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: 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.

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

• Muscle Unit Structures: Muscle fiber, myofibril, sarcolemma, sarcoplasmic reticulum.

Example: During contraction, calcium ions released from the sarcoplasmic reticulum enable myosin-actin interaction.

Action Potential 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.

• Motor Neuron: Releases neurotransmitter (acetylcholine) at the neuromuscular junction, causing depolarization of the muscle cell membrane.

• Order of Events: Nerve impulse → Acetylcholine release → Muscle cell depolarization → Calcium release → Sliding filament contraction.

Example: Electrical impulses cause calcium release, which binds to troponin, shifting tropomyosin and exposing actin binding sites.

Types of Muscle Contractions

Muscle contractions can be classified based on movement and tension.

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

• Isometric Contraction: Muscle tension increases, but length does not change (no movement).

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

Muscle Groups and Functions

Major muscle groups include the biceps, triceps, quadriceps, hamstrings, and muscles that section body cavities (e.g., diaphragm).

• Body Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

• Muscles Sectioning Cavities: The diaphragm separates 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, then distributed to the body.

• Importance: Cellular respiration requires oxygen; removal of CO2 prevents acidosis.

Structures of the Respiratory System

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

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

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

Example: The alveoli are the site of gas exchange due to their thin walls and large surface area.

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, drawing air in.

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

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

Example: During inspiration, the diaphragm moves downward, creating negative pressure in the lungs.

Respiratory Diseases and Disorders

Common disorders include asthma, bronchitis, pneumonia, and emphysema, affecting airflow and gas exchange.

Blood Flow Through the Heart

Oxygen-rich blood flows from the lungs to the left atrium, left ventricle, then out to the body.

• Order: Pulmonary veins → 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, anus.

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

Example: The pancreas produces digestive enzymes and bicarbonate to neutralize stomach acid.

Enzymes and Digestion

Enzymes catalyze the breakdown of macromolecules.

• Function: Speed up chemical reactions; specific for carbohydrates, proteins, fats.

• Production Sites: Salivary glands (amylase), stomach (pepsin), pancreas (lipase, proteases).

Surface Area and Digestion

Large surface area in the small intestine (villi, microvilli) increases nutrient absorption.

Metabolic Rates

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

• Standard Metabolic Rate (SMR): Energy used under specific conditions (e.g., fasting).

"My Plate" Purpose

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

Digestion Mechanics

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

• Molecule Digestion: Carbohydrates, proteins, and fats are digested in specific regions by enzymes.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

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

• Gene: A segment of DNA coding for a specific protein.

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

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

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pairs with the 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.

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

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Dominant and Recessive Disorders

• Dominant Disorders: Expressed with one dominant allele; can be lethal.

• Recessive Disorders: Expressed only with two recessive alleles; can persist in populations.

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 and Meiosis

• Linked Genes: Genes located close together on a chromosome; inherited together.

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

Sex-linked Genes and Nondisjunction

• Sex-linked Genes: Located on sex chromosomes; often affect males more.

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

Sample Table: Types of Genetic Inheritance

Type	Description	Example
Dominant	Trait appears with one dominant allele	Huntington's disease
Recessive	Trait appears only with two recessive alleles	Cystic fibrosis
Incomplete Dominance	Intermediate phenotype in heterozygotes	Red and white flowers produce pink
Codominance	Both alleles fully expressed	AB blood type
Polygenic	Multiple genes affect trait	Skin color

Sample Equation: Mendelian Probability

Probability of offspring genotype in a monohybrid cross:

$P = \frac{n!}{x!y!} \cdot p^x \cdot q^y$

Where n = total offspring, x = number with genotype p, y = number with genotype q.

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