Homeostasis, Cell Structure, and Endocrine System Overview

Homeostasis

Refers to the body's ability to maintain a stable internal environment despite changes in external conditions.

Atom

Basic unit of matter.

Molecule

Two or more atoms bonded together.

Organelle

Specialized structures within cells (e.g., mitochondria).

Cell

Basic unit of life.

Tissue

Groups of similar cells performing a common function (e.g., muscle tissue).

Organ

Composed of different types of tissues working together (e.g., heart).

Organ System

Group of organs that perform related functions (e.g., cardiovascular system).

Organism

A complete living entity capable of independent existence.

Local Control

Responses are confined to a specific area (e.g., blood vessel constriction in response to injury).

Negative Feedback

The response reduces the stimulus (e.g., body temperature regulation: when body temperature rises, mechanisms like sweating cool the body, bringing it back to normal).

Positive Feedback

The response amplifies the stimulus (e.g., childbirth: uterine contractions lead to more contractions until delivery).

General Purpose of Homeostasis

To maintain conditions favorable for cell function and survival.

Negative Feedback Example

Regulation of blood sugar by insulin.

Positive Feedback Example

Blood clotting cascade during injury.

Nucleus

Contains genetic material (DNA), controls cell activities.

Mitochondria

Site of ATP production through cellular respiration.

Ribosomes

Protein synthesis.

Rough ER

Has ribosomes; synthesizes proteins.

Smooth ER

Synthesizes lipids, detoxifies drugs.

Golgi Apparatus

Modifies, sorts, and packages proteins for transport.

Lysosomes

Digestion and waste removal.

Peroxisomes

Detoxification, breakdown of fatty acids.

Cytoskeleton

Provides structure, shape, and aids in cell movement.

Plasma Membrane

Controls movement of substances in/out of the cell.

Glycolysis

Location: Cytoplasm. ATP Produced: 2 ATP.

Citric Acid Cycle (Krebs Cycle)

Location: Mitochondria (matrix). ATP Produced: 2 ATP.

Electron Transport Chain (ETC)

Location: Inner mitochondrial membrane. ATP Produced: ~34 ATP.

Impact of Diseases/Drugs on Cellular Function

A drug that affects the mitochondria could impair ATP production, leading to symptoms like fatigue, muscle weakness, or organ dysfunction.

High Mitochondria Count

Cells with a lot of energy demand (e.g., muscle cells, neurons).

High Ribosome Count

Cells that produce a lot of protein (e.g., pancreas cells producing insulin).

Phospholipid Bilayer

Basic structural framework; hydrophilic heads, hydrophobic tails.

Integral proteins

Span the membrane, transport molecules.

Peripheral proteins

Attached to inner/outer membrane, involved in signaling and structure.

Cholesterol

Stabilizes membrane fluidity.

Carbohydrates

Form glycoproteins and glycolipids; involved in cell recognition.

Passive Transport

Movement of molecules from high to low concentration without energy required.

Facilitated Diffusion

Movement through a membrane protein (e.g., glucose transport).

Osmosis

Movement of water across a semipermeable membrane.

Active Transport

Energy required transport mechanism that moves molecules against their concentration gradient.

Primary Active Transport

Uses ATP to move molecules against their concentration gradient (e.g., Na+/K+ pump).

Secondary Active Transport

Uses the gradient of one molecule to move another against its gradient.

Penetrating Solutes

Solutes (e.g., ethanol) that can cross the membrane, affecting water movement.

Non-Penetrating Solutes

Solutes (e.g., Na+, Cl-) that cannot cross the membrane and influence water movement by osmosis.

Osmolarity

Concentration of solute particles in solution.

Osmolarity Example

1M NaCl → 2 Osm/L (because NaCl dissociates into two ions).

Diffusion

Movement from higher to lower concentration.

Osmosis

Water moves toward the higher solute concentration.

Isotonic

Equal solute concentration inside and outside the cell.

Hypotonic

Lower solute concentration outside, causing water to enter the cell.

Hypertonic

Higher solute concentration outside, causing water to exit the cell.

Carrier-Mediated Transport

Transport proteins bind to molecules, causing a conformational change to move the molecule across the membrane.

Symport

Carrier-mediated transport where molecules move in the same direction.

Antiport

Carrier-mediated transport where molecules move in opposite directions.

Fick's Law of Diffusion

Rate of diffusion = (Concentration gradient × Surface area × Permeability) / Distance.

Intracellular Fluid (ICF)

Fluid inside cells, comprising about 2/3 of body water.

Extracellular Fluid (ECF)

Fluid outside cells, comprising about 1/3 of body water.

Interstitial Fluid

Fluid surrounding cells.

Plasma

Fluid found in blood vessels.

Peptide Hormones

Hormones composed of chains of amino acids; water-soluble and produced in the rough endoplasmic reticulum.

Steroid Hormones

Hormones derived from cholesterol; lipid-soluble and synthesized in the smooth endoplasmic reticulum.

Amine Hormones

Hormones derived from amino acids (tyrosine or tryptophan) and produced by enzymatic modifications.

ADH (Antidiuretic Hormone)

Increases water reabsorption, reduces urine output

Oxytocin

Uterine contractions, milk ejection

LH (Luteinizing Hormone)

Stimulates ovulation and progesterone production in females; testosterone production in males

FSH (Follicle-Stimulating Hormone)

Stimulates follicle development and estrogen production in females; sperm production in males

ACTH (Adrenocorticotropic Hormone)

Stimulates cortisol release

TSH (Thyroid-Stimulating Hormone)

Stimulates release of thyroid hormones (T3/T4)

Prolactin

Stimulates milk production

Growth Hormone (GH)

Stimulates growth, protein synthesis, and metabolism

Testosterone

Promotes male secondary sex characteristics and sperm production

Estrogen

Promotes female secondary sex characteristics and regulates the menstrual cycle

Progesterone

Maintains pregnancy, regulates menstrual cycle

Aldosterone

Increases sodium reabsorption, regulates blood pressure

Cortisol

Regulates metabolism, suppresses immune response

Androgens

Precursor to sex hormones

Adrenaline (Epinephrine)

Increases heart rate, bronchodilation, glycogen breakdown

Thyroid Hormones (T3/T4)

Increases metabolism, heart rate, and growth

Parathyroid Hormone (PTH)

Increases blood calcium levels

Calcitonin

Lowers blood calcium levels

Insulin

Lowers blood glucose levels

Glucagon

Raises blood glucose levels

Hypophyseal portal system

Vascular link connecting hypothalamus and anterior pituitary

Neural connections (hypothalamic-hypophyseal tract)

Connects hypothalamus to posterior pituitary

Humoral Regulation

Hormone release in response to changing blood levels of ions/nutrients

Hormonal Regulation

One hormone stimulates the release of another

Nervous System Regulation

Hormone release triggered by neural input

Plasma

~55% of whole blood

Formed Elements

~45%

Red Blood Cells (Erythrocytes)

~99% of formed elements

Lifespan of Red Blood Cells

~120 days

White Blood Cells (Leukocytes)

<1%

Lifespan of Neutrophils

~6 hrs to a few days

Lifespan of Lymphocytes

days to years

Lifespan of Monocytes

months

Lifespan of Eosinophils

~5 days

Lifespan of Basophils

a few hours to days

Platelets (Thrombocytes)

<1%

Lifespan of Platelets

~8-10 days

Overall Functions of Blood

Transport: gases (O₂, CO₂), nutrients, hormones, waste; Regulation: pH, body temperature, fluid volume; Protection: against blood loss (clotting), infection (immune defense)