Circulation | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Heart Physiology Simplified

• Heart as a Pump:
  • The heart is a central organ in the circulatory system.
  • It acts as a muscular pump to ensure continuous blood circulation.
• Heart Structure:
  • Cone-shaped and muscular.
  • Comprises four chambers: right and left atria, right and left ventricles.
• Blood Circulation:
  • Right atrium receives venous blood, directs it to the right ventricle.
  • Right ventricle pumps blood to the lungs for oxygenation.
  • Left atrium receives oxygenated blood from the lungs.
  • Left ventricle pumps oxygen-rich blood into the body's circulation through the aorta.
• Cardiac Skeleton:
  • Non-contractile structures binding the heart's muscular parts.
  • Composed of dense connective tissue, located around large vessels at the heart's base.
• Chamber Walls and Pressures:
  • Atria have thin walls, low intra-atrial pressures.
  • Left ventricular wall is thicker than the right, with higher ventricular pressures.
  • Muscle fibers in ventricles have unique organization influencing contraction.
• Valves and Blood Flow:
  • Tricuspid valve in the right atrium-ventricle connection.
  • Mitral valve in the left atrium-ventricle connection.
  • Pulmonary valve and Aortic valve regulate blood flow from ventricles to lungs and body.

Cardiac Cycle Simplified

• Definition:
  • The cardiac cycle spans from atrial depolarization initiation to the next atrial depolarization.
  • Divided into systole (contraction) and diastole (relaxation) periods.
• Systole (Contraction): Three phases during intraventricular pressure recordings:
  • Isovolumetric ventricular contraction.
  • Rapid ventricular ejection.
  • Reduced ventricular ejection.
• Diastole (Relaxation):
  • Four phases during intraventricular pressure recordings:
  • Isovolumetric ventricular relaxation.
  • Rapid ventricular filling.
  • Slow ventricular filling (diastasis).
  • Ventricular filling assisted by atrial contraction.
• Cycle Measurement:
  • Starts from ventricular contraction to the beginning of the next.
  • Includes electric, acoustic, pressure, flow, and volume changes.
• Phases:
  • Two principal phases: ventricular contraction and ventricular relaxation.
  • Contraction phase is slightly affected by heart rate changes.
  • Relaxation phase shortens during cardiac acceleration.
• Beat Initiation:
  • Sinoatrial node, a pacemaker in the right atrium, determines the beat interval.
  • Cardiac cycle initiated by depolarization waves in the atrium, seen as the P wave in ECG.
• Events During Cycle:
  • Atrial contraction begins with the P wave, leading to A-V valve opening and blood ejection.
  • Atrial systole has a pressure rise known as the 'a' wave.
  • Ventricular or cardiac systole is from A-V valve closure to semilunar valve closure.
  • Ventricular or cardiac diastole is from semilunar valve closure to A-V valve closure in the next cycle.

Heart Sounds Simplified

• Generation of Sounds:
  • Normal heart contractions create vibrations.
  • Placing ear or stethoscope on the chest captures audible heart sounds.
• Types of Heart Sounds:
  • Each heartbeat produces two main sounds: lub-dub.
  • Additional sounds may occur: third and fourth heart sounds.
• Timing and Causes:
  • First Sound (lub):
    • Occurs as ventricular systole begins.
    • Caused by closure of atrioventricular (A-V) valves.
  • Second Sound (dub):
    • Occurs at the end of ventricular systole.
    • Caused by closure of semilunar valves.
  • Third Sound (S):
    • Occurs early in ventricular diastole.
    • Associated with rapid ventricular filling.
  • Fourth Sound (S):
    • Precedes the second sound (dub).
    • Associated with atrial systole.
• Characteristics: First sound is longer and lower pitched than the second sound.
• Categorization of Sounds:
  • Heart sounds can be normal or abnormal.
  • Normal sounds: lub-dub, third and fourth heart sounds.
  • Abnormal sounds categorized as transients or murmurs.
  • Transients: brief sounds during the cardiac cycle.
  • Murmurs: prolonged vibrations during silent intervals in the cardiac cycle.

