Physio B Midterm 2

what is the primary function of the kidneys?

filter plasma

what two outcomes occur to the plasma once filtered?

excreted through urine or reabsorbed into blood

what are four other functions of the kidneys?

regulate blood pressure, regulate pH of body, regulate water volume, maintain blood glucose level

what is gluconeogenesis?

the production of new glucose

besides the kidneys, what other organ participates in gluconeogensis?

the liver

what is the functional unit of the kidney?

the nephron

what are the two types of nephrons and their percentages?

juxtamedullary (20%) and cortical (80%)

what is the job of the juxtamedullary nephrons?

to dilute and concentrate urine

what is used to push filtrate into the Bowman’s capsule?

hydrostatic pressure

what are the three layers that the filtrate must cross through before getting into the Bowman’s capsule?

endothelium, basement membrane, podocytes

how do smaller molecules get into the Bowman’s capsule?

through the presence of small pores/slits

in other words, what type of pressure is needed to create pressure for filtration?

blood pressure

what is the Glomerular Filtration Rate (GFR)?

the rate at which blood can be pushed into the Bowman’s capsule

which type of arteriole has more effect on the GFR?

afferent arteriole

how will vasoconstriction of the afferent arteriole affect GFR?

the GFR will decrease

how will vasodilation of the afferent arteriole affect GFR?

the GFR will increase

how will vasoconstriction of the efferent arteriole affect GFR?

the GFR will increase

how will vasodilation of the afferent arteriole affect GFR?

the GFR will increase

what is the myogenic response?

an autoregulation response that adjusts blood pressure through contraction/relaxation of smooth muscle on the arterioles to maintain a constant GFR

what is the tubuloglomerular feedback?

when the macula densa sense NaCl flowing past; if the NaCl is too high, this means that the GFR is too high and the afferent arteriole will constrict; if the NaCl is too low, the afferent arteriole will vasodilate to increase GFR

which cells control vasoconstriction/dilation?

mesangial cells (smooth muscle)

what happens when you eat lots of salt in reference to the tubuloglomerular feedback?

the presence of lots of salt in the blood leads to vasoconstriction, causing GFR to decrease and lead to water retention; higher blood volume due to increase in water = higher stroke volume = higher blood pressure

what is the role of the proximal tubule?

to reabsorb glucose and amino acids

what fraction of solutes in the filtrate are reabsorbed in the proximal tubule/thick descending limb?

1/3 of solutes

which solutes are pretty much all reabsorbed?

glucose and amino acids

which solutes are still present in the filtrate after passing the proximal tubule/thick descending limb?

sodium chloride, water, calcium

what is a symptom of diabetes that can be seen in the urine?

the presence of glucose in the urine indicates diabetes, since this points to a very high blood glucose to the point where it cannot be completely reabsorbed

what is transcellular?

the reabsorption across the cell

what is paracellular?

the reabsorption between the cells

what does the solute reabsorption look like in the proximal tubule/thick descending limb?

really good at reabsorbing glucose and amino acids; 2/3 of solutes remain in filtrate

what does the water reabsorption look like in the proximal tubule/thick descending limb?

around 33%, not because there is active transport of water, but because due to osmosis, water follows the solutes out of the tubule

which molecules are reabsorbed through transcellular means in the proximal tubule/thick descending limb?

sodium, glucose, amino acids

which molecules are reabsorbed through paracellular means in the proximal tubule?

chloride ion, water, calcium

what is secondary active transport?

the act of transporting using an existing gradient (2 in 1 transport)

which molecules participate in secondary active transport in the proximal tubule?

sodium gradient facilitates reabsorption of glucose and amino acids that need to be absorbed (sodium wants to come into the cell)

what side of the epithelial cells is the sodium-potassium pump located?

the basolateral side

which parts make up the Loop of Henle?

thin descending limb, thin ascending limb, thick ascending limb

what happens in the thin descending limb?

lots of water reabsorption, little to no solute reabsorption

what is the name of the holes that allow water to be reabsorbed in the thin descending limb, and does water go transcellular or paracellular here?

aquaporins, which allow water reabsorption transcellularly

what are the thin ascending limb and thick ascending limb responsible for?

solute reabsorption (minimal and high)

what physical characteristics of the thick ascending limb increase its rate of solute reabsorption?

a longer tube with more surface area

what is the name of the secondary active transport mechanism in the thick ascending limb?

NKCC pump (stands for Na+, K+, Cl-, Cl-, where Na+ is the energy source through its concentration gradient)

what changes in how chloride is reabsorbed between the proximal tubule/thick descending limb and the thick ascending limb?

in the proximal tubule/thick descending limb, chloride is reabsorbed paracellularly; in the thick ascending limb, chloride is reabsorbed transcellularly

what is the concept of cocurrent?

the idea that two parallel systems have filtrate traveling in the same direction, and diffusion results in an eventual equilibrium of solutes in both systems

what is the concept of countercurrent?

the idea that two parallel systems have filtrate traveling in opposite directions; as a result, the exchange of solutes is always happening, which is how our bodies execute the reabsorption of solutes and water between the loop of Henle and vasa recta

how do you enhance the countercurrent?

1. slow down the rate of flow to maximize exchange

2. increase the length of the tube

what is micturition?

the action of urinating

what are the two stages of micturition?

filling and voiding

what happens in the filling stage of micturition?

the bladder sends signals to the PMC, creating the need to pee

what happens in the voiding stage of micturition?

the bladder releases the urine

what is the PMC?

