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 functional unit of muscle fibers, composed of actin and myosin filaments.

• Actin and Myosin: Protein filaments; actin is thin, myosin is thick. Their interaction causes muscle contraction.

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

• Function: Sarcomeres contract to generate force and movement.

• Example: During biceps contraction, sarcomeres shorten, pulling the forearm upward.

Action Potential and Muscle Contraction

Muscle contraction is initiated by electrical signals called action potentials from motor neurons.

• Action Potential: A rapid change in membrane voltage that triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases acetylcholine at neuromuscular junction.

  2. Muscle cell membrane depolarizes, generating an action potential.

  3. Action potential travels along the sarcolemma and into T-tubules.

  4. Calcium ions are released from the sarcoplasmic reticulum.

  5. Calcium enables actin-myosin interaction, leading to contraction.

• Electrical Impulses: Cause release of calcium ions, which are essential for contraction.

Muscle Groups and Body Cavities

Muscles are organized into groups that control movement and maintain posture.

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

• Body Cavities: Muscles such as the diaphragm section the thoracic and abdominal cavities.

Types of Muscle Contractions

Muscle contractions can be classified as isotonic or isometric.

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant. Produces movement.

• Isometric Contraction: Muscle length remains the same while tension increases. No movement produced.

• Example: Lifting a weight (isotonic); holding a weight steady (isometric).

Heat Generation

Most human body heat is generated by the muscular system during contraction.

• Function: Muscle activity produces heat as a byproduct of ATP hydrolysis.

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen to tissues and removing carbon dioxide.

• Importance: Oxygen is required for cellular respiration; carbon dioxide is a waste product.

Respiratory System Structures

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

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

• Lower Respiratory Structures: Trachea, bronchi, bronchioles, lungs. Functions: conduct air, gas exchange.

• Significance: Each structure ensures efficient and safe passage of air to the lungs.

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.

• 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 the lungs to the heart and is pumped throughout the body.

• Pathway: Pulmonary veins → left atrium → left ventricle → aorta → systemic circulation.

Respiratory Diseases and Disorders

Common respiratory diseases include asthma, bronchitis, pneumonia, and emphysema.

• Asthma: Inflammation and narrowing of airways.

• Emphysema: Damage to alveoli, reducing gas exchange.

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.

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

Enzymes and Digestion

Enzymes catalyze the breakdown of food molecules.

• Function: Speed up chemical reactions; produced in salivary glands, stomach, pancreas, small intestine.

• Example: Amylase (saliva), pepsin (stomach), lipase (pancreas).

Surface Area and Digestion

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

• Function: Maximizes contact with digested food for efficient absorption.

Metabolic Rates

Metabolic rate measures energy expenditure.

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

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

• Equation: $\text{BMR} = \text{Energy} / \text{Time}$

"My Plate" Purpose

"My Plate" is a nutritional guide for balanced eating.

• Purpose: Encourages proper proportions of fruits, vegetables, grains, protein, and dairy.

Digestion Process and Peristalsis

Digestion involves mechanical and chemical breakdown; peristalsis moves food through the digestive tract.

• Peristalsis: Rhythmic contractions of smooth muscle.

• Structures Involved: Esophagus, stomach, intestines.

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

Genetics is the scientific study of heredity and variation.

• 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 carry the same genes; karyotype is a visual representation of chromosomes.

• Function: Homologous chromosomes determine traits; karyotype identifies chromosome number and structure.

Genotype and Phenotype

Genotype is the genetic makeup; phenotype is the observable trait.

• Example: Genotype: Aa; Phenotype: brown eyes.

Punnett Square and Alleles

Punnett Squares predict genetic outcomes; alleles are gene variants.

• Dominant Allele: Expressed trait (A).

• Recessive Allele: Masked unless homozygous (a).

• Homozygous: Same alleles (AA or aa).

• Heterozygous: Different alleles (Aa).

Punnett Square Example

	A	a
A	AA	Aa
a	Aa	aa

Mendelian Laws

The Law of Segregation and Law of Independent Assortment explain inheritance patterns.

• Law of Segregation: Alleles separate during gamete formation.

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

Dominant and Recessive Disorders

Some dominant disorders are lethal; recessive disorders can persist in populations.

• Example: Huntington's disease (dominant); cystic fibrosis (recessive).

Non-Mendelian Inheritance

Inheritance can involve incomplete dominance, codominance, polygenic traits, and environmental effects.

• 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 modify phenotypic expression.

Linked Genes and Meiosis

Linked genes are inherited together; meiosis creates new allele combinations.

• Linked Genes: Located close together on the same chromosome.

• Meiosis: Crossing over produces genetic variation.

Sex-linked Genes and Nondisjunction

Sex-linked genes are on sex chromosomes; nondisjunction affects chromosome number in gametes.

• Sex-linked Genes: Traits linked to X or Y chromosomes (e.g., color blindness).

• Nondisjunction: Failure of chromosomes to separate, leading to conditions like Down syndrome.