Lecture 4 Flashcards
What 3 things have to happen stimultaneously in order for micturition (urination) to occur ?
- Detrusor muscles must contract
- Internal urethral sphincter must open (autonomic NS)
-
External urethral sphincter must relax to open (voluntary)
- At same level of urogenital diaphragm, which helps external u.s. stay closed
What are the steps of Micturition ?
- 200 ml of urine in bladder
- Distension sensed by stretch receptors in walls
- Triggers visceral reflex arc :
- Impulses travel via affarent nerve fibers to sacral region of spinal cord & efferent to bladder via Parasympathetic pelvic nerves - Detrusor muscle contracts + pulls internal sphincter open→ Urine enters through internal sphincter into upper part of urethra
- Affarent signals to brain ; one feels urge to pee / void
- External sphincter opens under voluntary control (affarent impulses decrease somatic efferent motor nerve activity that usu keep it closed)
- External sphincter relaxes to empty bladder
- only 10 ml of urine will remain - Reflex subsides in 1 min (occurs again as urine accumulates to keep reminding you, urge to void becomes greater & greater)
- Micturition usu occurs before urine volume exceeds 400 ml
Renal is ___________________ nerves but micturition is ___________________ nerves
sympa, parasympathetic
At age 2/3, reflexive urination can be overridden by matured higher-brain centers in the pons :
Bladder fullness –> Stretch receptors –> Affarent impulses to pons & higher-brain centers
- Pontine storage center inhibits micturition (usu activated by lower bladder voolumes)
- Pontine micturition center promotes micturition reflex
PMC promotes micturition by acting on all 3 spinal efferent reflexes :
1. ↑ paralympic activity
2. ↓ sympa activity
– detrusor muscles contract to open internal urethral sphincter –
- ↓ somatic motor activity
– external urethral sphincter opens –
PMC inhibits micturition by acting on all 3 spinal efferent reflexes :
1. ↓ paralympic activity
2. ↑ sympa activity
3. ↑ somatic motor nerve activity
What is urinary incontinence ?
Inability to control micturition voluntarily
- Weakened pelvic floor muscles
- Pregnancy (↑ pressure, decreased bladder space from bigger uterus carrying baby)
- NS problems
What is stress incontinence ?
Pee your pants when you cough, sneeze or laugh
- Sudden ↑ in intra-abdominal P pushes down on bladder, causing external urethral sphincter supported by urogenital diaphragm to open if weak
What is renal failure ?
Not enough functioning nephrons –> Causing reduced / stopped filtrate formation
- Nitrogenous wastes accumulate, blood becomes acidic –> diarrhea, vomiting, edema, labored breathing, cardiac irregularities (acid-base imbalances), convulsions, coma, death
- May present with anemia due to lack of EPO
Dialysis needed once apparent symptoms + renal functioning below 25 %
Causes of Renal Failure
- repeated damaging kidney infections
- phys damage
- prolonged pressure on skel muscles (creatinine clogs up filtration membranes)
- inadequate blood flow to kidney tubules (BP too low for NFP)
Hemodyalysis
can be done @ home or clinic, several x per week for 3 - 5 hr / session
- Blood coomes out of body, filtered outside, returned w/ correct osmolarity
- Allows blood to equilibrate w/ surrounding fluid / right conc of solutes
Peritoneal Dialysis
Works by using blood vessels / cap beds of peritoneal membrane of abdominal cavity
does NOT require weekly hospital visits, can be done more frequently
- Dialysate (composed of mostly salts, sugar) infused into peritoneal cavity through catheter to encourage filtration through peritoneum
- Extra fluid + wastes drawn from blood into dialysate, which is then removed
- Blood equilibrates itself
2 types of peritoneal dialysis
-
Continuous Ambulatory Peritoneal Dialysis (CAPD) : usu 4-5x / day
- Dialysate stays in peritoneal cavity for 4-5 h before drained back into bag, thrown away -
Continuous Cycling Peritoneal Dialysis (CCPD) : usu done @ home w/ cycler machine
- Similar to CAPD, except umber of cycles / exchanges occur
- Each cycle lasts 1-2 h
- Exchanges done during the night while patient sleeps
What are the body’s fluid compartments ?
a) Intracellular Fluid Compartment (ICF) –> within cells, 60 %
b) Extracellular Fluid Compartment (ECF) –> outside cells, 40 %
- Plasma – fluid portion of blood [ all we can monitor ]
- Interstitial Fluid (IF) – fluid in-between tissue cells
- other : lymphatic fluid, cerebrospinal fluid, eye fluid, GI fluids, etc
Why do electrolytes have greater osmotic power than non-electrolytes ?
