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7 - Anatomy of the Urinary System
Anatomy & Phys II (BIO-212-90 )
Camden County College
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7 Anatomy of the Urinary System Urinary system: Composed of a pair of kidneys, two ureters, one urinary bladder, and one urethra. - Each ureter drains from the corresponding kidney. The ureter drains into the urinary bladder, and then the urethra carries wastes as urine from the body. - The kidney serves many important funcDons, including fluid homeostasis, filtraDon of wastes, and homeostasis of blood volume and chemical composiDon. Kidney Anatomy - An adult kidney is bean-shaped, about the size of a can of soup and weighs around 5 ounces. - The right kidney lies slightly lower than the leJ because of the liver’s locaDon just above it. - Both kidneys are mostly protected by the rib cage because of their locaDon between T- 12 and L-3 vertebrae. - The kidney’s medial surface is concave and has a cleJ called the renal hilus leading to a space within the kidney called the renal sinus. - The ureters, blood vessels, and nerves in the sinus enter the kidney at the hilus. On top of each kidney is an adrenal gland. - The kidney surface is protected by three layers of specialized Dssue. - Renal capsule: Inner layer of protecDve Dssue, tough fibrous outer skin of the kidney that protects it from injury and infecDon. - Adipose capsule: FaUy layer that protects the kidney from trauma. - Renal fascia: Outer layer, dense fibrous connecDve Dssue that keeps the kidney in place inside the abdominal cavity. - Cross secDon of the kidney: The cortex, medulla, and pelvis - Outer renal cortex: Just inside the renal capsule, is a conDnuous outer region with several projecDons (corDcal columns) that extend down between the renal medulla pyramids. - Located within the cortex are the glomerular capsule and the distal and proximal convoluted tubule secDons of nephrons along the associated blood vessels. - Deeper within the kidney lies the renal medulla à divided into secDons called pyramids that point towards the center of the kidney. - Located within the medulla are the Loop of Henle and the collecDng duct secDons of the nephrons along with associated blood vessels. - The centermost secDon of the kidney near the renal hilus à renal pelvis: consDtutes a funnel-shaped tube that connects the ureter as it leaves the hilus. - Calyces: Collect urine, which drains conDnuously into the renal pelvis and subsequently into the ureter. - The ureter transports the urine to the bladder to be stored. Kidney Blood and Nerve Supply
The kidneys are innervated by many blood vessels so that they can filter the blood to regulate its composiDon with the renal arteries, delivering about 1200 mL of blood per minute directly from the abdominal aorta, which amounts to 20% of the cardiac output.
The renal arteries branch into five segmental arteries that divide further into lobar arteries, then further into interlobar arteries, which pass between the renal pyramids.
The interlobar arteries then divide into the arcuate arteries, which branch into several interlobular arteries that feed into the afferent arterioles that supply the glomeruli.
AJer filtraDon occurs, the blood moves into the efferent arterioles and either the peritubular or vasa recta capillaries and then drains into the interlobular veins, which converge into arcuate veins, then interlobar veins, then to the renal vein, which exits the kidney.
The kidney and nervous system interact through the renal plexus, whose fibers follow the renal arteries to reach the kidney.
Input from the sympatheDc nervous system adjusts the diameter of the renal arteries, thereby regulaDng renal blood flow. Ureters
Urine is carried from the kidneys to the bladder by thin muscular tubes called ureters.
Ureters begin as a conDnuaDon of the renal pelvis and descend to the base of the bladder.
Ureterovesical valves: Sphincters located where the ureters enter the bladder.
The downward flow of urine in addiDon to the ureterovesical valves help to prevent urine from flowing back toward the kidney.
The ureter has a wall made up of three layers of different types of Dssues.
The inner lining: made of transiDonal epithelium, is conDnuous with the kidney’s lining.
The middle layer: two sheets of muscle, one longitudinal and the other circular.
The outer advenDDa layer: fibrous connecDve Dssue.
DistenDon of the middle muscle layer by the urine as it enters the ureter causes it to contract and push the urine through the ureter. Urinary Bladder
The urinary bladder is the hollow, muscular, elasDc pouch that receives, and stores urine excreted by the kidneys before disposal through the urethra.
In males: the base of the bladder lies in front of the rectum and just behind the pubic symphysis.
In females: the bladder sits below the uterus and in front of the vagina, so the maximum capacity of the bladder is lower in females than in males.
Both ureters open into the bladder via the ureteral orifices.
The urethra begins as it opens at the base of the bladder. These three openings occupy the corners of the smooth, triangular center region of the bladder called the trigone.
The bladder has a wall made up of three layers of different types of Dssues.
Outer advenDDa: fibrous connecDve Dssue.
Detrusor muscle: Middle layer of muscle.
Glomerular capsule (renal corpuscle): Filters the blood.
Renal Tubule: Reabsorbs needed materials and the collecDng ducts carry the remaining material away as urine to be excreted.
Renal tubule parts: the proximal convoluted tubule (PCT), the loop of Henle, and the distal convoluted tubule (DCT).
