Tissues, Organs, and Organ Systems - Biology

At day 14 of a menstrual cycle, the LH surge begins, which causes the follicle to burst, resulting in ovulation. The LH surge is caused by a rise in estrogen, which causes the pituitary gland to release LH.

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.

Red bone marrow is found in the epiphyses, or ends of long bones. It is the site of hematopoiesis, or red blood cell development.

Yellow bone marrow is primarily composed of fat. Osteons are the functional units of bone, and house the cells that build and break down the bony matrix. Cartilage is found on the articular surfaces of bone, and helps provide support for joints.

The skeletal system has a variety of functions, including protecting internal organs, storing minerals and energy molecules, and assisting in movement.

The production of heat, however, is a function of the muscular system.

As an action potential is essentially an electrical current, it makes sense for it to open voltage-gated channels. Specifically, voltage-gated calcium channels are opened to allow calcium ions to flow into the cell and bind to synaptic vesicles.

The sympathetic nervous system is responsible for stress responses, while the parasympathetic nervous system is responsible for resting responses. The sympathetic nervous system causes increased heart rate, pupil dilation, suppressed digestion, inhibited salivation, and dilated bronchi.

Progesterone ("pro-gestation") is responsible for the maintenance of a pregnancy. Initially, the corpus luteum secretes progesterone in preparation for pregnancy. Then, after fertilization, human chorionic gonadotropin (hCG) is released which causes the corpus luteum to keep secreting progesterone. The placenta takes over it's function after 6 weeks gestation.

Eggs, or oocytes, are produced in the ovaries. During ovulation, the egg is released from the ovary into the fallopian tube. If fertilized, the egg transitions into a zygote and is implanted into the uterus for gestation and development.

The spleen is involved in filtering the blood and lymph, and is not involved in reproduction.

The epididymis is responsible for storing sperm in order for it to mature. Upon ejaculation, it will be propelled into the vas deferens and out of the urethral opening.

The epidermis is composed of five layers of flattened epithelial cells. This stratified squamous epithelium allows the skin to be a barrier for the body and prevent pathogens and foreign materials from entering.

Stratified epithelium has multiple layers, and squamous epithelium is flattened.

Epithelium describes the inner and outer surfaces of the body including; the skin, colons, and the stomach. These surfaces have distinct upper and lower sides, are kept in place by connective tissue, and are made up almost entirely of cells. However, they are not supported by blood cells.

Nervous tissues such as the brain, spinal cord, and nerves function to transmit impulses for coordination, sensory reception, and motor actions. Epithelial tissue protects (skin), secretes (glands), absorbs (kidneys), and produces germ cells (embryo).

Since capillaries are the site of diffusion of substances (oxygen and carbon dioxide, for example), they need to have extremely thin walls. Their walls are made of simple (single-layered) epithelium. The other options would be too thick to facilitate diffusion of substances.

The endothelium is a form of squamous epithelium consisting of flat cells that line the blood and lymphatic vessels. Endothelial cells are metabolically active and produce compounds that relax vascular smooth muscle and inhibit the adhesion of platelets.

Adipose, or fat cells, are modified for long-term energy storage and are considered connective tissue. Cone cells are found in the eye and serve as light receptors for the nervous system. Stem cells can develop into more specifically differentiated daughter cells. Dendritic cells help T-cells respond to foreign antigens as part of the immune system.

An epithelia is a sheet of cells that are closely associated. Cells within an epithelium are polarized, indicating that the cells have a "direction". One side of the epithelium is called "apical" while the other side is "basal." The apical region is oriented toward a lumen, while the basal region is oriented toward a basement membrane associated with connective tissue. Cells within an epithelium are innervated, but not vascularized; therefore, they must receive signals through other methods of intercellular signaling, such as tight junctions.

The primary function of epithelial tissue is to provide linings that separate the body from the external environment. Epithelial tissue lines blood vessels, the respiratory and digestive tracts, the excretory system, and composes the skins. Epithelial tissue also lines the ducts that connect the body to the exterior, such as those that allow the pancreas to secrete enzymes into the small intestine.

Epithelial tissue is avascular (does not have a blood supply); thus epithelial tissue is always found in close association with connective tissue that has a rich blood supply. Epithelial cells cover organs and are thus subject to lots of friction. As a result they are continually being renewed, and divide quickly. In particular, skin cells and the epithelium lining the digestive tract have a high rate of division.

Adipose tissue is the anatomical term assigned to fatty tissue. Keep in mind that adipose tissue is a type of connective tissue. Adipose tissue serves as an energy store, helps maintenain of core body temperature, and protects internal organs from damage caused by trauma. Epithelial tissue is responsible for covering body cavities, and comprising glandular tissue. Nervous tissue is responsible for receiving sensory input from the environment, integration of the sensory input, control of muscles and glands, maintenance of body homeostasis, and emotions/personality. Smooth and striated are subsets of muscle tissue: skeletal and cardiac muscle are striated, whereas smooth muscle is not.

Epithelial tissue forms membranes that cover the body, as well as lines body cavities and glands. Simple squamous epithelium consists of thin, flattened cells, that are one layer thick and allow for the easy movement of substances. This is especially important for gas exchange in the alveoli of the lungs and in the capillaries of the body. The minimal barrier provided by simple squamous epithelium allows molecules to easily diffuse across the membranes.

Stratified squamous epithelium is many layers thick and forms the skin and lining of mucous membranes. Simple cuboidal epithelium functions in absorption and secretion in the kidney tubules and salivary glands. Simple columnar epithelium forms a thick layer that lines the esophagus, stomach, intestines, and uterus. Pseudostratified columnar epithelium possess beating cilia and transport particles in the respiratory tract and reporductive system.

Keratinized stratified squamous epithelium makes up the outer layer of skin. Other types of epithelial tissues are found throughout the digestive and reproductive tracts, and other areas of the body.