Endocrine system and nutrition; Nutrition and endocrine system
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Transcript of 1 Review slides Lecture Exam 3. 2 Overview of the Endocrine System The endocrine system consists of...
1
Review slides
Lecture Exam 3
2
Overview of the Endocrine SystemThe endocrine system consists of
- collections of cells located in tissues scattered throughout the body
- that produce substances released into the blood (hormones)
- to ultimately affect the activity and metabolism of target cells.
Secrete into Affect activity
Endocrine glands Blood Inside cells
Exocrine glands Ducts or on to free surface Outside cells
3
Classification of Hormones
Hormones
Eicosanoids (cell membranes)(locally acting)
Steroids (cholesterol-derived)
Amino Acid Derivatives
Amino acids
Peptides
Proteins, glycoproteins
Lipid Derived
4
Actions of Steroid Hormones• hormone crosses membranes
• hormone combines with receptor in nucleus or cytoplasm
• synthesis of mRNA activated
• mRNA enters cytoplasm to direct synthesis of protein, e.g., aldosterone->Na/K Pump
Magnitude of cellular response proportional to the number of hormone-receptor complexes formed
(Thyroid hormone has a similar mechanism of action, even though it is a tyrosine derivative)
5
Actions of Amino Acid-Derived Hormones
• adenylate cyclase activated
• ATP converted to cAMP
• cAMP (second messenger) promotes a series of reactions leading to cellular changes
Magnitude of response is not directly proportional to the number of hormone-receptor complexes – it’s amplified
• hormone (first messenger) binds to receptor on cell membrane
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Control of Hormonal Secretions
• primarily controlled by negative feedback mechanism
1) Hormonal 2) Neural 3) Humoral
Control mechanisms for hormone release
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Target Cell Activation By Hormones
• Target cells must have specific receptors to be activated by hormones
• Magnitude of target cell activation depends upon– Blood levels of the hormone
• Rate of release from producing organ
• Rate of degradation (target cells, kidney, liver)
• Half-life
– Relative numbers of receptors for the hormone
• Cellular receptors can be up- or down-regulated
– Affinity (strength) of binding of the hormone to its receptor
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Pituitary Gland Control• Hypothalamic releasing hormones stimulate cells of anterior pituitary (adenohypophysis) to release their hormones
• Nerve impulses from hypothalamus stimulate nerve endings in the posterior pituitary (neurohypophysis) gland to release its hormones
Note the hypophyseal portal system of the adenohypophysis (two capillaries in series)
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Hormones of the Anterior Pituitary (SeT GAP)
Tropic hormones control the activity of other endocrine glands
All anterior pituitary hormones use second messengers
(an ‘axis’)
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Overview of the Pituitary Hormones
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
All anterior and posterior pituitary hormones bind to membrane receptors and use 2nd messengers (cAMP)
SeT GAP
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Hormone Summary Table I – Pituitary HormonesTissue
Name Origin Destination Action on Target Tissue Control of Release1
FOLLICLE STIMULATING
HORMONE (FSH)
anterior pituitary
males: semiiferous tubules of testes;females: ovarian
follicle
males: sperm productionfemales: follicle/ovum maturation
Gonadotropin Releasing Hormone (GnRH)
LUETINIZING HORMONE (LH)
anterior pituitary
In males: interstitial cells in
testes;in females: mature
ovarian follicle
males: testosterone secretionfemales: ovulation
Gonadotropin Releasing Hormone (GnRH)
THYROID STIMULATING
HORMONE (TSH)
anterior pituitary
thyroid secrete hormonesThyrotropin Releasing
Hormone (TRH)
GROWTH HORMONE (GH)
anterior pituitary
bone, muscle, fat growth of tissuesGrowth Hormone Rleasing
Hormone (GHRH)
ADRENOCORTICO-TROPIC HORMONE
(ACTH)
anterior pituitary
adrenal cortex secrete adrenal hormonesCorticotropin Releasing
Hormone (CRH)
PROLACTIN (PRL)anterior pituitary
mammary glands produce milkProlactin Releasing Hormone
(PRH)
ANTI-DIURETIC HORMONE (ADH)(VASOPRESSIN)
posterior pituitary
distal convoluted tubule (DCT)
reabsorption of water; increases blood pressure
increase in osmolarity of plasma or a decrease in blood
