25 The Urinary System

Urinary System renal vein

renal artery

1. regulate composition, volume, pH of extracellular fluid 2. secrete EPO to regulate RBC production

*urine

transportation

3. play a role in activating vitamin D

transportation

*temporary

4. secrete renin to regulate blood

*urine

storage

pressure and kidney function

*urine transportation

Internal Kidney Structure

Kidneys

• reddish-brown, bean shaped organ with a smooth surface • lie on either side of the vertebral column in a depression on the posterior abdominal wall • 12 cm long, 6 cm wide, 3 cm thick (bar of soap) • right kidney lower than left because of liver • 3 layers of supportive tissue around each kidney > renal fascia - anchors > perirenal fat capsule - cushioning > fibrous capsule - prevents infection

middle layer

outer

layer looks like fish tails

connects to ureter collects urine

inbetween pyramids

Nephrons

Blood Flow Through Kidney • • • • •

structural and functional unit of kidneys tiny blood-processing units that form urine roughly 1 million in each kidney nephron = renal corpuscle + renal tubule renal corpuscle glomerulus - tangled cluster of capillaries glomerular (Bowman's) capsule - surrounds glomerulus filters blood plasma forming filtrate (urine precursor) unfiltered fluid enter via afferent arteriole filter fluid leaves via efferent arteriole ("get the effe away from me")

• renal tubule

proximal convoluted tubule (PCT) - loops and coils loop of Henle - hairpin turn distal convoluted tubule (DCT) - loops and coils

• several DCTs empty filtrate into one collecting duct

25 The Urinary System cortical nephrons juxtamedullary nephrons

*help with filtration

Juxtaglomerular Apparatus

*may pass signals between

*chemoreceptors

macula densa and granular

that respond to

cells

changes in NaCl content of filtrate

*peritubular nephrons called vasa *85% of nephrons

recta

*mostly located in cortex

*loop of Henle

*peritubular capillaries

extends deep into medulla *important in making

*mechanoreceptors that sense blood pressure in afferent

glomerulus + Bowman's capsule

arteriole *modifies actions of afferent arteriole and

concentrated urine

ascending loop at point of contact

*allows for passage of water and

Darker shirt...parts of the

solutes smaller than proteins

urinary system & kidney structure 1 - allows everything 1 but blood cells 2 - allows small proteins and

2

everything else 3 - allows only solutes

3

Lighter shirt...blood flow and nephron structure. 1 What is the structural and functional unit of the kidney? A glomerulus B nephron C medulla D cortex

25 The Urinary System

2 Responsible for "cleaning" the blood. A

3 Modifies the actions of the glomerulus or ascending loop of Henle. A juxtamedullary neprhon B cortical nephron

B

C juxtaglomerulus apparatus D Bowman's capsule

C D

4 Most discriminating layer (lets the fewest things through) of filtration membrane.

5 What is this?

A fenestrations B capillary endothelium C basement membrane D foot processes of podocytes

6 What is this?

Urine Formation & Excretion

25 The Urinary System

Basic Over view

Glomerular Filtration

• PURPOSE: to "clean" blood • 3 processes 1. glomerular filtration - kidneys "dump" cell- and

protein-free blood into renal tubule 2. tubular reabsorption - everything the body needs is kept (glucose, amino acids, water, salt) 3. tubular secretion - other things are selectively added to the tubule

• final product = urine • kidneys process 180 L (47 gallons) of filtrate a day • less than 1% (about 1.5 L) is eliminated as urine, the rest is returned to circulation

Net Filtration Pressure (NFP) OUT

(glomerular

smaller molecules (3 nm or less) pass freely through membrane molecules larger than 5 nm (proteins and cells) stay in blood

Glomerular Filtration Rate (GFR)

IN

IN

blood pressure)

• a passive process driven by hydrostatic pressure gradients • filtration membrane has large surface area and is thousands of times more permeable to water and solutes

• glomerular filtration rate (GFR) volume of filtrate formed each minute by all 2 million glomeruli of the kidneys • affected by

> total surface area available for filtration > filtration membrane permeability > NFP

(mL/min)

• GFR is directly proportional to NFP • GFR is tightly regulated OUT > IN water and solute pushed out of afferent arteriole

Regulation of Glomerular Filtration • regulated by both intrinsic and extrinsic controls

> intrinsic - ensures a relatively constant GFR > extrinsic - ensures constant blood pressure and blood volume > extrinsic takes precedent over intrinsic

• intrinsic control - renal autoregulation

> myogenic mechanism - vasodilation/constriction > tubuloglomerular feedback mechanism - responds to changes in NaCl (low NaCl, increase GFR; high NaCl, decrease GFR)

• extrinsic control

> sympathetic NS controls - activates R-A mechanism during times of stress > renin-angiotensin mechanism - renin released by granular cells > renin angiotensin I angiotensin II

angiotensin II - restore blood pressure & volume

1. vasoconstriction* 2. release aldosterone (Na+ uptake)*5. decrease total surface area of glom 3. release ADH & activate thirst center 4. increase fluid reabsorption

capillaries available for filtration

25 The Urinary System Winner...Describe

High Card Wins...Best 2 out of 3

the forces that cause glomerular filtration. Nonwinner...What is GFR? How is it regulated?

