Components◦Kidneys◦Ureters◦Urinary bladder◦Urethra

The Urinary System: Anatomy and Physiology

Organs of the Urinary System

Kidneys

Ureters

Urinary bladder

Urethra

2

Function

1. Remove nitrogenous wastes (urine)2. Maintain electrolyte, acid-base, and

fluid balance of blood3. Homeostatic organ4. Acts as blood filter5. Release hormones: calcitriol &

erythropoietin

Kidneys are supplied with blood from renal arteries

• Located Retroperitoneally• Lateral to T 12 – L 3 Vertebra

The Urinary System: Anatomy and Physiology

Relationship of Kidneys to Vertebra and Ribs

Nephrons

About 1 million nephrons are in a kidney.

They are the functioning unit of the kidney

Consists of a renal corpuscle and a renal tubule.◦Glomerulus is a tangled cluster of blood

capillaries that makes up a renal corpuscle ◦Renal tubule leads away from the

glomerulus

Nephrons

PARTS OF NEPHRON

Formation of Urine Glomerular filtration initiates urine

formation.◦Plasma is filtered by the glomerular

capillaries.◦Most of this fluid is reabsorbed into the

bloodstream.

Formation of Urine Urine formation summary:

◦ Glomerular filtration◦ Reabsorption of substances◦ Secretion of substances

urine

blood

filtration

tubular reabsorption and secretion

General Functioning of the NEPHRON

General Functioning of the NEPHRON

“refreshed” blood

Renin also controls the filtration rate.◦Responds to three types of stimuli:

1. Drop in blood pressure2. Sympathetic stimulation3. Decrease in chloride, potassium, and

sodium ions

Formation of Urine

Renin reacts with angiotensinogen to form angiotensin I.

Angiotensin-converting enzyme converts to angiotensin II

Helps maintain sodium and water balance Vasoconstricts the efferent arteriole Helps decrease glomerular filtration rate Stimulates kidneys to secrete aldosterone

Formation of Urine

Atrial natriuretic peptide(ANP) increases sodium excretion by increasing the glomerular filtration rate.

Formation of Urine

Urea is a result of amino acid catabolism. Uric acid is a result of the metabolism of

certain organic bases in nucleic acids. Urine is about 95% water.

◦ Contains urea and uric acid

Formation of Urine

Ureter drains into the urinary bladder Bladder empties to the outside of the body

through the urethra 1.5 to 2 L of urine is extracted every day.

Formation of Urine

Internal urethral sphincter:• Smooth muscle• Involuntary control• More superiorly located

External Urethral sphincter:• Skeletal muscle• Voluntary control• Posteriorly located

Sphincter Muscles on Bladder