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afferent arteriole

In the kidney, the blood vessel supplying a nephron.

aldosterone

A steroid hormone that acts on tubules of the kidney to regulate the transport of sodium ions (Na+) and potassium ions (K+).

ammonia

A small, very toxic molecule (NH3) produced by nitrogen fixation or as a metabolic waste product of protein and nucleic acid metabolism.

angiotensin II

A peptide hormone that stimulates constriction of precapillary arterioles and increases reabsorption of NaCl and water by the proximal tubules of the kidney, increasing blood pressure and volume.

anhydrobiosis

A dormant state involving loss of almost all body water.

antidiuretic hormone (ADH)

A peptide hormone, also known as vasopressin, that promotes water retention by the kidneys. Produced in the hypothalamus and released from the posterior pituitary, ADH also has activities in the brain.

aquaporin

A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of water across the membrane.

atrial natriuretic peptide (ANP)

A peptide hormone secreted by cells of the atria of the heart in response to high blood pressure. ANP's effects on the kidney alter ion and water movement and thereby reduce blood pressure.

Bowman's capsule

A cup-shaped receptacle in the vertebrate kidney that is the initial, expanded segment of the nephron where filtrate enters from the blood.

collecting duct

The location in the kidney where processed filtrate, called urine, is collected from the renal tubules.

cortical nephron

In mammals and birds, a nephron with a loop of Henle located almost entirely in the renal cortex.

countercurrent multiplier system

A countercurrent system in which energy is expended in active transport to facilitate exchange of materials and generate concentration gradients.

distal tubule

In the vertebrate kidney, the portion of a nephron that helps refine filtrate and empties it into a collecting duct.

efferent arteriole

In the kidney, the blood vessel draining a nephron.

euryhaline

Referring to organisms that tolerate substantial changes in external osmolarity.

excretion

The disposal of nitrogen-containing metabolites and other waste products.

excretion

The disposal of nitrogen-containing metabolites and other waste products.

filtrate

Cell-free fluid extracted from the body fluid by the excretory system.

filtration

In excretory systems, the extraction of water and small solutes, including metabolic wastes, from the body fluid.

glomerulus

A ball of capillaries surrounded by Bowman's capsule in the nephron and serving as the site of filtration in the vertebrate kidney.

hypothalamus

The ventral part of the vertebrate forebrain; functions in maintaining homeostasis, especially in coordinating the endocrine and nervous systems; secretes hormones of the posterior pituitary and releasing factors that regulate the anterior pituitary.

isotonic

Referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cell.

juxtaglomerular apparatus (JGA)

A specialized tissue in nephrons that releases the enzyme renin in response to a drop in blood pressure or volume.

juxtamedullary nephron

In mammals and birds, a nephron with a loop of Henle that extends far into the renal medulla.

loop of Henle

The hairpin turn, with a descending and ascending limb, between the proximal and distal tubules of the vertebrate kidney; functions in water and salt reabsorption.

Malpighian tubule

A unique excretory organ of insects that empties into the digestive tract, removes nitrogenous wastes from the hemolymph, and functions in osmoregulation.

metanephridium

(plural, metanephridia) An excretory organ found in many invertebrates that typically consists of tubules connecting ciliated internal openings to external openings.

nephron

The tubular excretory unit of the vertebrate kidney.

osmoconformer

An animal that is isoosmotic with its environment.

osmolarity

Solute concentration expressed as molarity.

osmoregulation

Regulation of solute concentrations and water balance by a cell or organism.

osmoregulator

An animal that controls its internal osmolarity independent of the external environment.

peritubular capillary

One of the tiny blood vessels that form a network surrounding the proximal and distal tubules in the kidney.

pituitary gland

An endocrine gland at the base of the hypothalamus; consists of a posterior lobe (neurohypophysis), which stores and releases two hormones produced by the hypothalamus, and an anterior lobe (adenohypophysis), which produces and secretes many hormones that regulate diverse body functions.

protonephridia

An excretory system, such as the flame bulb system of flatworms, consisting of a network of tubules lacking internal openings.

proximal tubule

In the vertebrate kidney, the portion of a nephron immediately downstream from Bowman's capsule that conveys and helps refine filtrate.

purine

One of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring fused to a five-membered ring. Adenine (A) and guanine (G) are purines.

reabsorption

In excretory systems, the recovery of solutes and water from filtrate.

renal artery

The blood vessel bringing blood to the kidney.

renal cortex

The outer portion of the vertebrate kidney.

renal medulla

The inner portion of the vertebrate kidney, beneath the renal cortex.

renal pelvis

The funnel-shaped chamber that receives processed filtrate from the vertebrate kidney's collecting ducts and is drained by the ureter.

renal vein

The blood vessel that carries blood away from the kidney.

renin-angiotensin-aldosterone system (RAAS)

A hormone cascade pathway that helps regulate blood pressure and blood volume.

secretion

(1) The discharge of molecules synthesized by a cell. (2) The discharge of wastes from the body fluid into the filtrate.

stenohaline

Referring to organisms that cannot tolerate substantial changes in external osmolarity.

transport epithelium

One or more layers of specialized epithelial cells that regulate solute movements.

urea

A soluble nitrogenous waste produced in the liver by a metabolic cycle that combines ammonia with carbon dioxide.

ureter

A duct leading from the kidney to the urinary bladder.

urethra

A tube that releases urine from the mammalian body near the vagina in females and through the penis in males; also serves in males as the exit tube for the reproductive system.

uric acid

A product of protein and purine metabolism and the major nitrogenous waste product of insects, land snails, and many reptiles. Uric acid is relatively nontoxic and largely insoluble.

urinary bladder

The pouch where urine is stored prior to elimination.

vasa recta

The capillary system in the kidney that serves the loop of Henle.

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