urinary system i kidneys and urine formation l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Urinary System I: Kidneys and Urine Formation PowerPoint Presentation
Download Presentation
Urinary System I: Kidneys and Urine Formation

Loading in 2 Seconds...

play fullscreen
1 / 32

Urinary System I: Kidneys and Urine Formation - PowerPoint PPT Presentation


  • 864 Views
  • Uploaded on

Urinary System I: Kidneys and Urine Formation. Functions of the Urinary System Organs of the Urinary System The Kidney Coverings and Regions Blood Flow Nephrons: Glomeruli and Renal Tubules Urine Formation Urinalysis Ureters, Bladder, and Urethra.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Urinary System I: Kidneys and Urine Formation' - Ava


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
urinary system i kidneys and urine formation
Urinary System I: Kidneys and Urine Formation
  • Functions of the Urinary System
  • Organs of the Urinary System
  • The Kidney
    • Coverings and Regions
    • Blood Flow
    • Nephrons: Glomeruli and Renal Tubules
    • Urine Formation
  • Urinalysis
  • Ureters, Bladder, and Urethra
functions of the urinary system blood filtration
Functions of the Urinary System: Blood Filtration
  • Elimination of waste products
    • Nitrogenous wastes (amino groups from amino acids)
    • Toxins
    • Drugs
  • Regulate aspects of homeostasis
    • Water balance
    • Electrolytes
    • Acid-base balance in the blood
    • Blood pressure
    • Red blood cell production (erythropoietin)
    • Activation of vitamin D
organs of the urinary system
Organs of the Urinary system
  • Kidneys
    • Against the dorsal body wall
    • At the level of T12 to L3
    • The right kidney is slightly lower than the left
    • Retroperitoneal (posterior to and outside of parietal peritoneum)
    • Attached to ureters, renal blood vessels, and nerves at renal hilus
    • Covered with adipose
  • Ureters
  • Urinary bladder
  • Urethra
coverings of the kidneys
Coverings of the Kidneys
  • Renal capsule
    • Surrounds each kidney
  • Adipose capsule
  • Fascia layer/adventitia (connective tissue) substitutes for serosae outside of peritoneal cavity
    • Surrounds the kidney
    • Provides protection to the kidney
    • Helps keep the kidney in its correct location
regions of the kidney
Regions of the Kidney
  • Kidney Regions
    • Renal cortex – outer region
    • Renal medulla – inside the cortex
    • Renal pelvis – inner collecting tube
  • Kidney Structures
    • Medullary pyramids – triangular regions of tissue in the medulla
    • Renal columns – extensions of cortex-like material inward
    • Calyces – cup-shaped structures that funnel urine towards the renal pelvis
blood flow in the kidneys
Blood Flow in the Kidneys

Glomerular capillaries

Peritubular capillaries

Unique: Incoming vessels enter as an arteriole, narrow into a capillary bedin the glomerulus, leave in an arteriole, and then break into the peritubular capillary bed before leaving as venus blood.

glomerulus and bowman s capsule
Glomerulus and Bowman’s Capsule
  • A specialized capillary bed
  • Attached to narrow arterioles on both sides (maintains high pressure in capsule)
  • Fenestrated glomerular endothelium
    • Allows filtrate to pass from plasma into the glomerular capsule
  • Layers of Bowman’s capsule
    • Parietal layer: simple squamous epithelium
    • Visceral layer: branching epithelial podocytes
      • Extensions terminate in foot processes that cling to basement membrane
      • Filtration slits allow filtrate to pass into the capsular space

Filtration

slits

Capsular space

renal tubule
Renal Tubule
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule
  • Collecting duct

Figure 15.3b

two types of nephrons
Two Types of Nephrons
  • Cortical nephrons
    • Located entirely in the cortex
    • Includes most nephrons (> 85%)
  • Juxtamedullary nephrons
    • Found at the boundary of the cortex and medulla
    • Important in the production of concentrated urine

