Quiz 5 - Renal Physiology, Enzymes, Glucose Regulation and Formation Flashcards
Body fluid compartments
- Plasma - 3 L
- Interstitial fluid - 11 L
- Intracellular fluid - 28 L
TOTAL - 42 L
Blood volume
5 L, 3 in plasma, 2 intracellular in RBCs
How much volume can kidneys dispose of per day?
0.5 - 20 L
How is fluid lost other than kidneys?
Insensible loss (passive) from skin - 700ml/day
Sweat from heavy exercise - 100ml/day
Feces - 100ml/day
How do kidneys control blood volume?
Controlling urine volume can rapidly shed, or preserve pressure.
Controlling electrolyte balances regulate tonicity of cells by retention or excretion of ions.
Metabolic wastes excreted in urine
Urea - protein metabolism
Uric acid - nucleic acid metabolism
Creatinine - muscle metabolism
Bilirubin - hemoglobin metabolism
Foreign substances excreted in urine
Pesticieds, food additives, toxins, drugs (penicillin)
Renal regulation of pH
Excrete or retain H+, HCO3-
Generation of HCO3- and NH4+ from breakdown of glutamine
What hematopoetic cytokine is produced by the kidneys?
Erythropoietin (EPO)
Gluconeogenesis
Anabolic generation of glucose, performed in the liver and kidneys
Renal cortex
Outermost part of kidney
Renal medulla
Innermost part of kidney, contain renal pyramids and nephrons
Renal papilla
tube that connects pyramids to renal pelvis
Renal pelvis
Duct that collects urine and carries it to the ureter
Path of blood through kidneys
Renal Artery > Afferent arterioles > Glomerular Capillaries > Efferent Arterioles > Peritubular capillaries (Vasa Recta) > Renal vein
Glomerulus
Small cluster of glomerular capillaries, surrounded by a Bowman’s Capsule
Bowman’s Capsule
Surrounds glomerulus, collects filtrate and passes it to the proximal tubule
Path of filtration
Glomerulus/Bowman’s Capsule > Proximal Tubule > Loop of Henle > Distal Tubule > Collecting Duct > Papilla > Renal Pelvis > Ureter
Cortical nephrons
70% of nephrons, located in cortex, loop of Henle penetrates medulla
Juxtamedullary nephrons
30% of nephrons, located in medulla, long loop of Henle that penetrates deep into medulla
Vasa Recta
Peritubular capillaries that come from efferent arterioles and surround the loop of Henle
Urinary Excretion Rate
= (Filtration rate - reabsorption) + secretion
Filtration
Contents exit blood, are excreted
Reabsorption
Some or all of filtered materials are taken back into the blood
Secretion
After filtration, further materials are removed from blood and excreted
Glomerular Filtration Rate (GFR)
= Kf X Net Filtration pressure, Kf - glomerular capillary filtration coefficient
Net filtration pressure = sum of colloid and hydrostatic pressures across capillary
Around 180L/day, total plasma volume cycled through filtration 60 times/day
Reabsorption amount
Around 179L/day
What happens to glucose and creatinine in the kidneys
Glucose - 100% reabsorbed
Creatinine - 100% excreted
Glomerular capillaries
Endothelium - fenestrated, (-) charged
Basement membrane - collagen/proteoglycan mesh, (-) charged
Epithelium - podocytes (form slit pores) (-) charged
Pro filtration pressures
Glomerular hydrostatic pressure, around 60mmHg
Bowman’s capsule colloid pressure = 0
Anti filtration pressures
Bowman’s capsule hydrostatic pressure, around 18 mmHg
Glomerular Colloid presssure, around 32 mmHg
Diabetes and GFR
Retained glucose creates colloid osmotic pressure in bowman’s capsule, causing increased urine output.
