Cm5 renal function

• Renal Anatomy

• Renal Blood Flow

• Renal Physiology

• Urine formation

– Glomerular Filtration– Tubular Reabsorption– Tubular Secretion

Renal Anatomy

kidneyWhat is the average weight of the kidney?

115-170 g

What is its average size?

11 cm in length, 6 cm in width, 3 cm thick

What is the rate of blood flow into the kidney via the renal artery?

600 mL/min

kidney

Cortex

• Renal corpuscles

• Proximal tubules

• Distal tubules

Medulla

• Loop of Henle

• Vasa recta

• Collecting

tubules

2 regions of the kidney

What is the functional unit of the kidney?of the kidney?

NEPHRON

Renal Blood Flow

3a

2

1

3b

Renal Blood Flow

1 2

3a4a

3b

5b

7b

4b

5a

6a

6b

8b

Renal Physiology

MAJOR FUNCTIONS

The Body’s Filters: removing toxins & metabolic waste products

• Ultrafiltration

• Endocrine function

• Osmolarity regulation

• Volume regulation

• Acid-base regulation

ultrafiltration

ultrafiltration

Of the renal blood flow, how much is filtered

by the glomerulus?

125 mL/min

How many liters of blood is filtered by the

kidney each day?

180 liters

How much urine is produced per day?

1.5 liters

ultrafiltration

The kidneys possess extraordinary

mechanisms to reabsorb water while

removing metabolic waste by-products

and toxins.

How is kidney function measured?

GFR

Glomerular Filtration Rate

Endocrine function

1. Erythropoietin

2. Active form of vitamin D (1,25-

dihydroxy vitamin D3)

3. renin

Osmolarity regulation

ADH – synthesized in the hypothalamus &

released in the posterior pituitary in

response to an increase in osmolarity as

sensed by osmoreceptors in the anterior

hypothalamus

↓BP ↓PLASMA VOL ↑OSMOLARITY

↓venous pressure ↓venous return ↓ atrial pressure

↑ ADH secretion

↑ tubular permeability to water

↑ water reabsorption

↓ water excretion ↓ urine volume ↑ urine osmolarity

Volume Regulation

Regulation of ECF volume thru the

• Renin-Angiotensin-Aldosterone (RAA)

pathway

• Atrial Natriuretic Factor (ANF)

↓BP ↓PLASMA VOL ↓Na

↑ Renal symp nerves ↓ renal arterial pressure

↑ renin secretion (into afferent arteriole)

↑ plasma angiotensin (from adrenal cortex)

↑ aldosterone secretion

↑ tubular Na reabsorption ↓ Na excretion

↓ arterial pressure

ANF

Volume Regulation

Atrial Natriuretic Factor (ANF)

• Secreted by the cells in the atria of the

heart to inhibit Na+ reabsorption in the

kidneys

• Inhibits secretion of aldosterone which

stimulates Na+ reabsorption

Acid Base Regulation

Acid Base Regulation

• To excrete X’s alkali:

– Na2HPO4

– NaHCO3

• To excrete X’s acid:

– NH4Cl

– (NH4)2SO4

– NaH2PO4

What is the first step in urine formation?

GLOMERULAR FILTRATION

Glomerular Filtration

The filtration of a solute that is not reabsorbed or secreted

Unit: mL/min

Affected by: hydrostatic & oncotic pressure,

Renin-angiotensin-aldosterone system, structure

Glomerular FiltrationSubstances retained:

• Blood cells

• Serum proteins

• Substances filtered:

• Water

• Smaller molecules

(MW: <70,000)

– Ions

– Amino acids

– Glucose

– Urea

– Creatinine

– Uric acid

– ammonia

Glomerular Filtration• Approximately 20% of the volume of plasma

that passes through the glomerular tuft is caught in Bowman’s space and is called the glomerular filtrate.

• At this point, the filtrate is iso-osmotic with plasma and is called an ultrafiltrate. (sp. gr. 1.010 +/-0.002 ; pH 7.4)

What barriers are there to

the passage of the filtrate?

• Endothelium (glomerular capillary)

• Basement membrane– Lamina rara interna

– Lamina densa

– Lamina rara externa

• Podocytes (visceral layer)

Glomerular Filtration

Glomerular Filtration

• To pass through the filtration barrier:

– <4 nm in size

– Threshold

Glomerular Filtration

Tubular Reabsorption

• The movement of substances (by active or

passive transport)

– from the tubular ultrafiltrate into the

peritubular blood or the interstitium by the

renal tubular cells.

Tubular Reabsorption

Substances reabsorbed by active transport:

• Glucose, Amino acids, Salts (PCT)

• Chloride (LOH)

• Sodium (DCT)

Tubular Reabsorption

Substances reabsorbed by passive

transport:

• Water (all nephron parts except ascending

limb)

• Urea (PCT, ascending limb)

• Sodium (ascending limb)

Tubular Secretion

• The movement of substances (by active or

passive transport)

– from the peritubular blood or the interstitium

into the tubular ultrafiltrate by the renal tubular

cells

• To secrete substances the kidney is

unable to eliminate via ultrafiltration

Tubular Secretion

• Substances incompletely metabolized

– E.g. thiamine

• Substances not metabolized at all

– E.g. radiopaque contrast media / mannitol

• Substances not normally present

– Certain drugs

SUMMARY

• Close your notes...

•Glomerulus

FILTRATION: water (ADH not required)., Na+, Glucose, K+,

Cl-, Urea, Urate, Uric Acid, Proteins, Amino acids,

Bicarbonates, Creatinine, Phosphate, Inulin, PAH

REABSORPTION: --

SECRETION: --

•Proximal Tubule

Isotonic filtrate

FILTRATION: --

REABSORPTION: Water (ADH not required), Na+, Glucose,

K+, Cl-, Urea, Urate, Uric Acid, Proteins, Amino

acids, CO2

•Proximal Tubule

SECRETION: Creatinine, Hydrogen, PAH

•Loop of Henle

Hypertonic filtrate

REABSORPTION: Water, Na+, Cl-, Urate, Urea, CO2

SECRETION: --

•Distal Tubules

Area of dehydration (where ADH acts)

Iso or hypotonic filtrate; most common area of cast form’n

REABSORPTION: Water (ADH required), Na+, Cl-, Urate,

Urea, CO2

SECRETION: K+, Uric Acid, H+

Collecting Duct

Hypertonic or Hypotonic filtrate

REABSORPTION: Water (ADH required), Na+, Cl-, Urate,

Urea, CO2

SECRETION: K+, H+