Structure and function of heart Questions in English

(C) The venous system returns deoxygenated blood from the body tissues to the heart. In humans,the superior vena cava and the inferior vena cava are the two major veins that collect blood from the upper and lower parts of the body,respectively,and drain it into the right atrium of the heart. Therefore,the vena cavae are responsible for bringing blood to the heart.

(D) In many vertebrates,such as the rabbit,the pre-caval veins (also known as anterior vena cavae) are formed by the union of the external jugular vein and the subclavian vein on each side.
These veins collect deoxygenated blood from the anterior parts of the body,including the head,neck,and forelimbs,and drain it into the right atrium of the heart.

(B) The post-caval vein,also known as the inferior vena cava,is a large vein that carries deoxygenated blood from the lower parts of the body back to the heart.
It collects blood from the hind limbs,the pelvic region,the abdominal organs (including the kidneys and liver),and the trunk.
Therefore,it collects blood from both the hind limbs and the organs of the body cavity.

(C) The pre-caval veins,also known as the superior vena cava,are responsible for collecting deoxygenated blood from the anterior parts of the body,which include the head,neck,forelimbs,and the upper thoracic region. Therefore,the correct option is $C$.

(A) In the embryonic stage, the inter-auricular septum (the wall between the two atria) contains an opening called the $Foramen \text{ ovale}$. This opening allows blood to bypass the non-functional fetal lungs by flowing directly from the right atrium to the left atrium. After birth, this opening typically closes and becomes a shallow depression known as the $fossa \text{ ovalis}$.

(C) The Bundle of His (also known as the atrioventricular bundle) is a specialized collection of modified cardiac muscle fibres.
These fibres originate from the atrioventricular node $(AVN)$ and pass through the interventricular septum.
They are responsible for conducting electrical impulses from the atria to the ventricles,ensuring coordinated contraction of the ventricular walls.
Therefore,they are muscle fibres located specifically within the ventricular region.

(D) The sinus venosus is a large,thin-walled sac that acts as a receiving chamber for deoxygenated blood from the body in lower vertebrates like frogs. It collects blood from the systemic veins and opens into the right auricle (atrium) of the heart. Therefore,option $D$ is the correct statement.

(A) In mammals like rabbits,oxygenated blood from the lungs is carried by the pulmonary veins to the left auricle. During auricular systole (atrial contraction),the left auricle contracts,forcing the oxygenated blood through the bicuspid (mitral) valve into the left ventricle. Therefore,the flow of oxygenated blood from the left auricle to the left ventricle occurs during auricular systole.

(A) The electrical impulse in the heart originates at the $S-A$ node (sino-atrial node),which acts as the natural pacemaker.
From the $S-A$ node,the impulse is transmitted to the $A-V$ node (atrio-ventricular node).
Following this,the impulse travels through the Bundle of His and finally spreads through the Purkinje system to stimulate ventricular contraction.
The sequence is: $S-A$ node $\to$ $A-V$ node $\to$ Bundle of His $\to$ Purkinje system.

(B) The correct answer is $(b)$. The heart of an elephant,like all mammals,is myogenic. This means that the heartbeat is initiated by a specialized patch of modified cardiac muscle cells known as the sinoatrial node ($SA$ node),which acts as a pacemaker. It does not require external nerve stimulation to initiate the contraction of the heart muscle.

(D) . William Harvey ($1578-1657$ $AD$) explained many aspects of human physiology,one of which was the circulation of blood. He is also considered the 'father of blood circulation'.

(A) The $SA$ (Sino-Atrial) node is known as the natural pacemaker of the heart because it initiates the rhythmic contractile activity of the heart by generating action potentials.
If the $SA$ node becomes defective or fails to function properly,the heart's electrical conduction system is disrupted,leading to an irregular or slow heartbeat (bradycardia).
In such cases,an artificial pacemaker is surgically implanted to provide the necessary electrical impulses to maintain a normal heart rate.

