Name the process by which the energy stored in the sodium ion electrochemical gradient is used to transport other ions and molecules across the plasma membrane against their concentration gradient. Give an example of a symport that uses this process [2 marks]
- The process is called secondary active transport
2. SGLT1 symport uses sodium concentration gradient to transport glucose in the cells uphill in the small intestine
How do nerve axons transmit information along their length? [4 marks]
- Axon transmits info by means of action potentials
- A stimulus causes a depolarization of the axon membrane from the resting membrane potential (-70mV) to above a threshold of -50mV
- When this threshold is reached, voltage-gated sodium channels open, causing an influx of sodium ions into the the axon, generating an AP of around +40mV
- In UNMYELINATED axons, AP is propagated along the length of the axon as Na+ diffusion causes a continuous wave of depolarization; in MYELINATED axons, APs jump from one Node of Ranvier to another in a process called Saltatory Conduction
- After Na+ channels have opened, they simultaneously inactivate, limiting the duration of an action potential to approximately 1ms, after which they cannot reopen until they have spent a period of time at the resting membrane potential, known as the absolute refractory period
Name the FOUR steps in order of the muscle contraction cycle and what is needd for the steps to continuously repeat [5 marks]
- Ca2+ released from the sarcoplasmic reticulum and binds to troponin
- Exposing myosin binding sites on the actin filament
- Myosin heads bind to actin, releasing ADP, causing a conformational change in myosin, initiating the power stroke, causing filament to slide past one another
- ATP binds to myosin, causing it to release actin
- If calcium is returned to the SR, the muscle relaxes
For the cycle to continuously repeat calcium ions must remain available
Describe the inward forces of elastic recoil, and explain why the lungs do not normally collapse during expiration [4 marks]
- During expiration, the diaphragm smoothly relaxes
- The elastic recoil of the chest wall and lungs results in passive expiration
3 + 4. The lungs do not collapse because elastic recoil during expiration means that intrapleural pressure is always less than the pressure inside the lungs
In chronic emphysema, some alveoli merge together and some are replaced with fibrous connective tissue. In addition, the bronchioles are often inflamed, and expiratory volume is reduced. Give FOUR reasons why affected individuals will have problems with ventilation and external respiration [4 marks]
- The surface area for the lungs is greatly reduced so there is less area for diffusion
- Thickening of the alveolar membranes also greatly reuduces diffusion capacity
- The physiological dead space is increased which causes inadequate ventilation / gas exchange.
- As bronciholes become inflamed, the airways narrow, which increases resistance and limits gas exchange
Explain the roles of carbon dioxide and hydrogen ions in both direct and indirect stimulation of the breathing centre in the medulla oblongata [5 marks]
- A rise in plasma CO2 leads to increased CO2 uptake into the brain
- In the brain, CO2 is converted into bicarbonate and hydrogen ions via carbonic acid
- Hydrogen ions stimulate the central chemoreceptors
- This increases the rate and depth of respiration
- A fall in plasma CO2 has the opposite effect
How is oxygen carried in the blood? What factors determine the oxygen content of a given sample of blood? [5 marks]
- Oxygen is carried bound to haemoglobin (an oxygen-binding protein) in red blood cells
- At the centre of each of four haem groups that make up haemoglobin s a ferrous iron that can loosely bind one molecule of oxygen
- Therefore, each haemoglobin can carry four oxygen molecules
4+5. The affinity of haemoglobin for oxygen is determined by:
- pH
- partial pressure of CO2
- conc. of 2,3-biphosphoglycerate
Name the SIX main hormones secreted by the anterior pituitary gland and their principal target organs [6 marks]
- FSH - gonads
- LH - gonads
- ACTH - adrenal cortex
- GH - liver, bone, muscle
- TSH - thyroid
- Prolactin - mammary gland
The blood has many physiological functions within the body. Give FIVE distinct functions of blood [5 marks]
- MAINTENANCE OF CELLULAR FUNCTION
through the establishment of correct ion gradients between intracellular and extracellular - GASEOUS EXCHANGE
carriage of oxygen and CO2 between tissues and lungs - DELIVERY OF OTHER NUTRIENTS
between the gut, liver, and kidney for absorption, metabolism, and excretion - PROTECTION AGAINST INVADING ORGANISMS
blood provides immunological function - THERMOREGULATION
heat is exchanged with the environment by regulating blood flow to the skin
(also carries hormones)
Define the term hematocrit and give an approximate value for a normal individual living at sea level. If such a person were to live for two months at high altitude, what would happen to their hematocrit? [3 marks]
- DEFINITION: the ratio of the volume of red blood cells to the total volume of blood; i.e. the proportion of the total volume of blood occupied by red blood cells.
- An average value at sea level is about 0.47 litres per whole litre of blood.
- After two months at high altitude, the individual’s hematocrit would INCREASE
What causes the first two heart sounds and where do they occur relative to the ECG? [3 marks]
- S1 occurs at the beginning of ventricular contraction, and represents the closing of the mitral and tricuspid valves
- S2 occurs at the end of ventricular contraction, and represents the closing of the aortic and pulmonic valves
- S1 corresponds to the R wave;
S2 corresponds to the T wave
What determines the heart rate and how is it adjusted to meet the demands of the circulation? [4 marks]
- Heart rate is determined by the frequency at which action potentials are generated at the SA node
- The SA node is innervated by the autonomic nervous system
- The parasympathetic branch - VAGUS NERVE - releases ACETYLCHOLINE which slows down the heart rate
- The sympathetic branch - CARDIAC NERVES - releases NORADRENALINE which speeds up the heart rate
Draw and label a diagram of a typical electrocardiogram (ECG) trace [3 marks]
Things to include:
- P wave
- QRS complex
- T wave
Define the term preload as applied to the heart [3 marks]
3.
Briefly outline the possible fates of glucose in the body [4 marks]
- Glucose can be broken down to yield pyruvate in glycolysis
- Glucose can be converted to glycogen by glycogenesis
- Glucose can be converted into ribose-5-phosphate
- Glucose can be converted into amino acid intermediates
The G cells of the gastric mucosa produce the hormone gastrin and the duodenal mucosa produces secretin and cholecystokinin (CCK). What stimulates their release and what are the functions of these hormones? [6 marks total; 2 marks for each hormone]
Gastrin:
- Stimulation of the vagus nerve causes the release of gastrin via the enteric nervous system, as well as luminal factors such as peptides and alcohol
- Gastrin is an endocrine stimulant of H+, mucous, and pepsinogen secretion
Secretin:
- Secretin is an endocrine inhibitor of H+ secretion, and stimulates bicarbonate secretion and bile production
- It is secreted in response to low duodenal pH
Cholecystokinin (CCK):
- Released rapidly into the blood in response to a meal; greatest stimulator is the presence of fatty/amino acids in the chyme entering the duodenum
- CCK mediates digestion in the small intestine by inhibiting gastric emptying. It stimulates the acinar cells of the pancreas to release a juice rich in pancreatic digestive enzymes that catalyze the digestion of fat, protein, and carbohydrates
In which regions of the body are carbohydrates digested? In which region does the most digestion occur? [4 marks]
- Mouth
- Duodenum
- Upper jejunum
- Main site is the DUODENUM
