urinary system

micturition / urination

process of releasing urine from urinary bladder through urethra

what makes urine yellow in colour ?

urochrome/urobilin from haemoglobin breakdown

micturition can be accelerated using ?

diuretics

where are the kidneys located ?

retroperitoneal space

what structures make up the lobes of the kidney ?

renal pyramids

the kidneys are supplied by what artery ?

renal

blood supply to and from kidneys

arcuate, cortical radiate

3 major functions of kidneys

regulate blood volume

remove urea

regulate acid-base balance

what hormones do the kidneys produce ?

erythropoietin and renin

what is the glomerulus ?

tuft of capillaries adapted for filtration

the Bowman’s capsule is connect to the PCT by

the urinary pole

how much plasma is filtered per minute by the kidneys (avg. GFR rate) ?

120-140ml

what is filtrate ?

plasma without proteins or cells

how much plasma is reabsorbed after filtration ?

119 - 124ml

label the nephron structures

1 - bowmans capsule

2 - glomerulus

3, 4, 5 - loop of henle

6, 7 - collecting duct

8 - distal CT

9 - proximal CT

the loop of Henle lies in what section of the kidney ?

medulla

what are the functional units of the kidney ?

nephrons

3 stages of nephron function

1. glomerular filtration

2. tubular reabsorption

3. tubular secretion

what regulates GFR ?

• arteriole vasoconstriction

• mesangial cell contraction

• podocyte permeability

what is reabsorbed in the PCT ?

K+ Na+ amino acids glucose water

what is reabsorbed in the loop of Henle

Na+

what is reabsorbed in the collecting duct

water

how much urine is produced per minute on average ?

1ml / min

how long are the ureters and where are they located ?

20cm either side of vertebral column

what prevents urine back flow from the bladder to kidneys ?

ureterovesical valves

what are the three layers of the ureter wall ?

• inner mucosa

• muscularis

• outer adventitia

how much urine can the bladder hold ?

500ml (max 1000)

what are the 3 layers of the bladder ?

• mucosa - transitional epithelium

• muscular layer - longitudinal and circular muscles

• fibrous adventitia

the internal / bladder neck urethral sphincter is composed of what muscle type ?

smooth muscle - involuntary

what muscle controls voluntary urination ?

external urethral sphincter - skeletal muscle

urine passes from where to the ureter ?

renal pelvis

how do the male and female urethra differ ?

length - male urethra longer

nervous control of micturation

sympathetic - senses stretch relaxes bladder and internal sphincter

parasympathtic - external sphincter, automatically contracts bladder

blood in the urine indicates

infection

what is diuresis ?

increased production of urine

what’s the difference between water diuresis and osmotic diuresis ?

water - more water ingested than body requires

osmotic - more solute excreted than normal

how do diuretics work ?

increase water and NaCl excretion via kidneys

indirect vs direct diuretics

indirect - modify composition of filtered fluid

direct - act directly on cells of nephrons

role of kidneys in homeostasis

remove urea

control water/ion balance

regulate BP

maintain pH

what organ carries out the urea cycle ?

liver

where do the first 2 steps of the urea cycle occur ?

mitochondrial matrix

in the urea cycle ammonia is converted to

urea and excreted in urine

what is the waste product of protein metabolism ?

nitrogen - accumulates as ammonia

osmolarity

total number of dissolved particles in solution

what is the standard body fluid osmolarity ?

295mOsml/L

what is the juxtaglomerular complex ?

structure that regulates each nephron's function

next to glomerulus

isoosmotic solutions have

equal osmolarity

hypoosmotic

one solution has lower osmolarity

hyperosmotic

one solution has higher osmolarity than the other

what cells detect NaCl in the distal tubule ?

macula densa cells

in 1L of water what has higher osmolarity 1mmol of CaCl2 or NaCL ?

CaCl2 - dissociates into 3 molecules of Ca2+ and 2x Cl-

NaCl only dissociates into 2 - Na+ and Cl-

name 3 ways GFR is regulated

1. myogenic mechanism

2. tubuloglomerular feedback

3. renin-angiotensin-aldosterone system

what triggers renin release ?

low BP, low NaCl or SNS activation

how does ADH increase BP ?

increases water

urea and sodium reabsorption

vasoconstriction

where are macula densa cells located ?

end of ascending loop of Henle, distal CT

role of macula densa cells

chemo/osmoreceptors

respond to changes in solute conc. of filtrate

how does the myogenic mechanism regulate GFR ?

dilates and constricts afferent arteriole to maintain GFR despite fluctuations in BP - protects glomerulus from damage

how does tubuloglomerular feedback regulate GFR ?

senses changes in tubular fluid composition, particularly NaCL at macula densa and alters filtrate flow accordingly

decreases / increases reabsorption time by constricting / dilating afferent arteriole

what does high NaCl conc. in renal filtrate suggest ?

GFR too high

the renin-angiotensin-aldosterone system is the main mechanism for…

increasing BP

what are the 3 triggers for renin release ?

1. direct simulation by SNS

2. low NaCl - detected by macula densa cells

3. reduced stretch of granular cells (low BP)

renin is released by what cells ?

granular / juxtaglomerular

what enzyme circulates in pulmonary blood ?

angiotensin converting enzyme

where is ADH produced and released ?

hypothalamus - released by posterior pituitary

ADH is also referred to as…

vasopressin

how does aldosterone increase BP ?

increases sodium reabsorption and potassium excretion in kidneys

leads to water retention and thus increase in BP

what stimulates ADH release ?

hyperosmolarity - high solute conc. in blood

angiotensin II

what inhibits ADH release ?

high blood pressure

how does ADH increase BP ?

• increases water, Na+ and urea reabsorption

• vasoconstriction