Renal

What are the kidneys’ core functions?

They regulate water balance, osmolarity, electrolyte concentration, plasma volume, acid-base balance, and blood pressure; they excrete metabolic wastes and perform endocrine functions.

How do kidneys produce urine while maintaining homeostasis?

They process plasma, retain needed substances through reabsorption, and eliminate unwanted or excess substances in urine.

What happens when water or a solute is in excess?

The kidney increases its excretion into urine.

What happens when water or a solute is deficient?

The kidney conserves it and minimizes urinary loss, although it cannot create a missing substance.

Why are kidneys highly metabolically active organs?

They receive about 20% of cardiac output and require substantial oxygen to power continuous transport processes.

What body-fluid property do kidneys regulate through water balance?

Osmolarity, or solute concentration, of body fluids.

What happens to cells when extracellular fluid osmolarity is too high?

Cells shrink because water moves out of them.

What happens to cells when extracellular fluid osmolarity is too low?

Cells swell because water moves into them.

Which important electrolytes are regulated by the kidneys?

Na⁺, K⁺, Ca²⁺, H⁺, Mg²⁺, Cl⁻, HCO₃⁻, PO₄³⁻, and SO₄²⁻.

How do kidneys contribute to acid-base balance?

They regulate urinary excretion of H⁺ and HCO₃⁻, helping maintain blood pH.

Which metabolic wastes are eliminated by the kidneys?

Nitrogenous wastes such as urea, uric acid, creatinine, and other products including bilirubin-related compounds and hormone breakdown products.

What endocrine functions do kidneys have?

They produce erythropoietin, activate vitamin D, and synthesize renin to initiate the renin-angiotensin-aldosterone system.

What does erythropoietin do?

It stimulates red-blood-cell production in bone marrow, especially when oxygen delivery is low.

What is the urinary system composed of?

Urine-forming kidneys; ureters, urinary bladder, and urethra that carry/store/eliminate urine; and the renal blood vessels.

Where are the kidneys located?

They are paired, bean-shaped organs on the posterior wall of the abdominal cavity.

What vessels supply and drain each kidney?

A renal artery delivers blood to the kidney, and a renal vein returns blood to systemic circulation.

What is the renal pelvis?

A funnel-like collecting area at the medial aspect of the kidney where urine gathers before entering the ureter.

What is the flow of urine after it leaves renal collecting ducts?

Collecting ducts → papillary ducts → minor calyces → major calyces → renal pelvis → ureter → urinary bladder → urethra.

What is the ureter?

A smooth-muscle-walled duct that exits the kidney near the renal vessels and transports urine to the urinary bladder.

How do ureters move urine toward the bladder?

Smooth muscle in the ureter wall produces peristaltic contractions.

What is the urinary bladder?

A hollow, distensible, smooth-muscle-walled sac that temporarily stores urine.

How does the bladder empty?

Bladder smooth muscle contracts and urine exits through the urethra; sphincters regulate outlet resistance.

What is the urethra’s main function?

It conveys urine from the bladder to the outside of the body.

How does female urethral anatomy differ from male urethral anatomy?

The female urethra is short and relatively straight. The male urethra is longer and follows a more curved course.

Why is urethral anatomy clinically important for catheterization in male animals?

The male urethra can curve around the pelvic ischium and pass beneath the skin, creating a point of resistance during catheter passage.

What additional function does the male urethra have?

It serves as a passageway for semen from reproductive organs as well as a route for urine.

What can occur when ureters fail to empty into the bladder normally?

Ectopic ureters may bypass normal bladder entry and deliver urine distal to the sphincter, causing urinary incontinence.

What are the two gross regions of the kidney?

The outer renal cortex and the inner renal medulla.

What is found mainly in the renal cortex?

Renal corpuscles, including glomeruli and Bowman’s capsules, plus convoluted tubules.

What is found mainly in the renal medulla?

Striated renal pyramids containing loops of Henle and collecting ducts.

Why does the renal cortex look granular?

