Physiology Flashcards
When the micturition reflex is powerful enough, where does the signal pass through and what happens?
The reflex passes through the pudendal (somatic) nerves to inhibit external urethral sphincter (composed of skeletal muscle tissue)
What needs to be inhibited in order for urination to occur?
External urinary sphincter
Sensory signals from bladder stretch receptors (detrusor muscles) are sent where?
- sacral region of spinal cord via pelvic nerve
- conducted reflexively back to bladder via parasympathetic nerves
What is the mathematical expression for urinary excretion rate?
Filtration rate - reabsorption rate + secretion rate
Define filtration fraction and express it mathematically
- The fraction of renal plasma flow that is filtered ~0.2 (20% of plasma flowing through the kidney is filtered
- Filtration fraction= GFR/ renal plasma flow
What types of substances are not filtered by the nephron?
-Proteins and some LMW substances (because they are partially bound to proteins). Almost half of the plasma Ca and FAs are bound to proteins, and thus, do not filtered through the glomerular capillary
What are the components of the filtration barrier?
- Endothelium- with fenestrae and negative charge
- Basement membrane- with collagen, proteoglycans and strong negative charge. Has small spaces through which water and small solutes can pass through
- Podocytes- form slit filtration barrier with negative charges
What is the glomerular filtration rate?
125 ml/min = 180 L/day
Water has a filterability of 1.0
Define minimal change nephropathy
Loss of negative charges on the basement membrane. Some LMW proteins, especially albumin, are filtered and appear in urine –> proteinuria
Mathematically express GFR in terms of Starling forces
GFR= (K1) (Pg-Pb-Pig-Pib)
-Pg: glomerular hydrostatic pressure= 60mmHg
-Pb: Bowman’s capsule hydrostatic pressure= 18mmHg
-Pig: glomerular capillary colloid osmotic pressure= 32mmHg
-Pb: colloid osmotic pressure of Bowman’s capsule= 0mmHg
NET FILTRATION PRESSURE: 10mmHg
Explain the effect of the sympathetic system of GFR
- Strong activation of the sympathetic system will constrict renal arterioles which will decrease renal blood flow and GFR
- Moderate sympathetic activation has little effect
Describe the effects of NE and epinephrine of GFR and their source
- Derived from the adrenal medulla
- Constrict renal arterioles, decrease renal blood flow and GFR
What determines renal blood flow and what is the mathematical expression?
- Kidneys have 7x the blood flow of the brain but only 2x the oxygen consumption
- Most of the oxygen consumption by the kidneys is related to the high rate of active sodium reabsorption
- Renal blood flow= (renal artery pressure - renal vein pressure) / (total vascular resistance)
List the effects of endothelin on GFR and its source
- Released by damaged vascular endothelial cells of the kidney and other tissue
- May contribute to renal vasoconstriction leading to reduced GFR
- May contribute to hemostasis when a blood vessel is severed
List the affects of Angiotensin II on GFR and its source
- Formed in the kidneys
- Preferentially constricts the efferent arterioles
- Formed usually in situations associated with decreased arterial pressure or volume depletion- effects on the efferent arterioles will help to increase GFR
List the effects of NO on GFR and its source
- Derived from endothelial cells
- Basic level helps maintain renal vasodilation which decreases renal vascular resistance and increases GFR
- counteracts the effects of angiotensin II on afferent arterioles
List the effects of prostaglandins and bradykinin on GFR
- vasodilators that may offset effects of sympathetics and angiotensin II (especially on afferent arterioles)
- decrease renal vascular resistance which tends to increase GFR
List the three kinds of aquaporins and their specific locations in the renal tubules
- Aquaporin 1: widespread and includes the renal tubules
- Aquaporin 2: present in apical membranes of collecting tubules; is controlled by ADH***
- Aquaporin 3: present in basolateral membranes of collecting tubule cells
List the sodium-glucose co-transporters on the brush border of the proximal tubule cells and their functions
- SGLT2: reabsorbs 90% of glucose in early proximal tubule
- SGLT1: reabsorbs 10% of glucose in late proximal tubule
List substance that are actively secreted into the renal tubules
creatinine
para aminohippuric acid
Define transport maximum and the limiting factor and explain how this relates to glucose reabsorption
- Limit to the rate at which the solute can be transported due to the saturation of a specific transport system
- transport max for glucose: 375 mg/min –> if we exceed this, glucose will not be transported and you will have glucose in your urine
- small amounts of glucose will begin to appear in the urine after plasma [glucose] rises about 200mg/100ml
- filtered load for glucose: 125 mg/min
List reasons as to why some passively reabsorbed substances do not have a transport maximum
- Rate of diffusion is determined by electrochemical gradient of the substance
- Permeability of the membrane for the substance
- Time that the fluid containing the substance remains within the tubule
Describe characteristics of the proximal tubule, specifically that kinds of molecules/ions and direction transported
- Reabsorbs 65% of filtered sodium, chloride, bicarbonate, and potassium.
- Reabsorbs all filtered glucose and aa
- sodium reabsorption in the first half is via co-transport along with glucose, aa, and other solutes
- sodium reabsorption in the second half is mainly chloride ions
- H+, organic acids, and bases go back into the lumen
Describe characteristics of the thin descending loop of Henle, specifically the kinds of molecules/ions and direction transported
- highly permeable to water (reabsorbs about 20% of filtered water)
- moderately permeable to most solutes, including urea and sodium