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 called muscle fibers that contract to produce movement. The sliding filament mechanism is central to muscle contraction.

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

• Actin Filaments: Thin filaments that interact with myosin during contraction.

• Myosin Filaments: Thick filaments with heads that bind to actin, pulling them to shorten the sarcomere.

• Sliding Mechanism: Myosin heads attach to actin, forming cross-bridges, and pull actin filaments inward, causing contraction.

Example: During muscle contraction, ATP is hydrolyzed to provide energy for myosin movement.

Action Potential and Muscle Contraction

Muscle contraction is initiated by an action potential in a motor neuron, which triggers electrical impulses in muscle fibers.

• Action Potential: A rapid change in membrane potential that travels along neurons and muscle cells.

• Order of Events:

  1. Motor neuron releases acetylcholine at the neuromuscular junction.

  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.

Example: Electrical impulses cause calcium release, which is essential for contraction.

Types of Muscle Contractions

Muscle contractions can be classified as isotonic or isometric.

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant. Produces movement.

• Isometric Contraction: Muscle length remains unchanged while tension increases. No movement produced.

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

Muscle Groups and Functions

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

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

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

Example: Shivering increases heat production via rapid muscle contractions.

Human Respiratory System

Significance of Breathing

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

• Oxygen: Required for cellular respiration and energy production.

• Carbon Dioxide: Waste product that must be expelled to maintain pH balance.

Example: Without breathing, cells cannot produce ATP efficiently.

Respiratory System Structures

• Upper Respiratory System: Includes nose, nasal cavity, pharynx, and larynx. Functions in filtering, warming, and humidifying air.

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

Example: The alveoli are the primary 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: $\Delta P = P_{atm} - P_{lung}$

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

Example: Forced expiration uses abdominal muscles.

Blood Flow and Gas Exchange

• Oxygen-rich Blood: Flows from lungs to left atrium, then left ventricle, then systemic circulation.

• Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → body tissues.

Example: Oxygen-poor blood returns via vena cava to right atrium.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

• Significance: Affect gas exchange and overall health.

Example: Asthma causes constriction of airways, reducing airflow.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food into nutrients for absorption and energy.

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes for protein digestion.

• Small Intestine: Main site for nutrient absorption.

• Large Intestine: Absorbs water and forms feces.

Example: The small intestine has villi to increase surface area for absorption.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and releases bile.

• Pancreas: Produces digestive enzymes and hormones.

Example: Pancreatic enzymes digest carbohydrates, proteins, and fats.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion.

• Production Sites: Salivary glands, stomach, pancreas, small intestine.

Example: Amylase breaks down starch in the mouth.

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in the small intestine maximize nutrient absorption.

Example: Increased surface area allows for efficient uptake of nutrients.

Metabolic Rates

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

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

Example: BMR is measured after fasting and rest.

"My Plate" Purpose

• My Plate: A visual guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Example: My Plate helps individuals plan healthy meals.

Digestion Processes

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

Example: Peristalsis propels food from esophagus to stomach.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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

• Gene: A segment of DNA encoding a functional product.

• Chromosome: DNA molecule with associated proteins, carrying genetic information.

• Genome: The complete set of genes in an organism.

Example: Humans have 23 pairs of chromosomes.

Homologous Chromosomes and Karyotype

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

• Karyotype: The visual representation of chromosome number and structure.

Example: A normal human karyotype shows 46 chromosomes.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism.

• Phenotype: The observable traits resulting from genotype and environment.

Example: Brown eyes (phenotype) may result from a dominant allele (genotype).

Punnett Square and Alleles

• Punnett Square: A diagram used to predict genetic crosses.

• Alleles: Different forms of a gene; can be dominant or recessive.

• Homozygous: Two identical alleles for a trait.

• Heterozygous: Two different alleles for a trait.

Example: $AA$ (homozygous dominant), $Aa$ (heterozygous), $aa$ (homozygous recessive).

Mendelian Laws

• Law of Segregation: Each parent passes one allele for each gene to offspring.

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

Example: Traits for eye color and hair color are inherited separately.

Dominant and Recessive Alleles

• Dominant Allele: Expressed when present; can mask recessive allele.

• Recessive Allele: Expressed only when homozygous.

• Lethal Dominant Disorders: May cause early death, reducing prevalence.

• Recessive Disorders: Can persist if carriers are unaffected.

Example: Huntington's disease is a dominant disorder; cystic fibrosis is recessive.

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygotes show intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can modify phenotypic expression.

Example: Skin color is polygenic; blood type shows codominance.

Linked Genes and Meiosis

• Linked Genes: Genes located close together on the same chromosome, inherited together.

• New Allele Combinations: Crossing over during meiosis creates genetic diversity.

Example: Genes for hair and eye color may be linked.

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Located on sex chromosomes, often X-linked.

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

Example: Color blindness is X-linked; Down syndrome results from nondisjunction.

Term	Definition	Example
Gene	Segment of DNA coding for a trait	Eye color gene
Allele	Variant form of a gene	Brown or blue eye allele
Genotype	Genetic makeup	AA, Aa, aa
Phenotype	Observable trait	Brown eyes
Homozygous	Same alleles	AA or aa
Heterozygous	Different alleles	Aa
Dominant	Expressed allele	A
Recessive	Masked allele	a
Codominance	Both alleles expressed	AB blood type
Incomplete Dominance	Intermediate phenotype	Pink flowers
Polygenic	Multiple genes affect trait	Height
Sex-linked	On sex chromosome	Color blindness
Nondisjunction	Chromosome separation error	Down syndrome

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