Module 2- Membrane Physio + Osmoregulation + endocrine + renal Flashcards
(165 cards)
1
Q
phospholipids
A
phospholipids are amphipathic, meaning a substance with both hydrophobic and hydrophilic region
-this is a factor in membrane permeability
- hydrophobic molecules such as O2, CO2, and N2 can freely move through the phospholipid bilayer
- small uncharged polar molecules such as water and glycerol can semi move freely through
- large uncharge polar molecules such as glucose and sucrose cannot
- ions cannot move freely either
2
Q
cholesterol
A
cholesterol can fill spaces between phospholipids and interact with them to make the membrane more viscous (thick)
changes in viscosity are used when some animals acclimate to long term temperature changes
3
Q
Factors affecting membrane fluidity
A
- more saturated tails = less fluid
- longer tails = less fluid
- low temperature = less fluid
- cholesterol moderates the fluidity, increasing it at low temperature and decreasing it at high temperatures (generally it decreases fluidity, unless the organism lives in very cold environments)
4
Q
membrane proteins
A
serve many different roles : transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to cytoskeleton and extracellular matrix (ECM)
5
Q
passive transport
A
- can freely move through lipid membrane 2. passive transport down electrochemical gradient 3. carrier mediated passive transport
6
Q
active transport
A
- primary active transport against electrochemical gradient
- secondary active transport against electrochemical gradient, driven by ion movement down its gradient
7
Q
uniporter
A
type of facilitated transport–
8
Q
symporter
A
type of facilitated + coupled transport–
9
Q
antiporter
A
type of facilitated + coupled transport–
10
Q
coupled transport
A
allows the movement of multiple solute types
11
Q
conformation change
A
conformation change in carriers is most often caused by binding of the molecule being transported. carriers transport molecules down the concentration gradient
12
Q
simple diffusion
A
molecules move from area of high concentration to low concentration until they reach a steady state. the rate of simple diffusion is directly correlated and driven by the concentration of the molecule at the source side of the membrane
- charged molecules are still diffusion but instead of concentrations of individual molecules in isolation, the collective charge of different areas plays a role in the movement of molecules
-while diffusion of a solute is not directly influenced by concentration of other solutes, it may be influenced by the electrical gradient
13
Q
carrier mediated transport
A
like simple diffusion, it is directly correlated with concentration but only to a certain point. once the transport maximum (Tm) for a particular molecule is reached, the rate cannot increase any further
14
Q
electrochemical gradient
A
this is the combined concentration and electrical gradient. while diffusion of a solute is not directly influenced by concentration of other solutes, it may be influenced by the electrical gradient.
6 Na+ and 2 Cl-
(high concentration of Na+ and net + charge)
↓ electrochemical gradient for Na+
1 Na+ and 2 Cl-
(net - charge and low concentration of Na+)
15
Q
sodium-potassium-ATPase pump
A
- transporter binds 3 Na+ ions from cytosol
- phosphorylation by ATP favors conformational change
- Na+ is released, K+ binds
- De phosphorylation favors original conformation
- K+ is released to cytosol. cycle can repeat
16
Q
Fick’s law of diffusion
A
rate of diffusion is determined by the concentration gradient (delta C), membrane surface area (A), the diffusion constant (D), and the membrane thickness (delta X)
diffusion constant is based on lipid solubility of the substance being transported and the molecular weight of the substances being transported
Q= (delta C * A * D)/ delta X
17
Q
osmosis
A
diffusion of water across a selectively permeable membrane. water diffused across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides
AND from a region of lower non penetrating solute concentration to a region of higher non penetrating solute concentration
some cells have aquaporins which are water channels and allow water to move more quickly
18
Q
osmotic pressure
A
19
Q
hydrostatic pressure
A
20
Q
fluid homeostasis
A
- maintenance of internal solutes
- fluid volume (plasma volume)
- removal of harmful substances
- maintenance of osmotic balance
21
Q
tonicity
A
a measure of the ability of a solution to cause water to flow across a membrane into or out of a cell. it measures the osmotic pressure gradient across a semi permeable membrane. it is only influenced by non penetrating solutes
- hypotonic = solution has a lower osmolarity than the cell
-isotonic= solution has the same osmolarity as the cell
-hypertonic= the solution has higher osmolarity than the cell
22
Q
Hypotonic
A
solution has lower osmolarity than the cell so water flows into the cell –> lysis, the cells can swell with water and burst
23
Q
Isotonic
