Human Physiology: Body Fluids and Circulation

Comprehensive practice flashcards covering human circulatory pathways, blood composition, hematology, cardiac anatomy, nodal conduction, the cardiac cycle, ECG interpretations, vascular histology, neural/endocrine regulation, and cardiovascular pathologies.

From which embryonic germ layer does body fluid originate, and in which phylum was a well-developed circulatory system first observed?

Body fluid originates from the mesoderm, and a well-developed circulatory system (consisting of heart and blood) was first seen in the phylum Annelida.

What are the two major components of blood and their relative percentages in total blood volume?

Blood consists of Plasma ($55\%$) and Formed Elements ($45\%$).

What are the three major plasma proteins, their total percentage in plasma, and their individual primary functions?

Proteins make up $6\text{--}8\%$ of plasma and include: Albumin (maintains blood osmolarity), Globulin / Immunoglobulin (defense and antibody formation), and Fibrinogen (inactive clotting factor involved in blood coagulation).

What is blood serum, and what clinical condition results from a deficiency of plasma proteins?

Serum is defined as plasma without clotting factors ($\text{Serum} = \text{Plasma} - \text{clotting factors}$). A deficiency of plasma proteins leads to edema.

What are the normal values for erythrocyte count, lifespan, graveyard organ, and hemoglobin content in human blood?

Red blood cells (RBCs) have a count of $5\text{--}5.5\text{ million per }mm^3$, a lifespan of approximately $120\text{ days}$ ($\sim 4\text{ months}$), are destroyed in the spleen (the RBC graveyard), and contain $12\text{--}16\,g$ of hemoglobin per $100\,ml$ of blood.

What mnemonic lists the relative percentages of human leukocytes from most to least abundant?

"Never Let Me Enter Beaches": Neutrophils ($60\text{--}65\%$), Lymphocytes ($20\text{--}25\%$), Monocytes ($6\text{--}8\%$), Eosinophils ($2\text{--}3\%$), and Basophils ($0.5\text{--}1\%$).

Which white blood cells are classified as granulocytes versus agranulocytes, and what are their respective nuclear shapes?

Granulocytes include Neutrophils (multilobed/PMNL), Basophils (S-shaped nucleus), and Eosinophils (bilobed/headphone-like nucleus). Agranulocytes include Monocytes (kidney/bean-shaped nucleus) and Lymphocytes (round nucleus).

What chemical substances are secreted by basophils, and what are basophils called when situated within tissues?

Basophils secrete Histamine, Heparin, and Serotonin during inflammation; in tissues, they are referred to as mast cells.

What cell type gives rise to blood platelets, and what is the normal platelet count in healthy human blood?

Platelets (thrombocytes) are cell fragments formed from megakaryocytes in the bone marrow, with a normal count of $1.5\text{ lac}\text{--}3.5\text{ lac per }mm^3$ ($150{,}000\text{--}350{,}000\text{ per }mm^3$).

Why is blood group $O$ considered the universal donor and blood group $AB$ the universal recipient in the ABO grouping system?

Group $O$ RBCs lack both $A$ and $B$ surface antigens, so they will not be attacked by recipient antibodies. Group $AB$ plasma contains neither Anti-$A$ nor Anti-$B$ antibodies, so it will not attack incoming donor RBC antigens.

What causes Erythroblastosis Foetalis, and how is it clinically prevented?

It occurs when an $Rh^{-}$ mother carries a second $Rh^{+}$ fetus after being sensitized during the delivery of her first $Rh^{+}$ child, causing maternal anti-$Rh$ antibodies to cross the placenta and destroy fetal RBCs (leading to severe anemia and jaundice). It is prevented by administering an external injection of anti-$Rh$ antibodies immediately after the first delivery.

What is the biochemical cascade responsible for blood clot formation following vascular injury?

Platelets and damaged tissues activate the enzyme complex thrombokinase, which converts prothrombin to active thrombin in the presence of $Ca^{2+}$. Thrombin then converts soluble fibrinogen into insoluble fibrin monomers, forming a mesh that traps dead and damaged formed elements to produce a clot (coagulum).

What are plasma clotting factors I, II, III, and IV?

Factor I is Fibrinogen, Factor II is Prothrombin, Factor III is Thromboplastin, and Factor IV is Calcium ($Ca^{2+}$).

What is the pathological distinction between a thrombus and an embolus?

A thrombus is an internal, stationary blood clot attached to a vessel wall, whereas an embolus is a detached, circulating or moving clot.

What is the composition and primary function of lymph (tissue fluid)?

Lymph is colorless fluid with the mineral composition of plasma but lacking large proteins and erythrocytes; it contains specialized lymphocytes, collects trapped interstitial fluid and waste, transports nutrients and hormones, and absorbs dietary fats via lacteals in intestinal villi.

How do the heart structures and circulatory pathways differ among fishes, amphibians/reptiles, and mammals/birds?

