NOTES UNIT 9 part 2: Urinary (Excretory) System Urinary Processes

*Recall: the primary function of the urinary system is to filter the blood of ions and nitrogenous wastes; when combined with water, these wastes make up URINE.

Lipids Carbohydrates Proteins B and C QUESTION: The metabolism of ____ leads to most of the nitrogenous wastes that must be filtered. Lipids Carbohydrates Proteins B and C

NEPHRONS • NEPHRONS: the functional units of the kidneys -each kidney contains about a million nephrons! Test ?

Parts of a NEPHRON: • GLOMERULUS: tangled cluster of blood capillaries • GLOMERULAR CAPSULE (a.k.a. Bowman’s capsule): thin-walled structure surrounding glomerulus

Renal artery  arterioles Thoracic aorta  hepatic artery  arterioles QUESTION: Blood leading to the glomerulus to be filtered comes from which major vessel? Renal vein  venules Renal artery  arterioles Thoracic aorta  hepatic artery  arterioles Inferior Vena Cava  venules

Parts of a NEPHRON: • PROXIMAL CONVOLUTED TUBULE • LOOP OF HENLE -descending limb -ascending limb • DISTAL CONVOLUTED TUBULE

Parts of a NEPHRON: • COLLECTING DUCT (where distal tubules from several nephrons converge and drain into; from here, urine empties into the RENAL PELVIS)

Blood Supply of a Nephron: -blood is brought to a nephron from an afferent arteriole; -from here, it is passed to an efferent arteriole; -this gives rise to a system of peritubular capillaries that surround the renal tubules **this is the only example we will learn where blood goes from artery  arteriole  capillaries  arteriole  capillaries  venule  vein

URINE FORMATION *nephrons remove wastes from blood and regulate water and electrolyte concentrations. URINE IS THE END PRODUCT!

Three Steps of Urine Formation: FILTRATION – in the glomerulus 2) REABSORPTION – “good stuff” is reabsorbed back into the bloodstream; occurs in the tubular portion of the nephron 3) SECRETION – substances the body needs to get rid of at a faster rate are secreted; occurs in the tubular portion of the nephron (materials added into the nephron after filtration has occurred) Animation!

GLOMERULAR FILTRATION: • water and dissolved materials filter out of glomerular capillaries  if molecule is small enough, can filter into Bowman’s capsule • the composition of the filtrate is similar to that of plasma (water, salts, amino acids, nitrogenous wastes, etc.)

GLOMERULAR FILTRATION: • occurs due to pressure pushing the fluid into the capillaries *FILTRATION RATE varies with FILTRATION PRESSURE

CLICKER QUESTION: Blood is filtered as it runs through the glomerulus & materials pass into what nephron structure? Proximal convoluted tubule Distal convoluted tubule Bowman’s capsule Loop of Henle Collecting Duct

CLICKER QUESTION: If you drink a lot of water, what effect will this have on pressure in the glomerulus? Increase pressure & therefore, increase the filtration rate Decrease pressure & therefore, increase the filtration rate Increase pressure & therefore, decrease the filtration rate Decrease pressure & therefore, decrease the filtration rate

TUBULAR REABSORPTION: • substances are selectively reabsorbed from the glomerular filtrate • the capillaries around the nephron have increased permeability • most reabsorption occurs in the PROXIMAL TUBULE

TUBULAR REABSORPTION: • substances that remain in the filtrate become more concentrated as water is reabsorbed Substances reabsorbed into the blood: water, salt, glucose, amino acids (aka: the “good”stuff)

CLICKER QUESTION: TRUE or FALSE? Urea (nitrogenous waste) is reabsorbed into the blood.

TUBULAR SECRETION: • substances are selectively secreted into the filtrate • secretion occurs in both the PROXIMAL & DISTAL TUBULES Secreted: penicillin, creatine, H+ ions, ammonia, K+, caffeine, ibuprofen metabolized products, excess water soluble vitamins (ex: vitamin C)

URINE COMPOSITON:  about 95% water  usually contains urea and uric acid (byproducts of nitrogen metabolism) electrolytes, amino acids, glucose (only if in excess) *”normal” urine sample does NOT contain glucose or amino acids

URINE ELIMINATION (“MICTURITION”) • urine drains out of the kidneys into the URETERS • URETERS convey urine to the URINARY BLADDER via peristaltic waves • urine is stored in the URINARY BLADDER until the “micturition reflex” is triggered:

MICTURITION (URINATION) REFLEX: bladder is filled and stretched  stretch receptors stimulated 2) micturition reflex center in spinal cord sends motor impulses  muscle in bladder wall 3) as bladder fills, internal pressure increases, forcing the INTERNAL URETHRAL SPHINCTER open

MICTURITION (URINATION) REFLEX: 4) a second reflex relaxes the EXTERNAL URETHRAL SPHINCTER (can stay contracted under voluntary control…if you need to “hold it”!) 5) nerve centers in the brain and brainstem aid control of urination

CLICKER QUESTION: Which process is occurring here? Descending limb of loop Peritubular capillary CLICKER QUESTION: Which process is occurring here? Filtration Reabsorption Secretion Elimination

CLICKER QUESTION: Which of the following substances are NOT reabsorbed? NaCl Metabolized ibuprofen Glucose Water They are all reabsorbed.

CLICKER QUESTION: Which of the following substances would never normally be secreted? Glucose Excess fat soluble vitamins C and D

CLICKER QUESTION: The highest percentage of urine is made up of ____. Urea Water NaCL (salt) proteins

*Alcohol & caffeine interfere with the release of ADH.  **The hormone ADH increases the permeability of the distal convoluted tubule and the collecting duct to water. If your blood is too concentrated and you need more water in your blood, ADH is released, and more water leaves the filtrate & reenters the blood. This lowers the concentration of your blood. *Alcohol & caffeine interfere with the release of ADH. 