Tissues, Organs, and Organ Systems - Biology

Adipose tissue is one of the main types of connective tissue. It is also known as fat, and is a loose connective tissue composed mostly of adipocytes.

All of these areas of the body are subject to lots of friction. Thus, there would be multiple (stratified) layers of epithelium lining them.

Relay of electrical signals is performed by the nervous system, not by connective tissue.

Filtration occurs in the renal corpuscle, which is composed of the glomerulus and Bowman's capsule. The glomerulus filters the blood, resulting in the filtrate, which will then go through the tubules. The proximal and distal convoluted tubules are primarily involved in solute reabsorption, and the loop of Henle helps concentrate the urine.

Cartilage is a flexible connective tissue found throughout the body in places such as the ear, nose, bronchial tubes, and intervertebral discs. It is not as hard as bone, but it is stiffer and less flexible than muscle. Cartilage is composed of specialized cells named chondrocytes. These cells produce and maintain the cartilaginous matrix, which is composed of collagen and proteoglycan.

Since we are looking for a single layer of cells, we must rule out any area of the body that is subject to lots of friction. The skin is continually being rubbed and pushed by everything we touch, and the esophagus sustains abrasions from all the food we eat.

Microvilli are tiny projections on the apical surface of cells that increase the cell surface area. Since most of the absorption of food and nutrients occurs in the small intestine, it makes sense that we would want to increase the surface area of that region. Furthermore, since we are absorbing, we would want a single layer of cells to facilitate the diffusion of substances across the layer of epithelium. Thus, the correct answer is that simple columnar epithelium with microvilli will be found in the small intestine.

Most connective tissue cells are fibroblasts (fiber-producing cells), which secrete the proteins that comprise the extracellular matrix. All blood cells are considered connective tissue, including white blood cells and plasma cells (mature B-lymphocytes). Adipocytes (fat cells) are responsible for connecting and surrounding body organs, and providing structural support, as well as storing energy for the body.

Insulin stimulates the reuptake of glucose from the blood into the cells. Thus, the glucose levels in the blood decrease, as the glucose is taken into cells. The cells may either store it as glycogen (in liver and skeletal muscle) or use it in glycolysis to make ATP.

Blood cells, also called hematocytes, fall into three general categories: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Erythrocytes primarily carry oxygen and collect carbon dioxide through hemoglobin. Leukocytes are involved in the immune system, defending the body against infections and foreign materials. One type of leukocyte is a neutrophil. Thrombocytes are very small cell fragments that are involved in hemostasis (stopping bleeding) and the formation of blood clots.

Pinocytes do not exist. However there is a mechanism called pinocytosis by which cells ingest extracellular fluid and its contents.

The pituitary gland is known as the "master" endocrine gland because it secretes several hormones that control other endocrine glands. These are known as tropic hormones. Adrenocorticotropic hormone, thyroid-stimulating hormone, and follicle-stimulating hormone are some examples of pituitary tropic hormones.

There are four main categories of tissue: connective tissue, epithelial tissue, nervous tissue, and muscle tissue. Connective tissue is classified by loosely associated cells in an abundant medium, generally used to fill spaces and connect structures to one another within the body. Collagen fibers are particularly abundant in connective tissue. Adipose cells (fat), blood, cartilage, and bone are all specific types of connective tissue. Extracellular matrix is generally also considered connective tissue, but can vary in composition to some extent by location and includes loose connective tissue and dense connective tissue.

In contrast, epithelial tissue serves to line and protect regions of the body form the external environment. Any region of the body that is directly or indirectly connected to the environment is lined with epithelial cells, including the skin, digestive tract, respiratory tract, and excretory tract. Since material from the external environment (food) can enter the stomach, we know that the stomach lining must be made of epithelium.

Steroid hormones are the only ones derived from cholesterol and are always characterized by a four ring molecular structure. Some examples include sex hormones such as androgens and estrogens as well as some adrenal hormones like cortisol (a glucocorticoid) and aldosterone (a mineralocorticoid).

Increased potassium levels will stimulate aldosterone to increase potassium secretion. The main regulators of aldosterone are potassium and the renin-angiotensin pathway.

Connective tissue supports and connects other tissues and parts of the body. Connective tissue includes bone, cartilage, and fat. Epithelial cells form the epidermis of the skin and the linings of the digestive and respiratory tracts. Canaliculi are channels that allow osteocytes (bone cells) to remain in contact and transmit nutrients and gasses. Proteins are essential for the growth of new tissue or the repair of damaged tissues. Minerals are generally inorganic, but the mineral hydroxyapatite forms the matrix of bones.

Skin is part of the integumentary systemand is composed of stratified squamous epithelium.

Connective tissue is defined as a population fo cells suspended in an extensive extracellular matrix. For example, blood is classified as connective tissue because it consists of red blood cells (erythrocytes) suspended in a liquid matrix (plasma). Bone, cartilage, ligaments, and adipose tissue (fat) are also considered connective tissue.

Connective tissue is used to support, protect, and transport within the body. Bone tissue forms skeletons. Cartilage connects and supports bones, and adipose tissue stores energy and provides cushioning. Epithelial tissue refers to another type of tissue.

Connective tissue supports and connects other tissues and parts of the body. Connective tissue includes adipose (fat), cartilage, bone, and blood. Muscles produce movement. Muscles are attached to bone, in the walls of hollow internal organs, and in the heart. Nervous tissue transmits impulses in from sensory receptors and out to produce motor responses. Types of nervous tissue include the brain, spinal cord, and nerves. Epithelial tissue protects, secretes, absorbs, and excretes. Examples of epithelial tissues include skin, glands, and mucous membranes. In dentistry, the term "hard tissue" is used to describe the calcified tissue components of the tooth: enamel, dentin, and cementum.

Besides moving the body, muscles are also used to provide heat and stabilize the body. Certain muscles are constantly being stimulated to help maintain posture and stability, even when we are unaware of their action. When body temperature is low, muscles can contract to produce body heat. This is why we shiver when we are cold.

Though some calcium is stored in muscle cell, calcium storage and regulation is primarily accomplished by the skeletal system. Hormones are released to directly influence calcium release or uptake in bone.

There are three primary types of muscle. Cardiac muscle is composed of striated, mono-nucleated cells and is found in the heart. Additionally, cardiac muscle cells are joined by intercalated discs and are capable of auto-regulating contraction without nervous stimulation.

Skeletal muscle is composed of striated, multinucleated cells and is found around the bones of the body. Skeletal muscle is under voluntary control and is primarily responsible for causing movement of bones and limbs.

Smooth muscle is composed of non-striated, mono-nucleated cells and is found around the organs and blood vessels of the body. Smooth muscle helps control blood flow, digest food, and contract the diaphragm.

Skeletal muscle is striated due to its sarcomere composition. The bands of each sarcomere align, giving the muscle its striped appearance. Skeletal muscle cells have multiple nuclei, allowing them to synthesize more RNA (and proteins) to maintain muscle tone.

Intercalated discs are only found in cardiac muscle, and help with cell adhesion and signal transduction.