Pontine Micturition Center

what do detrusor muscles do during micturition?

they contract around the bladder

what are the two sphincters in the bladder?

internal and external sphincters

which sphincter of the bladder is voluntary and which one is involuntary?

external is voluntary, internal is involuntary

how does the prefrontal cortex interact with the external sphincter?

it can control the external sphincter to prevent voiding of urine

what does the limbic system do in relation to the bladder?

handles strong emotions; has the capability to override the prefrontal cortex and thus you can pee if you are experiencing too strong emotions

which drugs lower blood pressure?

diuretics

why do we use loop diuretics instead of another type of diuretic?

because loop diuretics impact important solute reabsorption the least; if diuretics targeted proximal tubule, would lose glucose and amino acids = death

what cotransporter does the loop diuretic impact?

the NKCC cotransporter

what other type of supplement may a doctor prescribe along with a loop diuretic and why?

a potassium supplement, since losing too much potassium can cause heart failure

if you have chronic low blood pressure, what responds to this to counteract it?

carotid & aortic bodies/baroreceptors

what effects do carotid and aortic bodies carry out? (Is there is low BP)

cause vasoconstriction to increase peripheral resistance and create thirst sensation in the hypothalamus; also increase conservation of water in kidneys

what is the renin-angiotensin aldosterone system?

your liver produces angiotensinogen, renin (found in granular cells) converts it into angiotensin I, ACE (from endothelial cells) converts it into angiotensin II

how does angiotensin II increase water conservation?

• signals hypothalamus, creates thirst

• vasoconstriction in afferent arterioles

• tells posterior pituitary to release ADH/vasopressin to encourage water retention

• adrenal gland releases aldosterone, which makes more channels to increase solute reabsorption

what does ADH do?

ADH binds to receptor, G protein activates AC which makes cAMP to change location of aquaporins to lumen side so more water reabsorption can occur transcellularly, hence more water retention

what happens if you have chronically high BP?

the atrial stretching leads to release of atrial natriuretic peptide/factor/hormone; this inhibits the NKCC cotransporter + vasodilates afferent arteriole

how does the body adjust to chronically high blood pressure?

increases water excretion through blocking solute reabsorption and increasing GFR

what is the average body pH?

7.4

why do we need an optimal body pH?

to ensure that the enzymes in the body function

what is the Henderson-Hasselbach equation and how does it help us wrt renal system?

pH = pKa + log ([HCO₃^-]/[CO₂]); this helps us determine how the body deals with acidosis

what is acidosis?

when the body’s pH decreases

what is alkalosis?

when the body’s pH increases

what causes respiratory acidosis and how is it solved?

when there is an increase in [CO₂], the pH decreases; to counteract, you increase [HCO₃^-] production

what are the three ways that [HCO₃^-] can be increased during respiratory acidosis?

1. lose less HCO₃^- by increasing the activity of the sodium-proton pump to create more HCO₃^- to travel into the blood

2. make more HCO₃^- by taking glutamine from the filtrate and converting it into bicarbonate to go into the blood

3. Using an intercalated cell type A, which takes carbon dioxide from the blood, converts it into bicarbonate, then puts the bicarbonate back into the blood and pumps out the proton, at the same time bringing in a potassium ion using ATP

what causes respiratory alkalosis and how is it solved?

this is when there is a decrease in [CO₂], leading to an increase in pH; to maintain pH, the [HCO₃^-] decreases

what are the two ways to counteract respiratory alkalosis?

1. lower production of bicarbonate by reducing the activity of the sodium-proton pump, so less HCO₃^- is made

2. Excrete more HCO₃^- by converting carbon dioxide into a proton and bicarbonate; pumping the bicarbonate out into the filtrate and bringing in a chloride ion, and then putting the proton back into the blood

what causes metabolic acidosis and how is it solved?

there is a decrease in bicarbonate due to production of lactic acid (acts as buffer) plus you may sweat out bicarbonate; carbon dioxide decreases through increased ventilation to solve

what causes metabolic alkalosis and how is it solved?

there is an increase in bicarbonate due to use of loop diuretics, which inhibits the NKCC cotransporter; less chloride ions coming in means the body makes more bicarbonate to maintain electrical neutrality; the response is to increase carbon dioxide through less ventilation (which isn’t necessarily a good thing)

what is a Davenport diagram?

a diagram detailing the relationship between bicarbonate and concentration of carbon dioxide in the blood

what are the groups of smooth muscle?

Unitary

• vascular

• respiratory

• gastrointestinal

• urinary

• reproductive (male + female during end of pregnancy)

Multi-unit

• reproductive (for majority of female life)

• ocular

• skin

what are the two types of smooth muscle?

• unitary/visceral

• multi-unit

what is unitary smooth muscle?

where the cells are electrically connected, resulting in a much stronger contraction

what is multi-unit smooth muscle?

where the cells are independently stimulated

which group of muscle can be either unitary or multi-unit?

female reproductive smooth muscle (dependent on pregnancy)

how do smooth muscle contractions work?

1. calcium goes into the cell, coming from the extracellular fluid

2. calcium binds to calmodulin

3. it stimulates/activates MLCK on myosin

4. this enzyme requires ATP so myosin can bind to the actin

5. everything after is exactly the same

* note no tropomyosin

how does relaxation of smooth muscle work?

nitric oxide is released by endothelial cells, which then activates MLCP to dephosphorylate the myosin chain, deactivates myosin heads, thus no contractions

what is muscle tone?

where smooth muscle is always in a partially contracted state to ensure dilation and constriction of certain vessels