Module 16: The Urinary System

Lesson 1: Characteristics of Urine

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Dưới đây là danh sách những thuật ngữ Y khoa của module The Urinary System.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: The Urinary System

anatomical sphincter
smooth or skeletal muscle surrounding the lumen of a vessel or hollow organ that can restrict flow when contracted
angiotensin I
protein produced by the enzymatic action of renin on angiotensinogen; inactive precursor of angiotensin II
angiotensin II
protein produced by the enzymatic action of ACE on inactive angiotensin I; actively causes vasoconstriction and stimulates aldosterone release by the adrenal cortex
angiotensin-converting enzyme (ACE)
enzyme produced by the lungs that catalyzes the reaction of inactive angiotensin I into active angiotensin II
angiotensinogen
inactive protein in the circulation produced by the liver; precursor of angiotensin I; must be modified by the enzymes renin and ACE to be activated
anuria
absence of urine produced; production of 50 mL or less per day
aquaporin
protein-forming water channels through the lipid bilayer of the cell; allows water to cross; activation in the collecting ducts is under the control of ADH
Bowman’s capsule
cup-shaped sack lined by a simple squamous epithelium (parietal surface) and specialized cells called podocytes (visceral surface) that participate in the filtration process; receives the filtrate which then passes on to the PCTs
brush border
formed by microvilli on the surface of certain cuboidal cells; in the kidney it is found in the PCT; increases surface area for absorption in the kidney
calyces
cup-like structures receiving urine from the collecting ducts where it passes on to the renal pelvis and ureter
cortical nephrons
nephrons with loops of Henle that do not extend into the renal medulla
countercurrent multiplier system
involves the descending and ascending loops of Henle directing forming urine in opposing directions to create a concentration gradient when combined with variable permeability and sodium pumping
detrusor muscle
smooth muscle in the bladder wall; fibers run in all directions to reduce the size of the organ when emptying it of urine
distal convoluted tubules
portions of the nephron distal to the loop of Henle that receive hyposmotic filtrate from the loop of Henle and empty into collecting ducts
diuretic
compound that increases urine output, leading to decreased water conservation
efferent arteriole
arteriole carrying blood from the glomerulus to the capillary beds around the convoluted tubules and loop of Henle; portion of the portal system
endothelins
group of vasoconstrictive, 21-amino acid peptides; produced by endothelial cells of the renal blood vessels, mesangial cells, and cells of the DCT
external urinary sphincter
skeletal muscle; must be relaxed consciously to void urine
fenestrations
small windows through a cell, allowing rapid filtration based on size; formed in such a way as to allow substances to cross through a cell without mixing with cell contents
filtration slits
formed by pedicels of podocytes; substances filter between the pedicels based on size
forming urine
filtrate undergoing modifications through secretion and reabsorption before true urine is produced
glomerular filtration rate (GFR)
rate of renal filtration
glomerulus
tuft of capillaries surrounded by Bowman’s capsule; filters the blood based on size
glycosuria
presence of glucose in the urine; caused by high blood glucose levels that exceed the ability of the kidneys to reabsorb the glucose; usually the result of untreated or poorly controlled diabetes mellitus
incontinence
loss of ability to control micturition
intercalated cell
specialized cell of the collecting ducts that secrete or absorb acid or bicarbonate; important in acid–base balance
internal urinary sphincter
smooth muscle at the juncture of the bladder and urethra; relaxes as the bladder fills to allow urine into the urethra
inulin
plant polysaccharide injected to determine GFR; is neither secreted nor absorbed by the kidney, so its appearance in the urine is directly proportional to its filtration rate
juxtaglomerular apparatus (JGA)
located at the juncture of the DCT and the afferent and efferent arterioles of the glomerulus; plays a role in the regulation of renal blood flow and GFR
juxtaglomerular cell
modified smooth muscle cells of the afferent arteriole; secretes renin in response to a drop in blood pressure
juxtamedullary nephrons
nephrons adjacent to the border of the cortex and medulla with loops of Henle that extend into the renal medulla
leaky tight junctions
tight junctions in which the sealing strands of proteins between the membranes of adjacent cells are fewer in number and incomplete; allows limited intercellular movement of solvent and solutes
leukocyte esterase
enzyme produced by leukocytes that can be detected in the urine and that serves as an indirect indicator of urinary tract infection
loop of Henle
descending and ascending portions between the proximal and distal convoluted tubules; those of cortical nephrons do not extend into the medulla, whereas those of juxtamedullary nephrons do extend into the medulla
macula densa
cells found in the part of the DCT forming the JGA; sense Na+ concentration in the forming urine
medulla
inner region of kidney containing the renal pyramids
mesangial
contractile cells found in the glomerulus; can contract or relax to regulate filtration rate
micturition
also called urination or voiding
myogenic mechanism
