Chapter 26: The Urinary System

1
Chapter 26 The Urinary System
2
An Introduction to the Urinary System
Figure 261
3
3 Functions of the Urinary System

• Excretion
• removal of organic wastes from body fluids
• Elimination
• discharge of waste products
• Homeostatic regulation
• of blood plasma volume and solute concentration

4
Kidneys

• Organs that excrete urine

Urinary Tract

• Organs that eliminate urine
• ureters (paired tubes)
• urinary bladder (muscular sac)
• urethra (exit tube)

Urination or Micturition

• Process of eliminating urine
• Contraction of muscular urinary bladder forces
  urine through urethra, and out of body

5
5 Homeostatic Functions of Urinary System

• Regulate blood volume and blood pressure
• by adjusting volume of water lost in urine
• releasing erythropoietin (increase RBC
  production) and renin (regulates blood pressure)

• Regulate plasma ion concentrations
• sodium, potassium, and chloride ions (by
  controlling quantities lost in urine)
• calcium ion levels (through synthesis of
  calcitriol)

• Help stabilize blood pH
• by controlling loss of hydrogen ions and
  bicarbonate ions in urine

6

• Conserve valuable nutrients
• by preventing excretion while excreting organic
  waste products

1. Assist liver to detoxify poisons

7
The Position of the Kidneys

• Are located either side of vertebral column
• left kidney lies superior to right kidney
• superior surface capped by adrenal gland

• Position is maintained by
• overlying peritoneum
• contact with adjacent visceral organs
• supporting connective tissues

Figure 262
8
Typical Adult Kidney

• Is about 10 cm long, 5.5 cm wide, and 3 cm thick
• Weighs about 150 g

9
Hilum

• Point of entry for renal artery and renal nerves
• Point of exit for renal vein and ureter

10
Renal Sinus

• Internal cavity within kidney
• Lined by fibrous renal capsule

11
Renal Capsule

• Bound to outer surfaces of structures in renal
  sinus
• Stabilizes positions of ureter, renal blood
  vessels, and nerves

12
Renal Cortex

• Superficial portion of kidney in contact with
  renal capsule
• Reddish brown and granular

13
Renal Lobe

• Consists of
• renal pyramid
• overlying area of renal cortex
• adjacent tissues of renal columns
• Produces urine

14
Renal Papilla

• Ducts discharge urine into minor calyx
• cup-shaped drain

15
Major Calyx

• Formed by 4 or 5 minor calyces

16
Renal Pelvis

• Large, funnel-shaped chamber
• Consists of 2 or 3 major calyces
• Fills most of renal sinus
• Connected to ureter, which drains kidney

17
Functional Anatomy of Nephron Collecting System
Figure 266
18
Nephron

• Consists of renal tubule and renal corpuscle
• Microscopic, tubular structures in cortex of each
  renal lobe
• Where urine production begins

19
Renal Tubule

• Long tubular passageway
• Begins at renal corpuscle

Renal Corpuscle

• Spherical structure consisting of
• Bowmans capsule
• cup-shaped chamber
• capillary network (glomerulus)

20
Filtration

• Occurs in renal corpuscle
• Blood pressure
• forces water and dissolved solutes out of
  glomerular capillaries into capsular space
• produces protein-free solution (filtrate) similar
  to blood plasma

21
3 Functions of Renal Tubule

1. Reabsorb useful organic nutrients that enter
   filtrate
2. Reabsorb more than 90 of water in filtrate
3. Secrete waste products that failed to enter renal
   corpuscle through filtration at glomerulus

22
Cortical and Juxtamedullary Nephrons
Figure 267
23
Cortical Nephrons (1 of 2 types)

• 85 of all nephrons
• Located mostly within superficial cortex of kidney

• Loop of Henle is relatively short
• Efferent arteriole delivers blood to a network of
  peritubular capillaries
• which surround entire renal tubule

24
The Renal Corpuscle

• Each renal corpuscle
• is 150250 µm in diameter
• includes Bowmans capsule and glomerulus

25
Filtration

• Blood pressure
• forces water and small solutes across membrane
  into capsular space
• Larger solutes, such as plasma proteins, are
  excluded

Filtration at Renal Corpuscle

• Is passive
• Solutes enter capsular space
• metabolic wastes and excess ions
• glucose, free fatty acids, amino acids, and
  vitamins

26
Reabsorption

• Useful materials are recaptured before filtrate
  leaves kidneys
• Reabsorption occurs in proximal convoluted tubule

