S1 Urinary system

Question 1

Describe the nature of urinary system

Answer 1

enables through filtration and selective reabsorption the precise control of substances inside the ECF ; ions , small organic molecules and water
kidney filters large amount of ECF, each litre of ECF filtered over 10 times a day. h/e nearly everything is recovered ; most filtered water, Na,Cl,HCO3, Glucose,AA but not urea

Question 2

where are the kidneys

Answer 2

retroperitoneal organs that sit in the abdominal cavity roughly at T12-L3, right kidney lower due to liver

Question 3

where is the bladder

Answer 3

the bladder sits right behind the pubic bone and distends upwards when it fills with urine

Question 4

where is the prostate

Answer 4

sits directly below the bladder, the urethra passes through it

Question 5

describe the kidney structure

Answer 5

the renal cortex contains the glomerulus and bowmans capsule, therefore ultrafiltration takes place in the cortex , it also contains the renal tubules, except for the parts of the loop of Henle, which descends into the medulla
the renal medulla is split into pyramids. the medulla contains the structures of the nephrons that are responsible for maintaining the salt and water balance of the blood

Question 6

what is the anatomy of the kidney

Answer 6

cortex is outer kidney, pelvis is inner

Question 7

what is the level of the the vessels associated with the kidney

Answer 7

Collecting tubules - T12
Superior mesenteric artery - L1
Renal Artery - L1-L2 ( renal vein is long as it passes over aorta)
Gonadal artery - L2
Inferior mesenteric artery - L3 ( where horseshoe kidney stops)

Question 8

what is the path of the ureters ?

Answer 8

over tips of transverse processes, psoas muscle ,sacro-iliac joint, bifurcation of the common iliac arteries

Question 9

what are the functions of the kidneys ?

Answer 9

Regulation : control the conc of key substances in ECF
Excretion
Endocrine - synthesis of renin, erythropoietin, prostaglandins
metabolism - active form of Vit D, catabolism of insulin, PTH calcitonin
Control - volume, osmolarity, Ph

Question 10

what is the volume of intracellular fluid in a 70kg human

Answer 10

28L

Question 11

what is the volume of extracellular fluid in a 70KG human

Answer 11

14L ; 11L interstitial, 3L plasma

Question 12

define osmolarity

Answer 12

osmoles per litre

Question 13

define osmolality

Answer 13

osmoles per KG

Question 14

what is normal level of osmolality

Answer 14

280-310 mmol/L
water moves from low osmolality (many water particles) to high
sodium pumps are used to maintain electrolyte balance via active transport

Question 15

describe the nature of a nephron

Answer 15

functional unit of the kidney

• filter at the glomerulus
• proximal convoluted tubule - in cortex major site of reabsorption
• loop of henle - dips into and out of medulla
• distal convoluted tubule - in cortex
• collecting duct - passes through medulla to pelvis

Question 16

describe filtration in the kidneys

Answer 16

kidneys produce an ultrafiltrate, made up of water, ions and small molecules, filtering occurs at glomeruli in the kidney cortex.
Specialised afferent and efferent arterioles which carry blood to and away from glomeruli, maintain a high filtration pressure,
this drives water and small molecules out of the plasma at 125 l/min (180l/day). this is the GFR, this leaves 1.5 L of urine per day.
once filtered, the ultrafiltrate enters the kidney tubule where water,ions, glucose etc are reabsorbed. this process is metabolically demanding so requires high oxygen and blood supply

Question 17

describe the mechanism of reabsorption in the kidneys

Answer 17

tubules lined with epithelial cells
reabsorption from ultrafiltrate in the nephron to the blood is first via transport proteins - from nephron to epithelial cells on the apical/luminal surface. then from the cells to the interstitial fluid by other transport proteins on the basolateral surface
for this to occur, epithelial cells must be polarised, also the ECF in basolateral and apical regions must be kept seperate, this is achieved via tight junctions

Question 18

describe the nature of sodium pumps in reabsorption

Answer 18

sodium pumps enters across luminal membrane down concentration gradient
this drives reabsorption of other substances such as glucose
water follows electrolytes osmotically

Question 19

what is the loop of henle and its function

Answer 19

further site of reabsorption of salts but main function to create a gradient of increasing osmolarity in the medulla by counter-current multiplication, this allows formation of concentrated urine if water has to be conserved

Question 20

describe the nature of the Distal convoluted tubule

Answer 20

major site of variable reabsorption of electrolytes and water
fluid leaving loop of henle is hypotonic
DT removes yet more sodium and chloride
also actively secretes hydrogen ions
water may or may not follow reabsorption of electrolytes
if it does not large volumes of dilute urine are formed - diuresis

Question 21

describe the nature of the collecting duct

Answer 21

the CD passes through the high osmolarity environment of medulla created by LoH
if water can cross the epithelium it will leave the urine down the osmotic gradient, producing low amount of concentrated urine
if it cannot urine remains dilute
NA recovery - controlled by RAAS, controlling ECF volume
Water recovery is controlled by ADH, controlling ECF osmolarity

Question 22

what do the nephrons do in summary

Answer 22

glomerulus filters huge volumes of ECF
reabsorption of most substances in PT
reabsorption of salts and waters in DT
controlled secretion of hydrogen ions
passive loss of waste products not reabsorbed

Question 23

describe what the kidney does in summary

Answer 23

recover filtered molecules which are essential (e.g glucose)
control plasma volume by filtering and recovering salts
control plasma pH by filtering and recovering bicarbonate and active secretion of hydrogen ions
control plasma osmolarity by filtering and recovering water