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

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system relies on specialized cells and structures to produce movement. 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 Filaments: Actin provides the track for myosin heads to attach and pull, causing contraction.

• Sliding Filament Theory: Myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Function: Sarcomeres enable muscles to contract and generate force.

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

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

Example: During bicep contraction, sarcomeres shorten as myosin pulls actin filaments inward.

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:

  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 enables myosin-actin interaction, leading to contraction.

• Heat Generation: Most body heat is produced by muscle activity (thermogenesis).

Example: Shivering increases muscle activity to generate heat.

Types of Muscle Contractions

Muscle contractions can be classified based on movement and tension.

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

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

Example: Lifting a weight is isotonic; holding a weight steady is isometric.

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen and removing carbon dioxide.

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide: Waste product expelled during exhalation.

Example: Without breathing, cells cannot produce ATP efficiently.

Respiratory System Structures

The respiratory system is divided into upper and lower regions, each with specific functions.

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.

• Lower Respiratory System: Includes trachea, bronchi, lungs. Functions: conduct air, gas exchange.

Example: The nasal cavity traps dust and pathogens.

Mechanics of Breathing

Breathing involves changes in lung pressure and muscle activity.

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

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

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

Example: Deep breathing uses both diaphragm and intercostal muscles.

Blood Flow and Gas Exchange

Oxygen-rich blood flows from the lungs to the heart, then to the body.

• Pathway: Pulmonary veins → left atrium → left ventricle → aorta → body tissues.

Example: Oxygenated blood is distributed to muscles during exercise.

Respiratory Diseases and Disorders

Common respiratory diseases include asthma, bronchitis, pneumonia, and emphysema.

• Asthma: Inflammation and narrowing of airways.

• Emphysema: Damage to alveoli, reducing gas exchange.

Example: Asthma attacks can restrict airflow and cause difficulty breathing.

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.

• Function: Each organ contributes to digestion and absorption.

Example: The pancreas produces digestive enzymes.

Enzymes and Digestion

Enzymes catalyze the breakdown of food molecules.

• Produced by: Salivary glands, stomach, pancreas, small intestine.

• Function: Speed up chemical reactions, specific to substrates (e.g., amylase for starch).

Example: Pepsin digests proteins in the stomach.

Surface Area and Digestion

Large surface area in the small intestine enhances nutrient absorption.

• Villi and Microvilli: Increase surface area for efficient absorption.

Example: Microvilli allow rapid uptake of glucose.

Metabolic Rates

Metabolic rates measure energy expenditure.

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

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

Example: BMR is higher in active individuals.

"My Plate" and Nutrition

"My Plate" is a guide for balanced nutrition, emphasizing proper proportions of food groups.

• Purpose: Promote healthy eating habits.

Example: Half the plate should be fruits and vegetables.

Peristalsis

Peristalsis is the wave-like muscle contraction that moves food through the digestive tract.

• Function: Propels food from esophagus to stomach and intestines.

Example: Swallowing triggers peristalsis in the esophagus.

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: Structure carrying genes; humans have 23 pairs.

• Genome: Complete set of genetic material.

• Homologous Chromosomes: Pair of chromosomes with same genes, one from each parent.

Example: Eye color gene located on chromosome 15.

Karyotype and Chromosome Number

A karyotype is a visual representation of chromosomes, used to detect abnormalities.

• Function: Identifies chromosome number and structure.

Example: Down syndrome is detected by karyotyping.

Genotype and Phenotype

Genotype refers to genetic makeup; phenotype is the observable trait.

• Genotype: Combination of alleles (e.g., AA, Aa, aa).

• Phenotype: Physical expression (e.g., brown eyes).

Example: Genotype Aa produces dominant phenotype.

Punnett Square and Alleles

Punnett Squares predict genetic outcomes.

• Dominant Allele: Expressed when present (A).

• Recessive Allele: Expressed only when homozygous (a).

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

Example: Crossing Aa x Aa yields 3:1 dominant:recessive ratio.

Punnett Square Table

	A	a
A	AA	Aa
a	Aa	aa

Mendelian Laws

Mendel's laws explain inheritance patterns.

• Law of Segregation: Alleles separate during gamete formation.

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

Example: Traits for eye color and hair color inherited independently.

Dominant and Recessive Disorders

Some genetic disorders are caused by dominant or recessive alleles.

• Dominant Disorders: Lethal if expressed (e.g., Huntington's disease).

• Recessive Disorders: Can persist if carriers are asymptomatic (e.g., cystic fibrosis).

Example: Sickle cell anemia is recessive.

Non-Mendelian Inheritance

Some traits do not follow simple Mendelian rules.

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed (e.g., blood type AB).

• Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).

Example: Pink flowers from red and white parents (incomplete dominance).

Environmental Impact and Linked Genes

Environment and gene linkage affect phenotypic expression.

• Environmental Impact: Nutrition, temperature, and other factors can modify traits.

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

Example: Sun exposure affects skin color.

Meiosis and New Allele Combinations

Meiosis creates genetic diversity through recombination.

• Crossing Over: Exchange of genetic material between homologous chromosomes.

Example: Siblings have different combinations of alleles.

Sex-Linked Genes and Nondisjunction

Sex-linked genes are found on sex chromosomes; nondisjunction affects chromosome number.

• Sex-Linked Genes: Traits linked to X or Y chromosomes (e.g., color blindness).

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers.

Example: Turner syndrome results from nondisjunction.

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