Organs of the Urinary System 13... · Urine Formation: Glomerular Filtration Water and dissolved...

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Organs of the Urinary System

Kidneys (2)

Ureters (2)

Urinary bladder (1)

Urethra (1)

1


Kidneys Regions

Renal cortex

Renal medulla

Renal pyramids

Renal pelvis

Renal capsule

Blood supply

Renal artery

Renal vein

2


Kidneys: Functions

Regulate blood volume and electrolytes

Regulate acid-base balance

Excrete nitrogenous waste

Regulate blood pressure

Regulate RBC production

Vit D production

3


Urinary Bladder: Micturition

Reflex Ureter smooth muscle involuntary

Bladder smooth muscle involuntary

Urethra smooth muscle involuntary

relaxation of internal sphincter (autonomic: smooth

muscle)

relaxation of external sphincter provides voluntary

control (skeletal muscle)

4


Urine Making: The Nephron Unit

Functional unit of the kidney

Composed of two parts

Renal tubules

Renal blood vessels

5


Nephron Unit: Tubular Structures

Renal tubules

Glomerular capsule (Bowman's capsule)

Proximal convoluted tubule does reabsorption

Loop of Henle

Distal convoluted tubule does most secretion

Collecting duct

7


Nephron Unit: Blood Vessels

Renal artery

Afferent arteriole

Glomerulus filter of the kidney

Efferent arteriole

Peritubular capillaries

Renal vein

8


Three Steps of Urine Formation

Glomerular filtration

Tubular reabsorption

Tubular secretion

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Overview of Urine Formation

10


Urine Formation: Glomerular

Filtration Water and dissolved solute filter across

glomeruli into Bowman’s capsule

Why filtration occurs

• It occurs when the pressure on one side of a membrane

is greater than the pressure on the opposite side

What substances are filtered

• Water, sodium, potassium, chloride, glucose, uric acid

pass easily

• Large blood cells and large proteins cannot fit through

pores

11


Urine Formation: Tubular

Reabsorption Returns filtrate from the tubules to the blood

of peritubular capillaries

Most reabsorption takes place in the proximal

convoluted tubule

The kidney chooses the type and quantity of

substances it reabsorbs

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Reabsorption, cont’d What is reabsorbed?

Sodium: >99%

Water: >99%

Glucose: 100%

Urea: 50%

Creatinine: 0%

13



Secretion Moves very small amounts of select

substances from the peritubular capillaries

into the tubules

Secreted substances: Potassium ions (K+),

hydrogen ions (H+), uric acid, ammonium

ions, and drugs and nitrogenous wastes

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Nitrogenous wastes

Kidneys remove enough to keep blood levels within tolerable limits

Ammonia & Urea Wastes from amino acid metabolism Amino acids ammonia converted to urea by the liver and

secreted out by the kidneys

Uric acid

Waste product of nucleic acid metabolism Most filtered uric acid is reabsorbed Enough is secreted to keep blood levels within normal range

Creatinine Waste product of muscle metabolism Actively secreted into the DCT


Renin-Angiotensin-Aldosterone

System Most important stimulus for the release of aldosterone is renin

Renin is an enzyme that activates the renin-angiotensin-aldosterone

system

Series of events:

Renin (released from kidney because of low BP)

Angiotensinogen (inactive form circulating in blood)

Angiotensin I (lungs release converting enzyme)

Angiotensin II

Aldosterone (released by adrenal cortex)

Distal tubule (kidney reabsorbs Na+ and H2O and excretes K+)

16


Aldosterone and Urine Formation

Works on distal tubule and upper collecting

duct of the nephron unit

The “salt-retaining” hormone

Effects

Increases Na+, H2O reabsorption

Increases blood volume

Blood pressure increased

17


Antidiuretic Hormone

Released by posterior pituitary in response to

low blood volume or high concentration

H2O reabsorbtion into the blood

ADH decreases the excretion of water and

causes excretion of a concentrated urine

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Regulation of Red Blood Cell

Production Low O2 level in blood

Kidney secretes

erythropoietin (EPO)

EPO stimulates bone

marrow to produce

RBCs

RBCs increase, thus

increasing O2

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Questions?

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Organs of the Urinary System 13... · Urine Formation: Glomerular Filtration Water and dissolved...

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