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Tutor profile: Brittany C.

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Brittany C.
Recently matched medical school graduate with 6+ years of tutoring experience
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Questions

Subject: Medicine

TutorMe
Question:

Describe the pathophysiological basis for gram negative organisms causing septic shock.

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Brittany C.
Answer:

1. Lysis of bacterial causes large amounts of lipopolysaccharide (LPS) to be released into the blood. (LPS is located on the outer membrane of the cell wall on gram negative organisms. The endotoxin Lipid A component of LPS is what becomes toxic.) 2. LPS causes activation of macrophages leading to the release of cytokines IL-1 and TNF alpha. - IL 1 - causes fever - TNF alpha - damages endothelial cells causing release of vasodilators like nitric oxide (NO), and prostaglandin (PGI2 causes hypotension.) 3. Endotoxin also activates the alternative complement pathway. Anaphlyatoxins (C3a and C5a) stimulate histamine release from mast cells causing edema. 4. Endotoxin damages tissue causing release of tissue thromboplastin. Tissue thromboplastin activates the extrinsic coagulation pathway, inevitably causing DIC (disseminated intravascular coagulation.) 5. Endotoxins activate neutrophil adhesion molecules circulating pool to become the marginating pool, leading to neutropenia. KEY POINT: Gram negative organisms have LPS located on their outer cell membrane of the cell wall. LPS contains an endotoxin-A which is responsible for the toxic effects seen in septic shock.

Subject: Psychology

TutorMe
Question:

Every time your roommate flushes the toilet in the upstairs bathroom, within minutes your shower becomes freezing cold causing you to immediately jump out of the shower. After occurring for several months, you begin to reflexively jump out of the shower immediately after you hear the flushing sounds safely avoiding the water temperature change. Which conditioning process is detailed above?

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Brittany C.
Answer:

This is a form of classical conditioning, also known as Pavlovian conditioning, which is a type of learning process that evokes a reflexive response. In classical conditioning a biologically potent, unconditioned stimulus (US) leads to a reflexive, natural unconditioned response (UR.) If the US is repeatedly paired with a neutral stimulus, the neutral stimulus can eventually turn into a conditioned stimulus (CS) which evokes the same natural response now called the conditioned response (CR.) Now lets look at our question! The US is the cold water. The UR is jumping out of the shower. The neutral stimulus is the sound of the flushing toilet. This neutral stimulus became the CS after a few months went by. The CR is jumping out of the shower in response to the sound of a flushing toilet. Classical conditioning is different, but often confused, with operant conditioning (instrumental conditioning). Operant conditioning (remember B.F Skinner?) is a learning theory that makes an association between a learned, voluntary behavior and its consequence. A key feature is that a desired behavior becomes more likely if it gets rewarded with either positive or negative reinforcement. Likewise, there will more likely be a decrease in a behavior if it is followed with either positive or negative punishment. KEY POINT: Both classical and operant conditioning are learning processes. Classical conditioning links two stimuli, while operant conditioning pairs a behavior and a response. The best way to tell the difference between the two is to think about if the behavior is voluntary or not. In classical conditioning the response is an involuntary reflex (ex: salivating to the sound of a bell); in operant conditioning the response is voluntary (ex: opening the door after the doorbell rings because a guest is expected.)

Subject: Anatomy

TutorMe
Question:

A newborn male infant born at 43 weeks gestation to a healthy 38 year old G1P0. The delivery was complicated by shoulder dystocia. Immediately after birth the newborn's vitals were BP 90/55 mmHg, RR 24/min, pulse 123 bpm, and temperature 99degrees F. He demonstrated a strong cry and pink upper and lower extremities. The right arm is adducted and internal rotated at the shoulder and extended at the elbow. Flexion and extension of the wrist and digits appear to be intact in the right upper extremity. Which brachial plexus lesion would cause the above presentation?

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Brittany C.
Answer:

The above presentation is suggestive of Erb's Palsy ("waiters tip"), which is an upper trunk (C5-C6) brachial plexus lesion. The most common cause of Erb's Palsy is shoulder dystocia (baby's shoulder gets stuck behind the mothers pubic bone), which causes a difficult childbirth or labor. It can occur due to excessive pulling, twisting, or pushing on a baby's head during delivery. Inevitably, the depression of the shoulder with displacement of the head away from the affected shoulder causes excessive traction on the upper trunk (C5-C6) of the brachial plexus causing difficulty with abduction and external rotation of the shoulder and flexion and supination of the elbow. This would lead to an adducted, internally rotated shoulder and an extended elbow consistent with the above presentation. C5 deficiency causes a(n): - Axillary nerve deficiency (C5-C6) Muscles affected and their normal function: 1. Teres minor- external rotation 2. Deltoid - mainly shoulder abduction - Suprascapular nerve deficiency (C5-C6) Muscle affected and it's normal function: 1. Supraspinatus muscle - shoulder abduction and external rotation - Musculocutaneous nerve deficiency (C5-C6) Muscles affected and their normal function: 1. Biceps - elbow flexion and elbow supination 2. Brachialis - elbow flexion C6 deficiency causes a(n) - Partial radial nerve deficiency (C5-T1) Muscles affected and their normal function: 1. Brachioradialis - elbow flexion and elbow supination 2. Supinator - elbow supination Muscles in the arm that are primarily innervated by C7 include the triceps, pectoralis major, and latissimus dorsi. These muscles would remain unaffected in a pure C5-C6 lesion. LEARNING POINTS: Now lets take time to review the brachial plexus! The brachial plexus is composed of a network of nerves derived from C5-T1 spinal nerves. These nerves give rise to peripheral nerves of the upper limb and shoulder. The order of branching is the following: Roots, Trunks, Divisions, Cords, Branches. A fun way to remember this is "Reach To Drink Cold Beer." KEY POINT: The upper trunk (C5-C6) of the brachial plexus (Erb's palsy) can lead to axillary, supra scapular, musculocutaneous, and partial radial nerve deficiencies. These deficiencies can present as unilateral adducted, internally rotated shoulder and an extended elbow. BONUS: Newborns with an upper trunk (C5-C6) lesion may also have an asymmetric Moro reflex (startle reflex). This primitive reflex is elicited by loud noises and sudden movements. The infant responds with abduction and extension of the arms with opening of the hands, which is then followed by adduction of the arms and flexion of the elbows. A unilaterally absent Moro reflex is indicative of an ipsilateral brachial plexus injury or an ipsilateral clavicular fracture. A bilaterally absent Moro reflex is indicative of a brain injury.

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