Renal System

Question 1

What structures form the renal system?

Answer 1

Two kidneys
Two ureters
Urinary bladder
Urethra

Question 2

What are the kidneys?

Answer 2

Paired organs situated on either side of the vertebral column on the posterior wall of the abdominal cavity
Right kidney lower than left due to position of liver

Question 3

Describe the macrostructure of the kidney

Answer 3

Renal capsule composed of tough fibrous tissue
Renal cortex dark in colour due to vascularity
Renal medulla pyramids that contain nephrons
Renal pelvis collects urine from pyramids and directs to the ureters

Question 4

Outline the microstructure of the kidney

Answer 4

Consists of nephrons and collecting ducts
Nephron:
Bowmans capsule surrounds the glomerulus (capillary network) blood is filtered small molecules only to pass
Proximal convoluted tubule
Loop of henle
Distal convoluted tubule

Collecting duct collect urine from several nephrons directing urine to the ureters

Question 5

Outline the physiology of urine formation

Answer 5

Glomerular filtration
Selective reabsorption
Tubular secretion

Question 6

Outline glomerular filtration

Answer 6

Afferent arteriole has a large diameter compared to efferent arteriole which drives blood and plasma through the walls of the capillaries into the bowmans capsule (away from high pressure of efferent arteriole)
Only small molecules pass through (most blood components except for red and white blood cells) no protein

Question 7

Outline selective reabsorption

Answer 7

The glomerular filtrate contains so lutes from the blood some of which require elimination whereas others are valuable to the body and are therefore reabsorbed
PCT- water and solutes dissolved in it are reabsorbed into the blood stream, water passively by osmosis. 80% is reabsorbed by PCT
Loop of henle- dips deep into medulla of the kidney then returns to cortex. Can absorb solutes in the collecting duct (as it runs parallel to it) without too much loss of fluid so essentially it concentrates the urine.
DCT- 95% of filtrate has be reabsorbed by this point. Fluid balance is achieved at this site as further reabsorption occurs

Question 8

Outline tubular secretion

Answer 8

Any harmful substances are moved from the tubule into the bloodstream
Excess hydrogen and potassium ions are removed in urine
Role in maintaining acid base balance

Question 9

Outline the composition of urine

Answer 9

Unwanted waste products with minimal water removed from the body

Question 10

What are the other functions of the kidneys

Answer 10

Synthesis of glucose during periods of fasting
Secretion of erythropoietin to sit,halted production of erythrocytes
Synthesis of vitamin d

Question 11

What are the supporting structures of the kidney

Answer 11

Firmly embedded in fat
Support from close proximity of other organs
Renal artery and vein to the descending aorta and inferior vena cava

Question 12

Outline the role and importance of urinalysis

Answer 12

Gives an indication of the functioning of the body, if metabolism isn’t operating efficiently etc
Protein in urine means bacteria or high blood pressure
Glucose means gestational diabetes sometimes- important to remember during pregnancy the kidneys may not be able to reabsorb all glucose in the increased blood volume (renal threshold may be exceeded) therefore common for some glucose in the urine

Question 13

Outline the blood, nerve and lymph supply to the kidneys

Answer 13

Kidneys receive 25% of cardiac output
Renal arteries branch directly from aorta
Intricate network of arteriole capillaries and venules surround the nephrons
Venous drainage into inferior vena cava
Nerve supply - sympathetic nervous system via renal plexus
Lymph vessels surround kidneys draining into aortic and lumbar lymph glands

Question 14

Outline the structure and function of the ureters

Answer 14

Situated in peritoneal cavity
Pass from pelvis of kidney to the bladder
Outer layer of fibrous tissue, middle muscular layer and inner layer of epithelium which is impermeable to water ensuring no water from adjacent blood vessels is absorbed and therefore excreted
Ureters enter the bladder at an oblique angle so that when the bladder is full it prevents the back flow of urine
Urine passed down ureters by peristaltic action

Question 15

Outline the structure and function of the bladder

Answer 15

Situated in the pelvic cavity
When filled with urine can rise into abdominal cavity and can be palates above symphysis pubis
Urethra from base of bladder

Question 16

Outline the macrostructure of the bladder

Answer 16

Pear shaped when empty
Holds up to 600ml urine
Desire to micturate after 300ml full
Fundus of bladder loosely covered with peritoneum
Uterovesicular pouch is the area between the bladder and uterus

Question 17

Outline the microstructure of the bladder

Answer 17

Outer layer of connective tissue
Middle layer of smooth muscle which cause the bladder to contract and regain shape when empty
Inner layer of transitional epithelium arranged in rugae to allow the bladder to fill

Question 18

What are the supporting structures of the bladder?

