The Urinary System: Kidney & Nephron Flashcards
The 2 kidneys of the urinary system
Filter blood & produce urine
The 2 ureters of the urinary system
Transport urine from the kidneys to the urinary bladder
The urinary bladder is
A temporary storage reservoir for urine
The urethra
Transports urine out of the body
The functions of the kidneys are
Excretion of nitrogenous waste (urea, ammonia, creating, uric acid, and urobilin), drugs & environmental toxins
Regulation of blood ion, pH & osmolarity
Regulation of blood volume & pressure
Hormone production (e.g., erythropoietin)
Regulation of blood glucose (gluconeogenesis)
The kidneys lie
Retroperitoneal in the superior lumbar region
◦Right kidney is lower than left (crowded by liver)
The 3 layers of supportive tissue surrounding the kidneys are
◦Renal fascia – outer layer of dense fibrous
connective tissue that anchors kidney & adrenal gland to surrounding structures
◦Perirenal fat capsule – surrounds & cushions the
kidney
◦Fibrous capsule – transparent capsule that
protects from surrounding infections & trauma
The renal hilum is
An indentation along concave border of the kidney
◦ Ureter, blood vessels, lymphatic vessels, nerves
Outermost region of the kidney is
The renal cortex
Middle region of the kidney is
The renal medulla (contains renal pyramids)
Innermost region of the kidney is
The renal pelvis, a funnel-shaped tube continuous with the ureter
◦ Minor & major calyces collect urine & empty it
into the renal pelvis
Blood enters each kidney through one renal artery via
Arterial blood flow
Blood flows into the renal cortex through
Progressively smaller arteries
Gives rise to microscopic vasculature that is a key element of kidney function
Afferent arterioles
Blood leaves the kidneys via the
Veins (renal arterial circulation in reverse)
The renal nerve plexus composed mostly of sympathetic fibres regulates renal blood flow by
Adjusting the diameter of renal arterioles & influencing the formation of urine by the nephron
The structural & functional units that form urine are
Nephrons (1 million+ per kidney)
Nephrons form a
Cell- & protein-free filtrate from blood that
◦ Recovers (reabsorbs) chemicals the body needs
◦Secretes selected chemicals to get rid of
Two main parts of a nephron are:
Renal corpuscle (filters plasma)
◦ Located in renal cortex
Renal tubules (regulates filtrate via selective absorption & secretion)
◦ Starts in renal cortex, passes into medulla, &
returns to cortex
The glomerulus of the renal corpuscle is composed of
Fenestrated capillaries that increase permeability to form a solute-rich, but protein-free, filtrate
The glomerular (Bowman’s) capsule of the renal corpuscle is
A Double-walled epithelial cup surrounding the glomerulus
◦Parietal layer – contributes to capsular structure
◦Visceral layer – associated with the glomerular capillaries (consists of podocytes)
The path of filtrate in the renal tubule of the kidneys is:
Proximal convoluted tubule (PCT)
Nephron loop (loop of Henle)
- descending then ascending limb
Distal convoluted tubule (DCT)
Collecting duct
The epithelium of the renal tubule & collecting duct is
Simple (1 layer)
The epithelium of the PCT has
Dense microvilli to ↑SA for absorption & secretion
The epithelium of the nephron loop is
◦ simple squamous in the thin descending limb
◦ both thin and thick (simple cuboidal) in the ascending limb
The cells of the DCT epithelium lack
Microvilli
Principal cells in the collecting ducts control
H2O & Na+ balance via Na+ channels & aquaporins
The intercalated cells in the collecting ducts control
pH by secreting/absorbing H+ or HCO3-
The collecting ducts collect filtrate from many nephrons & extend through the renal pyramid to the
Renal papilla, where they empty into a minor calyx
◦ Give the pyramids their striped appearance
The 2 classes of nephron are
Cortical and Juxtamedullary
Nephrons that are
◦ the majority (85%)
◦ located almost entirely within cortex
◦ have a short nephron loop
Cortical nephrons
Nephrons that are
◦ Located near the cortex-medulla junction
◦ Have a long nephron loop
◦ play an important role in kidney’s ability to concentrate urine (help with water conservation)
Juxtamedullary nephrons
The nephron capillary beds formed by the efferent arteriole are
Peritubular capillaries surrounding the cortical tubule
◦ Low-pressure, porous, absorb solutes & H2O from tubule cells
Vasa recta surrounding the medulla tubule
◦ Arise from the efferent arterioles near juxtamedullary nephrons & run parallel to longest nephron loops (counter current)
Being fed & drained by afferent & efferent arterioles maintains the
The high pressure in the glomerulus that is necessary for filtration
The juxtaglomerular complex if the region where
The afferent arteriole & distal convoluted tubule (DCT) meet
◦ Regulates rate of filtrate formation & systemic blood pressure
The macula densa cells (chemoreceptors) in the DCT monitor
The NaCl content of filtrate entering DCT
The juxtaglomerular cells in walls of the afferent arterioles act like mechanoreceptors to monitor
Blood pressure & house secretory vesicles containing the enzyme renin