Electrolytes dissociate into their component ions when dissolved in water, so they will be contributing more solute particles into the solution & consequently have a greater effect on osmotic P / mass vs compounds that do NOT dissociate in water (eg. glucose is a non-electrolyte), since those have covalent bonds that prevent that & don’t possess e- charges to conduct a current
Chief cations & anions
ECF
Cation – Sodium, Na
Anion – Chloride, Cl
ICF
Cation – Potassium, K
Anion – Phosphate, PO
Na & K opposite, ATP-dependent Na/K pumps keep intracellular [Na+] low (pump Na out) & maintain high intracellular [K+] (allow it to come in)
Changes in ______________________________ in blood plasma will affect intracellular fluid _____________
solute concentrations, volumes
Water Balance
water intake MUST = water output
water intake : liquids, foods ,cellular metabolism (rxns that gen H2O like dehydration synthesis)
water output : 60 % urine, lungs (expired air), skin (insensible water loss –> don’t control), sweat, feces
Water Balance Mechanisms – Increased plasma osmolality
- Thirst – ↑ water intake
- ADH stims renal water reabsorption (lose less water in urine)
Water Balance Mechanisms – Decreased plasma osmolality
Thirst & ADH secretion NOT STIMULATED
How is the thirst mechanism stimulated ?
-
Osmoreceptors – Hypetonic ECF detected through changes in plasma membrane stretch
- ↑ In plasma osmolality of 1-2 % causes dry mouth + ↓ salivation - ↓ in BV (or BP) from phys activity, blood loss, etc – Triggers thirst mechanism through detection by baroreceptors & angiotesin II
Thirst mechanism dampened once ____________________________________________________________
mucosa of mouth + throat moistened (prevents overdrinking while H2O moves to ECF)
Sources of Obligatory Water Losses
- insensible water loss via lungs / skin
- feces
- minimal sensible urinary loss = 500 ml / day (to get rid of waste, pulled back as much H2O as possible)
Disorders of Water Balance
- Dehydration – only fluid loss OR loss of fluids + salts
- Hypotonic hydration (overhydration) – dilutes out Na in ECF / loss of osmolality, causing H2O to move into cells TOO QUICKLY
- Edema – accumulation of fluid (incl. salts) in IF but not INSIDE cells, causing inc. P in tissues
Salt content of the body varies due to …
diet, sweating, feces, vomiting, etc
____________ follows ____________ if aquaporins are open
Water / H2O follows salt / Na if aquaporins are open because it follows the osmotic gradient
What constitutes 90 - 95 % of all solutes in the ECF ?
NaCl & NaHCO3
(contribute 280 / 300 mOsm total solute conc of ECF)
Na+ has the primary role in … ?
Controlling ECF volume through plasma osmolality & determining water distribution in the body (and in turn, blood volume)
While Na+ content in the body changes, why does its conc remain relatively stable in the ECF ?
due to immediate adjustments in volume of water
eg. After consuming a salty meal –> initial ↑Na in ECF –> balanced out by ↑H2O coming out of cells by osmosis –> overall ECF volume ↑ (even if fluids are not ingested) –> ↑ BP, which prompts the feeling of thirst –> encourages water intake to dilute overall Na content in body
What are the 3 factors influencing Na+ balance ?
Aldosterone, ADH, ANP
What are the effects of Aldosterone on Na+ balance ?
secreted by adrenal cortex, most influential at kidneys
SLOW effects… but ESSENTIAL TO LIFE by
↑BV / BP by targeting kidney tubules to enhance Na+ reabsorption & reduce blood K+ concentrations
When aldosterone secretion is high : virtually ALL the remaining filtered Na+ is actively reabsorbed in the DCT / CD
When aldosterone secretion is low : virtually NO Na+ reabsorpyion occurring beyond DCT
What are the 2 pathways of Aldosterone secretion ?
- Renin-angiotensin system : Renin will be secreted by granular cells in response to sympathetic NS stimulation, ↓ filtrate osmolarity or ↓ stretch (decreased BP) to catalyze angiotensinogen into angiotensin I (later will become angiotensin II)
- Direct effect of high K+ or low Na+
What is Addison’s Disease ?
Autoimmune condition, causing hyposecretionn of aldosterone, which results in an excess loss of NaCl & H2O in urine
What are the effects of ADH on Na+ / H2O balance ?
What are the effects of ANP on Na+ balance ?
What other hormones are involved in Na+ balance ?
What are the effects of cardiovascular baroreceptors on Na+ balance ?
