excretion system of urea in human revise by ahmed ghdhban alziaydi
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Excretory SystemThe kidneys regulate the amount of water, salts and other substances in the blood.
The kidneys are fist-sized, bean shaped structures that remove nitrogenous wastes (urine) and excess salts from the blood.
The ureters are tubes that carry urine from the pelvis of the kidneys to the urinary bladder.
The urinary bladder temporarily stores urine until it is released from the body.
The urethra is the tube that carries urine from the urinary bladder to the outside of the body.
The outer end of the urethra is controlled by a circular muscle called a sphincter.
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How blood is Filtered
The filtering units of the kidneys are the nephrons.
There are approximately one million nephrons in each kidney.
The nephrons are located within the cortex and medulla of each kidney.
The tubes of the nephron are surrounded by cells and a network of blood vessels spreads throughout the tissue. Therefore, material that leaves the nephron enters the surrounding cells and returns to the bloodstream by a network of vessels.
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Function of the Kidney
The principal function of the kidney is
to filter blood in order to remove
cellular waste products from the body.
2. They regulate the concentrations of
substances found in body fluids
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The kidney has other functions but it
is usually associated with the
excretion of cellular waste such as :
1) urea (a nitrogenous waste
produced in the liver from the
breakdown of protein. It is the main
component of urine) ;
Function of Excretory System1. Filtration and excretion of metabolic wastes
2. The regulation of blood content.
3. The regulation of blood pH.
4. Homeostasis.
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Function of urinary system
• Excretion• Keeping homeostasis• Keeping acid-base balance• Secretion (rennin,, erytropoetin)
Excreted products:• Product of the metabolism• Water• Hormones• Vitamins• Toxic substances
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Kidney function• Step 1: Filtration
• Step 2: Reabsorption
• Step 3: Secretion
• Step 4: Excretion.
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Filtration
• During filtration, substances pass from the blood into the Bowman’s capsule.
• Under pressure, water and many small molecules such as salts, urea, glucose and aminoacids pass from glomerulus into Bowman’s capsule.
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Reabsorbtion
• The absorbtion of needed materials such as glucose, amino acids and water from nephrons to blood capillaries is called reabsorbtion.
• Water is reabsorbed passively by osmosis. But reabsorbtion of glucose, aminoacids and salt ions occurs by active transport.
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• The cells of distal tubule excrete molecules such as penicilin, ammonia, potassium and excess acids. This process is called secretion.
• After secretion, the fluid remaining in the nephrons is called urine.
• Urine contains urea, uric acid, sodium, potassium, calcium, chlorine, phosphorus, water and small amount of cells.
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ExcretionExcretion is the removal of metabolic waste from the cells. Metabolic waste is the unwanted material that is formed as a result of the bodies metabolism. That is the large number of chemical reactions that occur in the cells, tissues and organs. The waste products of metabolism are frequently toxic and so must be removed from the body.
Excretory Substances
The metabolic wastes of cells are;
WATER, CO2, NITROGENOUS COMPOUNDS
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NITROGENOUS WASTES
•At the end of the catobolisation of aminoacids, AMMONIA(NH3) is formed.
•In some organisms, ammonia is removed frombody directly.
•But in some organisms ammonia is converted to
other substances such as UREA and URIC ACID.
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Deamination and Urea SynthesisIn the liver deamination is the process whichbreaks down excess amino acids in to ammoniaand keto acids. Ammonia is still very toxic so itis converted to urea by the process called ureasynthesis. Urea is less toxic than ammonia and socan travel in the blood, but it must be got rid ofquickly because it can still have ill effects. Ureais then transported by the blood from the liver tothe Kidneys where it forms part of urine.
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Ammonia reacts with CO2 in the liver to produce
UREA:
2 NH3 + CO2
+ H2O
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Catabolism of proteins and nucleic acids results in formation of
so called nonprotein nitrogenous compounds.
