Homeostasis, Tissues, and Body Systems Overview

Homeostasis

Maintenance of a stable internal environment despite external changes.

Dynamic equilibrium

Maintained via regulatory processes.

Feedback Cycles

Components: 1. Stimulus - disrupts homeostasis 2. Receptor - detects stimulus 3. Control center - processes information (usually brain/hypothalamus) 4. Effector - produces response.

Negative Feedback

Reverses the change.

Positive Feedback

Amplifies original stimulus.

Serous Membrane

Lines internal cavities; secretes serous fluid (e.g., pleura, pericardium, peritoneum).

Mucous Membrane

Lines tracts open to the outside (respiratory, digestive); secretes mucus.

Cutaneous Membrane

Skin; protects, waterproofs.

Epithelial Tissue

Structure: Tightly packed cells, avascular, basement membrane, high regeneration.

Simple squamous epithelium

Flat cells located in alveoli and capillaries; function in diffusion.

Simple cuboidal epithelium

Cube-shaped cells located in kidney tubules; function in secretion/absorption.

Simple columnar epithelium

Tall cells located in GI tract; function in absorption/secretion.

Stratified squamous epithelium

Multiple layers; located in skin and mouth; function in protection.

Pseudostratified epithelium

Irregularly shaped cells located in respiratory tract; function in secretion (mucus).

Transitional epithelium

Varies in shape; located in bladder; function in stretching.

Connective Tissue

Supports, binds, protects; has extracellular matrix.

Fibroblasts

Fixed cells that produce fibers.

Adipocytes

Fixed cells that store fat.

Macrophages

Transient cells that perform phagocytosis.

Cartilage

Avascular, gel-like matrix with chondrocytes in lacunae.

Hyaline Cartilage

Type of cartilage found in joints and ribs.

Mechanical Stress

Strengthens bone via osteoblast activity (Wolff's Law).

Vitamin D

Essential for calcium absorption.

Parathyroid Hormone (PTH)

Produced by parathyroid; targets bone and kidney to increase Ca²⁺ by resorption.

Calcitonin

Produced by thyroid; targets bone to decrease Ca²⁺ by deposition.

Diarthrosis

Freely movable joint.

Amphiarthrosis

Slightly movable joint.

Synarthrosis

immovable

Synovial

capsule, fluid-filled (e.g., knee)

Fibrous

sutures, syndesmoses

Cartilaginous

symphysis, synchondrosis

Flexion

joint action that decreases the angle between body parts

Extension

joint action that increases the angle between body parts

Abduction

joint action that moves a limb away from the midline

Adduction

joint action that moves a limb toward the midline

Rotation

joint action that turns a body part around its axis

Circumduction

joint action that moves a limb in a circular motion

Role of Calcium

Binds to troponin, exposing actin sites for myosin to bind

Electrical Excitability

Membrane potential allows action potentials to trigger contractions

Contraction Steps

1. ACh release 2. Action potential on sarcolemma 3. Ca²⁺ release from SR 4. Crossbridge cycle 5. Muscle contracts

Contraction Cycle

ATP hydrolysis → crossbridge → power stroke → detachment

Actin

Thin filament

Myosin

Thick filament

Troponin

Binds Ca²⁺

Tropomyosin

Blocks myosin-binding sites

Skeletal Muscle

Multinucleated, striated, voluntary control

Cardiac Muscle

Single nucleus, striated, involuntary control

Smooth Muscle

Single nucleus, non-striated, involuntary control

Functions of Nervous Tissue

Sensory input, integration, motor output

Saltatory Conduction

Faster, myelinated, jumps nodes

Continuous Conduction

Unmyelinated, slower

Depolarization

Na⁺ in

Repolarization

K⁺ out

Absolute Refractory Period

No action potential possible

Relative Refractory Period

Stronger stimulus needed for action potential

EPSP

Depolarization

IPSP

Hyperpolarization

Astrocytes

Blood-brain barrier, nutrient transfer

Oligodendrocytes

Myelinate CNS

Schwann Cells

Myelinate PNS

Microglia

Immune function

Ependymal Cells

CSF production

Monosynaptic Reflex

1 synapse (e.g., stretch)

Polysynaptic Reflex

Interneurons involved

Ipsilateral

Same side

Contralateral

Opposite side

Dermatome

Skin area innervated by specific spinal nerve

Cranial Nerves

Know basic functions of CN I-XII (smell, vision, facial muscles, etc.)

Cerebrum

Higher thinking

Cerebellum

Coordination

Brainstem

Vital functions

CSF

Produced by choroid plexus; cushions, removes waste, supports brain

Blood-Brain Barrier

Selective permeability; formed by astrocytes & tight junctions

SNS Neurotransmitter

Preganglionic ACh, Postganglionic NE

PNS Neurotransmitter

Preganglionic ACh, Postganglionic ACh

Parasympathetic Functions

Rest/digest (↓ HR, ↑ digestion)

Sympathetic Functions

Fight/flight (↑ HR, ↓ digestion)

Dual Innervation

Most organs receive both PNS and SNS input

Autonomic Targets

Smooth muscle, cardiac muscle, glands

Alpha Receptors

Adrenergic, located in smooth muscle, vessels

Beta Receptors

Adrenergic, located in heart, bronchi

Nicotinic Receptors

Cholinergic, all postganglionic neurons

Muscarinic Receptors

Cholinergic, effector organs of PNS

Photoreceptors

Vision (rods/cones)

Gustatory Receptors

Taste

Hair Cells

Hearing and balance

Basal Cells

Regeneration

Rods

B/W, low light

Cones

Color, bright light

Semicircular Canals

Rotational balance

Vestibule

Static balance (utricle/saccule)

Cochlea

Hearing

Taste Sensations

Sweet, sour, salty, bitter, umami