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Physiology: Neuro, Endo, & Haem Flashcards

Learn neural transmission, autonomic regulation, pain pathways, and endocrine responses relevant to anaesthesia. (237 cards)

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1
Q

What are pericytes?

A

Cells that project onto:

  • endothelial cells
  • mediating luminal diameter
  • synthesizing basement membrane components
  • releasing vasoactive agents
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2
Q

What is the thickness of a phospholipid bilayer?

A

Approximately 10 nanometers

This structure is essential for cell membrane integrity and function.

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3
Q

Which apolipoproteins are found on chylomicrons?

A
  • APO B-48
  • APO C-II
  • APO C-III
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4
Q

What happens to chylomicrons in the periphery?

A
  • APO C-II will activate lipoprotein lipase on the capillary endothelium.
  • This cleaves the chylomicron and releases fatty acids and monoglycerides which can then enter the cell.
  • Remnants of chylomicrons are taken up by hepatocytes.
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5
Q

Fats with what length of carbon chain will need to be absorbed via the lymphatics?

A

More than 12 carbons

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6
Q

What are the parts of a sarcomere?

A
  • Z-discs: ends of a sarcomere
  • I band: only actin (thin) filaments
  • A band: overlap of actin and myosin filaments
  • H zone: myosin filaments only
  • M line: anchoring point for thick filaments
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7
Q

Describe the function of the ryanodine receptor on the sarcoplasmic reticulum.

A

Calcium stimulates the release of more calcium from the sarcoplasmic reticulum
Inhibited by dantrolene.

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8
Q

What are the three main types of receptor on the sarcoplasmic reticulum?

A
  • Ryanodine Receptor (CICR)
  • Inositol Triphosphate Receptor (calcium channel)
  • Phospholamban (inhibits sarcoplasmic reticulum calcium ATPase)
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9
Q

Describe the structure of myosin.

A
  • Dimers arranged in a staggered helical fashion with globular heads in six rows.
  • Central portion of adjacent filaments joins at the M-disc via creatine kinase, M protein, and myomesin.
  • Tail consists of light meromyosin (LMM) and heavy meromyosin (HMM) in an alpha helix with a flexible hinge region.
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10
Q

Describe the structure of thin filaments.

A
  • Two actin filaments arranged in a helix.
  • Alpha-tropomyosin tetramer winds around actin, blocking myosin head binding.
  • Contains inhibitory (TnI), calcium-binding (TnC), and tropomyosin-binding (TnT) troponins.
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11
Q

What’s the difference between the Nernst equation and the Goldman Constant Field equation?

A
  • Nernst: predicts transmembrane potential based on one ion at a time
  • Goldman Constant Field: considers all major ions
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12
Q

What is each heme molecule composed of?

A

Protoporphyrin ring (four pyrrole rings) and iron in its ferrous (Fe²⁺) state.

Protoporphyrin is synthesized in the mitochondria from glycine and succinyl CoA, then combined with ferrous iron.

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13
Q

List three forms of haemoglobin.

A
  • Haemoglobin A: 2 alpha and 2 beta
  • Haemoglobin A2: 2 alpha and 2 delta
  • Haemoglobin F: 2 alpha and 2 gamma
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14
Q

How are red cells broken down?

A

By the reticuloendothelial system:

  • Globin chains are broken down into amino acids which are recycled
  • Iron is reused by the bone marrow to make more haemoglobin
  • Heme is broken down to biliverdin, which is metabolised to bilirubin
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15
Q

Describe the effect of carbon monoxide binding to haemoglobin on oxygen affinity.

A

Binding alters haemoglobin’s conformation, reducing oxygen release (shifts curve left) and decreasing available binding sites for oxygen.

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16
Q

How are glucose, fatty acids, and amino acids metabolized for Phase 2 reactions?

A
  • Glucose: 2 Pyruvate via glycolysis in the cytoplasm
  • Pyruvate: 2 Acetyl CoA via oxidative decarboxylation in mitochondria
  • Fatty Acids: Acetyl CoA via beta oxidation
  • Amino Acids: Pyruvate, Acetyl CoA, and Krebs Cycle intermediates via oxidation
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17
Q

What comes out of the Krebs cycle for each molecule of glucose?

A
  • 2 ATP
  • 2 CO₂
  • 6 NADH
  • 2 FADH
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18
Q

What occurs in the electron transport chain?

A

In the mitochondria, reduced enzymes (NADH and FADH₂) are reoxidized, releasing electrons and energy to convert ADP to ATP.

  • 1 NADH = 3 ATP
  • 1 FADH₂ = 2 ATP

Oxygen is the final electron acceptor, combining with hydrogen ions to produce water.

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19
Q

How many molecules of ATP are generated per molecule of glucose undergoing aerobic respiration?

A

38 ATP

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20
Q

Over what range in mean arterial pressure is cerebral blood flow constant?

A

50-150 mm Hg

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21
Q

Below what pO₂ does cerebral blood flow increase exponentially?

A

6.7 kPa

Brain consumes 20% of total body oxygen.

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22
Q

Which other endogenous hormone has similar effects to ADH when given in large doses?

A

Oxytocin

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23
Q

What is the half-life of ADH?

A

5 mins

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24
Q

In which part of the sympathetic nervous system is acetylcholine found as a neurotransmitter?

