Physiology

Question 1

what drives the force for ultrafiltration of virtually protein and fat-free fluid into the Bowman’s capsule?

Answer 1

hydrostatic pressure gradient of approximately 10mmHg - capillary pressure of 45mmHG minus 10mmHg of pressure within the Bowman’s space and 25mmHg of plasma oncotic pressure

Question 2

what is ultrafiltration rate (GFR)?

Answer 2

roughly 120-130mL/min per 1.73 m2 SA in adults

it does vary with age and sex though

Question 3

what are the functions of the Kidney and urinary tract?

Answer 3

1. Maintain water and electrolyte homeostasis, body fluid osmolarity and acid-base balance
2. Excrete toxic metabolic waste products (mainly urea and creatinine)
   • Urinary tract accomplishes 1 & 2 by the production, storage and voiding of urine
3. Act as an endocrine gland – producing renin and erythropoietin

Question 4

what is the medulla made up of?

Answer 4

-Divided into medullary pyramids with apices pointing towards the hilum (called papillae)
-Ending on the minor calyces
-Each eduallary pyramid and its associated cortical tissue is a lobe of the kidney

Question 5

what are the 2 cell layers separating the blood and glomerular filtrate in the glomerulus?

Answer 5

capillary endothelium

specialised epithelium which lies on top of the glomerular capillaries (podocytes)

Question 6

what are the 3 filter components if the glomerular filtrate system?

Answer 6

fenestrated endothelium of the capillary wall
thick basement membrane (shared by the endothelium and podocyte)
filtration slits between pedicels

Question 7

what lines the collecting parts of the urinary tract?

Answer 7

special epithelium

transitional epithelium/ urothelium

Question 8

what cells are at the luminal surface in the collecting parts of the urinary tract?

Answer 8

umbrella cells, domed facing the lumen and thickened inflexible membrane

Question 9

2 facts about the special structure of the epithelium?

Answer 9

variability in thickness of cells represents different states of distension
special surface structures are to provide a high impermeable barrier

Question 10

what is the urothelium?

Answer 10

o lumen of the ureter lined by transitional epithelium – backed by a lamina propria of connective tissue, combined these form the mucosa
o covered by an inner longitudinal layer of smooth muscle and an outer layer surrounded by aventitia or serosa
o near the bladder there are 3 layers of smooth muscle as another longitudinal layer is present

Question 11

characteristics of the urinary bladder?

Answer 11

lined with urothelium
lamina propria of connective tissue
smooth muscle layers - detrusor muscle - responsible for micturition and around the urethral opening the internal urethral sphincter
parasympathetic ganglia innervated by neurones in the sacral spinal cord can be found in the muscle and adventitia - control the micturition reflex

Question 12

parts of the urethra in men (20cm in length)

Answer 12

-Prostatic urethra: 3-4cm, extends from bladder and through prostate gland. Lined by transitional epithelium.

-Membranous urethra: approx. 1cm, extends from prostate to the bulb of the penis. Here transitional epithelium changes to stratified columnar.

-Penile urethra: approx. 15cm, lined by stratified columnar epithelium which near the tip of the penis becomes stratified squamous.

Question 13

what is osmolarity?

Answer 13

molar concentration x no. of osmotically active particles

units - osmol/l

Question 14

what are the units of osmolality?

Answer 14

osmol/kg water

Question 15

what is the osmolarity of body fluid?

Answer 15

300 mosmol/l

Question 16

tonicity

Answer 16

the effect of a solution on cell volume can be hypo-, hyper- or isotonic

Question 17

effect of hypotonic solution

Answer 17

cause increase in cell volume (<300mosmol/L)

Question 18

effect of isotonic solution

Answer 18

no change in cell volume (>300mosmol/L)

Question 19

what is facilitated diffusion?

Answer 19

passive carrier-mediated transport of a substance down it’s concentration gradient

Question 20

what is primary active transport?

Answer 20

energy is directly required to operate the carrier and move the substrate against its concentration gradient

Question 21

what is secondary active transport?

Answer 21

the carrier molecule is transported coupled to the concentration gradient of an ion (usually Na+)

Question 22

what is the transport maximum (Tm)?

Answer 22

as plasma glucose concentration is increase the filtration of glucose increases, the rate of reabsorption matches filtration up to a maximum - then less glucose is reabsorbed and excess is excreted
the transport maximum - maximum rate at which a substance can be reabsorbed

Question 23

what is the renal threshold?

Answer 23

10-12 mmol/l

Question 24

how do inorganic ions - notably Na+ move across the tubular epithelium?

Answer 24

sodium is freely filtered
60-80% of the sodium is reabsorbed in the late proximal tubule
apical membrane Na+/H+ exchanger trades hydrogen ions into the lumen for absorbed sodium - Cl- follows the sodium
diffuses through channels

Question 25

osmolarity

Answer 25

the measure of the number of osmotically active particles in a solute

Question 26

what is an increase in osmolarity?

Answer 26

increase in amount of particles dissolved in the solution

Question 27

what are the proportions of ICF and ECF total body water?

Answer 27

67% ICF

33% ECF

Question 28

what is GFR?

Answer 28

the rate that protein free plasma is filtered from the glomeruli into the bowman’s capsule
the major determinant is glomerular capillary pressure
changing the diameter of the afferent arteriole can change the rate of filtration

Question 29

actions of the descending loop of Henle?

Answer 29

doesn’t reabsorb NaCl

highly permeable

Question 30

actions of the ascending loop of Henle?

Answer 30

Na+ and Cl- reabsorption

impermeable to water

Question 31

what does ADH do?

Answer 31

water reabsorption

urine is therefore more concentrated

Question 32

what does aldosterone do?

Answer 32

increases Na+ reabsorption

increased H+/K+ secretion

Question 33

what does ANP do?

Answer 33

decreases Na+ reabsorption

Question 34

what does parathyroid hormone do?

Answer 34

increases Ca2+ reabsorption

decreased phosphate reabsorption

Question 35

actions of the late collecting duct?

Answer 35

low ion permeability

permeability to water (and urea) influenced by ADH