THE RENAL SYSTEM

Question 1

what does the urinary system comprise of?

Answer 1

*2 kidneys 
—located in abdominal cavity
*2 ureters 
*1urethra
*1urinary bladder

Question 2

where are the kidneys located?

Answer 2

• outside peritoneal cavity in back of upper abdomen

- one each side of vertebral column at level of 12th thoracic to 3rd lumbar vertebrae

Question 3

list 4 functions of the renal system?

Answer 3

1) maintain homeostasis of blood
—control volume (fluid balance and pH)
2) endocrine function
—erythropoietin mad renin (RAAS system)
3) vitamin D metabolism
4) main excretory organ of the body 
—remove waste from blood, filter, selectively reabsorb

Question 4

describe the structure of the kidney?

Answer 4

*encapsulated and surrounded by adipose fat
—extra protection e.g. shock absorb
*outer boarder is convex
*Inner boarder = hilum (indent medially)
—hilum opens into cavity = renal sinus

Question 5

describe the functions of the nephron?

Answer 5

• consist of a filtering unit (glomerulus) and tubule
• glomerulus = capillary network bringing blood from the renal artery (surrounded by glomerular capsule)
• four processes involved in formation of urine:
  1) glomerular filtration
  2) tubular reabsorption (H2O, Na+, glucose)
  3) tubular secretion (creative, drugs)
  4) urine concentration

Question 6

name the four processes j combed in forming urine?

Answer 6

1) glomerular filtration (100-125 mLs/m)
2) tubular reabsorption (H2O, Na+, glucose)
3) tubular secretion (creative, drugs)
4) urine concentration

Question 7

what is glomerular filtration?

Answer 7

• the rate that the glomerulus filters blood is relatively constant
• auto regulated (independent of CNS)

Question 8

in terms of glomerular filtration, what happens if blood pressure drops?

Answer 8

*stretch receptors in afferent arteriole wall detect the change
*vasoconstriction = less pressure at glomerulus so less fluid filtered
—causing fluid consolidation

Question 9

in terms of glomerular filtration, what happens if blood pressure rises?

Answer 9

*stretch receptors in the afferent arteriole wall detect change
*vasodilation of afferent arterioles = more pressure at glomerulus = more fluid filtered
—causing more fluid excretion

Question 10

explain blood volume in the kidney?

Answer 10

*20% to 25% total cardiac volume is directed to kidney via abdominal aorta + L/R renal arteries
*renal blood flow = 1.2L/min
*glomerular filtrate = 16%to 20% total cardiac volume
—females: 150L (filters total blood volume 30 times/day)
—males: 180L (filters total blood volume 30 times/day)
*more than 99% glomerular filtrate returns to bloodstream via tubular reabsorption
*1-2L fluid excreted as urine

Question 11

describe glomerular filtration rate (GFR) and creative clearance?

Answer 11

*glomerular filtration rate = the rate the glomerulus filters blood
*clearance = compete removal of substance from blood
*creatine = muscle waste, cleared by glomerulus (none reabsorbed)
—creative clearance indicates GFR and kidney health
*precisely measured from urine over 24 hr
*estimated using formula from a blood sample

Question 12

describe tubular reabsorption?

Answer 12

*proximal consulates tubule = most reabsorption occurs
—65% H2O, Na ions, K ions reabsorbed
—100% glucose, amino acids reabsorbed
*loop of henle
—15% water reabsorbed
—20-30% sodium and chloride ions reabsorbed

Question 13

describe how blood volume is controlled by RAAS?

Answer 13

RAAS = renin angiotensin aldosterone system
*if kidney detect fa,, I’m BP by stretch receptors
1) triggers secretion of renin
2) concerts angiotensinogen (formed in liver) to angiotensinogen I
3) when this reaches the lungs, converted to angiotensinogen II which:
—constricts vessels
—stimulates thirst
—triggers ADH release
—promotes aldosterone release, increasing tubular reabsorption of sodium

Question 14

other than RAAS, name and describe two hormones which control BP in the kidney?

