A&P Exam 4 - Urinary System

What are the four organs of the urinary system?

Kidneys, ureters, urinary bladder, and urethra.

What is the primary function of the urinary system?

Remove metabolic wastes from blood.

What are the kidneys' major functions?

Waste removal, BP regulation, acid-base and ion balance, EPO and calcitriol production, and gluconeogenesis.

What stimulates kidney EPO secretion?

Low blood oxygen.

What does erythropoietin (EPO) do?

Stimulates red blood cell production in bone marrow.

What is calcitriol?

Active vitamin D; increases calcium absorption in the small intestine.

When can kidneys perform gluconeogenesis?

During extreme nutrient deprivation.

Where are kidneys located?

Posterior abdominal wall, approximately T12–L3.

What is the renal cortex?

Outer kidney tissue.

What is the renal medulla?

Kidney tissue deep to the cortex.

How do ureters move urine to the bladder?

Peristalsis.

What carries urine from bladder to outside the body?

Urethra.

What is a nephron?

Functional filtration unit of the kidney.

Approximately how many nephrons are in each kidney?

1.2 million.

What are the two major parts of a nephron?

Renal corpuscle and renal tubule.

What structures form the renal corpuscle?

Glomerulus and glomerular (Bowman's) capsule.

What structures form the renal tubule?

PCT, nephron loop, and DCT.

What is the glomerulus?

Capillary cluster where blood filtration occurs.

What is the glomerular capsule?

Hollow capsule surrounding the glomerulus that collects filtrate.

What is filtrate?

Fluid and small substances filtered from glomerular blood.

Where is the PCT located?

Renal cortex.

Where does the nephron loop extend?

Down into the renal medulla and back toward the cortex.

Where is the DCT located?

Renal cortex.

What receives fluid from the DCT?

Collecting tubule, then collecting duct.

What does a collecting duct receive?

Fluid from multiple nephrons.

What is the order of tubular fluid flow?

Glomerular capsule → PCT → nephron loop → DCT → collecting tubule → collecting duct.

What are the three basic processes of urine formation?

Glomerular filtration, tubular reabsorption, and tubular secretion.

Where does glomerular filtration occur?

Renal corpuscle.

What is tubular reabsorption?

Movement from tubular fluid back to blood.

What is tubular secretion?

Movement from blood into tubular fluid.

Where do reabsorption and secretion occur?

Along the renal tubule and collecting duct.

Which arteriole carries blood into the glomerulus?

Afferent arteriole.

Which arteriole carries blood away from the glomerulus?

Efferent arteriole.

Which glomerular arteriole is normally wider?

Afferent arteriole.

How does the narrower efferent arteriole affect glomerular pressure?

Helps maintain high glomerular blood pressure for filtration.

What small substances enter filtrate?

Water, ions, glucose, amino acids, urea, some hormones, and a few small proteins.

What normally stays in glomerular blood?

Red blood cells and large proteins.

What is the main filtration criterion emphasized in lecture?

Molecule size.

What are the three layers of the glomerular filtration membrane?

Fenestrated endothelium, fused basement membrane, podocytes.

What are fenestrations?

Small holes in capillary endothelial cells.

What are podocytes?

Cells wrapping glomerular capillaries.

What are pedicels?

Podocyte extensions separated by filtration slits.

What drives glomerular filtration?

Glomerular hydrostatic pressure exceeds opposing pressures.

What is HPg?

Glomerular blood hydrostatic pressure; favors filtration.

What is HPc?

Capsular hydrostatic pressure; opposes filtration.

What is OPg?

Blood colloid osmotic pressure; opposes filtration.

What is the net filtration pressure equation?

NFP = HPg − HPc − OPg.

What are the lecture's example filtration pressures?

HPg 60, HPc 18, OPg 32 mmHg.

What is the example net filtration pressure?

10 mmHg outward.

Which filtration pressure is most adjustable?

HPg.

What is GFR?

Amount of filtrate formed per minute by both kidneys.

