Urinary System Part 1

Main function of the urinary system

Continuously filters blood plasma to maintain homeostasis.

Structures of the urinary system

Kidneys, ureters, urinary bladder, and urethra.

Function of the kidneys

Produce urine by filtering blood.

Function of the ureters

Transport urine to the bladder.

Function of the urinary bladder

Stores urine.

Function of the urethra

Eliminates urine from the body.

Main jobs of the kidneys

Remove metabolic wastes, regulate water balance, regulate ion concentrations, and help regulate blood pressure and pH.

How much fluid do the kidneys filter each day?

About 180-200 L.

How much urine is produced each day?

About 1.5-2 L.

Why is only a small amount of filtered fluid excreted as urine?

Most filtered material is returned to the blood.

Result of kidney function

Wastes are eliminated while useful substances are conserved.

Nitrogenous wastes

Metabolic wastes removed from the blood by the kidneys.

Urea

Produced during amino acid metabolism.

Uric acid

Produced during nucleic acid metabolism.

Creatinine

Produced by muscle metabolism.

What happens if nitrogenous wastes accumulate in the blood?

Cellular function becomes disrupted and homeostasis begins to fail.

Four major processes of urine formation

Filtration, reabsorption, secretion, and excretion.

Filtration

Fluid leaves the blood and enters the nephron.

Reabsorption

Useful substances move from the nephron back into the blood.

Secretion

Additional wastes move from the blood into the nephron.

Excretion

Remaining fluid leaves the body as urine.

Location of the kidneys

Retroperitoneal (behind the parietal peritoneum).

How are the kidneys protected?

Partially protected by the ribs.

Fibrous capsule

Supports kidney tissues.

Adipose capsule

Cushions the kidneys.

Renal fascia

Anchors the kidneys.

Renal cortex

Outer region of the kidney.

Renal medulla

Inner region containing renal pyramids.

Renal pyramids

Contain nephrons and blood vessels.

Where does urine formed in the nephrons drain?

Toward the center of the kidney before entering the ureter.

Hilum

Recessed area on the medial side of the kidney where blood vessels, nerves, and the ureter enter or leave.

Blood flow to the glomerulus

Renal artery → interlobar arteries → afferent arteriole → glomerulus.

Glomerulus

Beginning of the nephron where blood pressure creates filtrate.

What creates filtrate?

Blood pressure forcing fluid out of glomerular capillaries.

Where does blood leave the glomerulus?

Through the efferent arteriole.

Blood flow after the glomerulus

Efferent arteriole → peritubular capillaries.

Reabsorption in the nephron

Substances move from filtrate to blood.

Secretion in the nephron

Substances move from blood to filtrate.

Filtrate

Fluid filtered from the blood.

Pathway of filtrate through the nephron

Bowman's capsule → proximal convoluted tubule → nephron loop → distal convoluted tubule → collecting duct.

What happens to filtrate as it moves through the nephron?

Useful substances are reabsorbed and additional wastes may be secreted.

Urine

Fluid leaving the collecting duct.

Pathway of urine out of the kidney

Renal papilla → minor calyx → major calyx → renal pelvis → ureter.

What does urine composition reflect?

Kidney function, hydration level, and blood chemistry.

Renal corpuscle

Contains the glomerulus and Bowman's capsule; site where filtration begins.

Glomerulus (renal corpuscle)

Fenestrated capillary network.

Bowman's capsule

Surrounds the glomerulus.

Why does filtration occur in the renal corpuscle?

Blood enters under unusually high pressure, forcing water and small solutes out of capillaries.

What does filtrate initially resemble?

Blood plasma.

What does filtrate contain?

Water, ions, glucose, amino acids, and nitrogenous wastes.

What remains in the bloodstream during filtration?

Blood cells and most proteins.

Why is reabsorption necessary?

Filtration is mostly nonselective, so useful substances must be returned to the blood.