Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The muscular system enables movement and generates heat in the human body. Muscle contraction is based on the sliding filament mechanism within muscle cells.

• Sarcomere: The basic functional unit of muscle fibers, composed of actin (thin) and myosin (thick) filaments.

• Actin and Myosin Filaments: Actin provides the track for myosin heads to attach and pull, causing contraction. Myosin uses ATP to move along actin.

• Sliding Filament Theory: Myosin heads bind to actin, forming cross-bridges, and pull the actin filaments inward, shortening the sarcomere.

• Function of Sarcomere: Responsible for muscle contraction and force generation.

• Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and others.

• Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities.

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential in motor neurons triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases neurotransmitter (acetylcholine).

  2. Muscle cell membrane depolarizes, generating an action potential.

  3. Calcium ions are released from the sarcoplasmic reticulum.

  4. Calcium binds to troponin, exposing binding sites on actin.

  5. Myosin binds to actin, leading to contraction.

• Heat Generation: Most body heat is generated by muscle activity.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs).

• Isometric Contraction: Muscle length remains the same (no movement, but tension increases).

Table: Comparison of Isotonic and Isometric Contractions

Type	Muscle Length	Movement	Example
Isotonic	Changes	Yes	Bicep curl
Isometric	Unchanged	No	Wall sit

Additional info:

ATP is required for both contraction and relaxation of muscle fibers.

Human Respiratory System

Significance of Breathing

Breathing supplies oxygen for cellular respiration and removes carbon dioxide, a waste product.

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart and then to the body.

• Respiratory Diseases: Includes asthma, bronchitis, pneumonia, and emphysema.

Structures of the Respiratory System

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions: filters, warms, and moistens air.

• Lower Respiratory System: Includes trachea, bronchi, lungs, and alveoli. Functions: gas exchange and air conduction.

Mechanics of Breathing

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, drawing air in.

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air is expelled.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

• Intercostal Muscles: Assist in expanding and contracting the rib cage during breathing.

Table: Structures and Functions of the Respiratory System

Structure	Function
Nose/Nasal Cavity	Filters, warms, moistens air
Pharynx	Passage for air and food
Larynx	Voice production, air passage
Trachea	Conducts air to lungs
Bronchi	Branches air into lungs
Alveoli	Gas exchange

Additional info:

Gas exchange occurs by diffusion in alveoli.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Major Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

• Accessory Organs: Liver, pancreas, gallbladder. Functions: produce enzymes, bile, and aid digestion.

• Enzymes: Catalyze breakdown of macromolecules; produced in salivary glands, stomach, pancreas, small intestine.

• Large Surface Area: Villi and microvilli in small intestine increase absorption efficiency.

Metabolic Rates

• Basal Metabolic Rate (BMR): Energy used at rest.

• Standard Metabolic Rate (SMR): Energy used under specific conditions.

Table: Digestive System Structures and Functions

Structure	Function
Mouth	Mechanical and chemical digestion
Stomach	Protein digestion, food storage
Small Intestine	Nutrient absorption
Large Intestine	Water absorption, waste formation
Liver	Bile production
Pancreas	Enzyme production

Digestion Process

• Peristalsis: Wave-like muscle contractions move food through the digestive tract.

• "My Plate": Dietary guideline for balanced nutrition.

Additional info:

Enzymes such as amylase, pepsin, and lipase are essential for digestion of carbohydrates, proteins, and fats.

Human Genetics and Inheritance

Basic Concepts

Genetics is the scientific study of heredity and variation in organisms.

• Gene: Segment of DNA coding for a trait.

• Chromosome: DNA molecule with associated proteins; humans have 23 pairs.

• Genome: Complete set of genes in an organism.

• Homologous Chromosomes: Chromosome pairs with same genes but possibly different alleles.

• Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Genotype and Phenotype

• Genotype: Genetic makeup (allele combination).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram to predict genetic crosses.

• Dominant Allele: Expressed trait when present.

• Recessive Allele: Expressed only when homozygous.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Table: Allele Expression

Genotype	Phenotype
AA	Dominant trait
Aa	Dominant trait
aa	Recessive trait

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently.

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can affect phenotypic expression.

• Linked Genes: Genes located close together on a chromosome tend to be inherited together.

• Sex-linked Genes: Genes located on sex chromosomes (e.g., X-linked traits).

Meiosis and Genetic Variation

• New Allele Combinations: Crossing over and independent assortment during meiosis create genetic diversity.

• Nondisjunction: Failure of chromosomes to separate properly, leading to abnormal chromosome numbers in gametes.

Additional info:

Some dominant allele disorders are lethal because they affect essential functions, while recessive disorders persist due to carriers.