volume
OXYTOCIN (OT)posterior pituitary
uterine smooth muscle; breast
contraction during labor; milk letdownStretching of uterus; infant
suckling
Se(x)
T
G
A
P
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Hormone Summary Table IITissue
Name Origin Destination Action on Target Tissue Control of Release
TRIIODOTHYRONINE (T3) & THYROXINE
(T4)
Thyroid (follicular cells)
all cells increases rate of metabolism (BMR)Thyroid Stimulating Hormone
(TSH)
CALCITONIN Thyroid (C cells)Intestine, bone,
kidney
Decreases plasma [Ca2+]( intestinal absorp of Ca; action of
osteoclasts; excretion of Ca by kidney plasma [Ca2+]
PARATHYROID HORMONE (PTH)
ParathyroidsIntestine, bone,
kidney
Increases plasma [Ca2+]( intestinal absorp of Ca; action of
osteoclasts; excretion of Ca by kidney plasma [Ca2+]
EPINEPHRINE/NOREPINEPHRINE
(Catecholamines)Adrenal Medulla
cardiac muscle, arteriole and
bronchiole smooth muscle,
diaphragm, etc
increases heart rate and blood pressure...(fight or flight)
Sympathetic Nervous System
ALDOSTERONE(Mineralocorticoids)
Adrenal CortexKidneys; sweat glands; salivary glands; pancreas
reabsorption of water and Na (increases blood pressure) and excretion of K
(mineralocorticoid)
Angiotensin II plasma [Na+] plasma [K+]
CORTISOL(Glucocorticoids)
Adrenal Cortex all cellsDiabetogenic; anti-inflammatory
(glucocorticoid)ACTH
INSULINβ-cells of
Pancreatic Isletsall cells, liver and skeletal muscle
pushes glucose into cells from blood, glycogen formation (decreases blood glucose)
plasma [glucose]SNS
GLUCAGONα-cells of
pancreatic Isletsliver and skeletal
musclebreakdown of glycogen (increase in blood
glucose) plasma [glucose]
TESTOSTERONE Testessecondary sex
organsdevelopment and maintenance LH
ESTROGEN Ovariessecondary sex
organsdevelopment at puberty and maintenance
throughout lifeLH
NATRIURETIC PEPTIDES
atria and ventricles of heart
adrenal cortex, kidneys
increased excretion of sodium and water from kidneys, blood volume, blood pressure
Stretching of atria and ventricles
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Renin-angiotensin Pathway
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Stress
Types of Stress• physical stress• psychological (emotional) stress
(Stress is any condition, physical or emotional, that threatens homeostasis)
Stress Response (General Adaptation Syndrome [GAS])
• hypothalamus triggers sympathetic impulses to various organs• epinephrine is released• cortisol is released to promote longer-term responses
Three general phases of the GAS to stress ARE:
• Alarm phase• Resistance phase• Exhaustion phase
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Responses to StressExhaustion - lipid reserves
- production of glucocorticoids - electrolyte imbalance - damage to vital organs
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Diabetes (= Overflow)• Diabetes Mellitus (DM)
– Hyposecretion or hypoactivity of insulin– Three P’s of Diabetes Mellitus (mellitum = honey)
• Polyuria (increased urination)• Polydipsia (increased thirst)• Polyphagia (increased hunger)
– Hyperglycemia, ketonuria, glycosuria
• Renal Glycosuria– excretion of glucose in the urine in detectable amounts– normal blood glucose concentrations or absence of
hyperglycemia
• Diabetes Insipidus (insipidus = tasteless)– Hyposecretion or hypoactivity of ADH– Polyuria– Polydipsia
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Functions of the Kidneys
• Make urine
• Regulate blood volume and blood pressure
• Regulate plasma concentrations of Na+, K+, Cl-, HCO3
-, and other ions
• Help to stabilize blood pH
• Conserve valuable nutrients
• Assist the liver in detoxification and deamination
18
Anatomical Features of Kidneys
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
Helps maintain position of kidney
Kidneys are retroperitoneal
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Location of Kidneys
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
Located retroperitoneally from T12 to L3
Left kidney is slightly higher than right kidney
Adrenal glands sit on the medial and superior part of kidneys
Nephro(s) = kidney
Pyel(o) = pelvis
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The Nephron
Nephrons are the structural and functional units of the kidney
(80%)
(20%)Vasa recta are associated with juxtamedullary nephrons
Sympathetic nerve fibers from the ANS innervate the kidney
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Blood Flow Through Kidney and Nephron
Know this!
