Comprehensive Human Physiology and Homeostasis: Nervous, Cardiovascular, Respiratory, Renal, Endocrine, and Immune Systems

Homeostasis

Maintaining a stable internal environment through negative feedback mechanisms.

Components of negative feedback

Sensor → Integrator → Effector.

Glucose regulation example

High BG → pancreas releases insulin → cells uptake glucose → BG returns to normal.

Main determinant of resting membrane potential

K⁺ leak channels allowing K⁺ to leave the cell.

Na⁺/K⁺ pump ratio

3 Na⁺ out / 2 K⁺ in using 1 ATP.

Action potential phases

Resting → Depolarization → Repolarization → Hyperpolarization → RMP restored.

Ion responsible for depolarization

Na⁺ influx.

Ion responsible for repolarization

K⁺ efflux.

Absolute refractory period

No AP can be generated; Na⁺ channels are inactivated.

Saltatory conduction

AP jumps between nodes of Ranvier in myelinated axons → faster conduction.

EPSP vs IPSP

EPSP = depolarization; IPSP = hyperpolarization.

Sympathetic effects

↑ HR, ↑ BP, bronchodilation, pupil dilation, ↓ GI motility.

Parasympathetic effects

↓ HR, bronchoconstriction, ↑ digestion, pupil constriction.

Ion triggering muscle contraction

Ca²⁺ from the sarcoplasmic reticulum.

Role of troponin

Binds Ca²⁺ → moves tropomyosin → exposes actin binding sites.

Roles of ATP in muscle contraction

Detaches myosin, powers power stroke, pumps Ca²⁺ into SR.

Types of muscle

Skeletal (voluntary), Cardiac (involuntary, gap junctions), Smooth (slow/sustained).

Heart electrical conduction pathway

SA node → AV node → Bundle of His → Purkinje fibers.

ECG: P-wave

Atrial depolarization.

ECG: QRS complex

Ventricular depolarization.

ECG: T-wave

Ventricular repolarization.

Cardiac output formula

CO = HR × SV.

Factors increasing stroke volume

↑ preload, ↑ contractility, ↓ afterload.

Baroreceptor function

Detect acute changes in BP.

Cause of inspiration

Thoracic volume ↑ → alveolar pressure ↓ → air flows in.

Primary muscle of inspiration

Diaphragm.

Mechanism of gas exchange

Simple diffusion down partial pressure gradients.

Normal PO₂ of pulmonary capillaries

~100 mmHg.

Right shift of oxyhemoglobin curve

↓ affinity; ↑ CO₂, ↑ temperature, ↑ H⁺ (exercise).

Four nephron functions

Filtration, Reabsorption, Secretion, Excretion.

Hormone for water reabsorption

ADH opens aquaporins in collecting duct.

Function of aldosterone

Reabsorbs Na⁺, secretes K⁺ → increases blood volume.

Stimuli for renin release

Low BP, sympathetic activation, low Na⁺ delivery.

Effect of ANP

↓ Na⁺ reabsorption → ↓ blood pressure (opposes aldosterone).

Peptide vs steroid hormones

Peptide = membrane receptors; Steroid = intracellular receptors.

HPA axis hormones

CRH → ACTH → Cortisol.

Effect of thyroid hormone

↑ metabolic rate and heat production.

Insulin vs glucagon

Insulin lowers BG; glucagon raises BG.

Main site of nutrient absorption

Small intestine.

Stomach functions

Mechanical digestion, HCl secretion, pepsin, mixing chyme.

Pancreatic secretions

Enzymes + bicarbonate to neutralize stomach acid.

Innate immunity

Fast, nonspecific, no memory.

Adaptive immunity

Specific, slower, memory; involves B and T cells.

Antibodies produced by

Plasma cells (differentiated B cells).