[Question: 968286]

Heart Beats and Blood Pressure

• Influence on Blood Pressure:
  • Heartbeat affects blood pressure regulation.
  • Three factors influencing blood pressure: peripheral resistance, artery elasticity, and volume of flow.
• Systole and Diastole:
  • Systole (Heart Contraction):
    • Arterial pressure increases.
    • Blood rapidly enters arteries, exceeding drainage rate through arterioles.
    • Arterial pressure rises.
  • Diastole (Heart Relaxation):
    • Arterial pressure decreases.
    • Blood passes through arterioles into capillaries.
    • Arterial pressure falls.
• Heart Rate Impact:
  • Increased heart rate raises blood pressure.
  • Decreased heart rate lowers blood pressure.
  • The effect depends on constant factors like peripheral resistance, artery elasticity, and flow volume.
  • Opposing variations in rate and amplitude may nullify each other, causing no change in blood pressure.

Electrocardiogram (ECG) Simplified

• Purpose:
  • ECG records electrical potential differences during heart depolarization and repolarization.
• Factors Influencing ECG: Requires information on:
  • Geometry of heart's resting and active boundary.
  • Heart position in the thorax and body volume.
  • Electrode position on the body surface.
• P Wave and A-V Conduction Time:
  • During atrial depolarization, the small P wave appears.
  • PQ interval, from P wave onset to QRS complex onset, represents A-V conduction time.
  • Includes conduction over A-V node, atria, and Purkinje fibers.

Heart Excitation and Work Simplified

Heart Excitation

• Excitation Path:
  • Starts from left ventricular endocardium, moves through the interventricular septum to the right.
  • Generates a small positive or negative wave.
  • Large depolarization fronts in hearts of certain animals like dogs, cats, primates, and rodents.
  • In ruminants, horses, swine, and birds, depolarization traverses the base of the interventricular septum from apex to base.
• Ventricular Depolarization:
  • For animals like dogs and cats, apico-basilar activity in the basilar third of the interventricular septum.
  • Results in a relatively high magnitude deflection.
• Ventricular Repolarization:
  • T wave represents ventricular repolarization.
  • Low magnitude and rate of voltage change.

Work, Power, and Efficiency

• Pressure-Volume Work:
  • Product of ejected blood volume and resistance against which it is ejected.
  • Calculated using mean arterial pressure.
• Velocity Imparting Work:
  • Estimated as half the product of average velocity squared and the mass of blood.
• Total Work:
  • Sum of pressure-volume work and velocity imparting work.
  • Formula: W = PΔV + 1/2 * M * v².

Heart's Work and Efficiency Unveiled

• Kinetic Energy Expenditure:
  • Usually less than 5 percent of the heart's work equation.
  • Might rise to 20 percent under unusual conditioning.
• Pressure-Volume Work:
  • Left ventricle's work = Stroke volume (2 ml/kg) * Mean systemic arterial pressure (approx. 100 mm Hg) = 200 mm Hg ml/kg.
  • Right ventricle's work ≈ One-sixth of the left ventricle's, as it ejects against lower pulmonary arterial pressure (approx. 15 mm Hg).
  • Combined work of both ventricles = 7/6 times the left ventricle's work, around 230 units.
• Work Expression:
  • Often expressed as 7/8 * stroke volume * mean arterial pressure.
  • Units are considered dimensionally correct in gram centimeter.
• Efficiency Calculation:
  • Efficiency estimated by dividing thermal equivalent of useful work by potential work available from oxygen consumed.
  • Heart considered approximately 20 percent efficient as a mechanical pump.
• Power of the Heart:
  • Work per unit of time is power.
  • Stroke power, representing contraction vigor, is calculated by dividing stroke work by the duration of isotonic ejection.

Ions' Impact on Heart Function

• Resting Membrane Potential:
  • Dependent on Nn, K, and C1 ion distribution and permeability across the cell membrane.
  • Action potential characterized by depolarization and repolarization.
• Ion Effects on Heart:
  • Potassium and sodium (to a lesser extent) have a depressing effect and favor diastole.
  • Calcium promotes systole; heart poisoning with calcium ions leads to systolic arrest or calcium rigor.
  • Studied by perfusing isolated hearts with ion-containing fluid.