(A) $Lubb$ is the first heart sound,which is low-pitched and produced due to the closure of the bicuspid and tricuspid $(AV)$ valves at the beginning of ventricular systole.
$Dupp$ is the second heart sound,which is high-pitched and produced due to the closure of the semilunar valves at the beginning of ventricular diastole.
Therefore,option $A$ is the only correctly matched pair.

(D) Purkinje fibres are specialized conducting fibres located in the inner ventricular walls of the heart.
They are composed of modified cardiac muscle cells that are larger than ordinary cardiomyocytes.
These fibres are responsible for the rapid conduction of electrical impulses from the $AV$ node to the ventricular myocardium,ensuring coordinated contraction of the ventricles.
Therefore,they are modified muscle cells.

(A) The $Sinuatrial$ $node$ $(SAN)$ is known as the natural pacemaker of the heart because it generates the rhythmic contractile impulses that initiate the heartbeat. When the natural pacemaker fails to function normally,an artificial pacemaker is implanted to maintain the heart's rhythm. This device is typically grafted at the site of the $Sinuatrial$ $node$ to effectively stimulate the heart muscle and restore normal cardiac function.

(B) The $SA$ node (Sinoatrial node) is located in the right atrium of the heart and is responsible for initiating the electrical impulses that cause the heart to contract. Because it sets the rhythm of the heartbeat,it is commonly referred to as the natural pacemaker of the heart.
- Malleus is a bone in the middle ear,while the anvil is the common name for the incus bone; they are distinct.
- Leucocytes are white blood cells (a general category),while lymphocytes are a specific type of white blood cell.
- Haemophilia is a genetic bleeding disorder,whereas blood cancer is known as leukaemia.

(D) The walls of the ventricles are thicker than those of the atria because they need to pump blood out of the heart.
Among the chambers,the left ventricle has the thickest wall because it is responsible for pumping oxygenated blood to the entire body through the aorta,which requires generating high pressure.

(D) Cardiac output is defined as the volume of blood pumped by the heart per minute.
It is calculated by the product of stroke volume and heart rate.
Mathematically, $\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$.
Therefore, both heart rate and stroke volume determine the cardiac output.

(A) The $SA$ node (Sinoatrial node) is known as the 'pacemaker' of the heart because it initiates the rhythmic contraction of the cardiac muscles.
Since it controls the heartbeat and sets the pace for the entire heart,it is often referred to as the 'Heart of Heart'.

(B) The human heart is protected by a double-walled membranous sac known as the $Pericardium$.
This sac consists of two layers: the outer fibrous pericardium and the inner serous pericardium.
The space between these two layers is called the pericardial cavity,which contains pericardial fluid.
This fluid reduces friction between the heart walls and the surrounding tissues during the contraction and relaxation of the heart.

(B) Thrombosis (the formation of a blood clot within a blood vessel) occurs most frequently in the $Left$ $anterior$ $descending$ $(LAD)$ artery.
This artery is a branch of the left coronary artery and supplies a significant portion of the left ventricle,which is the primary pumping chamber of the heart.
Due to its anatomical position and the high flow dynamics,it is the most common site for atherosclerotic plaque rupture and subsequent thrombus formation,leading to myocardial infarction.

(C) The pulse is a rhythmic expansion and recoil of an artery resulting from heart contraction.
It is most easily detected in superficial arteries that lie close to the skin and over a bone,such as the radial artery located at the $Wrist$.
Other common sites include the carotid artery in the neck or the temporal artery in the temple.

(C) Systole refers to the phase of contraction of the heart chambers. During ventricular systole,the ventricular muscles contract,which increases the pressure inside the ventricles. This pressure causes the semilunar valves to open,allowing blood to be pumped out of the ventricles into the aorta and the pulmonary artery. Therefore,blood leaves the ventricle.

(C) The brain is highly sensitive to oxygen deprivation. If the blood supply to the brain is interrupted, the supply of oxygen and glucose to the neurons is cut off. $A$ person typically becomes unconscious within $5$ to $10$ seconds of the cessation of cerebral blood flow, as the brain's limited energy reserves are rapidly depleted. Among the given options, $10$ seconds is the standard threshold cited in physiological contexts for the onset of unconsciousness.