Glomerulus: Renal corpuscle composiDon. A network of Dny blood capillaries surrounded by the glomerular (bowman’s) capsule à a double-walled simple squamous epithelial cup.
The glomerular capillaries are extremely porous.
The capillary endothelium has fenestraDons (pores) that allow certain substances to leave the capillaries.
The glomerular capillaries are the only capillaries in the body that lie between two arterioles (the afferent and efferent arteriole) rather than between an artery and a vein.
Afferent arteriole: fed by the interlobular artery, is much larger in diameter than the efferent arteriole.
The different in diameter causes an extremely high blood pressure in the glomerular capillaries, forcing water and solutes out of the blood, thus making filtraDon possible.
Water and solutes leave the glomerulus, enter the glomerular capsule, and subsequently flow into the renal tubule.
Once water and solutes leave the blood and enter the glomerular capsule, it is called filtrate.
Most of the kidney nephrons are considered corDcal nephrons (85%).
CorDcal nephrons: In the cortex region of the kidney, except for a porDon of the loop of Henle, which extends into the medulla.
Juxtamedullary nephrons: Remaining nephrons. Pass deeply into the medulla because of their locaDon and their longer loops of Henle.
The renal tube has three disDnct parts each with specialized funcDons.
Proximal convoluted tubule: First secDon; specialized to reabsorb water and many solutes from the glomerular filtrate into the low-pressure peritubular capillaries that surround the renal tubule as well as secrete certain unwanted substances.
Loop of Henle: SecDon; the loop of Henle has the descending limb following the ascending limb. The descending limb allows water loss, and the ascending limb allows salt (NaCI) loss.
The last part of the tubule is highly coiled - > distal convoluted tubule allows for hormonally controlled reabsorpDon of water and solutes. The distal convoluted tubule is most responsible for the secreDon of unwanted substances. Nephron Capillary Beds
Three beds: Glomerular capillaries, peritubular capillaries, and the vasa recta.
Glomerular capillaries (glomerulus): Highly coiled capillary beds formed from the afferent arteriole, leaving as the efferent arteriole.
Because of the porosity and high pressure in the glomerular capillaries, they are specialized for filtraDon as it forces fluid and solutes out of the blood and into the glomerular (Bowman’s) capsule.
About 99% of this glomerular filtrate is reabsorbed through the renal tubule and returned to the blood in the peritubular capillary bed, which arise from the efferent arterioles as they leave the glomerulus.
The peritubular capillaries closely follow the renal tubules and drain into the interlobular vein.
Because of their porosity and low pressure, the peritubular capillaries are adapted for adsorpDon, reclaiming water and solutes from the filtrate.
There is also a third set of capillaries known as the vasa recta, which follow the loops of Henley in the juxtamedullary nephrons of the medulla. MicturiDon
MicturiDon: Emptying the bladder.
As urine accumulates, the rugae flaUen and the wall of the bladder thins as it stretches, allowing the bladder to store larger amounts of urine without a significant rise in internal pressure.
The urge to urinary usually starts when about 200 ml of urine has accumulated, causing distenDon of the bladder walls, which iniDates a visceral reflex arc. This causes the detrusor muscle to contract and the internal sphincter the relax, forcing stored urine through the internal sphincter into the upper part of the urethra.
A person can consciously resist this iniDal urge to urinate because the external sphincter is voluntarily controlled.
As the bladder conDnues to fill, the desire to urinate becomes stronger. Eventually, if the amount of urine reaches 100% of the bladder’s capacity, the voluntary sphincter opens, and micturiDon occurs involuntarily.
InconDnence: inability to control micturiDon voluntarily. This is a normal condiDon in infants and in later life with diagnoses, such as end-stage demenDa. InconDnence can also occur due to emoDonal trauma, pregnancy, or nervous system injuries, such as stroke or a spinal cord injury.
Urinary retenDon: The inability to expel stored urine. This is a common condiDon aJer general anesthesia since the detrusor muscle is slow to regain muscular acDvity. Male urinary retenDon can occur due to the overgrowth of the prostate gland, which marrows the urethra, making micturiDon difficult. InserDon of a thin rubber (catheter) tube into the urethra is necessary to allow the urine to empty from the bladder. 7 Physiology of the Urinary System Urine FormaDon
The kidneys filter the enDre blood plasma volume about 60 Dmes each day and subsequently use about 25% of the resDng body energy to excrete the wastes as urine.
About 47 gallons of glomerular filtrate containing the water, nutrients, and essenDal ions are removed daily from the blood plasma.
By the Dme filtrate enters the collecDng ducts, it contains about only 0 gallons of urine, with the other 99% being returned to the blood.
The filtrate loses most of its water, nutrients, and essenDal ions are removed daily from the blood plasma.
Maintenance of a relaDvely constant GFR is important for adequate reabsorpDon of water and other needed substances from the filtrate and filtraDon of wastes.
If flow is too rapid, needed substances cannot be adequately reabsorbed. If flow is too slow, nearly all the filtrate is reabsorbed, including most of the wastes that should be excreted.
7 - Anatomy of the Urinary System
Course: Anatomy & Phys II (BIO-212-90 )
University: Camden County College
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