Physiology Flashcards
what drives the force for ultrafiltration of virtually protein and fat-free fluid into the Bowman’s capsule?
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
what is ultrafiltration rate (GFR)?
roughly 120-130mL/min per 1.73 m2 SA in adults
it does vary with age and sex though
what are the functions of the Kidney and urinary tract?
- Maintain water and electrolyte homeostasis, body fluid osmolarity and acid-base balance
- Excrete toxic metabolic waste products (mainly urea and creatinine)
• Urinary tract accomplishes 1 & 2 by the production, storage and voiding of urine - Act as an endocrine gland – producing renin and erythropoietin
what is the medulla made up of?
-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
what are the 2 cell layers separating the blood and glomerular filtrate in the glomerulus?
capillary endothelium
specialised epithelium which lies on top of the glomerular capillaries (podocytes)
what are the 3 filter components if the glomerular filtrate system?
fenestrated endothelium of the capillary wall
thick basement membrane (shared by the endothelium and podocyte)
filtration slits between pedicels
what lines the collecting parts of the urinary tract?
special epithelium
transitional epithelium/ urothelium
what cells are at the luminal surface in the collecting parts of the urinary tract?
umbrella cells, domed facing the lumen and thickened inflexible membrane
2 facts about the special structure of the epithelium?
variability in thickness of cells represents different states of distension
special surface structures are to provide a high impermeable barrier
what is the urothelium?
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
characteristics of the urinary bladder?
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
parts of the urethra in men (20cm in length)
-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.
what is osmolarity?
molar concentration x no. of osmotically active particles
units - osmol/l
what are the units of osmolality?
osmol/kg water
what is the osmolarity of body fluid?
300 mosmol/l
tonicity
the effect of a solution on cell volume can be hypo-, hyper- or isotonic
effect of hypotonic solution
cause increase in cell volume (<300mosmol/L)
effect of isotonic solution
no change in cell volume (>300mosmol/L)
what is facilitated diffusion?
passive carrier-mediated transport of a substance down it’s concentration gradient
what is primary active transport?
energy is directly required to operate the carrier and move the substrate against its concentration gradient
what is secondary active transport?
the carrier molecule is transported coupled to the concentration gradient of an ion (usually Na+)
what is the transport maximum (Tm)?
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
what is the renal threshold?
10-12 mmol/l
how do inorganic ions - notably Na+ move across the tubular epithelium?
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
osmolarity
the measure of the number of osmotically active particles in a solute
what is an increase in osmolarity?
increase in amount of particles dissolved in the solution
what are the proportions of ICF and ECF total body water?
67% ICF
33% ECF
what is GFR?
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
actions of the descending loop of Henle?
doesn’t reabsorb NaCl
highly permeable
actions of the ascending loop of Henle?
Na+ and Cl- reabsorption
impermeable to water
what does ADH do?
water reabsorption
urine is therefore more concentrated
what does aldosterone do?
increases Na+ reabsorption
increased H+/K+ secretion
what does ANP do?
decreases Na+ reabsorption
what does parathyroid hormone do?
increases Ca2+ reabsorption
decreased phosphate reabsorption
actions of the late collecting duct?
low ion permeability
permeability to water (and urea) influenced by ADH