A
  • Ganglia
  • Sweat glands
  • Adrenal medulla

The rest uses noradrenaline

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25
What is the **total CSF volume** of an average person?
150 mL ## Footnote Total volume of CSF produced per day is 450 mL
26
How does the composition of CSF facilitate **control of ventilation**?
**Reduced protein concentration** in CSF limits buffering capacity allowing changes in pH to occur ## Footnote This affects central chemoreceptors which controls ventilation
27
Which **interleukin** is anti-inflammatory?
IL-10
28
What is the **difference** between muscle spindles and Golgi tendon organs?
* **Muscle spindles** are stretch transducers that maintain a constant muscle length despite a change in load. * **Golgi tendon organs** are found in muscle tendons and function to limit tension generated within the muscle.
29
What type of receptor is the **insulin receptor**?
Tyrosine kinase linked receptor
30
Describe how **adrenaline** is synthesized.
* L-tyrosine --> L-Dopa by tyrosine **hydroxylase** * L-Dopa --> dopamine by dopa **decarboxylase** * Dopamine --> noradrenaline by **dopamine hydroxylase** * Noradrenaline --> adrenaline by **PNMT** (phenylethanolamine N-methyltransferase)
31
What reaction is responsible for the conversion of **lactate to pyruvate**?
Cori cycle
32
What are the five types of **muscarinic** receptor.
* **M1:** brain and gastric parietal cells * **M2:** heart, affects pacemaker * **M3:** smooth muscle of bronchioles, arterioles and bladder, glandular secretion (e.g. saliva, sweat, pancreatic) * **M4:** CNS * **M5:** regulate dopamine release in the CNS ## Footnote M1, M3, M5: Gq coupled M2, M4: Gi coupled
33
What is the structure of the **nicotinic acetylcholine** receptor?
A **pentameric ligand-gated** ion channel composed of two alpha, one beta, one delta, and one epsilon subunit. ## Footnote In fetal development, the receptor contains a gamma subunit instead of epsilon.
34
How much blood flow goes to the **brain**?
15% of cardiac output at rest which is around **750ml/min**.
35
Which **electrolyte** is found in greater abundance in the CSF than in the plasma?
Chloride and Magnesium ## Footnote NOTE: osmolality is the same.
36
What are the two types of **mu opioid receptors** and what **effects** does stimulation bring about?
**Mu-1** = analgesic + physical dependance **Mu-2** = respiratory depression, reduced peristalsis, euphoria and miosis
37
Where are **delta opioid receptors** (DOP) found and what are the **effects** of stimulation?
**Brain**: Leads to analgesia, antidepressant effect and physical dependence.
38
Where are **kappa opioid receptors** (KOP) found and what are the **effects** of stimulation?
**Brain and spinal cord**: Leads to spinal analgesia, sedation and miosis.
39
Where are **NOP** receptors found and what are the **effects** of stimulation?
**Brain and spinal cord**: Leads to anxiety, depression, appetite modulation, and is thought to be involved in tolerance.
40
Describe how the **electrolyte levels** in the **CSF** differ from that of the **plasma**.
**In the CSF:** * Calcium: Lower * Sodium: Similar * H+: Higher (more acidic) * Magnesium: Higher * Chloride: Higher
41
Describe how **lactate** can be used as a **source of energy**.
* It is converted to **pyruvate** by **lactate dehydrogenase** in the cytoplasm of cells. * Pyruvate can then enter the **mitochondria** and enter the Krebs cycle or may be **converted to glucose** in the liver or kidneys. * In skeletal muscle, **75% of lactate** produced is **oxidised** and used as a fuel source. * **Gluconeogenesis** is an aerobic process. It is more efficient when muscle activity stops.
42
What is **noradrenaline** metabolised to?
**Vanillylmandelic acid** (VMA) by COMT and MAO.
43
Anatomically speaking where is the **chemoreceptor trigger zone** located?
Floor of the **fourth** ventricle
44
Why can **hyperkalaemia** lead to **acidosis** and vice versa?
In the collecting duct, **H+/K+ exchangers** in intercalated cells excrete more hydrogen ions during acidosis, leading to potassium retention.
45
What is the **Gibbs-Donnan** equilibrium?
Describes the **distribution of ion species** across a semi-permeable membrane when: * Some ions (typically large, charged molecules like proteins) cannot cross the membrane. * Small, diffusible ions can cross and distribute themselves to maintain electrochemical balance.
46
State the ATP yield of **glycolysis**.
4 produced, 2 consumed – 2 ATP gain. 2x NADH yield 6 ATP in oxidative phosphorylation
47
State the ATP yield of the **link reaction**.
2x NADH yield 6 ATP
48
State the ATP yield of the **Krebs' cycle**.
Direct production of two ATP. 6x NADH yield 18 ATP and 2x FADH2 yield 4 ATP
49
Which indicator is best for measuring **total body water**?
Deuterium oxide ## Footnote Inulin – Extracellular fluid Plasma – Radiolabelled albumin, Evan’s blue dye Red cell volume – Radiolabelled red cell
50
Which indicator is best for measuring **extracellular fluid volume**?
Inulin
51
Which indicator is best for measuring **plasma volume**?
* Radiolabelled albumin * Evan's blue
52
Why are glucagon levels high in **diabetic ketoacidosis**?
There is a perceived lack of glucose because the **glucose cannot enter cells**.
53
What are the **normal ranges** for **protein**, **glucose** and **white cells** in CSF?
* Protein: **0.2-0.4 g/L** * White Cells: **0-5 per µL** * Glucose: **60-70%** of blood glucose
54
Which enzyme prevents excessive signaling from **G protein-coupled receptors**?
GTPase ## Footnote The alpha subunit of the G-protein has an intrinsic GTPase that breaks down GTP into GDP and Pi, deactivating the receptor and returning the G-protein to its resting state.
55
What are the **daily requirements** for sodium, potassium, and calories?
* **Calories**: 35 kcal/kg/day * **Sodium (Na)**: 1 mmol/kg * **Potassium (K)**: 1 mmol/kg ## Footnote 1 gram of glucose = 4 kcal.
56
Describe the **structure** of the **NMDA receptor**.
* Two **NR1** subunits * Two **NR2** subunits Ionotropic receptor allowing Na⁺ and Ca²⁺ influx.
57
Describe the action of **magnesium** at the **NMDA receptor**.
* Mg blocks the receptor in its resting state. * Block is removed upon cell depolarization.
58
Describe the structure of the **sympathetic nervous system** and its neurotransmitters.
* Sympathetic nerves arise from the lateral horns of the spinal cord at T1-L5 (**thoracolumbar**). * **Short myelinated** preganglionic neurons synapse in ganglia near the vertebral column (sympathetic chain) using **ACh**. * **Long unmyelinated** postganglionic neurons synapse with target organs, releasing **adrenaline** or **noradrenaline**.
59
Which ions pass through **nicotinic acetylcholine receptors** at the neuromuscular junction upon acetylcholine binding?
Sodium and potassium. ## Footnote This causes depolarization of the post-synaptic membrane.
60
What is the **outflow** of the sympathetic nervous system?
Thoracolumbar T1 to L2
61