What typical GFR range is listed?

90–120 mL/min.

How much filtrate is produced daily?

About 180 L.

How much filtrate is reabsorbed?

About 99%.

How much urine is excreted daily?

About 1–2 L.

Why is GFR that is too high harmful?

Too little time for reabsorption of needed substances.

Why is GFR that is too low harmful?

Wastes are removed inefficiently.

How does higher HPg affect GFR?

Increases GFR.

What are the three GFR regulatory mechanisms?

Renal autoregulation, sympathetic neural control, and hormonal control.

What is renal autoregulation?

Local nephron adjustments that stabilize GFR without external signals.

What are the two renal autoregulation mechanisms?

Myogenic response and tubuloglomerular feedback.

Which arteriole is mainly adjusted in renal autoregulation?

Afferent arteriole.

How does increased blood pressure affect the afferent arteriole in the myogenic response?

It constricts to prevent excessive GFR.

How does decreased blood pressure affect the afferent arteriole in the myogenic response?

It dilates to help maintain GFR.

What is tubuloglomerular feedback?

DCT NaCl sensing triggers changes in glomerular blood flow and GFR.

What do macula densa cells detect?

NaCl concentration in DCT tubular fluid.

What happens if macula densa senses high NaCl?

Granular cells constrict the afferent arteriole, decreasing GFR.

What additional substance do granular cells release?

Renin.

What does afferent arteriole constriction do to GFR?

Decreases GFR.

What does afferent arteriole dilation do to GFR?

Increases GFR.

How does efferent arteriole constriction affect GFR in the lecture model?

Raises glomerular pressure and helps maintain/increase GFR.

What happens to GFR with increased sympathetic stimulation?

Afferent constriction decreases GFR.

When is sympathetic control of GFR activated?

Exercise, emergencies, fight-or-flight.

Why does sympathetic stimulation lower GFR?

Conserves water and electrolytes.

What stimulates ANP release?

Increased atrial stretch due to high blood volume or pressure.

What does ANP do to the afferent arteriole?

Dilates it.

What does ANP do to GFR and urine production?

Increases both.

What does ANP do to systemic blood volume and pressure?

Decreases both.

Which two hormone releases does ANP inhibit?

Renin and aldosterone.

What epithelium lines the PCT?

Simple cuboidal with tall microvilli.

What epithelium lines thick nephron loop segments?

Simple cuboidal.

What epithelium lines thin nephron loop segments?

Simple squamous.

What epithelium lines the DCT?

Simple cuboidal with short, sparse microvilli.

What is transcellular transport?

Transport through epithelial cells.

What is paracellular transport?

Transport between epithelial cells.

Which capillaries receive reabsorbed material?

Peritubular capillaries or vasa recta.

What are three possible fates of a substance in tubular fluid?

Reabsorbed, secreted, or left for excretion.

Where is all normally filtered glucose reabsorbed?

PCT.

What transporter couples Na+ and glucose uptake?

SGLT.

Why can Na+ drive glucose uptake through SGLT?

Na+ moves down its gradient while glucose moves up its gradient.

How does glucose leave PCT epithelial cells for blood?

Down its concentration gradient.

Where is most Na+ reabsorbed?

PCT, approximately 65%.

How do Na+ transport proteins move Na+ into cells?

Facilitated diffusion down its gradient.

What keeps intracellular Na+ low?

Na+/K+ pump.

What hormone increases Na+ reabsorption in collecting ducts?

Aldosterone.

How does aldosterone increase Na+ reabsorption?

Adds Na+ channels and Na+/K+ pumps.

Why does aldosterone promote water reabsorption?

Water follows reabsorbed Na+ by osmosis.

How does ANP oppose aldosterone?

Inhibits Na+ channels, reducing Na+ reabsorption.

Where are amino acids normally fully reabsorbed?

PCT.

How are small filtered proteins handled in PCT?

Endocytosed, broken into amino acids by lysosomes, returned to blood.