Physiology Flashcards
What do the parasympathetic and sympathetic fibres that supply the heart release?
Parasympathetic: Acetylcholine (alpha 1)
Sympathetic: noradrenaline (B1 receptors)
What is Starling’s law?
The law governs effects on stroke volume and states that an increased preload causing increased stretch of the cardiac muscle fibres will lead to a greater stroke volume (cardiac output)
Where are the baroreceptors found and via which nerve are their impulses carried by?
Found in aortic arch and carotid sinus
Carried by vagus from aortic arch
Carried by glossopharyngeal nerve from carotid sinus
Which part of the JVP waveform is absent during AF?
A wave
What are the 5 waves that make up the JVP waveform and what do they each represent?
- a wave: atrial contraction
- c wave: closure of tricuspid valve + ventricular contraction
- x wave: fall in atrial pressure during ventricular systole
- v wave: passive filling of atrium against a closed tricuspid valve
- y wave: opening of tricuspid valve + ventricular filling
What is the mechanism of the rapid depolarisation phase of the heart?
Rapid sodium influx
What is the mechanism of the early repolarisation phase of the heart?
Efflux of potassium
What occurs during the plateau phase of the myocardial action potential?
Slow influx of calcium
What occurs during the final repolarisation of the myocardial action potential?
Efflux of potassium
Which 2 receptors are found in blood vessels and cause vasoconstriction when stimulated?
Alpha 1
Alpha 2
What are the effects of binding to D1 and D2 receptors and where are they found?
D1: renal and spleen vasodilation
D2: Inhibits release of noradrenaline
Found in the kidneys
Which receptor is the main binding site for adrenaline?
Alpha 1
causes vasoconstriction
What are the preferred inotropes given during septic shock and anaphylaxis?
Septic shock: Noradrenaline (a1, a2, b1, b2)
Anaphylaxis: Adrenaline (a1, a2, b1, b2)
What is the main receptor site of noradrenaline to increase heart rate?
Beta 1 receptors
In a patient with cardiogenic shock, what is the most appropriate inotrope and why?
Dobutamine
Binds to B1 and B2 to increase HR and contractility of the heart
What is the normal pCO2 range?
4.7 - 6 kPa
45 - 35 mmHg
What is the normal range of HCO3?
22 - 26
<22 = acidosis
>26 = alkalosis
What ABG result shows T1RF?
Low PaO2
How is T2RF shown on an ABG?
- Hypoxemia = low paO2
- Hypercapnia = high pCO2
How long does metabolic compensation of acidosis / alkalosis take to start?
~2 days
How is the anion gap calculated and what is the normal range?
Normal range: 4 - 12
(Na + K) - (HCO3 + Cl)
What metabolic state can diarrhoea cause and why?
Metabolic acidosis
Due to increase excretion of HCO3
What are causes of a raised anion gap with metabolic acidosis?
- Lactate (shock, hypoxia)
- Ketones (DKA, ETOH)
- Urate (renal failure)
- Acid poisoning (salicylates, methanol)
In a patient with excessive vomiting (i.e secondary to pyloric stenosis), what metabolic and electrolyte state are they likely to be in?
Hypocholeraemic Hyperkalaemic Metabolic alkalosis
What is the mechanism of metabolic alkalosis?
- RAAS system activated secreting aldosterone
- Aldosterone causes reabsorption of Na+ in exchange for H+ in DCT
- H+ shifts into the cells and K+ will shift out of cells into the ECF to maintain ion neutrality
What would expect to see on an ABG in early salicylate poisoning?
Respiratory alkalosis followed later by metabolic acidosis
What is SIRS?
Systemic Inflammatory Response Syndrome
Parameters:
- Temp <36 / >38 degrees
- HR >90
- RR >20
- WCC >12 or <4
- Altered mental state OR hyperglycaemia (in absence of DM)
SIRS describes symptoms of SEPSIS
What is septic shock?
Sepsis with hypotension which does not respond to fluid resuscitation leading to tissue hypoperfusion
Characterised by:
- Decreased Systemic vascular resistance
- Increased HR
- Decreased cardiac output
- Normal pulmonary pressure
How many classes of haemorrhages shock are there?
4 classes
What is the normal rate of urine output?
0.5-1ml/kg/hr
What are the cardiovascular changes that occur in a patient with hemorrhagic/hypovolaemic shock?
