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

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Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system relies on specialized cells and structures to produce movement and generate heat. The sliding filament mechanism is central to muscle contraction.

Sarcomere: The basic contractile unit of muscle, composed of actin (thin) and myosin (thick) filaments.
Actin and Myosin: Proteins that interact to produce contraction. Myosin heads bind to actin, pulling the filaments past each other.
Sliding Filament Theory: Muscle contraction occurs as myosin heads attach to actin and pull, shortening the sarcomere.
Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, and others.
Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities.

Example: During a bicep curl, the biceps brachii contracts, shortening the sarcomeres and pulling the forearm upward.

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

Action Potential: A rapid change in membrane potential that triggers muscle contraction.
Order of Events: Motor neuron releases neurotransmitter (acetylcholine), causing depolarization of muscle cell membrane, leading to calcium release and contraction.
Release of Molecules: Calcium ions are released from the sarcoplasmic reticulum, enabling actin-myosin interaction.

Example: Nerve impulse causes muscle contraction by releasing calcium, which allows myosin to bind to actin.

Types of Muscle Contractions

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

Example: Holding a weight steady (isometric); lifting a weight (isotonic).

Heat Generation

Muscular System: Most body heat is generated by muscle activity.

Human Respiratory System

Significance of Breathing

Breathing is essential for oxygen intake and carbon dioxide removal, supporting cellular respiration and energy production.

Oxygen Transport: Oxygen-rich blood is circulated by the heart to tissues.
Respiratory Diseases: Includes asthma, bronchitis, pneumonia, and others.

Structures of the Respiratory System

Upper Respiratory Tract: Includes nose, pharynx, larynx; filters, warms, and moistens air.
Lower Respiratory Tract: Includes trachea, bronchi, lungs; site of gas exchange.

Example: The trachea conducts air to the lungs, while alveoli are the site of oxygen and carbon dioxide exchange.

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

Blood Flow Through the Heart

Order: Oxygen-rich blood enters left atrium → left ventricle → aorta → body tissues.

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.
Accessory Organs: Liver, pancreas, gallbladder; produce enzymes and bile.
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.

Example: Pancreatic amylase digests carbohydrates in the small intestine.

Metabolic Rates

Basal Metabolic Rate (BMR): Energy used at rest.
Standard Metabolic Rate (SMR): Energy used under specific conditions.

Example: BMR is measured after fasting and rest; SMR may be measured during activity.

Digestion Process and Peristalsis

Peristalsis: Wave-like muscle contractions that move food through the digestive tract.
Digestion: Chemical and mechanical breakdown of food; molecules absorbed in small intestine.

"My Plate" Purpose

My Plate: Dietary guideline for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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 genetic material in an organism.
Homologous Chromosomes: Chromosome pairs with similar genes, one from each parent.
Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Genotype and Phenotype

Genotype: Genetic makeup (alleles present).
Phenotype: Observable traits.

Punnett Square and Alleles

Punnett Square: Diagram to predict genetic crosses.
Alleles: Variants of a gene; can be dominant or recessive.
Homozygous: Two identical alleles (e.g., AA or aa).
Heterozygous: Two different alleles (e.g., Aa).

Mendelian Laws

Law of Segregation: Alleles separate during gamete formation.
Law of Independent Assortment: Genes for different traits are inherited independently.

Dominance, Incomplete Dominance, Codominance

Dominant Allele: Expressed trait when present.
Recessive Allele: Expressed only when homozygous.
Incomplete Dominance: Heterozygote shows intermediate phenotype.
Codominance: Both alleles are fully expressed.

Example: Incomplete dominance: red and white flowers produce pink offspring. Codominance: AB blood type.

Polygenic Inheritance and Environmental Impact

Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).
Environmental Impact: Environment can affect phenotypic expression (e.g., nutrition, temperature).

Linked Genes, Meiosis, and Sex-linked Genes

Linked Genes: Genes located close together on a chromosome; inherited together.
New Allele Combinations: Crossing over during meiosis creates genetic diversity.
Sex-linked Genes: Genes on sex chromosomes; often X-linked.

Nondisjunction

Nondisjunction: Failure of chromosomes to separate during meiosis; leads to abnormal chromosome numbers in gametes (e.g., Down syndrome).

Table: Comparison of Dominant vs. Recessive Alleles

Type	Expression	Example
Dominant	Expressed in heterozygous and homozygous state	Widow's peak (W)
Recessive	Expressed only in homozygous state	Attached earlobe (e)

Table: Types of Genetic Inheritance

Type	Phenotype in Heterozygote	Example
Complete Dominance	Dominant trait only	Brown eyes
Incomplete Dominance	Intermediate trait	Pink flowers
Codominance	Both traits expressed	AB blood type

Additional info: Academic context and examples were added to clarify concepts and provide self-contained explanations for exam preparation.