Download Urinary System

Urinary System
Functions of the Urinary
System
1. Excretion of metabolic wastes
2. Maintenance of water-salt balance
3. Maintenance of acid-base balance
4. Secretion of hormones
Components
Consists of organs that produce, store, and rid the body of urine
Kidneys:
- bean shaped, fist sized, reddish brown
- produce urine
- protected by lower ribs
Renal Artery and Renal Vein:
- enter/leave on concave side of kidney
Ureter:
-muscular tubes that carry urine from kidneys towards bladder by
peristalsis
Components
Urinary Bladder:
- stores urine (can hold up to 600 ml)
- hollow, muscular organ
- expands as urine enters
- small folds of bladder mucosa act like valve to prevent urine
from going back up ureters
- two sphincters control the exit of urine from the bladder to
the urethra
- internal sphincter is composed of smooth muscle –
involuntary control
- external sphincter is composed of skeletal muscle –
voluntarily controlled
Components
Urethra:
- carries urine from bladder to external opening
- shorter in women, thus more easily permits
infection of urinary tract
- in men, urethra is surrounded by prostate gland – if
it enlarges, it can restrict flow of urine
- in men, urethra also carries sperm during
ejaculation
Nervous System and Urination
• Stretch receptors and sensory nerve impulses to
empty bladder are sent to spinal cord when bladder
fills (250 ml)
• Motor nerve impulses from the spinal cord cause the
bladder to contract and the sphincters to relax
• Urination occurs
• In older children and adults, the brain controls the
reflex
Functions of the Urinary
System
1. Removal of the nitrogenous wastes (excretion)
A. Urea
- Amino acid metabolism (in liver) → ammonia
ammonia + CO2 → urea
- ammonia is very toxic to cells, urea is less toxic
B. Creatine Phosphate
- a high energy phosphate reserve molecule in
muscles
- break down → creatinine
- Creatinine is excreted by the kidneys
Functions of the Urinary
System
C. Nucleotides
- breakdown of nucleotides = Uric Acid
- excreted by kidneys
- too much in blood causes it to precipitate out
into crystals which accumulate in the joints = Gout
Functions of the Urinary
System
2. Maintain the water-salt balance
- kidneys maintain the appropriate amount of ions
(e.g. potassium, bicarbonate, calcium) in the blood
- salts cause diffusion of water into the blood,
therefore, more salts, more water, more blood… more
blood pressure
- in this way the kidneys are involved in regulating
blood pressure
Functions of the Urinary
System
3. Maintain the Acid-base balance of blood
- blood pH should be 7.4
- kidneys monitor and control pH by excreting H+ or
reabsorbing HCO3- ions as needed
- urine usually has a pH of 6 due to acidic foods in
diet
Functions of the Urinary
System
4. Hormonal Function
a. Secretes erythropoietin when oxygen carrying
capacity is reduced – stimulates RBC production
b. Helps activate vitamin D
c. Secretes renin – leads to secretion of aldosterone from
adrenal glands (on top of kidneys) which causes
reabsorption of sodium ions