BIOM2011 (2021) Exam SAQs Flashcards
List the FIVE (5) key steps of excitation-contraction coupling in skeletal muscle in the order that they occur.
- Generation of an action potential
- Propagation of the action potential
- Release of calcium ions
- Binding of calcium ions to troponin
- Cross-bridge formation and muscle contraction
What are exchangers and pumps and how do they move ions against ionic gradients?
Exchangers and pumps are integral membrane proteins involved in active ion transport across cell membranes. Exchangers use the energy from the electrochemical gradient of one ion to transport another ion in the opposite direction. Pumps, also known as ATPases, use energy from ATP hydrolysis to move ions against their concentration gradients. Both exchangers and pumps undergo conformational changes in their protein structure to transport ions.
How does the normal function of the Na+ -Ca2+ exchanger depend upon the normal function of the Na+ -pump on the plasma membrane?
the Na+-Ca2+ exchanger depends on the normal function of the Na+-pump to maintain the appropriate sodium concentration gradient across the plasma membrane. Without the Na+-pump actively maintaining the sodium gradient, the Na+-Ca2+ exchanger would not have the necessary energy source to transport calcium ions effectively. The coordinated activity of these two transporters helps regulate intracellular calcium levels, which is crucial for numerous cellular processes such as muscle contraction, neurotransmission, and cell signalling.
Describe the milk ejection reflex in lactation
step-by-step description of the milk ejection reflex:
Stimulation of sensory nerves: When a baby latches onto the breast and begins to suckle, the sensation of the baby’s mouth on the nipple and areola stimulates specialized nerve endings called mechanoreceptors and stretch receptors in the breast tissue.
Transmission to the hypothalamus: The sensory signals from the breast are transmitted to a region in the brain called the hypothalamus. The hypothalamus plays a crucial role in regulating various bodily functions, including the release of hormones.
Release of oxytocin: In response to the sensory stimulation, the hypothalamus signals the posterior pituitary gland to release the hormone oxytocin into the bloodstream. Oxytocin is known as the “milk let-down hormone.”
Contraction of myoepithelial cells: Oxytocin acts on specialized cells called myoepithelial cells that surround the alveoli (milk-secreting structures) within the mammary glands. Oxytocin triggers the contraction of these myoepithelial cells, causing them to squeeze or compress the alveoli.
Milk ejection: The contraction of the myoepithelial cells exerts pressure on the alveoli, forcing milk to be expelled into the milk ducts and out through the nipple. The milk flows through the milk ducts and can be accessed by the baby during breastfeeding.
What is a prolactinoma? Compare and contrast the consequences of a prolactinoma in women
and men.
A prolactinoma is a benign tumor of the pituitary gland that results in excessive production of the hormone prolactin. Prolactinomas are the most common type of pituitary tumor and typically occur in women of reproductive age, although they can also affect men.
Here is a comparison of the consequences of a prolactinoma in women and men:
Consequences in Women:
Irregular menstrual periods: Excess prolactin levels can disrupt the normal menstrual cycle, leading to irregular or absent periods (amenorrhea).
Galactorrhea: Increased prolactin can cause the production of breast milk even in the absence of pregnancy or breastfeeding. This condition is known as galactorrhea.
Infertility: Due to hormonal imbalances and disrupted menstrual cycles, women with prolactinomas may experience difficulties in conceiving.
Osteoporosis: Prolonged high levels of prolactin can interfere with estrogen production, which may lead to a decrease in bone density and increase the risk of osteoporosis.
Consequences in Men:
Sexual dysfunction: Excess prolactin can interfere with testosterone production in men, leading to decreased libido, erectile dysfunction, and infertility.
Decreased muscle mass: Testosterone plays a crucial role in maintaining muscle mass. Reduced testosterone levels due to a prolactinoma may result in decreased muscle mass and strength.
Enlarged breasts (gynecomastia): Elevated prolactin levels can stimulate breast tissue growth in men, causing the enlargement of breast glandular tissue.
Infertility: Similar to women, men with prolactinomas may experience difficulties in achieving fertility due to hormonal imbalances and suppressed testosterone levels.
What are the THREE (3) other specialised lateral junctions called and what are the major
extracellular proteins involved in their extracellular connections? What is the main function of
these lateral junctions?
- Tight junctions: Tight junctions are formed by interactions between transmembrane proteins called claudins and occludins. They create a tight seal between adjacent epithelial cells, preventing the leakage of molecules between cells and regulating the paracellular transport. The main function of tight junctions is to maintain the integrity and polarity of epithelial barriers.
- Adherens junctions: Adherens junctions are primarily composed of cadherin proteins, particularly E-cadherin. These cadherins interact with each other in a calcium-dependent manner to form adhesive bridges between adjacent cells. Adherens junctions provide mechanical strength to tissues and play a role in cell-cell adhesion, tissue organization, and signaling.
- Gap junctions: Gap junctions consist of connexin proteins that form channels connecting the cytoplasm of adjacent cells. These channels allow the direct exchange of small molecules, such as ions and metabolites, between cells. Gap junctions facilitate intercellular communication and coordination of cellular activities within tissues.
