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URINARY SYS - Coggle Diagram

- - - - CHARACT
        
        • Plasma osmolarity = 290 mOsm/L
        • Urine osmolarity reflects the hydration status of the body. The higher the osmolarity, the more concentrated the urine is.
        • Presence of high amount of proteins and glucose in the urine is a pathological finding.
  - - - Urine produced in the collecting duct will drain into the renal pelvis and finally into the ureter.
        
        Urine is actively transported by smooth muscle contractions (peristalsis) to the urinary bladder via ureters.
        • The urinary bladder functions to store urine temporarily before it descends into the urethra.
        • The anatomy of urethra in both sexes differ.
        
        STRETCHABLE
        
        Walls of urinary bladder are made up of smooth muscles layers, containing stretch receptors
        
        The proximal part of urethra is guarded by two types of urinary sphincters
        
        The internal sphincter (IUS) is made of smooth muscle
        
        The external sphincter (EUS) is made of skeletal muscle, part of the pelvic floor muscles
  - - - 3 LEVELS
        
        • spinal cord
        
        Like defecation, micturition is a spinal reflex,
        
        the operating center is located in the spinal column (S2-S4) rather than in the brain.
        
        However the process is facilitated by other regions in the brain.
        
        Contains afferent and efferent autonomic nerves that innervate the urinary bladder and IUS.
        
        • Sympathetic stimulation promotes storage reflex (continence).
        • Parasympathetic stimulation promotes micturition reflex.
        • Control the internal sphincter and urinary bladder.
        
        • pontine micturition center
        
        A group of neurons located in the brain stem that coordinate signals from the cerebral cortex and spinal cord when urination occurs.
        
        It promotes:
        • urinary sphincter relaxation
        • detrusor muscles contraction
        
        This coordination is important because it involves multiple structures in the body and to ensure micturition occurs appropriately without ‘embarrassing accidents’.
        
        • cerebral cortex
        
        Prefrontal cortex contains areas critical for maintaining continence.
        • Receives afferent signals from the bladder (sensations), brings them to conscious attention, and makes decisions whether to void
        • Controls the external sphincter (via pudendal nerve)
        
        • Cerebral cortex makes conscious decision to void or delay micturition.
        • If the decision is to void, signals from the cerebral cortex are relayed to the PMC.
        • The PMC will coordinate:
        --> inhibition of pudendal nerve resulting in relaxation of EUS
        --> maximum contraction of urinary bladder
        • Urine ejection occurs.
    - - • Regular peristaltic contractions (3- 5x/min) move urine from the renal pelvis to the bladder.
        • Normal functional bladder capacity in adults ranges from approx. 300 - 500 ml.
        • Stretch receptors are stimulated as the bladder fills. When the stretch reaches a certain threshold, signals are relayed to the spinal cord.
    - - • When bladder is half-full ~ 200 – 300 ml, we will experience the first sensation to void.
        • Bladder is slightly distended causing low afferent signals to be relayed to the spinal cord.
        • Signal are also relayed to the cerebral cortex.
        
        The sympathetic efferent signals are relayed to the bladder and urinary sphincters, to initiate the storage reflex. The results
        
        The results =
        • relaxation of detrusor muscles so more urine can be stored
        • contraction of IUS to prevent urine from flowing out
    - - The normal sensation to void comes when bladder reaches a threshold volume of 300 – 400 ml.
        • Increased urine vol --> increased bladder distension --> high afferent signals.
        • Signals are relayed to spinal cord and the PMC. This will activate the micturition reflex via the parasympathetic NS.
        
