Chapter 17 The Urinary System

Structures we’ll talk about tonight… Kidneys Ureters Bladder Urethra You can see the layout of the urinary system in this picture. You can see the urinary system is located mainly in the lower portion of the trunk of the body. Aside from the main structures, there are a lot of blood vessels that run through this system.

Kidneys Location—under back muscles, behind parietal peritoneum, just above waistline; right kidney usually a little lower than left Internal structure Renal cortex—outer layer of kidney substance Renal medulla—inner portion of kidney Renal pyramids—triangular divisions of medulla Renal papilla—narrow, innermost end of pyramid Kidneys form urine by filtration, secretion, and reabsorption. They are located…..

Kidneys Renal Microscopic structure—nephrons are microscopic units of kidneys They help with the formation of urine Cortical nephrons—85% of total Juxtamedullary nephrons—specialized role in concentrating urine They consist of: Bowman’s capsule—the cup-shaped top Glomerulus—network of blood capillaries surrounded by Bowman’s capsule The nephron is the functioning unit of the kidney. They consist of 6 parts including: Renal corpuscle contains: Bowman’s capsule – the cup-shaped top of a nephron. Bowman’s capsule surrounds the glomerulus to receive the glomerular filtrate or the water and dissolved substances filtered from blood. Glomerulus – a network of blood capillaries located inside of Bowman’s capsule. Water and dissolved substances pass through the walls of the capillaries into Bowman’s capsule.

Kidneys Nephron parts continued: Proximal convoluted tubule—first segment Loop of Henle—extension of proximal tubule; consists of descending limb, loop, and ascending limb Distal convoluted tubule—extension of ascending limb of loop of Henle Collecting tubule—straight extension of distal tubule Renal tubule contains: Proximal convoluted tubules, loop of Henle, and distal convoluted tubule Proximal convoluted tubule – the first segment of the renal tubule nearest (proximal) the Bowman’s capsule. “Convoluted” means that it has several bends and turns. Resorption begins here. Loop of Henle – an extension of the proximal tubule that consists of a straight descending limb, a hairpin loop, and a straight ascending limb. Resorption takes place here. Distal convoluted tubule – the part of the tubule that is distal to the ascending limb. Resorption and secretion take place here. Collecting tubule – the last part of the renal tubule. It is a straight tube; resorption and secretion take place here.

What are the functions of the kidneys What are the functions of the kidneys? What happens when you only have 1?

Kidneys Functions Not much changes when you only have 1 kidney! Excretes toxins and nitrogenous wastes Regulates levels of many chemicals in blood Maintains water balance Helps regulate blood pressure Not much changes when you only have 1 kidney! Excretes toxins and nitrogenous wastes such as urea and ammonia Regulate levels of many chemicals in blood such as chloride, sodium, potassium, and bicarbonate Maintain water balance by regulating proper balance between water and salt Help regulate blood pressure via secretion of renin from the juxtaglomerular apparatus

Formation of Urine Occurs by a series of three processes that take place in successive parts of nephron Filtration—goes on continually in renal corpuscles; glomerular blood pressure causes water and dissolved substances to filter out of glomeruli into Bowman’s capsule; normal glomerular filtration rate 125 ml per minute Urine formation begins with the process of filtration. Blood flowing through the glomerulus exerts pressure, and this pressure is sufficiently high to push water and dissolved substances out of the glomerulus into Bowman’s capsule. Normal glomerular filtration occurs at a rate of about 125 ml/minute.

Formation of Urine Reabsorption—movement of substances out of renal tubules into blood in peritubular capillaries; water, nutrients, and ions are reabsorbed; water is reabsorbed by osmosis from proximal tubules Secretion—movement of substances into urine in the distal and collecting tubules from blood in peritubular capillaries; hydrogen ions, potassium ions, and certain drugs are secreted by active transport; ammonia is secreted by diffusion Tubular reabsorption is the movement of substances out of the renal tubules back into the blood capillaries located around the tubules. Substances reabsorbed are water, glucose, and other nutrients, as well as sodium and other ions. Large amounts of water are also reabsorbed. This process of reabsorption prevents substances needed by the body from being lost in urine. Reabsorption begins in the proximal convoluted tubules and continues in the loop of Henle, distal convoluted tubules, and collecting tubules. Secretion is reabsorption in reverse; it moves substances out of the blood into the urine. Substances secreted include hydrogen ions, potassium ions, ammonia, and certain drugs. Secretion plays a crucial role in maintaining the body’s acid-base balance. The distal convoluted tubules and collecting tubules are the sites for secretion.

Formation of Urine Control of urine volume – Antidiuretic hormone (ADH) = “water-retaining hormone” or “urine-decreasing hormone” Aldoesterone = “salt- and water-retaining hormone” Atrial natriuretic hormone (ANH) = opposite effect of aldosterone A hormone from the posterior pituitary gland called antidiuretic hormone tends to decrease the amount of urine excreted by making the distal and collecting tubules permeable to water. If no ADH is present, both distal and collecting tubules are practically impermeable to water so little or no water is reabsorbed from them. As a result, more water is retained by the body. ADH is the “water-retaining hormone” or the “urine-decreasing hormone”. The hormone aldosterone, secreted by the adrenal cortex, plays an important part in controlling the kidney tubules’ reabsorption of salt. It stimulates the tubules to reabsorb sodium salts at a faster rate. It also increases the rate of tubular water reabsorption. Aldosterone is the “salt and water retaining hormone”. Another hormone, atrial natriuretic hormone (ANH), has the opposite effect of aldosterone. You’ll have the opportunity to discuss aldosterone in further detail along with ANH on the discussion board. These 3 hormones help maintain homeostasis of body fluids.

