Chapter 15 Urinary System

Chapter 15: Urinary System
Part A: Kidneys & Urine
1. Functions of the urinary system
a. Elimination of waste products:
i. Nitrogenous wastes: urea, uric acid, ammonia
ii. Toxins- harmful or fatal in small doses
iii. Drugs- have specific & significant effects on cells
b. Regulate aspects of homeostasis:
i. Water balance- osmosis
ii. Electrolytes: ions such as Na, Ca, Mg, Cl
iii. Acid-base balance in the blood
iv. BP = blood pressure
v. RBC = red blood cell production
vi. Activation of vitamin D
2. Organs of the system
a. Kidneys- where blood is actively processed
i. Renal= kidney
b. Ureters- tubes draining kidneys
c. Urinary bladder- urine storage
d. Urethra- from bladder to exterior of body
3. Kidneys
a. Location
i. Retroperitoneal = against the dorsal body wall
ii. At the level of the T12 to L3 vertebrae
iii. The right kidney is slightly lower than the left (due to position of the liver)
b. Features
i. Shape- kidney bean shaped
ii. Renal hilum
1. A medial indentation where several structures enter or exit the kidney (ureters, renal blood vessels, and nerves)
iii. Adrenal gland sits atop each kidney
c. Coverings
i. Fibrous capsule
1. Surrounds each kidney- connective tissue
ii. Perirenal fat capsule
1. Surrounds the kidney and cushions against blows
iii. Renal fascia
1. Outermost capsule that helps hold the kidney in place against the muscles of the trunk wall
d. Anatomical regions – renal:
i. Cortex- outer region
ii. Medulla- inside the cortex
iii. Pelvis- inner collecting tube, like a funnel
e. Internal structures
i. Renal or medullary pyramids- triangular regions of tissue in the medulla
ii. Renal columns- extensions of cortex-like material inward that separate the pyramids
iii. Renal calyces (calyx)- cup-shaped structures that funnel urine towards the renal pelvis
f. Blood supply
i. 25% of the total blood supply o the body passes through the kidneys each minute
ii. Renal artery provides each kidney with arterial blood supply
iii. Arterioles and capillary beds – details below
4. Nephrons
a. Structural and functional units of the kidneys
b. Over a million in each kidney
c. Responsible for forming urine
d. Main structures
i. Glomerulus- knot of capillaries
ii. Capillaries are covered with podocytes from the renal tubule
iii. Glomerulus sits within a glomerular (Bowman’s capsule) the first part of the renal tubule
e. Anatomy
i. Renal tubule extends from glomerular capsule and ends at the collecting duct
1. Bowman’s capsule
2. Proximal convoluted tubule (PCT)
3. Loop of Henle- deep into medulla
4. Distal convoluted tubule (DCT)
f. Types
i. Cortical nephrons:
ii. Located entirely in the cortex
iii. Includes most nephrons
iv. Juxtamedullary- next to the medulla
v. Found at the boundary of the cortex and medulla
vi. Extend deeper into kidney
g. Collecting ducts
i. Receives urine from many nephrons
ii. Runs through the medullary pyramids
iii. Delivers urine into the calyces and renal pelvis
h. Associated with two capillary beds
i. Glomerulus
1. Arterioles leading in and out
a. Afferent arterioles- arises from a cortical radiate artery and feeds the glomerulus
b. Efferent arterioles- receives blood that has passed through the glomerulus
2. Specialized for filtration
3. High pressure forces fluid and solutes out of blood and into the glomerular capsule
ii. Peritubular
1. Arise from efferent arteriole of the glomerulus
2. Normal, low pressure capillaries
3. Adapted for absorption instead of filtration
4. Cling close to the renal tubule to reabsorb some substances
5. Urine formation
a. Glomerular filtration
i. Tubular reabsorption
ii. Tubular secretion
iii. Nonselective passive process
iv. Water and solutes smaller than proteins are forced through capillary walls
v. Proteins and blood cells are normally too large to pass through the filtration membrane
vi. Filtrate is collected in the glomerular capsule and leaves via the renal tubule
b. Tubular reabsorption
i. Peritubular capillaries reabsorb useful substance-
1. Water
2. Glucose
3. Amino acids
4. Ions
ii. Some reabsorption is passive, most is active
iii. Most reabsorption occurs in the proximal convoluted tubule
iv. Materials not reabsorbed
1. Nitrogenous
a. Urea- protein breakdown
b. Uric acid- nucleic acid breakdown
c. Creatinine- associated with creatine metabolism in muscles
c. Tubular secretion = reabsorption in reverse
i. Some materials move from the peritubular capillaries into the renal tubules
ii. Examples: hydrogen and potassium ions, creatine, H+, K+, creatine, drugs, pH controls
iii. Materials left in the renal tubule move toward the ureter
d. Urine
i. Characteristics
1. Yellow color due to the pigment urochrome (from the destruction of hemoglobin) and solutes
a. Concentration
2. Odor
3. Sterile- kills many bacteria because:
4. Normal pH of around 6
5. Specific gravity = density
a. 1.001 to 1.035
6. Normal production in 24 hours, about 1.0 to 1.8 liters of urine are produced
7. Urine vs. filtrate
a. Filtrate = contains everything that blood plasma does (except proteins)
b. Urine = is what remains after the filtrate has lost most of its water, nutrients, necessary ions
ii. Urine contains nitrogenous wastes and substances that are not needed
