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: Actin filaments provide sites 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: Sarcomeres shorten during contraction, generating force and movement.

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

Example: During bicep contraction, the sarcomeres in the muscle fibers shorten, pulling the forearm upward.

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential in the motor neuron triggers neurotransmitter release.

• Neuromuscular Junction: The site where the motor neuron communicates with the muscle fiber.

• Order of Events:

  1. Motor neuron releases acetylcholine.

  2. Muscle fiber membrane depolarizes.

  3. Calcium ions released from sarcoplasmic reticulum.

  4. Calcium enables actin-myosin interaction.

  5. Muscle contracts.

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

Example: Shivering increases muscle activity, producing heat.

Types of Muscle Contractions

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

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

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

Muscles and Body Cavities

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

• Intercostal Muscles: Located between ribs; assist in breathing.

Human Respiratory System

Significance of Breathing

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

• Oxygen: Essential for ATP production in cells.

• Carbon Dioxide Removal: Prevents toxic buildup.

Respiratory System Structures

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

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

Example: The nasal cavity filters dust and pathogens from inhaled air.

Mechanics of Breathing

• Inhalation: Diaphragm contracts, intercostal muscles expand chest, lung pressure decreases, air enters.

• Exhalation: Diaphragm relaxes, chest contracts, lung pressure increases, air exits.

• Pressure Changes: $\Delta P = P_{atm} - P_{lung}$

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

Blood Flow and Oxygen Transport

• Oxygen-rich blood: Flows from lungs to left atrium, then left ventricle, then systemic circulation.

• Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → body.

Respiratory Diseases and Disorders

• Asthma: Airway inflammation and constriction.

• Emphysema: Damage to alveoli, reduced gas exchange.

• Pneumonia: Infection of lung tissue.

Human Digestive System

Major Structures and Functions

• 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, processes nutrients.

• Gallbladder: Stores bile.

• Pancreas: Produces digestive enzymes and hormones.

Enzymes and Digestion

• Function: Speed up breakdown of food molecules.

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

Example: Amylase breaks down starch in the mouth.

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.

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

"My Plate" Purpose

• My Plate: Dietary guideline for balanced nutrition.

Digestion Process and Peristalsis

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

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

• 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 and Karyotype

• Homologous Chromosomes: Pair of chromosomes with same genes, one from each parent.

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

Genotype and Phenotype

• Genotype: Genetic makeup (alleles).

• 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.

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 Alleles

• Dominant: Expressed if present.

• Recessive: Expressed only if homozygous.

• Lethal Dominant Disorders: Often eliminated quickly; recessive disorders can persist.

Incomplete Dominance, Codominance, Polygenic Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles fully expressed (e.g., blood type AB).

• Polygenic Inheritance: Multiple genes influence a trait (e.g., skin color).

Environmental Impact and Linked Genes

• Environment: Can affect phenotypic expression (e.g., nutrition, temperature).

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

Meiosis and New Allele Combinations

• Crossing Over: Exchange of genetic material during meiosis creates new allele combinations.

Sex-linked Genes and Nondisjunction

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

• Nondisjunction: Failure of chromosomes to separate properly; leads to abnormal chromosome numbers (e.g., Down syndrome).

Summary Table: Types of Inheritance

Type	Description	Example
Dominant	Trait appears if at least one dominant allele present	Huntington's disease
Recessive	Trait appears only if both alleles are recessive	Cystic fibrosis
Incomplete Dominance	Heterozygote shows intermediate phenotype	Red and white flowers produce pink
Codominance	Both alleles fully expressed	AB blood type
Polygenic	Multiple genes contribute to trait	Skin color
Sex-linked	Gene located on X or Y chromosome	Hemophilia