Overview of Human Body Systems and Homeostasis

Homeostasis

Maintained through negative feedback (stabilizes) and positive feedback (amplifies until stopped).

Dynamic equilibrium

Fluctuates within a range.

Regulatory mechanisms

Receptors detect change, Integration center processes info, Effectors respond to restore balance.

Intracellular fluid (ICF)

Inside cells (~2/3 total fluid).

Extracellular fluid (ECF)

Includes plasma, interstitial fluid.

Diffusion

Movement of molecules down a concentration gradient.

Osmosis

Diffusion of water across a membrane from low to high solute concentration.

Passive transport

No energy (simple diffusion, facilitated diffusion, osmosis).

Active transport

Uses ATP (pumps, cotransport, endocytosis/exocytosis).

Epidermis

Keratinized stratified squamous epithelium.

Dermis

Connective tissue with vessels, glands.

Hypodermis

Fat and connective tissue.

Functions of the integumentary system

Protection, thermoregulation, vitamin D production.

Osteoblasts

Build bone.

Osteoclasts

Break down bone.

Osteocytes

Maintain bone.

Osteoporosis

Bone resorption > formation → brittle bones.

Skeletal muscle

Striated, voluntary.

Cardiac muscle

Striated, involuntary, intercalated discs.

Smooth muscle

Non-striated, involuntary.

Sarcomere

Functional unit with actin/myosin; shortens by sliding.

Motor unit

One neuron + all fibers it controls.

Action potentials

Na⁺ in → depolarize; K⁺ out → repolarize.

Neurons

Dendrites, soma, axon, synapse.

Hormones

Steroids: hydrophobic, nuclear receptors; Peptides/amines: hydrophilic, membrane receptors w/ second messengers.

Blood types

A, B, AB, O; Rh factor determines +/-.

Cardiac output (CO)

CO = HR × SV.

Blood pressure (BP)

BP = CO × Peripheral Resistance.

Normal pH

Normal pH = 7.35-7.45.

Nephron

Glomerulus + tubule.

Filtration

Driven by hydrostatic pressure (GFR).

Reabsorption

Nutrients/water back to blood.

Secretion

Wastes added to urine.