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Anatomy and
Physiology
Chapter 18: Urinary System
Laura Herz, BA, RT (R)
• Function is to maintain the volume and composition of
body fluids within normal limits
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Rids the body of waste products
Regulates the amount of water that is excreted
Maintains the pH of blood
Secretes hormones important in blood cell formation and
blood pressure
Urinary System
• Filter blood, remove the wastes, and excrete the wastes in
the urine
• Bean-shaped organs located approximately from the
levels of T-12 to L-3 on each side of the spine
• Behind parietal peritoneum  “retroperitoneal”
• Held in place by connective tissue called renal fascia
• Surrounded by an outer cushion of adipose tissue and a
tough, inner connective tissue called the renal capsule
Kidneys
• Renal Hilum: indentation on medial side of each kidney;
leads into a cavity called the renal sinus
• Ureter and renal vein leave the kidney at the hilum
• Renal artery enters the kidney at the hilum
External Structure of
Kidneys
• Renal Cortex: outer, reddish region, next to the capsule
• Renal Medulla: inner, brownish portion
• Renal Pyramids: triangular divisions of the medulla
• Renal Papillae: narrow, pointed ends of the renal pyramids
• Renal Columns: rectangular portions in between the renal
pyramids
• Renal Pelvis: expansion of the upper ureter; collects urine as it
is produced
• Calyx (Calyces): cup-like portions of the renal pelvis
• Minor Calyx: surrounds the papillae of each pyramid
• Major Calyx: formed by the convergence of minor calyces
Internal Structure of
Kidneys
• Nephrons are the functional units of the kidneys
• More than 1,000,000 in each kidney
• Located within the cortex and medulla
• Two parts:
• Renal Corpuscle
• Renal Tubule
Microscopic Structure of
Kidneys
• Consists of two parts:
• Glomerulus: cluster of blood capillaries
• Afferent arteriole: delivers blood to the glomerulus; shorter, but
larger in diameter
• Efferent arteriole: takes blood away from the glomerulus;
longer, but smaller in diameter
• Glomerular Capsule/Bowman’s Capsule: double-layered
cup that surrounds the glomerulus
Renal Corpuscle
• Consists of three parts:
• Proximal Convoluted Tubule: highly coiled tubule
connected to the Bowman’s Capsule
• Nephron Loop/Loop of Henle: between the proximal
convoluted tubule and the distal convoluted tubule; has an
descending limb and an ascending limb with a u-shape in
the middle
• Distal Convoluted Tubule: final region of the renal tubule;
also highly coiled
Renal Tubule
• Distal convoluted tubules of several nephrons join to
form a _____________ _______
• Extend from the base of a renal pyramid to the renal
papillae
• Fluid flows from collecting ducts into the minor calyces
Collecting Ducts
• Juxtaglomerular
Apparatus: point where
ascending limb of the
Nephron Loop comes into
contact with the afferent
arteriole of the same
nephron
• Macula Densa Cells
• Juxtaglomerular Cells
Juxtaglomerular
Apparatus
• Blood is delivered to kidneys by the renal arteries
• At the hilum of the kidneys, the renal arteries divide and
more and more branching occurs
• Renal artery  segmental arteries  interlobar arteries  arcuate
arteries  interlobular arteries  afferent arterioles  glomerulus
Blood Flow Through the
Kidney
• Blood leaves the glomerulus through the efferent arteriole
• Each efferent arteriole divides to form a complex capillary network
called peritubular capillaries
• Peritubular capillaries eventually reunite to form a series of veins
that return blood to the inferior vena cava of the heart
• Glomerulus  efferent arteriole  peritubular capillaries  interlobular
veins  arcuate veins  interlobar veins  segmental veins  renal veins
Blood Flow Through the
Kidney (cont.)