What is the **difference** between the white and grey rami communiantes?
* **White**: myelinated and formed by preganglionic sympathetic neurones leaving the spinal cord. * **Grey**: postganglionic fibres join the spinal nerves through the grey rami.
62
How many **ganglia** are in the sympathetic chain?
23-24 ## Footnote 3 cervical 12 thoracic 4 lumbar 4-5 sacral
63
What is the outflow of the **parasympathetic nervous system**?
**Craniosacral:** nerves 3, 7, 9, and 10 **Sacral:** S2-S4 ## Footnote Parasympathetic ganglia are typically located near target tissues.
64
What type of **G protein** is associated with each **adrenoceptor**?
* **Alpha-1**: Gq * **Alpha-2**: Gi * **Beta-1** and **Beta-2**: Gs
65
How does **cerebral blood flow** change with **ventilation**?
Cerebral blood flow increases with **rising pCO₂** and remains stable with **pO₂ changes** until it **drops below ~8 kPa**. ## Footnote The relationship between pCO₂ and cerebral blood flow is linear, with a change of about 2% per mm Hg.
66
What are the relative proportions of **brain tissue**, **CSF** and **blood** within the cranium?
* Brain: 80% * CSF: 12% * Blood: 8%
67
Describe how **intracranial pressure** changes with increasing **intracranial volume**.
Initially, venous blood volume decreases, followed by a reduction in CSF volume, and finally arterial blood volume decreases. Above **20 mm Hg**, focal ischaemia occurs; above **45 mm Hg**, global ischaemia occurs.
68
How can **neurotransmitters** be classified?
* **Amines**: adrenaline, noradrenaline, dopamine, serotonin, histamine * **Amino Acids**: glycine, glutamate, GABA * **Polypeptides**: substance P, vasopressin, oxytocin * **Other**: acetylcholine, NO
69
Is the **knee jerk reflex arc** mono- or disynaptic?
It includes a **monosynaptic reflex** for agonist contraction and a **disynaptic reflex** for antagonist relaxation.
70
Outline the **Cohen and Woods classification** of **lactic acidosis**.
* **Type A**: inadequate tissue oxygen delivery (e.g., hypoperfusion) * **Type B**: non-hypoxic processes affecting production and elimination (e.g., lymphoma)
71
What is the basis of **strong ion difference**?
It refers to the difference between **strong cations and anions in solution**, affecting H⁺ concentration and pH. ## Footnote As per electroneutrality: SID + [H⁺] + [OH⁻] = 0
72
Outline the **A to C classification** of nerve fibres.
* **A-Alpha**: proprioception, voluntary motor * **A-Beta**: fine touch, pressure * **A-Gamma**: muscle spindle * **A-Delta**: pain, temperature * **B**: pre-ganglionic autonomic * **C** (unmyelinated): post-ganglionic autonomic, dull pain
73
Outline the stages of **red cell production**.
* Proerythroblast * Prorubricyte * Rubricyte * Normoblast * Reticulocyte * Erythrocyte ## Footnote Occurs in bone marrow and takes about 7 days.
74
Why does **alkalosis** reduce ionised calcium concentration?
It increases calcium binding to plasma proteins.
75
Describe the difference between drugs bound by **albumin** and **alpha-1 acid glycoprotein**.
* **Albumin**: binds acidic drugs (e.g., thiopental, midazolam, diazepam) * **Alpha-1 Acid Glycoprotein**: binds basic drugs (e.g., opioids, local anesthetics)
76
What is the breakdown of **total daily energy** expenditure?
* Basal Metabolic Rate (BMR) * Physical Activity Level (PAL) * Thermic Effect of Food (TEF) ## Footnote These components account for the calories burned throughout the day, including resting energy needs and energy used during activities.
77
Describe trends in **energy substrates** during fasting.
* **Glycogen**: depleted in 24 hours * **Gluconeogenesis**: peaks at 2 days * **Lipolysis**: increases beyond gluconeogenesis
78
How does **myelin** affect axon capacitance?
**Reduces capacitance** by increasing the distance between intracellular and extracellular sides of the membrane. ## Footnote This allows less charge to change the membrane potential, enabling faster action potential propagation.
79
What is a **space constant**?
Measure of how far an **electrical signal** travels along a neurone **before decaying to 37%** of its original value. ## Footnote Myelin increases the space constant by: * Increasing membrane resistance (less current leakage) * Reducing capacitance (less charge needed to change voltage)
80
An injury at which spinal level increases the risk of **neurogenic shock**?
Above **T5**
81
Why does **hyperkalaemia** cause muscle weakness?
It raises the resting membrane potential (**slightly depolarized**), opening voltage-gated sodium channels. However, prolonged depolarization leads to sodium channel **inactivation**.
82
How is **acetylcholine** synthesized in the body?
Acetylcholine is synthesized from **acetyl-CoA** and **choline** through the action of the enzyme **choline acetyltransferase**. ## Footnote This neurotransmitter plays a crucial role in muscle activation and neurotransmission.
83
What is the equation for corrected calcium?
Corrected calcium can be calculated using the formula: **Total calcium + 0.8 × (4 - serum albumin)**. ## Footnote This equation adjusts calcium levels based on albumin concentration in the blood.
84
Describe the forms of **iron** in the body.
* **Haemoglobin**: 2.5 g * **Ferritin** (in bone marrow, liver, spleen): 2 g * **Myoglobin** and **cytochromes**: 0.4 g * **Transferrin**: 0.04 g ## Footnote Total iron in the body is approximately 4-5 g.
85
Where are the different **glucose transporters** located?
* **GLUT1**: red blood cells * **GLUT2**: pancreatic beta cells, basolateral membrane of intestinal cells * **GLUT4**: skeletal muscle, adipose tissue * **SGLT1**: intestinal cells
86
How long do **glycogen**, **protein**, and **fat** stores last during starvation?
* Glycogen: 24-48 hours * Protein: 12 days * Fat: 25 days
87
Describe the mechanism by which **insulin** exerts its effects.
* **Tyrosine-kinase** linked receptor activates **IP3** * Activation of **PKB** * Translocation of **GLUT4** to membrane for glucose uptake ## Footnote Also, there is a reduction in **cAMP**.
88
What type of receptor is the **histamine-1 receptor**?
**Gq protein** coupled receptor.
89
What are the different types of **muscle fibers**?
* **1**: slow-twitch * **2a**: fast-twitch, fatigue resistant * **2b**: fast-twitch, fatiguable
90
What is the **sequence of reactions** in the Krebs' cycle?
* Citrate * Isocitrate * Alpha-Ketoglutarate * Succinate * Fumarate * Malate * Oxaloacetate
91
Which receptors are found in the **chemoreceptor trigger zone**?
* Histamine (H1) * Muscarinic * Dopaminergic (D2) * Serotonergic (5-HT3) * Opioid * Adrenoceptors (alpha 1 and alpha 2)
92
What is the **hydrogen ion concentration** at physiological pH?
40 nmol/L
93
Describe the **phases** of the vomiting reflex.
* In the **pre-ejection phase**, nausea, increased salivation, gastric relaxation, and retrograde peristalsis occur. Protective airway changes include a deep breath that elevates the hyoid and larynx, relaxes the upper gastro-oesophageal sphincter, elevates the soft palate, and closes the glottis. * In the **ejection phase**, abdominal and diaphragmatic contractions occur with retrograde oesophageal contraction, leading to forceful ejection of gastric contents.
