Biology

Human physiology basics

Homeostasis, circulation, nerves, immunity.

Basics

Homeostasis

Keeping the internal environment in a narrow range. Negative feedback is the default (temperature, blood glucose). Positive feedback is rare and amplifying (oxytocin in birth). Hormones are slow and broad; nerves are fast and local.

Circulation

Heart: right side → lungs → left side → body. Arteries are high pressure, capillaries exchange, veins return. Hemoglobin in red cells carries O₂. ABO and Rh set transfusion compatibility.

Nerves

Resting potential is mostly K⁺ leak. An action potential: Na⁺ in (depolarize), then K⁺ out (repolarize). Neurotransmitters at synapses. Central (brain, spinal cord) versus peripheral.

Immunity

Innate: barriers, phagocytes, inflammation. Adaptive: B-cell antibodies, T cells. Memory cells make a second exposure faster. Vaccines create memory without the full disease.

Formulas

Cardiac output

CO = HR × SV

Blood one ventricle pumps per minute. Exercise raises both HR and SV.

Symbols

HR heart rate
SV stroke volume

Equilibrium potential (K⁺, ~37 °C)

E_K ≈ 61 mV · log₁₀ ([K⁺]_o / [K⁺]_i)

Membrane voltage if only that ion permeated. Rest is a weighted mix.

Symbols

[K⁺]_o outside concentration
[K⁺]_i inside concentration

Key table

Blood types	A/B antigens; O has neither, AB both. Rh+ has D antigen
Core temperature	about 37 °C

In this field

The cell

Prokaryotes vs eukaryotes, organelles, membranes.

Genetics and molecular biology

DNA, transcription/translation, Mendel, meiosis.

Metabolism

Photosynthesis, respiration, ATP, enzymes.

Evolution and ecology

Natural selection, phylogeny, trophic levels, cycles.

Plants and development

Plant tissues, hormones, developmental stages.

Immunity and microbes

Pathogens, innate and adaptive immunity, antibiotics and vaccines.

Nervous and endocrine systems

Neurons, synapses, hormones, and homeostasis — fast electrical and slower chemical signals.

Molecular lab sketch

Restriction enzymes, electrophoresis, PCR, and sequencing — a short principle sketch.

Population ecology

Exponential and logistic growth, carrying capacity, life history, predator–prey sketch.

Life’s diversity

Domains, a phylogeny sketch, homology versus analogy, and binomial names.

Biological macromolecules

Carbohydrates, lipids, proteins, and nucleic acids — structure and role sketches.