Notes on Kidney Function and Structure • Kidney Basics: • Weight: ~0.5 kg. • Shape: Fist-shaped. • Function: Filter wastes from blood; hold up to 25% of the body’s blood at a time. • Urine Formation and Storage: • Filtration: Kidneys filter waste, conducting it to the bladder via ureters. • Storage: • Urinary sphincter muscle: Acts as a valve at the bladder’s base, allowing urine storage. • Urge Signals: • At ~200 mL: Bladder stretches slightly; nerves signal the brain. • At ~400 mL: Stretch receptors activate further; urgency increases. • At ~600 mL: Voluntary control is lost; sphincter relaxes, urine enters the urethra and is voided. • Kidney Anatomy (Referencing Figure 1): • Cortex: Outer layer of connective tissue encircling the kidney. • Medulla: Inner layer beneath the cortex. • Renal pelvis: Hollow chamber connecting the kidney to the ureter.

Nephron

Functional unit of the kidneys, approximately 1 million per kidney.

Afferent arteriole

Branches of the renal artery that supply blood to nephrons.

Glomerulus

Capillary bed receiving blood from afferent arterioles.

Bowman's capsule

Funnel-shaped structure surrounding the glomerulus, located in the cortex.

Proximal tubule

The thin tubule extending from Bowman's capsule.

Loop of Henle

Section of the nephron that descends into the kidney’s medulla, key in concentrating urine.

Distal tubule

The last segment of the nephron before urine moves to the collecting ducts.

Collecting ducts

Receive urine from multiple nephrons and merge in the renal pelvis.

Filtration

The movement of fluids from blood into the Bowman's capsule in the nephron.

Reabsorption

Transfer of essential solutes and water from the nephron back into the blood.

Secretion

The movement of materials from the blood into the nephron for excretion.

Osmotic gradient

Created by solutes actively transported in the nephron, drawing water into the blood.

Active transport

Movement of ions like Na⁺ across nephron cell membranes requiring energy.

Passive transport

Movement of negative ions following positive ions due to charge attraction.

Threshold level

The maximum level of a substance that can be reabsorbed before remaining in the nephron.

Nitrogen-containing wastes

Substances typically secreted into the nephron, including urea.

Excess ions

Includes excess H⁺ and K⁺ secreted into the nephron for excretion.

Penicillin

An example of a drug that may be secreted from the blood into the nephron.

Kidney filtration rates

Approximately 600 mL of fluid flows through the kidneys every minute.

Actual urine output

Only 1 mL of urine is formed per 120 mL of filtrate.

Glucose transport in kidneys

Glucose attaches to specific carrier molecules for active transport back to blood.

Fill in the blank: The _____ is the functional unit of the kidneys, responsible for filtering blood and forming urine.

Question: What is the primary function of the nephron?

The primary function of the nephron is to filter blood and form urine.

Fill in the blank: The _____ is the capillary bed receiving blood from afferent arterioles in the nephron.

Fill in the blank: The _____ is the structure in the nephron responsible for receiving urine from multiple nephrons and merging in the renal pelvis.