Cardiac Muscle Metabolism

• Syncytial Function:
  • Cardiac muscle cells function syncytially.
  • Nodal and Purkinje cells, specialized for action potential, lack contractile properties.
  • Nodal cells in sinoatrial and atrioventricular nodes; Purkinje cells in ventricular septum (Bundle of His).
• Pacemaker - Sinoatrial Node:
  • Sinoatrial node acts as the pacemaker, initiating spontaneous rhythmic contractions.
  • Action potentials generated here, transmitted across the Bundle of His.
  • Heart's ability for spontaneous depolarization waves termed chronotropism.
• Electrocardiogram (ECG):
  • Records electrical charge alternations in various body parts due to heart's electrical activity.
  • Essential for assessing heart health.
• Cardiac Output:
  • Volume of blood each ventricle ejects.
  • Expressed as stroke volume (ml/beat) or minute volume (ml/min).
  • Corrected for body weight (ml/kg/min) or body surface area as cardiac index (ml or Veq m/min).

[Question: 968288]

Nervous and Chemical Control of the Heart

Regulatory Mechanisms

• Extrinsic Regulation:
  • Involves external factors like nerves and hormones.
  • Sympathetic activation increases heart force and rate, while parasympathetic activation has the opposite effect.
  • Agents affecting contraction without altering fiber strain are termed inotropes.
• Intrinsic Regulation:
  • Involves autoregulation without external influence.
  • Heterometric: Alters force by changing fiber length.
  • Homeometric: Alters force without changing fiber length.

Autonomic Nervous System

• Sympathetic Activation:
  • Increases heart force and rate.
  • Originates from the hypothalamus, releasing norepinephrine via adrenal medulla.
  • Augments nerves play a role in heart rate control.
• Parasympathetic Activation:
  • Cardioinhibitory fibers in vagus nerves.
  • Preganglionic fibers with a negative chronotropic effect (slows heart rate).
  • Directly depresses atrial contraction (negative inotropic effect).

Effect of Temperature and Stress on the Heart

• Temperature Impact:
  • Regulated by homeostasis, ensuring balance in high or low temperatures.
  • Physiological and pathological cardiovascular responses to stress involve complex reflex mechanisms.
  • Neural reflexes in the central nervous system (CNS) can be modified based on stimuli and environmental factors.
• Stress on the Heart:
  • Cardiovascular reactions to stimuli like fear, anxiety, hypoxia, and temperature changes.
  • Neural systems adapt cardiovascular function to specific circumstances and stimuli.
  • Discreteness and differentiation of the nervous system are evident in responses like blushing, blood flow redistribution, and cardiac arrhythmias.
  • Intense or sustained adaptation reactions may indicate signs of disease.

Blood Pressure and Hypertension

• Blood Pressure Overview:
  • Force exerted on blood vessel walls, usually measured in mm Hg.
  • Pressure gradient exists from aorta to the right atrium, influencing blood flow.
  • Arterioles are the main site of resistance in the systemic circuit.
• Blood Pressure Measurements:
  • Pressure in arteries fluctuates during the cardiac cycle.
  • Systolic pressure is the peak, diastolic is the minimum, and pulse pressure is the difference between them.
  • Mean arterial pressure is an intermediate value, closer to diastolic pressure.
  • Two methods: direct (using catheter) and indirect (using a cuff and sphygmomanometer).
• Hypertension:
  • Persistently high blood pressure leading to heart disease.
  • Three types: essential hypertension, malignant hypertension, and hypertension associated with organic diseases (nephritis, arteriosclerosis).

Influences on Blood Pressure

• Factors Affecting Blood Pressure:
  • Heartbeat, peripheral resistance, arterial elasticity, and blood flow volume play roles in blood pressure regulation.
• Osmotic Regulation:
  • About two-thirds of body weight is water, distributed between intracellular and extracellular fluids.
  • Hydrostatic and colloid osmotic pressures, influenced by plasma proteins, sodium, and potassium, govern water distribution.
  • Oncotic pressure, a result of plasma proteins, restrains fluid movement from plasma to interstitial fluid.
• Na (Sodium) Regulation:
  • Na concentration controls 90% of osmotic pressure, influencing body fluid osmolality.
  • Osmo Na receptors, antidiuretic hormone, thirst mechanism, and aldosterone help regulate Na-dependent osmolality.
  • Various mechanisms involving dissolved solutes work to maintain total body fluid and osmolality.
• Arterial Pulse:
  • Pulse is the wave of expansion and elongation originating at the aorta's root due to varying aortic pressure during each heart beat.
  • The pulse travels through the arterial system and disappears at arterioles.
  • Left ventricular contraction forces blood into the aorta. Two ways accommodate the discharged blood: moving the entire blood mass forward or stretching arterial walls to accommodate new blood.

