Physiology
Basic Cellular
Regarding skeletal muscle contraction, which of the following statements is CORRECT:
Answer:
The A band represents the length of thick myosin filaments. The length of the myosin filaments does not change during an isotonic contraction; instead, the muscle shortens as myosin and actin filaments slide over one another and the sarcomere shortens (the I band (distance between A bands), the H zone (space between thin filaments), and the Z line (sarcomeres) will shorten). The sarcomere length does not change in isometric contraction. In concentric movements the muscle shortens and in eccentric movements the muscle lengthens.Isometric vs Isotonic Contraction
Physiology / Basic Cellular / Skeletal Muscle Physiology
Last Updated: 29th July 2024
Isometric Contraction
Isometric contraction occurs when the two ends of the muscle are held at a fixed distance apart, and stimulation of the muscle causes the development of tension within the muscle due to the tension being transferred to elastic filaments within the muscle without a change in muscle length e.g. holding a weight with an outstretched hand.
Isotonic Contraction
In isotonic contraction one end of the muscle is free to move and the muscle length changes. There are two types of isotonic contraction - concentric and eccentric.
In concentric movements the muscle shortens as the muscle fibres contract, thereby generating force e.g. repeatedly lifting a weight.
In eccentric movements the muscle lengthens in a controlled manner, due to the resistance being greater than the force the muscle is producing e.g. lowering a weight gently.
In practice, most contractions are made up of both isometric and isotonic contractions.
Isometric vs Isotonic Contraction. (Image by OpenStax [CC BY 4.0 , via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
