final exam Flashcards
describe the structure of the filtration membrane
Separates particles > 7nm and -ve charge
3 key components:
Capillary walls: fenestrated capillaries
Basement membrane: network of proteins e.g. collagen and prevent most proteins passing
Podocytes: specialised cells wrap around capillaries.
what is the filtration pathway
Single layer endothelial cells in glomerular capillary wall contain pores and fenestrations
Acellular basement membrane and -ve charge lipoproteins to stop large -ve charge particles passing
Filtration slits between podocytes in inner layer of Bowmans capsule
How is glomerular filtration regulated
- Glomerular capillary pressure
Difference in pressure in afferent and efferent arteriole maintains high pressure - Capsular hydrostatic pressure
Increased capsular pressure = decrease filtration - Blood colloid osmotic pressure
what are the 2 control mechanisms for glomerular filtration rate
autoregulation
extrinsic sympathetic control
explain what autoregulation is as a mechanism for controlling GFR
Prevents spontaneous changes in GFR
Involves myogenic mechanism and tubuloglomerular feedback
o Myogenic: restricts diameter of afferent arteriole with increased pressure. Revers is true
o Tubuloglomerular: adjust macula densa cells of juxtaglomerular apparatus with sodium and chloride flow changes. Reverse is true
explain what extrinsic sympathetic control is as a mechanism for controlling GFR
Short term regulation of arteriole blood pressure
Involved baroreceptor reflex
Vasoconstriction of afferent arteriole and conserves fluid
Mediated by sympathetic input to small arteries and afferent arterioles
Decrease blood pressure detectors by receptors in aortic arch and carotid sinus –> increase sympathetic output –> increase cardiac output –> increase arteriole pressure
what goes on in the proximal convoluted tubule
majority reabsorption
active transport Na+ across basal membrane
Na+ concentration gradient between filtrate and cytoplasm tubule provides energy for symport – sodium pumped into interstitial space, low sodium conc
Gradient also allows secondary active transport of glucose ions etc.
Reabsorbed glucose, a.a. potassium, chloride and sodium ions
what goes on in the descending loop of henle
highly water permeable
Osmosis movement
Concentrates/increases osmolarity filtrate
what goes on in the ascending loop of henle
highly solute permeable/impermeable water
Solute diffuse into interstitial fluid in thin segment of ascending limb
Solutes active transport through symport in thick segment
Filtrate dilutes again/decreased osmolarity
what goes on in the distal tubule and collecting duct
Under hormonal control – ADH
ADH created variable water permeability
Reabsorption e.g. K and H depend on bodies need – tightly regulated
what occurs during tubular secretion
Substance from blood to nephron tubules
Selective transfer
Elimination of metabolic toxins/drugs
Hydrogen, K and organic ions
Reverse transepithelial transport
o H+ antiport
o K+ active transport
o H+ K+ antiport
o Ammonia diffusion
o Neurotransmitters, toxins, bile pigments and uric - acid active transport
How is hydrogen secreted in the kidneys
Secreted by intercalated cells
Depends on acidity of body fluid balances
Antiport with Na+
H produced from CO2 entering cell – reacts with water for carbonic acid and dissociated to H –> bicarbonate and Na+ reabsorbed into blood to regulate acidity
what is potassium secretion in the kidneys
Secreted by intercalated cells
Controlled by aldosterone – increase K = increase Aldosterone
Stimulates secretion in DCT and collecting ducts
Antiport with sodium (as Na in, K out)
Maintains plasma K concentration for heart and muscle function
Transport is coupled with sodium: NaK pump –> creates low potassium in tubular cell, K diffuses into tubular cell
Then secreted into filtrate by antiport with Na
what is the micturation reflex
Bladder is a reservoir prior to urination
Reflex initiated when half full in response to stretch. Stretch receptors activated in bladder wall. Aps transmitted to sacral region of spinal cord.
Parasympathetic stimulation of bladder contraction to increase pressure and reinforce urination urge
Integrated in pons and cerebrum – descending pathways allow conscious control
what is filtration fraction
% plasma filtered from blood into tubule
Determined by plasma clearance of inulin and PAH
Renal plasma flow + glomerular filtration rate
Allows us to determine GFR
Filtration rate / renal plasma flow
what is filtered load
Amount of substance filtered each minute – amount of substance passing through filtration membrane into renal tubule
filtered load = plasma concentration of substance x GFR
what is tubular maximum
maximum rate at which a substance can be actively absorbed
determined by number of active transport carrier and rate at which they can transport substance
any substance beyond tubular maximum cannot be absorbed, and will be excreted (exception sodium)
what is extracellular fluid
plasma (20%) + interstitial fluid
highly permeable capillary walls: most substances freely exchange (NOT plasma proteins)
major Na+ cation, also Cl and bicarbonate ions
driven by hydrostatic and osmotic pressure differences – shifts between plasma and ISF
what is intracellular fluid
Composition difference by plasma membrane – control what enters/leaves cell
major K+ cation
shifts driven by osmotic pressure
what is the relationship between ECF volume and arterial BP
Na balance determines ECF volume
Na loss depletes plasma volume –> decrease mean arterial pressure
Na retention increases volume –> increase MAP
what are the 2 short term ways that blood pressure is controlled
Baroreceptor reflex
Baroreceptors in aortic arch and carotid sinus in heart alter cardiac output through sympathetic NS input –> vasoconstriction/dilation and cardiac output adjust –> pressure change
Fluid shift between plasma in ISF
automatic
Balance hydrostatic and osmotic forces
Decrease mean arterial pressure draws fluid out ISF to plasma
how does the juxtaglomerular apparatus regulate ECF volume
- Granular cells
* detect pressure change in afferent arteriole
* secrete renin when decreased BP (vice versa)
* Works with increased sympathetic stimulation also increases granular cell activity - Macula densa cells (tubular cells)
* Sensitive to NaCl in DT
* Decrease in NaCl increase secretion of renin (vice versa)
* Works with tubuloglomerular feedback mechanism (GFR)
what is hypertonicity in the ECF
Dehydration
Excess water loss
Diabetes (ADH deficiency)
Water deficit: solute conc in ECF increases –> high ECF osmolarity = hypertonic.