94
What **type of receptor** are opioid receptors?
**Gi protein-coupled** receptors.
95
Describe the activity of the **NMDA receptor**.
* Ligand-gated ion channel * Responds to **glutamate** and **glycine** * Depolarization unblocks Mg²⁺, allowing Ca²⁺ to flow.
96
State the equation for **strong ion difference**.
SID = (Na + K + Mg + Ca) - (Cl + lactate) SID = Na - Cl SID + H - OH = 0 ## Footnote A reduction in strong ion difference indicates greater water dissociation, resulting in higher H⁺ concentration.
97
What is the **complement system** and how does it function?
Series of proteins aiding antibodies and phagocytes in clearing pathogens (part of innate immune response). * **Classical**: antibody + antigen → C1 * **Alternative**: pathogen + C3 * **Lectin**: mannose-binding lectin + carbohydrate on pathogen surface. * **Common**: C3 → C5 → C6-9 to form **MAC**. * **MAC** coats the pathogen, creating transmembrane channels that lead to cell lysis.
98
What are the afferent and efferent fibres of the **muscle spindle reflex**?
* **Afferent**: 1a and 2 sensory fibres (1a are fast, 2 are slower adapting). * **Efferent**: A-alpha fibres to extrafusal muscle fibres for contraction + A-gamma fibres to maintain spindle tension.
99
Outline the process of **excitation-contraction coupling** in smooth muscle.
* Stimulus (electrical, chemical, mechanical) → ↑ intracellular Ca²⁺ (influx + SR release). * Ca²⁺ binds calmodulin → activates MLCK. * MLCK phosphorylates myosin → cross-bridge cycling with actin → contraction. * Relaxation: Ca²⁺ removed + MLCP dephosphorylates myosin.
100
What are the three types of **COX enzymes**?
**COX1**: constitutive and found in most cells **COX2**: inducible and normally undetectable in normal tissues but is found in abundance in macrophages and other inflammatory cells **COX3**: CNS variant of COX1 (site of action of paracetamol)
101
Where are the two types of **monoamine oxidases** found?
**MAO-A**: cerebral cortex (areas of serotoninergic transmission), liver, pulmonary vasculature, GI tract, placenta **MAO-B**: striatum and globus pallidus (noradrenaline), platelets NOTE: MAO-A present from birth, MAO-B develops afterwards
102
Describe the action of **acetylcholinesterase**.
Acetylcholinesterase has an **anionic site** which attracts a quaternary ammonium moiety and an **esteratic site** which binds to the ester group in ACh. ## Footnote Breakdown of ACh releases choline, and then it is hydrolysed to release acetic acid.
103
Describe the action of **phosphodiesterase**.
* Phosphodiesterase **hydrolyses** cAMP and cGMP. * cAMP normally **increases PKA activity** which opens L-type calcium channels. Therefore, PDE inhibitors increase cAMP levels leading to a **positive inotropic effect**.
104
What are the types of **G proteins** linked to **GPCRs**?
* **Gs**: stimulates adenylyl cyclase, increasing cAMP * **Gi**: inhibits adenylyl cyclase, decreasing cAMP * **Gq**: activates phospholipase C, producing DAG and IP3, leading to increased calcium release.
105
Outline the **Coombs' classification** of allergic reactions.
* **I**: IgE-Mediated (e.g., anaphylaxis) * **II**: Cytotoxic, Antibody-Dependent (e.g., AIHA) * **III**: Immune Complex-Mediated (e.g., rheumatoid arthritis) * **IV**: Cell-Mediated (e.g., contact dermatitis)
106
Which **chromosomes** contain the alpha and beta globin genes?
* **Alpha**: 14 * **Beta**: 11
107
Which types of receptors are in the **chemoreceptor trigger zone** (area postrema)?
* Mu opioid * Kappa * Dopamine D2 * Neurokinin 1 * Serotonin 5-HT3
108
What happens to the breakdown products of **haemoglobin**?
* Split into **haem** and **globin** components. * **Haem**: broken down to iron and biliverdin. * **Globin**: broken down to amino acids.
109
What happens to the **iron** from red cell breakdown?
* Iron binds to **transferrin**, transported to **muscle, liver, and spleen**. * Here, it detaches from transferrin, binds to ferritin and haemosiderin, and can be **sent to bone marrow for red blood cell production**.
110
Why is **haemoglobin** necessary?
Haemoglobin **increases the oxygen-carrying capacity** of the blood around 70-fold. ## Footnote Oxygen is quite insoluble in water (only 1.5% of oxygen is carried dissolved in plasma).
111
What is **thalassemia**?
**Autosomal recessive** disorder characterised by reduced synthesis of globin chains resulting in the formation of abnormal haemoglobin and, hence, microcytic anaemia ## Footnote It is described as alpha- or beta-thalassemia based on the type of globin chain affected
112
Describe the **structure** of **haemoglobin**.
* **Tetramer**: each subunit has a globin chain and haem group (with a central Fe²⁺ ion in a porphyrin ring). * **HbA**: 2 alpha, 2 beta * **HbA2**: 2 alpha, 2 delta * **HbF**: 2 alpha, 2 gamma
113
Why is the **oxyhaemoglobin dissociation curve** sigmoid?
Due to oxygen's binding characteristics to haemoglobin: * **Allosteric modulation**: Oxygen binding shifts haemoglobin to a 'relaxed' state. * **Cooperative binding**: The R state has a higher affinity for oxygen, facilitating further binding.
114
How does the **myoglobin dissociation curve** differ from that of **haemoglobin**?
Myoglobin has a **higher affinity for oxygen** than haemoglobin, featuring a single binding site, resulting in a rectangular hyperbola for its ODC with a P50 of 0.13 kPa, significantly lower than that of haemoglobin.
115
What is **myoglobin** and its function?
* **Oxygen-carrying** protein in skeletal muscle. * Takes up oxygen from Hb and releases it in exercising tissues at low pO₂ (provides oxygen during sustained contractions when flow may be restricted).
116
Describe the inputs to the **vomiting centre**.
**Chemoreceptor Trigger Zone** * Vagal afferents from **GI tract** → **5HT-3 receptors** * Located outside BBB to detect toxins. * Stimulated by volatiles. **Nucleus Tractus Solitarus** * Vagal afferents from **vestibular** system → **H1 + ACh receptors** * Signals from CTZ via D2 receptors. * Cortex can trigger vomiting.
117
What stimulates **ADH secretion**?
* Hyperosmolality * Volume depletion (low-pressure baroreceptors) * Angiotensin II
118
What are the **effects of ADH**?
* Increased water permeability in the collecting duct * Reduced urine volume * Release of factor 8 by endothelium * Arteriolar vasoconstriction (V1) * Platelet aggregation (V1)
119
What factors govern **sodium balance**?
* RAS system * Aldosterone and cortisol * ANP * GFR and tubuloglomerular feedback * ADH
120
What is an **osmole**?
* **1 osmole** = amount of solute that exerts an osmotic pressure of 1 atm when placed in 22.4 L of solution at 0 °C. * For substances that do not dissociate (i.e. glucose, 1 osmole = 1 mole). * For substances that dissociate into two osmotically active particles, e.g. NaCl, 1 osmole = 1 mole/2 (i.e. 1 mole = 2 osmoles).
