Urinary System

Question 1

Urinary system

Answer 1

• Maintain volume and composition of
  body fluids within normal limits
  > Osmoregulation
• Rid the body of waste products of cellular
  metabolism
• “Excretory system”
  *Close association with the reproductive
  system
• “Urogenital/urinogenital system”
• “Renal system” (renalis = of the kidneys)

Question 2

Learning Outcomes

Answer 2

Question 3

• Functions:

Answer 3

• Homeostasis
  > Water balance
• Electrolyte balance
• Removal of nitrogenous wastes
  > Removal of toxins
  > Blood pH balance
• maintains blood pH = 7.4
• Blood pressure regulation (renin)
• Red blood cell production (erythropoietin)

Answer 3

Question 4

Osmoregulation

Answer 4

All animals balance the gain & loss of water & dissolved solutes
* Nat, Cli, K+, Ca2+, HCO;

WATER GAIN
* Food
> Drink
* Metabolic water

WATER LOSS
* Urinating
* Defecating
* Evaporation
* Breathing
* Sweating

Question 5

The kidneys

Answer 5

• Play a major role in conserving
  water
• Regulate the osmotic pressure of blood.
• When fluid intake is high, the kidneys excrete dilute urine, excreting water, while conserving salts.
  > When fluid intake is low, the kidneys conserve water by forming
  concentrated urine.
• Can concentrate urine to ~ 4 x blood osmotic concentration.
• Enables excretion of wastes with minimal water loss.

Question 6

Excretion of niotrogenous waste

Answer 6

AMMONIA (NH3)
* Too toxic to be stored in the body
* Does not diffuse readily into the air
* Highly soluble in water
* Diffuses rapidly across cell membranes
* If an animal is surrounded by water, NH3 readily diffuses out of its cells.
* Must be transported & excreted in large volumes of very dilute solutions
UREA
* Highly soluble in water.
* 100,000 times less toxic than NH3
* Can be stored in a concentrated solution
* Water required for disposal
URIC ACID
: Relai ly pontonilecule
* Largely insoluble in water
* Excreting uric acid minimises water loss
* More energy required to excrete uric acid
* Energy cost balanced by savings in body water

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Question 11

Renal blood blood vessels

Answer 11

• Each kidney is supplied by a renal artery branching off the aorta
• Blood leaves the kidney via the renal vein and drains into the inferior vena cava
• Kidneys comprise <1% of body weight
• Receive 20 - 25% of total cardiac output
• Human blood volume ~ 5L
• 1,100-2,000L pass through the capillaries in our kidneys / day.
• Kidneys extract ~ 180 L of fluid (filtrate) / day
• If all the filtrate was excreted as urine → lose vital nutrients & dehydrate.
• Kidneys refine the filtrate, concentrating the urea and returning most of the water
  and solutes to the blood.
• 1.5 L of urine.

Question 11

Ureters

Answer 11

Question 12

Ureters

Answer 12

Question 12

Urinary Bladder

Answer 12

BLADDER
* Muscular sac located on floor of pelvic
cavity
* Capacity = 500 mL, (max 700 - 800 mL)
Muscularis (muscle wall)
: Nlae prosemeot mascle

mucosa

• Lined with transitional epithelium
• highly distensible
  As the bladder fills
  > it expands superiorly
  > rugae flatten
• epithelium thins from 5 - 6 layers to 2 or 3

Answer 12

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Question 14

Neural Control of Micturition

Answer 14

MICTURITION (the act of urinating)
* Bladder filling
* Stretch receptors in bladder wall
> Signals travel to the sacral spinal
cord
* Motor nerves contract the
muscle of bladder
* & relax internal urethral
sphincter
> Emptying of bladder

Answer 15

VOLUNTARY CONTROL
Input from stretch receptors travels to brain
If timely to urinate:
> Motor signals to muscle of the bladder to contract
* Relaxation of internal urethral sphincter.
Motor signals from the brain control the external urethral sphincter.

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Answer 18

Bowman's capsule: * Parietal (outer) layer = simple squamous epithelium * Visceral (inner) = podocytes (wrap around the capillaries of the glomerulus) * Capsular space separates the parietal & visceral layers * Vascular pole = where the afferent arteriole enters the corpuscle and the efferent arteriole leaves * Urinary pole = the opposite side of the corpuscle where the renal tubule begins Note the difference in diameter of the afferent arteriole and the efferent arteriole

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Question 23

Glomerular FmeBon Rate （GFR）

Answer 23

GLOMERULAR FILTRATION RATE: * Volume of filtrate formed by the two kidneys combined /day * GFR ~ 150 L/day (female) - 180 L/day (male) * ~ 30- 35 x volume of blood in the body!! * 99% of filtrate is reabsorbed * 1 - 2 L urine excreted per day If GFR too high > Fluid flows through renal tubules too rapidly to reabsorb enough water and solutes * Urine output rises * Leads to dehydration and electrolyte depletion If GFR too low * Wastes reabsorbed > Azotemia (high levels of nitrogen-containing compounds in the blood) CONTROL OF GFR: Autoregulation: : Mabresa sadius off espi cha es in systemic arterial blood filow Sympathetic nervous system & adrenaline: exercise or circulatory shock * Constriction of afferent arterioles reduces GFR and urine output. * Redirects blood from the kidneys to the heart, brain, and skeletal muscles

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Question 24

Renai tubules

Answer 24

Question 25

Convoluted Tubule Renal Cortex (PCT)

Answer 25

Filtrate passes first into the PCT * Located in the cortex * Great length * Surrounded by peritubular capillaries * Lined with simple cuboidal epithelia with prominent microvilli for absorption * Abundant mitochondria provide ATP for active transport Loop oT Renal Medulla * Reabsorbs ~ 65% of glomerular filtrate, returning water and solutes back into the blood. * Also removes some substances from the blood and secretes them into the tubular fluid for disposal in urine.

Question 25

Tubular reabsorption

Answer 25

Question 26

Transport maximum (renal trheshold)

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Answer 31

Vasa recta Vasa recta capillaries : * enter the medulla adjacent to the ascending limb of the loop of Henle * leave the medulla adjacent to the descending limb of the loop of Henle * blood flows in the opposite direction to the flow of filtrate. As blood flows downward into the medulla * water diffuses out of the capillaries * salt diffuses in to the capillaries As the blood flows back up to the cortex * salt diffuses out of the capillaries * water diffuses in to the capillaries * Maintains the concentration gradient (cortex to medulla)

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Question 34

Urea

Answer 34

* Glomerular filtration constantly adds urea to the filtrate * Thick segment of ascending limb and DCT are impermeable to urea > 1 [ureal filtrate in DCT COLLECTING DUCT (medulla) * permeable to urea > Urea leaks out * I concentration gradient in the interstitial fluid of medulla * Some urea enters the descending limb of the loop & the lower portion of the ascending limb > Urea travels back through the loop back to the collecting duct. > Constant recycling of urea maintains the high osmolarity of the deep medulla

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Answer 36

The varying ability of different mammals to form a concentrated urine correlates closely with length of the loops of Henle. 1 depth of medulla * 1 length of loops of Henle * 1 concentration gradient of medulla > 1 water reabsorption * 1 [urine] Aquatic mammals * short loops of Henle * Beavers can concentrate urine ~ 2 x [plasmal Humans * relatively longer loops of Henle * can concentrate urine ~ 4 x [plasma] Desert mammals * Very long loops of Henle * Camels: urine ~ 8 x [plasma] * Australian hopping mouse: urine ~ 22 x[plasma]

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