Sodium ions and glucose are actively absorbed in the small intestine and resorbed in kidney tubules.
a) What is the main transporter involved in the transport of these molecules? [1 mark]
b) What are the classifications of this transporter? [2 marks]
c) What kind of energy requirements are necessary for the transport of these molecules?
a) The main transporter involved in the transport of sodium ions and glucose in the small intestine and kidney tubules is the Sodium-Glucose Cotransporter 1 (SGLT1).
b) The SGLT1 transporter is classified as a secondary active transporter. It belongs to the Solute Carrier Family 5 (SLC5) of transport proteins.
c) The transport of sodium ions and glucose via SGLT1 requires the energy provided by the sodium gradient established by the Na+/K+-ATPase pump. The Na+/K+-ATPase pump uses ATP energy to actively pump sodium ions out of the cell, creating a low intracellular sodium concentration. This sodium gradient allows SGLT1 to transport both sodium ions and glucose against their concentration gradients. The energy derived from the sodium gradient drives the active co-transport of glucose into the cell along with sodium ions.
Describe how the location of a synapse on the dendritic tree influences the impact of synaptic
potentials at the axon initial segment.
The location of a synapse on the dendritic tree plays a crucial role in determining the impact of synaptic potentials at the axon initial segment (AIS). The AIS is the region of the neuron where the axon originates from the cell body. It contains a high density of voltage-gated sodium channels and serves as the initiation site for the generation of action potentials.
The impact of synaptic potentials on the AIS is influenced by several factors related to the location of the synapse on the dendritic tree:
Distance from the AIS: Synapses closer to the AIS have a more significant impact on the membrane potential at the AIS compared to synapses located farther away. This is because the electrical signals generated at the synapse decay as they propagate along the dendritic tree, and synapses closer to the AIS have a shorter distance for the signal to travel, resulting in less attenuation.
Dendritic branch size and length: Dendritic branches can vary in size and length, and these structural features affect the electrical properties of the dendritic tree. Thicker and shorter dendritic branches tend to have lower resistance, allowing synaptic potentials to spread more effectively towards the AIS. In contrast, thinner and longer dendritic branches introduce more resistance, leading to more significant signal attenuation.
Dendritic branching pattern: The branching pattern of the dendritic tree influences the convergence and divergence of synaptic inputs. If multiple synapses from different locations converge onto a single dendritic branch, the synaptic potentials will summate more effectively and have a stronger impact on the AIS. Conversely, if synaptic inputs are spread out across different branches, their impact on the AIS may be weaker due to the dilution of synaptic potentials.
Dendritic filtering: The dendritic tree can act as a filter for incoming synaptic potentials. Dendrites contain passive electrical properties, such as membrane capacitance and membrane resistance, which can selectively attenuate or amplify specific frequency components of synaptic inputs. This filtering effect can modify the temporal and spatial integration of synaptic potentials before they reach the AIS.
Overall, the location of a synapse on the dendritic tree influences the magnitude and spatial summation of synaptic potentials reaching the AIS. Synapses in closer proximity to the AIS, on thicker and shorter dendritic branches, and with converging inputs are more likely to have a stronger impact on the membrane potential at the AIS, leading to a greater likelihood of generating action potentials.
Describe the actions leading to the membrane potential of a rod cell upon stimulation with light
Upon stimulation with light, the following actions occur leading to changes in the membrane potential of a rod cell:
Photoreceptor activation: Light photons enter the eye and reach the retina, where they interact with the photoreceptor cells, specifically the rod cells. Rod cells contain a pigment called rhodopsin, which is sensitive to light.
Phototransduction cascade: When rhodopsin absorbs photons, it undergoes a structural change, activating a series of enzymatic reactions known as the phototransduction cascade. The key steps in the phototransduction cascade include the activation of a G-protein coupled receptor (GPCR) called rhodopsin, which leads to the activation of a G-protein called transducin.
Activation of transducin: The activated rhodopsin causes the exchange of GDP for GTP on transducin, resulting in the activation of transducin.
Activation of phosphodiesterase (PDE): Activated transducin binds to and activates an enzyme called phosphodiesterase (PDE). PDE plays a critical role in the phototransduction cascade by breaking down cyclic guanosine monophosphate (cGMP), which is a second messenger involved in the maintenance of the dark current in photoreceptor cells.
Decrease in cGMP levels: As PDE breaks down cGMP, the levels of cGMP in the cytoplasm of the rod cell decrease. This reduction in cGMP leads to the closure of cGMP-gated ion channels in the plasma membrane of the rod cell.
Hyperpolarization of the membrane: The closure of cGMP-gated ion channels reduces the influx of sodium ions into the rod cell, leading to a decrease in the dark current. This reduction in the dark current results in hyperpolarization of the rod cell membrane.
Inhibition of glutamate release: Hyperpolarization of the rod cell membrane inhibits the release of the neurotransmitter glutamate from the rod cell synapses onto bipolar cells. This inhibition of glutamate release alters the signaling to downstream retinal neurons, initiating the transmission of visual information to the brain.
