Chapter 15, Urinary System, Part B

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. 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, Prostate gland surrounds the neck of the bladder (and urethra)
vi. Bladder wall
1. Three layers of smooth muscle called Detrusor muscle
2. Mucosa made of transitional epithelium
3. Walls are thick and folded in an Empty bladder
4. Bladder expansion, 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 of holding twice that amount of urine
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
a. Voluntary and made if skeletal muscles
iii. Gender differences
1. Length: females more likely to get bladder infections
a. Females is 3-4 cm (1 inch)
b. Males 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 is a passageway for sperm cells
2. Micturition = peeing
a. Both sphincters muscles must open to allow voiding
b. Internal urethral sphincter sphincter is relaxed after stretching of the bladder
c. Pelvic nerves 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 voluntarily 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. Maintain water balance of the blood
3. Maintain electrolyte balance of the blood
4. Ensure 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. Universal solvent
ii. Distribution of body fluid
1. Intracellular (ICF)
a. Fluid inside cells
b. About two-thirds 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 for water intake
2. Sources for water output
a. Vaporization out of the lungs
b. Lost in perspiration
c. Leaves the body in the feces
d. Urine production
3. Dilute urine is produced if water intake is excessive
4. Concentrated urine (less urine) is produced if large amounts of water are lost
5. Proper Electrolyte concentrations 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. 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. When ADH is not released
2. Causes huge outputs of dilute urine
b. Aldosterone
i. From adrenal cortex
ii. Regulates sodium ion content of ECF
1. Sodium is the electrolyte most responsible for osmotic water flows
iii. Promotes reabsorption of sodium ions
1. Water follows 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