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Renal Corpuscle (Glomerulus + Capsule)
Efferent arteriole is smaller than the afferent arteriole
This creates a high pressure (~55-60 mm Hg) in the glomerular capillary bed
Filtrate in capsular space
Podocytes form the visceral layer of the glomerular capsule. Their pedicels (foot processes) form filtration slits (or slit pores) that function in forming filtrate.
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The Nephron
1. Glomerular capsule
2. PCT – simple cuboidal with a brush border
3. Thin segment of the descending nephron loop - simple squamous epithelium
4. Thick ascending nephron loop - cuboidal/low columnar
5. DCT - simple cuboidal with no microvilli (specialized for secretion, not absorption)
The order of the parts of the nephron is important to know
(PCT)
(DCT)
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Juxtaglomerular Apparatus
Juxtaglomerular cells (JG) - modified smooth muscle cells in the wall of the afferent arteriole that contract (and secrete renin)
Cells of the macula densa (MD) are osmoreceptors responding to solute concentration of filtrate
MD + JG cells = juxtaglomerular apparatus
25
Glomerular Filtrate and Urine Composition
Glomerular filtrate is about the same composition as plasma: H2O, glucose, amino acids, urea, uric acid, creatine, creatinine, Na, Cl, K, HCO3
-, PO43-,
SO42-. But notice how different the composition of urine is. Additionally, note
that protein is not normally present in urine.
(1.8 L/day)
26
Urine Formation
• Glomerular Filtration (GF) *Adds to volume of urine produced• substances move from blood to glomerular capsule
• Tubular Reabsorption (TR) *Subtracts from volume of urine produced
• substances move from renal tubules into blood of peritubular capillaries• glucose, water, urea, proteins, creatine• amino, lactic, citric, and uric acids• phosphate, sulfate, calcium, potassium, and sodium ions
• Tubular Secretion (TS) *Adds to volume of urine produced• substances move from blood of peritubular capillaries into renal tubules• drugs and ions, urea, uric acid, H+
Urine formation = GF + TS - TR
Fluid from plasma passes into the glomerular capsule and becomes filtrate at an average rate of 125 ml/minute. This is known as the Glomerular Filtration Rate (GFR)
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Glomerular Filtration
Glomerular filtrate is plasma that passes through
1) the fenestrae of the capillary endothelium, 2) the basement membrane around the endothelium, and 3) the filtration slits (slit pores) of the pedicels
This is called the ‘filtration membrane’
Glomerular filtration is a mechanical process based primarily on molecule size
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Glomerular Filtration and Urine Formation
Glomerular Filtration Rate (GFR) is directly proportional to the net filtration pressure
GFR 125 ml/min (180 L/day)
Urine output is only 0.6 – 2.5 L per day (an average of about 1.8 L, or about 1% of glomerular filtrate)
Net Filtration Pressure = force favoring filtration – forces opposing filtration (*glomerular capillary ( capsular hydrostatic pressure hydrostatic pressure) + glomerular capillary osmotic pressure )
NFP = HPg – (HPc + OPg)
99% of filtrate is reabsorbed!! * Blood pressure is the most important factor
altering the glomerular hydrostatic pressure (and NFP). A MAP fall of 10% will severely impair glomerular filtration; a fall of 15-20% will stop it.
