32/33. Urinary System Flashcards
Functions of the urinary system
Storage and excretion of urine
Regulation of blood volume (directly regulator of blood pressure)
Regulation of ion levels (Ca+, Na+, K+)
Regulation of acid-base levels (H+)
Regulation of erythrocyte production (secretion of erythropoietin)
Function of erythropoietin and relation to kidney disease:
In response to a drop in tissue oxygen pressure (hypoxia), erythropoietin is produced by cells in the renal cortex
Pts with chronic kidney disease cannot filter toxins and accumulation of toxins effects availability of erythropoietin and ability to produce new red blood cells
Result is lowered oxygen availability in organ tissue and subsequent organ failure
Initial Embryonic development of urinary system
Urogenital system derives from embryonic tissue called intermediate mesoderm
As the intermediate mesoderm runs down the posterior abdominal wall of the developing embryo, it will begin to condense and form two bilateral ridges, Known as urogenital ridge
Pronephros develop from urogenital ridge and instigate mesonephros development
Urogenital system development by week 4
Mesonephros act as a temporary set of excretory organs
They are composed of multiple saclike segments
The mesonephric duct drains each mesonephros to the developing bladder
Mesonephros persist till week 10
What occurs at 5th week of urogenital system development
Metanephros develop and act as temporary set of excretory organs
They are fully functional by week 10 and take over as final excretory organ
They develop from ureteric buds and metanephric mesoderm
Ureteric buds develop into
Structures that will collect urine
Ureter, renal calyces, renal pelvis, and collecting ducts
Metanephric mesoderm develops into
Nephron components of kidney
Structures that will produce urine
Glomerular capsule, proximal convoluted tubule, nephron loop, distal convoluted tubule
Characteristics of indifferent duct system
All embryos develop an indifferent duct system
Genetics will determine which duct system is retained
Retention of mesonephric duct will result in development of penis, etc
Retention of paramesonephric duct results in develop,ent of uterus, etc
Organs of urinary system and their overall functions
Paired kidneys: filter waste from bloodstream and convert filtrate into urine
Ureters, urinary bladder, urethra: (urinary tract) transport the urine out of body
Location of kidneys and what gland is also found nearby
Superior border sits just below T12 vertebrae
Inferior border sit at about L3
Kidney is retroperitoneal
Suprarenal or adrenal gland sits atop each kidney
Right kidney sits slightly more inferior than left kidney
Kidney sits on posterior aspect of abdomen so easily accessible in surfery
How are kidneys supported?
Cushioned by two layers of fat
Characteristics and functions of fibrous capsule of kidney
Dense, irregular connective tissue
Maintains shape of kidney
Protects kidney from damage
Prevents infection from spreading
Concave medial border: hilum
Internal structure of kidney
Consists of cortex and medulla
Cortex is outer region that divides the medulla into pyramidal shaped regions called pyramids
Base of medulla forms the corticomedullary junction with the cortex
At the apex of the medulla is the papilla
Drainage of urine in medulla
Urine formed in medulla drains from papilla into minor calyx
Urine collecting in multiple minor calyces will drain into one major calyx
Components of the collecting system
Medulla produces urine
Papilla
Minor calyx
Major calyx
Renal pelvis
Ureter
Bladder
Primary function of kidney
Blood filtration
Blood supply to and from kidney
Blood carried to kidney by renal arteries which branch off the abdominal aorta
Renal veins bring deoxygenated blood back to IVC
Renal veins lie superior to arteries and are asymmetrical due to location of IVC
Left renal vein is longer than right and collects blood from left gonadal vein
Order of blood supply to the kidney
Renal artery
Segmental arteries (5 branch off)
Interlobar arteries: between pyramids
Arcuate arteries: across tops of pyramids
Cortical arteries: penetrate cortex and give off afferent arterioles
Afferent arterioles are smallest branches which create capillary balls called glomeruli
What is a nephron
Functional unit of the kidney
Components of nephron
Corpuscle: glomerulus and capsule
Proximal convoluted tubule
Nephron loop (of Henle)
Distal convoluted tubule
Collecting ducts
Nephrons form urine from three processes
Filtration, reabsorption, secretion
Filtration
Movement of substances from blood to capsular space
Reabsorption
Movement of substances from tubular fluid back to blood
Secretion
Movement of substances from the blood to the tubular fluid
Structure of renal corpuscle
Renal corpuscle is made of glomerulus and glomerular capsule
Glomerulus is a tangle of capillaries that extend from the afferent arteriole
The glomerular capsule surrounds the glomerulus
Structure of glomerular capsule
Made of two layers: visceral and parietal
Parietal layer made of simple squamous epithelium
Visceral layer is adhered to glomerulus and is made of podocytes
Capsular space lies between two layers and collect filtrate
Glomerular development
The developing glomerulus presses into the renal tubule to form a visceral and parietal layer
