Case 4 - how the kidney works

Question 1

the capillaries of the cortex are continuous with what?

Answer 1

the capillaries of the cortex are continuous with the capillaries of the medulla

Question 2

Each capillary glomerulus is enclosed inside what?

Answer 2

Each capillary glomerulus is enclosed inside a bag of tissue called BOWMAN’S CAPSULE

Question 3

what is The first stage of urine formation?

Answer 3

The first stage of urine formation is the
filtering of plasma from the glomerular capillaries into the space of the capsule

Question 4

what is urine?

Answer 4

urine is an ultrafiltrate of blood

Question 5

capillaries have gaps b/w the endothelial cells. what are these gaps called?

Answer 5

fenestrations

Question 6

The capillaries are covered on the outside (which is the capsule side) by what?

Answer 6

podocytes - Podocytes are an extra layer of cells that cover the capillaries on the capsule side

Question 7

what do the podocytes have?

Answer 7

These podocytes have slits b/w them which form the filtration mechanism. [If the slits become inflamed and enlarged in renal disease, this allows solutes (in particular proteins) to enter the urine. This is called proteinuria and is a sign of glomerular inflammation.]

Question 8

The layer above the endothelial cells [of the capillaries] is called what?

Answer 8

basement membrane

Question 9

in a healthy individual, how is the filtration of water into the Bowman’s capsule controlled

Answer 9

The filtration of water into the capsule is controlled in a healthy individual by a
balance between the constriction of the afferent and efferent arterioles. [Normally these are adjusted so that a physical pressure of about 55 mm Hg is present in the glomerular capillaries.]

Question 10

starling’s principle of net filtration in the Bowman’s capsule

Answer 10

The net filtration pressure is the sum of a
physical (hydrostatic) pressure in the capillaries of about 55 mm Hg minus
an osmotic pressure of about 30 mm Hg.
The physical pressure of fluid in the capsule is
about 15mm Hg, and the osmotic pressure is
nearly zero (no proteins) so the net filtration
pressure is about 10 mmHg.

Question 11

what is the Glomerular Filtration Rate (GFR)?

Answer 11

The total amount of fluid filtered through ALL the glomeruli in BOTH kidneys
in a fit adult is about 120-125 ml/min. (depending on body size). This is the
Glomerular Filtration Rate (GFR).

Question 12

describe what happens with the glomerular capillaries and Bowman’s capsule

Answer 12

1) Filtration: Fluid passes from Bowman’s capsule into the proximal tubule
2) Reabsorption: Here filtered materials can be reabsorbed into the peritubular capillaries
3) Secretion: Materials can also be transported out of the peritubular capillaries and secreted into the tubular fluid
4) Excretion: The amount of a material
(eg glucose) excreted is the amount filtered
plus the amount secreted minus the
amount reabsorbed
Excretion = Filtration - Reabsorption + Secretion

Question 13

stages of chronic kidney disease

Answer 13

Stage 1: Kidney damage with normal kidney function - GFR is 90 or higher. 90-100% of kidney function
Stage 2: Kidney damage with mild loss of kidney function - GFR is 89 to 60. 89-60% of kidney function
Stage 3: mild to moderate loss of kidney function - GFR is 44 to 30. 44 to 30% of kidney function
Stage 4: severe loss of kidney function - GFR is 29 to 15. 29 to 15% of kidney function
Stage 5: kidney failure - GFR is less than 15. less than 15% of kidney function

Question 14

what is the Approximate urine flow in
adult?

Answer 14

Approximate urine flow in adult =1 ml/min

Question 15

what is diuresis?

Answer 15

Diuresis (production of urine by the kidney)

Question 16

how is there a steady influx of urine into the bladder?

Answer 16

a steady influx of
urine into the bladder via the
ureters from the kidneys

Question 17

what is the exit from the bladder?

Answer 17

The exit from the bladder is the
urethra. In males this is much
longer than in females, as it
travels through the penis.

Question 18

the urethra (the exit from the bladder) is normally held closed by what?

Answer 18

The exit from the bladder (the urethra) is
normally held closed by the
internal and external urethral
sphincters while the bladder
fills up

Question 19

what is the storage phase of micturition

Answer 19

when the urethra is held closed by the internal and external urethral sphincters while the bladder fills up

Question 20

what does the detrusor muscle of the bladder do to expel urine during diuresis?

Answer 20

Detrusor muscle contracts bladder to expel
urine during diuresis.

Question 21

what does The internal urethral sphincter
consists of

Answer 21

The internal urethral sphincter
consists of smooth (involuntary)
muscle

Question 22

how do the sympathetic efferents maintain a tonic contraction of the smooth muscle of the internal urethral sphincter of the bladder?

Answer 22

Sympathetic efferents travelling via the hypogastric nerve and plexus maintain a tonic
contraction of this smooth muscle of the internal urethral sphincter of the bladder during the filling & storage phase of
micturition

Question 23

what do the sympathetic efferents
tonically inhibit contraction of?

Answer 23

These sympathetic efferents also tonically inhibit contraction of the detrusor muscle, which forms a large part of the muscular wall of the bladder.

Question 24

how are the inhibitory actions by the sympathetic efferents on the detrusor muscle mediated?

Answer 24

The inhibitory actions on the detrusor are mediated by adrenergic beta receptors (beta 3 receptors)

Question 25

how are the excitatory actions by the sympathetic efferents on the smooth muscle of the internal urethral sphincter mediated?

Answer 25

the excitatory actions on the sphincter are mediated by alpha receptors (alpha 1 receptors)

Question 26

what do beta 3 receptors do and what do alpha 1 receptors do?

Answer 26

Beta (beta 3 receptors) keep bladder relaxed, alpha (alpha 1 receptors) keep sphincter closed.

Question 27

what do sympathetic efferents do?

Answer 27

Sympathetic efferents keeps sphincters closed and bladder muscle relaxed

Question 28

As the bladder fills the walls of the bladder become stretched. Receptors in the walls detect the stretch and activate afferents in the which nerves?

Answer 28

As the bladder fills the walls of the bladder become stretched. Receptors in the walls detect the stretch and activate afferents in the pelvic nerves

Question 29

the afferents in the pelvic nerve synapse on cells in which tract?

Answer 29

The afferents synapse on cells of the spinothalamic tract which relay to the genital area of the somatosensory cortex, so the person has a sense of bladder fullness

Question 30

if the conditions are not met for micturition (peeing/urinating), what happens?

Answer 30

the individual tightens the external urethral sphincter, which is a skeletal muscle under voluntary control. The lower motor neurones controlling this muscle run in the pudendal nerves (this makes the person not want to urinate)

Question 31

when someone decides it's the right time and place are appropriate for micturition, what happens?

Answer 31

a signal is sent from the forebrain to the pons, where a ‘micturition centre’ is situated. This nucleus activates the MICTURITION REFLEX In the reflex the micturition centre activates descending fibres in the reticulospinal tract which inhibit the sympathetic and somatic outputs controlling the internal and external urethral sphincters (the sphincters are no longer tightened) this allows for the parasympathetic efferents to stimulate the detrusor muscle in the wall of the bladder, causing the bladder to contract & urine to flow out of the urethra. Once contraction of the detrusor starts, afferents in the detrusor muscle increase its activity by positive feedback so contraction continues until the bladder is empty.

Question 32

what reflex is contraction of the bladder detrusor muscle?

Answer 32

Contraction of bladder detrusor muscle is a parasympathetic reflex, mediated by muscarinic receptors (M3 type).