A
solution has the same osmolarity as the cell so water flows in both directions –> no net change in cell shape
24
Q
Hypertonic
A
the solution has higher osmolarity than the cell –> crenation, cell becomes shriveled
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Osmolarity
is a property of every solution; it describes the number of dissolved solute particles (OsM). this measures the concentration of both non penetrating and penetrating solutes while comparing two solutions. osmolarity alone does not inform us about the movement of water
hyposmotic, isosmotic, and hyperosmotic
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hyposmotic
solution has lower osmolarity than the cell
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isosmotic
solution has the same osmolarity as the cell
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hyperosmotic
the solution has higher osmolarity than the cell
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tonicity v osmolarity
tonicity is the property of a solution relative to a cell while osmolarity is the property of a solution and comparisons between solutions but doesn't tell you what will happen to a cell
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carrier mediated transport in the kidney
glucose reabsorption in the kidney
- under normal blood glucose levels, all glucose is reabsorbed and so not found in the urine. but when glucose levels are very high, Tm is reached and glucose can be found in the urine
mechanism of reabsorption:
- Na+ moving down its electrochemical gradient uses the SGLT protein to pull glucose into the cell against its concentration gradient
- glucose diffuses out the basolateral side of the side using the GLUT protein
-Na+ is pumped out by Na+-K+-ATPase
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osmoregulation -- salt reabsorption
the process of salt reabsorption cause water to move from the lumen back to the ECF (extracellular fluid)
- Nephron/ loop of Henle
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endocrine signaling (glands)
a ductless gland releases hormones into the blood stream. the blood stream carries the hormone throughout the body. endocrine system regulates and coordinates distant organs through the secretion of the hormones
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neuroendocrine signaling
a neuron releases neurohormones into the bloodstream. the bloodstream carries the neurohormone to its target
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synaptic signaling (neurons)
a neuron releases neurotransmitter on a cell with receptors for the transmitter
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hormone
hormone means "to excite"
- hormones are signaling molecules that travel to target cells via transport fluid and communicate and regulate physiological and behavioral activities
- involved in metabolism, sensory perception, stress response, growth, reproduction
- presence and absence of hormone may have impacts
- are effective at extremely low concentrations (picomolar)
- their action is often amplified in target cells due to secondary messengers
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endocrine tissue
solely endocrine function: pituitary, thyroid, parathyroid, adrenal
endocrine tissues that also have non endocrine functions: pancreas, ovaries, testes
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hypothalamus
has a master regulatory role with mixed nervous and endocrine functions
- is nervous tissue and functions to integrate the endocrine and nervous systems
- integrates information from other nerves and external stimuli
-makes (neuro) hormones that are stored and secreted by posterior pituitary
-secretes (neuro) hormones that regulate the anterior pituitary
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peptide hormone
produced via transcription, translation, and post-translation processing
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amine hormones
derived from the amino acid tyrosine
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steroid hormones
produced through enzymatic reactions that modify cholesterol molecules
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Receptors for steroids maybe be cytoplasmic or nuclear
- most hydrophobic steroids are bound to plasma protein carriers. only unbound hormones can diffuse into the target cell
- steroid hormone receptors are typically in the cytoplasm or nucleus
-some steroid hormones also bind to membrane receptors that use second messenger systems to create rapid cellular responses
-the receptor hormone complex binds to DNA and activates or represses one or more genes
- activated genes create new mRNA that moves into the cytoplasm
- translation produces new proteins for cell processes
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hormone receptor complexes
hormone-receptor complexes usually serve as transcription factors
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signal transduction pathway
