Human Physiology May Content

What is the normal range of body water percentage?

50–70% of body mass.

How much water is typically lost during exercise?

1–2 liters per hour.

How does dehydration affect performance?

Dehydration exceeding 2.1% of body mass significantly impairs performance.

What mechanisms regulate body water movement?

Osmosis, governed by differences in osmotic pressure.

What are effective hydration strategies pre-exercise?

500ml of water 1–2 hours before activity.

What is recommended during exercise longer than 1 hour?

600–1200ml/hour with sodium for fluid and electrolyte balance.

How is hydration measured?

Urine osmolality, plasma osmolality, saliva testing, and bioelectrical impedance analysis (BIA).

What are hypotonic, isotonic, and hypertonic beverages?

Hypotonic: <4% carbs, quick hydration

Isotonic: 6–8%, balance of energy/hydration

Hypertonic: >10%, for glycogen replenishment

What is the normal core body temperature range?

36.5°C to 37.5°C.

What are the primary modes of heat loss?

Radiation (60%), convection (12%), evaporation (25%), and conduction (2%).

How does the body respond to heat stress?

Increased sweating and skin blood flow; core temperature rises.

What are signs of heat exhaustion and stroke?

Fatigue, dizziness, nausea, core temperature >38°C (heat stroke).

How does the body adapt to heat through acclimatization?

Earlier onset of sweating, more dilute sweat, reduced cardiovascular strain.

What are physiological responses to cold?

Vasoconstriction, shivering, and hormonal regulation (e.g. thyroxine, adrenaline).

What is the main thermoregulatory control center?

The hypothalamus.

What is the primary function of the respiratory system?

Gas exchange, acid-base balance, and vocalization.

How does Boyle’s Law apply to breathing?

An increase in thoracic volume reduces pressure, allowing air to flow in.

Where does gas exchange occur?

In the alveoli of the lungs.

What respiratory centers control breathing?

Medulla oblongata and pons.

How is CO₂ primarily transported in blood?

As bicarbonate ions (70%).

What is tidal volume (VT)?

The volume of air inhaled or exhaled during normal breathing (~500ml).

What is COPD and how does it affect respiration?

Chronic Obstructive Pulmonary Disease; causes airway narrowing and reduced gas exchange.

What are the four heart chambers?

Right atrium, right ventricle, left atrium, left ventricle.

What is the cardiac cycle composed of?

Diastole (filling) and systole (contraction).

What is cardiac output (CO)?

CO = Heart Rate (HR) × Stroke Volume (SV).

What is the equation for mean arterial pressure (MAP)?

MAP = DBP + 1/3(SBP - DBP).

What does the QRS complex represent in an ECG?

Ventricular depolarization.

What autonomic inputs regulate heart rate?

Sympathetic increases HR; parasympathetic (vagus nerve) decreases HR.

What is the significance of the rate pressure product (RPP)?

Indicates myocardial oxygen demand (RPP = SBP × HR).

What percentage of oxygen is transported by hemoglobin?

About 99%.

How is carbon dioxide transported in the blood?

70% as bicarbonate, 23% bound to hemoglobin, 7% dissolved in plasma.

What is the Bohr effect?

Lower pH reduces hemoglobin’s affinity for oxygen.

What is the Haldane effect?

Deoxygenated hemoglobin carries more CO₂.

What is hematocrit?

The percentage of red blood cells in total blood volume.

What hormones increase red blood cell production?

Erythropoietin (EPO), secreted by the kidneys.

How does PO₂ change with altitude?

Decreases from 160 mmHg at sea level to ~50 mmHg at 4000m.

What are acute responses to high altitude?

Increased ventilation and heart rate.

What chronic adaptations occur at high altitude?

Increased RBC production, capillary density, and myoglobin concentration.

What hormone mediates altitude adaptation?

Erythropoietin (EPO).

What are common altitude sickness symptoms?

Headache, nausea, dizziness, shortness of breath.

What is COPD?

Chronic lung disease causing airflow limitation and gas exchange impairment.

What are the major cell organelles?

Nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, ribosomes.

What is the primary role of mitochondria?

ATP production through aerobic respiration.

What is the function of the cell membrane?

Selectively allows substances in/out; phospholipid bilayer.

What are the types of membrane transport?

Passive (diffusion, osmosis), active (requires ATP).

What proteins form the cytoskeleton?

Actin (microfilaments), tubulin (microtubules), intermediate filaments.

What are the two main divisions of the nervous system?

Central (CNS) and Peripheral (PNS).

What is the function of myelin?

Speeds up action potential conduction.

What is the resting membrane potential of a neuron?

Approximately -70 mV.

What triggers an action potential?

Depolarization due to sodium influx.

What is the function of the synapse?

Transfers signals via neurotransmitters between neurons.

What is the role of the autonomic nervous system?

Controls involuntary functions (heart rate, digestion).

What are the major endocrine glands?

Pituitary, thyroid, adrenal, pancreas, pineal, parathyroid.

What are the types of hormones?

Steroid (lipid-soluble) and peptide (water-soluble).

What is negative feedback in hormone regulation?

A process that inhibits hormone secretion when levels are sufficient.

What is the stress response pathway?

Hypothalamus → pituitary → adrenal → cortisol/epinephrine.