- Increased HR
- Increased systemic vascular resistance
- Decreased BP
What causes shock during neurogenic shock?
Decreased sympathetic tone / Increased parasympathetic tone
- Decreased HR
- Decreased BP
- Decreased Cardiac output
- Decreased systemic vascular resistance
How is neurogenic shock managed acutely?
Fluid resus and inotropes (Dobutamine to bind to B1 receptors)
long term is surgery to fix neuropathic damage
What is the most common surgical and medical cause of cardiogenic shock?
Medically: IHD
Surgically/trauma: Cardiac tamponade
What happens to pulmonary pressures in cardiogenic shock?
Pressures are high
Basis of use of venodilators in treatment of pulmonary oedema
What dose of adrenaline is given in anaphylaxis and how often can it be given?
500mcg (1:1000) IM
can be given every 5mins if needed
How is cerebral perfusion pressure calculated?
CPP = MAP - ICP
Which fluid compartment holds the highest percentage of total body volume?
Intracellular = 60 - 65%
Extracellular: 35 - 40%
60% of body weight is water. 40% intracellular and 20% extracellular
What components can be found in CSF?
Glucose 50-80mg/dL
Protein 15-40 mg/dL
RBC: NIL
WCC: NIL to very minimal
How is mean arterial pressure calculated?
Diastolic pressure + 1/3(systolic pressure - diastolic pressure)
What are symptoms of raised ICP?
- Headaches
- Vomitng
- Papilloedema
- Seizures
- Focal neurological symptoms
If the raised ICP is caused by trauma, what is the medical management given initially?
Mannitol
What can low CPP lead to?
Secondary brain injury by hypo perfusion of brain tissue causing hypoxic brain injury
What is involved in the Extrinsic pathway of the coagulation cascade?
- Tissue is damaged releasing tissue factor
- Factor 7 binds to Tissue factor creating a complex
- This complex activates Factor 9
- Activated Factor 9 works with Factor 8 to activate Factor 10
- Factor 10 is part of the common pathway
What occurs in the common pathway of the coagulation cascade?
Activated Factor 10 causes the conversion of prothrombin to thrombin
Thrombin hydrolyeses fibrinogen to form FIBRIN and also activates Factor 8 to form links between the fibrin molecules
How is the extrinsic pathway monitored?
PT
How is the intrinsic pathway monitored?
APTT
Which factors of the coagulation cascade are Vitamin K dependent?
Factor 10, 9, 7, 2
1972
What part of the coagulation cascade does Heparin have an effect on?
Intrinsic pathway
Prevents activation of Factors 2, 9, 10, 11
Which factors does warfarin disrupt in the coagulation cascade?
Affects synthesis of Factors 10, 9, 7, 2 (1972) - extrinsic pathway
In which type of thrombophilia is heparin likely to be ineffective and why?
Antithrombin deficiency (unable to inactivate thrombin)
Heparin may be ineffective as it works via antithrombin
Which genetic thrombophilia is the most common genetic defect causing DVT?
Factor V Leiden
How is warfarin monitored?
INR + PT
How is raised INR secondary to warfarin usage corrected?
- Vit K (works over 24hrs)
- Prothrombin complex concentrate (works within 1hr)
- FFP
How long before an operation should warfarin be stopped?
4 days
How can the effects of unfractionated heparin be reversed?
Protamine sulfate
When would a high CRP post-operatively suggest evolving complications?
a CRP >150 after 48hrs post-operatively in cases of bowel anastomosis/resections suggest evolving complications
What are the signs and symptoms of hypocalcaemia?
CATS go NUMB
- Convulsions
- Arrhythmia
- Tetany
- Spasms and stridor (Chvosteks sign; twitching of facial muscles in response to tapping over facial nerve)
- Numbness in fingers
What effect does PTH have on calcium and phosphate levels and what is the mechanism?
Increases Calcium
Decreases Phosphate
- Directly works on osteoblasts to cause bone resorption to increase extracellular calcium levels
- Increases synthesis of Vitamin D in kidney which increases calcium absorption from the bowel and kidney tubules
Decreases renal resorption of phosphate
What is the function of calcitonin and where is it secreted from?
Secreted by C cells of thyroid
- Inhibits intestinal calcium absorption
- Inhibits osteoclast activity (reduces bone resorption)
- Inhibits renal absorption of calcium
What are causes of hypocalcaemia?
