Paper 2 Flashcards
(47 cards)
The islets of Langerhans are complex mini organs which are essential for maintaining glucose homeostasis. Briefly outline the important structural components of pancreatic islets, and include in your answer the hormones secreted by each cell type, and their functions.
To include: Insuloacinar portal system, capillary plexus & anastomosing cords of cells, branches of sympathetic and parasympathetic nerves (vagal), interneurons Beta cells – Insulin – cellular uptake of glucose (Glut4) – endocrine Alpha cells - Glucagon –- > hepatic glycogenolysis – endocrine
Delta cells - Somatostatin & gastrin –– SS inhibits glucagon & insulin release (paracrine – intraislet signalling)
F / PP cells - Pancreatic polypeptide –– inhibits somatostatin secretion– paracrine (also inhibits secretion of pancreatic enzymes and bile from gall bladder - endocrine) (also inhibits secretion of pancreatic enzymes
and bile from gall bladder - endocrine)
State which cell types provide myelination in the central nervous system (CNS) and peripheral nervous system (PNS), respectively.
Oligodendrocytes and Schwann cells
Briefly describe the main structural differences between the above cell types and their relationships to the axons.
Oligodendrocytes – one cell can myelinate several axon segments; Schwann cells – each cell myelinates only one axon segment
Both speed impulse transmission throughout the axon.
Explain how the myelin-forming cells of the PNS support axon regeneration.
Removal/recycling of cell debris;
provision of axon-growth promoting substrate (cell adhesion molecules); promotion of survival of injured neurons (neurotrophic factor release)
If Mr. Hanlie suffered damage to his brain tissue, briefly explain how survival of the neurons could be affected.
Immediate cell death (necrotic), as well as delayed death (apoptotic) through inflammatory processes, metabolic and respiratory stress
State whether disrupted connections between neurons in the injured brain are likely to functionally restore themselves. Provide the reasons for your
answer.
No, as injured CNS neurons often degenerate or fail to re-express the genes necessary for axonal regeneration. The CNS microenvironment (glia: oligodendrocytes, astrocytes and microglia) is not conducive for axon regrowth, and molecular guidance cues are not re-expressed in the adult brain
State under what name are the histological features of degenerating axonal pathways known.
Wallerian degeneration
Name the cutaneous mechanoreceptor that detects high-frequency vibration. (1⁄2 mark). State whether this receptor is rapidly or slowly adapting.
Pacinian corpuscle. Rapidly-adapting.
Give a concise definition of “sensory transduction” as applied to the somatosensory system
conversion of the physical (or chemical) energy stimulus into an electrical signal in a sensory neuron
List and discuss a three-step sequence of events to explain how vibration sense on the skin is converted into neuronal activity.
Step 1: Mechanical stimulus (e.g. pressure) deforms the receptor’s (Pacinian corpuscle) onion-like outer membrane.
Step 2: The receptor’s channels open and Na+ flows through membrane. The inside of the receptor
(1 marks)
depolarizes (voltage becomes more positive).
Step 3: If the graded potential (summed at the initial segment) is above a threshold level, action potentials are generated and propagated down the axon. Cutaneous mechanoreceptor afferents have myelinated axons in which action potentials jump from gap to gap in the myelin sheath. This sheath insulates the axon and speeds up the conduction of action potentials.
The response to a somatosensory stimulus has the ability to adapt. Explain how this occurs by using the Pacinian corpuscle as an example of a cutaneous mechanoreceptor.
The number of action potentials/second adapts because the receptor potential adapts. The receptor potential adapts in part because the onion-like laminae in Pacinian corpuscle. corpuscle slip back to their original shape, closing the channels.
Outline three (3) factors that predispose a patient to the pathogenesis of a diabetic foot.
Sensory neuropathy resulting in traumatic injury- accumulation of sorbitol and fructose in the schwaan cells.
b. Macrovascular – accelerated atherosclerosis- occlusion of vaso nervosa
c. Hyperglycemia predisposes to infection- poor inflammatory response to bacteria.
List four (4) complications of uncontrolled diabetes involving the kidney.
Nodular glomerulosclerosis (Kimmelstiel- Wilson)
- Diffuse glomerular basement membrane thickening with proteinuria - Pyelonephritis
- Renal papillary necrosis
List four (4) causes for a falsely increased level of HbA1c.
Iron deficiency anaemia
Splenectomy
Aplastic anaemia
Haemoglobinopathies (depends on method)
Name the biochemical class of hormone to which insulin belongs.
Peptide/ protein
Outline what happens to extracellular phosphate when insulin is administered.
When insulin is administered, glucose leaves blood and enters the cells via Glut-4. Phosphate It moves intracellularly and EC levels can decrease for glucose phosphorylation, an thus K + and Mg^2+ follows to maintain electroneutrality (intracellular levels drops)
Name (in full) the most likely organism responsible for this infection.
Clostridium perfringens
Briefly describe the pathogenesis of this infection.
Poor blood supply to the area thus less oxygen and anaerobes proliferate (1) also exotoxins produced by
organism (1
State the laboratory conditions that this organism requires in order to be cultured.
Anaerobic conditions
Briefly describe how you would manage this case.
Treat underlying cause/diabetes (1) Remove necrotic tissue (1) Penicillin or metronidazole (1)
The doctor decided to perform a thorough examination and finds that Miss Alberts has red itchy patches in her groin area. He suspects a yeast infection.
82. Name (in full) the organism that is the most likely causing the infection.
Candida albicans
Briefly describe how you would manage this condition candida.
Topical antifungal like nystatin/clotrimazole (amphotericin B / fluconazole (1/2) and correct underlying
condition (1/2), keep area dry (1/2)
Outline one reason why this infection is present in this patient.
The patient is diabetic which is an immunocompromised state
Outline why this infection is particularly common at this site.
The groin is a moist and warm fold area thus ideal for growth of yeast