Cortex

Medulla

juxtaglomerular apparatus jga
Juxtaglomerular Apparatus (JGA)
  • Macula densa: sensors of the filtrate
    • Tall, closely packed cells lining the ascending Lof H or PCT
    • Water and NaCl concentration detected by osmo -and chemoreceptors
    • If ↓filtrate water volume, then stimulation of renin release by JG, ↑blood water volume , ↑blood pressure .
    • If ↓NaCl in PCT filtrate; ↑dilation of afferent arteriole  ↓reduce filtration rate, ↑Na + stays in filtrate by tubules, ↑blood Na+ ,
    • If ↑NaCl in PCT filtrate; then ↑renin release by JG, ↑blood water volume , ↑blood pressure .
  • Granular cells (juxtaglomerular, or JG cells): pressure sensors of incoming blood and storage of renin
    • Enlarged, smooth muscle cells of blood afferent arteriole
    • Secretory granules release renin when epi & NE in blood
    • Act as mechanoreceptors that sense low blood pressure
    • Responds to stimuli by macula densa
  • Extraglomerular mesangial cells
peritubular capillaries
Peritubular Capillaries
  • Arise from efferent arteriole of the glomerulus
  • Cling to adjacent renal tubules in cortex
  • Low-pressure, porous capillaries adapted for absorption
  • Reabsorb (reclaim) some substances from collecting tubes
  • Empty into venules
  • Vasa recta are the long vessels parallel to long loops of Henle

Filtrate

efferent afferent arterioles

Water is reclaimed from filtrate into venous circulation via peritubular capillaries

slide13

Epithelia in the Tubules Are Designed for Filtration and Absorption

Glomerular capsule: parietal layer

Renal cortex

Basement

membrane

Renal medulla

Renal corpuscle

Podocyte

• Glomerular capsule

Renal pelvis

Fenestrated

endothelium

of the glomerulus

• Glomerulus

Distal

convoluted

tubule

Ureter

Glomerular capsule: visceral layer

Kidney

Microvilli

Mitochondria

Proximal

convoluted

tubule

Highly infolded plasma

membrane

Cortex

Proximal convoluted tubule cells

and thick ascending

L 0f H

Medulla

Thick segment

Distal convoluted tubule cells

Thin segment

Loop of Henle

• Descending limb

• Ascending limb

Collecting

duct

Loop of Henle (thin-segment) cells

Principal cell

Intercalated cell

Mostly cuboidal epithelium with modifications in membrane surfaces

Collecting duct cells

Figure 25.5

urine formation processes
Urine Formation Processes
  • A. Filtration
    • Nonselective passive process
    • Water and solutes smaller than proteins are forced through capillary walls, no cells - essentially plasma
    • Filtrate is collected in the glomerular capsule and leaves via the renal tubule
    • Blood pressure relatively high in glomerulus
    • Efficient filtration driven by hydrostatic pressure
  • B. Tubular Reabsorption
    • The peritubular capillaries reabsorb several materials: H2O, glucose, amino acids, ions
    • Some reabsorption is passive, most is active
    • Nitrogenous waste products not reabsorbed, nor excess water, urea, uric acid, or creatinine
    • Most reabsorption occurs in the proximal convoluted tubule
  • C. Tubular Secretion
    • Some materials pumped from the peritubular capillaries into the renal tubules: H+, K+, creatinine
    • Materials left in the renal tubule move toward the ureter
net filtration pressure nfp at the glomerulus
Net Filtration Pressure (NFP) at the Glomerulus

Afferent

arteriole

Glomerular

capsule

NFP = HPg – (OPg + HPc)

= (push outwards - back pressure inwards)

Glomerular (blood) hydrostatic pressure

(HPg = 55 mm Hg)

10

mm

Hg

Blood colloid osmotic pressure

(Opg = 30 mm Hg)

Net

filtration

pressure

Capsular hydrostatic pressure

(HPc = 15 mm Hg)