Vasomotor Regulation of Circulation

• Arterial Pulse:
  • The pulsating expansion and recoil of arterial walls transmit pulse waves, originating at the aorta and moving through the arteries.
  • Pulse reflects the distension and recoil of arterial walls.
• Vasomotor Regulation:
  • Deals with maintaining the caliber (diameter) of smaller blood vessels and ensuring blood supply to body tissues.
  • Involves various influences like nervous and chemical factors that alter blood vessel caliber.
  • Aims to regulate blood flow through tissues, control peripheral resistance, maintain blood pressure, and shift blood supply based on organ demands.
• Neural Control:
  • Vasomotor or arteriomotor nerves play a crucial role.
  • Two types: vasoconstrictor (narrows vessels) and vasodilator (widens vessels).
  • Vasomotor centers in the brain, originating nerves along the spinal cord, regulate vessel diameter.
• Vasoconstrictor Center:
  • Bilateral center between the pons and upper spinal cord.
  • Constrictor fibers descend in the spinal cord's lateral funiculus.
  • Tonus (baseline activity) is influenced by factors like increased carbon dioxide and continuous afferent impulses.
  • Subsidiary vasoconstrictor centers in the spinal cord under higher centers' control.
• Vasodilator Center:
  • Located bilaterally near vasoconstrictor centers.
  • Primarily involved in generalized vasodilation.
  • Stimulation leads to reciprocal inhibition of constrictor centers, causing a blood pressure drop.
• Vasomotor Reflexes:
  • Pressor reflex raises blood pressure, responding to reflex stimulation.
  • Depressor reflex lowers blood pressure in response to a decrease.
  • Other reflexes from the hypothalamus, cerebral cortex, cutaneous areas, chemoreceptors, and intestines affect vasomotor centers.
• Nerve Origin and Function:
  • Vasoconstrictor nerves from vasomotor center supply head, neck, limbs, lungs, coronary arteries, abdominal and pelvic organs, and hindlimbs.
  • Vasodilator nerves include cholinergic (parasympathetic) and adrenergic (sympathetic) fibers.
  • Sympathetic vasodilator fibers from the motor cortex have cholinergic and adrenergic components.

Circulatory Shock: Causes and Characteristics

Definition of Shock

• Circulatory shock is a condition marked by a severe lack of blood perfusion to tissues, often following injury.
• It results in low blood pressure, widespread tissue hypoperfusion, and oxygen deficiency.

Types of Shock

• Hypovolemic Shock: Caused by a significant loss of blood (more than 30% of total blood volume), as seen in trauma or severe dehydration.
• Cardiogenic Shock: Resulting from heart-related issues, such as a heart attack (myocardial infarction).
• Septic Shock: Triggered by severe infections, activating various pressor mechanisms.
• Traumatic Shock: Occurs due to local loss of plasma in injured areas.
• Anaphylactic Shock: Arises from severe allergic reactions, causing peripheral circulatory failure.

Clinical Signs of Shock

• Cold Skin: Exposed areas feel cold due to blood vessel constriction.
• Pale and Cyanotic Mucous Membranes: Visible membranes lack color due to reduced blood flow.
• Rapid Breathing: Increased breathing rate.
• Small, High-Pitched Pulse: Pulse is small in amplitude and elevated in rate.
• Dilated Pupils: Enlarged pupils, sometimes with lacrimation.
• Body Temperature Drop: A decrease in body temperature is observed.