It contains many renal corpuscles and convoluted tubules.

Why does the renal medulla look striated?

Parallel loops of Henle and collecting ducts run through the renal pyramids.

What is a nephron?

The kidney’s functional unit: the smallest structure that can perform the kidney’s basic urine-forming functions.

About how many nephrons does a human kidney contain?

Approximately 1 million.

What are the two broad components of a nephron?

A vascular component and a tubular component.

What structures make up the nephron vascular component?

Afferent arteriole, glomerulus, efferent arteriole, and peritubular capillaries.

What structures make up the nephron tubular component?

Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, and collecting duct.

What is the main function of the nephron vascular component?

It filters plasma at the glomerulus and exchanges substances with tubular fluid through peritubular capillaries.

What is the main function of the nephron tubular component?

It modifies filtered fluid through reabsorption and secretion to convert filtrate into urine.

What is the glomerulus?

A ball-like tuft of specialized capillaries in the renal cortex where water and small solutes filter from blood into Bowman’s capsule.

Why is the glomerulus described as a sieve?

It permits filtration of water and many small solutes while normally retaining blood cells and most plasma proteins.

What vessel brings blood into the glomerulus?

The afferent arteriole.

What vessel carries blood away from the glomerulus?

The efferent arteriole.

Why is glomerular hydrostatic pressure relatively high?

The efferent arteriole has a smaller diameter than the afferent arteriole, creating resistance to outflow and maintaining pressure that drives filtration.

What force primarily drives glomerular filtration?

Glomerular hydrostatic pressure pushing fluid from glomerular capillaries into Bowman’s capsule.

What is glomerular filtrate?

Protein-poor plasma-like fluid that enters Bowman’s capsule as the first step in urine formation.

What are peritubular capillaries?

Capillaries arising from the efferent arteriole that surround renal tubules and participate in reabsorption and secretion.

What is Bowman’s capsule?

The cup-like beginning of the nephron tubule that surrounds the glomerulus and receives filtrate.

What are the parietal and visceral layers of Bowman’s capsule?

The parietal layer forms the outer wall of the capsule. The visceral layer lies directly over glomerular capillaries and consists of podocytes.

What are podocytes?

Specialized cells of the visceral layer of Bowman’s capsule whose foot processes surround glomerular capillaries and contribute to the filtration barrier.

What is the filtration barrier?

The specialized barrier formed by fenestrated glomerular endothelium, basement membrane, and podocyte filtration slits; it limits passage of cells and most proteins.

What is the proximal tubule’s general role?

It performs bulk reabsorption of filtered water, sodium, nutrients, and many other useful solutes.

What is the loop of Henle’s general role?

It helps establish the medullary osmotic gradient needed to concentrate or dilute urine.

What is the distal tubule’s general role?

It fine-tunes electrolyte and acid-base handling and receives regulatory input from the juxtaglomerular apparatus.

What is the collecting duct’s general role?

It receives fluid from multiple nephrons and makes final hormone-regulated adjustments to water and solute excretion.

What does ADH do in the kidney?

Antidiuretic hormone increases water reabsorption, especially in collecting ducts, by increasing their water permeability. It helps conserve body water and produce more concentrated urine.

What stimulates ADH release?

Increased plasma osmolarity or decreased effective circulating volume/blood pressure stimulates ADH release.

What is the juxtaglomerular apparatus?

A specialized region where the distal tubule contacts the afferent arteriole; it helps regulate renin release and glomerular filtration.

What is renin?

An enzyme released by juxtaglomerular cells when renal perfusion, blood pressure, or sodium delivery is low.

What is the RAAS?

The renin-angiotensin-aldosterone system, a hormonal cascade that raises blood pressure and promotes sodium and water retention.

What does angiotensin II do?

It causes vasoconstriction, promotes aldosterone release, supports sodium retention, and helps maintain blood pressure and renal perfusion.

What does aldosterone do?

It increases sodium reabsorption and potassium secretion in the distal nephron; water follows retained sodium when water permeability permits.