Answer 18

Ligaments that extend from umbilicus, pelvic cavity lateral walls and pubic bone

Question 19

Where is the urethra

Answer 19

Leaves bladder at the base passes through muscle of peritoneum to the urethral orifice

Question 20

Describe the structure of the urethra

Answer 20

40mm long in female, shorter urethra predisposes them to more UTIs than men
Runs behind symphysis pubis in front of he vagina to the vestibule of the vulva
Outer layer of muscle
Middle sponge layer of blood vessels
Inner layer of transitional epithelium

Question 21

Describe the urethral orifice

Answer 21

Surrounded by a thicker layer of muscle situated within the pelvis floor muscles forming the external sphincter
Layer of elastic fibres which control voluntary and involuntary control

Question 22

How can pregnancy cause changes in the renal system?

Answer 22

Increasing bulk of gravid uterus can have the effect of inhibiting flow through the renal system as well as the storage in the bladder - causes an increased frequency in micturition both in early pregnancy due to the uterus being in the pelvic cavity and late in pregnancy when the uterus takes up most of the space in the abdominal cavity
Increased levels of progesterone in pregnancy can cause dilatation of renal pelvis causing obstruction on the ureters. Dilated blood vessels also do this. This predisposes pregnant women to UTIs
Increased micturition in the night - nocturia, due to poor venous return when upright in the day causing diminished passage of urine. Sodium is therefore retained. Once venous return is encouraged by lying down the raised sodium levels cause an increase in urine production.
Increase in circulating blood in the cardiovascular and lymphatic systems leads to increased glomerular infiltration rate of the kidneys. As a result kidneys are unable to reabsorb all the nutrients that are useful to the body. This is known as lowering the renal threshold. Explains why a lot of women who have glucose in the urine often have normal blood glucose levels.

Question 23

How is the renal system effected in labour?

Answer 23

During labour the bladder rises above the symphysis pubis as the fetus moves into the pelvis. This may lead to restriction of get urethra causing urine retention. If the bladder becomes distended it may obstruct the progress of labour. It can also effect the tone of the bladder and cause bruising of the urethra. Can cause dysuria (pain when urinating)
Regular urinalysis in labour is essential to understand whether the woman is coping with the increased physiological demands. To meet these demands the metabolic rate increases. Extra energy required comes initially from glucose stores but if as labour progresses these stores are not replaced by effective nutrition fat is utilised instead. A by product of this is ketones. These are excreted through the kidneys and seen on urinalysis - known at ketonuria. This can effect the progress of labour.

Question 24

How does the renal system change in the postnatal period?

Answer 24

Urinary output increases for the first 7 days after delivery. As the amount of circulatory fluid decreases and the waste products associated with the involution of the uterus are removed.
Bladder function may be slow to return to normal due to factors such as length of labour and whether the pelvis floor was damaged during delivery.
Psychological fear due to presence of sutures or brushing can effect a women’s ability to urinate normally.
Delivery with haemorrhage may lead to severe renal damage.
Takes approximately 6 weeks to return to non pregnant state.
UTIs occur in 2-4% of women in the puerperium, particularly those who were catheterised

Question 25

How are women predisposed to UTIs?

Answer 25

Short length of urethra
Hormones aggrevate this by relaxing the smooth muscle of the urinary tract
Cystitis,caused by an ascending infection results in inflammation of the bladder with painful, frequent voiding.

Question 26

Outline acute renal failure

Answer 26

May occur after a period of low blood pressure caused by a large haemorrhage or circulatory failure. Whenever the glomerular filtrate rate is decreased the nephrons suffer damage, this however is reversible.
An output of less than 400ml in 24 hours could be a sign of renal failure.

Question 27

Outline the renal system in the neonate

Answer 27

The placenta handles excretion during the fetal life. The kidneys are immature at term although anatomically complete. They are unable to dilute or concentrate urine as efficiently as an adult but can achieve fluid and electrolyte balance within a narrow range.
Any imbalance will occurs more rapidly especially in a preterm or unwell neonate.
In a healthy term infant urination is expected in the first 24 hours to indicate healthy renal function.