Phys. II Test One: Renal Flashcards
What is the function of the kidneys?
Regulate ECF water and concentrations of ions and regulate acid base balance as well as remove metabolic wastes.
What is gluconeogenesis?
During fasting glucose is synthesized from other molecules such as amino acids and released into the blood to keep blood glucose up.
What is the functional unit of the kidney?
Nephron. Which is made up of the renal corpuscle and renal tubule
What is the filtering component of the nephron?
Renal corpuscle
What extends out from the corpuscle and is surrounded by peritubular capillaries?
Renal tubule
What does the renal corpuscle consist of?
Glomerular capillaries with bowmans space and bowmans capsule
Where are renal corpuscles found?
Within the renal cortex
Where do Juxtamedullary nephrons have corpuscles?
Near the cortex/medulla junction
Where do cortical nephrons have their corpuscles?
Near the kidney surface
The renal tubule’s lumen is a continuation of what?
The space in Bowman’s capsule
What is the proximal tubule?
The first section of the tubule, it drains Bowmans capsule
What is the loop of henle?
The section following the proximal tubule it has a descending limb followed by an ascending limb
What is the distal convoluted tubule?
The section that follows the loop of henle ascending limb
What is the collecting duct?
The duct where the convoluted distal tubule drains. It is composed of a cortical collecting duct followed by a medullary collecting duct. IT contains the fluid that will be transported to the bladder and eliminated.
Afferent arteriole?
Carriesx blood into the glomerular capillaries
What is the efferent arteriole and what makes it?
Arteriole through which blood leaves the capillaries and it is formed by the glomerular capillaries recombining.
What does the efferent arteriole divide into?
Peritubular capillaries
What type of substances are filtered across the glomerular membrane?
Low molecular weight substances such as water, glucose, urea, and ions.
What is glomerular filtration?
The process of low weight molecular substances in the glomerular capillary plasma being filtered across the membrane of the capillaries and bowmans capsule into the space. This produces glomerular filtrate and will contain the substances in the same concentrations that they are found in the plasma.
Are there cells or proteins in the filtrate?
Neither because they are both too large to cross the membrane.
What is tubular re-absorption?
Selective movement of filtered substances from tubular lumen into the peritubular capillaries
What is tubular secretion?
Selective movement of nonfiltered substances from peritubular capillaries into the tubular lumen.
Give an example of total excretion?
Substance X is freely filterable and can’t be reabsorbed and undergoes 100% secretion
What is partial excretion?
When a substance is filterable and undergoes partial reabsorption and can’t be secreted
When would no excretion occur?
When a substance is filterable but undergoes 100% reabsorption and can’t be secreted. For example glucose.
What are filtration slits?
Spaces between foot processes
What is the force that drives filtration?
Glomerular capillary fluid pressure that is high comparted to pressure in other capillaries.
*Pressure gradient
What two forces oppose filtration?
The hydrostatic pressure in bowman’s space and the osmotic force from proteins in the plasma that aren’t seen in Bowman’s space.
What is the net pressure favoring filtration?
10 mmHg
What is the GFR?
The volume of fluid that is filtered into the combined bowmans spaces per unit time.
What is filtered load?
The total amount of one substance that is filtered per unit time. So GFR times the plasma concentration of the substance.
What must have occured if less of a substance is excreted than filtered?
Tubular reabsorption
What must have occurred if more is excreted than filtered?
Tubular secretion
What inputs can change the net glomerular filtration pressure?
Constriction of the afferent arteriole decreases glomerular capillary BP by increasing the pressure drop between arteries and capillaries.
Also constriction of the efferent arteriole which will increase glomerular capillary blood pressure causing blood to dam up in the capillaries.
If no reabsorption occured what would happen?
Body water would be quickly depleted and would be urinated out within 30 minutes
Why can excretion occur quickly?
Because quantities excreted are only fractions of the flittered amounts
What undergo nearly complete re absorption?
Glucose, Na, and water
Can reabsorption regulate plasma glucose levels? (Minimize changes from a set point.) Assume ideal level is 80 mg glu/100 ml plasma.
No, glucose is always reabsorbed whether the blood glucose levels are high or low.
Can reabsorption regulate plasma water levels?
Yes, water reabsorption rate is constantly changing due to physiological control.
If your water intake increases what happens to water reabsorption rate?
The reabsorption rate goes down and the excretion rate increases to restore the plasma water level to normal. And vise versa.
