Reproductive Physiology Flashcards
What is the most obvious function of the kidney?
Regulate composition and function of plasma
What are some of the other renal functions?
Regulate blood pressure and volume (water concentration and fluid volume ; inorganic ion composition), acid-base balance ; excretion (urea, uric acid, creatinine [muscle breakdown], bilirubin [hemoglobin breakdown]) ; remove foreign chemicals (drugs, food additives, pesticides) ; synthesis of glucose (glucoseneogenesis) ; secretion (hormone/enzyme [erythropoietin, 1,25-dihygroxy Vitamin D, renin]
Which ions are higher in extracellular fluid? Which ions are higher in the intracellular fluid?
Extra: Na+, Cl-, HCO3-
Intra: K+, Mg2+, Pi, Protein
What dictates the rate of diffusion?
Chemical properties
What’s the difference between polar and non-polar compounds during diffusion?
Polar molecules generally are unable to diffuse across membrane bilayer (amino acids, glucose, water) whereas non-polar molecules diffuse rapidly (CO2, fatty acids, steroids)
What are aquaporins?
Water channels that regulate the diffusion of water through cell membranes
What is water concentration measured in?
Osmoles: 1 osmoles (osm) is equal to 1 mole of solute particles
What is osmolarity?
Number of solutes per unit volume of solution expressed in moles per liter
What is osmosis?
Net diffusion of water across a selectively permeable membrane from a region of high water concentration to one with a lower water concentration
What is osmotic pressure?
The pressure necessary to prevent solvent movement
What is tonicity determined by?
The concentration of non-penetrating solutes (NPS) [sodium and chloride ions] of an extracellular solution relative to the intracellular environment of a cell.
What is isotonic?
Same concentration of NPS outside and inside the cell; cell volume do not change
What is hypertonic?
Higher concentration of NPS outside than inside of the cell; cells shrink
What is hypotonic?
Lower concentration of NPS outside than inside of the cell; cells swell
What are the factors determining fluid movement along capillaries?
Capillary hydrostatic pressure (Pc), interstitial fluid hydrostatic pressure (Pif), osmotic force due to plasma protein concentration (PIc), osmotic force due to interstitial fluid protein concentration (PIif)
What does the starling law measure?
The net filtration pressure
What are the organs that are part of the urinary system?
Kidney, ureter, bladder and urethra
What is micturition?
The process by which urine is voided out of the body
What is the anatomy of the kidney?
Capsule, outer cortex, inner medulla, nephron (renal corpuscle, renal tubule)
What is the renal corpuscle made up of?
Glomerulus, bowman’s capsule
What does the renal tubule comprised of?
Proximal convoluted tubule, loop of henle, distal convoluted tubule (lined with epithelial but vay in each structure and function in each tubule)
What kind of blood goes through the glomerulus?
Protein-free blood
Explain the 3 stages of the development of renal corpuscle.
Stage 1: Nephrons develop as blind-ended tubules composed of single layer of simple epithelium
Stage 2: Growing tuft of capillaries penetrate the expanded end of tubules
a. Basal lamina is trapped in between endothelial cells of capillaries and epithelial layer
b. Epithelial cell layer differentiates into parietal (outer) and visceral (inner) layer
Stage 3: parietal layer flattened to become wall of Bowman’s capsule Visceral layer becomes podocyte cell layer
What are the layers of the glomerular capillary?
- Fenestrated endothelial layer
- Basement membrane (made up of proteins)
- Podocytes with filtration slits
What are the two types of nephron in the kidney?
- Cortical
- Juxtamedullary (close to the medulla area)
What is the difference between the corticol and juxtamedullary?
The portions of the loop of the corticol nephrone dip slightly into the medulla whereas the loop of henle and ascending limb of the juxtamedullary are found in the renal medula
What are the basic functions of neprhons?
Filtration, reabsorption and secretion
What are the 3 types of capillaries in kidneys?
- Glomerular
- Peritubular
- Vasa recta
What is the function of the afferent arteriole in the kidney?
Branches off from the renal artery and diverges into the capillaries of the glomerulus. The arteriole that brings blood into the glomerular capillary network.
What is the function of the efferent arteriole?
Blood exits the glomerulus through the efferent arteriole. The arteriole branches around to form a set of capillaries called the peritubular capillary network. The peritubular capillaries fuse together to form the renal vein.
What is the function of vasa recta?
Capillaries that are found mostly associated with justamedullary nephrons in the medullary portion of the kidney
Why are the large proteins or albumins are held back?