        • Upon activation of parasympathetic system, efferent signals are relayed to bladder and IUS:
        --> contraction of detrusor muscles
        --> relaxation of internal sphincter
        • Urine passes into proximal urethra first. EUS still not open.
        • Signals are also relayed to cerebral cortex so we feel the urge to urinate.
  - - - • If the signal is to delay micturition, signals from the cerebral cortex are relayed to the PMC.
        • PMC will inhibit the parasympathetic stimulation and activate the sympathetic:
        --> relaxation of bladder
        --> contraction of IUS
        --> contraction of EUS
    - - • Spinal cord injuries (S2-S4)
      - • Trauma to urinary sphincters
      - • Childbirth (weak urinary sphincters, pelvic floor muscles)
      - • Old age (loss of muscle tone)
      - • Enlarged prostate
- - - - • About 60% of our total body weight is body fluids.
        • Body fluids = water + dissolved solutes
        
        ELECTROLYTES - Na+, K+, Cl-, Ca2+, Mg2+
        
        non-electrolytes - glucose, urea, creatinine
        
        BALANCE
        
        Body fluid balance is not just about maintaining total volume at all times, but also other aspects:
        
        • osmolarity (290 mOsm/L)
        
        • acid base (7.0 - 7.4)
        
        • ratio between compartments
    - - 70kg adult male
        
        comp
        
        ICF (2/3 TBW) = 28L
        
        ECF (1/3 TBW = 14 L
        
        TBW (60% BW) = 42 L (remain same, follow BW)
    - - Osmolarity is defined as the number of solutes (Na+) per liter of fluid.
        
        Physiologic osmolarity = 290 mOsmol/L
        
        Blood osmolarity
        
        •Number of solutes dissolved in 1 liter of blood.
        •Measured in millimoles per liter (mmol/L).
        
        sodium is responsible for 97% of the blood osmolarity
        P osm = 2 x (Na+) + (glu/18) + (urea/2.8)
        
        Osmolarity reflects the salt-water balance in the blood. Too much water or salt is not good for cell structures and functions.
        --> osmolarity of the blood must be maintained at all times!
        
        DISORDER
        
        HYPONATREMIA - cell dysfunction, confusion, death
        
        HYPERNATREMIA - cellular dehydration, CVS failure, death
        
        REGULATION
        
        Small 1-2% changes in plasma osmolarity are detected by osmoreceptors in the hypothalamus
        --> which stimulates or inhibits ADH release
        
        When referring to body fluid osmolarity, we primarily consider the sodium ion (Na+) in the ECF compartment.
        
        Changes to Na+ content in blood will affect plasma osmolarity and therefore disrupts the osmotic equilibrium between ECF and ICF.
  - - - FX
        
        body fluid balance
        
        BP reg.
        
        acid base balance
        
        waste excretion
        
        vit D prod.
        
        synthesis of erythropoeitin
    - - NEPHRON
        
        Each kidney contains ~ 1 million nephrons.
        
        These nephrons are not replaceable if damaged.
        
        COMP
        
        GLOMERULUS
        
        glomerular capillaries – acting as filter
        
        RENAL TUBULES
        
        filtered fluids become urine
        
        FLOW
        
        GLOMERULUS --> PROXIMAL TUBULE --> LOOP OF HENLE --> DISTAL TUBULE --> COLLECTING DUCT
        
        Urine Formation
        
        The process of urine formation involved three basic processes:
        
        glomerular filtration,
        
        tubular reabsorption, and
        
        tubular secretion.
        - Excretion is the final process in which urine is eliminated from the body (which will be discussed in the Micturition
        
        Reabsorption
        
        As the filtrate flows through the renal tubules, 99% of the water and solutes are reabsorbed into the blood capillaries.
        
        Fluid remaining in renal tubules now becomes urine.
        
        as the filtrate moves through the tubules of the nephron, 99% of the vital substances are reabsorbed by the peritubular capillaries and into the blood, and the remaining becomes urine.
        
        Tubular
        
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    - - Blood enters kidney via renal artery and branches into arterioles --> glomerulus.
        
        ARTERIOLE
        
        AFFERENT - deliver blood to glomerulus for filtration
        
        EFFERENT
        
        • blood exit from glomerulus
        • returns blood to renal veins
      - Renal Nerve Supply
        
        • The kidneys receive only sympathetic innervation from the renal plexus to:
        
        • renal arteries
        
        • afferent arterioles
        
        • juxtaglomerular cells
  - - - For the kidneys to perform effective filtration, the process must possess one important characteristic: ultra-filtration.
      - HOW
        
        Removal of microscopic particles at high pressures via a semi- permeable membrane.
        