This forms a space separating the layers which is where filtrate will collect and drain into proximal convoluted tubule
Layers of the filtration membrane
- Epithelium of the glomerulus
- Basement membrane of the glomerulus
- Visceral layer of the glomerular capsule
Function of filtration membrane
Allows only smallest solutes to exit glomerulus
Solutes are pressed out of blood due to high pressure in the glomerulus
Non selective method of filtration
Characteristics of proximal convoluted tubule
Simple cuboidal epithelium with microvilli help increase reabsorption capacity
Actively reabsorbs glucose, amino acids, electrolytes, and plasma proteins
Characteristics of nephron loop (of henle)
Loops down into middle
Primary function is to reabsorption water and solutes to bloodstream
Made of two limbs:
Each limb has thick and thin portion
Thick and thin regions are made of different epithelium which will function in the reabsorption or secretion of different substances
Characteristics of distal convoluted tubule
Simple cuboidal epithelium with sparse microvilli
Primary function is to secrete ions (K+) into tubular fluid and also to reabsorb water
Blood flow around the nephron
Peritubular capillaries surround the proximal and distal convoluted tubules
Vasa recta surround the nephron loop
Types of nephrons
Cortical nephrons: Work under normal conditions
Juxtamedullary nephrons: work during periods of high activity
Regulation of collecting tubules
Act under influence of anti-diuretic hormone (ADH) and aldosterone to limit the loss of water and sodium ions from blood
Purpose of anti-diuretic hormone (ADH)
Released in response to dehydration
Triggers conversion of water and sodium ions
Purpose of aldosterone
Increases blood ion concentrations and blood volume
Functions to increase amount of water in blood by increasing amount of sodium present
Characteristics of juxtaglomerular apparatus
Group of cells that control production of aldosterone
Made of:
Macula dense cells in the Distal convoluted tubule
JG cells in afferent arteriole
Macula dense and JG cells communicate to regulate the blood fluid volume (blood pressure)
Action of the juxtaglomerular apparatus
Macula densa cells in the DCT monitor the sodium ion concentration in the filtrate
If ion concentration is too high, macula densa cells tell JG cells to contract
Contraction narrows the wall of the afferent arteriole, reduces the pressure inside the glomerulus
Effect of renin
Triggering of JG cells also releases renin
Renin stimulates the production of aldosterone
Aldosterone will act upon the collecting duct to make it more permeable to water
Water is the secreted from the duct and reabsorbed back into the blood
Overall mechanism of the juxtaglomerular apparatus
Macula densa cells sense an increase in Na+ concentrations in filtrate
Macula densa stimulates JG cells to contract the afferent arteriole and release renin
Contraction reduces flow of filtrate in PCT, thus retaining more water and Na+
Renin triggers aldosterone
Aldosterone stimulates reabsorption of Na from collecting duct back to blood
Increase in sodium ions in the blood will increase the reabsorption of water from filtrate
Result is increase in blood volume/pressure
How does urine exit the kidney
Through ureter
Ureters carry urine into pelvic cavity to empty into urinary bladder
Ureters insert in the posterolateral wall of the bladder
A one way valve prevents urine from re-entering the ureter
Where do kidney stones occur
Ureters are narrow in the lower pole of the kidney, iliac vessels, and entrance of the bladder
These are locations where kidney stones are most likely to get stuck as they travel through the ureter
Three layers of the ureter
- Mucosa (transitional epithelium)
- Muscularis (smooth muscle layers)
- Adventitia (collagen and elastic fibers)
Sine (without) uterine pelvic contents
Bladder, rectum, ureters
Uterine pelvic contents
Uterus, rectum, bladder, ureters
Four layers of urinary bladder
- Mucosa (transitional epithelium)
- Submucosa (dense, irregular connective tissue)
- Muscularis (detrusor muscle)
- Adventitia (outer loose connective tissue)
Epithelium components of the bladder
Transitional epithelium allows the epithelium to stretch
Mucosal folds called rugae allow for increased storage within the bladder
Trigone is a triangular area formed by the entrance of the ureters and the formation of the internal urethral sphincter
Characteristics the urethra
Urethra is made from smooth muscle of the bladder
Internal urethral sphincter is also made of smooth muscle and is under autonomic control
The distal end of the urethra is surrounded by the skeletal muscle forming the external urethral sphincter
The difference between male and female urethrae
Male includes prostatic urethra following bladder, then membranous urethra, and finally penile urethra
Female has external urethral orifice following bladder
Micturition reflex center in brain
- Stretch receptors in the bladder trigger the micrurition reflex center
- Impulses travel to the detrusor muscle and the internal urethral sphincter
- Smooth muscle in internal urethral sphincter relaxes
- Smooth muscle in detrusor contracts
- Person must consciously relax the external urethral sphincter
Parasympathetics of the bladder
Stimulate micturition
Sympathetics to the bladder
Inhibit micturition
