Renal/Urinary System Flashcards
Functions of the renal system:
- Formation of urine
- Elimination of waste products
- Homeostasis of
- acid-base balance
- water balance
- electrolyte balance
- blood pressure regulation
- erythropoietin (RBC production)
- vitamin D activation
- glucogenesis
Describe the order that fluid moves through the kidneys:
Nephron Collecting duct Renal papillary duct Minor calyx Major calyx Renal pelvis Ureter Urinary bladder
What position are the kidneys in?
Upper, posterior abdominal wall (between T12-L3)
What are the kidneys protected by?
Thick outer fibrous capsule
Surrounded by fat
Lower ribs
Function of the ureters:
Drain urine from the kidneys to the bladder by peristalsis
Features of the ureters:
- Enter the bladder posteriorly
- Fibrous coat, muscular layer and inner lining of mucous membrane, which protects epithelial cells from the varying pH levels.
Function of the bladder:
The bladder is a reservoir for urine
Where is the bladder situated?
Situated in the pelvic cavity but extends into the abdominal cavity when full
Layers of the bladder:
- Outer layer of loose connective tissue
- 3 layers of smooth (detrusor) muscle and elastic fibres
- Inner and outer layers = longitudinal muscle fibres
- Middle layer = circular muscle fibres
What is the urethra?
A muscular (smooth muscle) tube carrying urine from the bladder and out of the body
What is the urethral junction?
At the urinary bladder, the urethral junction is a thickening of muscle acting as an internal sphincter to prevent bladder leakage.
Describe the external urethral sphincter:
The external urethral sphincter is striated muscle under voluntary control.
Describe the nephron:
A nephron is the functional unit of the kidneys that regulates substances in the blood by filtering it, reabsorbing what is needed, and excreting the rest as urine.
Describe the structure of a nephron:
For each nephron, an afferent arteriole flows into the glomerulus (which is a high-pressure capillary bed). Blood is filtered by the glomerulus to produce filtrate which is collected by the Bowman’s capsule, which surrounds the glomerulus.
Filtrate travels through the rest of the tubule to the proximal convoluted tubule (PCT), loop of Henle and distal convoluted tubule (DCT), before exiting the nephron into common collecting ducts shared by many nephrons.
Describe the renal arterioles:
The renal artery enters the kidney branching into renal arterioles.
An afferent arteriole enters the Bowman’s capsule of each nephron forming a capillary network (glomerulus). An efferent arteriole leaves the glomerulus and surrounds the rest of the nephron.
Features of the glomerular capillaries:
They are lined with fenestrated endothelium to aid filtration due to increased pores. They are leaky as they are 1000 times more permeable than other capillaries.
What are the 3 stages of urine formation?
Filtration, reabsorption and secretion
What is bladder capacity?
The amount of urine a bladder can hold
30mls x age + 30mls
What is filtration?
A non-selective, passive process where small solutes and water filter out of the blood.
What remains in the blood during filtration and why?
Proteins and blood cells are too large to pass through the filtration membrane so they remain in the blood.
What causes filtration?
Blood pressure in the glomerular capillaries is higher than in other capillaries, which forces water and small solutes out f the blood through capillary walls.
What process occurs after filtration?
Reabsorption
How does reabsorption occur?
By both passive diffusion and active transport
Describe reabsorption:
Most of the water and solutes that were filtered out of the blood are reabsorbed back into the blood stream. This occurs as fluid passes through the tubules.
What solutes are reabsorbed?
Glucose, amino acids, 80-90% bicarbonate, 65% sodium, potassium and water are reabsorbed.
What is reabsorbed in the loop of Henle?
15% water is reabsorbed in the descending limb and and solutes (sodium, potassium, bicarbonate and chloride) are reabsorbed in the ascending limb.
What occurs in the DCT and collecting ducts?
Solutes continue to be reabsorbed
What stage follows reabsorption?
Secretion
What substances aren’t passed into filtrate in the Bowman’s capsule?
Some drugs, hydrogen, urea and creatinine are secreted into filtrate as it passes along the tubule.
Describe the effect of ADH:
Antidiuretic hormone (ADH) acts on the collecting ducts. It increases reabsorption of water from filtrate when dehydrated so less urine is passed.
Describe the effect of aldosterone:
Aldosterone increases reabsorption of sodium (Na+) in the DCT and collecting duct, and as water moves passively with sodium by osmosis, more water is reabsorbed as a result, so less urine is passed.
When is filtrate classed as urine?
After leaving the collecting duct as the processes of urine formation are complete
What is urine?
Urine is what remains after the filtrate has lost most of its water, nutrients and solutes. It contains substances that are not needed by the body so are excreted.
Why is urine yellow in colour?
Due to the pigment, urochrome, from haemoglobin destruction.
Features of urine:
Sterile, slightly aromatic, normal ph of 6.
Minimum urine outputs for age:
Infants - 1-2mls/kg/hour
Children - 1ml/kg/hour
Adolescents - 0.5ml/kg/hour
What does urine contain?
Water Na+ and K+ ions Urea, uric acid and creatinine Ammonia Bicarbonate ions
What should urine not contain?
Glucose Proteins Blood cells Haemoglobin Bile
What are electrolytes?
Inorganic compounds which dissociate into ions (carry a +ve or -ve charge) in solution
Name 4 substances in intracellular fluid:
Potassium
Phosphate
Magnesium
Proteins
Name 4 substances in extracellular fluid:
Sodium
Chloride
Bicarbonate
Calcium
How does urine production regulate the acid-base balance of blood?
Acid-base balance is related to the number of hydrogen ions present (more H+ = more acidic)
Acid-base balance is affected by urine formation as it is dependent on how much hydrogen is filtrated or reabsorbed in the kidneys.
What pH is arterial blood maintained at?
7.35-7.45
How do H+ levels affect the pH of blood?
As H+ increases, pH decreases = ACIDOSIS (pH<7.35)
As H+decreases, pH increases = ALKALOSIS (pH>7.45)
What is the carbonic-acid-bicarbonate buffering system formula?
Hydrogen + Bicarb –> Carbonic acid –> Water + CO2
How does fluid imbalance affect electrolyte balance?
Dehydration increases plasma concentrations of ions
Sodium and potassium depletion could be due to
- loss of gastric aspirate
- vomitting and diarrhoea
Electrolyte imbalance can lead to acidosis/alkalosis