- Vit D deficiency (osteomalacia)
- Acute pancreatitis
- Chronic renal failure
- Hypoparathyroidism
- Magnesium deficiency (due to end organ PTH resistance)
What are the main 3 causes of hypercalcaemia?
- Malignancy (IP pts)
- Primary hyperparathyroidism (OP pts)
- Sarcoidosis
What are the clinical features of hypercalcaemia?
Stones, bones, abdominal groans and psychiatric moans
- Kidneys stones
- Weak/brittle bones
- Constipation
- Confusion
What is the management of hypercalcaemia?
- IVF
- Diuretics (furosemide)
- Calcitonin
- Bisphosphonates
Which bisphosphonate is used to treat hypercalcaemia associated with malignancy?
IV Zolindronate
What is the effect of insulin on potassium levels?
Causes hypokalaemia
What is the effect of aldosterone on potassium?
Increases potassium by exchanging sodium for potassium in the renal tubules
Hence why hyperkalaemia occurs in Addison’s disease
What are ECG features of hypokalaemia?
- U waves
- small/absent T waves
- Prolonged PR
- ST depression
- Long QT interval
How is hyperkalaemia managed?
1- Calcium gluconate
2- Insulin/Dextrose (50 units insulin in 50mls saline given at rate of 0.1units/kg/hr)
3- IVF given alongside insulin
What are the causes of hypomagnasaemia?
- Diuretics
- TPN
- Alcohol
- Diarrhoea
A patient had a TURP. They now have hyponatraemia. What is the most likely cause of this imbalance?
Water excess
TURP uses saline/dextrose as part of the procedure which can cause water excess leading to a dilution effect on sodium
If a patient with hyponatraemia has a urinary sodium <20mmol/L, where is it likely their sodium is being depleted?
Extra-renal loss
Causes:
- D+V
- Sweating
- Burns
If a patient with hyponatraemia has a urinary sodium >20mmol/L, where is it likely their sodium is being depleted?
Renal loss
Causes:
- Hypovolaemia/euvolaemic
- Diuretics
- Addison’s
- SIADH
What is the max rate of Na correction and why?
Pts with Na <120, correction should be no more than 10mmol per 24hrs
To prevent Central pontine Myelinosis
Where in the GIT is iron mostly absorbed?
Duodenum and upper Jejunum
What can reduce absorption of iron in the GIT?
- PPIs
- Tannin (found in tea)
- Tetracyclines
How can pulmonary artery occlusion pressures differentiate between ARDS and Pulmonary oedema (overload)?
ARDS: low pressures with pulmonary oedema (<5mmHg)
Overload: High pressures (>18mmHg)
What are the 3 classifications of hyponatraemia?
Normal osmolality: Hyperproteinaemia // hyperlipidaemia
Hypotonic hyponatraemia: further divided based on fluid status (hypovolaemic, euvolaemic, hypervolaemic)
Hypertonic hyponatraemia: Hyperglycaemia // radiocontrast agents // mannitol and sorbitol
What are the causes of hypotonic hyponatraemia in a euvolaemic patient?
- SIADH
- Hypothyroidism
- Endurance exercise
- Thiazides and ACEi
- Post-operative hyponatraemia
What effects on sodium does Diabetes insipidus cause?
- Serum Na+ is high
- Serum osmolality is high
- Urine osmolality is low
How is diabetes insipidus investigated and what can DI be further divided?
Vasopressin stimulation test
- if no change after vasopressin: Nephrogenic DI. Treat underlying cause
- if improvement after vasopressin: Cranial DI and managed with vasopressin
What is vital capacity?
Inspiratory reserve volume + Tidal volume + Expiratory reserve volume
Maximal volume of air that can be forcefully exhaled after maximal inspiration
In a patient who has post-operative oliguria, how would you initially manage them?
Fluid challenge
- 500ml STAT
- up to 4 fluid challenges
- if no improvement, HDU + inotropes
What fluid resuscitation fluids would you use in post-operative oliguria and trauma patients?
Ringer or Hartmanns
When would you use normal saline with K+ as a resuscitation fluid?
Obstructive gastric outlet or repeated vomiting
To replace loss of Cl and K+ from vomiting
What can overuse of NaCl cause when resuscitating?
Hypercholeraemic metabolic acidosis
What is meant by Forced vital capacity?
Volume of air that can be maximally forcefully exhaled
In the medulla, how is the respiratory centre here divided and what are their respective functions?