121
What is the equation for **osmolality**?
(2 × Na+) + glucose + urea
122
Where are **osmoreceptors** found?
* Anterior hypothalamus (outside BBB) * Respond to change in osmolality and stimulate thirst and secretion of vasopressin
123
What is an **action potential** in a mixed nerve?
A rapid change in **membrane potential** that occurs when a neuron is activated, leading to **depolarization** and **repolarization** phases. ## Footnote This process is essential for the transmission of electrical signals along nerves.
124
What is the **Nernst** equation?
* Calculates the **electrical potential for an individual ion**, thus helping to predict how each ion affects the cell membrane potential. * Represents electrical potential required to balance a given ionic concentration gradient across a membrane so that there is no net flux.
125
What is the **Goldman constant field equation**?
Calculates **overall membrane potential** considering ion **permeabilities** and **concentration** gradients.
126
Describe **cerebral blood flow autoregulation**.
* Global cerebral blood flow: 50 mL/100 g/min. * Regulated by myogenic theory and metabolic activity (K⁺, H⁺, adenosine). * TBI can impair autoregulation; thus, blood pressure control is crucial.
127
Describe the effects of PaO2 and PaCO2 on cerebral blood flow.
PaO2 < 8 kPa causes an increase in CBF
128
Describe the effect of **anaesthetic drugs** on **cerebral blood flow**.
* **Volatiles**: increase CBF and reduce cerebral metabolic oxygen requirement. * **Nitrous**: increase CBF and CMRO. * **Induction agents**: all reduce CBF and CMRO *except* **ketamine**.
129
What is the normal **intracranial pressure**?
10-15 mm Hg
130
How is intracranial **pressure** related to intracranial **volume**?
Initially, intracranial pressure remains stable due to **compensatory mechanisms**, such as reduced venous blood volume. However, once these mechanisms are exhausted, **intracranial pressure rises** rapidly. ## Footnote This relationship is crucial in understanding conditions like traumatic brain injury and hydrocephalus.
131
What is the **osmolar gap**?
Difference between measured **serum osmolality** and **calculated osmolarity**. ## Footnote (2 Na + Glu + Urea) Normally < 10 mOsmol/kg. A larger gap indicates other **osmotically active particles** (e.g., alcohol, methanol, ethylene glycol, hypertriglyceridaemia).
132
List some causes of **nephrogenic diabetes insipidus**.
* Lithium * Hypercalcaemia * Hypokalaemia * Kidney disease (e.g. PKD)
133
What is the maximum recommended rate of resolution of **serum sodium concentration**?
* **10 mmol/L** in the first 24 hours * **8 mmol/L** every 24 hours thereafter ## Footnote Risk of central pontine myelinolysis.
134
How much **hypertonic saline** should be given for severe **hyponatraemia**?
Administer a **150 mL bolus of 2.7% hypertonic saline** (3-5 mL/kg). ## Footnote Repeat until a 5 mmol/L increase in Na concentration is observed.
135
How long does a **normal sleep cycle** last?
90 mins (4-6 cycles per night) ## Footnote REM fraction increases with subsequent cycles.
136
How do heart rate and respiratory rate change during **NREM** and **REM** sleep?
During **NREM** sleep, heart rate and respiratory rate decrease **as sleep deepens**. In **REM** sleep, heart rate increases, breathing becomes irregular, and the body is functionally paralyzed, making it easier to rouse than in stage 3 NREM.
137
What EEG patterns occur during **NREM** and **REM** sleep?
**NREM**: frequency decreases with sleep depth (delta waves in stage 3) **REM**: EEG resembles awake state.
138
Which areas of the **central nervous system** are affected by general anaesthetics?
* Cerebral cortex * Pontine reticular activating formation * Thalamus * Spinal cord
139
What is the **size** of a red cell?
6-8 µm
140
Why does **Cushing's reflex** occur?
Brainstem ischaemia triggers a **massive increase** in sympathetic outflow, causing widespread vasoconstriction to maintain cerebral perfusion by raising MAP. ## Footnote This results in reflex bradycardia.
141
What are the layers of the **blood-brain barrier**?
* Capillary endothelial cells (with tight junctions) * Thick basement membrane * Astrocyte foot processes (regulate endothelial cells)
142
Which areas of the **CNS** have **fenestrated capillaries** that detect changes in blood composition?
* Hypothalamus * Chemoreceptor trigger zone * Anterior pituitary gland * Choroid plexus
143
Over what range of **cerebral perfusion pressure** is **autoregulation** effective?
50-150 mm Hg
144
State the **Nernst equation**.
Potentials: **K⁺**: -90 mV **Na⁺**: +50 mV **Cl⁻**: -70 mV ## Footnote Due to higher permeability of the cell membrane to K⁺, the RMP is closest to the equilibrium potential of K⁺.
145
Describe the **nerve action potential**.
* RMP: -70 mV * Small depolarization reaches threshold (-55 mV) * Voltage-gated sodium channels open, causing sodium influx * Potential approaches +30 mV; VGNCs inactivate (refractory) * K⁺ influx through VGKCs leads to repolarization; delayed closure causes brief hyperpolarization.
146
List factors affecting **action potential conduction velocity**.
* **Axon diameter**: larger diameter increases velocity due to lower resistance. * **Transmembrane resistance**: high resistance (myelination) reduces current leak, favoring longitudinal flow. * **Membrane capacitance**: decreased capacitance (myelination) reduces time to alter polarity. * **Temperature**: higher temperature increases ion channel activity and conduction velocity.
147
How does **myelin** affect action potential propagation?
Myelinated areas have **higher resistance** and **lower capacitance**, reducing charge leak and enabling rapid transmission. At nodes of Ranvier, a full action potential is triggered to maintain signal strength.
148
Describe the **absolute** and **relative refractory periods** of the nerve action potential.
* **Absolute**: Begins with VGNC opening, lasts ~1 msec; VGNC inactivated until membrane potential restores. * **Relative**: Occurs 2-3 msec after ARP; stronger stimulus needed to overcome hyperpolarization from increased K⁺ efflux. ## Footnote Ensures unidirectional flow and limits potential frequency.
149
What is a **nociceptor**?
Free, **unmyelinated** nerve ending that generates action potentials in response to various stimuli (e.g., K⁺ from damaged cells, bradykinin, histamine, serotonin, leukotrienes, prostaglandins).
150
Which neurotransmitters do first-order **nociceptive neurones** release?
* Substance P * Glutamate
151
How is **pain sensation** from the face transmitted?
* 1st order **C** or **Aδ** fibers of the trigeminal nerve to the trigeminal nucleus. * Trigeminal nucleus has **three parts**: **SPINAL** (pain and temperature), **MAIN** (touch and proprioception), **MESENCEPHALIC** (jaw proprioception). * 2nd order neurons cross immediately and ascend to the thalamus, synapsing with 3rd order neurons.
152
What mechanisms **modulate pain**?