        Large molecules and plasma proteins cannot pass through the filtration membrane
        
        COMP OF FILTRATE
        
        The composition of filtrate in Bowman capsule is almost identical to the composition of plasma
        
        EXCEPT, the filtrate has no proteins and cells.
        
        Anything bound to plasma proteins will not be filtered.
        
        High-pressure system
        
        The afferent arteriole is larger than the efferent arteriole, creating a high-pressure system in the glomerulus for efficient filtration process
    - - About 1 L of blood goes into glomeruli each minute.
        
        Of that, 120 ml of plasma ends up as the glomerular filtrate, also known as the primary urine.
      - GFR
        
        the amount of fluid filtered into the Bowman capsule each minute by both kidneys.
        
        GFR in healthy individuals is 120 mL.min-1.
        
        the best test to measure kidney function and determine stages of kidney disease.
        
        Factors determining
        
        • Renal blood flow
        
        Kidneys receive a high blood flow (20% of CO), which is necessary to ensure an efficient filtration process.
        
        High RBF --> increase glomerular blood flow à increase GFR
        
        •Diameter of afferent arteriole
        
        A larger diameter of afferent arteriole compared to efferent arteriole creates a high-pressure system in the glomerulus.
        
        Altering the arteriole diameters will affect GFR.
        
        • Systemic blood pressure
        
        Renal BF is dependent of systemic BP.
        
        If BP decreases, renal BF will decrease.
        
        Renal BF decreases --> GFR
        
        So, any changes in systemic BP will affect GFR,
        and ultimately urine production.
        
        Factors Affecting
        
        Renal autoregulation
        
        Autoregulation maintains GFR at constant rate despite fluctuations in BP.
        
        At MAP ~ 100 mmHg : • GFR 180 L per day = 1.5 L urine
        
        At MAP ~ 125 mmHg : • GFR 225 L per day = 46 L urine
        
        • Tubuloglomerular feedback
        
        important when there is a reduction of filtrate in the tubules.
        
        It involves detection of NaCl concentration in the filtrate in order to normalise GFR.
        
        There is a specialised group of cells that do this – juxtaglomerular apparatus:
        
        • macula densa
        
        1 more item...
        
        • granular cells (JGcells)
        
        • lacis cells
        
        REGULATION
        
        Low GFR --> low NaCL in filtrate arriving at DCT --> macula densa is stimulated --> release of prostaglandins --> aff. arteriole vasodilation --> increase blood flow to glomeruli --> Increase GFR to normal
        
        vasodilation of aff. arteriole results in increased hydrostatic pressure in glomerulus à increase GFR
        
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        SHORT TERM - increase GFR
        
        •Neural mechanism
        
        This mechanism is represented by the sympathetic nervous system.
        
        The afferent and efferent arterioles at the glomeruli are innervated by sympathetic fibers.
        
        Activation of these fibers in times of ‘flight or fight’ situations results in both afferent and efferent vasoconstriction, leading to decrease in GFR.
        
        Furthermore, JG cells contain adrenergic receptors, and so activation of the sympathetic fibers will stimulate renin release and activation of the RAAS.
        
        Constriction of both arterioles reduce blood flow into glomerulus --> reduce GFR
        
        Constriction of both arterioles reduce blood flow into glomerulus --> reduce GFR
        
        Sympathetic activation leads to ⇣ GFR and conservation of blood volume. Very useful during exercise and blood loss
        
        Myogenic Mechanism
        
        The myogenic response is the reflex response of the afferent arterioles to changes in blood pressure.
        
        Increased BP increases the tension in the vascular wall, and results in vasoconstriction.
        
        BP ▲, renal BF ▲ --> GFR above normal
        
        Blood vessel constricts --> Blood flow ▼, GFR ▼
        
        Similarly, decreased BP results in less tension of the vascular wall, producing vasodilation.
        
