MCAT Biology › MCAT Biological Sciences
The brain is a very delicate structure with little room to move around. Surrounding the brain and the spinal cord are three protective layers in addition to the skull and the vertebral column. Directly surrounding the brain and spinal cord is the pia mater. Following the pia mater is the arachnoid mater. Between the pia mater and the arachnoid mater is the sub-arachnoid space where the cerebrospinal fluid circulates. Finally, the protective layer is the dura mater is loosely attached to the arachnoid mater but is strongly associated with the skull bone.
Depending on the type of injury, a certain type of vein and/or artery are more susceptible to injury. For example, the meningeal artery and vein run through the foramen spinosum and travel between the two layers making up the dura mater. As the artery and the vein are traveling in between the dura mater, there is a vulnerable region at the temple. A strike to the temple region could rupture these vessels and result in a epidural hematoma.
Traveling from the cerebral cortex to the venous dural sinus (located at certain regions between the two layers of the dura mater) is the cerebral vein. When an injury results in the dura mater shifting away from the arachnoid mater, the cerebral vein could rupture and lead to a subdural hematoma.
A hematoma that affects both the brain and spinal cord could affect which part of the nervous system?
I. Sympathetic nervous system
II. Parasympathetic nervous system
III. Enteric nervous system
I, II, and III
I only
III only
III only
I and II only
The brain and the spinal cord makes up the Central nervous system (CNS). The CNS is broken down into the sympathetic and the parasympathetic branches. The enteric nervous system (nervous system innervating the digestive tract) is a portion of the parasympathetic nervous system.
Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the loss of tolerance to self antigens leading to the presence of high autoantibody titers. There are several underlying causes behind SLE, one of which is a dysregulation in the clearance of apoptotic cells, which can lead to secondary necrosis. This leads to the leakage of danger signals which contributes to the loss of peripheral tolerance and chronic inflammation.
A deficiency in the clearance of apoptotic cells can be attributed to which immune cell type?
Macrophages
Cytotoxic T cells
Plasma cells
Natural killer cells
Germinal center B cells
The defect in clearance of apoptotic cells in SLE is mainly attributed to macrophages, which serve integral roles in phagocytosis of dead cells and debris. An inability to clear these apoptotic cells over time leads to secondary necrosis, which results in the production and release of several DAMPS or damage-associated molecular pattern molecules which are potent inducers of the immune response.
The brain is a very delicate structure with little room to move around. Surrounding the brain and the spinal cord are three protective layers in addition to the skull and the vertebral column. Directly surrounding the brain and spinal cord is the pia mater. Following the pia mater is the arachnoid mater. Between the pia mater and the arachnoid mater is the sub-arachnoid space where the cerebrospinal fluid circulates. Finally, the protective layer is the dura mater is loosely attached to the arachnoid mater but is strongly associated with the skull bone.
Depending on the type of injury, a certain type of vein and/or artery are more susceptible to injury. For example, the meningeal artery and vein run through the foramen spinosum and travel between the two layers making up the dura mater. As the artery and the vein are traveling in between the dura mater, there is a vulnerable region at the temple. A strike to the temple region could rupture these vessels and result in a epidural hematoma.
Traveling from the cerebral cortex to the venous dural sinus (located at certain regions between the two layers of the dura mater) is the cerebral vein. When an injury results in the dura mater shifting away from the arachnoid mater, the cerebral vein could rupture and lead to a subdural hematoma.
A hematoma that affects both the brain and spinal cord could affect which part of the nervous system?
I. Sympathetic nervous system
II. Parasympathetic nervous system
III. Enteric nervous system
I, II, and III
I only
III only
III only
I and II only
The brain and the spinal cord makes up the Central nervous system (CNS). The CNS is broken down into the sympathetic and the parasympathetic branches. The enteric nervous system (nervous system innervating the digestive tract) is a portion of the parasympathetic nervous system.
Which of the following explains why there is a blind spot in the eye?
This is the location where the optic nerve exits the eye
This is the location where there are no rods
This is the location where there are no cones
This is the location where the lens of the eye is not transparent
This is the location where the retina does not focus light
The optic nerve collects stimuli from the retina and exits through the back of the eye to relay the information to the occipital lobe of the cerebrum. The point at which the optic nerve exits the eye contains no photoreceptors (rods and cones), and is unable to interpret light signals. This leads to a blind spot in the eye at the optic disk.
