25 The Urinary System

Urinary Systemrenal vein renal artery

1. regulate composition, volume, pH of extracellular fluid

2. secrete EPO to regulate RBC production

3. play a role in activating vitamin D

4. secrete renin to regulate blood pressure and kidney function

*temporary storage

*urine transportation

*urine transportation

*urine transportation

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

Internal Kidney Structure outer layer

inbetween pyramids

middle layerlooks like fish tails

connects to uretercollects urine

Blood Flow Through Kidney Nephrons• 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 capillariesglomerular (Bowman's) capsule - surrounds glomerulusfilters blood plasma forming filtrate (urine precursor)unfiltered fluid enter via afferent arteriolefilter fluid leaves via efferent arteriole ("get the effe

away from me")• renal tubule

proximal convoluted tubule (PCT) - loops and coilsloop of Henle - hairpin turndistal convoluted tubule (DCT) - loops and coils

• several DCTs empty filtrate into one collecting duct

25 The Urinary Systemcortical nephrons

juxtamedullary nephrons

*85% of nephrons

*mostly located in cortex

*peritubular capillaries

*peritubular nephrons called vasa recta

*loop of Henle extends deep into medulla

*important in making concentrated urine

Juxtaglomerular Apparatus

*mechanoreceptors that sense blood pressure in afferent arteriole

*modifies actions of afferent arteriole and ascending loop at point of contact

*chemoreceptors that respond to changes in NaCl content of filtrate

*may pass signals between macula densa and granular cells

*help with filtration

glomerulus + Bowman's capsule

1

2

3

*allows for passage of water and solutes smaller than proteins

1 - allows everything but blood cells

2 - allows small proteins and everything else3 - allows only solutes

Darker shirt...parts of the urinary system & kidney

structure

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

B

C

D

3 Modifies the actions of the glomerulus or ascending loop of Henle.

A juxtamedullary neprhon

B cortical nephron

C juxtaglomerulus apparatus

D Bowman's capsule

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

A fenestrations

B capillary endothelium

C basement membrane

D foot processes of podocytes

5 What is this?

6 What is this? Urine Formation & Excretion

25 The Urinary System

Basic Overview• 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

Glomerular Filtration• 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

smaller molecules (3 nm or less) pass freely through membrane

molecules larger than 5 nm (proteins and cells) stay in blood

Net Filtration Pressure (NFP)(glomerular

blood pressure)

OUT IN

IN

OUT > INwater and solute pushed out of afferent arteriole

Glomerular Filtration Rate (GFR)

(mL/min)

• 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

• GFR is directly proportional to NFP• GFR is tightly regulated

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 & volume1. vasoconstriction*2. release aldosterone (Na+ uptake)*3. release ADH & activate thirst center4. increase fluid reabsorption

5. decrease total surface area of glom capillaries available for filtration

25 The Urinary System

RIGHT LEFT

High Card Wins...Best 2 out of 3 Winner...Describe the forces that cause glomerular filtration.

Nonwinner...What is GFR? How is it regulated?

1 MATA: What processes are needed to produce urine?

A tubular reabsorption

B tubular secretion

C glomerular filtration

D renal excretion

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

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

*water only*nutrients

only

Tubular Secretion• 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.

PullPull

4 Water is reabsorbed in all of the following EXCEPT the

A PCT

B descending limb of the loop of Henle

C ascending limb of the loop of Henle

D DCT

E colecting duct

5 Tubular secretion moves material

A into the glomerular capsule

B from blood into neprhon

C from nephon into blood

D from collecting duct into mino calyx

25 The Urinary System

6 MATA: The PCT is the major site of

A glomerular filtration

B tubular reabsorption

C tubular secretion

Hormones that Influence Urine Formation

• renin-angiotensin mechanismrenin angiotensin I angiotensin IIhelps maintain Na+ and water balance, and blood

pressure (glomerular filtration)• 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

hydrated

dehydrated

less urine (concentrated)

more urine (dilute)

7 MATA: If ADH increases,

A reasborption increases

B more urine is produced

C urine is concentrated

water leaving descending limb

makes filtrate more concentrated

Na+ leaving ascending limb makes filtrate

more dilute

Countercurrent Mechanism for Osmolality *osmolality establishes gradient for osmosis

*by making filtrate dilute in ascending limb, we can reabsorb more water in DCT and collecting duct if the body needs it

Dilute Urine Concentrated Urine

low ADHcollecting duct essentially impermeable to waterdilute urine from ascending limb of loop of Henle continues into collecting duct and on to renal pelvisDCT and collecting duct can continue to reabsorb Na+ making urine even more dilute

high ADH

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

25 The Urinary System

Urine Composition• physical characteristics

color and transparency - clear and pale to deep yellowabnormal color or cloudiness

may be a result of diet or infection

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

• chemical characteristics95% water5% solutes - urea, uric acid, creatinine, electrolytes

yellow color - urochrome (made from hemoglobin breakdown)

a.a. nucleic acid CP

Abnormal Urinary Constituents - Table 25.2

WORK TOGETHER...How does the countercurrent mechanism change the concentration of urine?

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 sexual activity

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 epithelium2. thick muscular layer - detrusor muscle forms the internal

urethral sphincter3. serosa

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.

A trigone

B urethra

C bladder

D ureter

10 MATA: What is true about the female urethra?

A shorter than male urethra

B 3 types of urethral tissue

C more prone to infection

D extends through prostate

25 The Urinary System

11 Micturition is part voluntary and part involuntary.

True

False