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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 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 Mechanism: Myosin heads bind to actin, forming cross-bridges, and pull the actin filaments inward, shortening the sarcomere.

  • Function of Sarcomere: Facilitates muscle contraction by shortening during activation.

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

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

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical impulses 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 binds to troponin, exposing binding sites on actin.

    5. Myosin binds to actin, causing contraction.

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

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 produces movement; isometric stabilizes joints and maintains posture.

Summary Table: Muscle Contraction Types

Type

Muscle Length Change

Movement

Isotonic

Yes

Yes

Isometric

No

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.

  • Importance: Cellular respiration requires oxygen; removal of CO2 prevents acidosis.

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, 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.

Respiratory Diseases and Disorders

  • Common Disorders: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

  • Impact: Affect gas exchange and breathing efficiency.

Summary Table: Respiratory System Structures

Structure

Location

Function

Nose/Nasal Cavity

Upper

Filters, warms, humidifies air

Pharynx

Upper

Passage for air and food

Larynx

Upper

Voice production

Trachea

Lower

Conducts air to lungs

Bronchi

Lower

Branches airways

Lungs

Lower

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.

  • Function: Each organ contributes to digestion, absorption, or excretion.

Enzymes and Digestion

  • Enzymes: Biological catalysts that speed up digestion; produced in salivary glands, stomach, pancreas, small intestine.

  • Function: Break down carbohydrates, proteins, and fats.

Surface Area and Digestion

  • Large Surface Area: Villi and microvilli in the small intestine increase surface area for nutrient absorption.

Metabolic Rates

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

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

  • Equation for BMR:

"My Plate" Purpose

  • My Plate: A guide for balanced nutrition, emphasizing proper proportions of food groups.

Digestion Process and Peristalsis

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

  • Digestion: Chemical and mechanical breakdown of food; absorption occurs mainly in the small intestine.

Summary Table: Digestive System Structures

Structure

Function

Mouth

Mechanical breakdown, saliva starts digestion

Stomach

Protein digestion, acid breakdown

Small Intestine

Absorption of nutrients

Large Intestine

Water absorption, waste formation

Liver

Bile production, metabolism

Pancreas

Enzyme production

Gallbladder

Bile storage

Human Genetics and Inheritance

Genes, Chromosomes, and Genome

Genetics is the scientific study of heredity and variation in organisms.

  • Gene: A segment of DNA coding for a specific protein.

  • Chromosome: DNA molecule with associated proteins; humans have 23 pairs.

  • Genome: The complete set of genes in an organism.

  • Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.

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

Genotype and Phenotype

  • Genotype: Genetic makeup (allele combination).

  • Phenotype: Observable traits.

Punnett Square and Alleles

  • Punnett Square: Diagram used to predict genetic crosses.

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

  • Homozygous: Two identical alleles (e.g., AA or aa).

  • Heterozygous: Two different alleles (e.g., Aa).

Mendelian Laws

  • Law of Segregation: Each parent passes one allele for each gene to offspring.

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

Dominant and Recessive Alleles

  • Dominant Allele Disorders: Can be lethal if expressed in homozygous form.

  • Recessive Disorders: May persist due to carriers (heterozygotes).

Non-Mendelian Inheritance

  • Incomplete Dominance: Heterozygotes show 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 the same 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 (e.g., hemophilia).

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

Summary Table: Types of Inheritance

Type

Expression

Example

Dominant

Trait appears if at least one dominant allele

Huntington's disease

Recessive

Trait appears only if both alleles are recessive

Cystic fibrosis

Incomplete Dominance

Intermediate phenotype

Snapdragon flower color

Codominance

Both alleles fully expressed

AB blood type

Polygenic

Multiple genes contribute

Height, skin color

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