Notes, summaries, assignments, exams, and problems for Biology

The Absorption and Egestion

As a result of nutrient digestion, small molecules are obtained, allowing them to pass through the walls of the digestive tract and enter the blood. This process is called absorption.

Most substances are absorbed in the jejunum and ileum. In these sections, the inner walls of the small intestine are highly folded to form villi. Inside the villi, blood vessels collect and distribute digested substances to all body cells.

Egestion

Substances that have not been absorbed pass into the large intestine through peristaltic movements of its walls. In this part, almost all the water and mineral salts are absorbed, so the residues of digestion grow stronger until they become stool.

The large intestine also contains a large number... Continue reading "Digestive System: Absorption, Egestion, and Common Disorders" »

Digestive System

Initial Stage: Stomach

The first stage of digestion occurs in the stomach. Here, digestive substances break down food. The stomach cavity is wider than the intestinal walls and secretes gastric juices. This section also includes glands like the liver, which secrete substances that convert food molecules into smaller ones.

Second Stage: Small Intestine

In the second stage, nutrients are absorbed in the small intestine. This organ's extensive length and folded inner walls maximize absorption surface area.

Final Stage: Large Intestine

The last stage takes place in the large intestine (colon), where water is absorbed. This section is wider than the small intestine and lacks the folds of the previous section.

Transport of Nutrients

Blood

Classification of Nerves

Classification of Nerves by Origin

Nerves can be classified based on their origin (where they exit the central nervous system):

• Cranial Nerves: Nerves exiting the brain. They are responsible for transmitting information regarding sight, hearing, smell, chewing, speech, and other vital functions.
• Spinal Nerves: Nerves exiting the spinal cord. They manage the transmission of information to control internal organs such as the heart, lungs, liver, kidneys, and so on.

Functional Classification of Nerves

According to their function, nerves can be classified as:

• Sensory (Afferent) Nerves: Receive the sensations perceived by receptor organs and transmit them to the Central Nervous System (CNS).
• Motor (Efferent) Nerves: Transmit impulses

Negative and Positive Feedback in Hormonal Regulation

Negative feedback: This is the most widespread type and occurs when increased hormone levels, above a certain value, inhibit hormone secretion. Positive feedback: In this case, an increase in the values of a hormone causes an increase in its secretion. This type of regulation occurs in special situations, such as ovulation.

Immune System Barriers

The immune system can recognize and usually eliminate altered elements of itself.

In humans and higher vertebrates, three types of defensive barriers are distinguished: primary, secondary, and tertiary. Their function is to prevent the entry and development of pathogens.

Primary Barriers

• The skin: The first defensive barrier that prevents the entry of

There are eight fundamental characteristics of the structure of animals that distinguish this group from other groups of living things. These features are:

1. Animals are multicellular. This means that all individuals belonging to the animal kingdom consist of more than one cell, no matter what species they belong to.

   This feature clearly separates the animals from protozoa. Protozoa are a group of unicellular organisms (composed of a single cell) that were formerly classified in the animal kingdom but are now classified in a different group, the kingdom Protozoa, also known as Protista or Protoctista.

2. Animals are eukaryotic. All animals have true cells with nuclei and different organelles in the cytoplasm that perform specific functions. Deoxyribonucleic

The Human Digestive System Structure

The digestive system is made by the gastrointestinal tract and accessory glands.

The Digestive Tract

The digestive tract begins in the mouth and ends at the anus. It includes the oral cavity, pharynx, esophagus, small intestine, and the large intestine.

Accessory Glands

Accessory glands are organs that pour their secretions into the digestive tract. These include the salivary glands (producing saliva in the mouth), gastric glands (in the stomach), and intestinal glands (in the intestine). The liver and pancreas are also glands that discharge their secretions into the digestive tube.

Initial Stages of Digestion

Mastication (Chewing)

Mastication is a mechanical process that breaks food into pieces. This is done by... Continue reading "Human Digestive System: Structure and Initial Processes" »

Genetic Variations

All individuals within a population possess unique characteristics that distinguish them from one another. These individual differences are called variations and result from an individual's genetic makeup and environmental influences.

Types of Variations:

• Genotype: These are inherited differences passed from parents to offspring and are contained within an individual's genes.
• Phenotypic and Environmental: These variations result from the interaction of genes with the environment. In most cases, the phenotype does not fully express the genotype.

Gene Pool

Each individual in a population carries a unique combination of genes. The gene pool represents the sum of all genes within a population.

Populations evolve through changes in their... Continue reading "Understanding Genetic Variations, Gene Pools, and Stem Cells" »

Vital Functions of Living Beings

Vital functions refer to the specific actions that support life. There are three main functions:

1. Nutrition: Living beings obtain the matter and energy necessary to sustain life through this function.
2. Interaction: Living beings relate to their surrounding environment through this function.
3. Reproduction: Individual living beings are produced; this ensures the perpetuation of the species.

Biomolecules: The Building Blocks of Life

Biomolecules are the fundamental components of living organisms. They are mainly composed of carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus.

Organic Biomolecules

Organic molecules are exclusive to living beings. There are four main types:

1. Carbohydrates (Saccharides)

   These are the most

Pulmonary Ventilation Explained

Pulmonary ventilation refers to the processes that facilitate airflow between the atmosphere and the alveoli through inspiration and expiration.

Physiology of Breathing

Breathing is performed by muscles that change the volume of the chest cavity, creating pressures that move air in and out of the lungs. During normal breathing, at rest, inspiration is active, while expiration is passive.

The diaphragm, the main inspiratory muscle, causes the movement of the rib cage down and out, changing the size of the chest cavity horizontally. Other muscles involved in ventilation include the intercostal muscles, abdominal muscles, and accessory muscles.

Respiratory System Anatomy

Respiratory organs are responsible for transporting... Continue reading "Breathing Basics: Anatomy, Physiology, and Common Ailments" »