Because the pore size are not large enough to allow passage;
Pores and BM have negative charges and repels negatively charged proteins;
Podocytes have slits that remain covered with fine semiporous membranes
What is the fine semiporous membranes made up of?
Nephrins and Podocins
What is the function of Nephrins and Podocins?
Cover the slits of the podocytes ; Prevent the passage of substance through the barrier
What is filtered through the glomerulus?
Water, electrolytes, glucose, amino acids, fatty acid, vitamins, and waste products such as urea, uric acid, and creatinine
What is non-filtered?
Plasma protein and blood cells, large anions, anything bound to plasma proteins (ie calcium)
What is Ultrafiltrate?
The concentration of a substance filtered through the filtration layers is the same in the plasma and in the filtrate
What is proteinuria?
A condition where some of the proteins that are not suppose to pass through the filtration barrier show up in the filtrate and ultimately in the urine
What are the forces involved in Glomerular Filtration?
Glomerular capillary hydrostatic pressure (Pgc), Bowman’s space hydrostatic pressure (Pbs), Osmotic force due to proteins in the plasma (Pigc), Starling forces
What is Glomerular capillary hydrostatic pressure (Pgc)?
Hydrostatic pressure of the blood that is found in the glomerular capillaries; this pressure pushes fluid outward into the Bowman’s space, or from the capillary side into Bowman’s space; favours filtration
What is the Bowman’s space hydrostatic pressure (Pbs)?
Fluid pressure in Bowman’s space; opposes filtration
What is the osmotic force due to proteins in the plasma (Pigc)?
Due to proteins that are present in the plasma; the positive pressure which pushes fluid or water containing the substances that are filtered into Bowman’s space
What fraction of the volume entering the glomerular capillaries is filtered?
20%
What is the final volume of fluid is excreted?
1%
What is Glomerular Filtration Rate (GFR)?
The volume of fluid filtered frm the glomerulus into the Bowman’s space per unit time
What are the factors that influence the GFR?
- Net glomerular filtration pressure
- Permeability of the corpuscular membrane
- Surface area available for filtration
- Neural and endocrine control
What happens when mesengial cells on GFR contracts?
Decreases the surface area of the glomerular capillaries and decreases GFR
What is the autoregulation of GFR?
Occurs by changing renal blood vessel resistance to compensate for any changes in blood pressure
What are the two responses during autoregulation of GFR?
- Myogenic response
- Tubuloglomerular feedback effect
What is the effect of tubuloglomerular feedback effect?
- Increased tubular flow which causes constriction of the afferent arteriole to reduce GFR
What is the tubuloglomerular feedback effect regulated by?
Paracrine actions on the juxtaglomerular apparatus
What is the purpose of autoregulation of GFR?
Protection of the glomerular capillaries from trauma related to hypertension
How do you calculate mean arterial blood pressure?
Diastolic pressure + 1/3 (systolic pressure - diastolic presure)
What are the two cells involved in the juxtaglomerular apparatus?
Macula densa and juxtaglomerular cells
What are the function of macula densa?
- sense increase fluid flow through distal tubule
- secretes vasoactive compounds (such as adenosine)
- paracrine effect changes afferent arteriolar resistance
- signals the JG cells
What is the function of the juxtaglomerular cells?
Controls renin release based on [Na+]
What occurs during a high blood flow? (Tubuloglomerular feedback)
- GFR increases
- Flow through tubule increases
- Flow past macula desa increases
- Paracrine from macula densa to afferent arteriole
- Afferent arteriole constricts
- Resistance in afferent arteriole increases
- Hydrostatic pressure in glomerulus decreases
- GFR decreases
What is the filtered load?
The total amount of non-protein or non-protein bound substance filtered into Bowman’s space
What are the different renal handling of 3 different substances?
- Filtration + secretion (organic acids and bases)
- Filtration + partial reabsorption (electrolytes)
- Filtration + complete reabsorption (glucose, amino acids)
- Filtration (inulin, creatinine) [rare]
What is reabsorption is mediated by?
- Mediated transport (transepithelial) [major]
2. Diffusion across tight junctio (paracellular)
What occurs during the reabsorption of Na+ by mediated transport?
- Pathway of transepithelial transport
- across luminal or apical membrane
- across basolateral membrane
- Active transport does not happen on both sides of membranes for Na+
- passive diffusion across luminal/apical side
- depend on type of channel and/or transport protein
- counter transport, cotransport (PCT)
- diffusion via Na+ channel CCD
- active transport on basolateral membrane by Na+/K+ ATPase
- passive diffusion across luminal/apical side
Procedure:
- Na+ enters cells through membrane proteins, moving down its electrochemical gradient
- Na+ is pumped out the basolateral side of cell by the Na+/K+ ATPase
How is glucose reabsorbed?