In the medulla, there is the:
- Dorsal respiratory group: Inspiration
- Ventral respiratory group: Forced voluntary Expiration
Which respiratory centre is affected by opioid use?
Mainly medullary centres
What is the function of the apneustic centre and where is it located?
Stimulates inspiration and prolongs inhalation.
Found in Lower Pons
Where are the central and peripheral chemoreceptors found?
Central: Medulla
Peripheral: bifurcation of carotid arteries AND arch of aorta
In a patient with COPD, which lung volume will be increased?
Residual volume
What is the significance of a right shift on the oxygen dissociation curve and what causes this shift?
Raised oxygen delivery
CADET face right
- CO2 (raised)
- Acidosis (raised H+, lactic acid)
- 2-3 DPG
- Exercise
- Temp (raised temp)
What is affected in the lung in a patient with ARDS?
Decreased gas diffusion
What are causes of a reduced TLCO?
FIGHT EM
- Fibrosis
- Infection
- Embolism
- Emphysema
- Anaemia
- Emptying of heart (low CO)
How are lung functions affected in Obstructive lung disease (e.g. COPD)?
FVC: normal
FEV1: Decreased
FEV1/FVC ratio: <0.8 (decreased)
How are lung functions affected in restrictive lung diseases?
FVC: Decreased
FEV1: decreased
FEV1/FVC ratio: Normal (as both FEV1 and FVC both decreased)
What is the mechanism of RAAS in maintaining blood pressure?
- Renin converts Angiotensinogen (made by liver) into Angiotensin 1
-Angiotensin 1 is converted into Angiotensin 2 by ACE (made by lungs and kidneys)
- Angiotensin 2 increases sympathetic activity causing vasoconstriction of arterioles
- Angiotensin 2 also increases ADH for water retention and causes increased excretion of sodium and retention of K+ by stimulating the adrenal cortex to secrete aldosterone
In which part of the kidney is glucose reabsorbed?
In PCT
In PCT, also absorbed is:
- 65% of water
- Glucose
- A.A
- Phosphate
On which part of the kidney does Furosemide work?
Loop of Henle (thick ascending limb)
What is the descending limb of the loop of Henle permeable and impermeable to?
Permeable to water
Impermeable to solutes
Which part of renal physiology does thiazide affect?
DCT
Where are the Na+/K+ pumps found in the kidney?
Collecting Duct and DCT
What factors stimulate renin secretion?
- Hypotension
- Hyponatraemia
- Catecholamines (Adrenaline)
- Erect posture
What drugs reduces renin secretion?
Beta blockers
NSAIDS
What are the 4 phases of wound healing?
1- Haemostasis
2- Inflammation
3- Regeneration
4- Remodelling
What occurs in each stage of wound healing and what is their respective durations?
1- Haemostasis
Vasospasm in adjacent vessels + Platelet plug formation. Lasts from SECONDS TO MINUTES
2- Inflammation
Neutrophils migrate into the wound (impaired in DM). Growth factors are released. Macrophages and fibroblasts couple matrix regeneration and clot substitution. Lasts for DAYS
3- Regeneration
Platelet derived growth factors stimulate fibroblasts and epithelial cells which produce a collagen network. Angiogenesis occurs and wound resembles granulation tissue now. Takes WEEKS.
4- Remodelling
Longest phase. Fibroblasts become differentiated and facilitate wound contraction. Collagen fibres are remodelled and micro vessels regress leaving a pale scar. Last 6 WEEKS TO A YEAR
What is the most important cell involved in acute and chronic inflammation?
Acute: Neutrophils
Chronic: Macrophages
What hormones are increased in response to surgery?
- GH
- Cortisol
- Renin
- ACTH
- Aldosterone
- ADH
- Glucagon
What 3 hormones are decreased in response to surgery (stress)?
Insulin
Testosterone
Oestrogen
What is the mechanism of the HPA in relation to cortisol production?
- Hypothalamus releases CRH
- CRH stimulates Anterior pituitary gland to secrete ACTH
- ACTH stimulates adrenal cortex to secrete cortisol
This is controlled by a negative feedback system
What are the effects of cortisol on the body?
- breakdown of skeletal muscle proteins to provide gluconeogenic precursors
- Stimulates lipolysis
- Anti-insulin effect
- Anti-inflammatory effects
What are the symptoms and findings in a patient with an Addisonian crisis and what can precipitate this?
