Cellular Processes and Body Systems
Mitosis
Mitosis is the process of forming two daughter nuclei through a single division. The resulting cells, or daughter nuclei, are identical. Daughter nuclei are diploid (2n). Mitosis occurs in somatic cells for growth and repair processes. There is no pairing of homologous chromosomes.
Endocrine System
The endocrine system is the set of organs and tissues that release hormones. Endocrine organs are also called ductless glands or endocrine glands because their secretions are released directly into the bloodstream. Exocrine glands, in contrast, release their secretions onto the inner or outer surface of tissues, such as the skin, the lining of the stomach, or the lining of the pancreatic ducts.
Hormones secreted by the endocrine glands regulate the growth, development, and function of many tissues, and coordinate metabolic processes. The organs that produce hormones can be classified into three groups:
- Endocrine glands: Their sole function is hormone production.
- Endo-exocrine glands: They produce hormones in addition to other secretions.
- Glandular tissues: Certain tissues, such as the nervous tissue of the autonomic nervous system, produce hormone-like substances.
The most important glands are:
- Pituitary gland
- Thyroid
- Parathyroid
- Pancreas
- Adrenals
- Ovaries
- Testes
Key Endocrine Organs and Their Functions
Hypothalamus: Part of the brain that connects with the pituitary gland. It produces substances that link the nervous system to the endocrine system.
Pituitary Gland (Hypophysis): Produces hormones that control body growth and the functioning of other endocrine glands.
Thyroid: Its hormones control metabolic processes within cells.
Parathyroid: The hormones produced control calcium concentration in the blood.
Testes: Form sperm and hormones that determine distinctive male characteristics.
Pancreas: Some of its cells produce hormones that control the concentration of glucose in the blood.
Ovaries: Form eggs and produce hormones that determine female characteristics and prepare the uterus for pregnancy.
Hormone Action
Hormones, produced by glands, have a three-dimensional shape that identifies the specific cell in which they must act. The target cell has a receptor with a complementary three-dimensional structure suitable for only one type of hormone.
Nervous System
The nervous system receives information from the environment and the body’s interior and generates responses, such as regulating heart rate. It is divided into:
- Sympathetic Nervous System: Active during emergency situations, associated with the “fight or flight” response. For example, it inhibits the digestive tract but dilates the pupils and accelerates heart rate and breathing.
- Parasympathetic Nervous System: Related to internal responses associated with relaxation. For example, it constricts the pupils, aids in food digestion, and decreases heart rate.
Arthro-Osteo-Muscular System
The arthro-osteo-muscular system consists of the bones (osteoarticular system), joints, and ligaments. The muscular system comprises muscles and tendons, which attach to bones. The integrated operation of these three components forms the locomotor system of vertebrates.
DNA and Genetics
DNA contains the hereditary information for a species. Its function is the transmission of genetic codes. Chromosomes are formed by two strands of repeating DNA. The only variation in the DNA structure is in the nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). DNA is the material that makes up genes. Genes are sets of nucleotides linked together, containing information for a particular characteristic. Therefore, a chromosome can be considered a set of genes. Genes determine the hereditary characteristics of each cell or organism.
Crossing Over
Crossing over is the exchange of genetic material during meiosis between male and female parents. The chromatids of homologous chromosomes break at chiasmata and rejoin, allowing for the recombination of linked genes. Crossing over leads to an increase in genetic variation. It occurs within chromosomes.