        BP ▼, renal BF ▼ --> GFR below normal
        
        Blood vessel dilates --> Blood flow ▲, GFR ▲
        
        CLINICAL
        
        LOW
        
        decreased capability of the kidneys to regulate fluid balance and excrete waste products
- - - - • volatile acids (gaseous form)
      - • fixed acids (H+, lactic acid, hydroxybutyric acid, etc)
  - - - BUFFER SYS
        
        A buffer is a chemical system that prevents a radical change in blood pH by adjusting H+ concentrations in situations of excess acid or base.
        
        The buffer systems in the human body are extremely efficient, and different systems work at different rates.
        
        LINE OF DEFENSE AGAINST pH SHIFT
        
        1ST
        
        CHEMICAL
        
        BICARBONATE
        
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        PHOSPHATE
        
        PROTEIN
        
        1 more item...
        
        Chemical buffers are chemicals that exist in the plasma that neutralise H+ temporarily.
        
        It takes only seconds for the chemical buffers in the blood to adjust pH.
        
        These H+ are rendered harmless until they are eliminated via the lungs or kidneys.
        
        2ND
        
        PHYSIOLOGICAL
        
        RESPIRATORY
        
        RENAL (H+ excretion)
        
        1 more item...
        
        Without the chemical buffering systems, the lungs
        and kidney cannot help to maintain the blood pH
        
        IN URINE
        
        BUT, the kidney tubules cannot retain extremely high concentrations of free H+. At pH <5, many antiporter and pumps stop working.
        • Urinary buffers will help to absorb free H+ to keep the pH high enough for secretion of H+ to continue in the tubules.
        
        Urinary Buffers Are Important
        
        • pH 4.5 is the lowest pH limit for urine. For each liter of urine, only 0.03 mEq of H+ can be secreted.
        • If kidney were to secrete all H+ as free ions, we would have to excrete 666 L of urine per day.
        • So combining H+ with buffers allow for more H+ to be excreted without increasing the amount of urine.
        
        BUFFERING
        
        • bicarbonate ions
        
        In tubules, H+ combines with filtered HCO3 to form CO2.
        
        Some of these CO2 can move back into tubular cell to reverse the reaction.
        
        But we cannot use to much HCO3 as urinary buffers because they need to be reabsorbed.
        
        • hydrogen phosphate ion (HPO4 - )
        
        • In the PCT, glutamine (amino acid) enters the tubular cells to be metabolised and produce ammonia (NH3).
        • NH3 combines with H+ to form NH4 + (ammonium) which are nondiffusible.
        • Accounts for two-third of acid excretion daily.
        
        • ammonia (NH3)
        
        • Hydrogen phosphate (HPO4 2- ) and Na2HPO4 are filtered into tubules glomerulus and not much is reabsorbed.
        • Free HPO4 2- and Na2HPO4 can absorb free H+, reducing the acidity in the tubular fluid.
  - - - ACID - metabolic acidosis
        
        Primary criteria: low serum HCO3, increased H+
        • Due to diarrhea, renal tubular damage, diabetic ketoacidosis (increased acids).
        
        Compensation mechanisms:
        • increased urinary excretion of H+ (acidic urine)
        • increased synthesis and reabsorption of HCO3
        
        Diabetic Ketoacidosis
        
        Life-threatening complication of diabetes and is usually seen in T1DM patients.
        • Deficiency of insulin, leading to impaired glucose utilization and increased fatty acid oxidation as well as ketogenesis.
        • Characterized by hyperglycemia, ketonemia and metabolic acidosis.
        • Polyuria, polydipsia and polyphagia.
        • Reduced fluid volume à low GFR.
      - BASE - metabolic alkalosis
        
        Primary criteria: high serum HCO3, decreased H+
        • Due to diuretics (acid loss), severe vomiting (acid loss), antacids overuse, hyperaldosteronism.
        
        Compensation mechanisms:
        • reduced urinary excretion of H+ (alkaline urine)
        • increased urinary excretion of bicarbonate