EXCRETORY SYSTEM

THE PARTS…

2 kidneys

2 ureters

1 urinary bladder

1 urethra

Adrenal glands

Renal Cortex

Renal MedullaRenal Artery

Renal Vein

Ureter

The KIDNEY Fig. 18-2

Adipose tissue/fat

KIDNEYS (INTERNAL ANATOMY)

The NEPHRON…Functioning unit of the kidney

• ~ 1 million / kidney• 2 main parts

1. Renal Corpuscle – expanded bulb-like end• Bowman’s capsule – bowl shaped structure

that partially surrounds the capillary network called the…

• Glomerulus – capillary network w/in the Bowman’s capsule that resembles a ball of yarn• Membrane is more permeable than most

capillaries• High pressure

KIDNEYS (INTERNAL ANATOMY)

2. Renal tubule – thin twisted tube• Proximal convoluted tubule (PCT) –

• Coiled segment that leads from its union (i.e. closest) w/Bowman’s capsule and then makes several turns

• Loop of Henle – • Part of the tube that descends into medulla, makes a sharp U-

turn, then ascends back toward the cortex.• Descending loop – descends from the PCT into the U-turn

w/in the medulla• Ascending loop – ascends from the U-turn w/in medulla

back into the cortex • Distal convoluted tubule (DCT) –

• Coiled segment away from Bowman’s capsule that enters the collecting duct

KIDNEYS (INTERNAL ANATOMY)

3. Extra Parts• Collecting ducts –

• Collect newly formed urine from DCT and channels it to the… ureter

• Peritubular capillaries – • Porous, low-pressure capillaries that permit the

exchange/movement of materials between the bloodstream and renal tubules

Blood Flow through the NephronPg. 537 Fig. 18-6

HL

Afferent arteriole

Efferent arteriole PCT

Bowman’sCapsule

Glomerulus

Renal corpuscle

filtrate

1. Anatomy – difference in diameter between the afferent & efferent arteriolesPhysiology – filtration

• Boyle’s Law2. Anatomy –

Glomerulus is more permeable than most capillaries (i.e. large pores)Physiology – increase filtration

• Hydrostatic pressure of the capillary (CAP-HP)

Volume issues…• (45 gal/180 liters filtered)/day

• do we “pee” this much?• so what must happen to it?

Capillary Exchange (pg. 387)

Arteriole end Venous end

High CAP-HP• BP of capillaries

• close to the heart• more fluid

Low CAP-HP• BP of capillaries

• far from the heart• less fluid

ISF

plasmaalbumins

4 Fluids1. Plasma – blood volume2. ISF – Interstitial fluid surrounding cells3. Lymph – lymphatic vessels4. CSF – cerebral spinal fluid

filtration reabsorption

A) Hypertonic environment• ↑ solute• ↓ H2O

B) Hypotonic environment• ↓ solute• ↑ H2O

↑ CAP-COP - ↑ Capillary Colloidal Osmotic Pressure

• albumins• less H2O

Capillary Colloidal Osmotic Pressure

Plasma Proteins (pg. 347)

3 main groups, primarily made by the liver and found in the blood1. albumins

• ~ 55% of the plasma proteins• Responsible for blood viscosity• Maintains bloods osmotic pressure

2. globulins• ~ 38% of the plasma proteins• Primarily help w/bodies immune response as antibodies

3. Fibrinogen• ~ 7% of the plasma proteins• Blood-clotting factor

1. Glomerular Filtration: • Water and solutes from plasma pass from blood in glomerulus into Bowman’s capsule which empties into renal tubule.

• Pressure forces water and smaller solutes through the capillary membrane • capillaries are designed to allow

small things through but not larger molecules, such as…• proteins, blood cells, and

platelets (which should not be found in urine).

• Glomerulus: specialized for its job

a) large surface area for filtrationb) thin, pourous membrane makes for a

very “leaky” capillaryc) high capillary blood pressure (high

pressure = more filtrate)

2. Tubular reabsorption returning of most of the filtered water and many filtered solutes to the blood stream

• results in concentration of waste that remains in tubes to become urine• filtrate returns to blood

• renal tubes peritubular capillaries (blood)• via active & passive (osmosis & diffusion)

transport3. Tubular secretion movement of materials from blood and tubule cells into tubular fluid (H+, K+, ammonium …H+ controls blood pH)• Removal of harmful wastes not

removed by filtration (reverse of reabsorption)

• peritubular capillaries (blood) renal tubules

• via active & passive (O/D) transport4. Anything that remains (metabolic waste)

in the collecting duct eventually ends up in post nephron structures & secreted as urine

HL

KIDNEYS (INTERNAL ANATOMY)

1. Glomerular Filtration:

Water and solutes from plasma pass from blood in glomerulus into Bowman’s capsule which empties into renal tubule.

• 150-180 liters/day• 99% returns back into blood• 1-2 liters is excreted as urine

3 tasks of nephron and collecting tubule:1. Glomerular filtration

2. Tubular reabsorption3. Tubular secretion

KIDNEYS (INTERNAL ANATOMY)

Pressure forces water and smaller solutes through the capillary membrane. Capillaries are designed to allow small things through but not larger molecules such as proteins, blood cells, and platelets (which should not be found in urine).

a. large surface area for filtrationb. Thin, pourous membrane

makes for a very “leaky” capillary

c. High capillary blood pressure (high pressure = more filtrate)

1. Glomerulus: specialized for its job (26.9)

KIDNEYS (INTERNAL ANATOMY)

2. Tubular reabsorption returning of most of the filtered water and many filtered solutes to the blood stream

• reabsorbed substances include: glucose, Na+, K+, Ca2+, Cl-, etc…

3. Tubular secretion movement of materials from blood and tubule cells into tubular fluid (H+, K+, ammonium …H+ controls the blood pH)

Anything that remains in the collecting duct eventually ends up in renal pelvis and is secreted as urine

Secretion in nephron results in formation of urine which is excreted from the body

KIDNEYS

Fluid homeostasis in the body is controlled by the kidneys

The hormone ADH (antidiuretic hormone) controls water reabsorption

Fluid intake… • if high • if low (or loss of fluid)

Absence of ADH – less water reabsorbed = dilute urine

Presence of ADH – more water reabsorbed = concentrated urine

Alcohol inhibits secretion of ADH

large volume of dilute urine

small volume of concentrated urine

THE END