• Carry urine from the renal pelvis to the bladder
• About 25 centimeters long and 6 millimeters in diameter
• Retroperitoneal; enter bladder on posterior, inferior surface
• Walls consists of three layers:
• Mucosa: transitional epithelium; secretes mucus to protect the
surface of the cells
• Muscular Coat: smooth muscle; peristalsis
• Fibrous Coat: fibrous connective tissue; provides support
Ureters
• Temporary storage reservoir for urine
• Located behind pubic symphysis and below parietal peritoneum
• Males: rests on prostate
• Females: in front of uterus
• Consists of four layers:
• Mucous membrane: transitional epithelium; folds called ________
• Submucosa: supports the mucous membrane
• Muscularis: smooth muscle fibers interwoven in all directions;
collectively called the detrusor muscle
• Fibrous Connective Tissue: covers all of the bladder, except the
superior surface
Urinary Bladder
• Final passageway for the flow of urine
• Internal Urethral Sphincter: surrounds area between the bladder
and the start of the urethra; ________________ muscle
• External Urethral Sphincter: surrounds urethra where it passes
through the pelvic floor; ________________ muscle
• External Urethral Orifice: opening to the outside of the body
• Females: 3-4 centimeters long; external orifice opens just anterior
to the vagina
• Males: 20 centimeters long; transports urine and semen
• Prostatic Urethra: first portion; passes through the prostate gland
• Membranous Urethra: second portion; passes the pelvic floor
• Spongy (Penile) Urethra: distal portion; extends the length of the penis
Urethra
Recapitulate
•Function of the Urinary System is to maintain the volume and
composition of body fluids within normal limits
•Rids the body of waste products
•Regulates the amount of water that is excreted
•Maintains the pH of blood
•Secretes hormones important in blood cell formation and blood pressure
• Nephrons in the kidneys form urine by three processes:
• Glomerular Filtration
• Tubular Reabsorption
• Tubular Secretion
Urine Formation
• Glomerular Filtration
• First step of urine formation
• Blood plasma moves from the glomerulus across the
filtration membrane and enters the Bowman’s Capsule
• Filtrate: fluid that enters the capsule
Urine Formation (cont.)
• Tubular Reabsorption
• Movement of useful substances out of the filtrate in the
renal tubule and collecting ducts and into the blood
capillaries
• Water, glucose, sodium, and other ions and nutrients are
absorbed
• Only about 1% of the filtrate remains in the renal tubule and
becomes urine
Urine Formation (cont.)
• Tubular Secretion
• Movement of unwanted substances out of the blood
capillaries into the renal tubule and collecting ducts
• Certain drugs
• Hydrogen and potassium ions
• Plays an important role in maintaining the body’s acid/base balance
Urine Formation (cont.)
Glomerular
Filtration
Tubular
Reabsorption
Tubular
Secretion
• Glomerulus, Filtration Membrane, Bowman’s Capsule
• Removes water and solutes from the blood
• Renal Tubule and Collecting Duct
• Removes water and nutrients from filtrate and returns them to
blood
• Renal Tubule and Collecting Duct
• Moves toxic substances from blood into the filtrate
Urine Formation (cont.)
• Cells in the hypothalamus sense changes in the blood and
initiate a response that effects the kidneys
• Blood solute concentration increases  kidneys excrete
small volume of concentrated urine
• Blood solute concentration decreases  kidneys excrete
large volume of dilute urine
Control of Urine
Concentration
• Urine volume is regulated by how much reabsorption
takes place in the renal tubule and collecting duct
• Accomplished by hormones
• Antidiuretic hormone (ADH)
• Aldosterone
• Atrial natriuretic hormone (ANH)
Control of Urine Volume
• Antidiuretic hormone (ADH)
• Released by posterior pituitary
• Makes distal convoluted tubule and collecting duct more
permeable to water
• More water is reabsorbed, which reduces volume of urine
Control of Urine Volume
(cont.)
• Aldosterone
• Secreted by cells of adrenal cortex
• Acts on renal tubule to increase the reabsorption of sodium
• Water follows sodium by osmosis
• Reduces urine volume
Control of Urine Volume
(cont.)
• Atrial natriuretic hormone (ANH)
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Produced by special cells in the heart
Opposite effect as aldosterone
Acts on renal tubule to excrete sodium
Water follows sodium by osmosis
• Increases urine volume
Control of Urine Volume
(cont.)