Alterations to GFR
Constriction of afferent arterioles will decrease GFR
Dilation of afferent arterioles will increase GFR
Constriction of efferent arterioles will increase GFR
Dilation of efferent arterioles will decrease GFR
Neural and hormonal control of GFR
Sympathetic Nervous system and Norepinephrine (chatecholamines) reduce GFR
Angiotensin II doesn’t effect GFR but lowers RBF
Prostaglandins and Endothelial-derived Nitric Oxide increase GFR
Macula Densa
Sensory region in on distal tubule forms juxtaglomerular complex with afferent and efferent arterioles, monitors a decrease in NaCl in distal tubule, indicating a decreased GFR, causes secretion of Renin to increase GFR
Diabetic Neuropathy
Increased flow out because increased glucose filtered, therefore increased water and Na+ excretion
Leads to damage of nephron, decreased function.
Filtration summary
Bowman’s capsule - 100% filtrate produced
Proximal tubule - 80% filtrate reabsorbed (active and passive)
Loop of Henle - 6% filtrate reabsorbed, H20 and salt conservation
Distal tubule - 9% of filtrate reabsorbed, variable reabsorption and active secretion
Collecting tubule - 4% filtrate reabsorbed, variable salt and H2O reabsorption
Urine volume - 1% of total filtrate
Na/K ATPase in the tubules
Primary active transporter sets up gradient for secondary active transport. Na+ reabsorption highly linked to the reabsorption of many other things
Cotransport
Na+ brings in Glucose and amino acids
Counter-transport
Na+ in pushes H+ out
What happens in the proximal tubule?
65% of water reabsorbed, Na+, Cl-, glucose, amino acids and HCO3- reabsorbed.
Na+ amount decreases but concentration does not because water follows it.
What happens in the loop of Henle?
Thin descending segment - permeable to water, but not ions (20% H20 reabsorbed)
Thick ascending segment - not permeable to water, lots of active transporters for Na+, Cl- and K+ and other ions
Countercurrent Exchange
The extraction of ions in the ascending thick segment creates a concentration gradient that pulls water out of the thin descending cycle, further concentrating the fluid in the tubes. This positive feedback cycle leads to the high concentration gradient within the loop of Henle and allows the minimum amount of water to be excreted with the maximum amount of waste.
What does the distal tubule do?
Proximal part is impermeable to water, reabsorbes ions.
Distal half contains Principal Cells (for reabsorbing Na+ and water and secreting K+) and Intercalated cells (that reabsorb K+ and HCO3- and secrete H+)
Late distal tubule is permeable to water, controlled by ADH. Less permeable = more water excretion
What do the collecting ducts do?
Reabsorb 10% of filtered water and Na+, regulated by ADH. Pump H+ into lumen to regulate pH
Permeable to urea, allowing some back into medulla
What does urea do?
Maintains hyperosmotic state in interstitial fluid of renal medulla. Urea is removed from tubule in collecting ducts, and secreted back into tubule in the lower parts of the loop of Henle.
What do enzymes do?
Increase chemical reaction rate
Reduce free energy needed to drive reactions
Increase probability of reaction occurrance
Globular proteins
Almost all proteins are globular in shape with a specific binding site or pocket
Substrate selective
Proteins bind to specific parts, of specific subtrates. Functional group, charge, region, etc.
Coenzymes
Other proteins or organic components that bind to enzymes to compliment their function
Cofactors
Inorganic ions that bind to enzymes to compliment their function. Ex.) Cu2+, Mn2+, Zn2+, Fe2+
Holoenzyme
Complete catalytically active enzyme with coenzymes and cofactors bound.
Weak interactions
Enzymes generally bind to their substrates with weak interactions
Oxidoreductase
Transfer of electrons
Transferase
Group transfer
Hydrolase
Hydrolysis reactions
Lyase
Cleavage of C-C, C-O, C-N or other bonds leaving double bonds or rings
Isomerases
Transfer groups to yield isomeric forms
Ligases
Formation of C-C, C-S, C-O, C-N bonds by condensation. Requires ATP or other cofactor
Lock and Key model
Untrue. Substrate does not fit perfectly into enzyme or activation energy would increase because bound substrate would be in lower energy state
Induced Fit model
Enzyme is complimentary to transition state rather than substrate or product, lowers activation energy by decreasing energy needed to meet transition state.
