The prostate gland is primarily supplied by the inferior vesical artery, which branches off from the anterior division of the internal iliac artery. The inferior vesical artery supplies the base of the bladder, the distal ureters, and the prostate. The branches to the prostate communicate with the corresponding vessels of the opposite side.

The inferior vesical artery branches into two main arteries:
1. Urethral artery – supplies the transition zone and is the main arterial supply for the adenomas in BPH
2. Capsular artery – supplies the glandular tissue

The venous drainage of the prostate is from the prostatic venous plexus, which drains into the paravertebral veins.

The electrons in the outer shell of an oxygen molecule are unpaired, thus it has paramagnetic properties and is attracted into a magnetic field.

It utilizes null deflection -True
Null deflection is a crucial principle in paramagnetic analysers (reflected beam of light on two photocells) which gives very accurate results (typically 0.1%).

It can be used to measure the concentration of diamagnetic gases – False
Since most other gases are weakly diamagnetic they are repelled by a magnetic field (nitric oxide is also paramagnetic).

Can measure gases dissolved in the blood – False
For accurate analysis the sample gas must be dried before passing into the analysis cell, for example, by passage through silica gel. Therefore, they are unsuitable to measure gases dissolved in blood.

Does not require calibration – False
As with most measurement instruments paramagnetic analysers must be calibrated before use.

E) The readings are unaffected by water vapour – False
Water vapour affects the readings hence for accurate analysis the sample gas must be dried before passing into the analysis cell, for example, by passage through silica gel. That is why they are unsuitable to measure dissolved blood gases.

The basilar artery is a large vessel that is formed by the union of the vertebral arteries at the junction of the medulla and pons. It lies in the pontine cistern and follows a shallow groove on the ventral pontine surface, extending to the upper border of the pons.

The basilar artery then bifurcates into the two posterior cerebral arteries that form part of the Circle of Willis.

The subclavian artery and vein have a similar path throughout their course, with the subclavian vein running anterior to the subclavian artery. The artery and vein are separated by the insertion of the scalenus anterior muscle.

There are three scalene muscles, found on each side of the neck:
1. Anterior scalene
2. Middle scalene
3. Posterior scalene

The scalenus anterior muscle is the anterior most of the three scalene muscles. It originates from the transverse processes of vertebrae C3-C6 and is inserted in the first rib.

There are 4 different types of globin chains which surround 4 heme molecules in haemoglobin (Hb) – α, β, γ and δ.
α chains are essential.
δ2β2 and β2γ2 are not found in a healthy adult.
97% of the Hb in a healthy adult is made of α2β2 (2 α chains and 2 β chains).
α2δ2 accounts for around 1.5-3% of the adult Hb.
α2γ2 accounts for less than 1%.

With respect to oxygen transport in cells, almost all oxygen is transported within erythrocytes. There is limited solubility and only 1% is carried as solution. Thus, the amount of oxygen transported depends upon haemoglobin concentration and its degree of saturation.

Haemoglobin is a globular protein composed of 4 subunits. Haem is made up of a protoporphyrin ring surrounding an iron atom in its ferrous state. The iron can form two additional bonds – one is with oxygen and the other with a polypeptide chain.
There are two alpha and two beta subunits to this polypeptide chain in an adult and together these form globin. Globin cannot bind oxygen but can bind to CO2 and hydrogen ions.
The beta chains are able to bind to 2,3 diphosphoglycerate. The oxygenation of haemoglobin is a reversible reaction. The molecular shape of haemoglobin is such that binding of one oxygen molecule facilitates the binding of subsequent molecules.

The oxygen dissociation curve (ODC) describes the relationship between the percentage of saturated haemoglobin and partial pressure of oxygen in the blood.
Of note, it is not affected by haemoglobin concentration.

Chronic anaemia causes 2, 3 DPG levels to increase, hence shifting the curve to the right

Haldane effect – Causes the ODC to shift to the left. For a given oxygen tension there is increased saturation of Hb with oxygen i.e. Decreased oxygen delivery to tissues.
This can be caused by:
-HbF, methaemoglobin, carboxyhaemoglobin
-low [H+] (alkali)
-low pCO2
-ow 2,3-DPG
-ow temperature

Bohr effect – causes the ODC to shifts to the right = for given oxygen tension there is reduced saturation of Hb with oxygen i.e. Enhanced oxygen delivery to tissues. This can be caused by:
– raised [H+] (acidic)
– raised pCO2
-raised 2,3-DPG
-raised temperature

Understanding of the cardiac action potential helps with the understanding of the ECG which measures the electrical activity of the heart. This is reflected in its waveform.
The rapid depolarisation phase is reflected in the QRS complex. After this phase comes the plateau phase which is represented by the ST segment. Lastly, the T wave shows repolarisation, phase 3.