process by which signal received by the cell is converted into specific cellular response
- hydrophilic hormones function through STPs
-form a cascade and amplify the signal
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three steps of signal transduction pathways
1. reception ; different receptor types (G-protein coupled, receptor Tyrosine Kinases, Ion channels (ligand-gated))
2. transduction ; uses secondary messengers and protein kinases
-second messenger: small, water-soluble molecule or ion that relays a signal as part of a STP --> common in G protein coupled receptors and often active protein kinases
- protein kinases: enzyme that activates/deactivates protein by phosphorylating them
3. response ; cytoplasmic or nuclear
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epinephrine STP MOA
-epinephrine is both a hormone and a neurotransmitter
1. epinephrine binds to a G protein-coupled receptor
2. GTP binds to G protein to activate it
3. adenylyl converts ATP to cAMP
4. second messenger protein kinase A
5. cellular response
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ligand-gates ion channel receptor
membrane receptor with region that acts as a gate for specific ions --> ligand binding to receptors controls gate that either opens or closes
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Receptor tyrosine kinase
relays the message by activating protein kinases (enzymes that transfer phosphate from ATP to a particular intracellular protein)
- binding of 1 ligands can trigger multiple pathways at once
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G Protein coupled receptors
these receptors are very common
-G protein: GTP-binding protein, inactivate when bound to GDP
- GPCR pathways use 1 of 2 enzymes, which "turn on" 1 of 2 secondary messengers
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GPCR enzymes and 2nd messenger pairs
- Adenylyl Cyclase/ cAMP
- Phospholipase C/ IP3 and DAG
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GPCR adrenaline response - Phospholipase and alpha receptor
-Phospolipase C cleaves PIP into IP3 and DAG -->> Ca2+ release ->> smooth muscle contraction, glycogenolysis
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GPCR adrenaline response- Adenyl cyclase and alpha receptor
blocks adenyl cyclase from producing cAMP and releases calcium ->> inhibition of noradrenaline release and smooth muscle contraction
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GPCR adrenaline response- adenyl cyclase and beta receptor
produces cAMP ->> contraction of cardiac muscle, smooth muscle relaxation, glycogenolysis
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G protein couple receptors MOA
1. binding of extra cellular messenger to receptor activates a G protein, the subunit of which shuttles to and activates adenylyl cyclase
2. Adenylyl cyclase converts ATP to cAMP
3. cAMP activates protein kinase A
4. protein kinase A phosphorylates inactive designated protein, activating it
5. active designated protein brings about desired response
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hormone general MOA
general MOA = (1) change in membrane potential (2) alteration in the levels of intracellular "second messenger" molecules (3) activates catalytic activity (4) direct gene action
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hormone general pathway
hormones...
(1) are released from an endocrine cell
(2) travel through the bloodstream
(3) enter interstitial fluid
(4) interact with specific receptors in/on a cell
(5) cause a physiological response/responses via STPs
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Receptor/Ligand
the type and location of a receptor matches the chemical properties of its ligand (the hormone)
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Water-soluble (hydrophilic) hormone
-peptides
-bind to receptors on cell surface
-initiates a signal transduction pathway
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lipid-soluble (hydrophobic) hormone
-steriods
-bind to intracellular receptor
-signal-receptor complex often directly involved in gene regulation
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amines (amino-acid derived) hormone
-hydrophilic or hydrophobic
-depends on the specific molecule
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Hydrophilic hormone (water soluble) examples
all hypothalamic hormones, all pituitary hormones, epinephrine, insulin, glucagon, leptin, ghrelin, growth hormone, parathyroid hormone, insulin like growth factor, atrial natriuretic peptide
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lipophilic hormone (lipid soluble) examples
adrenal cortex hormones, major gonadal hormones, estrogens (estradiol, estrone, estriol), progesterone, testosterone, aldosterone, cortisol, thyroid hormone
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a single hormone can have different effects on different tissues
due to..
