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 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, forming cross-bridges and pulling actin filaments inward.

• Function of Sarcomere: To shorten during contraction, generating force.

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

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

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical signals 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 actin-myosin interaction.

  5. Muscle contracts.

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

Types of Muscle Contractions

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

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

Summary Table: Muscle Contraction Types

Type	Muscle Length	Movement
Isotonic	Changes	Yes
Isometric	Constant	No

Key Molecules and Structures

• Calcium Ions: Released from sarcoplasmic reticulum, trigger contraction.

• Acetylcholine: Neurotransmitter released by motor neuron.

Equation:

$\text{ATP} + \text{Myosin} \rightarrow \text{Myosin-ATP} \rightarrow \text{Myosin-Actin Crossbridge}$

Human Respiratory System

Significance of Breathing

Breathing supplies oxygen for cellular respiration and removes carbon dioxide, a waste product.

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

• Respiratory Diseases: Include asthma, bronchitis, pneumonia, and emphysema.

Structures of the Respiratory System

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

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

Mechanics of Breathing

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

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air flows out.

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

Equation:

$\text{Pressure}_{\text{lungs}} \propto \frac{1}{\text{Volume}_{\text{thoracic}}}$

Blood Flow Through the Heart

• Oxygen-rich blood enters the left atrium, passes to the left ventricle, and is pumped to the body.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Mouth: Mechanical and chemical digestion begins.

• Esophagus: Transports food to stomach.

• Stomach: Secretes acid and enzymes, churns food.

• Small Intestine: Main site of nutrient absorption.

• Large Intestine: Absorbs water, forms feces.

• Accessory Organs: Liver (produces bile), pancreas (produces enzymes), gallbladder (stores bile).

Enzymes and Digestion

• Enzymes: Biological catalysts produced in salivary glands, stomach, pancreas, and small intestine.

• Function: Speed up breakdown of carbohydrates, proteins, fats.

Surface Area and Digestion

• Large Surface Area: Villi and microvilli in small intestine increase absorption efficiency

Metabolic Rates

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

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

Peristalsis

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

"My Plate"

• Purpose: Dietary guideline for balanced nutrition.

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: Pairs with same genes, may have different alleles.

• Karyotype: Visual display of chromosomes; used to detect abnormalities.

Genotype and Phenotype

• Genotype: Genetic makeup.

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram predicting genetic crosses.

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

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Law of Segregation and Independent Assortment

• Law of Segregation: Alleles separate during gamete formation.

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

Dominant and Recessive Disorders

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

• Recessive Disorders: Require two recessive alleles; can persist in populations.

Complex Patterns of 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: Genes located close together on a chromosome, inherited together.

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

Meiosis and Genetic Variation

• New Allele Combinations: Crossing over and independent assortment during meiosis.

• Nondisjunction: Failure of chromosomes to separate; leads to abnormal chromosome numbers in gametes.

Summary Table: Types of Inheritance

Type	Phenotype	Example
Dominant	Trait appears with one allele	Huntington's disease
Recessive	Trait appears with two alleles	Cystic fibrosis
Incomplete Dominance	Intermediate phenotype	Red and white flowers produce pink
Codominance	Both traits expressed	AB blood type
Polygenic	Multiple genes, continuous variation	Height, skin color

Equation:

$\text{Phenotype} = \text{Genotype} + \text{Environment}$

Punnett Square Example:

$\begin{array}{c|cc} & A & a \\ \hline A & AA & Aa \\ a & Aa & aa \end{array}$

Karyotype Example:

$\text{Human Karyotype: 46, XX (female) or 46, XY (male)}$