Explain the difference between vital capacity and FEV1 (forced expiratory volume at 1
second). How does the FEV1 of a normal subject differ from that of a subject having an
asthmatic attack? [4 marks]
- The vital capacity is the total volume of air that can be breathed out after a maximal inspiration.
- It is the difference between the total lung volume and the residual volume.
- It is normally around 5 litres
- The FEV1 is the percentage of the vital capacity that can be expired in one second.
- Full expiration to residual volume takes around 4 seconds
- For a normal subject this is around 80% (1 mark) but during an asthmatic attack the FEV1 is decreased and can be as low as 40%
Explain the processes by which glucose is absorbed by the small intestine. [5 marks]
- Glucose is absorbed into the enterocytes against its concentration gradient by the sodium-dependent cotransporter SGLT1(symport) which binds to both sodium and glucose.
- The carrier links the inward movement of sodium down its electrochemical gradient to the uptake of glucose against its concentration gradient. Glucose is transported across the baso-lateral surface via the glucose carrier GLUT2 (antiport) it permits the movement of glucose from the cell interior down its concentration gradient into the space surrounding the baso-lateral surface.
- This is an example of facilitated diffusion. The energy for the uptake of glucose is provided by the sodium gradient established by the sodium pump. This is known as secondary active transport.
How is vitamin B12 absorbed by the gut? [3 marks]
- Absorption of vitamin B12 requires intrinsic factor, which is secreted by the parietal cells of the stomach.
- B12 and intrinsic factor bind together in the jejunum and are absorbed as a complex in the terminal ileum.
Distinguish clearly between segmentation and peristaltic movements. How are they
initiated and what are their functions? [5 marks]
- Segmentation occurs both in the small and large intestines: mixes chime with digestive enzymes present in the small intestine and in facilitating the absorption of the products of digestion. Contraction of the circular smooth muscle layer of the colon, constricts the lumen.
- Peristalsis occurs in the small and large intestines: Peristaltic waves, short contractions, these serve to propel the contents along the GI tact. Waves initiated by distension of the small intestine.
- Movements initiated by intrinsic reflex pathways resulting from the distension of the stomach and the duodenum.
Define the term compliance as applied to the respiratory system. What factors influence
the compliance of the chest? [5 marks]
- Compliance: is a measure of the ease with which the lungs can be inflated.
- Change in lung volume and change in inflation pressure
- Lung compliance depends on the elasticity of the lung tissue and the surface tension forces at the gas/liquid interface within the lung
Whatchemoreceptorscontroltherateanddepthofrespirationinmanandwhereinthe
bodyaretheysituated? [3marks]
Central Chemoreceptors on the ventral surface of the medulla detect the H+ and CO2 concs
Peripheal detect O2,CO2,H+
Hypothalamus intergrates axiety, fear, pain
Inervation of C1-C3: exandion of lungs
Inervation of C3-C5: diaphram
Inervation of T1-T11: intercostal
Inervation of T6-L1: abdominal
How is the arterial blood pressure adjusted as someone stands up after being in a lying
position? [4 marks]
- When someone is lying down venous return to the heart increases – preload increases. When a person stands up after lying down, blood tends to collect in the lower extremities; return to the heart is reduced.
- The output of the right ventricle and the left ventricle are equalised. There is an increase in the filling of the right part of the heart (lying down) then there is also an increase in right heart output. This increases left heart filling and so increases left heart output. This maintains normal circulation
Where does the cardiac action potential originate? Outline the pathway by which the
cardiac action potential spreads from the pacemaker to the ventricles. [3 marks]
- The action potential originates at the natural pacemaker of the heart - in the sino-atrial node (SA)
- The AP propagates homogeneously across the atrial walls.
- The AP is delayed at the atrio-ventricular node (AV)
- Then AP is propagated rapidly along the Purkinje fibres to rapidly activate the ventricles.
- Long duration is due to calcium influx through VGCC
- The cardiac action potential originates at the SA node.
- It then travels via the atrial myocytes to the AV node and thence via the bundle of His and the Purkinje fibres to excite the ventricular muscle
What causes the first two heart sounds? [2 marks]
- Closure of the heart valves, first sound at the onset of ventricular systole. Associated with the closure of the AV valves.
- The second heart sound occurs on the closure of the aortic and pulmonary valves at the start of ventricular relaxation
How is oxygen carried in the blood? What factors determine the oxygen content of a
given sample of blood? [4 marks]
- Oxygen is bound to haemoglobin found in red blood cells
- Haemoglobin contains four globin molecules, each contains one haem group each of which contains one iron ion. The iron is the site of oxygen binding; each iron can bind one O2 molecule.
- Oxygen content is affected by temperature, pH, PCO2 and 2-3-DPG. These affect the degree of oxygen saturation.
- An increase in any of those factors causes the oxygen dissociation curve to shift to the right, haemoglobin has less affinity for O2
- If there is a decrease in any of those factors, the curve shifts to the right and haemoglobin has a higher affinity for O2.
How do motor nerves activate skeletal muscles? [4 marks]
- Action potential reaches axon terminal, opening of voltage-gated calcium channels. Passive influx of calcium ions down electrochemical gradient causes the binding of vesicles containing Ach to fuse with the plasma membrane. Ach is secreted, diffuses across cleft and binds to nicotinic ACh receptors.
- This causes sodium channels to open, causing an influx of sodium ions, which causes depolarisation of the sarcolemma and generates end plate potential (EPP)
- Depolarisation spreads down the T-tubules opens voltage-gated calcium channels in the sarcoplasmic reticulum. Calcium ions diffuse out and bind to troponin. Troponin moves tropomyosin, which exposes myosin binding sites on actin molecules.
In what respects does the contractile response of cardiac muscle differ from that of
skeletal muscle? [6 marks]
- Contractile response of skeletal muscle: Activated by action potentials in the motor nerves, neurogenic contractions.
- Contractile response of cardiac muscle: Have an intrinsic rhythm that is modulated by action potentials in the autonomic nerves, myogenic contractions. Long duration of the cardiac action potential due to calcium, AP in skeletal much shorter. Cardiac cannot be tetanized like skeletal muscle. If the heart muscle is placed in a physiological solution lacking calcium, it quickly stops contracting, whereas skeletal muscle will continue to contract each time it is stimulated.
. Name the six main hormones secreted by the anterior pituitary gland and their principal
target organs. [6 marks]
Growth Hormone (GH) Liver
Prolactin (PRP) Breasts
Adrenocorticotrophin (ACTH) Adrenals
Thyroid stimulating hormone (TSH) Thyroid
Melanocyte-stimulating hormone (MSH) Melanocytes
The Gonadotrophins - Luteinizing hormone (LH) and Follicle stimulating hormone (FSH) Gonads
