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Nutritional physiology > final exam > Flashcards

final exam Flashcards

1
Q

describe the structure of the filtration membrane

A

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.

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2
Q

what is the filtration pathway

A

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

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3
Q

How is glomerular filtration regulated

A
  1. Glomerular capillary pressure
    Difference in pressure in afferent and efferent arteriole maintains high pressure
  2. Capsular hydrostatic pressure
    Increased capsular pressure = decrease filtration
  3. Blood colloid osmotic pressure
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4
Q

what are the 2 control mechanisms for glomerular filtration rate

A

autoregulation

extrinsic sympathetic control

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5
Q

explain what autoregulation is as a mechanism for controlling GFR

A

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

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6
Q

explain what extrinsic sympathetic control is as a mechanism for controlling GFR

A

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

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7
Q

what goes on in the proximal convoluted tubule

A

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

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8
Q

what goes on in the descending loop of henle

A

highly water permeable

Osmosis movement

Concentrates/increases osmolarity filtrate

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9
Q

what goes on in the ascending loop of henle

A

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

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10
Q

what goes on in the distal tubule and collecting duct

A

Under hormonal control – ADH

ADH created variable water permeability

Reabsorption e.g. K and H depend on bodies need – tightly regulated

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11
Q

what occurs during tubular secretion

A

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

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12
Q

How is hydrogen secreted in the kidneys

A

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

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13
Q

what is potassium secretion in the kidneys

A

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

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14
Q

what is the micturation reflex

A

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

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15
Q

what is filtration fraction

A

% 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

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16
Q

what is filtered load

A

Amount of substance filtered each minute – amount of substance passing through filtration membrane into renal tubule

filtered load = plasma concentration of substance x GFR

17
Q

what is tubular maximum

A

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)

18
Q

what is extracellular fluid

A

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

19
Q

what is intracellular fluid

A

Composition difference by plasma membrane – control what enters/leaves cell

major K+ cation

shifts driven by osmotic pressure

20
Q

what is the relationship between ECF volume and arterial BP

A

Na balance determines ECF volume

Na loss depletes plasma volume –> decrease mean arterial pressure

Na retention increases volume –> increase MAP

21
Q

what are the 2 short term ways that blood pressure is controlled

A

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

22
Q

how does the juxtaglomerular apparatus regulate ECF volume

A
  1. 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
  2. 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)
23
Q

what is hypertonicity in the ECF

A

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

24
Q

What is hypotonicity in the ECF

A

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

25
Q

How does ADH regulate water output

A

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

26
Q

describe the relationship between ADH and thirst

A

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

27
Q

what are some sources of H+ input in the body

A

Carbonic acid

Inorganic acids (vegetables)

Organic acids (lactic acid)

28
Q

what are the 3 body responses to balancing H+ input/output

A
  1. chemical
  2. respiratory
  3. renal
29
Q

Describe the CHEMICAL response to balancing H+ input/output

A

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

30
Q

Describe the RESPIRATORY response to balancing H+ input/output

A

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

31
Q

Describe the RENAL response to balancing H+ input/output

A

Long term acid base balance

Hours – days

Kidneys control body fluid pH by adjusting:
o H+ excretion
o Bicarbonate excretion
o Ammonia secretion

32
Q

Compare how H+ secretion is adjusted in the proximal and distal tubules

A

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.
33
Q

What are 2 urinary buffers used to regulate H+ (acidity)

A

filtered phosphate

ammonia

34
Q

How is filtered phosphate used as a urinary buffer to H+

A

Phosphate is reabsorbed in kidneys (controlled by PTH)

Tubular fluid now contains phosphate

Phosphate binds with secreted H+

35
Q

How is ammonia used as a urinary buffer to H+

A

Allows greater H+ secretion and excretion

Tubular cells secrete ammonia in tubular fluid (only occurs when phosphate buffer reaches capacity)

Regenerates bicarbonate

36
Q

what is the hypothalamohypophysial portal system

A

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

37
Q

What is the hierarchic chain of command

A

3 hormone sequence:
1. Hypophysiotropic hormone
2. Anterior pituitary tropic hormone
3. Target endocrine gland hormone

Involves negative feedback at multiple levels

38
Q

What are the 6 major hormones secreted by the anterior pituitary gland

A
  1. Growth hormone
  2. Prolactin
  3. Luteinizing hormone
  4. FSH
  5. Thyroid stimulating hormone
  6. Adrenocorticotropic hormone
39
Q

What is the pineal gland

A

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

Nutritional physiology (3 decks)

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