Influence of water on urine production Predict the changes that would occur in the urine of a runner who had just completed a marathon. Predict the changes that would occur in the urine production of a person who just ate a jumbo bag of popcorn with extra salt.

Practical Application Marathon runner Bag of salty popcorn Proteinuria will probably occur Probably dehydrated Urine production less than normal Salt loss via sweat – impact on hormone production? What if they drank a lot of water during the marathon? Sports drinks? Decreased salt reabsorption with the greatly increased salt intake. Larger amount of salt excreted through the urine. Marathon runner probably had more aldosterone production in order to conserve salt and water. Salt and water lost via sweat.

What urine can tell us Urinalysis—examination of the physical, chemical, and microscopic characteristics of urine; may help determine the presence and nature of a pathological condition What sort of info can we obtain in doing a urinalysis? A urinalysis can tell us: protein and glucose content, ammonia concentration, drug and alcohol presence, byproducts from metabolism such as ketones, nitrogen balance

Ureters Structure—narrow long tubes with expanded upper end (renal pelvis) located inside kidney and lined with mucous membrane and muscular layer Function—drain urine from renal pelvis to urinary bladder The ureters are narrow long tubes with expanded upper end (renal pelvis) located inside the kidney and lined with mucous membrane: a thick muscular wall moves urine by peristalsis.

Urinary Bladder Structure Functions Elastic muscular organ, capable of great expansion Lined with mucous membrane arranged in rugae, like stomach mucosa Functions Storage of urine before voiding Voiding Elastic muscular organ capable of great expansion. Contracts to empty itself Lined with mucous membrane arranged in rugae, like stomach mucosa

Urethra Structure Functions Narrow tube from urinary bladder to exterior Lined with mucous membrane Opening of urethra to the exterior called urinary meatus Functions Passage of urine from bladder to exterior of the body Passage of male reproductive fluid (semen) from the body 1 ½ inches long in females and 8 inches long in males: how does this difference affect urinary health between the 2 sexes?

Micturition Passage of urine from body (also called urination or voiding) Regulatory sphincters Internal urethral sphincter (involuntary) External urethral sphincter (voluntary) Bladder wall permits storage of urine with little increase in pressure Internal urethral sphincter is located at the bladder exit. External urethral sphincter circles the urethra just below the neck of the bladder. Bladder wall permits storage of urine with little increase in pressure until a volume of 3000-4– ml is reached. Adult bladder may hold 600 ml of urine.

Micturition Emptying reflex Initiated by stretch reflex in bladder wall Bladder wall contracts Internal sphincter relaxes External sphincter relaxes, and urination Enuresis—involuntary urination in young child There are a serious of actions that occur to initiate the emptying reflex. As the bladder wall stretches, nervous impulses are transmitted to the second, third, and fourth sacral segments of the spinal cord and an emptying reflex is initiated. Bladder wall contracts. Internal sphincter relaxes External sphincter relaxes, and urination occurs. What happens with paralysis?

Micturition Urinary retention—urine produced but not voided Urinary suppression—no urine produced but bladder is normal Incontinence—urine is voided involuntarily May be caused by spinal injury or stroke Neurogenic bladder—paralysis or abnormal function of the bladder, preventing normal flow of urine out of the body Types include urge, stress, and reflex A few conditions to be aware of… Retention of urine may cause cystitis. Overactive gladder – urge for frequent urination. Called interstitial cystitis. Amounts voided are small. Extreme urgency and pain are common.

Renal and Urinary Disorders Obstructive disorders interfere with normal urine flow, possibly causing urine to back up and cause hydronephrosis or other kidney damage Renal calculi (kidney stones) may block ureters, causing intense pain called renal colic Tumors—renal cell carcinoma (kidney cancer) and bladder cancer are often characterized by hematuria (blood in the urine)

Renal and Urinary Disorders Urinary tract infections (UTIs) are often caused by gram- negative bacteria Urethritis—inflammation of the urethra Cystitis—inflammation or infection of the urinary bladder Pyelonephritis—inflammation of the renal pelvis and connective tissues of the kidney; may be acute (infectious) or chronic (autoimmune) Hydronephrosis—enlargement of renal pelvis and calyces

Renal and Urinary Disorders Glomerular disorders result from damage to the glomerular– capsular membrane of the renal corpuscles Nephrotic syndrome accompanies many glomerular disorders Proteinuria—protein in the urine Hypoalbuminemia—low plasma protein (albumin) level; caused by loss of proteins to urine Edema—tissue swelling caused by loss of water from plasma as a result of hypoalbuminemia Edema related to hypoalbuminemia….called third spacing

Renal and Urinary Disorders Acute glomerulonephritis is caused by delayed immune response to a streptococcal infection Chronic glomerulonephritis is a slow inflammatory condition caused by immune mechanisms and often leading to renal failure

Renal and Urinary Disorders Kidney failure or renal failure occurs when the kidney fails to function Acute renal failure—abrupt reduction in kidney function that is usually reversible Chronic renal failure—slow, progressive loss of nephrons caused by a variety of underlying diseases Early in this disorder, healthy nephrons often compensate for the loss of damaged nephrons

Renal and Urinary Disorders Loss of kidney function ultimately results in uremia (high BUN levels) and its life-threatening consequences Complete kidney failure results in death unless a new kidney is transplanted or an artificial kidney substitute is used