What is the pathway for reabsorption?
Filtrate moves from the lumen of the tubule across the tubular cells through the renal interstitial fluid and through the peritubular capillaries. Takes two paths to get across tubular cells.
What are the two ways for filtrate to get through the renal tubule?
- Go through the cells Transcellular pathway
2. Go in between cells Paracellular path
Describe transcellular pathway out of tubular lumen.
The filtrate goes through the PM forming the luminal borders and through the cells and occurs by diffusion or active transport.
Describe paracelllular path out of tubular lumen.
The filtrate moves through tight junctions and between cells by diffusion.
How is sodium reabsorbed?
Through active transport.
How do substances move from renal interstitial fluid into the peritubular capillary plasma?
Combination of bulk flow and diffusion
Describe carrier mediated diffusion and give example.
The substance needs a carrier molecule to move it across the membranes. For example glucose is reabsorbed by secondary active high transport, so you can move glucose from a level of low to high concentration gradient
How is it possible for glucose to be excreted?
The carrier protein has a transport maximum and if glucose concentration in plasma is very high there aren’t enough carrier molecules to reabsorb all of it and some can get by and be excreted in the urine. Therefore it exceeds transport maximum. Can happen In diabetes.
Describe how urea is reabsorbed by diffusion.
Urea is filtered at the renal corpuscle and its concentration is equal to the concentration in the first portion of the tubule. As the filtrate moves along the tubule water gets reabsorbed and creates a concentration gradient that will drive the diffusion of Urea. Urea is accidentally reabsorbed due to the concentration gradient.
How does most K and H in urine enter the tubule?
Through secretion
What is secretion
Movement from peritubular capillary plasma into the renal tubule
How does secretion occur?
Through diffusion or carrier mediated transport similar to reabsorption. Carrier mediated transport is coupled to sodium usually.
What is clearance?
It describes the rate at which substances are removed from the plasma by the kidneys
What is renal clearance?
The volume of plasma that is completely cleared of a substance per unit time by the kidneys.
Accounts for the mass of a substance secreted in the urine.
Constriction of afferent arteriole ____ glomerular capillary bp by ____ the pressure drop between arteries and capillaries.
Decreases, increasing
Constriction of efferent arterioles ___ glomerular capillary bp by ______.
Causing blood to dam up in the capillaries
Does the kidney set and regulate plasma glucose levels?
no
What type of flow allows substances to move from renal interstitial fluid into peritubular capillary plasma?
Combo of diffusion and bulk flow
How is glucose reabsorbed?
Secondary active transport (Na co transport) and uses energy to move glucose against the concentration gradient
`How is urea reabsorbed?
It starts off equal concentrations in the interstitial fluid and capillary plasma. As the filtrate flows along prox tubule water gets reabsorbed increasing the tubular concentration of urea. Urea passively diffused down its concentration gradient from tubule to peritubular capillary.
Clearance equation?
C= U(V)/P
U=urine conc. of substance
V= urine volume per unit time
P= plasma concentration of S
What is the clearance of creatine?
The GFR of creatine
High creatine is an indicator of what?
low GFR which is a hallmark of kidney disease
How does water enter the body?
Through food and drink also produced in metabolic reactions
How is water lost?
Skin, lungs (insensible), sweat, feces, urine
Do sodium and water undergo tubular secretion?
No, so the amount excreted is = to the amount filtered minus the amount reabsorbed
Where does most sodium and water reabsorption occur?
Proximal tubule, but main hormonal control occurs in DT and CD
Is the proximal tubule regulated for reabsorption?
No. Regulation occurs in the DT and CD
How does sodium get reabsorbed?
Active transport carrier mediated against the gradient
How does water reabsorption occur?
Diffusion and depends on reabsorption of sodium as they are coupled
How does sodium get from lumen of tubule into the cells forming the walls of the tubule?
Occurs across luminal membrane downhill for sodium through co transport with glucose or aa, or counter transport with H, or diffusion through sodium channels.
Where is the higher concentration of water found?
Tubular fluid. Due to Na being actively removed from lumen into interstitial fluid, this (lowers osmolarity) increases water conc in tubular fluid and decreases water concentration (raises osmolarity) in interstitial fluid.
Is the proximal convoluted tubule permeable to water?
Yes always
What is the final step in reabsorption?
Water sodium and everything else in interstitial fluid move together by bulk flow into peritubular capillaries.