Overall, the stimulation of rod cells by light triggers the phototransduction cascade, leading to the closure of cGMP-gated ion channels, a decrease in cGMP levels, hyperpolarization of the rod cell membrane, and inhibition of glutamate release. These changes in membrane potential and neurotransmitter release are the initial steps in converting light signals into electrical signals for visual perception.
Explain the TWO (2) mechanisms by which high and low frequency sounds are localised along
the horizontal plane (azimuth) and why they differ.
The localization of high and low-frequency sounds along the horizontal plane (azimuth) involves two mechanisms: interaural time difference (ITD) and interaural level difference (ILD). These mechanisms differ because of the way sound waves interact with the physical characteristics of the head and ears.
Interaural Time Difference (ITD):
ITD refers to the difference in the arrival time of sound between the two ears. When a sound source is located to one side of the head, the sound wave takes slightly longer to reach the ear on the opposite side compared to the ear closer to the sound source. The brain detects this time difference and uses it to localize the sound.
The ITD is more effective for low-frequency sounds because the wavelength of low-frequency sounds is relatively long compared to the size of the head. As a result, the sound wave wraps around the head, causing a significant phase delay between the two ears. The brain can detect this time delay and localize low-frequency sounds based on the ITD.
Interaural Level Difference (ILD):
ILD refers to the difference in sound intensity or level between the two ears. When a sound source is off-center, the head acts as an acoustic shadow, attenuating the sound reaching the ear on the side opposite the sound source. As a result, the ear closer to the sound source receives a higher sound intensity compared to the ear on the other side.
The ILD is more effective for high-frequency sounds because the short wavelength of high-frequency sounds allows them to be easily diffracted by the head. This diffraction leads to a reduction in the sound intensity reaching the ear on the opposite side of the sound source. The brain utilizes this level difference to localize high-frequency sounds along the azimuth.
In summary, high-frequency sounds are localized based on the interaural level difference (ILD), where the head acts as an acoustic shadow, attenuating the sound reaching the opposite ear. On the other hand, low-frequency sounds are localized based on the interaural time difference (ITD), as the sound wave wraps around the head, causing a phase delay between the two ears. These two mechanisms differ because high-frequency sounds are diffracted by the head, leading to level differences, while low-frequency sounds have longer wavelengths that result in significant time differences.
A new bacterial infection establishes in the epithelium of the skin.
a) Describe the general barriers of the epithelium that must be overcome to facilitate this infection.
b) Describe the process of innate immune cell recruitment to this infection as it penetrates into the underlying tissue.
a) The epithelium of the skin serves as the first line of defense against infections. To facilitate the infection, the bacteria must overcome several general barriers of the epithelium. These barriers include:
Physical barrier: The epithelial layer provides a physical barrier that prevents the entry of microorganisms. The tight junctions between epithelial cells restrict the movement of bacteria and other pathogens.
Chemical barrier: The skin produces antimicrobial substances, such as defensins and cathelicidins, which have bactericidal properties. These antimicrobial peptides help to kill or inhibit the growth of invading bacteria.
Microbiota barrier: The skin has a diverse microbial community known as the microbiota. The commensal bacteria that make up the microbiota can compete with pathogenic bacteria for resources and produce antimicrobial substances that help maintain a healthy microbial balance and inhibit the growth of harmful bacteria.
Epithelial innate immune response: The epithelial cells of the skin have pattern recognition receptors (PRRs) that can detect pathogen-associated molecular patterns (PAMPs) present on the surface of bacteria. Activation of these PRRs triggers the release of cytokines and chemokines, which initiate the innate immune response and attract immune cells to the site of infection.
b) As the bacterial infection penetrates into the underlying tissue, the innate immune system responds by recruiting immune cells to the site of infection. The process of innate immune cell recruitment involves several steps:
Recognition of infection: Immune cells, such as macrophages and dendritic cells, detect the presence of bacteria through their pattern recognition receptors (PRRs) that recognize specific PAMPs on the bacterial surface.
Release of chemotactic factors: Upon recognition of the infection, immune cells and damaged epithelial cells release chemotactic factors, such as chemokines, which act as signals to attract immune cells to the site of infection.
Rolling and adhesion: Circulating immune cells, particularly neutrophils and monocytes, roll along the endothelial lining of blood vessels near the infection site, mediated by selectins and their ligands. This rolling slows down the immune cells and allows them to interact with adhesion molecules on the endothelial cells.
Diapedesis: Chemokines and other inflammatory mediators induce a change in the expression of adhesion molecules on endothelial cells, promoting the firm adhesion of immune cells. This leads to the extravasation of immune cells from the bloodstream into the tissue through a process called diapedesis.
Migration to the infection site: Immune cells migrate through the tissue, guided by chemotactic gradients towards the source of infection. The migration is facilitated by the recognition of chemokines and other signaling molecules.
Phagocytosis and destruction of bacteria: Once at the infection site, phagocytes, such as neutrophils and macrophages, engulf and destroy the bacteria through phagocytosis. These immune cells release antimicrobial substances and generate an inflammatory response to eliminate the bacteria.
By recruiting and activating immune cells, the innate immune response helps contain the bacterial infection and initiate the subsequent adaptive immune response, if necessary
