Urinary System
Nephrology - the study of the kidney Urology - branch of medicine dealing with the male and female urinary systems and the male reproductive system
Functions of the Urinary System 1. Regulation of ions (electrolytes) - Ca +2, Na +, K +, Cl -, HPO 4-2 2. Regulation of blood volume - does this through conservation and elimination of water 3. Regulation of blood pressure
4. Regulation of blood ph - secretes H + into the urine & conserves HCO 3-6. Regulation of blood glucose levels - makes & secretes glucose from amino acids 5. Hormone production -calcitriol - (Vitamin D) stimulates absorption of calcium from the digestive tract -erythropoietin - stimulates production of red blood cells
7. Excretion of wastes into urine - removes water soluble wastes such as drugs, ammonia & urea (from breakdown of amino acids), bilirubin (from catabolism of hemoglobin), creatinine (from breakdown of creatine phosphate in muscle fibers), uric acid (from catabolism of nucleic acids) ** dehydration affects kidney function because wastes build up in the cells which cause death **Can only survive 4-5 days without water**
Consists of: 1. Kidneys (2) - filter blood - returns most of water & solutes to blood; remaining water & solutes make up urine - Located retroperitoneal - Each kidney receives 600 ml of blood/minute - Renal hilus - area where ureters, blood vessels and lymphatic vessels enter and exit the kidney - Renal artery - branches to increase surface area for more filtration
2. Ureters (2) - tubes that take urine from the kidneys to the bladder -urination is controlled by the urinary sphincter at the base of the bladder 3. Urinary bladder - stores urine; capacity is ~500 ml (females); 700-800 ml (males) - baroreceptors in the bladder send message to brain when it is ½ full, resulting in the urge to urinate
4. Urethra - tube connecting urinary bladder to outside of body; - longer in males than in females - three regions in males: 1. Prostatic urethra 2. Membranous urethra 3. Spongy urethra - also the route semen takes in men
External Anatomy of the Kidney Renal capsule - fibrous outer covering of the kidney Renal cortex - outer portion Renal medulla - middle portion made of 8-18 renal pyramids Renal papilla - apex of the renal pyramid
External Anatomy of the Kidney (cont.) Renal pelvis - innermost portion extension of the ureter contains major/minor calyces that drain urine from the renal pyramids (2-3 major, 8-18 minor per kidney) where kidney stones move into the ureters Renal sinus - cavity within the kidney that contains part of the renal pelvis, the calyces, along with renal blood vessels and nerves
Microscopic Anatomy of Kidney nephrons - functional unit of kidneys; ~ 1 million nephrons per kidney; you are born with these nephrons...can t regenerate them if they are damaged Parts of nephron 1. renal corpuscle - where plasma is filtered; - consists of two components - Glomerulus - tangled network of capillaries (has a large surface area) - Bowman s capsule - cup-like structure around the glomerulus that captures the filtrate
2. renal tubule - collects fluid that has been filtered by the renal corpuscle fluid goes into the proximal convoluted tubule, descending loop of Henle, ascending loop of Henle and then into distal convoluted tubule, then into collecting duct both the renal corpuscle and renal tubule lie within the renal cortex the loop of Henle extends into the renal medulla
Blood Supply to the Kidneys Renal arteries branch several times until they form an afferent arteriole, which brings blood into the kidney Each nephron gets one afferent arteriole, which divides into the glomerulus The glomerular capillaries form an efferent arteriole, which drains blood out of the glomerulus Afferent arterioles are larger in diameter than efferent arterioles, which causes glomerulus to be under high pressure. Changes in the arteriole pressure causes changes in blood pressure.
Nephron functions Filter blood Return useful substances to blood Remove substances from the blood that are not needed by the body **nephrons maintain homeostasis of blood and produce urine**
Steps in Urine Formation 1. Glomerular Filtration The glomerulus has pores, which allows blood plasma to pass into Bowman s capsule 150-180 L of fluid is filtered every day 99% of this filtrate returns to the bloodstream by reabsorption 1-2 L are excreted as urine
Renal clearance - the amount of product passing into Bowman s capsule Small substances have 100% clearance, like water, ions, amino acids, glucose Larger substances have 0% clearance, like proteins, blood cells and platelets
Steps in Urine Formation (continued) 2. Tubular Reabsorption - takes place in peritubular capillaries Stuff that is reabsorbed goes back through the walls of the tubules and into the blood (filtered water and needed solutes) All glucose is reabsorbed (if not, some spills out into the urine...this is indicative of diabetes)
Steps in Urine Formation (continued) 3. Tubular Secretion - movement of wastes and other materials (H + ) from tubule cells into tubule fluid Allows for control of blood ph Also affects blood pressure: If blood volume is high, it gets rid of excess water If blood volume is low, it reabsorbs all the water
Summary of Fluid Movement blood renal artery kidney afferent arteriole glomerulus Bowman s capsule proximal convoluted tubule descending loop of Henle ascending loop of Henle distal convoluted tubule collecting duct papillary ducts minor calyces major calyces renal pelvis ureter bladder urethra OUT
Fluid Homeostasis Antidiuretic hormone (ADH) - secreted from the posterior pituitary gland, this hormone regulates fluid volume by controlling water reabsorption Low ADH - less water is reabsorbed, causing more water in the urine; (high volume, dilute urine is produced) High ADH - more water is reabsorbed, causing less water in the urine; (low volume, concentrated urine is produced) Alcohol and diuretics (caffeine) inhibit the secretion of ADH
Urine Composition Micturation - the discharge of urine from the urinary bladder - Under both voluntary and involuntary muscle control Urine - 95% water, 5% sodium, potassium, chlorine, ammonia, urea, uric acid and creatinine - Normally, glucose and proteins should NOT be present in urine
Creatinine - looks at creatinine levels (breakdown of creatine phosphate from skeletal muscle); high levels = kidney problems Urinalysis -lab test that looks at the composition of urine including the volume, physical, chemical and microscopic properties Lab tests: BUN - blood urea nitrogen - looks at urea level present in the urine (a breakdown product of amino acids); high levels = kidney problems
Aging and the Urinary System -typically, kidney function decreases as we age (a 70 year old kidney is half as efficient as a 40 year old kidney) - polyuria (excessive urine production), nocturia (excessive urination at night), dysuria (painful urination), incontinence (lack of voluntary control over urination), and UTI s (urinary tract infections) increase as you age
Urinary System Disorders 1. Renal calculi - kidney stones; usually caused by an accumulation of crystals of calcium oxalate, uric acid or calcium phosphate 2. Urinary tract infections - (UTI) presence of bacteria in urine; more common in females due to shorter urethra -symptoms include painful urination, burning, low back pain, urgent urination 3. Glomerulonephritis - inflammation of the kidneys that involves the glomerulus -Symptoms include hematuria (blood in urine) & proteinuria
4. Renal failure - kidneys stop working Acute renal failure - kidneys stop working abruptly -characterized by scant urine production (oliguria) less than 250 ml/day Chronic renal failure - progressive and irreversible decline in glomerular filtration 5. Polycystic kidney disease - inherited disorder where the kidney tubules become filled with hundreds or thousands of cysts - accounts for 6-12% of kidney transplants
Dialysis A machine that is used to filter your blood if your kidneys are damaged Over 100,000 people a year begin dialysis Kidney donation - the other kidney enlarges to make up for the missing kidney (80% efficiency)