Protein
Proteolysis, principally enzymatic
Amino acids
Transamination and oxidative deamination
Ammonia
Enzymatic synthesis in the “urea cycle”
Urea
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PARTS OF HUMAN EXCRETORY SYSTEM
1. Kidneys
2. Ureter
3. Urinary bladder
4. Urethra
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The urinary
system
Kidney
Ureter
Aorta
Renal vein
Bladder
Renal artery
Vena cava
Urethra
© 2008 Paul Billiet ODWS
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The Kidney
Cortex
Medulla
Calyx
Pelvis
Ureter
PapillaPyramid
Column
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The nephronBowman’s capsule
Glomerulus
Proximal
convoluted tubule
Capillary
Loop of Henlé
Collecting duct
Distil convoluted
tubule
Branch of renal
vein
Branch of renal
artery
© 2008 Paul Billiet ODWS
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Key functions of the nephron
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Functions of the Nephron
Filtration
Reabsorption Secretion
Excretion
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URINARY BLADDER
Stores urine
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URETHRA
Tube that carries urine
from the bladder to the
outside of the body
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Reabsorption stage:
water, minerals,
amino acids and
glucose are
reabsorbed by active
transport from the
renal tubule into the
capillaries
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Filtration in the glomerulus
Blood enters the glomerulus from a branch of the renal artery
This blood is under high pressure
The capillary walls are one cell thick
The plasma filters though the membrane under pressure
Proteins do not pass Southern Illinois School of Medicine
© 2008 Paul Billiet ODWS
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Filtration in the glomerulus
A membrane surrounds
each capillary of the
glomerulus
The blood plasma is
filtered at about 150 litres
per day
Southern Illinois School of Medicine
© 2008 Paul Billiet ODWS
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The remaining material is
urine which contains water,
salt and urea
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Excretory System Problems
• Kidney stones – crystalized mineral salts and uric acid salts in the urine. Stones block flow of urine and cause excruciating pain.
• Kidney failure - can be caused by long-term diabetes, infections, physical injuries, chemical poisoning. Causes toxic materials to build up to lethal levels.
Dialysis or kidney transplant is the treatment.
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Effects of Aging upon Urinary System
• Reduced blood supply to kidneys – less filtering of blood.
• On top of that, the kidney become less efficient with respect to the filtering process.
• Poorer salt-water/pH balance – dehydration more evident in the elderly.
• Bladder control adversely affected.
• In men, the prostate may enlarge and apply pressure to the urethra making urination difficult (surgery required).
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Excretory System
UTI (Urinary Tract Infection)
• Is a very common disorder. If the bladder has
become infected, it is known as cystitis. If the
urethra is infected., it is called urethritis.
• Symptoms include painful urination burning
sensation), frequent urination (even if no urine
present) and bloody or brown urine.
• This can lead to chills, fever, nausea, vomiting and
upper abdomen tenderness.
Disorders of the Excretory System
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Renal function tests
Detect renal damage
Monitor functional damage
Help determine etiology
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glomerular filtration
rate (GFR)
plasma creatinine
plasma urea
urine volume
urine urea
minerals in urine
urine protein
urine glucose
hematuria
osmolality
Laboratory tests of renal function
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Biochemical Tests of Renal Function
Measurement of GFR
Clearance tests
Plasma creatinine
Urea, uric acid and β2-microglobulin Renal tubular function tests
Osmolality measurements
Specific proteinurea
Glycouria
Aminoaciduria
Urinalysis
Appearance
Specific gravity and osmolality
pH
osmolality
Glucose
Protein
Urinary sediments
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Why Test Renal Function?
To identify renal dysfunction.
To diagnose renal disease.
To monitor disease progress.
To monitor response to treatment.
To assess changes in function that may impact on therapy (e.g. Digoxin, chemotherapy).
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When should you assess renal
function?
Older age
Family history of Chronic Kidney disease (CKD)
Decreased renal mass
Low birth weight
Diabetes Mellitus (DM)
Hypertension (HTN)
Autoimmune disease
Systemic infections
Urinary tract infections (UTI)
Nephrolithiasis
Obstruction to the lower urinary tract
Drug toxicity
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Studies about Urea Excretion in human
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References:
1- Cotran, RS S.; Kumar, Vinay; Fausto, Nelson; Robbins, Stanley L.; Abbas, Abul K. (2005). Robbins and Cotran pathologic basis of disease. St. Louis, MO: Elsevier Saunders. ISBN 0-7216-0187-1.
2- Glodny B, Unterholzner V, Taferner B, et al. (2009). "Normal kidney size and its influencing factors - a 64-slice MDCT study of 1.040 asymptomatic patients". BMC Urology 9: 19. doi:10.1186/1471-2490-9-19. PMC 2813848. PMID 20030823.
3- Bålens ytanatomy (Superficial anatomy of the trunk). Anca Dragomir, Mats Hjortberg and Godfried M. Romans. Section for human anatomy at the Department of medical biology, Uppsala university, Sweden.
4- Walter F. Boron (2004). Medical Physiology: A Cellular And Molecular Approach. Elsevier/Saunders. ISBN 1-4160-2328-3.
5- Clapp, WL. "Renal Anatomy". In: Zhou XJ, Laszik Z, Nadasdy T, D'AgatiVD, Silva FG, eds. Silva's Diagnostic Renal Pathology. New York: Cambridge University Press; 2009.
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