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Summary of Factors Affecting GFRFactor Effect
Vasoconstriction
Afferent arteriole (Δ radius GFR) GFR
Efferent arteriole (Δ radius 1/GFR) ↑ GFR
Vasodilation
Afferent arteriole ↑ GFR
Efferent arteriole GFR
Increased capillary hydrostatic pressure ↑ GFR
Increased colloid osmotic pressure GFR
Increased capsular hydrostatic pressure GFR
Know this table – it’s important!
30
Three Major Ways of Regulating GFR
1) Autoregulation
– Maintains GFR despite changes in local blood pressure and blood flow (between 90 – 180 mm Hg mean systemic pressure)
– Myogenic (muscular) mechanism – contraction of afferent arteriolar vascular smooth muscle when stretched (increased BP); relaxation occurs when BP declines
– Tubuloglomerular mechanism – MD cells detect flow rate and/or osmolarity of filtrate in DCT -> JG cells contract -> afferent arteriole constricts -> GFR
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Three Major Ways of Regulating GFR
2) Neural (Autonomic) Regulation– Mostly sympathetic postganglionic fibers =
vasoconstriction of afferent arterioles GFR (conserves water, redirects blood to other organs)
– Stimulates juxtaglomerular apparatus to secrete renin– May override autoregulatory mechanism at afferent
arteriole
3) Hormonal Regulation– Renin-angiotensin system – ECF volume and BP– Atrial Natriuretic Peptide (ANP) - ↑ GFR, ↑ fluid loss
(dilates afferent arteriole, constricts efferent arteriole)
32
Renin-Angiotensin System
Renin is released by the juxtaglomerular apparatus due to:
1) Decline of BP (Renin 1/Pressure)
2) Juxtaglomerular stimulation by sympathethic NS
3) Decline in osmotic concentration of tubular fluid at macula densa( Renin 1/[NaCl] )
Stabilizes systemic blood pressure and extracellular fluid volume
(ACE)
Actions of Angiotensin II
33
Tubular Reabsorption in PCT
65% of filtrate volume is reabsorbed in the PCT
8 mm Hg
COP
Tubular fluid
All uric acid, about 50% of urea, and no creatinine is reabsorbed
Tubular reabsorption - reclaiming of substances in filtrate by body (tubule blood)
Peritubular cap: 1) Low hydrostatic pressure 2) High COP 3) High permeability
Renal threshold is the plasma level (concentration) above which a particular solute will appear in urine, e.g., 180 mg/dl
34
Summary of Reabsorption and Secretion
Nephron Loop (of Henle)
Process PCT Descending Ascending DCT Collecting duct
Reabsorption
Glucose, aa, protein,
urea, uric acid, Na+, Cl-, HCO3
-
H2O Na+/Cl-, K+
(NO H2O)
Na+/Cl-
H2OHCO3
-
H2O (only if ADH is present),
urea
Secretion
Creatinine
H+
Some drugs
Urea - H+/K+
NH4+ -
35
Reabsorption in the PCTSubstance Mechanism of
ReabsorptionNotes
Na+ (Cl-) Primary Active Transport Na+ reabsorption is the driving force for most
other reabsorption
H2O Osmosis Closely associated with movement of Na+
(Obligatory water reabsorption)
Glucose Secondary Active transport Limited # of molecules can be handled
(Tm = 375 mg/min); attracts H20
Amino Acids Secondary Active transport Three different active transport modalities; difficult
to overwhelm
Other electrolytes Secondary Active transport
36
Secretion in the PCT and DCTIn the DCT potassium ions or hydrogen ions may be secreted in exchange for reabsorbed sodium ions. Reabsorption of Na+ in the DCT is increased by the hormone, aldosterone.
Other compounds are actively secreted as well, e.g., histamine, ammonia, creatinine, penicillin, phenobarbital.
