The Urinary System rev 1-13

Name: The Urinary System rev 1-13
Uploaded: 2017-09-07T15:26:56+00:00
Duration: PTM16S34
Channel: Melinda Smith
Description: The Urinary System rev 1-13

The Urinary System rev 1-13
Excretion processes that remove wastes and excess materials from the body. Urinary system has primary responsibility for homeostasis of water and most solutes in blood and other body fluids. Urine is essentially water and solutes. Water is the most abundant molecule in our bodies. We excrete about 2 ½ liters of water per day. 14- Urinary System BIO 102 HANDOUT

14- Urinary System BIO 102 HANDOUT
Regulates nitrogenous and other solute waste (nitrogen from protein metabolism made into urea as waste) Others: sodium, chloride, potassium, calcium, hydrogen ions, creatinine (waste product from muscle metabolism) toxic chemicals, waste produced from liver and cellular metabolism, drugs, vitamins Water is lost in urine, evaporation, feces. The urinary system is composed of the organs that produce, transport, store and excrete urine: 2 kidneys, 2 ureters, one bladder and one urethra The bladder stores urine. 14- Urinary System BIO 102 HANDOUT

The Kidneys are bean shaped organs, ~size of a clenched fist Renal artery connects kidney to the aorta Renal vein connects it to the inferior vena cava are located in the abdominal cavity*, lateral to the 2nd lumbar vertebrae and close to our back. 14- Urinary System BIO 102 HANDOUT

Kidney’s Role in Homeostasis
Besides making urine, the kidney: Maintains water balance: adjusts blood volume and blood pressure Maintains acid–base balance and blood pH Regulates red blood cell production (via the hormone erythropoietin) Activates an inactive form of vitamin D 14- Urinary System BIO 102 HANDOUT

Gross anatomy of the kidneys: capsule is the protective outer covering of the kidney interior of the kidney has 2 distinct areas: cortex and the medulla cortex is the outer portion. It has most of the capillary blood flow, contains nephrons (functional unit of the kidney). 14- Urinary System BIO 102 HANDOUT

Kidney medulla is composed of cone shaped areas called pyramids. The base of each pyramid faces toward cortex and the point faces toward middle of body. pyramids appear striped because they are formed of parallel bundles of microscopic urine collecting tubules, many loops of Henle and the collecting ducts. 14- Urinary System BIO 102 HANDOUT

Tips of pyramids are called the papillae. These insert into the opening of a tube called the calyx. Filtered urine is transported from the calyx to the kidney pelvis, the innermost hollow, muscular part of the kidney. Kidney pelvis empties into the ureters. 14- Urinary System BIO 102 HANDOUT

Smooth muscle of the ureters create peristaltic waves which move the urine into the bladder The bladder can usually hold between ounces before we feel the need to go to the bathroom. Women typically have smaller bladder capacity than men because the uterus compresses the bladder. internal and external urethral sphincter prevent the bladder from emptying until we are ready to do so. During urination, urine passes into the urethra, a muscular tube that extends from the bladder to the body’s opening. 14- Urinary System BIO 102 HANDOUT

The nephron is divided into several different areas: a glomerular or Bowman’s capsule which surrounds the glomerulus a proximal convoluted tubule (a thin hollow tube of epithelial cells) a loop of Henle, composed of a descending tubule, a loop, and an ascending tubule a distal convoluted tubule a collecting duct blood vessels that supply the tubules 14- Urinary System BIO 102 HANDOUT

How a Nephron works to produce urine and also reclaim substances the body still needs: The glomerular capsule surrounds the glomerulus which is a network of capillaries. blood plasma fluid is filtered out of the capillaries and into the space between the 2 layers of the glomerular capsule A tubule exits from the back of the glomerular capsule and continues as a long, thin tube with 4 areas: the proximal convoluted tubule The loop of Henle (composed of the descending limb, the actual loop and the ascending limb) 14- Urinary System BIO 102 HANDOUT

the distal convoluted tubule the collecting duct - Up to 1,000 distal tubules can join together to become a collecting duct The collecting duct leads into the renal pelvis where the final urine is deposited. 14- Urinary System BIO 102 HANDOUT

Blood vessels which supply the tubule The renal artery supplies the kidney and branches many times. Each nephron is supplied by a single afferent arteriole which enters a Bowman’s capsule and then divides to become the network of capillaries that makes up the glomerulus. After filtering the blood, the capillaries rejoin to become the efferent arteriole. This divides again into the peritubular capillaries, another capillary network that surrounds the proximal and distal tubules in the cortex. 14- Urinary System BIO 102 HANDOUT

The peritubular capillaries remove water, ions and nutrients which are reabsorbed by the proximal and distal tubules. Some efferent arterioles descend into the medulla and divide into capillaries called the vasa recta which supply the loop of Henle and the collecting duct. After this, the efferent arterioles meet with efferent venules which flow into the renal vein. 14- Urinary System BIO 102 HANDOUT

Formation of Urine: Glomerular Filtration
How do the kidneys select what to keep and what to excrete in urine? Urine formation involves 3 processes: Glomerular filtration: filters fluid from glomerulus into Bowman’s capsule Glomerular filtration is caused by the high blood pressure in the glomerulus, about twice as high as other capillaries. The high blood pressure is due to the difference in diameter between the afferent (incoming) and efferent (outgoing) arterioles (afferent arteriole is diameter is greater) 14- Urinary System BIO 102 HANDOUT

