Notes, abstracts, papers, exams and problems of Biology

Conjunctival Autoimmune Diseases

Autoimmune diseases associated with skin and mucocicatricial conditions that affect the cornea and conjunctiva:

• Ocular Cicatricial Pemphigoid: Chronic bilateral conjunctivitis that typically appears around 50 years of age, leading to fibrosis, keratinization, and symblepharon. Treatment includes corticosteroids, cyclophosphamide, and dapsone.
• Erythema Multiforme: Includes Stevens-Johnson syndrome (affecting skin and mucosa) and toxic epidermal necrolysis (Lyell's syndrome), often triggered by medication or an infectious process.

Neurotrophic Keratopathy

Etiology: Ablation of the fifth cranial nerve, infection (such as herpes), topical medications (anesthetics), systemic diseases (diabetes mellitus, vitamin A deficiency)... Continue reading "Understanding Common Eye Conditions and Treatments" »

Nervous System Coordination

Nervous coordination is carried out by the nervous system. Neurons are divided into three parts: the cell body, the dendrites, and the axon.

• The cell body contains the nucleus and other organelles.
• Dendrites are short, branch-like projections.
• The axon is a longer projection. It ends in a series of slender branches which widen slightly at the tip and are called axon terminals.

In general, axons are protected by a white substance called myelin. The axons of various neurons sometimes group together to form nerve fibers, and these in turn can group together to form nerves.

Neuron Connection: The Synapse

Neurons are connected to each other. The place where one neuron connects to another is called a synapse. A nerve impulse... Continue reading "Nervous and Endocrine Systems: Coordination and Regulation" »

Work of the Cell: Metabolism and Disease

Metabolism: The set of biochemical transformations that occur in living cells. It has two parts: anabolism and catabolism.

Anabolism

Anabolism is the part of metabolism dedicated to the production of molecules that comprise cells from nutrients.

Catabolism

Catabolism is the part of metabolism involved in the production of energy that the cell constantly needs to perform its functions. It uses organic nutrients.

Nutrients are essential substances that cells need but are unable to synthesize; therefore, they must be obtained through diet.

Healthy Lifestyles

Healthy lifestyles include:

• Personal hygiene
• Domestic hygiene
• Occupational hygiene
• Proper eating habits
• Adequate sleep
• Regular exercise
• Avoiding drugs
• Avoiding a sedentary

Understanding the Human Immune System

Innate and Acquired Immunity

The immune system is a complex network of organs and structures responsible for defending the body from toxic microbial aggression. It operates through two primary mechanisms:

• Innate (Natural) Immunity:
  • Passive: Represented by maternal antibodies.
  • Active: Involves antigen-antibody reactions.
• Acquired Immunity:
  • Active: Developed through vaccines.
  • Passive: Achieved via the administration of antibodies, such as those found in antibiotics.

Key Components of the Immune System

The immune response involves several processes, including:

• Chemotaxis: The attraction of immune cells to the site of infection.
• Diapedesis: The movement of immune cells out of blood vessels.
• Phagocytosis: The process of

Tumors

In normal tissues, cells divide to replace old or damaged cells. This balance can be disrupted, leading to tumor formation. Tumors are defined as a mass of disorganized tissue. Most tumors are benign, meaning they grow locally and do not spread.

Malignant Tumors: Cancer

Cancer is a malignant tumor whose cells can spread from the initial tumor site to other parts of the body. These cells have two key characteristics:

1. Invasiveness: Ability to penetrate and spread through adjacent tissues.
2. Metastasis: Capacity to enter the blood and lymph systems, travel to other parts of the body, and form secondary tumors.

Cancer Treatment

• Surgery: Removal of the tumor mass.
• Radiotherapy: Use of radiation to shrink cancer cells.
• Chemotherapy: Administration of

Thyroid

Origin: Endodermal derivative, initially from the floor of the pharyngeal gut. It is a solid organ.

Capsule: Connective tissue rich in collagen fibers (fibrosis), surrounding the thyroid tissue.

Stroma: Septa extend inward (including into the parathyroid), containing reticular fibers surrounding the thyroid follicles. It is highly vascularized (by the superior and inferior thyroid arteries) with fenestrated capillaries.

Parenchyma: The gland consists of thousands of thyroid follicles, lined by simple cuboidal epithelium (flat or cylindrical) on a thin basal lamina. The cavity contains thyroid colloid.

Cells:

• Follicular cells: Cuboidal [low height indicates underactivity, high height indicates overactivity (less colloid)].
• Parafollicular cells:

Five Kingdoms of Life

1. Monera

This kingdom includes bacteria and cyanobacteria. Bacteria are prokaryotic, lacking a true nucleus. Key components include the cell membrane, nuclear region (or nucleoid), ribosomes, cytoplasm, and often a cell wall. Cyanobacteria, also known as blue-green algae, are thought to have originated atmospheric oxygen around 2 billion years ago through photosynthesis.

Bacteria

Bacteria reproduce asexually, typically through binary fission. Some can form cysts for protection in unfavorable conditions. Cyanobacteria are crucial for various ecological processes.

2. Protists

Protists are unicellular, heterotrophic eukaryotes. They possess organelles like the Golgi apparatus, lysosomes, ribosomes, centrosome, mitochondria, endoplasmic... Continue reading "Exploring the Five Kingdoms of Life: A Comprehensive Overview" »

Mitosis: Cell Division Explained

Mitosis is the process where a single cell divides into two identical daughter cells. DNA is duplicated, creating two identical nuclei. This process ensures each new cell receives a complete set of chromosomes.

Mitosis Phases

• Prophase: Chromosomes condense and become visible. The nuclear membrane breaks down.
• Metaphase: Chromosomes align along the metaphase plate in the center of the cell.
• Anaphase: Sister chromatids separate and move to opposite poles of the cell.
• Telophase: The nuclear membrane reforms around the separated chromosomes, and the cytoplasm divides (cytokinesis), resulting in two identical daughter cells (diploid).

Meiosis: Sexual Reproduction and Genetic Diversity

Meiosis is a type of cell division that... Continue reading "Mitosis, Meiosis, and Ecosystem Roles: Producers to Decomposers" »

Respiratory System

The respiratory system is formed by the ducts through which air circulates, and by small cavities called alveoli, which are capable of entering the bloodstream. At the same time, blood circulates CO2 through the tubes of the respiratory system.

Upper Respiratory Tract

• Nose and nostrils: Two cavities located in the center of the face. Function: To warm and moisten the air.
• Pharynx: Connects the mouth with the larynx and nasal passages. It also communicates through the auditory tube. It forms part of the respiratory and digestive tracts.
• Larynx: Formed by cartilage and bone, it connects the pharynx with the trachea. It contains the vocal cords, which vibrate with airflow to produce the voice.

Lower Respiratory Tract

• Trachea: A tube

Cell Adhesion Molecules (CAMs): Types and Functions

Structurally, there are five families of CAMs: Cadherins, Immunoglobulin superfamily, Integrins, Selectins, and Proteoglycans.

Cadherins

Cadherins are monomeric molecules, which are receptors that bind *homophilically* (to identical cadherins) or *heterotypically* (to different cadherins) expressed on cells for cell-cell contact. Their action is calcium and temperature-dependent. A cell can express more than one type of cadherin. At least twelve types are known, but the most studied are:

• E-cadherin: Present in epithelia of various tissues, such as liver and kidney.
• N-cadherin: Found in neural tissue and heart muscle.
• P-cadherin: Found in the placenta.

Cadherins allow cell adhesion and maintenance... Continue reading "Cell Adhesion Molecules: Types and Functions" »