Fishes have a 2-chambered venous heart ($1\text{ atrium} + 1\text{ ventricle}$) with single circulation; amphibians and reptiles have a 3-chambered arterio-venous heart ($2\text{ atria} + 1\text{ ventricle}$) with incomplete double circulation and mixed blood; mammals, birds, and crocodiles have a 4-chambered heart ($2\text{ atria} + 2\text{ ventricles}$) with complete double circulation and no mixing of blood.

What is the functional role of the chordae tendineae and papillary muscles in the human heart?

They anchor the cuspid (atrioventricular) valves to the ventricular walls, preventing the valve flaps from eversion or reopening into the atria during ventricular systole, thereby preventing backflow.

What is the anatomical route of an electrical action potential through the heart's specialized nodal conduction system?

SA node $\rightarrow$ AV node $\rightarrow$ AV bundle (Bundle of His) $\rightarrow$ Right and Left bundle branches $\rightarrow$ Purkinje fibres.

Why is the Sino-Atrial (SA) node designated the 'pacemaker' while the Atrioventricular (AV) node is termed the 'pacesetter'?

The SA node initiates impulses at the highest intrinsic frequency ($70\text{--}75\text{ action potentials per minute}$), setting the heart's rhythm. Because the fibrous AV septum blocks direct electrical spread, the AV node must pick up the impulse and generate a fresh signal to conduct through the ventricles.

What are the three phases of the human cardiac cycle and their respective durations in a typical $0.8\text{-second}$ cycle?

Joint Diastole ($0.4\text{ sec}$, where all four chambers relax and $70\%$ of ventricular filling occurs passively), Atrial Systole ($0.1\text{ sec}$, which adds the remaining $30\%$ of blood to ventricles), and Ventricular Systole ($0.3\text{ sec}$, where ventricles contract to eject blood).

What mechanical events cause the first ('Lub') and second ('Dub') heart sounds?

'Lub' (first sound) is caused by the closure of the atrioventricular (cuspid) valves at the beginning of ventricular systole. 'Dub' (second sound) is caused by the closure of the semilunar valves at the end of ventricular systole.

How are stroke volume and cardiac output calculated in a healthy resting adult?

$\text{Stroke Volume} = \text{End-Diastolic Volume } (120\,ml) - \text{End-Systolic Volume } (50\,ml) = 70\,ml$. $\text{Cardiac Output} = \text{Stroke Volume } (70\,ml) \times \text{Heart Rate } (72\,beats/min) \approx 5040\,ml/min$ ($\approx 5\,litres/min$).

What electrical cardiac events are represented by the P wave, QRS complex, and T wave on a standard electrocardiogram (ECG)?

The P wave represents atrial depolarisation (leading to atrial contraction); the QRS complex represents ventricular depolarisation (masking atrial repolarisation; ventricular contraction starts right after Q); the T wave represents ventricular repolarisation (marking the end of ventricular systole).

What clinical defects are indicated by an extended QRS complex and a flat T wave on an ECG?

An extended QRS complex indicates low $O_2$ supply to the ventricles, while a flat T wave indicates myocardial infarction.

What are the three concentric tissue layers found in arteries and veins, and how do capillaries differ?

Arteries and veins have three layers: Tunica intima (innermost simple squamous epithelium/endothelium), Tunica media (middle smooth muscle and elastic fibres), and Tunica externa (outermost fibrous connective tissue with collagen). Capillaries consist only of a single-layered Tunica intima (endothelium).

How do sympathetic and parasympathetic nerves from the medulla oblongata regulate cardiac function?

Sympathetic nerves (via adrenaline/noradrenaline) increase heart rate, conduction velocity, stroke volume, contraction strength, and blood pressure. Parasympathetic nerves (via acetylcholine) decrease heart rate, conduction velocity, stroke volume, contraction strength, and blood pressure.

What is the hepatic portal system, and what is its biological arrangement?

A vascular system where deoxygenated, nutrient-rich blood from the digestive tract (intestines) travels through the hepatic portal vein to the capillary bed of the liver before entering the general systemic circulation to the heart.

What is the difference between atherosclerosis and arteriosclerosis?

Atherosclerosis is the narrowing of the coronary arterial lumen due to the deposition of cholesterol, calcium, fat, and fibrous tissue ($C^2F^2$). Arteriosclerosis is the hardening and loss of elasticity of the arterial wall caused by calcium deposition within the tunica media.

What defines angina pectoris, what are its symptoms, and what clot-dissolving agent can be administered?

Angina pectoris is acute chest pain and heaviness caused by insufficient oxygen supply to the heart musculature (due to a clot/embolus or plaque). Symptoms include chest heaviness radiating to the left arm; it can be treated using the clot buster Streptokinase (produced by GMO) or aspirin/Disprin.

How do heart failure, cardiac arrest, and myocardial infarction (heart attack) differ clinically?

Heart failure occurs when the heart cannot pump sufficient blood to meet body demands (often causing pulmonary congestion). Cardiac arrest occurs when the heart abruptly ceases all pumping and beating. Myocardial infarction (heart attack) involves sudden necrosis/damage of a localized patch of heart muscle due to inadequate blood and oxygen supply.