Chapter 23, Lesson 4: Tubular Reabsorption and Secretion

Flashcards from Chapter 23, Lesson 4 of McGraw Hill Anatomy and Physiology, Tenth Edition, by Kenneth S. Saladin.

Proximal convoluted tubule (PCT)

Reabsorbs about 65% of glomerular filtrate, removes substances from blood and secretes them into tubular fluid

Mostly for absorption with long length, microvilli, and mitochondria (6% of resting ATP)

Tubular reabsorption

The process of reclaiming water and solutes from tubular fluid and returning them to blood; has a transcellular and paracellular route

Transcellular route

Passing substances through the cytoplasm of PCT epithelial cells and out their base

Paracellular route

Passing substances between PCT cells

Solvent drag

The carrying of a variety of dissolved substances as water passes through the paracellular route

Sodium-glucose transporters (SGLTs)

Transporters of glucose using facilitated diffusion; normally all glucose is absorbed with none in the urine

Nitrogenous waste absorption

• Urea passes through with water; about half is reabsorbed to safe levels

• PCT reabsorbs nearly all uric acid, later portions secrete it

• Creatinine is passed in urine

Transport maximum

The maximum rate of reabsorption for a solute, which is reached when all transport proteins are saturated—any excess appears in urine

Glycosuria

Glucose in urine as a result of blood glucose over 220 mg/dL, a sign of untreated diabetes mellitus

Tubular secretion

Process where the renal tubule extracts chemicals from capillary blood and secretes them into tubular fluid; aiding acid-base balance, waste removal, and drug clearance

Nephron loop

Urinary organ that functions to generate osmotic gradients to enable urine concentration, water conservation by collecting duct

Principal cells

The most abundant cell in the DCT, sensing aldosterone, natriuretic peptides, antidiuretic hormone, parathyroid hormone for salt and water balance

Aldosterone

Steroid hormone that simulates sodium reabsorption and potassium secretion; secreted by the adrenal cortex for use in ascending nephron loop, DCT, cortical portion of collecting duct to maintain blood volume and pressure

aldos = salt retaining

Natriuretic peptides

Peptides secreted by the heart in response to hypertension, resulting in more salt and water excretion to reduce blood volume and pressure

Antidiuretic hormone (ADH)

Stimulates water retention by the kidney, caused by dehydration, loss of blood volume, rising blood osmolarity for a more water permeable collecting duct

Aquaporins

Water channels for transcellular absorption through osmosis

Obligatory water reabsorption

Reabsorbing water independent of hormones in the PCT at a constant rate

Parathyroid hormone (PTH)

Secreted from parathyroid glands in response to hypocalcemia to increase calcium reabsorption