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Endocrine Glands: Histology and Function

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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:
... Continue reading "Endocrine Glands: Histology and Function" »

Exploring the Five Kingdoms of Life: A Comprehensive Overview

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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, Meiosis, and Ecosystem Roles: Producers to Decomposers

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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" »

Male Reproductive Anatomy and Function

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Sexual Reproduction Basics

The male and female germ cells are called gametes. They have 23 pairs of chromosomes. This means 46 chromosomes. The chromosomes that make up each pair are called homologous. The sex chromosomes are referred to by the letters X and Y. The other 22 pairs of chromosomes are autosomes.

The gonads are represented by the testes in males and ovaries in females.

Male Reproductive System

The Scrotum

It is a membranous sac that hangs from the root of the penis. From the outside, it appears formed by a layer of skin, divided into two parts (right and left) by a raphe. The interior is divided by a membranous septum and a muscle called the tunica dartos muscle.

The Testicles

They are ovoid structures that are the male gonads, weighing... Continue reading "Male Reproductive Anatomy and Function" »

Respiratory and Circulatory Systems: Anatomy and Diseases

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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
... Continue reading "Respiratory and Circulatory Systems: Anatomy and Diseases" »

Cell Adhesion Molecules: Types and Functions

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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" »

Human Sensory and Locomotor Systems: Functions & Health

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Touch

The skin is the largest organ of our body, composed of two layers:

  • Epidermis: The outer layer is formed by epithelial tissue. The outer cells are dead and continuously shed as flakes and dandruff.
  • Dermis: The inner layer, formed by connective tissue, provides elasticity to the skin. The dermis contains numerous blood vessels and tactile receptors.

Smell

The inside of the nostrils is lined by a mucosa called the pituitary gland. Two regions can be distinguished:

  • Red pituitary: Occupies the lower part, has several blood vessels that warm the incoming air.
  • Yellow pituitary: Occupies the upper part, contains numerous olfactory receptors.

Taste

At the top of the tongue are numerous projections called taste papillae. These contain sensitive cells (chemoreceptors)... Continue reading "Human Sensory and Locomotor Systems: Functions & Health" »

Heart Anatomy and Function

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Structure and Location

The heart is a hollow, muscular organ about the size of a clenched fist. It's located in the chest cavity, between the lungs, within the mediastinum. Its shape resembles a triangular pyramid with a base and upper left and lower right edges. The heart is enclosed by the pericardium, a double-layered sac. The outer layer is fibrous, while the inner layer is the serous pericardium. Pericardial fluid between these layers lubricates the heart's movement.

Chambers and Valves

Internally, the heart has four chambers: two atria and two ventricles. The atria, located superiorly, have thin walls. The ventricles, situated inferiorly, have thicker walls (approximately 4mm). The right ventricle's wall is about 0.5cm thick, while the... Continue reading "Heart Anatomy and Function" »

Protein Tertiary Structure Explained

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Tertiary structure is the three-dimensional arrangement of all atoms making up the protein. The tertiary structure of a protein is directly responsible for its biological properties. For proteins that consist of a single polypeptide chain (lacking quaternary structure), the tertiary structure represents the maximum structural information obtainable.

Types of Tertiary Structure

There are two types of tertiary structure:

  • Fibrous tertiary structure: Proteins where one dimension is much larger than the other two.
  • Globular tertiary structure: More frequent type, where one dimension predominates over the others, and its shape is roughly spherical.

Forces Stabilizing Tertiary Structure

The forces that stabilize the tertiary structure of a protein are established... Continue reading "Protein Tertiary Structure Explained" »

Chromosomes, Genes, and Cell Division: Mitosis vs. Meiosis

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Fundamentals of Genetics and Chromosomes

In humans, there are 46 chromosomes, occurring in 23 pairs. The diploid number refers to the total number of chromosomes in each body cell of a plant or animal.

Key Genetic Terms

  • Gene: A length of DNA that is the code for making a specific protein molecule. Genes are always located in the same position on a chromosome.
  • Allele: Different versions of the same gene.
    • A dominant allele is expressed and affects the appearance (phenotype) of the individual.
    • A recessive allele is only expressed if two copies are present or if the dominant allele is absent.
  • Genotype: The specific combination of alleles an organism possesses for a trait.
    • Homozygous: Having two identical alleles for a trait (e.g., TT or tt).
    • Heterozygous:
... Continue reading "Chromosomes, Genes, and Cell Division: Mitosis vs. Meiosis" »