Activation Barriers
- Entropy of molecules in solution
- Solvation shell - water molecules surrounding substrate
- Substrate conformation
- Substrate orientation
Enzyme solutions to activation barriers
- Organize substrates, reduce entropy
- Weak bonds desolvate substrates
- Weak bonds alter conformation
- Enzymes induce fit
Enolase reaction
Glycolysis reaction. 2 Mg2+ cofactors stabilize the transition state while the enzyme shifts charges and electrons to form the product
Kinetics
Rate at which enzymes create products
Velocity
Measure of reaction rate. Affected by enzyme, substrate, cofactors and coenzymes, enzyme modifications, pH, temperature
Michaelis-Menten Equation
V = (Vmax[S])/(Km+[S]) Plots Velocity over Substrate concentration. Involves only single substrate reactions
Michaelis-Menten Constant
Km. Substrate concentration at which the initial reaction velocity (Vo) equals one-half the maximum reaction velocity (Vmax)
Ternary Complex
An enzyme bound to 2 substrates to create products.
Can bind in a random or order
Irreversible inhibition
Inhibitor binds covalently to the tenzyme, preventing function and leading to degradation.
Reversible Inhibition
Inhibitor binds to enzyme or substrate to temporarily affect catalysis. Can be competitive, uncompetitive, mixed, noncompetitive
Competitive Inhibition
Inhibitor binds in substrate binding site.
Shifts Km to right, but Vmax unchanged
Uncompetitive Inhibition
Inhibitor binds to enzyme in place other than substrate binding site. Km either unchanged or shifted left, Vmax decreased
Mixed Inhibition
Separate binding site from substrate, may bind to substrate or enzyme. Km shifted right and Vmax reduced.
Noncompetitive
Rare, Vmax reduced, but not Km
Allosteric Enzymes
Function of enzyme regulated by modifications
Enzyme conformation changed by effector binding.
Complex proteins
Do not follow Michaelis-Menten
Types of post-translational modifications of enzymes
Phosphorylation - addition of PO3 Methylation - addition of CH3 Myristoylation - addition of myristoyl (long chain ketone) Acetylation - addition of acetyl group Ubiquitination - addition of ubiquitin Adenylation - addition of tyrosine ADP-ribosylation - addition of NAD
Homotropic Regulation
The substrate itself is the molecule that modifies activity
Ex.) Hemoglobin binding to O2
Heterotropic regulation
Involves post-translational modifications
4 Functions of Glucose
- Source of ATP
- Energy Storage
- Molecular Precursor
- Structural Backbone
Catabolic Pathways
Glycolysis
Citric Acid Cycle
Oxidative Phosphorylation
Glycogenolysis
Anabolic Pathways
Gluconeogenesis
Glycogenesis
How presence regulates metabolic activity
Concentration - production or modification of enzymes
Localization - protein complexes, etc.
How kinetics regulate metabolic activity
Substrates and modification of enzymes change kinetics
Where does glucose initially come from
Diet. Enzymes digest food into glucose and other small sugars where it is absorbed and distributed to where it is needed.