27
The Thick Descending Limb

• Has functions similar to PCT
• pumps sodium chloride ions out of tubular fluid

• Ascending Limbs

• Of juxtamedullary nephrons in medulla
• create high solute conc. in peritubular fluid

• The Thin Segments

• Are freely permeable to water, not to solutes
• Water movement helps conc. tubular fluid

• The Thick Ascending Limb

• Ends at a sharp angle near the renal corpuscle -
  where DCT begins

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3 Processes of the DCT

• Active secretion of ions, acids, drugs, and
  toxins
• Selective reabsorption of sodium and calcium ions
  from tubular fluid
• Selective reabsorption of water
• concentrates tubular fluid

29

• Transports tubular fluid from nephron to renal
  pelvis
• Adjusts fluid composition
• Determines final osmotic concentration and volume
  of urine

30
Renal Physiology

• The goal of urine production
• is to maintain homeostasis
• by regulating volume and composition of blood
• including excretion of metabolic waste products
• Urea
• Due to breakdown of aa
• Creatinine
• Due to breakdown of creatinine kinase (important
  in muscle contraction)
• Uric acid
• Formed due to recycling of ATGCU

31
Organic Waste Products

• Are dissolved in bloodstream
• Are eliminated only while dissolved in urine
• Removal is accompanied by water loss
• Concentrated urine
• 12001400 milliosmols/L (4 times plasma
  concentration)

32
Differences between Solute Concentrations in
Urine and Plasma
Table 262
33
3 Basic Processes of Urine Formation

• FILTRATION
• Hydrostatic pressure forces water through
  membrane pores
• small solute molecules pass through pores
• larger solutes suspended materials are retained

• Occurs across capillary walls
• as water and dissolved materials are pushed into
  interstitial fluids

• In some sites (ie liver), pores are large
• plasma proteins can enter interstitial fluids

• At the renal corpuscle
• specialized mem. restricts all circulating
  proteins

34
2 3 Reabsorption and Secretion

• At the kidneys involve
• Diffusion passive molecular movement from an
  area of high conc to area of low conc
• Osmosis-movement of water across semi-perm mem
  from area of low conc of solute to higher con of
  solute
• channel-mediated diffusion- specific channel
  used, no energy, conc. dependent
• carrier-mediated transport next slide

35
The Transport Maximum (Tm)

• Concentration higher than transport maximum
• exceeds reabsorptive abilities of nephron
• some material will remain in the tubular fluid
  and appear in the urine

• Determines the renal threshold
• the plasma concentration at which
• a specific compound or ion begins to appear in
  urine

36
Renal Threshold for Glucose

• Is approximately 180 mg/dl
• If plasma glucose is greater than 180 mg/dl
• Tm of tubular cells is exceeded
• glucose appears in urine

Glycosuria

• Is the appearance of glucose in urine

37
Renal Threshold for Amino Acids

• Is lower for glucose (65 mg/dl)
• Amino acids commonly appear in urine
• after a protein-rich meal

Aminoaciduria

• Is the appearance of amino acids in urine

38
Aldosterone

• Is a hormone produced by adrenal cortex
• Reduces Na lost in urine

Hypokalemia

• Produced by prolonged aldosterone stimulation
• Dangerously reduces plasma concentration

Natriuretic Peptides

• Oppose secretion of aldosterone

39
Parathyroid Hormone and Calcitriol

• Circulating levels regulate reabsorption at the
  DCT

40
Acidosis

• Lactic acidosis
• develops after exhaustive muscle activity
• (bulging muscles can cut off blood supply)
• due to anaerobic respiration
• Ketoacidosis
• Lower blood pH, higher acid, due to presence of
  ketones
• develops in starvation or diabetes
• Body does not have suff. glucose/glycogen to
  sustain met activity
• Muscle loss can occur - dieting

41
Control of Blood pH

• By H removal and bicarbonate production at
  kidneys
• Is important to homeostasis

Alkalosis

• Abnormally high blood pH
• Can be caused by prolonged aldosterone
  stimulation
• which stimulates secretion

42
Response to Acidosis

• PCT and DCT deaminate amino acids
• ties up H
• yields ammonium ions (NH4) and HCO3(carbonic
  acid)

• Ammonium ions are pumped into tubular fluid
• Bicarbonate ions enter bloodstream

43
ADH antidiuretic hormone

• Hormone causes special water channels to appear
• Increases rate of osmotic water movement

• Higher levels of ADH increases
• number of water channels
• water permeability of DCT and collecting system

• No ADH, water is not reabsorbed
• All fluid reaching DCT is lost in urine producing
  large amounts of dilute urine

