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 Filaments: Actin provides the track for myosin heads to attach and pull, causing contraction.

• Sliding Filament Theory: Myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Function: The sarcomere's contraction generates force and movement in muscle tissue.

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

Muscle Contraction Mechanism

Muscle contraction is initiated by electrical impulses and involves a series of events.

• Action Potential: A nerve impulse travels down a motor neuron, triggering the release of neurotransmitters.

• Electrical Impulse: Causes the release of calcium ions from the sarcoplasmic reticulum.

• Order of Events:

  1. Nerve impulse arrives at neuromuscular junction.

  2. Acetylcholine is released, depolarizing the muscle cell membrane.

  3. Calcium ions are released, enabling actin-myosin interaction.

  4. Muscle contracts.

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

Types of Muscle Contractions

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

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

• Function: Isotonic contractions produce movement; isometric contractions stabilize joints.

Muscles and Body Cavities

• Intercostal Muscles: Located between ribs, important for breathing.

• Diaphragm: Separates thoracic and abdominal cavities; essential for respiration.

Example

• During running, isotonic contractions of leg muscles propel the body forward, while isometric contractions stabilize the torso.

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 circulated from the lungs to the heart and then to the body.

• Importance: Cellular respiration requires oxygen to produce energy.

Structures of the Respiratory System

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

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

Mechanics of Breathing

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

• 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.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, bronchitis, pneumonia, emphysema.

• Impact: Affect airflow, gas exchange, and overall health.

Blood Flow Through the Heart

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

Example

• During exercise, breathing rate increases to supply more oxygen and remove excess carbon dioxide.

Human Digestive System

Major Structures and Functions

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

• Main Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum.

• Accessory Organs: Liver, pancreas, gallbladder. Functions: produce enzymes, bile, and aid digestion.

Enzymes and Digestion

• Function: Enzymes catalyze the breakdown of macromolecules.

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

Surface Area in Digestion

• Importance: Increased surface area (villi, microvilli) enhances nutrient absorption.

Metabolic Rates

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

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

• Equation: $\text{BMR} = \text{Energy expenditure at rest}$

"My Plate" Purpose

• Purpose: Guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Digestion Process and Peristalsis

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

• Digestion: Chemical and mechanical breakdown of food into absorbable molecules.

Example

• After eating, peristalsis moves food from the esophagus to the stomach, where enzymes begin digestion.

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 containing DNA; humans have 23 pairs.

• Genome: Complete set of genetic material in an organism.

Homologous Chromosomes and Karyotype

• Homologous Chromosomes: Pairs with similar genes, one from each parent.

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

Genotype and Phenotype

• Genotype: Genetic makeup (alleles).

• Phenotype: Observable traits.

Punnett Square and Alleles

• Punnett Square: Diagram predicting genetic outcomes.

• Dominant Allele: Expressed trait if present.

• Recessive Allele: Expressed only if both alleles are recessive.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Laws of Genetics

• Law of Segregation: Alleles separate during gamete formation.

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

Inheritance Patterns

• 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; affect traits like color blindness.

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

Example

• Using a Punnett Square, the probability of inheriting a recessive disorder can be calculated based on parental genotypes.

Term	Definition	Example
Genotype	Genetic makeup of an organism	AA, Aa, aa
Phenotype	Observable traits	Brown eyes, blue eyes
Dominant Allele	Expressed if present	A
Recessive Allele	Expressed only if homozygous	a
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Incomplete Dominance	Intermediate phenotype	Red + White = Pink
Codominance	Both alleles expressed	AB blood type