The liver primarily serves to help detoxify both endogenous and exogenous substances from the blood and intestines. Once blood from the intestines (delivered by the portal vein) or from the systemic circulation (delivered by the hepatic artery) enters the liver, it is filtered over liver cells called hepatocytes. Endogenous substances, such as bilirubin, and exogenous substances, such as drugs, are taken up by transporters on hepatocytes and undergo three phases of metabolism. The three phases allow the transported compound to be detoxified by a method of electron transfer (phase I), by addition of amino acid derivatives (phase II), and finally by exocytosis from the hepatocyte into the bile (phase III). The bile is then transported into the small intestine, and finally excreted from the body.
Amino acid derivatives are often taken from the Krebs cycle, added to sugar nucleotides, and transferred to molecules for detoxification. A common example of an enzyme responsible for this is UDP-glucuronosyl transferase.
How does phase I metabolism in the liver, conducted primarily by the cytochrome P450 system, serve to change an exogenous drug?
As we are told in the passage, phase I metabolism occurs by the transfer of electrons, commonly called an oxidation-reduction reaction. Phase I metabolism in the liver serves primarily to oxidize endogenous and exogenous molecules by passing electrons from a substrate to iron, and finally to oxygen. These oxidation reactions are carried out by the cytochrome P450 system and allow metabolites to become more soluble in urine for excretion. The other reactions listed are carried out by various transferases during phase II metabolism in the liver.
Which of the following is an alternative to sexual reproduction?
Parthenogenesis
Isogamy
Hermaphroditism
Pseudohermaphroditism
Parthenogenesis is the activation and development of an egg without sperm. Parthenogensis, therefore, is not sexual reproduction, but can still result in a fully developed offspring.
Isogamy is a condition of indistinguishable male and female gametes, but they retain the ability to join in sexual reproduction. Hermaphroditism and pseudohermaphroditism are rare conditions in which a single organism produces both sperm and eggs and is able to self-fertilize in sexual reproduction.
What is the most likely hormonal response immediately following a significant blood loss?
Increased level of ADH
Increased level of ACTH
Decreased level of insulin
Increased level of calcitonin
Decreased level of ADH
Significant amount of blood loss results in a sudden and large drop in blood pressure due to the decreased fluid volume in the body. To compensate for this change, the body will attempt to increase fluid retention. This is directly accomplished by increasing the level of ADH (anti-diuretic hormone) that allows reabsorption of water in the kidneys. Therefore, increased ADH level is the best response.
If a gene has a sequence of 5'-AGCTGCCTT-3', what would be the complementary mRNA sequence that leaves the nucleus to be translated?
3'-UCGACGGAA-5'
5'-AGCTGCCTT-3'
3'-TCGACGGAA-5'
5'-UCGACGGAA-3'
5'-UCGUCGGAA-3'
The correct answer is 3'-UCGACGGAA-5'.
In order to arrive at this answer, it is important to note that we are starting with DNA and finding the complementary mRNA. We must remember that there is no thymine in RNA; instead of thymine, RNA has uracil. The last thing to remember is that the mRNA strand will be anti-parallel, meaning that the 5' end of the DNA sequence must match up with the 3' end of the RNA sequence. Cytosine and guanine will form pairs. Adenine bases in DNA will pair to uracil bases in RNA, and thymine bases in DNA will bind to adenine in RNA.
DNA: 5'-AGCTGCCTT-3'
RNA: 3'-UCGACGGAA-5'
An environmental toxin has been found to directly disrupt normal gamete production in women. What tissue or organ is the toxin likely localizing to?
Ovaries
Endometrium
Oviduct
Uterus
None of these
The most likely localization of the toxin would be to the ovaries, since this is where gamete production begins for females. For males, gametes are produced in the testes. The incorrect answers are all parts of the female reproductive system. The oviduct is where fertilization takes place. The endometrium (the lining of the uterus) is where the embryo will eventually implant.
Which of these is a lymphoid organ that is active in young children, but decreases in size and importance in adulthood?
Thymus
Spleen
Tonsils
Adenoids
Lymph nodes
The thymus is a lymphoid organ located in the mediastinal space. The thymus is the site of T-lymphocyte differentiation. The mature T-cells leave the thymus and migrate to the spleen, lymph nodes, and other lymphoid tissues where they control cell-mediated immune responses. The thymus grows from birth to puberty, at which point it begins to shrink. The reason for this involution may be that the organ has produced enough T-cells and is no longer necessary.
The spleen is another lymphocyte-producing organ. The spleen filters blood, exposing it to lymphocytes that destroy foreign particles. The size of the spleen remains constant, except in cases of infections such as mononucleosis. The tonsils are a patch of lymphoid tissue that contain lymphocytes located in the pharynx. The tonsils and adenoids form a ring of immunologically active tissue. These tissues remain at a constant size except when infected by bacteria. Lymph nodes receive lymph from a single organ or region of the body. An increase in size, known as lymphadenopathy, could result from combating infection or cancer.