This difference in BP forces the following out of the glomerular capillaries Most water, salts, glucose, ureaglomerular filtrate Blood cells and plasma proteins are NOT filtered through the glomerular capillaries because they are too large Rate of filtration: Resting rate is under local chemical control Stress causes sympathetic nervous system to reduce blood flow to kidneys 14- Urinary System BIO 102 HANDOUT

Formation of Urine: Tubular Reabsorption
Tubular reabsorption begins in PCT and continues in the loop of Henle and DCT, and collecting tubules. returns water and needed solutes (glucose, nutrients and sodium ions and other ions) back to peritubular capillaries 99% of glomerular filtrate is reabsorbed into the blood as it passes through the nephron) Typically all glucose is reabsorbed unless too much is present and the tubules reach the limit of their ability to pass sugar back into the bloodstream Reabsorption varies according to which substances the body needs 14- Urinary System BIO 102 HANDOUT

Formation of Urine: Tubular Secretion
3. Tubular secretion: substances are added back to the DCT and collecting tubule to be excreted; can be performed either by passive diffusion or active transport Purpose: removing or regulating chemical levels in body; excretion of harmful chemicals; maintenance of blood pH Substances which can be secreted: drugs, pesticides, preservatives, hydrogen ions, ammonium, potassium, urea 14- Urinary System BIO 102 HANDOUT

Concentration or Dilution of Urine: ADH
The ability to dilute or concentrate urine depends on a high concentration of solutes in the renal medulla along with the ability to change the collecting ducts’ permeability to water Dilute urine: excreting excess water If you drink a lot of liquids, they are absorbed by the digestive system, enter your blood, increasing blood volume and decreasing the concentration of ions in your blood and body fluids. 14- Urinary System BIO 102 HANDOUT

Most of the water enters your cells To prevent osmotic swelling and damage to cells, the kidneys reasorb less water and produce dilute urine. Mechanism: cycling of NaCl and urea create a concentration gradient in the medulla that allows water to diffuse from the renal tubules into the interstitial fluid and then into the blood capillaries 14- Urinary System BIO 102 HANDOUT

Concentrated urine: conserving water If we drink too little liquid or sweat a lot, we may lower our blood volume, decrease our blood pressure, and risk dehydrating our cells. The kidneys compensate by reabsorbing more water and making a more concentrated urine. Mechanism: Countercurrent exchange mechanism allows us to produce a more concentrated urine 14- Urinary System BIO 102 HANDOUT

Because of the hairpin turn in the loops of Henle, fluid flows in opposite directions in the 2 sides of the loop. This is called a countercurrent flow. This allows a small difference in composition between the tubular fluid and the interstitial fluid to trigger reabsorption of liquid. Increased ADH causes increased permeability to the collecting tubules and increased conservation of water 14- Urinary System BIO 102 HANDOUT

Urination Depends on a neural reflex: Micturation reflex Internal urethral sphincter: composed of smooth muscle; is an extension of the smooth muscle of the bladder. External urethral sphincter: skeletal muscle; controlled by our brain As the bladder fills, it starts to stretch. This sends a message to the spinal cord Spinal cord nerves begin an involuntary reflex that contracts the smooth muscle of the bladder and relaxes the internal urethral sphincter. 14- Urinary System BIO 102 HANDOUT

Stretch receptor input also goes to the brain which allows the external urethral sphincter to relax. The brain can voluntarily override the micturation reflex by increasing the activity of the nerves that control the external sphincter. 14- Urinary System BIO 102 HANDOUT

Disorders of the Urinary System
Kidney stones Minerals in urine crystallize in the renal pelvis and form kidney stones Most are excreted with no problems Others can grow larger and block urine flow along with causing significant pain Can be removed surgically, crushed with shock waves which allows the fragments to be excreted with less pain 14- Urinary System BIO 102 HANDOUT

Urinary tract infections Refers to the presence of microorganisms in urine or in any part of the urinary system Symptoms include swelling and redness around the urethral opening, a burning sensation or pain while urinating, difficulty urinating, bed wetting, low back pain, visible blood or pus in urine Most are caused by bacteria that make their way up the urethra and can travel up the ureters to the kidneys Most can be cured with antibiotics 14- Urinary System BIO 102 HANDOUT

Acute and chronic renal failure: Kidney function impairment that is short term (acute) or long term (chronic) Acute causes: Sustained decreases in BP, large stones in the renal pelvis, infections, transfusion reactions, burns, severe injuries and toxic drugs or chemicals Chronic (may also be called end stage renal disease—ESRD): Long term irreversible damage leading to a reduction in functioning nephrons with failure of the kidneys to function properly 14- Urinary System BIO 102 HANDOUT

Therapies: Dialysis tries to duplicate the kidney function CAPD-continuous ambulatory peritoneal dialysis (acess permanently implanted into the abdominal wall; fluid left in abdomen for several hours) Hemodialysis: blood is circulated through an artificial kidney machine; treatment in a hospital; takes a morning or afternoon Kidney transplant—originally, biggest challenge is to find a good immunological match so the person’s body will not reject the foreign kidney Now not enough people have offered to donate their organs after death 14- Urinary System BIO 102 HANDOUT

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