The cardiac action potential has several phases which have different mechanisms of action as seen below:
Phase 0: Rapid depolarisation – caused by a rapid sodium influx.
These channels automatically deactivate after a few ms

Phase 1: caused by early repolarisation and an efflux of potassium.

Phase 2: Plateau – caused by a slow influx of calcium. (ST segment)

Phase 3 – Final repolarisation – caused by an efflux of potassium. (T wave)

Phase 4 – Restoration of ionic concentrations – The resting potential is restored by Na+/K+ATPase.
There is slow entry of Na+into the cell which decreases the potential difference until the threshold potential is reached. This then triggers a new action potential

Of note, cardiac muscle remains contracted 10-15 times longer than skeletal muscle.

Different sites have different conduction velocities:
1. Atrial conduction – Spreads along ordinary atrial myocardial fibres at 1 m/sec

2. AV node conduction – 0.05 m/sec

3. Ventricular conduction – Purkinje fibres are of large diameter and achieve velocities of 2-4 m/sec, the fastest conduction in the heart. This allows a rapid and coordinated contraction of the ventricles

Oxygen delivery depends on 2 variables.
1) Content of oxygen in blood
2) Cardiac output

Oxygen content (arterial) = (Hb (g/dL) x 1.39 x SaO2 (%) ) + (0.023 x PaO2 (kPa))

Oxygen content (mixed venous) = (Hb (g/dL) x 1.39 x mixed venous saturation) + (0.023 x mixed venous partial pressure of oxygen in kPA)

Huffner’s constant = 1.39 = 1g of Hb binds to 1.39 ml of O2

Oxygen delivery DO2 (ml/min) = 10 x Cardiac output (L/min) x Oxygen content
Normally 1000ml/min

Oxygen consumption VO2 (ml/min) = 10 x Cardiac output (L/min) x Difference in arterial and mixed venous oxygen content
Normally 250 ml/min

Oxygen extraction ratio (OER) = VO2/DO2
Normally approximately 25%

In patients with an intact hypothalamic-pituitary axis, serial TSH measurements are used to determine the adequacy of treatment with thyroid hormones . changes in TSH levels becoming apparent after approximately eight weeks of therapy with thyroid hormone replacement. Change in T3/T4 levels are seen before changes in TSH .

In patients taking thyroid replacement therapy, the most frequent reason for persistent elevation of serum TSH is poor compliance. Patients who do not regularly take their L-thyroxine try and catch up just before a visit to a clinician for blood test.

Tissue-level unresponsiveness to thyroid hormone is caused by mutation in the gene controlling a receptor for T3 and is rare.

Reduced responsiveness of target tissues to thyroid hormone aka resistance to thyroid hormones (rTH) occurs when there is a mutation in the thyroid hormone receptor β gene. It is a rare autosomal dominant inherited syndrome of reduced end-organ responsiveness to thyroid hormone and has two types:

Generalised resistance (GrTH)
Pituitary resistance (PrTH)

Patients with rTH have normal or slightly elevated serum thyroid stimulating hormone (TSH) level, elevated serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations.

Drugs that increase metabolism of thyroxine include:

Warfarin
Rifampin
Phenytoin
Phenobarbital
St John’s Wort
Carbamazepine

These drugs lower circulating thyroid hormones and would be associated with a raised TSH but low T3/T4.

Number needed to treat can be defined as the number of patients who need to be treated to prevent one additional bad outcome.

It can be found as:

NNT=1/Absolute Risk Reduction (rounded to the next integer since number of patients can be integer only).

where ARR= (Risk factor associated with the new drug group) — (Risk factor associated with the currently available drug)

So,

ARR= (165/1050)-(132/1044)

ARR= (0.157-0.126)

ARR= 0.031

NNT= 1/0.031

NNT=32.3

The oxygen content of arterial blood can be calculated by the following equation:
(10 x haemoglobin x SaO2 x 1.34) + (PaO2 x 0.0225).
This is the sum of the oxygen bound to haemoglobin and the oxygen dissolved in the plasma.

Oxygen content x cardiac output = The amount of oxygen delivered to the tissues in unit time which is known as the oxygen flux.

Any factor that increases the metabolic demand will encourage oxygen offloading from the haemoglobin in the tissues and this causes the oxygen dissociation curve (ODC) to shift to the right. This subsequently reduced the oxygen content of arterial blood.

Conditions like fever, metabolic or respiratory acidosis lowers the oxygen content and shifts the ODC to the right.
A low level of 2,3 diphosphoglycerate (2,3-DPG) is usually related to an increased oxygen content as there is less offloading, and so the ODC is shifted to the left.

So for a given PaO2, a high blood oxygen content is related to any factors that can shift the ODC to the left and not to the right.

A low haematocrit usually means that there is a decreased haemoglobin concentration, and therefore is associated with decreased oxygen binding to haemoglobin.