Introduction to Renal System Flashcards
gross function of Kidneys (the renal system)
Produce urine (filtration, reabsorption, secretion)
gross function of Ureter
Ureter (one per kidney) carry urine away from the kidneys and to the urinary bladder
gross function of Urinary bladder
The urinary bladder is a muscular, elastic sac which stores urine arriving via each ureter
gross function of Urethra
A duct which allows urine to leave the bladder (and body itself) via the process of urination.
Kidney – anatomy
Two kidneys
• Located either side of vertebral column
- Average kidney measures 11 x 7 x 3 cm
- Left kidney often slightly larger than the right
• Right kidney usually slightly lower than the left
– Thought to be due to positioning of the liver
Kidneys surrounded in layer of fat for support
Organs of urinary system
Kidney, ureter, bladder, urethra
Hilum
Indentation – entry of renal artery and nerves, exit of renal vein and ureter
Renal pelvis
The enlarged portion of the ureter as it leaves the kidney. Also the point of mergence for the major calyces
Cortex
Outer layer of kidney
Medulla
Inner part of kidney
Nephron
– Structural and functional unit of kidney
– Site of urine production
– 1 million/kidney
Veins
carry deoxygenated blood towards the heart
Arteries
carry oxygenated blood away from the heart
Typical direction of blood flow
Arteries → Arterioles → Capillaries → Venules → Veins
Renal vein
carries blood away from the kidney
Renal artery
carries blood towards the kidney
Blood flow through kidney
approximately 1200 mL/min
Kidney – primary functions
Main organs of excretion
- Filter blood to make urine
- Remove excess water, ions, urea, toxic substances
• Involved in blood homeostasis – Osmotic pressure – Volume – Pressure – Ion concentration – pH
Produce the hormone erythropoietin (kidney)
Also known as haematopoietic or haemopoietin
Hormone released into bloodstream in response to low blood-oxygen levels (hypoxia)
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Carried to the bone marrow
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Stimulates stem cells (called pluripotent stem cells)
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Cells undergo maturation – become red blood cells (erythrocytes)
Produce the hormone renin (kidney)
Renin – Enzyme secreted by kidneys
– Increases blood pressure
– Regulate extracellular fluid (plasma, lymph)
– Allows for arterial vasoconstriction
• Narrowing of arteries → increase in pressure
Kidneys - Urine
– Filter blood to make urine
– Remove excess water, ions, urea, toxic substances
Nephron - Urine
– Structural and functional unit of kidney
– Site of urine production and electrolyte balancing
Electrolyte balancing - Urine
Key to blood homeostasis
Urine – facts and composition
- Main role of kidneys – filter blood to produce urine
- Adult bladder holds 400-600 mL of urine
• Urine is ~95% water, ~5% dissolved substances
• Most important of the 5% being:
– Toxins
• Toxic substances produced by harmful bacteria during an infection
– Nitrogenous waste
• Urea, uric acid, ammonia
Hormones - Urine
Excess hormone levels
Electrolytes - Urine
Diet dependant but in general: Na+, Cl- , K+ phosphate, bicarbonate
Pigments - Urine
Mostly from breakdown products of old red blood cells, these products are often yellow in colour
Abnormal elements - Urine
Stones (calculi), mucus, blood, sugar (glucose)
Urine – formation
3 key stages
- Glomerular filtration
- Tubular reabsorption
- Secretion
Glomerular filtration
Movement of plasma from glomerulus to lumen of Bowman’s capsule (filtrate is formed at 120 mL/min)
- Water, ions, small molecules are filtered as a result of osmosis (water) and diffusion
- Blood cells and protein are not filtered
Tubular reabsorption
- 99% of filtrate is reabsorbed
- Occurs within proximal tubule, loop of Henle and convoluted tubule
- Purpose: to retain water, vital nutrients and ions (recovery of energy)
- Urine output/production → 1-4 mL/min
- Main substances reabsorbed are water, salt, calcium, glucose and amino acids
- Osmosis and diffusion make reabsorption possible
Secretion
- Potassium, hydrogen and ammonium ions can be actively secreted into urine
- The balancing of fluids and electrolytes in this way contributes to blood homeostasis
- Main substances secreted are excess water, excess hormones, ions, urea, uric acid, ammonia, bile salts and abnormal elements such as kidney stones, mucus and glucose.
What is Dialysis
Artificial filtration/cleaning of the blood to remove waste
products, toxins etc.
– Dialysis is a means of keeping someone suffering latestage chronic kidney disease alive while a suitable kidney donor is located
– One of two methods:
• Pump passing blood via special membrane in place of kidneys to remove waste products
• Allowing waste products to diffuse directly into special dialysis fluid within the body
Why is Dialysis needed?
In cases of severely depressed kidney function, kidney damage and failure - provides a means of artificially filtering waste products out of the blood
– If kidneys are not working properly waste products will build up in the bloodstream to dangerous levels
– number of consequences for the normal functioning of the other systems of the body and will eventually lead to death
How does Dialysis work
– Relies on the processes of osmosis and diffusion
– Two types haemodialysis and peritoneal dialysis
Haemodialysis
Blood from radial artery passed through membrane - allows small waste particles such as urea to diffuse out and into a special dialysis fluid; large particles (e.g. blood cells) are retained
filtered blood returned to the patient via a suitable vein in the leg or wrist
Haemodialysis will typically be carried out 3 times / week
First few visits are generally carried out as an outpatient in hospital
Training often given during the visits to enable the procedure to be carried out at home
Peritoneal dialysis
Sterilised dialysis fluid is introduced into the peritoneal cavity of the patient through the abdominal wall
membrane of the cavity allows waste products from the blood to pass through and into the dialysis fluid via diffusion
After 2-3 hours the dialysis fluid is drained from the patient and replaced with fresh for another cycle
Patient will typically go through 4-6 cycles / day
Hormonal control
The endocrine system plays in crucial role in regulating the function of the renal system.