RIGHT

LEFT

1 MATA: What processes are needed to produce urine?

2 The force that pushes filtrate out of the afferent arteriole into the glomerular capsule is the

A tubular reabsorption B tubular secretion C glomerular filtration D renal excretion

A glomerular hydrostatic pressure B capsular hydrostatic pressure C blood colloid osmotic pressure D glomerular colloid osmotic pressure

3 MATA: Regarding regulation of GFR, ,_____ takes precedent over _____. A constant BP and blood volume, constant GFR B constant GFR, constant BP and blood volume C extrinsic control, intrinsic control D intrinsic control, extrinsic control

Tubular Reabsorption

• filtered substances returned to bloodstream (from nephron to blood) • aims to recover useful materials • most reabsorption takes place in PCT > all glucose, lactate, and amino acids, 65% Na+ and water (water follows salt - NaCl)

• loop of Henle

> descending limb - water > ascending limb - Na+ and ions (NO water)

• DCT & collecting duct > controlled by hormones; based on need – aldosterone - Na+ – antidiuretic hormone (ADH) - water – PTH - Ca2+

• other nutrients and ions are also reabsorbed throughout the nephron (K+, Ca2+, Cl-, urea, etc.)

25 The Urinary System

Tubular Secretion

*water only

*nutrients only

• reabsorption in reverse • secretions enter nephron from bloodstream (last chance to get rid of stuff we don't want in the blood) • PCT major site of secretion • major secretions - H+, K+, NH4+, creatinine, organic acids • reasons for secretion

> dispose of substances attached to proteins > eliminate undesired substances or end products that have been reabsorbed (urea) > get rid of excess K+ > control blood pH (H+ and HCO3-)

...describing how urine is formed.

Pull

4 Water is reabsorbed in all of the following EXCEPT the

5 Tubular secretion moves material

A PCT

A into the glomerular capsule

B descending limb of the loop of Henle

B from blood into neprhon

C ascending limb of the loop of Henle

C from nephon into blood

D DCT

D from collecting duct into mino calyx

E colecting duct

25 The Urinary System

Hormones that Influence Urine Formation

6 MATA: The PCT is the major site of

• renin-angiotensin mechanism

A glomerular filtration

renin angiotensin I angiotensin II helps maintain Na+ and water balance, and blood pressure (glomerular filtration)

B tubular reabsorption C tubular secretion

• aldosterone stimulates reabsorption of Na and secretion of K+ (tubular reabsorption and secretion)

• antidiuretic hormone (ADH) stimulates H20 reabsorption (tubular reabsorption) increase ADH, increase H20 reabsorption, decrease urine volume (more concentrated) decrease ADH, decrease H20 reabsorption, increase urine volume

dehydrated

7 MATA: If ADH increases, A reasborption increases B more urine is produced less urine

C urine is concentrated

(concentrated)

hydrated

more urine (dilute)

Countercurrent Mechanism for Osmolality *osmolality establishes gradient for osmosis

Dilute Urine low ADH

Concentrated Urine high ADH

collecting duct essentially impermeable *by making filtrate dilute in ascending limb, we can reabsorb more water in DCT and

water leaving

to water dilute urine from ascending limb of loop of Henle continues

collecting duct if

into collecting duct

the body needs it

and on to renal pelvis

descending limb

Na+ leaving ascending

makes filtrate more

limb makes filtrate

concentrated

more dilute

DCT and collecting duct can continue to reabsorb Na+ making urine even more dilute

diuretic - increase urinary output (ex. alcohol, caffeine)

25 The Urinary System

Urine Composition

• physical characteristics

WORK TOGETHER...How does the countercurrent

color and transparency clear and pale to deep yellow

mechanism change the concentration of urine?

abnormal color or cloudiness may be a result of diet or infection

odor - slightly aromatic pH - slightly acidic (pH = 6)

• chemical characteristics a.a. nucleic acid 95% water

CP

5% solutes - urea, uric acid, creatinine, electrolytes yellow color - urochrome (made from hemoglobin breakdown)

Abnormal Urinary Constituents - Table 25.2

Best 2 out of 3 WINNER...Describe normal urine composition. NONWINNER...Why the different colors?

8 MATA: Urine becomes more concentrated A as water leaves the descending loop of Henle B when ADH increases C when using diuretics D as tubular secretion adds K+ to filtrate

*take urine from kidneys to bladder *not a free fall, peristalsis pushed urine to bladder (similar to esophagus to stomach)

*take urine from bladder to external environment

25 The Urinary System Differences Between The Male and Female Urethra

*shorter urethra in women makes them more likely to develop urinary tract infections (UTIs) due to improper bowel habits and/or

Urinary Bladder

• smooth, collapsible, muscular sac that temporarily stores urine • when empty the inner lining is folded (similar to stomach) • inner lining becomes smooth as bladder fills with urine • trigone - triangular structure on internal floor with openings from 2 ureters and 1 urethra • 3 layers

1. mucosa - transitional epithelium 2. thick muscular layer - detrusor muscle forms the internal urethral sphincter 3. serosa

sexual activity

Micturition

• aka urination or voiding • process that expels urine from the urinary bladder • distention of bladder wall stimulates stretch receptors which trigger micturition reflex • reflex center (pontine micturition center) send parasympathetic impulses to the detrusor muscle which begins to contract rhythmically (provides a sense of urgency) • max capacity = 800-1000 mL • the urge to urinate begins around 150 mL • urgency kicks into around 400 mL • when a person decides to urinate, the external urethral sphincter relaxes (voluntary), detrusor muscle contracts and internal urethral sphincter relaxes (involuntary), and urine is excreted via urethra

9 MATA: Responsible for transporting urine.

10 MATA: What is true about the female urethra?

A trigone

A shorter than male urethra

B urethra

B 3 types of urethral tissue

C bladder

C more prone to infection

D ureter

D extends through prostate

25 The Urinary System

11 Micturition is part voluntary and part involuntary. True False