- secondary active transport on the luminal side by SGLT protein
- facilitated diffusion on the baso-lateral side using carrier protein GLUT
What is diabetes mellitus?
The capacity to reabsorb glucose is normal, but filtered load is greatly increased and is beyond the threshold level to reabsorb glucose by the tubules
What is renal glucosuria (benign glucosaria/familial renal glucosuria)?
The genetic mutation of the Na+/glucose cotransporter, that normally mediates active reabsorption of glucose in the proximal tubules
How does the reabsorption of urea occur?
The reabsorption is dependent on water reabsorption because urea diffuses down concentration gradient
What are the substances or ions involved in tubular secretion?
H+, K+, choline, creatinine, penicillin
What is renal clearance used to quantify?
A way of quantifying kidney function in removing substances from plasma
What is creatinine in the kidney for?
Used to measure GFR clinically because creatinine is filtered and not reabsorbed, but undergo slight secretion
What are the water channels in the kidney?
Aquaporins
Why are there large amount of water reabsorbed in the proximal tubulues?
Aquaporins are always open in the proximal tubule cells (PCT)
What is water reabsorption dependent on?
Na+ reabsorption. The osmotic gradient set up by Na reabsorption acts as the driving force.
Which hormone regulates water reabsorption in the cortical collecting duct (CCD) and medullary collecting duct (MCD)?
Vasopressin or antidiuretic hormone (ADH)
What are the aquaporins that are involved in the large distal tubule and collecting duct?
AQP-2, -3, -4
What is the difference between the thin descending limb and the thick ascending limb in the loop of Henle?
There is only salt reabsorption in the thick ascending limb because it is impermeable to water
What is the counter-current multiplier?
The multiplication of the gradient down the length of the loop of Henle
What is the function of ADH in the cortical collecting duct?
It works on the collecting duct and fluid inside the tubule becomes isoosmotic with the interstitial space
How does water permeate out of the medullary collecting tube?
The high osmolarity gradient that is establish in the interstitial space
How does the vasa recta help the counter-current exchange?
- Helps in maintaining the Na+ and Cl- gradient
- Prevent solute loss in medulla
- Vasa recta does not create medullary hyperosmolarity, but prevents it from being washed out, and therefore maintains it
Why is there a need for concentrated urine?
Kidneys save water by producing hyperosmotic urine
What are the mechanisms used to maintain the hyperosmotic environment of the medulla?
- Counter-current anatomy and opposing fluid flow through the Loop of Henle of the juxta medullary nephrons
- Reabsorption of NaCl in ascending limb
- Impermeability of ascending limb to water
- Trapping of urea in medulla
- Hairpin loops of vasa recta maintains the hyperosmotic interstitium in medulla
What are the 3 characteristics of the ADH/vasopressin?
- Peptide hormone
- Produced by cells of the SON of the hypothalamus when osmoreceptors sense increases in plasma osmolarity
- Secreted fromt he posterior pituitary
What occurs when vasopressin is released?
- Vasopressin receptor activates the Adenylate cyclase
- ATP is converted to cAMP which activates PKA (phosphorylates its substrates)
- Phosphorylated proteins helps the synthesized AQP2 to be transported to the luminal side of the membrane (next to the tubular lumen)
- Water flow through the channels, out to the other side
What is diuresis?
When the body excretes a large volume of urine
What is the difference between water diuresis and osmotic diuresis?
Osmotic diuresis is when excess solute in urine is also associated with high levels of water excretion.
How is low concentration of sodium handled in the short term and long term?
Short term: baroreceptors regulate GFR
Long term: Aldosterone promotes Na+ reabsorption (renin, angiotensin II needed for aldosterone secretion)
What happens when there is high concentration of Na+ in plasma?
The Atrial Natriuretic Peptide (ANP) regulates GFR and inhibits Na+ reabsorption. It also works by inhibiting aldosterone actions
What are baroreceptors?
Nerve endings that are sensitive to stretch
What can baroreceptors sense?
Changes in blood volume, blood pressure
What happens to Na concentration when there is a low plasma concentration?
Low plasma volume > low arterial blood pressure > activation of baroreceptors (less stretch) > increased acitivity of renal sympathethic nerves > increased afferent arteriolar constriction > decreased GFR > Less Na+ filtered, decreased excretion of Na+ > Increased Na+ in plasma
What are the 3 functions of aldosterone?
- Induces synthesis of Na+ transport protein
- Stimulates Na+ reabsorption
- Reduces Na+ excretion
How does aldosterone regulate Na+ level?
