Renal System, Fluids and Electrolytes

Question 1

What are the functions of the renal system?

Answer 1

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

Question 2

Where are the kidneys positioned?

Answer 2

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

Question 3

What are the properties of the ureters?

Answer 3

• 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

Question 4

What is the function of the bladder?

Answer 4

Reservoir for urine. It is a muscular sac that can expand considerably

Question 5

Where is the bladder situated?

Answer 5

• Pelvic cavity

- Extends into the abdominal cavity when full

Question 6

Describe the properties of the bladder

Answer 6

• 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

Question 7

What does the urethra do?

Answer 7

Is a muscular (smooth muscle) tube that carries urine from the bladder and out of the body

Question 8

What is the urethral junction?

Answer 8

at the bladder the urethral junction is a thickening of the detrusor muscle which acts as an internal sphincter to prevent bladder leakage

Question 9

What is the structure of the urethra?

Answer 9

The external urethral sphincter is striated muscle and under voluntary control

Question 10

Describe the blood flow in the nephron?

Answer 10

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

Question 11

Describe the properties of the bowman’s capsule

Answer 11

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

Question 12

Describe the formation of urine

Answer 12

• 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)

Question 13

What is the bladder capacity?

Answer 13

30mls for each year of age +30

Question 14

Describe the process of filtration

Answer 14

• 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

Question 15

Describe the process of reabsoption

Answer 15

• 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

Question 16

Describe the process of secretion

Answer 16

• 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

Question 17

Describe the role of hormones

Answer 17

• 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)

Question 18

Describe the properties of urine

Answer 18

-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

Question 19

What does urine contain?

Answer 19

• Water
• Sodium and potassium ions
• Urea, uric acid and creatinine
• Ammonia
• Bicarbonate ions

Question 20

What should urine not contain?

Answer 20

• Glucose: this is filtered but rapidly reabsorbed in the PCT
• Blood proteins
• Red blood cells
• Haemoglobin
• White blood cells (put)
• Bile

Question 21

What are electrolytes?

Answer 21

Defined as inorganic compounds which dissociate into ions (carry a positive or negative charge) in solution
Different fluid compartments contain different electrolytes

Question 22

What electrolytes are contained in ICF?

Answer 22

• Potassium (K+)
• Protein (-)
• Phosphate (HPO4-)
• Magnesium (Mg++)

Question 23

What electrolytes are contained in ECF?

Answer 23

• Sodium (Na+)
• Chloride (Cl-)
• Bicarbonate (HCO3-)
• Calcium (Ca++)

Question 24

What is acid base balance?

Answer 24

• 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

Question 25

What happens within fluid and electrolyte imbalance

Answer 25

• Dehydration may increase plasma concentrations of ions
• Sodium and potassium depletion, could be due to loss of gastric aspirate, vomiting or diarrhoea
• Acidosis or alkalosis (H+)
• In health, the kidneys maintain fluid, electrolyte and pH within very narrow ranges (balance)
• An accurate fluid balance chart is very important