mechanism by which smooth muscle responds to stretch by contracting; an increase in blood pressure causes vasoconstriction and a decrease in blood pressure causes vasodilation so that blood flow downstream remains steady
nephrons
functional units of the kidney that carry out all filtration and modification to produce urine; consist of renal corpuscles, proximal and distal convoluted tubules, and descending and ascending loops of Henle; drain into collecting ducts
net filtration pressure (NFP)
pressure of fluid across the glomerulus; calculated by taking the hydrostatic pressure of the capillary and subtracting the colloid osmotic pressure of the blood and the hydrostatic pressure of Bowman’s capsule
oliguria
below normal urine production of 400–500 mL/day
osteomalacia
softening of bones due to a lack of mineralization with calcium and phosphate; most often due to lack of vitamin D; in children, osteomalacia is termed rickets; not to be confused with osteoporosis
pedicels
finger-like projections of podocytes surrounding glomerular capillaries; interdigitate to form a filtration membrane
peritubular capillaries
second capillary bed of the renal portal system; surround the proximal and distal convoluted tubules; associated with the vasa recta
physiological sphincter
sphincter consisting of circular smooth muscle indistinguishable from adjacent muscle but possessing differential innervations, permitting its function as a sphincter; structurally weak
podocytes
cells forming finger-like processes; form the visceral layer of Bowman’s capsule; pedicels of the podocytes interdigitate to form a filtration membrane
polyuria
urine production in excess of 2.5 L/day; may be caused by diabetes insipidus, diabetes mellitus, or excessive use of diuretics
principal cell
found in collecting ducts and possess channels for the recovery or loss of sodium and potassium; under the control of aldosterone; also have aquaporin channels under ADH control to regulate recovery of water
proximal convoluted tubules (PCTs)
tortuous tubules receiving filtrate from Bowman’s capsule; most active part of the nephron in reabsorption and secretion
renal columns
extensions of the renal cortex into the renal medulla; separates the renal pyramids; contains blood vessels and connective tissues
renal corpuscle
consists of the glomerulus and Bowman’s capsule
renal cortex
outer part of kidney containing all of the nephrons; some nephrons have loops of Henle extending into the medulla
renal fat pad
adipose tissue between the renal fascia and the renal capsule that provides protective cushioning to the kidney
renal hilum
recessed medial area of the kidney through which the renal artery, renal vein, ureters, lymphatics, and nerves pass
renal papillae
medullary area of the renal pyramids where collecting ducts empty urine into the minor calyces
renal pyramids
six to eight cone-shaped tissues in the medulla of the kidney containing collecting ducts and the loops of Henle of juxtamedullary nephrons
renin
enzyme produced by juxtaglomerular cells in response to decreased blood pressure or sympathetic nervous activity; catalyzes the conversion of angiotensinogen into angiotensin I
retroperitoneal
behind the peritoneum; in the case of the kidney and ureters, between the parietal peritoneum and the abdominal wall
sacral micturition center
group of neurons in the sacral region of the spinal cord that controls urination; acts reflexively unless its action is modified by higher brain centers to allow voluntary urination
specific gravity
weight of a liquid compared to pure water, which has a specific gravity of 1.0; any solute added to water will increase its specific gravity
systemic edema
increased fluid retention in the interstitial spaces and cells of the body; can be seen as swelling over large areas of the body, particularly the lower extremities
trigone
area at the base of the bladder marked by the two ureters in the posterior–lateral aspect and the urethral orifice in the anterior aspect oriented like points on a triangle
tubuloglomerular feedback
feedback mechanism involving the JGA; macula densa cells monitor Na+ concentration in the terminal portion of the ascending loop of Henle and act to cause vasoconstriction or vasodilation of afferent and efferent arterioles to alter GFR
urethra
transports urine from the bladder to the outside environment
urinalysis
analysis of urine to diagnose disease
urochrome
heme-derived pigment that imparts the typical yellow color of urine
vasa recta
branches of the efferent arterioles that parallel the course of the loops of Henle and are continuous with the peritubular capillaries; with the glomerulus, form a portal system
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Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
The urinary system’s ability to filter the blood resides in about 2 to 3 million tufts of specialized capillaries—the glomeruli—distributed more or less equally between the two kidneys. Because the glomeruli filter the blood based mostly on particle size, large elements like blood cells, platelets, antibodies, and albumen are excluded. The glomerulus is the first part of the nephron, which then continues as a highly specialized tubular structure responsible for creating the final urine composition. All other solutes, such as ions, amino acids, vitamins, and wastes, are filtered to create a filtrate composition very similar to plasma. The glomeruli create about 200 liters (189 quarts) of this filtrate every day, yet you excrete less than two liters of waste you call urine.