Figure 25.11

glomerular filtration rate
Glomerular Filtration Rate
  • Volume of filtrate formed per minute by the kidneys (120–125 ml/min)
  • Governed by (and directly proportional to)
    • Total surface area available for filtration
    • Filtration membrane permeability
    • Flow rate (GFR) is tightly controlled by two types of mechanisms
      • Intrinsic controls (renal autoregulation)
      • Extrinsic controls (nervous and endocrine regulation
intrinsic controls renal autoregulation of gfr
Intrinsic Controls (Renal Autoregulation) of GFR
  • Local action within the kidney
    • Myogenic mechanism
      •  BP  constriction of afferent arterioles
        • Helps maintain normal GFR
        • Protects glomeruli from damaging high BP
      •  BP  dilation of afferent arterioles
        • Helps maintain normal GFR
    • Tubuloglomerular feedback mechanism, which senses changes in the juxtaglomerular apparatus
      • Flow-dependent mechanism directed by the macula densa cells
      • If GFR increases, filtrate flow rate increases in the tubule
      • Filtrate NaCl concentration will be high because of insufficient time for reabsorption
      • Macula densa cells of the JGA respond to NaCl by releasing a vasoconstricting chemical that acts on the afferent arteriole  GFR
extrinsic controls of gfr
Extrinsic controls of GFR
  • Nervous and endocrine mechanisms that maintain blood pressure, but affect kidney function
  • Under normal conditions at rest
    • Renal blood vessels are dilated
    • Renal autoregulation mechanisms prevail
  • Under extreme stress
    • Norepinephrine is released by the sympathetic nervous system; epinephrine is released by the adrenal medulla
    • NE and Epi cause constriction of afferent arterioles, inhibiting filtration and triggering the release of renin from JGA cells leading to renin-angiotensin cascade
extrinsic controls renin angiotensin mechanism
Extrinsic Controls: Renin-Angiotensin Mechanism
  • Triggered when the granular cells of the JGA release renin

angiotensinogen (a plasma globulin)

renin

angiotensin I

angiotensin converting enzyme (ACE)

angiotensin II

effects of angiotensin ii
Effects of Angiotensin II
  • Constricts arteriolar smooth muscle, causing mean arterial pressure to rise (hypertensive)
  • Stimulates the reabsorption of Na+
    • Acts directly on the renal tubules
    • Triggers adrenal cortex to release aldosterone (hypertensive
  • Stimulates the hypothalamus to release ADH and activates the thirst center (increases hydration)
  • Constricts efferent arterioles, decreasing peritubular capillary hydrostatic pressure and increasing fluid reabsorption (saves water)
  • Causes glomerular mesangial cells to contract, decreasing the surface area available for filtration (saving water)
extrinsic controls renin angiotensin mechanism21
Extrinsic Controls: Renin-Angiotensin Mechanism
  • Triggers for renin release by granular cells
    • Reduced stretch of granular cells (MAP below 80 mm Hg)
    • Stimulation of the granular cells by activated macula densa cells
    • Direct stimulation of granular cells via 1-adrenergic receptors by renal nerves
slide22

SYSTEMIC BLOOD PRESSURE

(–)

Blood pressure in

afferent arterioles; GFR

Baroreceptors in

blood vessels of

systemic circulation

Granular cells of

juxtaglomerular

apparatus of kidney

GFR

Release

(+)

Stretch of smooth

muscle in walls of

afferent arterioles

Filtrate flow and

NaCl in ascending

limb of Henle’s loop

(+)

(+)

Renin

Sympathetic

nervous system

Catalyzes cascade

resulting in conversion

Targets

Vasodilation of

afferent arterioles

Angiotensinogen

Angiotensin II

(+)

(+)

(+)

Macula densa cells

of JG apparatus

of kidney

Adrenal cortex

Systemic arterioles

Releases

Vasoconstriction;

peripheral resistance

Aldosterone

Release of vasoactive

chemical inhibited

Targets

Kidney tubules

Vasodilation of

afferent arterioles

Na+ reabsorption;

water follows

(+)

Stimulates

(–)

Inhibits

Increase

Decrease

GFR

Blood volume

Systemic

blood pressure

Tubuloglomerular

mechanism of

autoregulation

Myogenic mechanism

of autoregulation

Hormonal (renin-angiotensin)

mechanism

Neural controls

Intrinsic mechanisms directly regulate GFR despite

moderate changes in blood pressure (between 80

and 180 mm Hg mean arterial pressure).

Extrinsic mechanisms indirectly regulate GFR

by maintaining systemic blood pressure, which

drives filtration in the kidneys.

Figure 25.12

urine formation processes23
Urine Formation Processes
  • A. Filtration
    • Nonselective passive process
    • Water and solutes smaller than proteins are forced through capillary walls, no cells - essentially plasma
    • Filtrate is collected in the glomerular capsule and leaves via the renal tubule
    • Blood pressure relatively high in glomerulus
    • Efficient filtration driven by hydrostatic pressure
  • B. Tubular Reabsorption
    • The peritubular capillaries reabsorb several materials: H2O, glucose, amino acids, ions
    • Some reabsorption is passive, most is active
    • Nitrogenous waste products not reabsorbed, nor excess water, urea, uric acid, or creatinine
    • Most reabsorption occurs in the proximal convoluted tubule
  • C. Tubular Secretion
    • Some materials pumped from the peritubular capillaries into the renal tubules: H+, K+, creatinine
    • Materials left in the renal tubule move toward the ureter
mechanism of urine formation
Mechanism of Urine Formation

