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

Surfactant is a vital detergent needed for gas exchange between the lungs and the blood stream. Its role is to lower the surface tension on the interior of the alveolar sac. Without surfactant, alveoli would collapse and gas exchange would be inhibited.

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.

Granulocytes are cells categorized because they have vesicles within their membrane that look similar to a granule. Basophils, eosinophils and neutrophils all present granule-like figures and are categorized as granulocytes. Although they derive from the same myeloid stem cells as the granulocytes, monocytes are categorized as agranulocytes.

This question requires knowledge of the different cell types in the human male’s reproductive anatomy. The cells of Leydig (also known as the interstitial cells) secrete testosterone and other androgens (male sex hormones), while the Sertoli cells are responsible for nourishing developing sperm. Spermatogonia are sperm cell precursors, and the zona pellucida refers to one of the layers surrounding an ovum.

In terms of MHC restriction, students should be familiar with the fact that cytotoxic T-cells are CD8+ and MHC I restricted. The alternative T subset, the helperT-ell, is CD4+ and MHC II restricted. Both cells rely on cytokines for growth, survival, and their effector functions.

Juxtaglomerular cells respond to low levels of sodium and secrete renin in response, which results in the release of aldosterone from the adrenal cortex. Aldosterone, as a result, will increase sodium reabsorption from the collecting duct. This will in turn increase blood pressure, however, the direct role of the cells themselves is to regulate blood osmolarity.

The circulatory system arises from the mesoderm. Other mesoderm structures include the muscles, bones, gonads, and kidneys.

The ectoderm gives rise to the epidermis, nervous system, and lens of the eye. The neural crest originates from ectoderm cells.

The endoderm gives rise to several internal organs, including the liver and pancreas, as well as the linings of the digestive and respiratory tracts.

The bladder develops from the endoderm. The heart, kidney, skeletal muscle, and bone develop from the mesoderm.

The correct order is listed below.

1. Fertilization: the joining of an egg and sperm

2. Cleavage: early cell division in an embryo before a specific structure is formed

3. Blastula Formation: the cells of the embyro form a hollow structure filled with fluid

4. Gastrulation: the cells in the embryo migrate to form the three germ layers; the hole with fluid formed during the blastula stage is now filled with cells

The lower esophageal sphincter separates the esophagus from the stomach. When stomach acid and contents leak through the lower esophageal sphincter, the acid irritates the esophagus and can lead to pain around the area of the heart. The heart is not actually affected.

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

Immovable joints are fused shortly after birth, so that they are no longer functional for articulation. The bones of the skull remain open, joined with strips of cartilage, until an infant has passed through the birth canal. They stay open for a short period, giving the baby's brain room to grow. After the brain has finished its major growth stages, the bones of the skull knit together, forming a protective barrier.

Tendons connect muscles to bones, allowing for the muscle contraction to affect the bone and result in articulation. Tendons are essential to provide articulation and leverage points to for motion and locomotion.

Vasopressin acts on the collecting duct in order to increase its permeability to water. This results in more water being reabsorbed, and increases blood pressure.

Blood pressure tends to be the greatest near the heart, and decreases as blood flows to the capillaries. The pressure is greatest at the aorta and gradually decreases as blood moves from the aorta to large arteries, smaller arteries, and capillaries. The pressure is lowest in the venous system, which is why blood can pool in the veins and act as a "blood reservoir". Veins contain valves that allow them to pump blood back to the heart.

The endoderm develops into a number of internal organs, including the lung, which are vital for breathing.

The kidneys (urine production), muscles (movement), and blood vessels (blood circulation) develop from the mesoderm. The brain (thought) develops from the ectoderm.

When blood passes from the right atrium into the right ventricle, it must pass through the tricuspid valve.

The mitral, or bicuspid, valve separates the left atrium and ventricle. The semilunar valves are the aortic and pulmonary valves. The aortic valve separates the left ventricle and aorta, while the pulmonary valve separates the right ventricle and pulmonary arteries.

The four types of tissue are muscular, connective, nervous, and epithelial.

Muscular tissue encompasses skeletal, cardiac, and smooth muscle. Nervous tissue creates the central and peripheral nervous systems (CNS, PNS) and consists of all neurons and glial cells. Epithelial tissue makes up "borders" and lines most organs. Connective tissue generally fills spaces and provides the suspensory matrices for the body, such as bone, fat, blood, and cartilage.

The semilunar valves refer to the aortic valve and pulmonary valve, both of which have three flaps. The atrioventricular valves separate the atria from the ventricles. The right side of the heart is separated by the tricuspid valve, while the left is separated by the bicuspid, or mitral, valve. The mitral valve is the only heart valve with two flaps.