1. same receptors but different intracellular proteins
2. different receptors
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Example of same receptors, different intracellular proteins
Epinephrine causes liver cells to break down glycogen so glucose can be released
epinephrine causes skeletal muscles in the blood vessels to cause vessel dilation
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Example of different receptors
Epinephrine causes vessel dilation with beta receptors in skeletal muscle blood vessels
epinephrine causes vessel constriction with alpha receptors in intestinal blood vessels
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calcium
calcium functions as an important second messenger in several tissues
-roles include altering intracellular charge, activating regulatory proteins, and triggering secretory vesicle exocytosis
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cellular cytoplasmic response in STP
-regulates enzyme activity
-ex: in liver cells, epinephrine activates enzyme glycogen phosphorylase that breaks down glycogen to glucose
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cellular nuclear response in STP
- regulates the synthesis of enzymes or other proteins (up/down regulation genes)
-the final activated molecule in the signaling pathway may function as a transcription factor
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endocrine stimulus
-an agent that causes a change in the activity of a hormone secreting cell
- 3 different types of immediate stimuli
(a) humoral stimulus
(b) neural stimulus
(c) hormonal stimulus
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humoral stimulus on endocrine cell
changes in extracellular fluids such as blood or the ion concentration in the blood
-example: calcium levels falling or rising
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neural stimulus on endocrine cell
based on environmental factors such as fear, surprise, stress
-example: upon receiving a "stress" signal, the hypothalamus stimulates the nerve that innervates the adrenals. epinephrine is released from the adrenal medulla
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hormonal stimulus on endocrine cell
-often involve a hormone cascade involving multiple endocrine glands/tissues and different hormones
-example: thyroid hormone levels drop
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synergistic hormones
enhance similar physiological responses (epinephrine and cortisol)
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antagonistic hormones
oppose each other's actions (insulin and glucagon, parathyroid hormone and calcitonin)
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Anterior v Posterior Pituitary
The anterior and posterior pituitary are separate and distinct structures and have different connections to the hypothalamus
SAME: both secrete hormones to systemic circulation
POSTERIOR: is an extension of the hypothalamus -- axons from neurons that end in the PP --> secrete neurohormones
ANTERIOR: true endocrine tissue (epithelial). endocrine cells that produce and secrete hormones
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Posterior Pituitary Hormones
- made in the hypothalamus (all water soluble)
- stored and released into general circulation by PP
1. ADH; antidiuretic hormone (vasopressin) --> enhances water reabsorption in kidneys
2. Oxytocin; stimulates uterine contractions and release of milk
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Hypothalamic-Posterior Pituitary Step
1 step: neurohormone --> system target
-PP functions in storage of ADH and Oxytocin and providing connection to blood stream
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Hypothalamic-Anterior Pituitary Step
2 steps: neurohormone --> AP cells --> system target
- AP is endocrine and produces its own hormones
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Non tropic v tropic hormones
Non-tropic hormones are hormones that directly stimulate target cells to induce effects. This differs from the tropic hormones, which act on another endocrine gland. Non-tropic hormones are those that act directly on targeted tissues or cells, and not on other endocrine gland to stimulate release of other hormones.