Main control via hormones produced outside of the kidney which travel to the kidney via the blood, acting as chemical messengers (endocrine function)
Kidneys themselves also produce hormones to aid regulation but the effects of these are more localised (paracrine function)
Antidiuretic hormone (ADH)
ADH – hormone produced in the hypothalamus and stored in the pituitary gland
Pituitary gland situated at bottom of the hypothalamus at base of the brain
ADH stored in the posterior pituitary – i.e. the back of the pituitary gland
ADH prevents excessive loss of water
Without ADH you would dehydrate
Diuretic
something which causes increased urine production (termed diuresis)
Antidiuretic
something which causes decreased urine production
ADH actions
– ADH targets distal tubule and collecting duct
– Increases their permeability to water
ADH Effects
– Water flows out of the tubules (i.e. reabsorbed by body) via osmosis (a passive process not requiring energy)
– Decreased urine volume
– Increased blood pressure
Aldosterone
produced in the adrenal cortex of the adrenal gland
Adrenal glands situated just above each kidney
Aldosterone Actions
– Like ADH, Aldosterone also targets the distal tubule
and collecting duct
– Causes sodium (Na+ ) to leave the tubules (i.e. reabsorbed by body)
– This in turn causes water to leave the tubules
Aldosterone Effects
– Water flows out of the tubules via osmosis and is retained by the body
– Decreased urine volume
– Increased blood pressure
Atrial natriuretic hormone (ANH)
produced in the atria of the heart
– Secreted from both the left and right atrium
• Secreted by specialised muscle fibres
has the opposite function of aldosterone
ANH Actions
– ANH also targets the distal tubule and collecting duct
– Causes sodium (Na+) to move into the tubules (i.e. to be removed)
– This in turn causes water to move into the tubules
ANH Effects
– Water flows into the tubules via osmosis and is thus
removed by the body
– Increased urine volume
– Decreased blood pressure
Atrial natriuretic hormone
🡩 urine volume
🡫 blood pressure
Antidiuretic hormone
🡫urine volume
🡩blood pressure
Aldosterone
🡫urine volume
🡩blood pressure
Fluid & electrolyte regulation
- Deficits require increased intake and retention
- Excesses require increased renal excretion
- Remember: Hypo – lower. Hyper – higher
hyponatraemia or hypernatraemia
Failure to effectively regulate blood sodium content can result in hyponatraemia or hypernatraemia
hypokalaemia or hyperkalaemia
Failure to effectively regulate blood potassium content can result in hypokalaemia or hyperkalaemia
dehydration or water intoxication
Failure to keep water-electrolyte balance within the normal range can result in dehydration or water intoxication
Dehydration
Where you use (lose) more fluid than you take in
Stages of dehydration can broadly be defined by the % loss of body weight as follows: • 5% – Mild • 10% – Moderate • 15% – Severe
Primary presenting symptoms of dehydration
Dry and irritated skin, loose skin, bags under the eyes, headaches, dry mouth, difficulty swallowing, dry and tired feeling eyes
Dehydration features
Changes the osmotic balance of the body
changes balance of minerals in your body
Turgidity of body cells eventually decreases as water leaves cells
Severe dehydration can result in rupture and death of cells (cell lysis)
Water intoxication
Where you take in more water than you use, resulting in dilution of salts and other minerals
Water intoxication results in hyponatremia
– situation where sodium content of your blood is below normal.
Typically defined as a sodium concentration <135 mmol/L blood
Water intoxication features
- Changes the osmotic balance of the body
- Balance of minerals in your body also changes, you risk dangerously diluting out your electrolytes
- Turgidity of body cells eventually increases as water enters cells
- Severe water intoxication can result in death as cells of the body swell, rupture and die (cell lysis)
Primary presenting symptoms of Water intoxication
Nausea, headaches, pressure in your head, altered vision, feeling cold and confused; eventually leading to coma
Why analyse urine
– Good indicator of overall health
– Diagnosis of a wide range of medical conditions
– Monitoring of existing medical conditions
3 main methods of urinalysis
visual, microscopic, ‘dipstick test’
Most common, primary method of quick, indicative testing of urine…
test strips / ‘dipstick test’
Test strips - urinalysis
Specially designed test strips can provide insight into the functioning of vital organs
Test strips are for qualitative / semi-quantitative detection of a range of analytes
Strips contain a series of reactive patches
Each patch is able to detect the presence of analytes through a specific reaction mechanism
Urinalysis steps
- Strips dipped into urine ensuring all patches covered
- Remove from urine and leave to react for a brief period (~30 – 120 seconds)
- Patches change colour in response to amount of analyte present
- Colour change compared against chart to determine whether or not the analyte in question falls within the normal, healthy range.
Urinalysis in pathology
A vast range of medical conditions cause changes in urine composition.
Urine analysis is therefore a crucial tool in diagnosis
Common conditions which can be detected through urinalysis
– Kidney stones (acidic pH)
– Other kidney damage (high protein levels)
– Liver disease (presence of bilirubin)
– Diabetes (presence of high glucose levels)
glycosuria
High glucose level in urine
proteinuria
High protein level in urine
