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25 P A R T A The Urinary System.

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Presentation on theme: "25 P A R T A The Urinary System."— Presentation transcript:

1 25 P A R T A The Urinary System

2 Kidney Functions-water and salt balance
Next six slides are for renal physiology lab.

3 Kidney Functions Filter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine Regulate volume and chemical makeup of the blood Maintain the proper balance between water and salts, and acids and bases

4 Na+ Reabsorption Insert fig. 17.26 90% filtered Na+ reabsorbed in PCT.
In the absence of aldosterone, 80% of the remaining Na+ is reabsorbed in DCT. Final [Na+] controlled in CD by aldosterone. When aldosterone is secreted in maximal amounts, all Na+ in DCT is reabsorbed. Insert fig

5 Physical Characteristics of Urine
Color and transparency Clear, pale to deep yellow (due to urochrome) Concentrated urine has a deeper yellow color Drugs, vitamin supplements, and diet can change the color of urine Cloudy urine may indicate infection of the urinary tract

6 Physical Characteristics of Urine
Odor Fresh urine is slightly aromatic Standing urine develops an ammonia odor Some drugs and vegetables (asparagus) alter the usual odor

7 Physical Characteristics of Urine
Slightly acidic (pH 6) with a range of 4.5 to 8.0 Diet can alter pH Specific gravity Ranges from to 1.035 Is dependent on solute concentration

8 Chemical Composition of Urine
Urine is 95% water and 5% solutes Nitrogenous wastes: urea, uric acid, and creatinine Other normal solutes include: Sodium, potassium, phosphate, and sulfate ions Calcium, magnesium, and bicarbonate ions Abnormally high concentrations of any urinary constituents may indicate pathology

9 Kidney Functions Filter 200 liters of blood daily, allowing toxins, metabolic wastes, and excess ions to leave the body in urine Regulate volume and chemical makeup of the blood Maintain the proper balance between water and salts, and acids and bases

10 Other Renal Functions Gluconeogenesis during prolonged fasting Production of rennin to help regulate blood pressure and erythropoietin to stimulate RBC production Activation of vitamin D

11 Urinary System Organs Figure 25.1a

12 Internal Anatomy Figure 25.3b

13 The nerve supply is via the renal plexus
Blood and Nerve Supply Approximately one-fourth (1200 ml) of systemic cardiac output flows through the kidneys each minute Arterial flow into and venous flow out of the kidneys follow similar paths The nerve supply is via the renal plexus PLAY InterActive Physiology ®: Anatomy Review, page 5

14 Nephron Anatomy Figure 25.5a

15 Renal Tubule Figure 25.4b

16 Cortical nephrons – 85% of nephrons; located in the cortex
Juxtamedullary nephrons: Are located at the cortex-medulla junction Have loops of Henle that deeply invade the medulla Have extensive thin segments Are involved in the production of concentrated urine

17 Vascular Resistance in Microcirculation
Afferent and efferent arterioles offer high resistance to blood flow Blood pressure declines from 95mm Hg in renal arteries to 8 mm Hg in renal veins

18 Vascular Resistance in Microcirculation
Resistance in afferent arterioles: Protects glomeruli from fluctuations in systemic blood pressure Resistance in efferent arterioles: Reinforces high glomerular pressure Reduces hydrostatic pressure in peritubular capillaries

19 Juxtaglomerular Apparatus (JGA)
Figure 25.6

20 Juxtaglomerular Apparatus (JGA)
Where the distal tubule lies against the afferent (sometimes efferent) arteriole Arteriole walls have juxtaglomerular (JG) cells Enlarged, smooth muscle cells Have secretory granules containing renin Act as mechanoreceptors

21 Juxtaglomerular Apparatus (JGA)
Macula densa Tall, closely packed distal tubule cells Lie adjacent to JG cells Function as chemoreceptors or osmoreceptors Mesanglial cells: Have phagocytic and contractile properties Influence capillary filtration PLAY InterActive Physiology ®: Anatomy Review: page 16

22 It is composed of three layers
Filtration Membrane Filter that lies between the blood and the interior of the glomerular capsule It is composed of three layers Fenestrated endothelium of the glomerular capillaries Visceral membrane of the glomerular capsule (podocytes) Basement membrane composed of fused basal laminae of the other layers

23 Filtration Membrane Figure 25.7a

24 Filtration Membrane PLAY
InterActive Physiology ®: Anatomy Review, page 11 Figure 25.7c

25 Mechanisms of Urine Formation
The kidneys filter the body’s entire plasma volume 60 times each day The filtrate: Contains all plasma components except protein Loses water, nutrients, and essential ions to become urine The urine contains metabolic wastes and unneeded substances

26 Mechanisms of Urine Formation
Urine formation and adjustment of blood composition involves three major processes Glomerular filtration Tubular reabsorption Secretion Figure 25.8

