Systems Biology - GED Science

The heart has four chambers: two atria and two ventricles. The atria are responsible for receiving blood returning from the body, while the ventricles pump blood out of the heart. The right ventricle pumps blood to the lungs, while the left ventricle pumps blood to the rest of the body.

The flow of blood through the heart is: right atrium, right ventricle, lungs, left atrium, left ventricle, body.

Arteries are the high pressure blood vessels responsible for carrying blood away from the heart. All arteries in the body travel away from the heart toward other tissues.

Most arteries carry oxygenated blood, but the pulmonary arteries carry deoxygenated blood; these vessels are responsible for transporting deoxygenated blood from the right side of the heart to the lungs. Veins are responsible for returning blood back to the heart. Arteries do not allow for diffusion of nutrients; this process primarily occurs in capillaries.

The heart is able to pump independently of the brain thanks to a collection of cells that fire impulses automatically. These cells are located in the sinoatrial node, which leads to the node's nickname as the "pacemaker" of the heart. Even without stimulation by a nerve, the heart can continue beating.

The heart is made of cardiac muscle tissue; smooth muscle tissue lines internal organs and blood vessels. Both sides of the heart pump at the same rate, but the left side pumps with more force. Each side of the heart must pump the same volume, but the left side must pump it a greater distance since it pushes blood to the entire body. A normal resting heart rate is around 60-80 beats per minute. A heart rate of 120 would be more typical during exercise.

The respiratory system allows air to travel to the lungs. Air enters the mouth or nasal passages, travels through the trachea, and then into the bronchi. The bronchi split into smaller and smaller bronchioles before terminating in small sacs called alveoli.

The aorta is a major artery that carries blood away from the heart. The urethra carries urine from the bladder. The small intestine is a portion of the digestive tract that carries nutrients from the stomach to the large intestine.

Blood is composed of multiple cell types that have specific functions in the body. The red blood cells (erythrocytes) help carry oxygen to the tissues in the body. The white blood cells (leukocytes) help defend the body from bacteria and other illnesses. Platelets are cell fragments responsible for helping blood clot, and are created by megakaryocytes.

The esophagus assists moving food into the stomach using a wave-like contracting motion called peristalsis. Swallowing initiates the process of peristalsis, but unlike swallowing, peristaltic contractions are not voluntary and are generated by smooth muscle.

Mastication is another term for "chewing." Emulsification refers to the grouping together of fat molecules when in an aqueous environment, particularly during digestion in the small intestine.

Food is digested to some degree in many different parts of the digestive system. The mouth, stomach, and small intestine all contribute to food digestion. The mouth contains salivary amylase, which breaks down carbohydrates. The stomach contains pepsin, which breaks down proteins. The small intestine contains several enzymes, such as lipase and trypsin, and breaks down carbohydrates, lipids, and proteins.

The esophagus, however, does not contribute to chemical digestion in any way.

Bile is created by the liver and released into the small intestine from the gall bladder during digestion. Because fat tends to clump in the aqueous environment of the duodenum, bile helps to increase the surface area of fat, a process called emulsification. This helps lipase break down the fats adequately.

The chief cells are responsible for releasing pepsinogen. Pepsinogen is an inactive enzyme that will only become activated in acidic conditions, such as those found in the stomach. Acid converts pepsinogen into pepsin, which helps chemically digest protein nutrients in the stomach.

Parietal cells release hydrochloric acid into the stomach, which activates pepsinogen. Goblet cells, or mucous cells, secrete mucous to help prevent degradation of the stomach lining.

Muscles do not attach directly to bones. Instead, a tendon is used to attach the two structures. Ligaments connect a bone to another bone, while joints are the locations where bones move around one another.

There are three types of muscle in the body: skeletal, cardiac, and smooth muscle. Of the three, skeletal muscle is the only one that can be consciously controlled. Cardiac and smooth muscle are controlled involuntarily.

An example of skeletal muscle is your biceps brachii muscle; you can voluntarily control this muscle to flex your arm. An example of smooth muscle is the muscle surrounding your arteries; you cannot voluntarily contract this muscle to constrict your arteries. Cardiac muscle is found in the heart; you cannot voluntarily choose to slow your heart rate.

Red bone marrow is found in the ends (epiphyses) of long bones such as the femur and is responsible for red blood cell development. Yellow bone marrow is found in the center (diaphysis) of long bones and can store fat for energy.

Blood filtration primarily occurs in the spleen or kidney. Glycogen is primarily stored in the liver. Calcium is released from the mineral matrix of the bone, but is not actually found in the bone marrow.

Skeletal and cardiac muscle have quite a bit in common: both are examples of striated muscle that use the sarcomere as the basic functional unit. Sarcomeres are small units that are capable of contracting. When these units line up in a cell, they create a striped appearance known as "striated" or "striations." Both skeletal and cardiac muscle are capable of contracting; this is a key characteristic of any muscle cell.

A primary difference between skeletal and cardiac muscle cells is the number of nuclei each cell possesses. Skeletal muscle cells usually have several nuclei, but cardiac muscle cells usually have only one nucleus per cell.

The germ cells (eggs/oocytes and sperm) contain only one copy of each chromosome. This reduction in the amount of DNA occurs through meiosis. Most cells in the body contain two copies of each chromosome and are considered diploid. Since they only contain ne copy of each chromosome, germ cells are considered haploid.

Neurons and lymphocytes (white blood cells) contain two copies of each chromosome; they are diploid. Erythrocytes (red blood cells) do not have nuclei, and do not contain any genetic material.

Ovulation, or the release of the egg from its follicle, is initiated by a temporary spike in estradiol (estrogen) levels. This positive feedback event is referred to as the luteal surge.

Menstruation follows ovulation. Gastrulation is a phase of development during which the primary germ layers are generated in an embryo, and is not related to the female cycle.

There are several stages of embryonic development. The first stage is the zygote, which is simply a single cell formed after the sperm fuses with the egg. The cell then begins to divide, creating more cells without actually expanding in size. This process is called cleavage and the embryo is now call a morula. Eventually, the cells orient such that they form a ball with a hollow center and begin to expand in total size. This stage is known as the blastula or blastocyst stage. During this stage, the embryo will enter the uterus and implant into the uterine wall. As the cells continue to divide and orient, the blastocyst develops an inner cell mass, which will be become the new organism. The cells in this area begin to differentiate into the different germ layers through a process known as gastrulation; the resulting embryo is known as a gastrula.

Following gastrulation, the three primary germ layers are formed. They are the ectoderm, the mesoderm, and the endoderm. The ectoderm develops into the skin and the nervous system. The mesoderm develops into the bones and muscle. The endoderm develops into the lining of the digestive tract and most internal organs.

Spermatozoa formation is accomplished in the seminiferous tubules in the testes. Once created, the spermatozoa are taken to the epididymis for storage and maturation. During ejaculation, the sperm is expelled through the vas deferens then through the urethra and out of the penis.

The germ cells (eggs/oocytes and sperm) contain only one copy of each chromosome. This reduction in the amount of DNA occurs through meiosis. Most cells in the body contain two copies of each chromosome and are considered diploid. Since they only contain ne copy of each chromosome, germ cells are considered haploid.

Neurons and lymphocytes (white blood cells) contain two copies of each chromosome; they are diploid. Erythrocytes (red blood cells) do not have nuclei, and do not contain any genetic material.