Hormone regulated reabsorption of Ca2+ ( by PTH), water ( ADH) Na+ ( aldosterone and ANP)

Most reabsorption occurs here

  • In general:
  •  ADH
  • Concentrated urine
  • Water conservation

----------------

  •  Aldosterone (often triggered by  Angio-tensin II)
  • Dilute urine
  • Na+ conservation
  • Blood pressure

H2O

 Urea reabs. with  ADH

Reduces the volume and saltiness of the filtrate

Na+, K+ resabsorbed

countercurrent mechanism
Countercurrent Mechanism
  • Occurs when fluid flows in opposite directions in two adjacent segments of the same tube
    • E.g. Filtrate flow in the loop of Henle (countercurrent multiplier)
    • E.g. Blood flow in the vasa recta (countercurrent exchanger)
  • Role of countercurrent mechanisms
    • Establish and maintain an osmotic gradient
    • Allow the kidneys to vary urine concentration (but especially make dilute urine)
    • Allow for more efficient exchange of ions or gases
countercurrent multiplier loop of henle
Countercurrent Multiplier: Loop of Henle
  • Descending limb
    • Freely permeable to H2O, which passes out of the filtrate into the hyperosmotic medullary interstitial fluid
    • Filtrate osmolality increases to ~1200 mOsm
  • Ascending limb
    • Impermeable to H2O
    • Selectively permeable to solutes
      • Na+ and Cl– are passively reabsorbed in the thin segment, actively reabsorbed in the thick segment
    • Filtrate osmolarity decreases to 100 mOsm
slide27

Countercurrent in Loop of Henle Extracts Water thenSalt

Osmolality

of interstitial

fluid

(mOsm)

H2O

NaCI

Cortex

Active transport

Passive transport

NaCI

H2O

Water impermeable

NaCI

H2O

The salty outer medulla created by the ascending loop amplifies the extraction of water in the descending loop. Without countercurrent, much less water would be removed and therefore would be less efficient.

NaCI

H2O

Outer

medulla

H2O

NaCI

H2O

H2O

Inner

medulla

Loop of Henle

Renal function online animation

Figure 25.16a

(a) Countercurrent multiplier.

The long loops of Henle of the

juxtamedullary nephrons

create the medullary

osmotic gradient.

countercurrent exchanger vasa recta
Countercurrent Exchanger: Vasa Recta
  • The Vasa Recta (peritubular capillaries parallel to the Loop of Henle
    • Maintain the osmotic gradient
    • Deliver blood to the medullary tissues
    • Protect the medullary osmotic gradient by preventing rapid removal of salt, and by removing reabsorbed H2O
slide29

Countercurrent in Loop of Henle Peritubular Capillaries Maintains Salt Gradient

Osmolality

of interstitial

fluid

(mOsm)

Blood from

efferent

arteriole

Passive transport

To vein

NaCI

H2O

NaCI

H2O

Cortex

The saltier cortex created by the ascending vasa recta peritubular capillaries amplifies the extraction of water in the descending loop. Without countercurrent, much less would remain in the blood.

NaCI

H2O

NaCI

H2O

Online kidney physiology animation

Outer

medulla

NaCI

H2O

NaCI

H2O

NaCI

H2O

NaCI

H2O

Inner

medulla

Vasa recta

(b) Countercurrent exchanger.

The vasa recta preserves the

medullary gradient while

removing reabsorbed water

and solutes.

Figure 25.16b

urea recycling
Urea Recycling
  • Urea moves between the collecting ducts and the loop of Henle
    • Secreted into filtrate by facilitated diffusion in the ascending thin segment
    • Reabsorbed by facilitated diffusion in the collecting ducts deep in the medulla
    • More collecting duct reabsorption if ADH present
  • Contributes to the high osmolality in the medulla
diuretics
Diuretics
  • Chemicals that enhance the urinary output
    • Osmotic diuretics: substances not reabsorbed, (e.g., high glucose in a diabetic patient) causes increased water and urine volume
    • ADH inhibitors such as alcohol
    • Substances that inhibit Na+ reabsorption and obligatory H2O reabsorption such as caffeine and many drugs
kidney dialysis
Kidney Dialysis

Continuous ambulatory peritoneal dialysis (CAPD)