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

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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.
Order of Events: Nerve impulse → Action potential in motor neuron → Release of neurotransmitter (acetylcholine) → Depolarization of muscle cell membrane → Calcium release from sarcoplasmic reticulum → Myosin binds actin → Contraction.
Electrical Impulses: Action potentials trigger calcium release, which enables contraction.
Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

Example: During exercise, muscle contractions increase body temperature due to ATP hydrolysis.

Muscle Groups and Functions

Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and gluteals.
Muscles Sectioning Body Cavities: Diaphragm separates thoracic and abdominal cavities.

Types of Muscle Contractions

Isotonic Contraction: Muscle changes length (movement occurs), e.g., lifting a weight.
Isometric Contraction: Muscle length remains the same (no movement), e.g., holding a weight steady.

Sarcomere Substructures

Z-line: Defines the boundaries of a sarcomere.
A-band: Contains the length of the myosin filaments.
I-band: Contains only actin filaments.
H-zone: Area with only myosin, disappears during contraction.

Function: The sarcomere is responsible for muscle contraction and force generation.

Summary Table: Muscle Contraction Types

Type	Muscle Length	Movement
Isotonic	Changes	Yes
Isometric	Constant	No

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.
Respiratory Diseases: Includes asthma, bronchitis, pneumonia, and emphysema.

Structures of the Respiratory System

Upper Respiratory Tract: Includes nose, nasal cavity, pharynx, and larynx. Functions: filter, warm, and humidify air.
Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, and lungs. Functions: conduct air, gas 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:
Intercostal Muscles: Assist in expanding and contracting the rib cage during breathing.

Example: During inspiration, the diaphragm contracts and moves downward, increasing lung volume.

Blood Flow Through the Heart

Oxygen-rich blood enters the left atrium → left ventricle → aorta → systemic circulation.

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 via peristalsis.
Stomach: Secretes acid and enzymes for protein digestion.
Small Intestine: Main site for nutrient absorption.
Large Intestine: Absorbs water, forms feces.

Accessory Organs

Liver: Produces bile for fat digestion.
Pancreas: Secretes digestive enzymes and hormones.
Gallbladder: Stores and releases bile.

Enzymes and Digestion

Function: Enzymes catalyze breakdown of macromolecules.
Production Sites: Salivary glands, stomach, pancreas, small intestine.

Surface Area in Digestion

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

Metabolic Rates

Basal Metabolic Rate (BMR): Energy used at rest.
Standard Metabolic Rate (SMR): Energy used under specific conditions.

"My Plate" Purpose

Guides healthy eating by balancing food groups.

Peristalsis

Wave-like muscle contractions move food through the digestive tract.

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: DNA molecule with associated proteins; humans have 23 pairs.
Genome: Complete set of genetic material.
Homologous Chromosomes: Pairs with same genes, may have different alleles.
Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Genotype and Phenotype

Genotype: Genetic makeup (e.g., AA, Aa, aa).
Phenotype: Observable traits (e.g., eye color).

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 (AA or aa).
Heterozygous: Two different alleles (Aa).

Mendelian Laws

Law of Segregation: Each parent passes one allele to offspring.
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 if homozygous.
Recessive Disorders: Expressed only when both alleles are recessive; can persist in populations.

Non-Mendelian Inheritance

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).
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 during meiosis, leading to abnormal chromosome numbers in gametes.

Summary Table: Types of Inheritance

Type	Expression	Example
Dominant	One allele needed	Huntington's disease
Recessive	Both alleles needed	Cystic fibrosis
Incomplete Dominance	Intermediate phenotype	Snapdragon flower color
Codominance	Both alleles expressed	AB blood type
Polygenic	Multiple genes	Height, skin color

Example: A Punnett Square can predict the probability of offspring inheriting a particular trait.

Additional info: The notes have been expanded to include definitions, examples, and tables for clarity and completeness.