27 Glomerular Filtration
Principles of fluid dynamics that account for tissue fluid in all capillary beds apply to the glomerulus as well The glomerulus is more efficient than other capillary beds because: Its filtration membrane is more permeable Glomerular blood pressure is higher It has a higher net filtration pressure Plasma proteins are not filtered and are used to maintain oncotic pressure of the blood

28 Net Filtration Pressure (NFP)
The pressure responsible for filtrate formation NFP equals the glomerular hydrostatic pressure (HPg) minus the oncotic pressure of glomerular blood (OPg) combined with the capsular hydrostatic pressure (HPc) NFP = HPg – (OPg + HPc)

29 Glomerular Filtration Rate (GFR)
The total amount of filtrate formed per minute by the kidneys Factors governing filtration rate at the capillary bed are: Total surface area available for filtration Filtration membrane permeability Net filtration pressure

30 Glomerular Filtration Rate (GFR)
GFR is directly proportional to the NFP Changes in GFR normally result from changes in glomerular blood pressure

31 Glomerular Filtration Rate (GFR)
Figure 25.9

32 Regulation of Glomerular Filtration
If the GFR is too high: Needed substances cannot be reabsorbed quickly enough and are lost in the urine If the GFR is too low: Everything is reabsorbed, including wastes that are normally disposed of

33 Regulation of Glomerular Filtration
Three mechanisms control the GFR Renal autoregulation (intrinsic system) Neural controls Hormonal mechanism (the renin-angiotensin system)

34 Autoregulation entails two types of control
Intrinsic Controls Under normal conditions, renal autoregulation maintains a nearly constant glomerular filtration rate Autoregulation entails two types of control Myogenic – responds to changes in pressure in the renal blood vessels Flow-dependent tubuloglomerular feedback – senses changes in the juxtaglomerular apparatus

35 When the sympathetic nervous system is at rest:
Extrinsic Controls When the sympathetic nervous system is at rest: Renal blood vessels are maximally dilated Autoregulation mechanisms prevail

36 Sympathetic Regulation of GFR
Stimulates vasoconstriction of afferent arterioles. Preserves blood volume to muscles and heart. Cardiovascular shock: Decreases glomerular capillary hydrostatic pressure. Decreases urine output (UO). Insert fig

37 Extrinsic Controls Under stress:
Norepinephrine is released by the sympathetic nervous system Epinephrine is released by the adrenal medulla Afferent arterioles constrict and filtration is inhibited The sympathetic nervous system also stimulates the renin-angiotensin mechanism PLAY InterActive Physiology ®: Glomerular Filtration, pages 3–14

38 Renin-Angiotensin Mechanism
Is triggered when the JG cells release renin Renin acts on angiotensinogen to release angiotensin I Angiotensin I is converted to angiotensin II Angiotensin II: Causes mean arterial pressure to rise Stimulates the adrenal cortex to release aldosterone As a result, both systemic and glomerular hydrostatic pressure rise

39 Renin release is triggered by:
Reduced stretch of the granular JG cells Stimulation of the JG cells by activated macula densa cells Direct stimulation of the JG cells via 1-adrenergic receptors by renal nerves Angiotensin II

40 Other Factors Affecting Glomerular Filtration
Prostaglandins (PGE2 and PGI2) Vasodilators produced in response to sympathetic stimulation and angiotensin II Are thought to prevent renal damage when peripheral resistance is increased Nitric oxide – vasodilator produced by the vascular endothelium Adenosine – vasoconstrictor of renal vasculature Endothelin – a powerful vasoconstrictor secreted by tubule cells

41 Transported substances move through three membranes
Tubular Reabsorption A transepithelial process whereby most tubule contents are returned to the blood Transported substances move through three membranes Luminal and basolateral membranes of tubule cells Endothelium of peritubular capillaries Only Ca2+, Mg2+, K+, and some Na+ are reabsorbed via paracellular pathways

42 Tubular Reabsorption All organic nutrients are reabsorbed Water and ion reabsorption is hormonally controlled Reabsorption may be an active (requiring ATP) or passive process

43 Sodium Reabsorption: Primary Active Transport
Sodium reabsorption is almost always by active transport Na+ enters the tubule cells at the luminal membrane Is actively transported out of the tubules by a Na+-K+ ATPase pump

44 Sodium Reabsorption: Primary Active Transport
From there it moves to peritubular capillaries due to: Low hydrostatic pressure High osmotic pressure of the blood Na+ reabsorption provides the energy and the means for reabsorbing most other solutes

45 Routes of Water and Solute Reabsorption
Figure 25.11

46 Reabsorption by PCT Cells
Active pumping of Na+ drives reabsorption of: Water by osmosis, aided by water-filled pores called aquaporins Cations and fat-soluble substances by diffusion Organic nutrients and selected cations by secondary active transport

47 Reabsorption by PCT Cells
PLAY InterActive Physiology ®: Early Filtrate Processing, pages 3–15 Figure 25.12

48 Nonreabsorbed Substances
A transport maximum (Tm): Reflects the number of carriers in the renal tubules available Exists for nearly every substance that is actively reabsorbed When the carriers are saturated, excess of that substance is excreted