* **Segmental Inhibition**: rubbing the injured area (gate control theory) * **Endogenous Opioids**: hyperpolarize cells * **Descending Inhibition**: from periaqueductal grey matter
153
What is **hyperalgesia**?
**Increased pain sensation** from a normally painful stimulus. ## Footnote **Primary**: in damaged tissues (e.g., sunburn) due to release of substance P, bradykinin, and histamine, which sensitize nociceptors and lower threshold potential. **Secondary**: in surrounding tissues, increased neurotransmitter release by 2nd order neurons affecting adjacent neurons (somatotopic organization).
154
What is **allodynia**?
Sensation of pain to a stimulus that **does NOT normally provoke pain** ## Footnote May be due to reorganisation of circuitry of spinal cord
155
Describe the structure of the **muscle spindle**.
Contains two types of intrafusal muscle fibers: **nuclear bag** and **nuclear chain** fibers based on nucleus distribution. **Afferent**: 1a signals length and rate of change; 2 signals static length only. **Efferent**: Gamma-motor neurons innervate contractile portions to maintain sensitivity during skeletal muscle shortening.
156
What is an example of a **polysynaptic reflex**?
Withdrawal reflex
157
Which descending pathways control **muscle tone**?
* **Pyramidal** tract * **Extrapyramidal** neurons (innervate gamma motor neurons) ## Footnote Examples: tectospinal, rubrospinal, vestibulospinal, reticulospinal tracts.
158
Describe the structure of a **sarcomere**.
Functional unit of a myocyte with thick and thin filaments: * **Thick**: myosin with 2 globular heads and long tail, surrounded by 6 thin filaments. * **Thin**: 2 strands in helix with binding sites for myosin, blocked by tropomyosin (associated with TnT, TnI, TnC).
159
Describe **excitation-contraction coupling** in skeletal muscle.
* Motor endplate **depolarizes**, transmitting action potential along sarcolemma and T-tubules. * Depolarization causes conformational change in **DHPR** (L-type calcium channel), triggering **RyR** on SR to open and **release Ca**. * Ca binds to TnC, moving tropomyosin away and **enabling actin-myosin binding**.
160
What is the passage of the **corticospinal tract**?
The corticospinal tract is a major neural pathway that originates in the **motor cortex** and descends through the **brainstem and spinal cord**, facilitating **voluntary motor control**. ## Footnote It is crucial for the coordination of fine motor movements and is involved in the control of skeletal muscles.
161
Outline the **synthesis** of red blood cells.
* Stem Cell * Myeloid Progenitor Stem Cells * Burst Forming Unit - Erythroid Cells * Colony Forming Unit - Erythroid Cells * Erythroblast Phases (nucleus present) * Reticulocyte (nucleus lost) ## Footnote Globin is produced in the cytoplasm; haem is produced in the mitochondria.
162
What is the main mechanism for controlling **iron** content?
* **Hepcidin** is produced by the liver when iron levels are high. * Hepcidin binds to and inhibits **ferroportin**. ## Footnote Fe²⁺ is converted to Fe³⁺ by **hephaestin** and **caeruloplasmin**, which then binds to **transferrin**.
163
What are the three stages of **haemostasis**?
* Vasoconstriction * Soft platelet plug * Coagulation (fibrin clot)
164
What are the **three phases** of the cell-based coagulation model?
* **Initiation**: triggered by vessel damage, activating platelets and clotting factors. * **Amplification**: further activation of platelets and clotting factors. * **Propagation**: activated platelets form large amounts of thrombin.
165
What are the main classes of **hormones**?
* **Amine**: catecholamines, thyroxine * **Peptide**: vasopressin, insulin, GH, TSH, LH, FSH * **Steroid**: cortisol, sex hormones * **Eicosanoids**: prostaglandins, thromboxane, leukotrienes
166
What are the main physiological effects of **glucocorticoids**?
* **Metabolic**: increased plasma glucose, increase gluconeogenesis (incl. increased lipolysis) * **Cardiovascular**: increases sensitivity of vasculature to catecholamines
167
Describe the **differences** in hormones produced by the **thyroid gland**.
* **T3**: Active form, 10% of release, 99.7% bound to albumin, half-life 24 hours. * **T4**: Less active, 90% of release, highly protein-bound to thyroid-binding globulin, half-life 7 days, 50% converted to T3, 50% to reverse T3 (inactive).
168
Outline the steps in the synthesis of **thyroid hormone**.
* **Iodide uptake**: TSH stimulates I- uptake via Na/I cotransporter into the follicular lumen. * **Oxidation to iodine**: Iodide is oxidized using H₂O₂, catalyzed by thyroid peroxidase. * **Reacts with tyrosine**: Iodine reacts with tyrosine in thyroglobulin to form mono- or di-iodotyrosine. * **Oxidative coupling**: Iodinated tyrosines couple to form T3 and T4.
169
What is a **hapten**?
Small molecule that may stimulate the immune system when **attached to a larger carrier protein**.
170
How is **acquired immunity** developed?
* APC carrying antigen travels to lymph node * APC interacts with matching B and T helper cells * Activated T helper cells proliferate, producing clones, some become memory T cells * Activated B cells produce clones that become plasma cells (mostly) or memory B cells * Plasma cells rapidly produce antibodies ## Footnote Somatic hypermutation and affinity maturation improve antibody response over time.
171
What are the functions of **antibodies**?
* **Opsonization**: marks pathogens for destruction * **Agglutination**: clumps pathogens for easier targeting by leukocytes * **Inactivation**: neutralizes pathogens * **Complement activation**: triggers the complement system
172
What is the role of **hCG** in pregnancy?
* Produced by the placenta to prolong the corpus luteum's life * Maintains progesterone production, preventing endometrium breakdown * hCG levels rise for 10 weeks, after which the placenta takes over progesterone and estrogen production.
173
Describe the **roles** of oestrogen and progesterone in pregnancy.
**Oestrogen** * Increase uteroplacental blood flow * Stimulate uterine growth * Sensitise myometrium to oxytocin **Progesterone** * Relaxation of myometrium * Formation of mucus plug * Breast development
174
What are the **effects of relaxin** during pregnancy?
* Increased cardiac output * Increased renal blood flow * Relaxes pelvic ligaments ## Footnote Produced by the placenta, peaks in the first trimester.
175
What are the functions of the **placenta**?
* Exchange of nutrients * Endocrine (hPL, oestrogen and progesterone) * Immunological (barrier between mother and baby)
176
How are **proteins** broken down for energy?
* Amino acids are deaminated or transaminated to form **ketoacids**. * Ketoacids enter the Krebs cycle or convert to glucose or fatty acids. * Amino groups are disposed of via the urea cycle.
177
What substrates can be used to produce glucose in gluconeogenesis?
Lactate Pyruvate Glycerol Amino Acids
178
Which areas of the brain control **body temperature**?
