Section 1: Functions of the Urinary System Ch 25: The Urinary System Section 1: Functions of the Urinary System

Role of the Urinary System - Plays a crucial role in maintaining homeostasis - Major challenge: *Remove wastes without losing too much water or dissolved nutrients in the process. Danger!! - If water levels fluctuate too much, chemical processes that run the body may shut down.

Role of the Urinary System Kidneys - Organs in which the fluid portion of the blood is collected - Allow H2O/important nutrients to be reabsorbed into bloodstream - Filter out toxic substances & cellular wastes. - Combine excess vitamins, salts, hormones, water & excrete them as urine

Functions of the Urinary System The urinary system helps maintain homeostasis in several ways: Regulates various ions in the blood (Na, K, Cl-, & Ca) Regulates water content in the blood Maintains proper pH of the blood Retains important nutrients (glucose, proteins, etc) Secretes hormones that stimulate RBC production Eliminates cellular waste products (urea)

Dealing with Amino Acid Metabolism - The digestion & processing of proteins Important things to note about A. A. Metabolism: - Some amino acids have their amino groups removed & used by the body. - All other amino groups are released as ammonia (very toxic) - Ammonia sent to liver & converted to urea (much less toxic) - Urea filtered from blood by kidneys & excreted as urine

Section 2: Structures & Functions of the Human Urinary System Ch 25: The Urinary System Section 2: Structures & Functions of the Human Urinary System

Anatomy of the Urinary System Urinary system consists of: - Kidneys - Ureters - Urinary Bladder - Urethra

Anatomy of the Urinary System Kidneys - “Paired” organs located on either side of spinal column & slightly above the waist - Shaped like beans (5 in long, 3 in wide, 1 in thick) - Blood carrying wastes enters kidney thru renal artery - After being filtered, blood exits kidney thru renal vein - Urine is created from wastes

Anatomy of the Urinary System

Anatomy of the Urinary System Ureters - Long tubes connecting each kidney to the bladder - Carry urine from the kidney to the bladder

Anatomy of the Urinary System Urinary Bladder - Temporarily stores urine from the kidneys - Smooth, collapsible, muscular bag - Walls composed of transitional epithelium giving it the ability to stretch - When bladder stretches, receptors in the walls trigger the bladder to contract (reflex action) - Capable of holding up to 500mL of fluid - Desire to urinate begins at about 100mL

Anatomy of the Urinary System Female bladder is much smaller than male bladder due to space taken up by uterus. Therefore, females have a legitimate reason for needing more pit stops on long trips. 

Anatomy of the Urinary System Urethra - Thin-walled tube that carries urine from bladder to outside of body - Release of urine controlled by two sphincters: 1) Internal urethral sphincter (involuntary) 2) External urethral sphincter (voluntary)

The Nephron & Urine Formation Nephrons - Structural & functional units of the kidneys - 1 million of them located in the outer cortex of kidney - Tiny filters responsible for forming the urine

The Nephron & Urine Formation Parts of a Nephron: Glomerulus Dense knot of capillaries where wastes & fluid from blood is filtered Bowman’s Capsule Cuplike structure that surrounds glomerulus Collects water, nutrients, & wastes

The Nephron & Urine Formation Parts of a Nephron: Proximal Tubule Returns H2O & nutrients back to bloodstream Loop of Henle Helps create accurate H2O/Salt concentrations in bloodstream

The Nephron & Urine Formation Parts of a Nephron: Distal Tubule Absorbs any remaining wastes in bloodstream Collecting Ducts Urine is completely formed at this point Continued H2O removal further concentrating urine

The Nephron & Urine Formation

Section 3: Control of the Urinary System Ch 25: The Urinary System Section 3: Control of the Urinary System

Regulation of Urinary System Regulation primarily governed by hormones: 1) Antidiuretic hormone (ADH) - Prevents excessive water loss in urine - Causes distal tubule to allow more H2O to be reabsorbed from the urine 2) Aldosterone - Regulates sodium ion content

Regulation of Urinary System Kidneys help regulate blood pressure : 1) Renin - Enzyme released from kidneys when BP drops - Directly affects angiotensin 2) Angiotensin - Hormone always found in bloodstream - When it comes in contact w/ Renin, it causes arterioles to constrict…raises BP

Regulation of Urinary System Kidneys help regulate O2 levels: 1) Erythropoietin - If oxygen levels drop, this is released by kidneys. - Travels to bone marrow & stimulates RBC growth - ↑ RBC = ↑ hemoglobin = ↑ O2 **Kidney failure almost always leads to anemia (low RBC count) due to insufficient erythropoietin production.

Section 4: Homeostatic Imbalances Ch 25: The Urinary System Section 4: Homeostatic Imbalances

Homeostatic Imbalances The kidney is a relatively rugged organ. However… If the kidney fails, death occurs fast! (Usually within 2 weeks) The kidneys are vulnerable to attack from several sources: Some painkilling medications can destroy kidney function Infection by bacteria can also be a major problem Most common form of kidney failure is diabetes

Homeostatic Imbalances Urinary Tract Infections (UTI) - Infections of urethra caused by bacteria Bladder Infections - Infections of bladder caused by bacteria *Both significantly more likely in women than men…why?

Homeostatic Imbalances Kidney Stones - Solid mass composed of tiny crystals - Formed in kidneys when urine contains too much of a certain substance…usually calcium or phosphate - Chronic dehydration plays a major role in formation - Irregularly shaped, usually w/ very sharp edges - Usually will pass through ureters & out of body - Sometimes must be pulverized w/ ultrasound - Worst case scenario = surgical removal

Homeostatic Imbalances Treatment of Kidney Disease: 1) Hemodialysis - Done with dialysis machine (developed in 1945) - Utilizes principle of diffusion across a semi-permeable membrane - Acts as an artificial kidney

Homeostatic Imbalances Treatment of Kidney Disease: 1) Hemodialysis (Cont.) - Blood supply is diverted from body, through machine where filtration takes place, & then returned to body - Patient must remain on dialysis for 4-6 hrs at a time 3 times per week. - Only works for about 10 years (at most)…food/drink intake must be very carefully regulated

Homeostatic Imbalances Treatment of Kidney Disease: 2) Kidney Transplant - Only an option when kidney is too damaged for dialysis - Only one required to sustain life 3) Bioartificial kidney - Still in clinical phase…but high hopes that this will be a viable option in the future 4) Science fiction or Real possibility?? - Pharamaceutical companies currently funding research into genetically engineered pig kidneys that wouldn’t be rejected by humans

Aging and the Urinary System As you get older… - there is a progressive decline in urinary function - bladder shrinks - urinary retention becomes more common in males due to enlarging prostate gland

Interesting Fact One of the early diagnostic tests for diabetes… …doctor would take urine sample & taste it! If sweet tasting, patient almost certainly was a diabetic…urine contained excess sugars from blood