Animal Structure, Nutrition, and Immune System: Study Notes

Animal Structure and Function

Tissue Types in Animals

Animal bodies are composed of four primary tissue types, each with specialized structures and functions.

• Epithelial Tissue: Covers body surfaces and lines internal organs and cavities. Forms protective barriers and is involved in absorption, secretion, and sensation.

  • Simple epithelium: Single layer of cells (e.g., lining of intestines).

  • Stratified epithelium: Multiple layers (e.g., skin epidermis).

  • Examples: Skin, lining of mouth, lining of digestive tract.

• Connective Tissue: Supports, binds, and protects other tissues and organs. Contains cells scattered in an extracellular matrix.

  • Loose connective tissue: Binds epithelia to underlying tissues.

  • Fibrous connective tissue: Forms tendons and ligaments.

  • Adipose tissue: Stores fat.

  • Cartilage and bone: Provide structural support (e.g., skeleton, fingernails).

  • Blood: Transports substances.

  • Examples: Fingernails (keratinized tissue), tendons, fat tissue.

• Muscle Tissue: Responsible for movement. Contains contractile proteins (actin and myosin).

  • Skeletal muscle: Voluntary movement (e.g., biceps).

  • Cardiac muscle: Found only in the heart.

  • Smooth muscle: Involuntary movement in organs (e.g., intestines, blood vessels).

  • Examples: Heart, muscles attached to bones, muscles in digestive tract.

• Nervous Tissue: Senses stimuli and transmits signals throughout the body.

  • Neurons: Conduct electrical impulses.

  • Glial cells: Support and nourish neurons.

  • Examples: Brain, spinal cord, nerves.

Organs and Organ Systems

An organ is a structure composed of two or more tissue types working together to perform specific functions. An organ system is a group of organs that work together to carry out major body functions.

Major Organ Systems and Their Primary Functions

Organ System	Primary Function
Skeletal System	Provides support, protects organs, enables movement, produces blood cells
Respiratory System	Gas exchange (oxygen in, carbon dioxide out)
Digestive System	Breaks down food, absorbs nutrients, eliminates waste
Muscular System	Movement, posture, heat production
Urinary System	Removes waste from blood, regulates water and salt balance
Integumentary System	Protects body, regulates temperature, sensory reception (includes skin)
Immune System	Defends against pathogens and disease
Circulatory System	Transports nutrients, gases, wastes, and hormones
Reproductive System	Produces gametes, enables reproduction

Homeostasis and Negative Feedback

Homeostasis is the maintenance of a stable internal environment despite external changes. Negative feedback control is a regulatory mechanism in which a change in a variable triggers responses that counteract the initial change, maintaining balance.

• Example: Regulation of body temperature—if body temperature rises, mechanisms such as sweating are activated to cool the body.

Animal Structures Are Not Perfect

This statement refers to the fact that animal structures are shaped by evolutionary history and constraints, not by design for perfection. Adaptations are often compromises, and structures may have limitations or inefficiencies.

Layers of the Skin

• Epidermis: Outermost layer, provides protection.

• Dermis: Middle layer, contains connective tissue, blood vessels, nerves.

• Hypodermis (subcutaneous layer): Deepest layer, stores fat and anchors skin to underlying tissues.

Nutrition and Digestion

The Alimentary Canal

The alimentary canal is the digestive tract, a continuous tube from mouth to anus where food is processed. About 7 liters of water are secreted into the canal daily, with 90% reabsorbed.

Digestive Adaptations and Feeding Types

• Gizzard: A muscular organ (in some animals like worms and birds) that grinds food, often with the aid of ingested stones.

• Feeding Types:

  • Suspension feeders: Filter small particles from water (e.g., clams, baleen whales).

  • Bulk feeders: Eat large pieces of food (e.g., humans, lions).

  • Substrate feeders: Live in or on their food source (e.g., caterpillars).

  • Fluid feeders: Suck nutrient-rich fluids (e.g., mosquitoes, hummingbirds).

Order of the Digestive System in Mammals

1. Mouth

2. Pharynx

3. Esophagus

4. Stomach

5. Small intestine

6. Large intestine

7. Rectum

8. Anus

Functions of Digestive Structures

• Tongue: Shapes food into a bolus and pushes it to the pharynx.

• Epiglottis: Flap that covers the trachea during swallowing to prevent food from entering the airway.