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tropic hormones pathways
1. hypothalamus is stimulated to secrete a (neuro) hormone
2. hypothalamic hormone stimulates (or inhibits) secretion of AP (tropic) hormone
3. AP hormone's target tissue is an endocrine gland and stimulates secretion of another hormone
- negative feedback turns off response loop at different levels
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Absorptive state
- after a meal
-major energy source: glucose
-excess nutrients are stored as glycogen or triglycerides
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postabsorptive state
-between meals/fasting
-major energy source: energy stores
-fatty acids are the major energy source for most tissues
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factors that increase blood glucose
- glucose absorption from digestive tract
-hepatic glucose production through ... (a) through glycogenolysis of stored glycogen (b) through gluconeogenesis
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factors that decrease blood glucose
-transport of glucose of cells for... (a) for utilization for energy production (b) for storage as glycogen through glycogenesis or as triglycerides
-urinary excretion of glucose (abnormal, if very high blood glucose levels)
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blood glucose homeostasis hormones
-regulated by antagonistic hormones insulin and glucagon
SAME ; both are protein hormones and are produced in pancreas by islets of langerhans
DIFF; alpha cells secrete glucagon, beta cells secrete insulin
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Insulin effects (summary)
- decrease in blood glucose
- decrease in blood fatty acids
-decrease in blood amino acids
-increase in protein synthesis
-increase in fuel storage
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insulin effects
- promotes the uptake of glucose from blood into target cells (most cells)
-promotes conversion of glucose into glycogen (liver, muscle)
- promotes uptake of some amino acids, increases protein synthesis (muscle)
-promotes uptake of glucose, fatty acid conversion into triglycerides, blocks lipolysis (adipose)
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too high blood glucose homeostasis
blood glucose levels rise --> beta cells of pancreas release insulin into the blood --> body cells take up more glucose + liver takes up glucose and stores it as glycogen --> glucose in the blood declines --> homeostasis
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insulin receptor
uptake of glucose is promoted by insulin through the activation of Tyrosine Kinase Receptors
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too low blood glucose homeostasis
decreased blood glucose (hypoglycemia) --> alpha cells of pancreas release glucagon --> liver promotes glycogenolysis + gluconeogenesis --> glucose levels increase
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glucagon effects
- stimulates gluconeogenesis (liver)
-stimulates glycogen, protein, and/or lipid breakdown (liver, muscle, adipose)
-activation of a variety of enzymes involved in both processes through Adenylyl Cyclase activation
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blood glucose synergistic hormones
- when hormones have synergistic interactions, the effects of interacting hormones is more than additive
-glucagon + epinephrine + cortisol = highhh increase in blood glucose
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permissive hormones
Permissive function of hormones means one hormone exterts its full effect only in the presence of other hormone
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short term stress
-adrenal medulla hormones
-epinephrine and norepinephrine
-responds to nerve impulses from hypothalamus
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long term stress
-adrenal cortex hormones (Corticosteriods)
-glucocorticoids (cortisol)
and mineralocorticoids (aldosterone; salt/water balance)
- responds to endocrine signals (tropic hormones)
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stress response -- epinephrine + norepinephrine
-glycogen broken down to glucose
-increased blood pressure
-increased breathing rate
-increased metabolic rate
-changed in blood flow patterns, leading to increased alterness and decreased digestive, excretory, and reproductive system activity
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stress response -- glucocorticoids
-proteins and fats broken down and converted to glucose, leading to increased blood glucose
-possible suppression of immune system
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cortisol secretion + cascade pathway
1. a stimulus (like a stressful event) causes hypothalamus to secrete corticotropin-releasing hormone (CRH)
2. CRH stimulates anterior pituitary to secrete Adrenocorticotropic hormone (ACTH)
3. ACTH stimulates adrenal cortex to secrete cortisol
4. negative feedback: cortisol inhibits hypothalamus from secreting CRH and anterior pituitary from secreting ACTH
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epinephrine secretion
`1. upon receiving a "stress" signal, the hypothalamus stimulates the nerve that innervates the adrenals
2. epinephrine and norepinephrine is released from the adrenal medulla
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epinephrine MOA on liver cells
1. epinephrine binds to receptor
2. activation of G protein
3. adenylyl cyclase catalyzes formation cAMP (2nd messenger)
4. activation of protein kinase A
5. activation of phosphorylase kinase
