Human Biology Study Notes: Muscular, Respiratory, Digestive Systems & Genetics

Muscular System

Types of Muscle Tissue

The human body contains three main types of muscle tissue, each with distinct structure and function.

• Skeletal Muscle: Attached to bones via tendons, responsible for voluntary movements. Cells are long, multinucleated, and striated.

• Cardiac Muscle: Found only in the heart, cells are shorter, branched, and usually have one nucleus. Involuntary control.

• Smooth Muscle: Surrounds many internal organs (e.g., digestive tract, blood vessels), cells are spindle-shaped with a single nucleus. Involuntary control.

Example: Skeletal muscles contract to move limbs, cardiac muscle contracts to pump blood, and smooth muscle contracts to move food through the digestive tract.

Muscle Contraction Mechanism

Muscle contraction is initiated by motor neurons and involves the shortening of sarcomeres, the functional units of muscle fibers.

• Sarcomere: Composed of thin (actin) and thick (myosin) filaments.

• Calcium: Binds to proteins on the thin filament, allowing myosin to interact with actin and shorten the fibers.

• ATP: Required for muscle contraction and relaxation.

• Motor Neurons: Stimulate muscle contraction by releasing neurotransmitters.

Equation:

$\text{ATP} + \text{Myosin} \rightarrow \text{Myosin-ATP complex} \rightarrow \text{Muscle contraction}$

Types of Muscle Contractions

• Isometric: Muscle length remains constant; maintains stable position.

• Isotonic: Muscle length shortens; produces movement.

Energy Sources for Muscles

• Stored ATP

• Creatine phosphate

• Metabolism of glucose

Muscle Twitch and Tetanus

• Muscle Twitch: Complete cycle of contraction and relaxation in response to a stimulus.

• Latent Period: Time delay between stimulus and contraction.

• Tetanus: Bacterial infection (Clostridium tetani) causing sustained muscle contraction.

Respiratory System

Structure and Function

The respiratory system is responsible for gas exchange and consists of upper and lower tracts.

• Upper Respiratory Tract: Nose, pharynx

• Lower Respiratory Tract: Larynx, trachea, bronchi, lungs

Functions:

• Filters, warms, and humidifies incoming air

• Gas exchange between blood and tissues

• Produces sound (larynx)

Breathing Regulation

• Respiratory Center: Located in the medulla oblongata; establishes basic breathing pattern.

• Conscious Control: Resides in the cerebral cortex.

• Opioid Overdose: Causes respiratory depression; naloxone can reverse effects.

Disorders of the Respiratory System

• Asthma: Spasmodic contraction of bronchi, often due to allergic responses.

• Emphysema: Permanent damage to alveoli, loss of elasticity; commonly caused by smoking.

• Bronchitis: Inflammation of bronchi; can be acute or chronic.

• Cystic Fibrosis: Inherited condition; thick mucus impedes airflow.

• Colds: Caused by numerous viruses; affects upper respiratory tract.

• Influenza: Caused by influenza virus; higher risk for young and elderly.

• Pneumonia: Infection of lungs by bacteria or viruses.

• Tuberculosis: Lung infection with scarring; caused by Mycobacterium tuberculosis.

• Botulism: Poisoning by bacterial toxin.

• COVID-19: Viral infection caused by SARS-CoV-2.

• Cancer: Uncontrolled growth of abnormal cells; includes mesothelioma.

• Pneumothorax: Collapse of lung lobes.

• Atelectasis: Lack of gas exchange due to alveolar collapse or fluid buildup.

• Congestive Heart Failure: Heart becomes less efficient; left side failure affects lungs.

Digestive System

Structure of the GI Tract

The digestive system consists of the gastrointestinal (GI) tract and accessory organs.

