urine formation overview

Question 1

renal function big picture

Answer 1

Control volume and composition of body fluids  Maintains environment cells need for proper function
 Rid body of waste materials produced by body or ingested
 Filter the plasma  Reabsorb much of the filtrate (return to blood)  Secrete some substances (Remove from blood)
 Substances that are secreted or not reabsorbed are excreted in the urine

Question 2

Renal Function – More Specific

Answer 2

Excretion of metabolic waste products and foreign chemicals
 Regulation of water and electrolyte balances*  Regulation of body fluid osmolality and electrolyte*
concentrations  Regulation of blood pressure*  Regulation of acid-base balance  Secretion, metabolism, and excretion of hormones  Gluconeogenesis

Question 3

metabolic waste removal

Answer 3

Primary way metabolic waste products are removed from the body
 Urea: amino acid metabolism  Creatinine: from muscle creatine
 Creatine used to create phosphocreatine which serves as energy source for production of ATP in muscle. Each day 1 to 2% of muscle creatine converted to creatinine.
 Uric acid: from nucleic acids  End products of hemoglobin break down (bilirubin)  Hormone metabolites
 Most toxins / foreign
 Pesticides / drugs / food additives

Question 4

acid base regulation

Answer 4

Kidneys work with lungs and body-buffer systems
 Lungs remove carbon dioxide
 Kidneys control hydrogen ion and bicarbonate concentration
 Kidneys only way to remove sulfuric and phosphoric acid
 Byproducts of protein metabolism

Question 5

Regulation Erythrocyte Production

Answer 5

 Kidneys secrete erythropoietin (almost all) – which stimulates red blood cell production
 Hypoxia major stimulus for production
 Patient’s with severe renal disease will develop severe anemia due to lack of erythropoietin production

Question 6

Glucose Synthesis

Answer 6

During prolonged fasting, new glucose is produced from amino acids and other items
 Significant quantities can be produced

Question 7

Glomerular Capillaries

Answer 7

High pressure (60 mmHg) produces high rate of filtratio

Question 8

Peritubular Capillaries

Answer 8

 Low pressure (13 mmHg) produces high rate fluid reabsorption

Question 9

Pelvic nerves provide primary supply

Answer 9

Sensory and motor fibers
 Sensory fibers from posterior urethra responsible for initiating micturition reflex
 Motor fibers are parasympathe

Question 10

Pudendal nerve

Answer 10

skeletal muscle fibers provide voluntary control of external sphincter

Question 11

Sympathetic control via

Answer 11

hypogastric nerves

 Control blood vessels

Question 12

Ureters well supplied with pain nerves – stimulated

Answer 12

when blocked ureters respond with intense reflex constriction which sends sympathetic stimulation back to kidneys to constrict renal arterioles [ureterorenal reflex]

Question 13

composition of urine does not change once

Answer 13

it leaves the collecting ducts

Question 14

Renal calyces act as

Answer 14

pacemaker for peristaltic contraction of smooth muscle forcing urine down into the renal pelvis, down the ureters into the bladderIncreased stretch of calyces increases peristaltic rate  Innervated by parasympathetic (enhances peristalsis) and
sympathetic (inhibits peristalsis) nerves

Question 15

Detrusor muscle prevents

Answer 15

backflow from bladder to ureters (especially during bladder contraction)
 Peristaltic waves down ureter increases pressure with ureter to open passage to bladder
 If ureter is not long enough to pass through wall of bladder, reflux will occur

Question 16

Pressure spikes – micturition contractions stimulated

Answer 16

stretch receptors in bladder wall

 Provides positive feedback to stretch receptors resulting in further increase in pressure

Question 17

Once micturition reflex is strong enough it stimulates inhibitor signals

Answer 17

to the external sphincter

Question 18

Urination occurs when inhibitor signals are

Answer 18

stronger than the voluntary constrictor signals being sent to external sphincter