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 fiber, composed of actin (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin, pulling the filaments past each other.

• Actin and Myosin: Actin provides the track, while myosin uses ATP to generate force.

• Order of Events: Nerve impulse → Action potential → Calcium release → Myosin-actin interaction → Contraction.

• Electrical Impulses: Action potentials in motor neurons trigger calcium release from the sarcoplasmic reticulum.

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

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

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle tension increases, but length does not change (no movement).

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

Sarcomere Substructures and Functions

• 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: Sarcomeres contract to shorten muscle fibers, enabling movement.

Action Potential and Muscle Contraction

• Action Potential: Electrical signal in motor neuron triggers muscle contraction.

• Mechanism: Depolarization opens voltage-gated calcium channels, leading to neurotransmitter release.

• Order of Events:

  1. Motor neuron releases acetylcholine.

  2. Muscle cell membrane depolarizes.

  3. Calcium released from sarcoplasmic reticulum.

  4. Myosin binds to actin.

  5. Muscle contracts.

Formula:

$\text{ATP} + \text{Myosin} \rightarrow \text{Myosin-ATP} \rightarrow \text{Myosin-Actin} \rightarrow \text{Contraction}$

Human Respiratory System

Significance of Breathing

Breathing is essential for oxygen intake and carbon dioxide removal, supporting cellular respiration and energy production.

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart, then distributed to tissues.

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

Structures of the Respiratory System

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

• Lower Respiratory Tract: Trachea, bronchi, lungs, alveoli. Functions: gas exchange.

Example: The alveoli are the site of oxygen and carbon dioxide exchange.

Mechanics of Breathing

• Inhalation: Diaphragm contracts, intercostal muscles lift rib cage, lung volume increases, pressure decreases, air enters.

• Exhalation: Diaphragm relaxes, rib cage lowers, lung volume decreases, pressure increases, air exits.

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

• Intercostal Muscles: Assist in expanding and contracting the thoracic cavity.

Blood Flow Through the Heart

• Order: Pulmonary veins → Left atrium → Left ventricle → Aorta → Body tissues.

Formula:

$\text{Oxygen-rich blood}: \text{Lungs} \rightarrow \text{Left Atrium} \rightarrow \text{Left Ventricle} \rightarrow \text{Aorta} \rightarrow \text{Body}$

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), pancreas (produces enzymes), gallbladder (stores bile).

Enzymes and Digestion

• Function: Enzymes catalyze breakdown of macromolecules.

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

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.

"My Plate" Purpose

• My Plate: Visual guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Peristalsis

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

Formula:

$\text{Peristalsis}: \text{Contraction} \rightarrow \text{Relaxation} \rightarrow \text{Movement of food}$

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 in an organism.

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

• Karyotype: Visual representation of chromosome number and structure.

Genotype and Phenotype

• Genotype: Genetic makeup (allele combination).

• 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.

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

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

Dominant and Recessive Alleles

• Dominant: Expressed in heterozygous state.

• Recessive: Expressed only in homozygous state.

• Lethal Dominant Disorders: Often eliminated quickly; recessive disorders can persist if carriers are unaffected.

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• Polygenic Inheritance: Multiple genes influence a trait.

• Environmental Impact: Environment can modify 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 (X or Y).

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

Term	Definition	Example
Gene	DNA segment coding for a trait	Eye color gene
Allele	Variant of a gene	Blue or brown eye allele
Genotype	Allele combination	BB, Bb, bb
Phenotype	Observable trait	Brown eyes
Homozygous	Same alleles	BB or bb
Heterozygous	Different alleles	Bb
Dominant	Expressed allele	B
Recessive	Masked allele	b

Formula:

$\text{Punnett Square}: \text{Parent Genotypes} \rightarrow \text{Possible Offspring Genotypes}$

Example: Hemophilia is a sex-linked recessive disorder.