvis as it exits hilum of kidney
3 layers;
-mucosa (inner lining)
-muscularis (need to close off ureter and move urine along)
-adventitia (connective tissue that attaches it to body wall)
Urinary Bladder- function
- trigone
- location in females and males
- Main function = reservoir of urine
- located immediately posterior to pubic symphosis
- trigone - posteroinferior triangular area - defined by two ureteral opening and urethral opening
Females: anteroinferio to uterus and directly anterior to vagina
Males: anterior to rectum and superior to prostrate gland
Wall of urinary bladder (4 layers)
- Mucosa: transitional epithelium that lines internal surface of bladder; rugae allow distension of bladder
- Submucosa - suuports urinary bladder wall
- Muscularis - 3 layers o smooth muscled called detrusor muscle; an internal urethral sphincter muscle present at urethral opening
- Adventitia - outer layer of areolar connective tissue
Urethra
-2 sphincters
- fibromuscular tube that originates at neck of urinary bladder and conducts urine to exterior of body
- 2 sphincters control release:
- Internal urethral sphincter
- external urethral sphincter
Female Urethra
- has single function of transporting urine
- very short & close to anus
Male urethra - 3 segments
- 2 functions: urinary & reproductive
- partitioned into three segments;
- Prostatic urethra (trigone opening thru prostate)
- Membranous urethra (continues from prostatic to body diaphragm)
- Spongy urethra (through shaft of penis)
*ends in opening called eternal urethral orifice
Micturition
-AKA urination
-initated by micturition reflex
Controlled by 2 nervous systems;
1. Parasympathetic (rest/digest): allows internal sphincter to relax & contracts detrusor muscle - results in micturition/urination)
2. Sympathetic (fright/fight/flight): contracts internal sphincter & inhibits detrusor muscle - prevents urination
Process of micturition (6 steps)
- bladder fills and distends - activates stretch receptors which signal micturition reflex
- impulses sent via parasympathetic axons to internal sphincer and detrusor muscle
- internal urethral sphincter smooth muscle relaxes and detrusor muscle contracts
- Person’s conscious decision to urinate causes relaxation of external urethral sphincter
- Contractions o abdominal and respiratory muscles help empty/void bladder
- Detrusor muscle relaxes and micturition reflex centre is inactivated