• Peristalsis: Rhythmic contractions of smooth muscle that move food through the digestive tract.

• Sphincters: Muscular rings that regulate passage of food between digestive organs (e.g., between stomach and small intestine).

Enzymes and Digestion

• Amylase: Enzyme secreted by salivary glands and pancreas; breaks down starch into sugars.

• Chymotrypsin: Enzyme produced by the pancreas; digests proteins in the small intestine.

• Mucus-producing cells: Line the stomach, protect it from acidic gastric juices.

Key Digestive Concepts

• Digestion: The process of breaking down food into absorbable molecules.

• Chyme: Semi-liquid mixture of partially digested food and digestive juices in the stomach.

• Heartburn: Caused by stomach acid entering the esophagus (acid reflux).

• Bacteria: Some bacteria in the digestive tract aid digestion; pathogenic bacteria can cause illness.

• Most nutrient absorption: Occurs in the small intestine.

• Microvilli: Tiny projections on the surface of small intestine cells that increase surface area for absorption.

Accessory Organs and Their Functions

• Pancreas: Secretes digestive enzymes and bicarbonate to neutralize stomach acid.

• Bile salts: Emulsify fats for digestion; produced by the liver, stored in the gallbladder.

• Fat digestion: Begins in the small intestine with the help of bile and pancreatic enzymes.

• Liver: Produces bile, processes nutrients, detoxifies substances.

• Water reabsorption: Occurs mainly in the large intestine.

Evolutionary Adaptations

• Lions: Can survive periods of famine due to large fat reserves and metabolic adaptations.

• Herbivores: Have specialized digestive tracts (e.g., longer intestines, symbiotic microbes) to digest cellulose.

Nutrition and Metabolism

• Metabolic rate: The rate at which the body uses energy.

• Amino acids: Building blocks of proteins; essential amino acids must be obtained from the diet.

• Weight loss: Most effective through caloric restriction and increased physical activity.

• BMI (Body Mass Index): A measure of body fat based on height and weight.

  • Formula: $BMI = \frac{\text{weight (kg)}}{\text{height (m)}^2}$

• Types of human teeth: Incisors (cutting), canines (tearing), premolars and molars (grinding).

The Immune System

Innate Defense Barriers

• Physical barriers: Skin, mucous membranes.

• Chemical barriers: Enzymes in saliva, stomach acid.

• Cellular defenses: Phagocytic cells, natural killer cells.

Immune Responses

• Primary cell-mediated immune response: First exposure to an antigen; T-cells are activated to destroy infected cells.

• Secondary immune response: Faster and stronger response upon subsequent exposure to the same antigen due to memory cells.

• Passive immunity: Temporary immunity gained by receiving antibodies from another source (e.g., maternal antibodies in breast milk).

• Humoral immunity: Involves B-cells producing antibodies that circulate in body fluids.

Inflammatory Response and Interferons

• Inflammatory response: Localized response to injury or infection; increases blood flow and recruits immune cells.

• Interferons: Proteins released by virus-infected cells to help protect neighboring cells from infection.

Allergic Reactions

• During an allergic reaction, cells release histamine, causing inflammation and other symptoms.

Lymphatic System Functions

• Returns excess fluid to the bloodstream.

• Provides sites for immune cell activation and maturation.

Key Immune Terms

• Antigen: Any substance that elicits an immune response (e.g., proteins on pathogens).

• Antibody: Protein produced by B-cells that binds to specific antigens; belongs to the class of proteins called immunoglobulins.

• Antigen-binding site: Region of an antibody that specifically recognizes and binds to an antigen.

• Macrophages: Large phagocytic cells that engulf pathogens and debris.

• T-cells: Lymphocytes that mediate cellular immunity; destroy infected cells and coordinate immune responses.

• Natural killer cells: Destroy virus-infected and cancerous cells without prior activation.

• Autoimmune diseases: Disorders in which the immune system attacks the body's own tissues (e.g., type 1 diabetes, rheumatoid arthritis).

Vaccines and Herd Immunity

• Most vaccines use a harmless variant or component of a pathogen to stimulate immunity without causing disease.

• Example: Polio, measles, and influenza vaccines.

• Human disease without a vaccine: HIV/AIDS currently has no effective vaccine.

• Herd immunity: When a high percentage of the population is vaccinated, the spread of disease is limited, protecting unvaccinated individuals. Typically, 85-95% vaccination coverage is needed for herd immunity.