NaCl depletion > increased renin secretion > incresed plasma renin concentration > increased plasma angiotensin I concentration > increased plasma angiotensin II concentration > increased aldosterone release > increased aldosterone concentration > increased Na+ transporter synthesis/activity in cells of collecting ducts > increased Na+ reabsorption > decreased Na+ excretion
What controls aldosterone secretion?
- Low total body [Na+]
2. Angiotensin II acts on adrenal cortex to control secretion of aldosterone
What is the renin-angiotensin system?
Liver secretes angiotensinogen > renin secreted by the juxtaglomerulus cells in the kidney convert it to angiotensin I > converted to angiotensin II (active) by angiotensin converting enzyme (ACE) > signals adrenal cortex to release aldosterone
What are the 3 inputs that the JG cells receive to determine the concentration of renin?
- Sympathetic input from external baroreceptors
- Intrarenal baroreceptors
- Signals from macula densa
What is the difference between the JG cells and macula densa?
The JG cells are mechanoreceptors while the macula densa are chemoreceptors; the JG cells sense circulating plasma volume while the macula densa sense NaCl load of the filtrate
What stimulates Atrial natriuretic peptide (ANP)?
- Increased Na+ concentration
- Increased blood volume
- Atrial distension
Where is the site of ANP action and what are the 3 actions?
- On cells of several tubular segments
- ANP inhibits aldosterone actions
- Inhibit Na+ reabsorption
- Increases GFR and Na+ excretion
What is excess K+ in blood called?
Hyperkalemia
How is K+ regulated in the tubules?
Most of the filtered K+ is reabsorbed in the proximal tubule and loop of Henle; collecting duct can secrete a small amount of K+; [K+] in urine is regulted in the cortical collecting duct
What controls homeostasis of K+ in the body?
Aldosterone secreting cells in adrenal cortex are sensitive to extracellular [K+]
Why is balance of H+ important for body functions?
- Enzymes are protein in nature and shape changes can alter their activity
- Changes in neuronal activity
- Coupled to K+ imbalances
- Irregular cardiac beats
At what pH is considered acidosis and alkalosis?
Acidosis: pH < 7.35
Alkalosis: pH > 7.45
What is the differences between volatile and nonvolatile acid?
Volatile means something that is vapour or gaseous state in room temperature
What are the sources of hydrogen ion ?
- Generation of H+ from CO2
- Production of nonvolatile acids from the metabolism of proteins and other organic molecules
- Gain of H+ due to loss of HCO3- in diarrhea or other non gastric GI fluids
- Gain of H+ due to loss of HCO3- in the urine
What are the sources of H+ loss?
- Utilization of H+ in the metabolism of various organic anions
- Loss of H+ in vomitus
- Loss of H+ in the urine
- Hyperventilation
What is a buffer?
Any substance that binds to H+
What is the function of a buffer?
Modify or adjust the change in pH following the addition of acids or bases
How does the kidney regulation the [H+] in the body?
- decrease of [H+] = kidneys excrete more bicarbonate
- increase of [H+] = kidney cells synthesize new bicarbonate and send it to blood
What are the transporters involved in the reabsorption of HCO3-?
- H+ ATPase
- H+/K+ ATPase
- Na+/H+ ATPase
What happens when excess H+ is secreted than there is HCO3- in lumen to bind H+?
- Extra H+ binds to HPO4,2-
- HCO3- is still generated by tubular cells and diffuses into plasma
- NET gain of HCO3- in plasma
What happens when there is no HCO3- and HPO4,2- to regulate H+?
- Uptake of glutamine from glomerular filtrate or peritubular plasma
- NH4+ and HCO3- are formed inside the cells
- NH4+ is actively secreted via the Na+/NH4+ counter transport into the lumen
- HCO3- is added to plasma
What is the renal regulation of acidosis?
- Increased secretion H+, thus increased reabsorption of bicarbonate
- New bicarbonate is generated using non-bicarbonate buffers and reabsorbed in the plasma
- Tubular glutamine metabolism produces more bicarbonate to be reabsorbed in the plasma
Net result = more bicarbonate synthesized by tubular cells and reabsorbed, plasma bicarbonate increased, plasma pH returns to 7.4, while urine pH is acidic
What is the renal regulation of alkalosis?
- Few H+ ions present in the filtrate, thus bicarbonate is lost in the urine
- Decrease of glutamine metabolism and ammonium excretion
Net result = bicarbonate is lost in the urine, plasma bicarbonate decreases, plasma pH returns to 7.4, while urine pH is alkaline