6. activation of a glycogen phosphorylase
7. production of glucose from breakdown of glycogen
8. glucose leaves cell to bloodstream
100
Renin-Angiotensin-Aldosterone; Vasopressin
Conserve salt and H2O to expand the plasma volume; help sustain blood pressure when acute loss of plasma volume occurs
-Angiotensin II and vasopressin cause arteriolar vasoconstriction to increase blood pressure
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osmoregulation
regulation of water volume and ion (salt) concentration
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summary of excretory system steps
1. absorption
2. filtration
3. reabsorption
4. secretion
5. excretion
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step 1. absorption
movement of water and nutrients into body fluids from the gut tube
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step 2. filtration
formation of filtrate by the non-discriminate removal of water, nutrients, and wastes small enough to fit through a sieve-like filter
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step 3. reabsorption
movement of water and nutrients back into the body fluids across transport epithelium from the filtrate. water is reabsorbed by diffusion to regions of higher solute concentration; reabsorption of additional water can be regulated through the amount of salts that are reabsorbed because water follows solutes
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step 4. secretion
active movement of wastes (toxins and other unwanted solutes) from body fluid into the filtrate
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step 5. excretion
movement of nitrogenous metabolites (urea and other wastes) out of the body. urine is what remains of the filtrate after secretion and reabsorption is complete; often stored in the bladder before excretion
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renal artery
blood to kidney
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renal vein
blood from kidney
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ureter
urine exits the bladder
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urinary bladder
stores urine
112
urethra
empties bladder to outside
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two types of nephrons within the kidney
1. cortical nephron
2. medullary nephron
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cortical nephron
bulk of the nephron stays within outer cortical region; very short loop of hence
-contains all Bowman's capsules, proximal and distal tubules
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medullary nephron
while glomerulus may be in cortical region, has long loop of hence and associated vasculature that dips well into the medullary region
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glomerulus
capillaries in Bowman's capsule. filters a protein free plasma into the tubular component
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Afferent arteriole
supplies nephron with blood; carries blood to the glomerulus
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efferent arteriole
carries blood exiting glomerulus
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peritubular capillaries
surrounds proximal and distal tubules. supply the renal tissue; involved in exchanges with the fluid in lumen
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vasa recta
vasculature that surround loop of hence
-300 mOsm blood in vasa recta gains salts from ascending limb
-higher osmolarity of vasa recta draws water in by osmosis in descending limb
-this dilutes blood osmolarity returning it to 300mOsm
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Bowman's capsule
collects glomerular filtrate
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proximal tubule
uncontrolled reabsorption and secretion of selected substances occur here
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loop of henle
establishes osmotic gradient in renal medulla that is important in the kidney's ability to produce urine of varying concentration
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distal tubule and collecting duct
variable, controlled reabsorption of Na+ and H2O and secretion of K+ and H+ occur are; fluid leaving collecting duct is urine, which enters renal pelvis
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step 2. glomerular filtration (detail)
- blood enters Bowman's capsule via afferent arterioles and forms a leaky capillary network called the Glomerulus at high pressure
-pressure forces water, wastes. salts, nutrients out of the glomerulus and into the capsule surrounding them forming filtrate
126
step 3. tubular reabsorption (detail)
- filtrate moves from the bowman's capsule into and through the renal tubules
-efferent arterioles leaving Bowman's capsule form a second capillary network
- peritubular capillaries; form around the proximal and distal convoluted tubules
- vasa recta; forms around the loop of hence such that the direction of blood flow is opposite that of the filtrate flow
- water, nutrients, ions, and some wastes are reabsorbed back into the blood stream
- NaCl, H2O, HCO3, glucose, amino acids, K+ by active or passive transport
127
step 4. tubular secretion (detail)
-substances are actively secreted into the tubules from the blood
-certain drugs not initially filtered
-wastes that have been reabsorbed
-K+ and H+ (regulate pH)
-transport epithelium cells secrete H+ into lumen
-ammonia secreted to buffer acid in filtrate
-transport epithelium cells secrete toxins processed from filter
