URINARY SYSTEM GENERAL STRUCTURE &
FUNCTION
Learning Objectives
1. Describe the structure of the kidney.
2. List the homeostatic functions of the kidney.
3. Describe the structure of the kidney nephron.
4. Explain the regional functions of the kidney tubule.
KIDNEY STRUCTURE
Capsule
Renal
cortex
Renal
medulla
Ureter conducts urine to bladder
ORGAN FUNCTIONS:
• Fluid balance
• Electrolyte balance
• Liquid waste removed
• Excretion of drugs
• Endocrine secretions:
erythropoietin
renin
Vitamin D3 (calcitriol)
NEPHRON STRUCTURE
Million filtering units
cortex
medulla
Tubule regions include:
1. Bowman’s Capsule (start of tubule)
surrounds glomerulus
2. Proximal convoluted tubule (PCT)
3. Loop of Henle
4. Distal convoluted tubule (DCT)
5. Collecting Duct (CD)
Cortical Nephron is
the most common
type in humans
cortex
medulla
2 TYPES OF
NEPHRONS
Juxtamedullary
Nephron maintains
hyperosmotic
medullary gradient
REGIONAL CHANGES IN
VOLUME & OSMOLARITY
REGIONAL FUNCTIONS
Excretion (E) = Amt Filtered (F) - Amt Reabsorbed (R)+ Amt Secreted (S)
IMPORTANT TERMS
1. Filtration is the movement of solutes and water
from the blood into the lumen of the renal tubule to
generate a filtrate.
2. Reabsorption is the movement of solutes and water
from the lumen of the renal tubule across the epithelial
cells and back into the blood.
3. Secretion is the movement of solutes directly from
the blood across the epithelial cells and into the luminal
filtrate.
4. Excretion is the removal of solutes and water from
the body as urine.
GENERAL CONCEPTS
1. The kidneys’ primary functions are to maintain fluid
volumes of the body by regulating salt balance and to
maintain the osmolarity of the body by regulating water
balance.
2. Additional homeostatic functions include removal of
wastes and detoxification of drugs.
3. The kidney secretes hormones, including erythropoietin
in response to hypoxia, renin in response to low blood
pressure, and active Vitamin D3.
4. The kidney contains a million filtration units, called
nephrons. Each nephron is fed by a portal system.
5. Filtration occurs across the first capillary bed
(glomerulus). Reabsorption and secretion occur along
the renal tubule to alter the composition of the filtrate.
The final product is urine which leaves the kidney by the
ureter.