* **Anterior hypothalamus**: lowers temperature (sweating, vasodilation) * **Posterior hypothalamus**: raises temperature (shivering, vasoconstriction)
179
Describe the **sensors** and **effectors** regulating plasma osmolality.
**Osmoreceptors** in the **anterior hypothalamus** stimulate thirst and increase **ADH** secretion from the posterior pituitary.
180
What are the main **immunological complications** of blood transfusion?
* **Febrile non-haemolytic transfusion reaction**: recipient antibodies vs donor leukocytes * **Allergic reaction**: recipient IgE vs donor protein * **TRALI**: recipient pulmonary neutrophils activated by donor antibodies/lipids/cytokines * **Graft-versus-host disease**: T cells in donor blood attack recipient tissues. ## Footnote TRALI is the leading cause of death following transfusion.
181
What important **homeostatic changes** occur during a transfusion?
* Hypothermia * Dilutional coagulopathy * Hypocalcaemia (citrate) * Hyperkalaemia * Acidosis (stored blood pH 6.8)
182
What is the rate-limiting step of **adrenaline synthesis**?
Tyrosine hydroxylase ## Footnote PNMT is only found in the adrenal medulla.
183
Describe the action of **dopamine receptors**.
**D1**: Gs coupled * CNS: extrapyramidal * PNS: vasodilation of splanchnic nerves **D2**: Gi coupled * CNS: reduces pituitary hormone secretion (prolactin) * PNS: inhibits noradrenaline release ## Footnote Dopamine receptors are a type of adrenoceptor.
184
What are the effects of **post-synaptic alpha-2 receptors**?
* Hyperpolarization of CNS neurons * Platelet aggregation
185
What is a **catecholamine**?
A compound with a **catechol** (benzene with hydroxyl groups at C3 and C4) and an amine group at C1.
186
What are the two uptake mechanisms for noradrenaline?
**UPTAKE 1: neuronal** Main mechanism of inactivation for endogenous noradrenaline Recycled and metabolised by MAO **UPTAKE 2: extra-neuronal** Metabolised by COMT in tissues to VMA and normetadrenaline
187
Describe the actions of **protein C**, **protein S**, and **thrombomodulin**.
* **Protein C**: vitamin K-dependent anticoagulant that inactivates factors Va and VIIIa. * **Protein S**: cofactor for protein C. * **Thrombomodulin**: endothelial receptor that binds thrombin, switching its role from procoagulant to anticoagulant (via activation of protein C).
188
What are the main roles of **thrombin**?
* Activates factor 13 (stabilizes fibrin strands) * Generates positive feedback loop (activates factors 5 and 8, increasing thrombin production) * Activates protein C (via thrombomodulin, leading to anticoagulant effect)
189
What are the main classes of **antidepressants**?
* **TCAs** (e.g., amitriptyline): prevent reuptake of NA and serotonin * **SSRIs** (e.g., sertraline) * **SNRIs** (e.g., venlafaxine) * **MAOIs** (e.g., phenelzine): inhibit metabolism of noradrenaline and serotonin
190
Which substances do **platelets** release upon activation?
* Vasoconstrictors (e.g., serotonin, thromboxane A2) * ADP * Platelet activating factor * vWF * Fibrinogen * Thrombin * Calcium
191
What is the **incretin** effect?
* **Enhances insulin secretion** after *oral* glucose compared to IV glucose, caused by gut-derived hormones GLP-1 and GIP. ## Footnote GLP-1 analogues and DPP inhibitors act via these pathways.
192
By what mechanism does **pregnancy** cause insulin resistance?
Human placental lactogen antagonizes insulin, along with hormones like progesterone, cortisol, prolactin, and growth hormone.
193
Why does **hypomagnesaemia** lead to **hypokalaemia**?
**Hypomagnesaemia** causes renal potassium wasting due to loss of inhibition of **ROMK** channels, leading to increased urinary potassium loss.
194
Describe the mechanism of **oxytocin** release during **labour**.
**Oxytocin** is synthesised in the **hypothalamus** and released by the **posterior pituitary**. Uterine contractions cause the fetal head to press on the cervix, triggering more oxytocin release (positive feedback).
195
What is the **vomiting centre**?
Region in the **medulla** that controls vomiting.
196
Why is **vitamin B12** important for the body?
It is a cofactor for **methionine synthase** which is needed for DNA synthesis and myelination of neurones.
197
What is the **innate immune system** and what are its components?
First line of defense against infection; non-specific and rapid. * **Physical**: skin, mucous, stomach acid * **Cellular**: neutrophils, monocytes, NK cells, eosinophils, basophils * **Molecular**: acute phase proteins (CRP, complement)
198
Outline the physiological changes with **ageing**.
* **Respiratory**: edentulous, weak inspiratory muscles, rigid thoracic cage, compliant lungs, raised closing capacity * **Cardiovascular**: hypertension, conduction abnormalities, valve degeneration * **CNS**: cognitive impairment * **Renal**: reduced GFR * **Liver**: decreased drug clearance, reduced protein synthesis * **Musculoskeletal**: fragile tissues/veins, sarcopenia, impaired thermoregulation
199
What is the haemoglobin threshold for **anaemia**?
Men: < 130 g/L Women: < 120 g/L
200
What are the physiological effects of **thyroid hormones**?
* **Metabolic**: increased BMR * **Respiratory**: increased minute volume due to increased VO₂ * **CVS**: increased beta-adrenergic receptors, increased HR and contractility * **CNS**: anxiety * **MSK**: protein catabolism
201
Which **antibodies** are implicated in **thyroid disease**?
* **Hashimoto's**: thyroid peroxidase, thyroglobulin * **Graves'**: TSH receptor stimulating antibodies
202
Describe the effects of **calcitonin**.
* **intestine**: decreased absorption of Ca and PO4 * **Kidneys**: decreased reabsorption of Ca and PO4, decreased 1-alpha hydroxylase activity * **Bone**: decreased osteoclast activity ## Footnote Calcitonin is secreted by parafollicular C cells in the thyroid gland
203
What is the subunit composition of the **GABA-A receptor**, **nicotinic acetylcholine receptor**, and **NMDA receptor**?
* **GABA-A**: 2 alpha, 2 beta, gamma * **nAChR**: 2 alpha, beta, delta, epsilon * **NMDA**: NR1 and NR2
204
Describe the activity of **G-protein coupled receptors**.
* Ligand binding induces a conformational change. * Alpha subunit exchanges **GDP for GTP**, dissociating from βγ subunit. * Alpha-GTP interacts with effector enzyme/ion channel (e.g., adenylate cyclase). * Alpha subunit hydrolyzes **GTP to GDP** (intrinsic GTPase activity) and **reassociates with βγ**. ## Footnote Gi, Gs, and Gq depend on the alpha subunit.
205
How long does a **neuronal action** potential last?
1-2 msec
206
What is a **threshold potential** with regards to action potentials?
Critical membrane potential that the membrane must reach to **trigger an action potential** (all of nothing).
207
What is the threshold potential of **mixed nerve action** potential?
-55 mV
208
What factors affect the speed of **diffusion** across a membrane?