ActiveActive and Passive
Renal threshold is the plasma level (concentration) above which a particular solute will appear in urine, e.g., 180 mg/dl
37
Summary of Events in the Nephron1. Filtrate produced
2. Reabsorption of 65% of filtrate
3. Obligatory water reabsorption
4. Reabsorption of Na+ and Cl- by active transport (NO H2O reabsorption)
5,6. Facultative reabsorption of water (ADH is needed)
7. Absorption of solutes and water by vasa recta to maintain osmotic gradient
(Aldosterone)
(Aldosterone)
38
The Countercurrent Multiplier
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
The mechanism shown is called the “countercurrent multiplier”
Countercurrent multiplier allows the kidneys to vary the concentration of urine
Vasa recta maintains the osmotic gradient of the renal medulla so the countercurrent multiplier can work
Approximate normal osmolarity of body fluids
Reduced osmolarity of tubular fluid due to action of counter-current multiplier
39
Urea,Uric Acid, and DiureticsUrea
• product of amino acid catabolism• plasma concentration reflects the amount or protein in diet• enters renal tubules through glomerular filtration• 50% reabsorbed• rest is excreted
Uric Acid• product of nucleic acid metabolism• enters renal tubules through glomerular filtration• 100% of filtered uric acid is reabsorbed• 10% secreted and excreted
A diuretic promotes the loss of water in the urine.
Anything that adds more solute to tubular fluid will attract H2O and can function as a diuretic to increase the volume of urine, e.g., glucose (osmotic diuretic)
40
Urine• Urine composition varies depending upon
– Diet– Level of activity
• Major constituents of urine– H2O (95%) – Creatinine (remember, NONE of this is reabsorbed)– Urea (most abundant solute), uric acid– Trace amounts of amino acids– Electrolytes– Urochrome (yellow color), urobilin, trace of bilirubin
• Normal urine output is 0.6-2.5 L/day (25-100 ml/hr)• Output below about 25 ml/hour = kidney failure
(oliguria -> anuria)
41
Terms to know…
• Anuria – absence of urine
• Diuresis – increased production of urine
• Dysuria – difficult or painful urination
• Enuresis – uncontrolled (involuntary) urination
• Glycosuria (glucosuria) – glucose in the urine
• Hematuria – blood in the urine
• Oliguria – scanty output of urine
• Polyuria – excessive urine output
42
Elimination of Urine
• nephrons• collecting ducts• renal papillae• minor and major calyces• renal pelvis• ureters• urinary bladder• urethra• outside world
Flow of Urine
Know this…
43
Ureters and Urinary Bladder
Ureters - retroperitoneal tubes about 25 cm long - carry urine from kidneys to bladder by peristaltic contractions
Urinary bladder (cyst[o]) - temporary storage reservoir for urineSmooth muscular layer runs in all directions (detrusor muscle) under parasympathetic control. Contraction compresses the bladder and causes urine to flow into urethra
Internal sphincter is thickening of detrusor muscle at neck of bladder – closed when detrusor is relaxed; open when detrusor contracts
Urinary elimination system is lined mostly by transitional epithelium
44
Urethra
Note the long male urethra (about 18-20 cm). There are three sections to the male urethra:
- Prostatic urethra - Membranous urethra - Penile urethra
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
Note the short urethra in females (about 4 cm)
45
Micturition (Urination) Reflex
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007
46
Fluid and Body Compartments
‘Compartments’ commonly behave as distinct entities in terms of ion distribution, but ICF and ECF osmotic concentrations (about 290-300 mOsm/L) are identical. This is because H2O is free to flow between compartments and any disturbance in osmolarity is quickly corrected by H2O movement.
