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

Answer 24

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)

Answer 26

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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)

Answer 32

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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

Answer 35

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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