Answer 14

*LOW BP = anti diuretic hormone (ADH)
—released by pituitary gland when angiotensinogen II present, increases tubular reabsorb of water
*HIGH BP = atrial natriuretic peptide (ANP)
—released by heart muscle when overstretched as circulatory overload
—blocks the reabsorption of sodium
—indirectly stops water reabsorption by reducing renin and aldosterone in the blood

Question 15

describe tubular secretion?

Answer 15

*opposite of tubular reabsorption
*substance move from peritubular blood vessels into tubular fluid
—(name for the filtrate following the reabsorption phase of urine formation)
*e.g. of substances excreted inc. hydrogen ions (key for acid-base balance in blood + drugs)

Question 16

name the main constituents of urine?

Answer 16

*normal urine = clear, straw coloured, slightly acidic containing:
—excess water from fluid which the body doesn’t need
—urea is a waste product from protein
—electrolytes and minerals e.g. sodium/ potassium
—pigment bilirubin (<3) - the colour from RBC breakdown

Question 17

describe colour as a characteristic of normal urine?

Answer 17

• varies from pale to a deep golden colour

* darker the urine the greater the concentration

Question 18

describe clarity as a characteristic of normal urine?

Answer 18

• normal urine is clear

* cloudy, turbid urine = pus, bacteria, bladder or kidney infection, specimen standing over half hr

Question 19

describe odour as a characteristic of normal urine?

Answer 19

• normal urine is aromatic

* has a strong but agreeable odour

Question 20

describe specific gravity as a characteristic of normal urine?

Answer 20

• normal urine has a specific gravity of 1.003 - 1.030

* specific gravity = measurement of amount of solids in the urine

Question 21

describe pH as a characteristic of normal urine?

Answer 21

*normal urine is slightly acidic, pH of 6.0

—pH ranges 4.5 to 8.0

Question 22

describe protein as a characteristic of normal urine?

Answer 22

• normal urine may have small amounts of protein present

* km,y in insignificant amounts, too small to be detected by a reagent strip

Question 23

describe glucose as a characteristic of normal urine?

Answer 23

*normal urine does not contain glucose

Question 24

describe ketones as a characteristic of normal urine?

Answer 24

• normal urine does not contain ketone bodies

* ketones result from the breakdown of fats

Question 25

what are the ureters of the renal system?

Answer 25

• muscular tubes lined with mucous membrane
• one leads from each kidney down to the urinary bladder
• urine is propelled from renal pelvis through ureters by wavelike contractions (peristalsis)

Question 26

what is the urinary bladder of the renal system?

Answer 26

• hollow, muscular sac in pelvic cavity
• location = men: between the pubic symphysis (pelvis) and rectum
  woman: between pubic symphysis and uterus/ vagina
• detrusor muscle (smooth) in the wall of the bladder
• serves as a temporary reservoir for urine
• spherical shaped when full, inverted pyramid when empty

Question 27

describe how urine is stored and emptied?

Answer 27

*involves both voluntary (SNS) and involuntary (ANS) control
—ANS = parasympathetic NS promotes bladder emptying (internal sphincter)
sympathetic NS promotes bladder filling
—SNS = muscles in external sphincter and pelvic floor provide for voluntary control of urine

Question 28

state how micturition (urination) is controlled?

Answer 28

• negative feedback system
• spinal cord reflex
• micturition centre in the pons varoli (brain)
• cortical and subcortical areas

Question 29

what is the urethra?

Answer 29

*mucous membrane-lined tube that leads from bladder to exterior of the body
—urine exits bladder through urethra
—external opening of urethra is urinary meatus
*female urethra carries only urine, approx 4cm + opens to exterior immediately to vaginal opening
*male urethra carries both urine and semen during ejaculation, approx 17cm