Characteristics of the urine change, depending on influences such as water intake, exercise, environmental temperature, nutrient intake, and other factors (Table 1). Some of the characteristics such as color and odor are rough descriptors of your state of hydration. For example, if you exercise or work outside, and sweat a great deal, your urine will turn darker and produce a slight odor, even if you drink plenty of water. Athletes are often advised to consume water until their urine is clear. This is good advice; however, it takes time for the kidneys to process body fluids and store it in the bladder. Another way of looking at this is that the quality of the urine produced is an average over the time it takes to make that urine. Producing clear urine may take only a few minutes if you are drinking a lot of water or several hours if you are working outside and not drinking much.
Urinalysis (urine analysis) often provides clues to renal disease. Normally, only traces of protein are found in urine, and when higher amounts are found, damage to the glomeruli is the likely basis. Unusually large quantities of urine may point to diseases like diabetes mellitus or hypothalamic tumors that cause diabetes insipidus.

The color of urine is determined mostly by the breakdown products of red blood cell destruction (Figure 1). The “heme” of hemoglobin is converted by the liver into water-soluble forms that can be excreted into the bile and indirectly into the urine. This yellow pigment is urochrome. Urine color may also be affected by certain foods like beets, berries, and fava beans. A kidney stone or a cancer of the urinary system may produce sufficient bleeding to manifest as pink or even bright red urine. Diseases of the liver or obstructions of bile drainage from the liver impart a dark “tea” or “cola” hue to the urine. Dehydration produces darker, concentrated urine that may also possess the slight odor of ammonia. Most of the ammonia produced from protein breakdown is converted into urea by the liver, so ammonia is rarely detected in fresh urine. The strong ammonia odor you may detect in bathrooms or alleys is due to the breakdown of urea into ammonia by bacteria in the environment. About one in five people detect a distinctive odor in their urine after consuming asparagus; other foods such as onions, garlic, and fish can impart their own aromas! These food-caused odors are harmless.

Urine volume varies considerably. The normal range is one to two liters per day (Table 2). The kidneys must produce a minimum urine volume of about 500 mL/day to rid the body of wastes. Output below this level may be caused by severe dehydration or renal disease and is termed oliguria. The virtual absence of urine production is termed anuria. Excessive urine production is polyuria, which may be due to diabetes mellitus or diabetes insipidus. In diabetes mellitus, blood glucose levels exceed the number of available sodium-glucose transporters in the kidney, and glucose appears in the urine. The osmotic nature of glucose attracts water, leading to its loss in the urine. In the case of diabetes insipidus, insufficient pituitary antidiuretic hormone (ADH) release or insufficient numbers of ADH receptors in the collecting ducts means that too few water channels are inserted into the cell membranes that line the collecting ducts of the kidney. Insufficient numbers of water channels (aquaporins) reduce water absorption, resulting in high volumes of very dilute urine.