Causes and Therapeutic Approaches

• Septic Shock: Initiated by acute septicemia, may involve hypovolemia.
• Cardiogenic Shock: Linked to myocardial infarction (heart attack).
• Hemorrhagic Shock: Irreversible or reversible hypovolemic shock due to significant bleeding.
• Traumatic Shock: Resulting from localized loss of plasma in injured areas.
• Anaphylactic Shock: Caused by severe allergic reactions.

Management

• Treatment varies based on the type of shock.
• Septic Shock: Requires surgical drainage and antibacterial therapy.
• Cardiogenic Shock: May involve the use of medications like digitalis.
• Anaphylactic Shock: Treatment often includes epinephrine.
• Hemorrhagic Shock: Involves volume replacement.

[Question: 968287]

Coronary and Pulmonary Circulation Simplified

Coronary Circulation

• Heart Muscle Blood Supply:
  • The heart muscle receives blood through two vessels: the right coronary artery and the left coronary artery.
  • Blood circulation begins at the coronary orifices in the aorta, connecting to the ventricular muscle.
• Arterial Network:
  • Arteries branch into numerous capillaries within the heart muscle, ensuring sufficient blood supply.
  • Capillaries eventually reunite to form coronary veins.
• Venous System:
  • Two main parts: a superficial network and a deep vein system.
  • The coronary sinus, part of the superficial system, drains most of the left heart, while anterior cardiac veins drain the right heart.
  • The deep system includes arterioluminal, arteriocapillary, and Thebesian systems, draining directly into heart chambers.
• Communication with Aorta:
  • Orifices in the aorta allow continuous communication during both heart contraction (systole) and relaxation (diastole).
  • In some animals, the left coronary artery is more critical, while in mammals, including humans, the right coronary artery is more developed.

Pulmonary Circulation

• Blood Flow to Lungs:
  • Pulmonary circulation involves blood flow between the heart and the lungs.
• Right Side of the Heart:
  • Deoxygenated blood from the body enters the right atrium.
  • It then moves to the right ventricle, which pumps it to the lungs via the pulmonary artery.
• Gas Exchange in Lungs:
  • In the lungs, oxygen is taken in, and carbon dioxide is released.
• Left Side of the Heart:
  • Oxygenated blood returns to the left atrium through the pulmonary veins.
  • From the left atrium, it goes to the left ventricle, which pumps it out to the rest of the body.

Blood-Brain Barrier Simplified

• Specialized Barrier:
  • The central nervous system (CNS) has limited fluid.
  • A unique structure, the blood-brain barrier (BBB), controls the movement of substances between the blood and CNS cells.
• BBB Location:
  • Astrocytes, a type of glial cell in the CNS, house the BBB.
  • Capillaries in the CNS are covered with astrocyte processes.
• Material Transport:
  • Materials move from capillaries to the CNS interstitial space.
  • Some substances directly reach nerves, while others enter astrocyte processes.
  • Astrocytes transport materials to neurons through their processes.
• Selective Entrance:
  • Astrocytic cells act as a medium for material transport from blood to CNS neurons.
  • Selectivity is maintained, allowing lipid-soluble substances to pass rapidly, while water-soluble materials are mostly restricted to the CNS extracellular space.
• Functional Importance:
  • BBB creates a functional barrier between blood and brain.
  • Crucial for nutrient utilization by the brain, drug effectiveness, and protection against the harmful effects of viruses and toxins on brain tissue.

Cerebrospinal Fluid Simplified

• Complete CNS Coverage:
  • Cerebrospinal fluid (CSF) surrounds the brain and spinal cord, acting as a protective cushion.
• Functions:
  • Cushions and supports the central nervous system.
  • Provides essential nutrients.
  • Acts as a drainage system for metabolic waste products from the CNS.
• Formation:
  • Produced by choroid plexuses in the brain's ventricles.
  • Different from blood plasma due to selective permeability.
  • Ultrafiltrate of blood, with lower protein concentrations.
• Composition:
  • Watery and thin, resembling a 'neural urine.'
  • Low protein content; higher sodium, chloride, and magnesium; lower potassium, calcium, urea, and glucose compared to plasma.
  • Similar pH to plasma; usually lacks cellular elements.
• Cushioning Role:
  • Fills spinal cord canal, brain ventricles, and subarachnoid space, providing a cushion for the brain and spinal cord.
  • Balances changes in blood volume within the cranium to maintain constant cranial content.
• Chemical Composition in Cattle (mg/100 ml):
  • Calcium: 5.1-6.3
  • Chloride: 650-725
  • Potassium: 11.2-13.8
  • Total Protein: 16-33
  • Creatinine: 1.4
  • Non-protein Nitrogen: 16
  • Urea Nitrogen: 10.8
  • Glucose: 35-70
• Pressure and Production:
  • Normal pressure: 110-175 mm of H2O.
  • Continuously produced at a rate of 0.1-0.3 ml per minute.
  • Average CSF volume in humans: 60-80 ml.