44
The Hypothalamus

• Continuously secretes low levels of ADH
• At normal ADH levels
• collecting system reabsorbs 16,800 ml fluid/ day
  (9.3 of filtrate)

• A healthy adult produces
• 1200 ml urine per day (0.6 of filtrate)

45
Diuretics

• Are drugs that promote water loss in urine
  (diuresis)
• Diuretic therapy reduces
• blood volume
• blood pressure
• extracellular fluid volume

46
The Composition of Urine

• Results from filtration, absorption, and
  secretion activities of nephrons
• Some compounds (such as urea) are neither
  actively excreted nor reabsorbed along nephrons

• Organic nutrients are completely reabsorbed
• other compounds missed by filtration process
  (e.g., creatine)

47

• The Concentration of components
• in a urine sample depends on osmotic movement of
  water

• Normal Urine
• Is a clear, sterile solution
• Yellow color (pigment urobilin) generated in
  kidneys from urobilinogens

48
A Summary of Renal Function
Figure 2616a
49
Step 1 Glomerulus

• Filtrate produced at renal corpuscle has the same
  composition as blood plasma
• without plasma proteins

50
Step 2 Proximal Convoluted Tubule (PCT)

• Active removal of ions and organic substrates
• produces osmotic water flow out of tubular fluid
• reduces volume of filtrate
• keeps solutions inside and outside tubule isotonic

51
Step 3 PCT and Descending Limb

• Water moves into peritubular fluids, leaving
  highly concentrated tubular fluid
• Reduction in volume occurs by obligatory water
  reabsorption

52
Step 4 Thick Ascending Limb

• Tubular cells actively transport Na and Cl out
  of tubule
• Urea becomes higher proportion of total osmotic
  concentration

53
Step 5 DCT and Collecting Ducts

• Final adjustments in composition of tubular fluid
  
• Osmotic concentration is adjusted through active
  transport (reabsorption or secretion)

54
Step 6 DCT and Collecting Ducts

• Final adjustments in volume and osmotic
  concentration of tubular fluid
• Exposure to ADH determines final urine
  concentration

55
Step 7 Vasa Recta

• Absorbs solutes and water reabsorbed by loop of
  Henle and the ducts
• Maintains concentration gradient of medulla

56
Urine Transport, Storage, and Elimination

• Takes place in the urinary tract
• ureters
• urinary bladder
• urethra

57
Organs for the Conduction and Storage of Urine
Figure 2618a
58
Organs for the Conduction and Storage of Urine
Figure 2618b
59
Wall of the Urinary Bladder

• Contains mucosa, submucosa, and muscularis
  layers
• form powerful detrusor muscle of urinary bladder
• contraction compresses urinary bladder and expels
  urine

60
The Urethra

• Extends from neck of urinary bladder
• To the exterior of the body

The Male Urethra

• Extends from neck of urinary bladder
• To tip of penis (1820 cm)

61
The Female Urethra

• Is very short (35 cm)
• Extends from bladder to vestibule
• External urethral orifice is near anterior wall
  of vagina

62
The External Urethral Sphincter

• In both sexes
• is a circular band of skeletal muscle
• where urethra passes through urogenital diaphragm
• Acts as a valve
• Is under voluntary control
• via perineal branch of pudendal nerve
• Has resting muscle tone
• Voluntarily relaxation permits micturition

63
How is urination regulated voluntarily and
involuntarily and what is the micturition reflex?
64
The Micturition Reflex

• Coordinates the process of urination

• As the bladder fills with urine
• stretch receptors in urinary bladder (gt500 ml)
• stimulate pelvic nerve
• stimulus travels from pelvic nerves
• stimulate ganglionic neurons in wall of bladder
• postganglionic neuron in intramural ganglion
• stimulates detruscor muscle contraction
• interneuron relays sensation to thalamus and
  deliver sensation to cerebral cortex
• voluntary relaxation of external thus internal
  urethral sphincter

65
Infants

• Lack voluntary control over urination
• Corticospinal connections are not established

Incontinence-Is the inability to control
urination voluntarily
66
Age-Related Changes in Urinary System

• Decline in number of functional nephrons
• Reduced sensitivity to ADH
• Problems with micturition reflex

67
3 Micturition Reflex Problems

• Sphincter muscles lose tone
• leading to incontinence

• Control of micturition can be lost due to
• a stroke
• Alzheimers disease
• CNS problems affecting cerebral cortex or
  hypothalamus
• In males, urinary retention may develop if
  enlarged prostate gland compresses the urethra
  and restricts urine flow