Excretion The removal of metabolic wastes from the body Kidneys are the primary organ of this...
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Excretion The removal of metabolic wastes from
the body Kidneys are the primary organ of this
process
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1. Excretion of Metabolic Wastes Removing metabolic waste products, notably
nitrogenous waste from breakdown of amino acids (aa):
Urea Breakdown of amino acids releases ammonia which is
toxic to cells) Liver converts the ammonia to urea so it be safely
transported in the blood to the kidney where it is eliminated in urine
Creatinine Uric acid
if too much uric acid crystals can form in joints This is known as gout
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2. Maintenance of Water-Salt Balance Blood volume is associated with salt
balance in body Salt (NaCl) can cause water diffusion into blood ↑ salt = ↑ blood volume = ↑ blood pressure
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3. Maintenance of Acid-Base Balance Kidneys regulate acid-base in blood Excretion of hydrogen ions and
reabsorption of bicarbonate to keep pH around 7.4
Urine often has a pH of 6
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4. Secretion of Hormones Renin
Leads to secretion of aldosterone Reabsorption of sodium ions
Erythropoetin Stimulates red blood cell production
Activates vitamin D from the skin Helps promote calcium absorption from the
digestive tract.
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16-9
Fig. 16.1
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Kidneys Two bean-shaped organs Located near lumbar region on either side
of vertebral column Has a depression called the
hilum where the Renal artery Renal vein are located
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Ureters Conduct urine from the kidneys to the
bladder Small, muscular tube 25cm long, 5 mm
thick
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Urinary Bladder Stores urine until it is expelled from the
body Located in the pelvic cavity 3 openings (orifices):
2 for the ureters 1 for urethera
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Urinary Bladder con’t... Expandable
Detrusor Muscle – bladder wall Sphincter Muscles – surround bladder neck
and urethra
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While the bladder is filling: the detrusor muscle is relaxed so the
bladder wall can expand and the sphincter muscles are contracted to keep the urethra closed
When the bladder empties: the detrusor muscle contracts to squeeze
the urine out, and the sphincter muscles relax so the urethra can open up
http://www.aboutkidshealth.ca/en/howthebodyworks/kidneysandbladderoverview/bladderfillingandemptying/pages/default.aspx
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Urethra Small tube that extends from the urinary
bladder to an external opening females
4 cm long Increases likelihood of urinary tract infection
Not connected to reproductive system Males
20 cm long Common pathway for reproductive and urinary
tracts
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16-17
Micturition When the bladder fills to 250ml
Stretch receptors in the bladder wall send sensory impulse to the spinal cord
Motor impulses from spinal cord send a signal the bladder
Bladder contraction and sphinter to relax
This is called an involuntary reflex Present in infants and young children
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In older children and adults the brain can control this reflex and delay urination until a suitable time Stretch receptors in the bladder send a
sensory signal to micturition center in the pons
If not appropriate it will send an inhibitory signal to keep the sphinter closed
This is called a voluntary response https://www.youtube.com/watch?v=US0vNoxsW-k