Water moves out of cell to ECF by osmosis to balance solute conc.
Shrinking cells
What is hypotonicity in the ECF
overhydration
Renal failure
Rapid water ingestion
ADH secretion impairment
Water excess: solutes in ECF dilute –> low ECF osmolarity = hypotonic.
H2O moves into cell
Cell swelling
How does ADH regulate water output
Osmoreceptors in hypothalamus detect increase ECF osmolarity
Increases ADH from post. Pit.
Acts on DT and CD – increases tubule water permeability
ADH binds to receptor of basolateral membrane of cells in CD and DT –> activates cAMP pathway
Aquaporin 2 water channels inserted into luminal membrane
Water moves through AQP2 channels for water reabsorption
* More free water absorbed
* Decreased urine volume – higher urine conc.
* Less water excretion decreases ECF osmolarity
describe the relationship between ADH and thirst
Thirst centre in hypothalamus located near vasopressin secreting cells
Both activated by free water deficit / suppressed by free water deficit
Hypothalamic osmoreceptors stimulated
Stimulates hypothalamic neurons
Vasopressin released in post pit and stimulation of thirst centre
Also Increased vasoconstriction
Total ECF volume increased
Decrease osmolarity
what are some sources of H+ input in the body
Carbonic acid
Inorganic acids (vegetables)
Organic acids (lactic acid)
what are the 3 body responses to balancing H+ input/output
- chemical
- respiratory
- renal
Describe the CHEMICAL response to balancing H+ input/output
Immediate intracellular and extracellular response
Removes H+ from solution, but CANNOT ELIMINATE
Proteins and bicarbonates
E.g. carbonic acid-bicarbonate buffer pair (reversible). ECF
E.g. protein buffer system. ICF
Describe the RESPIRATORY response to balancing H+ input/output
Responds in minutes
Increase CO2 levels cause adjustment in breathing levels
Respiratory centre in brain stem increase resp rate and depth and remove carbon dioxide generated hydrogen
Describe the RENAL response to balancing H+ input/output
Long term acid base balance
Hours – days
Kidneys control body fluid pH by adjusting:
o H+ excretion
o Bicarbonate excretion
o Ammonia secretion
Compare how H+ secretion is adjusted in the proximal and distal tubules
Proximal tubule
* H+ secreted by H+ATPase pump and NaH antiporters
Distal tubule
* Type A intercalated cells secrete H+ by H+ATPase pumps and HK pumps (luminal)
- Type B reabsorb H+ by H+ATPase pumps and HK pumps (basolateral). Secrete Bicarbonate in urine.
What are 2 urinary buffers used to regulate H+ (acidity)
filtered phosphate
ammonia
How is filtered phosphate used as a urinary buffer to H+
Phosphate is reabsorbed in kidneys (controlled by PTH)
Tubular fluid now contains phosphate
Phosphate binds with secreted H+
How is ammonia used as a urinary buffer to H+
Allows greater H+ secretion and excretion
Tubular cells secrete ammonia in tubular fluid (only occurs when phosphate buffer reaches capacity)
Regenerates bicarbonate
what is the hypothalamohypophysial portal system
Hypothalamus control ant pit hormone secretion via portal system
Specialized set of blood vessels ensure blood supply to anterior pituitary must first pass through hypothalamus
Immediate direct delivery
Bypasses general circulation
What is the hierarchic chain of command
3 hormone sequence:
1. Hypophysiotropic hormone
2. Anterior pituitary tropic hormone
3. Target endocrine gland hormone
Involves negative feedback at multiple levels
What are the 6 major hormones secreted by the anterior pituitary gland
- Growth hormone
- Prolactin
- Luteinizing hormone
- FSH
- Thyroid stimulating hormone
- Adrenocorticotropic hormone
What is the pineal gland
Located in epithalamus
Secretes:
1. Melatonin
o A.a. derivative
o May regulate circadian cycle
o Decreased hypothalamic
GnRH secretion (inhibit reproductive functions)
o Antioxidant
