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Ch. 14
Part 3
Kidney and Excretion
Major Organs to Know
• Kidney
– producing hormones
– absorbing minerals
– filtering blood
– producing urine
• Liver
– Detoxification of blood
Excretion
• Removal of unwanted metabolic products made in body cells
– Toxic
– Excess molecules
• 2 biggest waste products:
– Carbon Dioxide
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Review respiratory
Produced by AEROBIC respiration
Dissolves in water  weak acid (carbonic acid)
Too much = decrease pH = BAD
Carried to lungs in blood plasma and expired and released when we breath out
– Nitrogenous Excretory Products
• Urea
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From catabolism of protein
Produced in liver
Carried in blood plasma to liver
Leaves in urine
• Creatinine
– From breakdown product of creatine phosphate in muscle
– Made from Creatine (produced in liver using certain amino acids)
» Most used in muscles as creatine phosphate as ENERGY STORE
» Excess creatine converted to creatinine and excreted
• Uric Acid
– From Catabolism of nucleic acids
– made from break down of PURINES from nucleotides
Urea
• Adults produce 25 – 30 grams per day
• Made from excess amino acids
• DEAMINATION in liver occurs
– Removal of amine group form amino acid
• Amino Acid  Keto acid and Ammonia
– Keto acid Carbon skeleton of AA
• Enters KREBS CYCLE for respiration
• Changed to: glucose, glycogen, or fat
– Ammonia Soluble and Toxic (build up in blood BAD)
• What happens to amine group?
– Hydrogen atom added to Amine group (NH2) to make it NH3
(ammonia)
– Ammonia immediately converted to UREA (via Urea cycle)
• Ammonia + Carbon Dioxide = Urea
Step 1
In Liver…
Step 2
In Liver…now urea can be
carried in blood to kidney
Step 3
Urea will be dissolved with water and leave body as urine…once out of body, it will
degrade back to AMMONIA
Kidney
• “Renal” pertaining to kidneys
• MAIN Function
– process the plasma portion of blood by removing
substances from it (or adding)
• Variety of other Functions:
– Regulation of Water and inorganic ion balance
– Removal of metabolic wastes from blood and excrete
through urine
– Removal of foreign chemicals from blood and excretion
through urine
– Gluconeogenesis
– Production of hormones/enzymes (endocrine glands)
The Kidney
• Every minute 1300 mL of blood enter the
kidneys
• 1299 mL leave the kidney
• 1 mL leaves as urine.
• Location:
– Posterior (back)
– Outside the abdominal cavity
• Behind the peritoneum of abdominal cavity
Structure of Kidney
• Renal Artery delivers
blood TO the kidney
• Renal Vein blood
LEAVES the kidney from
here
• Ureter narrow tube that
caries URINE away from
kidney to bladder
• Urethra tube from
bladder to outside of body
• Contains about 1 MILLION
subunits called nephrons
– Nephrons contain:
• Renal corpuscle
Major Areas of Kidney
• Capsule
– Tough outermost covering of kidney
• Cortex
– Beneath outer capsule
– Contains cup-shaped beginning structure of
nephron called the renal capsule
– contains about one million blood
filtering nephrons
• Medulla
– Central area of kidney
– Very SALTY!!!! (Hypertonic)
– inner region of the kidney contains 8-12 renal
pyramids
– pyramids empty into the calyx
• Medullary pyramids – formed by the collecting ducts,
inner part of the kidney
• Pelvis
– basin-like area that collects urine from the
nephrons
– narrows into the upper end of the ureter
– Calyx – extension of the renal pelvis; they
channel urine from the pyramids to the renal
pelvis
Nephron
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Glomerulus
– Special type of network of
capillaries
– Only oxygenated blood
here
– Components of blood ill be
squeezed out through
these capillary walls
• FILTRATE
– No RBCs or small proteins
leave
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Bowmans Capsule
– C-shaped structure that
surrounds the glomerulus
– Receives filtrate
– Beginning of nephron
tubes
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Afferent arteriole
– Brings blood to glomerulus
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Efferent arteriole
– Leaves the glomerulus
– Leads to there peritubular
capillaries (go all around
all the tubules of the
nephron)
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Nephron
Reabsorption = when molecules LEAVE nephron and go back onto blood
Proximal Convoluted Tubule (PCT)
– In CORTEX of kidney
– Receives filtrate Bowman’s Capsule
– Reabsorption of many molecules occurs here
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Water, glucose, ions, amino acids
Sodium-Potassium pump important (Na-K)
Co-Transport Symport important (Glucose)
Loop of Henle (LOH)
– Dips into MEDULLA
– Descending LOH
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Water reabsorption
Passive transport of water
– Ascending LOH
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Distal Convoluted Tubule (DCT)
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Ion reabsorption (Na and Cl)
Active transport
Important in osmolarity
Back in CORTEX
Receives filtrate from LOH
More reabsorption
Important in maintaining blood pressure
Collecting Duct
– Dips back into MEDULLA and eventually into
the PELVIS of kidney
– Receives filtrate from MANY DCT
– Reabsorption of water
– Reabsorption of some UREA (to maintain
osmolarity of medulla)
2 Stages
1. Ultrafiltration
– Involves filtering small molecules out of blood
and into Bowman’s Capsule
– Molecules flow through nephron and to ureter
2. Selective Reabsorption
– When useful molecules (amino acids, glucose.
Ions) are taken back from filtrate fluid and into
the blood