49 Nonreabsorbed Substances
Substances are not reabsorbed if they: Lack carriers Are not lipid soluble Are too large to pass through membrane pores Urea, creatinine, and uric acid are the most important nonreabsorbed substances

50 Absorptive Capabilities of Renal Tubules and Collecting Ducts
Substances reabsorbed in PCT include: Sodium, all nutrients, cations, anions, and water Urea and lipid-soluble solutes Small proteins Loop of Henle reabsorbs: H2O, Na+, Cl, K+ in the descending limb Ca2+, Mg2+, and Na+ in the ascending limb

51 Absorptive Capabilities of Renal Tubules and Collecting Ducts
DCT absorbs: Ca2+, Na+, H+, K+, and water HCO3 and Cl Collecting duct absorbs: Water and urea

52 Na+ Entry into Tubule Cells
Passive entry: Na+-K+ ATPase pump In the PCT: facilitated diffusion using symport and antiport carriers In the ascending loop of Henle: facilitated diffusion via Na+-K+-2Cl symport system In the DCT: Na+-Cl– symporter In collecting tubules: diffusion through membrane pores

53 Atrial Natriuretic Peptide Activity
ANP reduces blood Na+ which: Decreases blood volume Lowers blood pressure ANP lowers blood Na+ by: Acting directly on medullary ducts to inhibit Na+ reabsorption Counteracting the effects of angiotensin II Indirectly stimulating an increase in GFR reducing water reabsorption

54 Tubular secretion is important for:
Essentially reabsorption in reverse, where substances move from peritubular capillaries or tubule cells into filtrate Tubular secretion is important for: Disposing of substances not already in the filtrate Eliminating undesirable substances such as urea and uric acid Ridding the body of excess potassium ions Controlling blood pH

55 Regulation of Urine Concentration and Volume
Osmolality The number of solute particles dissolved in 1L of water Reflects the solution’s ability to cause osmosis Body fluids are measured in milliosmols (mOsm) The kidneys keep the solute load of body fluids constant at about 300 mOsm This is accomplished by the countercurrent mechanism

56 Countercurrent Mechanism
Interaction between the flow of filtrate through the loop of Henle (countercurrent multiplier) and the flow of blood through the vasa recta blood vessels (countercurrent exchanger) The solute concentration in the loop of Henle ranges from 300 mOsm to 1200 mOsm Dissipation of the medullary osmotic gradient is prevented because the blood in the vasa recta equilibrates with the interstitial fluid

57 Loop of Henle: Countercurrent Mechanism
Figure 25.14

58 Osmotic Gradient in the Renal Medulla
Figure 25.13

59 Loop of Henle: Countercurrent Multiplier
The descending loop of Henle: Is relatively impermeable to solutes Is permeable to water The ascending loop of Henle: Is permeable to solutes Is impermeable to water Collecting ducts in the deep medullary regions are permeable to urea

60 Loop of Henle: Countercurrent Exchanger
The vasa recta is a countercurrent exchanger that: Maintains the osmotic gradient Delivers blood to the cells in the area PLAY InterActive Physiology ®: Early Filtrate Processing, pages 16–21

61 Loop of Henle: Countercurrent Mechanism
Figure 25.14

62 Formation of Dilute Urine
Filtrate is diluted in the ascending loop of Henle Dilute urine is created by allowing this filtrate to continue into the renal pelvis This will happen as long as antidiuretic hormone (ADH) is not being secreted

63 Formation of Dilute Urine
Collecting ducts remain impermeable to water; no further water reabsorption occurs Sodium and selected ions can be removed by active and passive mechanisms Urine osmolality can be as low as 50 mOsm (one-sixth that of plasma)

64 Formation of Concentrated Urine
Antidiuretic hormone (ADH) inhibits diuresis This equalizes the osmolality of the filtrate and the interstitial fluid In the presence of ADH, 99% of the water in filtrate is reabsorbed

65 Formation of Concentrated Urine
ADH-dependent water reabsorption is called facultative water reabsorption ADH is the signal to produce concentrated urine The kidneys’ ability to respond depends upon the high medullary osmotic gradient PLAY InterActive Physiology ®: Late Filtrate Processing, pages 3–12

66 Formation of Dilute and Concentrated Urine
Figure 25.15a, b

67 Summary of Nephron Function
Figure 25.16

68 Chemicals that enhance the urinary output include:
Diuretics Chemicals that enhance the urinary output include: Any substance not reabsorbed Substances that exceed the ability of the renal tubules to reabsorb it Substances that inhibit Na+ reabsorption

69 Osmotic diuretics include:
High glucose levels – carries water out with the glucose Alcohol – inhibits the release of ADH Caffeine and most diuretic drugs – inhibit sodium ion reabsorption Lasix and Diuril – inhibit Na+-associated symporters


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