The pH (hydrogen ion concentration) of the urine can vary more than 1000-fold, from a normal low of 4.5 to a maximum of 8.0. Diet can influence pH; meats lower the pH, whereas citrus fruits, vegetables, and dairy products raise the pH. Chronically high or low pH can lead to disorders, such as the development of kidney stones or osteomalacia.

Specific gravity is a measure of the quantity of solutes per unit volume of a solution and is traditionally easier to measure than osmolarity. Urine will always have a specific gravity greater than pure water (water = 1.0) due to the presence of solutes. Laboratories can now measure urine osmolarity directly, which is a more accurate indicator of urinary solutes than specific gravity. Remember that osmolarity is the number of osmoles or milliosmoles per liter of fluid (mOsmol/L). Urine osmolarity ranges from a low of 50–100 mOsmol/L to as high as 1200 mOsmol/L H2O.

Cells are not normally found in the urine. The presence of leukocytes may indicate a urinary tract infection. Leukocyte esterase is released by leukocytes; if detected in the urine, it can be taken as indirect evidence of a urinary tract infection (UTI).

Protein does not normally leave the glomerular capillaries, so only trace amounts of protein should be found in the urine, approximately 10 mg/100 mL in a random sample. If excessive protein is detected in the urine, it usually means that the glomerulus is damaged and is allowing protein to “leak” into the filtrate.

Ketones are byproducts of fat metabolism. Finding ketones in the urine suggests that the body is using fat as an energy source in preference to glucose. In diabetes mellitus when there is not enough insulin (type I diabetes mellitus) or because of insulin resistance (type II diabetes mellitus), there is plenty of glucose, but without the action of insulin, the cells cannot take it up, so it remains in the bloodstream. Instead, the cells are forced to use fat as their energy source, and fat consumed at such a level produces excessive ketones as byproducts. These excess ketones will appear in the urine. Ketones may also appear if there is a severe deficiency of proteins or carbohydrates in the diet.

Nitrates (NO3–) occur normally in the urine. Gram-negative bacteria metabolize nitrate into nitrite (NO2–), and its presence in the urine is indirect evidence of infection.

There should be no blood found in the urine. It may sometimes appear in urine samples as a result of menstrual contamination, but this is not an abnormal condition. Now that you understand what the normal characteristics of urine are, the next section will introduce you to how you store and dispose of this waste product and how you make it.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

CharacteristicNormal values
ColorPale yellow to deep amber
OdorOdorless
Volume750–2000 mL/24 hour
pH4.5–8.0
Specific gravity1.003–1.032
Osmolarity40–1350 mOsmol/kg
Urobilinogen0.2–1.0 mg/100 mL
White blood cells0–2 HPF (per high-power field of microscope)
Leukocyte esteraseNone
ProteinNone or trace
Bilirubin<0.3 mg/100 mL
KetonesNone
NitritesNone
BloodNone
GlucoseNone
Volume conditionVolumeCauses
Normal1–2 L/day
Polyuria>2.5 L/dayDiabetes mellitus; diabetes insipidus; excess caffeine or alcohol; kidney disease; certain drugs, such as diuretics; sickle cell anemia; excessive water intake
Oliguria300–500 mL/dayDehydration; blood loss; diarrhea; cardiogenic shock; kidney disease; enlarged prostate
Anuria<50 mL/dayKidney failure; obstruction, such as kidney stone or tumor; enlarged prostate
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Script:
  1. The kidney glomerulus filters blood mainly based on particle size to produce a filtrate lacking cells or large proteins.
  2. Most of the ions and molecules in the filtrate are needed by the body and must be reabsorbed farther down the nephron tubules, resulting in the formation of urine.
  3. Urine characteristics change depending on water intake, exercise, environmental temperature, and nutrient intake.
  4. Urinalysis analyzes characteristics of the urine and is used to diagnose diseases.
  5. A minimum of 400 to 500 mL urine must be produced daily to rid the body of wastes.
  6. Excessive quantities of urine may indicate diabetes insipidus or diabetes mellitus.
  7. The pH range of urine is 4.5 to 8.0, and is affected by diet.
  8. Osmolarity ranges from 50 to 1200 milliosmoles, and is a reflection of the amount of water being recovered or lost by renal nephrons.
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