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renal corpuscle
bowman's capsule + glomerulus
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3 filtration barriers
1. glomerulus endothelium
2. basement membrane
3. Bowman's capsule epithelium
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the filtration fraction
plasma volume entering afferent arteriole = 100% --> 20% of volume passes through the glomerulus filtered --> 19% of fluid is reabsorbed and 1% is excreted
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3 filtration pressures
filtration is driven by glomerular capillary blood pressure but opposed by colloid osmotic pressure and hydrostatic pressure
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glomerular filtration rate (GFR)
net filtration pressure * filtration coefficient
= filtration coefficient is dependent on surface area of glomerular capillaries and permeability between capillaries and Bowman' capillary
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reabsorption barriers
1. the luminal cell membrane
2. the cytosol
3. the basolateral cell membrane
4. the interstitial fluid
5. the capillary fluid
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a ride through the nephron
(a) filtration at renal corpuscle
(b) proximal tubule: reabsorption
(c) proximal tubule: secretion
(d) descending loop of hence: reabsorption of water
(e) ascending loop of hence: reabsorption of NaCl
(f) distal tubule: filtrate processing/ fine tuning
(g) collecting duct: final filtrate processing
(h) micturition: the excretion of urine
135
descending loop of henle
Reabsorption of water
- several aquaporin channels
-very permeable to water
-impermeable to salt/solutes
-reduces volume of filtrate which increases osmolarity of filtrate
-filtrate becomes more concentrated as water is reabsorbed (becomes hyper osmotic)
136
ascending loop of henle
Reabsorption of NaCl
-transport epithelium impermeable to water, permeable to NaCl
- thin segment: NaCl diffuses out into interstitial fluid
- Thick segment: NaCl actively transported out
-filtrate becomes more dilute
-contributes to osmolarity of interstitial fluid in nephron medulla
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distal tubule: filtrate processing
regulation of K+, NaCl, and pH
-K+ and H+ secreted
-NaC; and HCO3 reabsorbed
- water follows
-regulated by hormones
-solutes and water move into peritubular capillaries
-filtrate is isosmotic to blood
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collecting duct: final filtrate processing
regulation of urine concentration
- when concentrating urine: aquaporins; permeable to water, impermeable to NaCl
-when diluting urine: NaCl actively transported out of filtrate, impermeable to water
-urea contributes to solute concentration gradient in nephron (loop of henle)
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plasma clearance
the volume of plasma that is completely cleared of a substance by the kidneys per minute. this expresses the kidneys' effectiveness in removing substances from the ECF
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plamsa clearance equation
clearance = (urine concentration)(urine flow)/plasma concentration of the substance
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countercurrent exchanger
blood in the Vasa Recta flows in the opposite direction as the ascending and descending limbs of the hoop of Henle. The opposite flow of filtrate and blood helps maintain the osmotic concentration gradient. As blood flows down the ascending limb, it picks up salts and carries them deep into the medulla. As blood flows up the descending limb, it picks up water which it carries out of the medulla
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vasopressin
-release prevented by low osmolarity and high ECF volume
-mediates insertion of aquaporin in epithelial cells
-allows for reabsorption of water from tubules
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Renin-Angiotensin-Aldosterone System effects
-release of renin stimulated by drop in blood pressure or volume
- leads to increase sodium reabsorption, increased arteriole vasoconstriction, thirst, and increased vasopressin release
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atrial natriuretic peptide
-release stimulated by high blood pressure, when mycordial cells stretch beyond set point
-mediates decrease in blood pressure
-effects kidney, hypothalamus, sympathetic nervous system, adrenal
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atrial natriuretic peptide effects (detail)
- post glomerular vasoconstriction increases NFP and GFR
-peripheral vasodilation
-inhibits Na+ reabsorption in renal tubules
-antagonizes effect of ADH in collecting duct
-inhibits renin secretion
-inhibits aldosterone secretion
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countercurrent multiplier
A positive feedback mechanism is established between the ascending and descending limbs which establishes the high osmotic gradient in the medulla of the kidney
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countercurrent multiple (details)
- at the top of the ascending limb, salt actively pumped out causes the osmolarity of the extracellular space to drop to 500
-water on the opposing descending limb leaves to the extracellular space until the filtrate becomes 500
-the 500 mOsm filtrate move around the loop to the ascending limb
-active pumping of salt builds on the previous gradient making the extracellular space 700 mOsm
- water on the opposing descending limb leaves to the extracellular space until the filtrate becomes 700
