Processes in the Nephron

• Filtration

• Reabsorption

• Secretion

Nephron

• 1.25 million nephrons in a kidney

• FILTER blood

Parts of the Nephron

• Glomerulus– Bed of capillaries– Receives “DIRTY” blood from the renal

ARTERY

• Bowman’s capsule– CUP-LIKE structure that surrounds the

GLOMERULUS– “Dirty” blood (FILTRATE) is forced here by

a FILTRATION process

Parts of the Nephron

• Renal tubule– Proximal convoluted tubule– Loop of Henle– Distal convoluted tubule– Walls are PERMEABLE

• Collecting duct– SURROUND the

renal tubule– Leads to the ureter

Filtration

• General Definition– Passing liquid or gas through a filter to

remove impurities

• Nephron– Small particles in the blood are forced out of

the GLOMERULUS into the BOWMAN’S CAPSULE.

– This solution is now referred to as the FILTRATE (similar to plasma except that it does not contain protein.)

Filtration

• Materials that ARE filtered include…– WATER– MINERAL SALTS– Nutrients (Glucose & amino acids)– NITROGENOUS WASTES

Filtration

• Materials that ARE NOT filtered include…– Proteins– Large Cells– Red Blood Cells

Two pathways

1. Some materials will flow through the RENAL TUBULE into the COLLECTING DUCT and be excreted as URINE.

2. Some materials will be REABSORBED into the blood through CAPILLARIES that surround the renal tubule.

Reabsorption

• Process where a LIQUID is taken back into a VESSEL

• FILTRATE flows through the RENAL TUBULE

• Material that the body need is REABSORBED by surrounding CAPILLARIES

Reabsorption

• Materials reabsorbed by…

– ACTIVE TRANSPORT• NaCl,nutrients (glucose & amino acids)

– PASSIVE TRANSPORT

• H20 (osmosis)

Reabsorption

• 75% of reabsorption occurs in the PROXIMAL CONVOLUTED TUBULE

• Rest of reabsorption occurs in the LOOP OF HENLE and the DISTAL CONVOLUTED TUBULE

Reabsorption

• Concentration gradient formation by ACTIVE TRANSPORT– Causes blood in capillaries to become

HYPERTONIC, therefore WATER follows by simple DIFFUSION, (OSMOSIS).

Secretion

• Release of specific substances from the BLOOD (capillaries) back into the FILTRATE (now known as urine) in the renal tubule. – Nitrogenous wastes (passive transport)– Hydrogen ions (active transport)

• Adjusts the pH of the filtrate (urine) to about 6.

– Potassium ions (active transport)

Secretion

• Occurs mostly in the DISTAL CONVOLUTED TUBULE

• Some in the PROXIMAL CONVOLUTED TUBULE

Collecting duct

• Continues to concentrate the urine by removing water from the urine

Hormones

• Antidiuretic Hormone

Antidurietic Hormone (ADH)

• Regulates WATER conservation• Increases water absorption by making walls of

the collecting ducts MORE PERMEABLE• Regulated by the BRAIN (PITUITARY GLAND)

Feeling thirsty?

What’s happening to your ADH levels (and the concentration of your urine)?

– ADH levels INCREASE– MORE water is retained– Urine is CONCENTRATED

Had enough water?

• ADH levels DECREASES

• LESS water is retained

• Urine is NOT concentrated

Last stages…

• Urine collects in the COLLECTING DUCTS of NEPHRONS

• Urine enters the hollow area of the kidney called the RENAL PELVIS

• Urine passes through the URETERS

• Urine gets stored in the URINARY BLADDER where the SPHINCTER muscles CONTROL when urine is expelled through the URETHRA.