- Abdominal pain
- Hyperkalaemia
- Unexplained shock
- Hyponatraemia
Patient on steroids prior to surgery is at risk of Addisonian crisis
If a patient is on a regular dose on prednisolone above 15mg daily prior to surgery and they are due for a major operation, what steroid regimen should they receive after surgery?
> 15mg + major surgery requires IV hydrocortisone 100mg for 3 days before tapering down to normal dose
Which hormones are secreted from the anterior pituitary gland?
- TSH
- Prolactin
- FSH
- LH
- GH
- ACTH
Which 2 hormones are secreted from the posterior pituitary gland?
- Oxytocin
- ADH
What drugs classes inhibit release of insulin?
Alpha adrenergic drugs
Beta blockers
What is mechanism by which T3 and T4 are formed in the thyroid?
- Iodide is actively pumped into the follicular cells
- Iodide + TPO = Iodine
- Iodine + thyroxine = MIT and DIT
- Mono-IT + Di-IT = T3
- DIT + DIT = T4
What is stress incontinence and how is it managed?
Caused by urethral hyper mobility or intrinsic sphincter deficiency. Brought on by increases in intra-abdominal pressures (sneezing, lifting etc.)
Managed by pelvic floor muscle strengthening and weight loss
What causes urge incontinence and how is it treated?
Caused by overactivity of detrusor muscle. Presents as a leak with urge to void
Managed by bladder training and/or antimuscarinics (e.g. Oxybutinin)
What is beriberi caused by?
Vit B1 (thiamine) deficiency
What is ascorbic acid (Vit C) responsible for?
Wound healing and collagen synthesis
What are the causes of Vitamin B12 deficiency?
- Pernicious anaemia
- Post-gastrectomy
- Poor diet
- Disorders of terminal ileum (site of absorption) e.g. Crohn’s
What are the signs and symptoms of Vit B12 deficiency?
- Macrocytic anaemia
- Sore tongue and mouth
- Neurology (e.g. Ataxia)
- Psychiatric symptoms (e.g. mood disturbances)
What is the mechanism of excretion of bilirubin?
- breakdown of RBCs to form unconjugated bilirubin (not water soluble)
- Unconjugated bilirubin travels to the liver where it is conjugated to glucuronic acid (now water soluble)
- Conjugated bilirubin is transported through the biliary system to the duodenum
- Conjugated bilirubin in the duodenum is converted to Urobilinogen by bacterial proteases
- Urobilinogen (90%) is oxidised to form Stercobilinogen which is excreted in the faeces
What are the 3 phases of gastric secretion and what occurs during each phase?
1) Cephalic phase:
- Sight, smell, taste, thought of food
- Mediated by parasympathetic (vagus)
2) Gastric phase (60%):
- Stretch receptors detect distention of stomach when eating
- Chemoreceptors detect rise in pH stimulating increase in gastric juice, increased gastric peristalsis and increased gastric emptying
3) Intestinal phase:
- Receptors detect distention of duodenum
- Chemoreceptors detect increased fatty acids and glucose causing CCK, secreting secretion and enterogastric reflex
How much bile is secreted in a 24hr period?
500ml
What volume is secreted by the pancreas in a 24hr period?
1L
What is the total 24hr volume of intestinal secretions by the stomach and duodenum?
1.5L
What are 3 factors that increase production of gastric juices?
- Vagal nerve stimulation
- Gastrin release
- Histamine release
What is secreted by chief cells?
Pepsinogen
Where is gastrin secreted from?
G cells in antrum of stomach
Where is somatostatin secreted from?
D cells in the pancreas and stomach
What is the most specific enzyme to diagnose pancreatitis?
Lipase
What is responsible for auto digestion of the pancreas?
Trypsin
What is the usual cause of primary hyperparathyroidism?
Hyperplasia, adenoma or carcinoma of the parathyroid
Managed usually by surgery
What are the causes of secondary hyperparathyroidism and how does it present biochemically?
Caused by Chronic renal failure or Vit D deficiency
Low/normal Calcium
High Phosphate
What is the pH of stomach acid?
pH 2 - 5
What is the most common cause of high output diarrhoea in a patient who has had an ileocaecal resection and how is it managed?
Malabsorption of bile salts causes high output diarrhoea
Managed with oral cholestyramine
Which factor does von Willebrand factor stabilise?
Factor VIII (8)
Which cell secretes the majority of tumour necrosis factor (TNF)?
Macrophages