-continue this process until the osmolarity of the deep medulla is 1100 mOsm
-urea in the collecting duct is very concentrated and is able to diffuse down its concentration ration gradient only in the deep medulla. as it does so it contributes to the osmolarity there, helping it to achieve the 1200 mOsm of the normal healthy kidney
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transport epithelia
specialized epithelial cells that regulate solute concentration in interstitial fluid
- transport specific solutes in specific directions
-solutes move via membrane transport proteins or paracellularly
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Fixed rate of reabsorption
location and rate depends on the type and number of transport proteins
-fixed rate of reabsorption (no regulation) ; fixed number of transporters determines transport maximum
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hydrostatic pressure
lower hydrostatic pressure in peritubular capillaries results in net reabsorption of interstitial fluid
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the active reabsorption of sodium is the primary driving force for most renal reabsorption
1. Na+ enters cell through various membrane proteins, moving down its electrochemical gradient
2. Na+ is pumped out the basolateral side of cell by the Na+-K+-ATPase
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Reabsorption of glucose (and other solutes) is driven by sodium reabsorption
1. Na+ moving down its electrochemical gradient uses the SGLT protein to pull glucose into the cell against its concentration gradient
2. Glucose diffuses out the basolateral side of the cell using the GLUT protein
3. Na+ is pumped out by the Na+-K+-ATPase
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secretion
secretion is an active process because it requires moving solutes against their concentration gradients
154
regulation of sodium reabsorption in the collecting duct
reabsorption of sodium in collecting duct is regulated by hormonal mediation of pumps and transporters
-synthesis of Na+ channels and Na-K-ATPase mediates sodium reabsorption and water reabsorption
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Factors affecting the osmotic gradient of interstitial fluid
1. NaCl is actively transported out of distal tubule resulting in...
2. Osmotic water reabsorption from upper tubules (in cortex and outer medulla)
3. urea freely moves from areas of high concentration (collecting duct)
4. NaCl diffuses out of thin portion of the ascending limb and is actively transported out of the thick portion, raising the osmolarity of the inner medulla. this results in...
5. water reabsorption from the descending limb and collecting duct. the urine at the bottom of the loop of henle is very concentrated
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Aldosterone
-regulated gene transcription of Na+ and K+ ion channels and pumps
-results in more Na+ from lumen --> ISF
-causes distal tubules and collecting duct to reabsorb more H2O, increasing blood pressure and volume
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Aldosterone MOA
1. Aldosterone combines with a cytoplasmic receptor
2. hormone-receptor complex initiates transcription in the nucleus
3. translation and protein synthesis makes new protein channels and pumps
4. aldosterone-induced proteins modulate existing channels and pumps
5. result in increased Na+ reabsorption and K+ secretion
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Juxtaglomerular Apparatus
the juxtaglomerular apparatus contains three cell types which assist in regulating renal activity
(1) Juxtaglomerular cells
(2) macula densa
(3) mesangial cells
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juxtaglomerular cells
stretch receptors (baroreceptors) and chemoreceptors which secrete the hormone renin
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macula densa
secrete unidentified signaling molecules which regulates glomerular filtration rate
-signal to juxtaglomerular cells to secrete renin
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mesangial cells
-contractile cells which can alter the size (surface area) of the filtration membrane
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renin-angiotensin hormone cascade start
renin is secreted by the juxtaglomerular cells in response to...
(1) decreased blood pressure in the afferent arterioles
(2) sympathetic stimulation of the afferent arteriole
(3) signals from macula dense cells (due to decreased NaCl concentration)
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renin-angiotensin hormone cascade
angiotensinogen --> renin--> angiotensin I --> angiotensin II --> ADH (stimulate the collecting duct to reabsorb more water) + Aldosterone (stimulates the DCT to reabsorb more Na+ and therefore water) + systemic vasoconstriction, thirst centers in the hypothalamus, causes mesangial cells to contract decreasing the surface area for GFR
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diagrams to look at
look at diagrams from page 44 and after in lecture 9
(last diagram is integrated systems)
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Alcohol effects on the renal system
-alcohol inhibits secretion of ADH (vasopressin) by posterior pituitary
-with maximal vasopressin, the collecting duct is freely permeable to water. water leaves by osmosis and is carried away by the vasa recta capillaries. urine is concentrated
-in the absence of vasopressin, the collecting duct is impermeable to water and urine is dilute