**Fick's Law**: Proportional to surface area and concentration gradient; inversely proportional to membrane thickness. **Graham's Law**: Proportional to solubility; inversely proportional to the square root of molecular weight.
209
What changes occur during **early starvation**?
Glycogenolysis ## Footnote Liver glycogen breaks down to glucose. High glucagon + low insulin activate cAMP/PKA, leading to glycogen phosphorylase activation.
210
What changes occur during **intermediate starvation** (1-3 days)?
Gluconeogenesis ## Footnote Substrates: lactate (Cori cycle), amino acids, glycerol. High glucagon, high cortisol, low insulin. Cortisol-driven proteolysis frees amino acids for gluconeogenesis.
211
What changes take place in **prolonged starvation** (> 3 days)?
Ketogenesis ## Footnote Fatty acids converted to ketone bodies High Glucagon + Low Insulin Increased hormone sensitive lipase (HSL) activity in adipocytes will breakdown triglycerides to release fatty acids for ketogenesis
212
What are the functions of **CSF**?
* Cushioning/buoyancy * Constant ionic environment * Buffer changes in ICP * Control of respiration * Removal of metabolic waste products
213
What is the **specific gravity** of CSF?
1.003-1.009
214
What is the difference between **osmolarity** and **osmolality**?
**Osmolarity** measures osmoles per liter of solution. **Osmolality** measures osmoles per kg of solvent. ## Footnote Osmolality is preferred as solvent volume changes with temperature, but weight remains constant.
215
Describe the path of **CSF** flow through the brain.
Lateral ventricles → foramen of Monro → third ventricle → aqueduct of Sylvius → fourth ventricle → subarachnoid space via: * Foramen of Magendie (medially) * Foramen of Luschka (laterally) ## Footnote Reabsorbed into dural venous sinuses.
216
What is the mechanism of action of **carbimazole**?
* Prodrug * Converted to active form * Inhibits thyroid peroxidase * Interferes with T3 and T4 synthesis
217
State the equation for **cerebral perfusion pressure**.
CPP = Mean Arterial Pressure - Intracranial Pressure ## Footnote Use central venous pressure instead of ICP if higher.
218
What proportion of **total body weight** is **water**?
60% ## Footnote The simple rule is 60-40-20: TBW 60% - ICF 40% and ECF 20%.
219
What is the normal range for **intra-ocular pressure**?
10-20 mm Hg
220
What are the components of the **laryngeal reflex**?
**Afferent**: Superior Laryngeal Nerve (branch of vagus) **Efferent**: Vagus Nerve ## Footnote Effector muscles are the intrinsic laryngeal muscles (especially the adductors)
221
What is the **delta ratio** in **blood gas analysis**?
Ratio of change in anion gap to change in bicarbonate concentration. **< 0.4**: NAGMA (small change in anion gap, large change in bicarbonate) **1-2**: HAGMA (similar changes in both anion gap and bicarbonate) **0.4-0.8**: combination of normal and high anion gap metabolic acidosis.
222
Which drugs reduce **intraocular pressure**?
* **Reduce humor production**: beta-blockers (e.g., timolol) * **Increase drainage**: prostaglandin analogues, cholinergics (e.g., pilocarpine) * **Both**: ephedrine, alpha-2 agonists (e.g., brimonidine)
223
What is the pathway of the **pupillary light reflex**?
Pupillary light reflex pathway involves **optic nerve** sensing light, transmitting signals to **pretectal nucleus** in midbrain, then to **Edinger-Westphal nucleus**. Efferent signals travel via **oculomotor nerve (CN III)** to **ciliary ganglion**, where post-ganglionic fibers innervate iris sphincter, resulting in pupil constriction. ## Footnote This reflex helps regulate the amount of light entering the eye and protects the retina from excessive brightness.
224
Which cell types are part of the **myeloid lineage**?
* Red cells * Platelets * Granulocytes * Monocytes * Mast Cells
225
What are some features of a **post-splenectomy blood film**?
* Howell-Jolly bodies (nuclear remnant in red cell) * Target cells * Mild thrombocytosis
226
What is the mechanism of action of **tetanus toxin**?
Tetanus toxin acts as a **zinc-dependent endopeptidase**. ## Footnote Cleaves synaptobrevin which disrupts vesicle fusion and prevents the release of inhibitory neurotransmitters (GABA and glycine)
227
What is the **difference** between **B and T cells** in terms of the threats they neutralise?
* B cells: humoral immunity by producing antibodies against **extracellular pathogens** and toxins. * T cells: cell-mediated immunity, killing **virus-infected** or abnormal cells and activating other immune cells to combat **intracellular pathogens**.
228
What is **autonomic dysreflexia**?
* Sudden, **excessive sympathetic response** to noxious stimuli below a spinal cord lesion (≥T6), causing severe hypertension, bradycardia, and autonomic symptoms above the lesion. * Local sympathetic reflex arcs are intact, but descending inhibitory pathways are disrupted, leading to **severe vasoconstriction**. * Triggers include **bladder distension** and **constipation**.
229
What are the main **circumventricular organs**?
* Area postrema – part of CTZ * Subfornical organ (SFO) - osmolality * Organum vasculosum of the lamina terminalis - osmolality * Posterior pituitary - ADH, oxytocin * Pineal gland - melatonin
230
Which fibres of the autonomic nervous system are **unmyelinated**?
* **Pre-ganglionic**: myelinated * **Post-ganglionic**: unmyelinated
231
Which **tissues** receive only **sympathetic innervation**?
* Sweat glands * Arrector pili * Adipose cells * Kidneys * Most blood vessels ## Footnote Lacrimal glands only receive parasympathetic innervation.
232
What are the main actions of **cortisol**?
* **Metabolic**: increase protein catabolism, increase hepatic gluconeogenesis and lipolysis * **Vascular**: maintain vascular sensitivity to catecholamines * **Immune**: anti-inflammatory, impair wound healing
233
Outline the causes of **raised intraocular pressure**.
* **Increased extrinsic pressure**: prone position, retrobulbar hemorrhage, suxamethonium * **Increased aqueous humor**: glaucoma * **Increased choroid blood volume**: head down, hypoxia, hypercarbia, hypertension
234
Outline the **descending inhibitory pain pathways**.
* **Periaqueductal grey matter**: main pathway; transmitters include endorphins, enkephalins, and serotonin. * **Locus coeruleus**: brainstem nucleus projecting inhibitory pathways.
235
What are the actions of the main **prostaglandins**?
* **PGI2**: vasodilation, platelet aggregation * **PGE2**: ↓ gastric acid secretion, ↑ gastric mucous secretion * **PGF2α**: uterine contraction, bronchoconstriction ## Footnote Both PGE2 and PGI2 cause renal afferent arteriolar dilation.
236
What are the physiological consequences of **acidosis**?
* **CVS**: myocardial depression, reduced catecholamine response, arrhythmias * **RESP**: hyperventilation, pulmonary vasoconstriction * **Electrolytes**: hyperkalaemia * **Enzyme/Channel**: reduced enzyme activity, impaired clotting
237
What is the normal range for **cerebral perfusion pressure**?
60-80 mm Hg
Primary FRCA
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