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High altitude has no consensus definition. It is most commonly defined as corresponding to >2500 m above sea level, where most individuals begin to show physiological adaptations. Long-term habitation at high altitude is possible – 100 million people live at altitudes >2500 m. Extreme altitude is defined as >6000 m – Mount Everest is 8848 m high. Humans are able to adapt their physiology to survive for short periods of time at extreme altitude, but long-term habitation is impossible.
The word ‘acid’ is derived from the Latin acidus, meaning sour. Early chemists defined an acid as a chemical substance whose aqueous solution tastes sour, changes the colour of litmus paper to red and reacts with certain metals to produce the flammable gas, hydrogen. Likewise, a base is a chemical substance whose aqueous solution tastes bitter, changes the colour of litmus paper to blue and reacts with acids to produce a salt.
The stress response is a complex neuroendocrine response to physiological stress. The most commonly encountered stressors are trauma, burns, surgery and critical illness; the magnitude of the neuroendocrine response is directly related to the magnitude of the stressor. In addition to its metabolic effects, the stress response leads to activation of the immunological and haematological systems.
The kidneys are solid, ‘bean-shaped’ retroperitoneal organs located at vertebral levels T12 to L3. From inside to outside, the kidney is surrounded by the renal capsule, perirenal fat, renal fascia and pararenal fascia. At the midpoint of the concave medial border of each kidney is the hilum, the point of entry of the nerves, vessels and lymphatics. In cross-section, the kidney contains.
The rate and character of the arterial pulse has been used for millennia for the diagnosis of a wide range of disorders. Perhaps more useful, however, is the direct cannulation of an artery, which allows quantitative information to be extracted.
The central venous pressure (CVP) waveform is measured using a central venous catheter positioned just above the right atrium (RA), within the superior vena cava. Starting from mid-diastole, key features of the normal CVP waveform are (Figure 38.1).
Water is the most abundant component of the human body. On average, 60% of the body is composed of water (this value varies with sex, body habitus and age). Body water is distributed between the two major body compartments: intracellular and extracellular. For the average 70‑kg man.
Metabolism refers to the whole range of biochemical reactions that occur within living organisms. Metabolism broadly encompasses anabolism (the building up of larger molecules from smaller ones) and catabolism (their breaking down into smaller entities with the extraction of energy).
The O2 cascade concept draws together areas of respiratory physiology covered in the previous few chapters. In an examination setting, it allows the examiner to assess your knowledge of more than one topic within a single question.
It comes as no surprise that there are major endocrine changes during pregnancy. These endocrine changes are the driving force for many of the other physiological and anatomical changes associated with pregnancy.
The basic filtration unit of the kidney is the renal corpuscle, consisting of a glomerulus surrounded by a Bowman’s capsule. The high glomerular capillary hydrostatic pressure forces a fraction of the plasma (i.e. water and solutes) through the capillary wall and into the Bowman’s space. This filtration barrier is composed of three layers.
In 2003, the completion of the Human Genome Project resulted in the sequencing of every human gene and subsequently heralded the ‘age of the genome’. Whilst the knowledge of genetics has revolutionised medicine, the phenotypic significance of most genes remains poorly understood. This will be a major focus of physiological research in the future.
Ageing involves processes not only of physical but also of psychological and social change. Increasing numbers of elderly people are undergoing elective and emergency surgery, with post-operative complications being more common in the older population. It is important to understand the normal changes that occur with advancing age so that anaesthetic techniques can be modified and to allow early identification of anaesthetic and surgical complications.
The cell membrane is the lipid bilayer structure that separates the intracellular contents from the extracellular environment. It controls the passage of substances into and out of the cell. This allows the cell to regulate, amongst other parameters, intracellular ion and solute concentrations, water balance and pH. The integrity of the cell membrane is of crucial importance to cell function and survival.
Exercise is a major physiological challenge to the body, affecting all the main body systems. An accompanying increase in muscle metabolic rate results in an increase in O2 demand and a requirement for an increased rate of removal of CO2 and other metabolites, including lactic acid and ketone bodies. Exercise thus requires substantial increases in muscle blood flow with maintenance of mean arterial pressure (MAP). In addition, despite the increased rate of energy metabolism, normoglycaemia must be preserved. Finally, exercising muscle generates a large amount of heat, yet core temperature must be controlled.