About 40 L of fluid (avg. adult male; less in females due to greater proportion of body fat)
25L
15L
Major forces affecting movement of fluid between compartments:
1) Hydrostatic pressure 2) Osmotic pressure
(ICF)
(ECF)
47
Body Fluid Ionic Composition
ECF major ions:
- sodium, chloride, and bicarbonate
ICF major ions:
- potassium, magnesium, and phosphate (plus negatively charged proteins)
You should know these chemical symbols and charges of ions
48
Fluid (Water) Balance
* urine production is the most important regulator of water balance (water in = water out)
Balance; =
49
Major Regulators of H2O Intake and Output
• Regulation of water intake• increase in osmotic pressure of ECF → osmoreceptors in hypothalamic thirst center → stimulates thirst and drinking
• Regulation of water output• Obligatory water losses (must happen)
• insensible water losses (lungs, skin)• water loss in feces• water loss in urine (min about 500 ml/day)
• increase in osmotic pressure of ECF → ADH is released• concentrated urine is excreted• more water is retained
• LARGE changes in blood vol/pressure → Renin and ADH release
50
Dehydration and OverhydrationDehydration
• osmotic pressure increases in extracellular fluids• water moves out of cells• osmoreceptors in hypothalamus stimulated• hypothalamus signals posterior pituitary to release ADH• urine output decreases
Overhydration• osmotic pressure decreases in extracellular fluids• water moves into cells• osmoreceptors inhibited in hypothalamus• hypothalamus signals posterior pituitary to decrease ADH output• urine output increases
‘Drunken’ behavior (water intoxication), confusion, hallucinations, convulsions, coma, death
Severe thirst, wrinkling of skin, fall in plasma volume and decreased blood pressure, circulatory shock, death
51
Osmolarity and Milliequivalents (mEq)
• Recall that osmolarity expresses total solute concentration of a solution (Osmolarity = Amt of solute / Vol of H2O)
– Osmolarity (effect on H2O) of body solutions is determined by the total number of dissolved particles (regardless of where they came from)
– The term ‘osmole’ reflects the number of particles yielded by a particular solute (milliosmole, mOsm, = osmole/1000)
• 1 mole of glucose (180g/mol)• 1 mole of NaCl (58g/mol)
• An equivalent is the positive or negative charge equal to the amount of charge in one mole of H+
– A milliequivalent (mEq) is one-thousandth of an Eq– Used to express the concentration of CHARGED particles in
a solution
-> 1 osmole of particles
-> 2 osmoles of particles
52
Electrolyte BalanceElectrolyte balance is important because:
1. It regulates fluid (water) balance
2. Concentrations of individual electrolytes can affect cellular functions
ElectrolyteNormal plasma
concentration (mEq/L)
Major mechanism(s) regulating retention and loss
Na+ 140 1. Renin-angiotensin pathway2. Aldosterone (Angiontensin II, Na+, K+)3. Natriuretic peptides
Cl- 105 Follows Na+
K+ 4.0 1. Secretion at DCT (aldosterone sensitive)
Ca2+ 5.0 1. Calcitonin (children mainly)2. Parathyroid hormone3. Vitamin D (dietary uptake from intestines)
53
Summary Table of Fluid and Electrolyte Balance
Condition Initial Change Initial Effect Correction Result
Change in OSMOLARITY
(**Corrected by change in H2O levels)
H2O in the ECF
Na+ concentration,
ECF osmolarity
Thirst → H2O intake
ADH → H2O output H2O in the ECF
H2O in the ECF
Na+ concentration,
ECF osmolarity
Thirst → H2O intake
ADH → H2O output H2O in the ECF
Change in VOLUME(**Corrected by change
in Na+ levels)
H2O/Na+ in the ECF volume,
BP
Renin-angiotensin: Thirst ADH
aldosterone vasoconstriction
H2O intake
Na+/H2O reabsorption
H2O loss
H2O/Na+ in the ECF volume,
BP
Natriuretic peptides: Thirst ADH
aldosterone
H2O intake
Na+/H2O reabsorption
H2O loss
You should understand this table
54
Acid/Base Buffers
Buffer Type Speed Eliminate H+ from body?
Examples
Chemical Physical(first line of
defense)
Seconds No Bicarbonate, phoshate, proteins (ICF, plasma proteins, Hb)
Respiratory Physiological Minutes Yes (indirectly as
CO2)
H2O + CO2 H+ + HCO3-
Renal Physiological Hours - Days
Yes H+ excretionHCO3
- excretion/retention*
A buffer resists changes in pH
*Normal plasma [HCO3-] ≈ 25 mEq/L
55
Acidosis and AlkalosisIf the pH of arterial blood drops to 6.8 or rises to 8.0 for more than a few hours, survival is jeopardized
Classified according to:
1. Whether the cause is respiratory (CO2), or metabolic (other acids, bases)
2. Whether the blood pH is acid or alkaline
Respiratory system compensates for metabolic acidosis/alkalosisRenal system compensates for respiratory acidosis/alkalosis