Bird Circulation Simplified

• Heart Position:
  • The heart in birds is situated in the cranial part of the body cavity, beneath the sternum, within the pericardium.
• Heart Structure:
  • Avian hearts closely resemble mammalian hearts.
  • Notable difference: Thick muscular fold in the right atrioventricular valve, distinct from mammals.
• Blood Flow:
  • Venous blood returns to the right atrium via three vena cavae.
  • Oxygenated blood from lungs returns through a single pulmonary vein.
  • Left ventricle powers high-pressure systemic circulation, thicker than the right ventricle.
  • Normally, two coronary arteries exist, with the right one dominant.
• Veins and Blood Return:
  • Four major veins return blood from the myocardium to the right atrium.
  • Dorsal cardiac vein is the largest.
  • Left cardiac vein is the second largest.
  • Additional routes for venous blood return have been described.
• Node System:
  • Sinoatrial and atrioventricular nodes, atrioventricular bundle, and branches in birds resemble mammalian systems.
  • Some birds may have a third node (truncobialbar).
• Blood Distribution:
  • Blood volume remains constant but varies in distribution based on tissue metabolic activity.
  • Left side acts as the "Pressure Pump," handling pressure changes.
  • Right side functions as the "Volume Pump," handling variable blood volumes.
• Blood Pressure:
  • Blood pressure varies with age, sex, breed, and health state.
  • Average: 168 mm Hg (systolic), 136 mm Hg (diastolic), with a pulse pressure of about 30 mm Hg.
• Heartbeat Frequency:
  • Adult fowl heartbeat ranges from 350 to 450 beats per minute.
• Cardiac Output:
  • Varies among bird species; in chickens, it's about 250 to 280 ml per minute.

Major Arteries and Veins in Birds Simplified

Major Arteries

• Aorta: Main artery originating from the heart.
• Coronary Arteries: Left and right coronary arteries supplying the heart muscle.
• Brachiocephalic Trunks: Supplying blood to various parts including flight muscles, wings, and thoracic spaces.
• Subclavian Artery: Branching from the ascending aorta, supplies pectoral and brachial arteries.
• Internal Thoracic Artery: Supplies cranial body cavity and ventral intercostal spaces.
• Common Carotid Artery: Short artery supplying structures in the head and neck.
• Vertebral and Vagus Arteries: Supplying structures in the neck, forming anastomoses with the occipital artery.
• Internal Carotid Artery: Continuing from the common carotid, terminates in external ophthalmic and cerebral carotid arteries.
• Intercarotid Anastomoses: Avian counterpart of mammalian circle of Willis, providing collateral blood supply to the brain.

Descending Aorta

• Branching into left and right pulmonary arteries, supplying various body parts along its course.
• Cranial Aorta Structure: Different from caudal aorta, efficiently resisting over-dilation and preventing atherosclerosis.
• Caudal Aorta: Becomes less elastic, more muscular, and prone to atherosclerosis after the cranial mesenteric artery.

Veins

• Generally parallel to arteries.
• Alimentary Canal Drainage: Drains into hepatic portal and renal portal systems.
• Hepatic Veins: Connect to the posterior vena cava, a short distance below the heart.
• Structure: Veins have similar layers as arteries but greater innervation, with nerves penetrating the entire thickness.

Cardiac Features

• Atrial Subendocardial Purkinje Fibre System: Present in the avian heart.
• Purkinje Fibre System of Muscular A-V Valve: Present in the muscular right atrioventricular valve.