What is the difference between Type 1 and Type 2 diabetes?

Type 1: insulin deficiency (autoimmune); Type 2: insulin resistance.

What is the functional unit of skeletal muscle?

The sarcomere.

How does muscle contraction occur?

Via sliding filament theory: actin and myosin interaction powered by ATP.

What triggers contraction at the molecular level?

Calcium binds troponin, revealing binding sites on actin.

What are the types of muscle fibers?

Type I (slow-twitch), Type IIa/b (fast-twitch).

What causes muscle fatigue?

Lactic acid buildup, hydrogen ions, and glycogen depletion.

What are the types of muscle contractions?

Isometric (static), concentric (shortening), eccentric (lengthening).

What are the main components of a sarcomere?

Actin, myosin, troponin, tropomyosin, and titin.

What is the role of actin in muscle contraction?

Forms the thin filaments that myosin binds to during contraction.

What is atmsopheric pressure?

(760 mmHg or 1 ATM)

What is pulmonary ventilation?

The process of moving air into and out of the lungs, facilitating gas exchange.

What is external respiration?

The exchange of gases between the lungs and the blood, specifically the intake of oxygen and the release of carbon dioxide.

What is the conduction zone & what is it composed of?

movement of air to the respiratory zone: trachea, terminal bronchioles, bronchi tree

What is the respiratory zone and what is it composed of?

exchange of gases as oxygen diffuses into lung capillaries and exchanges CO2: respiratory bronchioles, alveolar ducts, alveoli.

What happens during the contracted stage of diaphragm movement?

Contracted Diaphragm:

Atm = 760mm Hg

Alveolar volume increases – 759mm Hg

Pleural cavity volume increases – 754mm Hg

Intrapleural pressure decreases

Air in (500mL)

Interpulmonary pressure decreases

What happens during the relaxed stage of diaphragm movement?

Relaxed Diaphragm:

Atm = 760mm Hg

Alveolar volume decreases – 761mm Hg

Intrapulmonary pressure increases

Pleural cavity volume decreases – 756mm Hg

Intrapleural pressure increases

Air out (500mL)

How has inspiratory muscle training been shown to improve respiratory function in those with spinal cord injuries?

Increase inspiratory muscle strength & reduce dyspnoea

Diaphragm thickness (22%), Maximal inspiratory pressure (11%), Wpeak (16%) & VO2peak (22%)

What is Inspiratory reserve volume

Maximum volume of air that can be inhaled

what is expiratory reserve capacity

Maximum volume of air that can be exhaled

What is residual volume

volume of air remaining in the lungs after maximal exhalation

What is inspiratory capacity

volume of air that can be inspired at the end of passive expiration

What is functional residual capacity

volume of air present in the lungs at the end of passive expiration

What is total lung capacity

6L

What is the pneumotaxic area?

Superior pons and medulla rhythmicity area that helps regulate the rate and pattern of breathing by inhibiting inspiration to stop lungs becoming too full with air

What is the apneustic area?

Area in the lower pons that promotes prolonged inspiration by stimulating the inspiratory neurons, contributing to slower, deep breathing. Coordinates between inspiration and expiration.

What is the premise for use of the apneustic area

Only occurs when Pneumotaxic area is inactive, Apneustic is overridden by Pneumotaxic

What are the components of the medulla respiratory centres?

rhythmicity area, ventral group, dorsal group

What are the components of breathing dictation?

1.     Voluntary control via motor cortex

2.     Involuntary control via feedback

What are features of central chemoreceptors?

Only co2 diffuses across, stimulated by high PCO2 or low pH

What are features of peripheral chemoreceptors - carotid body?

Glossopharyngeal (CN9), Sensitive to decreases in the partial pressure of oxygen (PO2 )

What are features of peripheral chemoreceptors - aortic body?

Vagus (CN10), Measures changes in BP

What are respiratory stretch receptors and how are they activated?

By overinflation of the lungs. Inhibitory discharge sent to inspiratory area

1. Expiration begins

2. Lungs deflate

What are the atrioventricular valves?

Mitral (bicuspid) valve, Tricuspid valve

What are the semilunar valves?

Aortic, Pulmonary

What are the phases of the diastole cardiac cycle?

Relaxation phase – 75% blood entry, 25% blood entry when atria contracts

Fills blood with atria when atria pressure > ventricular (= AV valves are open)

What are the phases of the systole cardiac cycle?

Contraction phase- pressure in ventricles rises & semi-lunar valves open

Blood enters pulmonary & systemic circulation when ventricular pressure>aortic

What does the ‘lub’ sound of the heart signify?

closing of AV valve

What does the ‘dub’ sound of the heart signify?

closing of SL valve

What are the components of the SA node?

Anterior Internodal Tract

Middle Internodal Tract

Posterior Internodal Tract

Bachmann’s Bundle

What are the components of the AV node?

Bundle branch

Conduction pathways

What does the P wave signify?

Atrial depolarisation

What does the T wave signify?

Ventricular repolarisation

What does the QRS complex signify?

Ventricular Depolarisation, Hides Atrial Repolarisation

What are determinants of BP?

1.     Blood Volume

2.     Peripheral resistance

3.     Blood viscosity

4.     Stroke volume

5.     HR