Important Functions of the Kidneys

24 PART 1

The Urinary System

•Important functions of the kidneys

•Maintain the chemical consistency of blood

•Filter many liters of fluid from blood

•Send toxins, metabolic wastes, and excess water out of the body

•Main waste products are three nitrogenous compounds

•Urea

•Uric acid

•Creatinine

Organs of the Urinary System

•Kidneys

•Ureters

•Urinary bladder

•Urethra

Location and External Anatomy of Kidneys

•Kidneys are red-brown in color

•Located retroperitoneally

•Behind the peritoneum

•Lateral to T12–L3 vertebrae

•Average kidney is 12 cm tall, 6 cm wide, 3 cm thick

•Hilum

•Is the concave surface

•Vessels and nerves enter and exit

Location and External Anatomy of Kidneys

•Fibrous capsule

•Capsule of dense connective tissue surrounds the kidney

•Inhibits spread of infections

•Perirenal fat capsule

•External to renal capsule

•Renal fascia

•External to perirenal fat capsule

•Contains fat

Internal Gross Anatomy of the Kidneys

•Frontal section through the kidney

•Renal cortex

•Superficial region, granular appearance

•Renal medulla consists of

•Cone-shaped renal pyramids

•Renal pelvis

•Major calices

•Minor calices

Internal Gross Anatomy of the Kidneys

•Gross vasculature

•Renal arteries branch into segmental arteries

•Segmental arteries branch into interlobar arteries

•Arcuate arteries branch from interlobar arteries

Internal Gross Anatomy of the Kidneys

•Nerve supply—renal plexus

•A network of autonomic fibers

•An offshoot of the celiac plexus

•Supplied by sympathetic fibers from

•Lowest thoracic splanchnic nerve

•First lumbar splanchnic nerve

Microscopic Anatomy of the Kidneys

•Nephron is the functional unit of the kidney

•Over 1 million nephrons in each kidney

Mechanisms of Urine Production

•Filtration

•Filtrate of blood leaves kidney capillaries

•Resorption

•Most nutrients, water, and essential ions reclaimed

•Secretion

•Active process of removing undesirable molecules

Nephron Structure

•Nephron is composed of

•Renal tubule

•Renal corpuscle

24 PART 2

The Urinary System

Nephron Structure

•Renal corpuscle—first part of nephron

•Glomerulus and glomerular capsule

•Glomerulus—tuft of capillaries

•Capillaries of glomerulus are fenestrated

•Glomerular (Bowman’s) capsule

•Parietal layer—simple squamous epithelium

•Visceral layer—consists of podocytes

Filtration Membrane

•The filtration membrane

•Filter that lies between blood in the glomerulus and capsular space

•Consists of three layers

•Fenestrated endothelium of the capillary

•Filtration slits between foot processes of podocytes

•Basement membrane

Filtration Membrane

•Basement membrane and slit diaphragm

•Hold back most proteins

•Allow passage of

•Water

•Ions

•Glucose

•Amino acids

•Urea

Renal Tubule

•Filtrate proceeds to renal tubules from glomerulus

•Proximal convoluted tubule

•Nephron loop

•Descending limb

•Descending thin limb (DTL)

•Ascending thin limb (ATL)

•Thick ascending limb (TAL)

•Distal convoluted tubule

Renal Tubule

•Collecting ducts

•Receive urine from several nephrons

•Play an important role in conserving body fluids

•Posterior pituitary secretes ADH

•Increases permeability of collecting ducts and distal convoluted tubules to water

Classes of Nephron

•Cortical nephrons

•85% of nephrons

•Juxtamedullary nephrons

•15% of nephrons

•Contribute to kidney’s ability to concentrate urine