• GI Tract: Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas

Layers of the GI Tract

• Mucosa: Innermost layer; mucous membrane in contact with lumen

• Submucosa: Connective tissue with blood vessels, lymph vessels, nerves

• Muscularis: 2-3 layers of smooth muscle; responsible for movement

• Serosa: Outermost layer

• Sphincters: Muscular rings separating organs

Digestive Processes

• Mechanical Processing: Chewing and mixing

• Chemical Digestion: Breakdown of food by enzymes and acids

• Absorption: Nutrients and water move into blood vessels across mucosal layer

• Elimination: Undigested material expelled as feces

• Food Storage: Temporary storage until digestion

Digestion of Nutrients

• Proteins: Digested by stomach (pepsin), pancreas (proteases), and small intestine enzymes

• Carbohydrates: Polysaccharides digested to monosaccharides by salivary amylase and pancreatic amylase

• Lipids: Broken down to monoglycerides and fatty acids by lipases

• Water: Absorbed by osmosis

• Minerals: Actively transported or absorbed by facilitated diffusion

Stomach Functions

• Hydrochloric Acid: Lowers pH to about 2; breaks down food

• Intrinsic Factor: Needed for vitamin B12 absorption

• Mucus: Protects stomach lining

• Pepsinogen: Converted to pepsin by acid

• Chyme: Mixture of partially digested food and gastric juice

Small Intestine Functions

• Duodenum: Most digestion occurs

• Jejunum & Ileum: Absorption of nutrients

• Villi & Microvilli: Increase surface area for absorption

Accessory Organs

• Salivary Glands: Secrete saliva with amylase

• Pancreas: Secretes digestive enzymes (proteases, amylase, lipase)

• Liver: Produces bile

• Gallbladder: Stores and concentrates bile

Large Intestine Functions

• Absorbs water and nutrients

• Includes cecum, appendix, colon

Hormones and Nutrition

• Hormones: Gastrin, secretin, CCK regulate digestion

• Saturated Fats: From meat and dairy

• Unsaturated Fats: From plant sources

• Trans Fats: From processed vegetable oils

• Vitamins: Fat-soluble (stored in adipose), water-soluble (stored briefly)

Digestive Disorders

• Peptic Ulcer: Forms if mucus barrier is damaged

• Food Poisoning: Caused by bacterial toxins

Genetics & Inheritance

Chromosomes and Genes

Chromosomes are structures within the nucleus composed of DNA and protein. Genes are located on chromosomes.

• Humans: 23 pairs of chromosomes (22 autosomes, 1 pair of sex chromosomes)

• Homologous Chromosomes: One inherited from each parent

• Alleles: Alternative forms of a gene

• Locus: Location of a gene on a chromosome

• Karyotype: Display of an individual's chromosomes

Genotype and Phenotype

• Genotype: Complete set of alleles

• Phenotype: Observable traits (e.g., eye color, blood type)

Punnett Square and Patterns of Inheritance

• Punnett Square: Used to predict inheritance patterns

• Dominant Allele: Masks expression of recessive allele

• Recessive Allele: Expressed only if homozygous

Law of Segregation: Two alleles of each gene separate during gamete formation.

Law of Independent Assortment: Genes for different traits are separated independently during meiosis.

Examples of Genetic Disorders

• Cystic Fibrosis: Recessive allele of CFTR gene; thick mucus in lungs

• Polydactyly: Extra finger/toe; dominant allele

• Dwarfism: Dominant allele causes short stature

• Sickle Cell Disease: Substitution of a single amino acid in hemoglobin; codominance

• Down Syndrome: Three copies of chromosome 21

Complex Patterns of Inheritance

• Incomplete Dominance: Heterozygotes have intermediate phenotype

• Codominance: Heterozygotes express both alleles equally

• Epigenetic Inheritance: Modification and transmission of traits without changes in DNA sequence

• Linked Alleles: Located on the same chromosome

• Sex-linked Genes: Located on sex chromosomes

Chromosomal Abnormalities

• Deletions: Piece of chromosome breaks off

• Translocations: Piece of chromosome attaches to a different chromosome

Table: Comparison of Dominant and Recessive Alleles

Allele Type	Expression	Example
Dominant	Expressed in heterozygotes and homozygotes	Polydactyly, Dwarfism
Recessive	Expressed only in homozygotes	Cystic Fibrosis

Table: Types of Muscle Tissue

Type	Location	Control	Cell Structure
Skeletal	Bones	Voluntary	Long, multinucleated, striated
Cardiac	Heart	Involuntary	Short, branched, one nucleus
Smooth	Organs, vessels	Involuntary	Spindle-shaped, one nucleus

Table: Layers of the GI Tract

Layer	Description
Mucosa	Innermost, mucous membrane
Submucosa	Connective tissue, blood vessels, nerves
Muscularis	Smooth muscle layers
Serosa	Outermost layer

Additional info: Academic context was added to clarify mechanisms, provide definitions, and expand on brief points for completeness.