• Renin: enzyme produced by the juxtaglomerular cells in
response to low blood pressure or decreased sodium
concentration
• Promotes production of angiotensin II, a _______________
• Increases blood pressure and stimulates secretion of
aldosterone
Kidneys role in Blood
Pressure
• Elimination of urine from the bladder
• Micturition reflex is normally triggered by 200-400
milliliters of urine
• Urinary incontinence: inability to control urination
Micturition
• Urinalysis: chemical and microscopic examination of
urine
• Physical characteristics
• Normally clear and has a yellowish color
• pH of 4.6-8.0
• Slightly heavier than water
• Chemical characteristics
• 95% water
• 5% solutes from metabolic waste products or drugs
Characteristics of Urine
• Maintaining fluid and electrolyte balance is a very
important body function
• Fluids per body weight:
• Adult male: 60%
• Adult female: 50%
• Newborn: 80%
• These amounts change with age and amount of body fat
Body Fluids
• Body fluid is not evenly distributed; it is separated into
compartments
• Intracellular fluid
• 2/3 of body fluids; found inside the cells
• Extracellular fluid
• 1/3 of body fluids; found outside the cells
• Intravascular fluid  blood plasma
• Interstitial fluid  in tissue spaces
Body Fluid Compartments
• Body’s Goal: fluid intake = fluid output
• Average fluid intake is 2500 milliliters per day
• Beverages, foods, and metabolic water
• Fluid output happens in four ways
• Kidneys, skin, exhalation of water vapor, gastrointestinal tract
Intake and Output of Fluid
• Electrolytes: substances that dissociate in solution to form
charged particles, or ions
• Called electrolytes because they can conduct an electrical
current
• Cations (+): Sodium, calcium, potassium, magnesium
• Anions: (-): Chloride, bicarbonate, phosphate, and many
proteins
• Required for cellular activities, nerve conduction, and
muscle contraction
Electrolyte Balance
• Regulation of electrolytes is through active reabsorption
of positive ions
• Negative ions follow by electrochemical attraction
• Electrolytes are in balance when their concentrations in
body fluids are normal and relatively constant
• Balance is very easily disturbed
• Water moves from a region of high concentration of water
molecules to a region of low concentration of water molecules
Electrolyte Balance
• Ex.: High Na+ concentration (low H2O concentration) in
the extracellular fluid
• Cause H20 to move from intracellular fluid to extracellular
fluid
• Opposite is also true; if water concentration in a fluid
compartment increases, the concentration of the
electrolyte will decrease
• Fluid balance and electrolyte balance are so
interdependent, that if one deviates from normal, so does
the other
Electrolyte Balance
• pH: a number that indicates the hydrogen ion (H+)
concentration of a fluid
• pH greater than 7 = alkaline
• pH of 7 = neutral
• pH less than 7 = acid
• Normal blood pH is about 7.35 to 7.45
Acid-Base Balance
• Maintaining an acid-base balance refers to keeping the
concentration of hydrogen ions in our body fluids at a
relatively constant level
• Effective functioning of many proteins is dependent upon
this level; veering away from the normal level can result in
illness or death
• Maintaining an acid-base balance uses three mechanisms:
• Buffers (Blood)
• Respiratory Mechanism
• Urinary Mechanism (Kidneys)
Acid-Base Balance
• Buffers: substances that prevent a sharp change in the pH
of a fluid when an acid or base is added to it
• Consists of two substances and are called _______ ____
• Common pair in the blood:
• Sodium bicarbonate (NaHCO3)
• Carbonic acid (H2CO3)
Acid-Base Balance
Buffers
Strong Acid Present
Strong Base Present
• Carbon dioxide is a byproduct of cellular metabolism
• Combination with water produces carbonic acid, which
lowers the pH of the blood
• Lungs are important in regulating pH because they
remove one of the sources of acids (CO2) through
exhalation
Acid-Base Balance
Respiratory Mechanism
• Blood is too acidic
• Kidney tubules take hydrogen ions from blood in
peritubular capillaries into the urine
• Blood is too alkaline
• Kidney tubules conserve hydrogen ions
Acid-Base Balance
Urinary Mechanism
• Acidosis and alkalosis are the two kinds of acid-base or
pH imbalances
• Acidosis: blood pH falls as H+ ion concentration increases
• Alkalosis: blood pH is higher than normal due to loss of
acids or accumulation of bases
pH Imbalances
• Acidosis and alkalosis can be classified according to
cause as either respiratory or metabolic
• Respiratory represents problems with the respiratory
mechanisms
• Metabolic imbalances represent problems with all other
acid-base imbalances
pH Imbalances
• Respiratory Acidosis (_________ ____ ______): result of
a lack of movement of CO2 from the blood to the alveoli
and into the atmosphere
• Caused most often by slow breathing  drugs, anesthesia,
emphysema, pulmonary edema
• Respiratory Alkalosis (Carbonic Acid Deficit): excessive
loss of CO2
• Caused by hyperventilation  anxiety, oxygen deficiency
in high altitudes, aspirin or caffeine overdoses
Respiratory Disturbances
• Metabolic Acidosis (______ ________ _______): often
caused by an accumulation of metabolic acids or a loss of
bicarbonate ions
• Accumulation of metabolic acids  uncontrolled diabetes
and starvation
• Loss of bicarbonate ions  diarrhea, renal dysfunction,
poisoning from toxic chemicals
• Metabolic Alkalosis (Sodium Bicarbonate Excess):
occurs when there is a non-respiratory loss of acids or an
excessive intake of alkaline substances
• Loss of acids  repeated vomiting
• Ingestion of alkaline substances  excessive antacid tablets
Metabolic Disturbances