Digestive enzymes
Amylase
Lactase
Sucrase
Maltase
3 major pathways of glucose metabolism
- Respiration - forms ATP
- Storage - forms glycogen, glucose
- Regenerative - forms glucose
Key regulators of glucose pathways
Insulin Glucagon Epinephrine Glucose ATP/AMP
Which metabolic pathways are exclusive
Glycolysis =/= gluconeogenesis
Glycogenesis =/= glycogenolysis
Glycogen
Stores intercellular glucose
Branched glucose homopolysaccharide
Primary mechanism for intracellular energy storage
Primarily found in liver (10% of liver weight) and muscle (2% of muscle weight)
Necessary to maintain cellular osmolarity
Forms large molecular complexes
Stored in granule organelles
Glycogenolysis pathway
Glucose + Hexokinase > Glucose-6-phosphate + Phosphoglucomutase > Glucose-1-phosphate + UDP-glucose pyrophosphorylase > Uracil diphosphate-glucose + Glycogen synthase > Glycogen chain + Glycogen branching enzyme > Glycogen particle
Which is the point of regulation in glycogenesis
Uracil diphopshate-glucose > Glycogen chain
Glycogen Synthase Enzyme
Glycogenin
Protein required as anchor point for formation of large glycogen complexes
Glycogenolysis pathway
Glycogen + Glycogen Phosphorylase + debranching enzyme > Glucose 1-phosphate + Phosphoglucomutase > Glucose 6 phosphate + Glucose 6-phosphatase (in ER) > Glucose
Glycogen Synthase regulation
Insulin promotes activation and inhibits inactivation of GS
Glucagon/Epinephrine blocks activation
Glucose and Glucose 6-phosphate promote activation
Glycogen phosphorylase regulation
Glucagon in the liver and epinephrine in the muscles promote conversion of Glycogen Phosphorylase to a more active state
Glucose will inhibit phosphorylase by occupying glycogen binding sites
Insulin inhibits phosphorylase by promoting PP1 to convert phosphorylase to a less active state
How does Insulin activate Glycogenesis
Insulin binds to TYRK receptor > Self phosphorylates > PI3K activated > PIP2 becomes PIP3 > Series of proteins Phosphorylates GS > PP1 activates GS
Insulin, G6P and Glucose promote PP1 function
Glucagon, epinephrine inhibit PP1 function
Glucagon/Epinephrine
Glucagon will cause the Liver to increase blood glucose by promoting Glycogen phosphorylase
Epinephrine will increase intracellular glucose of that particular cell
Pathway involves Adenylyl Cyclase, Phosphorylase
Gluconeogenesis
Synthesis of glucose
Can occur in all cells but occurs primarily in the liver
Converts lactate or pyruvate
Energetically costly
PEP formation pathway from lactate
Lactate + Lactate dehydrogenase > Pyruvate (enters mitochondria) + Pyruvate Carboxylase > Oxaloacetate + mitochondrial PEP carboxykinase > Phosphoenolpyruvate (PEP) (Leaves mitochondria
Gluconeogenesis pathway from PEP
PEP + Enolase > 2-phosphoglycerate + phosphoglycerate reductase > 3-phosphoglycerate + phosphoglycerate kinase > 1,3 biphosphoglycerate + glyceraldehyde 3-phosphate dehydrogenase > glyceraldehyde 3-phosphate + triose phosphate isomerase > dihydroxyacetone phosphate + glyceraldehyde 3 phosphate + aldolase > Fructose 1,6-bisphosphate + fructose 1,6-bisphosphatase > fructose 6 phosphate + phosphohexoisomerase > glucose 6-phosphate + glucose 6-phosphatase > glucose
Which steps in gluconeogenesis are regulated
Fructose 1,6-bisphosphate > fructose 6-phosphate
- AMP inhibits FBPase-1
Pyruvate > Oxaloacetate
- Acetyl-CoA promotes pyruvate carboxylase
Insulin causes generation of Glucose 6-phosphatase and PEP carboxylase by activating PKB and FOX01
Challenge of Metabolic System
Organism-wide metabolic homeostasis
Cellular energetics change rapidly
Global metabolic demands change rapidly
Intracellular states drive physiologic changes that influence energetics
Intracellular ATP/AMP content regulates metabolic function
Does the body recognize changes in ATP or AMP faster and why?
AMP because the relative change is much greater with AMP over ATP.
