Renal System, Fluids and Electrolytes Flashcards
(25 cards)
What are the functions of the renal system?
HOMEOSTASIS, FORMATION OF URINE AND ELIMINATION OF WASTE
Homeostasis:
Acid-base balance
Water (fluid balance)
Electrolyte balance
Blood pressure regulation (renin-angiotensin) pathway
Red blood cell production
Formation of urine:
Formed in the kidneys
Elimination of waste products:
- Nitrogenous wastes
- Toxins
- Drugs
Where are the kidneys positioned?
Left kidney higher than the right as (large) liver above right kidney
Position: upper, posterior, abdominal wall
Well protected:
-Thick outer fibrous capsule
-Surrounded by bed of fat
-Also protected by lower ribs
What are the properties of the ureters?
- Drain urine from the kidneys to the bladder
- About 25-30cm long
- Smooth muscle propels the urine along the structures (peristaltic waves)
- Turn and enter posterior wall of bladder
- Renal pelvis and ureters lined with a mucosal membrane, layer of mucous protects the epithelial cells from urine as the pH of urine can differ drastically and would damage cells
What is the function of the bladder?
Reservoir for urine. It is a muscular sac that can expand considerably
Where is the bladder situated?
- Pelvic cavity
- Extends into the abdominal cavity when full
Describe the properties of the bladder
- Outer layer of loose connective tissue
- 3 layers of smooth muscle (detrusor muscle) and elastic fibres: inner and outer layers of longitudinal muscle fibres and a middle layer of circular muscle fibres
- Lined with mucosal membrane
What does the urethra do?
Is a muscular (smooth muscle) tube that carries urine from the bladder and out of the body
What is the urethral junction?
at the bladder the urethral junction is a thickening of the detrusor muscle which acts as an internal sphincter to prevent bladder leakage
What is the structure of the urethra?
The external urethral sphincter is striated muscle and under voluntary control
Describe the blood flow in the nephron?
Renal artery enters the kidney: branches into arterioles
An arteriole enters the glomerular (bowmans) capsule on each nephron and divides into capillary network called the glomerulus
Afferent arteriole: enters glomerulus (wider than efferent)
Efferent arteriole: leaves glomerulus
The efferent arteriole then forms another capillary network which surrounds the rest of the nephron before reforming as veins
Describe the properties of the bowman’s capsule
Endothelium of capsule: fenestrated (many pores)
Afferent arteriole carries blood into the capsule
Divides into capillaries called the glomerulus
Glomerular capillaries are very leaky; 1000 times more permeable than other capillaries
Efferent arteriole carries blood away from glomerulus
Describe the formation of urine
- Urine is formed in the kidneys by functional units called nephrons
- Once urine is formed it drains from kidneys down into the bladder
- When 250-300 millilitres collects in the bladder, the bladder empties and urine is expelled from the body via the urethra
- The first stage is FILTRATION: water and solutes in blood are ‘filtered’ out of the blood stream into the glomerular capsule
- Filtrate flows out of glomerular capsule through tubule
- Much of filtrate is reabsorbed back into blood as it passes through the tubule (REABSORPTION)
- Some substances pass from blood into filtrate (SECRETION)
What is the bladder capacity?
30mls for each year of age +30
Describe the process of filtration
- Blood pressure in glomerulus higher than in other capillaries: blood pressure forces water and small solutes out of capillaries
- Is a nonselective, indiscriminate, passive process -Water and solutes smaller than proteins are forces through capillary walls into glomerulus to form filtrate
- Proteins and blood cells: too large to pass through the filtration membrane, they remain in the blood
- Filtrate is collected in the glomerular capsule and leaves via the renal tubule
Describe the process of reabsoption
- As the fluid passes through the tubules, much of the water and solutes that were filtered out of the blood are reabsorbed back into the blood stream
- Some by passive diffusion and some are actively transported which is a more selective process and depends on the bodies needs
- Glucose and amino acids, 80-90% bicarbonate, 65% potassium and sodium, and water are reabsorbed
- In the loop of henle 15% water is reabsorbed
- In the loop of henle, 15% water is reabsorbed in the descending limb, solutes such as NA+, K+, bicarbonate and CL- reabsorbed in the ascending limb
- Water and solutes continue to be reabsorbed in the DCT and collecting ducts
Describe the process of secretion
- Not all substances are cleared from the blood into the filtrate in the glomerular capsule, e.g. some drugs, H+, urea and creatinine are secreted into the filtrate as it passes along the tubule
- Secretion of substances is regulated by amounts of different substances present in the blood, e.g. K+ secretion can vary depending on dietary intake, if more is secreted
Describe the role of hormones
- Most water moves back into blood passively with solutes
- Antidiuretic hormone acts on the collecting ducts, increases re-absorption of water from filtrate when dehydrated so less urine passed
- Aldosterone increases reabsorption of sodium (NA+) in the DCT and collecting duct, (water moves back passively via osmosis with NA+, not a direct effect of aldosterone)
Describe the properties of urine
-After leaving the collecting duct, the processes of re-absorption and secretion are completed
-The fluid is now classed as ‘urine’
-Urine is what remains after the filtrate has lost most of its water, nutrients and necessary ions
-Urine contains nitrogenous waste and substances that are not needed by the body
-Yellow colour due to the pigment urochrome (from the destruction of haemoglobin) and solutes
-Sterile
-Slightly aromatic
-Normal pH of around 6
-Specific gravity of 1.001 to 1.035 (density compared to H20)
-Minimum output:
INFANTS: 1-2mls/kg.hr
CHILDREN: 1ml/kg/hr
ADOLESCENTS: 0.5mls/kg/hr
What does urine contain?
- Water
- Sodium and potassium ions
- Urea, uric acid and creatinine
- Ammonia
- Bicarbonate ions
What should urine not contain?
- Glucose: this is filtered but rapidly reabsorbed in the PCT
- Blood proteins
- Red blood cells
- Haemoglobin
- White blood cells (put)
- Bile
What are electrolytes?
Defined as inorganic compounds which dissociate into ions (carry a positive or negative charge) in solution
Different fluid compartments contain different electrolytes
What electrolytes are contained in ICF?
- Potassium (K+)
- Protein (-)
- Phosphate (HPO4-)
- Magnesium (Mg++)
What electrolytes are contained in ECF?
- Sodium (Na+)
- Chloride (Cl-)
- Bicarbonate (HCO3-)
- Calcium (Ca++)
What is acid base balance?
- Related to the number of hydrogen ions present
- pH in arterial blood is maintained between very narrow limits- 7.35-7.45
- All metabolic reactions generate H+ so constantly being produced
- As H+ increases, pH decreases= acidosis <7.35
- As H+ decreases, pH increases= alkalosis >7.45
