Lecture 26: Urinary System Physiology Flashcards
(25 cards)
What force determines glomerular filtration?
Glomerular capillary hydrostatic pressure is equal to blood pressure in the glomerulus and promotes filtration (Outward force)
Opposing forces: Blood colloid osmotic pressure and capsular hydrostatic pressure.
What is the net filtration pressure equation?
NFP = HP (gc) - [ HP(cs) + OP(gc) ]
(Outward - Inward Forces)
What is the relationship between glomerular filtration rate and blood pressure?
- Increased GFR = Increased urine output = Decreases blood volume = decreases blood pressure
- Decreased GFR = Decreased urine output = Increased blood volume = increased blood pressure
What are factors that affect glomerular filtration rate (GFR)?
- Glomerular capillary hydrostatic pressure
- Capsular hydrostatic pressure (blockages in the nephron tubules)
- Blood colloid osmotic pressure (plasma protein content)
What are two special features of the juxtaglomerular complex?
- Macula Densa cells
- Granular cells
What is the function of macula densa and granular cells?
Macula Densa: They are chemoreceptors which monitor sodium and chlorine content of the filtrate entering into the distal convoluted tubule.
Granular cells: They are mechanoreceptors which release renin into the blood stream when blood pressure is too low.
What is the normal mean arterial pressure for kidneys?
80-180mmHg
Which are the two different mechanisms for kidney autoregulation?
- Myogenic
- Tubulo-glomerular feedback
What is myogenic autoregulation?
When blood pressure gets too high, the afferent arteriole tighten (contract) to slow down the blood flow.
When blood pressure gets too low, the afferent arteriole relax (widen) to let more blood flow through.
What is tubulo-glomerular feedback autoregulation?
- GFR increases
- [Na+] and [Cl-] remain high because filtrate passes through nephron at a higher rate.
- Macula densa cells sense the change in concentration.
- Vasoconstriction of afferent arteriole which decreases GFR.
Which are the two different mechanisms for extrinsic control?
- Neural mechanism (baroreceptor reflex)
- Hormonal mechanism (renin-angiotensin-aldosterone) mechanism
What causes an increase/decrease of NFP and GFR?
Vasodilation of afferent arteriole (increase in NFP and GFR)
Vasoconstriction of afferent arteriole
(decrease in NFP and GFR)
Which capillary allows for reabsorption into the blood stream?
Peritubular capillaries
Outline the reabsorption pathway.
- Tubule lumen
- Inside the tubule cell
- Interstitial fluid
- Blood in peritubular capillary
How does reabsorption of sodium help capture nutrients from filtrate?
Sodium/ potassium pumps are found in the basolateral of tubule and keeps sodium concentrations low in the cell. Since sodium is low, more Na+ comes from the filtrate along with water, glucose, and vitamins. This happens through symporters.
What does it mean when there is presence of urine in the blood?
protein transporters in the renal tubules become saturated and incapable of reabsorbing all the glucose present in the filtrate.
Is secretion an active transport process?
Yes, it follows active transport. Helps to control pH, get rid of metabolic wastes and certain drugs.
Where does secretion of urea, H+ and ammonium occur?
Urea: Loop of Henle
H+ and ammonium: Proximal convoluted tubule
What plasma solute concentration must kidneys maintain for Isotonicity?
300 mOsm
What are the two types of nephrons and their function?
- Cortical (Short loop of Henle and help in excretion of substances)
- Juxtamedullary (15% of nephrons; loop of Henle goes deep into renal medulla and pull more water out of the filtrate when needed).
How does the osmotic gradient change in kidneys?
Osmolarity increases as you go down the medulla and helps to modify the concentration and volume of urine produced.
How does osmolarity change along the loop of Henle?
Osmolarity increases as you go down the loop with 1200mOsm at its deepest position. Whereas osmolarity decreases to 100mOsm by the ascending limb of the loop.
What is the relation between osmolarity and ADH?
Greater osmolarity results in increase number of aquaporins in the collecting ducts. Increased reabsorption of water in the blood. As a result, small amount of urine produced due to ADH release.
What are some abnormal components of urine?
- Glucose
- Proteins
- Ketone bodies
- Bile pigments
- Erythrocytes
- Leukocytes
