Systems Biology and Tissue Types - MCAT Biological and Biochemical Foundations of Living Systems

Homeostasis, or "steady-state" physiology, is the system of feedback loops that enables an organism to create a stable, adaptive environment. For example, the pancreas and the brain together work to regulate the blood sugar levels via the hormones insulin and glucagon.

Once blood enters the left ventricle, the left ventricle contracts and pushes blood out of the heart into the aorta. The contraction of the left ventricle pumps blood into the aorta at a fast velocity. Blood velocity becomes slower as it reaches the capillaries and then speeds up again in the veins. Veins must use valves to pump blood against gravity, and therefore does not move blood as quickly as the aorta. The aorta is the best answer.

This a simple anatomy question. The mitral (bicuspid) valve lies between the left atrium and ventricle, therefore the answer must be the mitral valve. The tricuspid valve lies between the right atrium and ventricle.

The vagus nerve is a major nerve of the parasympathetic nervous system, responsible for mediating numerous responses in the body. In relation to the heart, the vagus nerve provides constant inhibition to the sinoatrial node, slowing the heart rate. The sinoatrial node naturally fires at about 80 to 100 beats per minute, while a healthy resting heart rate is closer to 60 due to innervation by the vagus nerve.

The radial nerve is located in the forearm; the femoral nerve is located in the thigh; the subcostal nerve is located along the lower ribs.

As mentioned in the passage, carbonic anhydrase inhibitors will prevent the reabsorption of sodium and water at the proximal tubule. By preventing water reabsorption, the blood volume decreases. Lowering the blood volume will lower the blood pressure. The heart is constantly pushing blood against a pressure. The higher the blood pressure is, the more work the heart will have to do to push the blood out. Therefore, by lowering the blood pressure, the heart does not have to work as hard.

High levels of carbon dioxide (CO2), low pH, and high temperatures all act to decrease oxygen's affinity toward human hemoglobin. Think of working muscle, which produces hot, acidic, high CO2 conditions in the blood; in this environment, it is important for hemoglobin to release transported oxygen to provide an aerobic environment to the muscle.

When blood returns to the heart via the superior and inferior vena cavae, it is deoxygenated. It remains this way as it passes through the right atrium, the right ventricle, and the pulmonary arteries, through which it travels to the lungs to conduct gas exchange with the alveoli. Both the right ventricle and the pulmonary artery contain deoxygenated blood.

All of the other answer choices contain at least one component that carries oxygenated blood.

The scrotum is a bag of skin containing the testes. The importance of the scrotum is to regulate temperature because sperm synthesis in the testes must occur at a few degrees below body temperature. The testes are the location of sperm synthesis, androgen synthesis occurs in the interstitial cells, nourishment of the sperm takes place in the seminal vesicles, and lubrication occurs in the bulbourethral glands.

Gastrulation is the phase in embryogenesis in which the single-layered blastula is reorganized into a trilaminar structure called the gastrula. These three germ layers are called the endoderm, mesoderm, and ectoderm and give rise to individual organs during organogenesis.

The blastula is implanted into the uterine lining and the morula undergoes rapid cell divisions (cleavage) after fertilization of the zygote.

Most cells contain a complete genome, but not all genes are activated in each cell. Activation of particular genes produces appropriate protein function.

During the absolute refractory period, no action potential can occur. In the relative refractory period, an action potential can occur with more stimulation than is normally required.

Remember that an action potential starts with the diffusion of sodium into the cell. As more sodium enters the cell, more voltage gated sodium channels open up. This leads to depolarization of the cell. With a steady diffusion of sodium into the cell, the threshold stimulus will eventually be attained, and an action potential will be generated. It is the steady diffusion of sodium into the autorhythmic cells which results in an action potential.

The medulla oblongata, a part of the hindbrain, is primarily responsible for the control of ventilation and heart rate. The midbrain serves as a relay station for visual and auditory information. The cerebellum is responsible for balance and coordination. The corpus callosum is a connective tissue between the two hemispheres of the brain and allows for their intercommunication. The temporal lobes are primarily responsible for auditory processing. Therefore, the patient is most likely suffering from a damage to the medulla oblongata.

The cochlear and vestibular nerves join to form the auditory nerve. The crista are specialized hair cells that help in postural equilibrium and send information via the vestibular nerve. The incus is one of the three auditory bones (the others include the malleus and the stapes), the motion of which is part of sound reception. This information is transmitted via the cochlear nerve. Finally, the cochlea is the fluid-filled structure of the inner ear that translates movement into vibrations (also involved in sound reception). All of the given structures take part in transmitting information to the acoustic nerve.

Somatosensory neurons are most sensitive to mechanical force, temperature change, and tissue damage. Nociception is the processing of pain signals, which could result from any of these stimuli.

The sarcoplasmic reticulum contains a large amount of Ca2+ ions. This calcium is released from the sarcoplasmic reticulum when an electrical signal is sent to the cell. This release of calcium allows for contraction.

The proteins troponin and tropomyosin are attached to the actin filaments in sarcomeres. These proteins function to block the myosin-binding site on the actin protein, preventing unnecessary contraction. When calcium is released from the sarcoplasmic reticulum, it will attach to troponin. The troponin will then pull tropomyosin away from the actin filament, which allows myosin heads to attach and cause a contraction.

ATP binds myosin to release it from the actin binding site and is converted to ADP in order to adjust the myosin head to a high-energy position.

An antagonist is defined as the muscle that strecthes when another muscle (the agonist) is contracting. When the antagonist contracts, it will stretch the agonist and move the bone in the opposite direction.

The biceps brachii is responsible for flexion of the forearm, while the triceps brachii is responsible for the extension of the forearm. As a result, we say that the triceps brachii is the antagonist of the biceps brachii.

Cardiac muscle and skeletal muscle are both composed of sarcomeres. This layout gives both muscle types a striated appearance, alternating dark bands of myosin with lighter bands of actin. Only cardiac muscle has intercalated discs and skeletal muscle is the only type that is multinucleated. No muscle type is attached directly to bone, but skeletal muscle is linked to bone via tendons.

Skeletal muscle is under voluntary control, and are innervated by the somatic nervous system. Skeletal muscle is responsible for skeletal movement, such as swinging the arms or lifting the legs.

Cardiac and smooth muscle are under the control of the autonomic nervous system. Cardiac muscle contracts the heart autonomously, without additional neuronal input.