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 a muscle fiber, composed of actin (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin filaments and pull them inward, shortening the sarcomere.

• Actin and Myosin: Actin provides the track, while myosin uses ATP to generate force and movement.

• Substructures: Includes Z-lines, M-line, A-band, I-band, and H-zone, each with specific roles in contraction.

• Muscle Heat Generation: Most body heat is generated by muscle activity, especially through ATP hydrolysis during contraction.

Example: During exercise, muscle contractions increase heat production, helping maintain body temperature.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical signals called action potentials from motor neurons.

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

• 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.

• Electrical Impulses: Cause release of calcium ions, which are essential for contraction.

Example: The release of acetylcholine is the first step in voluntary muscle contraction.

Types of Muscle Contractions

• Isotonic Contraction: Muscle changes length (movement occurs), tension remains constant.

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

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

Major Muscle Groups and Functions

• Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, etc.

• Body Cavities: Muscles such as the diaphragm section the thoracic and abdominal cavities.

Human Respiratory System

Significance of Breathing

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

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

• Respiratory Diseases: Disorders such as asthma, bronchitis, and emphysema affect breathing efficiency.

Structures of the Respiratory System

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

• Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, and lungs. Functions in gas exchange.

Example: The cilia in the trachea help remove particles from inhaled air.

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: During inspiration, the diaphragm moves downward, increasing lung capacity.

Blood Flow Through the Heart

• Order of Flow: Oxygen-rich blood enters the left atrium, passes to the left ventricle, and is pumped to the body via the aorta.

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; produce enzymes and bile for digestion.

Enzymes and Digestion

• Enzymes: Biological catalysts that speed up digestion; produced in salivary glands, stomach, pancreas, and small intestine.

• Function: Break down carbohydrates, proteins, and fats into absorbable units.

Example: Amylase breaks down starch in the mouth.

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in the small intestine increase surface area for nutrient absorption.

Metabolic Rates

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

• Standard Metabolic Rate (SMR): The energy expended under standardized conditions.

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

"My Plate" Purpose

• My Plate: A guide for balanced nutrition, emphasizing proper proportions of food groups.

Digestion Mechanics

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

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; humans have 23 pairs.

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

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

• Karyotype: The visual representation of chromosomes in a cell.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism.

• Phenotype: The observable traits of an organism.

Punnett Square and Alleles

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

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

• Homozygous: Two identical alleles for a trait.

• Heterozygous: Two different alleles for a trait.

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.

Inheritance Patterns

• Dominant Allele Disorders: Can be lethal if expressed in homozygous form.

• Recessive Disorders: May persist due to carriers.

• 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.

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

• Sex-linked Genes: Genes located on sex chromosomes; often show different inheritance patterns in males and females.

Meiosis and Genetic Variation

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

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

Sample Table: Comparison of Inheritance Patterns

Pattern	Genotype	Phenotype	Example
Dominant	AA, Aa	Trait expressed	Huntington's disease
Recessive	aa	Trait expressed	Cystic fibrosis
Incomplete Dominance	Aa	Intermediate	Red and white flowers produce pink
Codominance	AB	Both traits expressed	AB blood type

Example: Sickle cell anemia is an example of codominance.

Additional info: Academic context and examples have been added to clarify and expand upon the review guide points.