iii. Does not contain things that are valuable or are too large to diffuse through membranes:
Chapter 15: The Urinary System
Part B
1. Urinary structures
a. Ureters
i. Slender tubes attach each kidney to the bladder
ii. Run from renal pelvis to the posterior aspect of the bladder
iii. Runs behind the peritoneum
iv. Peristalsis aids gravity in urine transport
b. Urinary bladder
i. Smooth, collapsible, muscular sac
ii. Temporary stores urine
iii. Trigone- triangular region of the bladder base
iv. Three openings
1. Two from the ureters
2. One to the urethra
v. In males, the prostate gland surrounds the neck of the bladder and urethra
vi. Bladder wall
1. Three layers of smooth muscle collectively called the detrusor muscle
2. Mucosa made of transitional epithelium
3. Walls are thick and folded in an empty bladder
4. Bladder can expand significantly without increasing internal pressure
vii. Capacity
1. Moderately full bladder is about 5 inches long and holds about 500 mL of urine
2. Maximum
c. Urethra
i. Thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis
ii. Urine release is controlled by two sphincters:
1. Internal urethral sphincter
a. Involuntary and made of smooth muscle
2. External urethral sphincter
iii. Gender differences
1. Length: females more likely to get bladder infections
a. Female is 3-4 cm (1 inch)
b. Male is 20 cm (8 inches)
2. Location
a. Female- along wall of the vagina
b. Male- through the prostate and penis
3. Function
a. Female- only carries urine
b. Male- carries urine and sperm
2. Micturition = voiding (peeing)
a. Both sphincters muscles must open to allow voiding
b. Internal urethral sphincter is relaxed after stretching of the bladder
c. Pelvic nerves initiate bladder to go into reflex contractions
d. Urine is forced past the internal urethra sphincter and the person feels the urge to void
e. External urethral sphincter must be voluntary relaxed to void
3. Fluid, electrolyte, acid-base balance
a. Blood composition depends on three factors:
i. Diet
ii. Cellular metabolism
iii. Urine output
iv. Four roles of kidneys in maintaining blood composition
1. Excretion of nitrogen-containing wastes (previously discussed)
2. Maintaining water balance of the blood
3. Maintaining electrolyte balance of the blood
4. Ensuring proper blood pH
b. Water balance
i. Normal amount in body by mass
1. Young adult female = 50%
2. Young adult male = 60%
3. Babies = 75%
4. The elderly = 45%
5. Water is necessart for manly body functions, and levels must be maintained
6. “Universal” solvent
ii. Distribution of body fluid
1. Intracellular (ICF)-
a. Fluid inside cells
b. About 2/3 of body fluid
2. Extracellular (ECF)
a. Fluid outside cells
b. Interstitial fluid
c. Blood plasma
iii. Link between water and salt
1. Solutes in the body include electrolytes like sodium, potassium, and calcium ions
2. Changes in electrolyte balance causes water to move from one compartment to another (osmosis)
a. Alters blood volume and blood pressure
b. Impairs the activity of cells
iv. Water in = water out
1. Sources for water intake-
a. Ingested foods and fluids
b. Water produced from metabolic processes (-10%)
c. Thirst mechanism is the driving force of water intake
2. Sources for water output
a. Vaporization out of the lungs
b. Lost in perspiration
c. Leave the body in the feces
d. Urine production
3. Dilute urine is produced if water intake is excessive
4. Less urine (concentrated) is produced if large amounts of water are lost
5. Proper concentrations of various electrolyte must be present
v. Regulation of water and electrolyte reabsorption
1. Osmoreceptors: cells in the hypothalamus
a. React to changes in blood composition by becoming more active
2. Regulation occurs primarily by hormones
a. ADH = antidiuretic hormone
i. Prevents excessive water loss in urine
ii. Causes the kidney’s collecting ducts to reabsorb more water
iii. Alcohol suppresses ADH, causing urination
iv. Diabetes insipidus
1. Occurs when ADH is not released
2. Leads to huge outputs of dilute urine
b. Aldosterone
i. From adrenal cortex
ii. Regulates sodium ion content of ECF
iii. Sodium is the electrolyte most responsible for osmotic water flows
iv. Aldesterone promotes reabsorption of sodium ions
v. Remember, water flows salt!
c. Rennin-angiotensin mechanism
i. Juxtaglomerular (JG) apparatus
1. Cells stimulated by
2. Rennin produces
3. Angiotensin II causes
4. Results in
c. Maintaining acid-base balance in blood
i. Blood pH between
1. Alkalosis =
2. Acidosis =
3. Physiological acidosis =
ii. Body acids
1. P , L, A
2. Carbon dioxide
3. Ammonia
4. Acid-base control systems/organs
a. Kidneys
b. Respiration
c. Blood buffers
i. Acids =
ii. Strong acids =
iii. Weak acids =
iv. Bases =
v. Strong bases =
vi. Weak bases =
vii. Action
1. Bind to H+
2. Release H+
viii. Three major systems
1. Protein
2. Phosphate
3. Bicarbonate
a. H2CO3 and NaHCO3
b. Carbonic acid
c. Bicarbonate ions
d. HCl + NaHCO3 H2CO3 + NaCl
4. Developmental aspects of the urinary system
a. Early life
i. Functional kidneys
ii. Newborn
1. Bladder
2. Urine
3. Void
iii. Young children
1. Control of voluntary sphincter
2. Nighttime control
3. Bladder infections
iv. Elderly
1. Bladder changes
2. Associated problems
a. Urgency
b. Frequency
c. Nocturia
d. Incontinence
e. Urinary retention