Physiology - Urinary System Terms

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Aldosterone

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Aldosterone: a steroid hormone released from the adrenal cortex that regulates the reabsorption of sodium and secretion of potassium

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Angiotensin Converting Enzyme (ACE)

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Angiotensin converting enzyme (ACE): enzyme that converts angiotensin I to angiotensin II

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Antidiuretic hormone (ADH)

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Antidiuretic hormone (ADH): hormone secreted by the posterior pituitary that regulates water reabsorption by the kidneys; also called vasopressin

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Atrial Natriuretic Peptide (ANP)

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Atrial natriuretic peptide (ANP): hormone secreted from the atrium that regulates plasma sodium levels

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Bowman's Capsule

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Bowman’s capsule: in each nephron, a cup-shaped structure that surrounds the glomerulus and conducts filtrate into the renal tubule at the inflow end of the renal tubules; site where filtrate enters the renal tubules.

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Calcitonin

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Calcitonin: peptide hormone released from C cells of the thyroid gland that regulates plasma calcium levels

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Calcitriol

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Calcitriol: steroid hormone derived from vitamin D that regulates plasma calcium levels

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Clearance

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Clearance: virtual measure of the volume of plasma from which a substance is completely removed or “cleared” by the kidneys per unit time

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Collecting Ducts

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Collecting ducts: ducts that collect fluid from several different renal tubules and carry it to the renal pelvis for eventual elimination

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Cortex

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Cortex: outer portion of an organ such as cerebral cortex, adrenal cortex, and renal cortex

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Detrusor Muscle

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Detrusor muscle: smooth muscle fibers of the bladder

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Distal Convoluted tubule

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Distal convoluted tubule: portion of nephron furthest from renal corpuscle

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Excretion

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Excretion: elimination from the body through the kidneys (urine) or GI tract (feces)

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External Urethral Sphincter

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External urethral sphincter: ring of skeletal muscle that regulates the excretion of urine

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Filtered Load

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Filtered load: the quantity of a certain solute that is filtered at the glomerulus per unit time; equals the product of the GFR and the plasma concentration of the solute

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Glomerular Filtration

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Glomerular filtration: the bulk flow of protein-free plasma from the glomerular capillaries into Bowman’s capsule

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Glomerular Filtration Pressure

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Glomerular filtration pressure: sum of the Starling forces acting to move fluid across the capillary walls of the glomerulus

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Glomerular Filtration Rate (GFR)

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Glomerular filtration rate (GFR): the volume of the plasma filtered per unit time from all renal glomeruli combined

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Glomerulus

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Glomerulus: in each nephron, a ball-like cluster of capillaries in the renal corpuscle; site of filtration

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Granular Cells

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Granular cells: specialized cells in the wall of the afferent and efferent arterioles that secrete renin; also called juxtaglomerular cells

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Internal Urethral Sphincter

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Internal urethral sphincter: ring of smooth muscle that regulates the excretion of urine

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Juxtaglomerular Apparatus

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Juxtaglomerular apparatus: a collection of specialized cells in the distal tubules and the afferent and efferent arterioles near where the three structures come together in the kidney; regulates glomerular filtration and renin secretion

Juxtaglomerular cells: see granular cells

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Loop of Henle

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Loop of Henle: the portion of the renal tubule that forms a hairpin loop that dips into the medulla, including the descending limb, the thin ascending limb, and the thick ascending limb

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Macula Densa

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Macula densa: specialized cluster of epithelial cells found in the distal convoluted tubule in the region adjacent to the afferent and efferent arterioles

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Medulla

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Medulla: internal compartment of certain organs such as adrenal medulla and renal medulla

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Metabolic Acidosis

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Metabolic acidosis: decrease in blood pH in response to changes other than carbon dioxide levels

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Metabolic Alkalosis

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Metabolic alkalosis: increase in blood pH in response to changes other than carbon dioxide levels

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Micturition

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Micturition: the elimination of urine from the body or urination

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Myogenic Regulation

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Myogenic regulation: means of autoregulating glomerular filtration rate by the inherent ability of smooth muscle of the afferent arterioles to contract when stretched

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Nephrons

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Nephrons: functional units of the kidneys that filter the blood and form urine; each consists of a renal corpuscle (a glomerulus and Bowman’s capsule) and renal tubule

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Obligatory Water Loss

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Obligatory water loss: minimum volume of water that must be excreted in urine to eliminate solutes

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Osmoreceptor

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Osmoreceptor: receptors that detect the osmolarity of various body fluids

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Parathyroid Hormone (PTH)

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Parathyroid hormone (PTH): peptide hormone released from the parathyroid glands that regulates plasma calcium levels

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Peritubular Capillaries

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Peritubular capillaries: capillary bed that branches off the efferent arterioles of cortical nephrons and is located close to the renal tubules; functions in exchange with renal tubules during reabsorption and secretion

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Proximal Tubule

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Proximal tubule: portion of the renal tubule nearest the renal corpuscle; includes proximal convoluted tubule and the proximal straight tubule

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Reabsorption

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Reabsorption: transport of a substance into blood

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Renal Arteries

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Renal arteries: arteries that branch off the aorta and provide the kidneys with their blood supply

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Renal Corpuscle

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Renal corpuscle: site of glomerular filtration; consists of glomerulus and Bowman’s capsule

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Renal Pelvis

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Renal pelvis: funnel-shaped passage forming the initial portion of the ureter

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Renal Threshold

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Renal threshold: the plasma concentration of solute at which the transport maximum is exceeded and excess solute appears in the urine

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Renal Tubule

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Renal tubule: a portion of a nephron, consisting of a long, coiled tube

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Renal Veins

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Renal veins: transport of blood from the kidneys back into general circulation

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Renin

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Renin: enzyme released by the kidney; converts angiotensinogen to angiotensin I

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Secretion

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Secretion: movement of substance from the internal environment to the external environment by transport across an epithelium; movement of a substance from inside a cell to outside the cell by movement across the plasma membrane

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Transport maximum (Tm)

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Transport maximum (Tm): rate of transport by carrier proteins when carriers are 100% saturated

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Tubuloglomerular feedback

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Tubuloglomerular feedback: autoregulatory mechanism in which a change in glomerular filtration rate is regulated by paracrines secreted from the macula densa, located downstream from the glomerulus

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Urinary System

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Urinary system: organ system that consists of two kidneys, two ureters, the urinary bladder, and the urethra

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Urine

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Urine: a fluid produced by the kidneys and eliminated from the body

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Vasa recta

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Vasa recta: capillary bed that branches off the efferent arteriole of a juxtamedullary nephron and surrounds the loop of Henle; functions in maintaining medullary osmotic gradient