(C) The total blood volume in the human body is distributed across various organs and vessels.
Approximately $9\%$ of the total blood volume is present within the heart at any given time.

(C) The $Spleen$ is a unique organ in the vertebrate circulatory system that receives blood exclusively from the systemic circulation via the splenic artery, which carries oxygenated blood.
Unlike the lungs (which receive deoxygenated blood from the heart via the pulmonary artery) or the liver (which receives a significant portion of blood from the hepatic portal vein), the spleen is supplied only by oxygenated arterial blood.

(A) The distribution of cardiac output to various organs in a resting human is approximately as follows:
$1$. Heart muscles receive about $5\%$ of the blood flow.
$2$. The brain receives about $15\%$ of the blood flow.
$3$. The liver and digestive tract receive about $25\%$ of the blood flow.
$4$. The kidneys receive about $25\%$ of the blood flow.
$5$. The skeletal muscles and bones receive about $15\%$ of the blood flow.
$6$. Other organs receive the remaining $15\%$ of the blood flow.
Therefore,option $A$ represents the most accurate physiological distribution.

(B) The liver is the primary site of the urea cycle,where ammonia produced from the deamination of amino acids is converted into urea.
Since the liver synthesizes urea,the blood leaving the liver via the hepatic vein contains the highest concentration of urea in the body.
In contrast,the renal vein carries blood away from the kidneys,which filter urea out of the blood,resulting in the lowest concentration of urea.

(A) The initiation of the heart beat is controlled by specialized bundles of cardiac muscles known as nodal tissue or autorhythmic cells.
This nodal tissue is composed of the $S.A.$ node,$A.V.$ node,the bundle of $His$,and Purkinje fibres.
Therefore,Purkinje fibres are a key component of the nodal tissue responsible for conducting electrical impulses through the heart.

(B) In a $4$-chambered heart,the heart is divided into two atria and two ventricles.
This complete separation ensures that oxygenated (arterial) blood and deoxygenated (venous) blood do not mix.
In contrast,$2$-chambered hearts (found in fish) have a single circulation where blood passes through the heart once,and $3$-chambered hearts (found in amphibians and most reptiles) allow for the mixing of oxygenated and deoxygenated blood in the single ventricle.

(C) During ventricular systole,the pressure increases in the ventricles. This contraction forces the deoxygenated blood from the right ventricle into the pulmonary artery,which carries it to the lungs for oxygenation. Simultaneously,oxygenated blood from the left ventricle is forced into the systemic aorta.

(C) In the mammalian heart,the right atrium and the right ventricle are separated by a valve consisting of three flaps or cusps.
This valve is known as the $Tricuspid$ valve.
Its primary function is to prevent the backflow of blood from the right ventricle into the right atrium during ventricular systole.

(D) The heart rate of an animal is inversely proportional to its body size. Larger animals like elephants and whales have a slower metabolic rate and a lower heart rate to conserve energy. Conversely,smaller animals like mice have a very high metabolic rate to maintain their body temperature,which necessitates a significantly higher heart rate. Therefore,among the given options,the mouse has the highest heart rate.

(B) The Eustachian valve is a fold of the endocardium located at the opening of the inferior vena cava into the right atrium of the heart.
In the fetal stage, it directs oxygenated blood from the inferior vena cava towards the foramen ovale, allowing it to bypass the non-functional fetal lungs.
After birth, as the circulation pattern changes and the foramen ovale closes, the Eustachian valve loses its functional significance and becomes a vestigial structure.
It is considered a remnant or vestige of the $Sinus venosus$, which is the embryonic structure that gives rise to parts of the right atrium in the mammalian heart.

(D) The pacemaker,specifically the $SA$ node,is responsible for initiating and regulating the rhythmic contraction of the heart. It generates electrical impulses that spread across the heart,ensuring that the cardiac muscles contract in a coordinated and sequential manner. If the pacemaker is absent or non-functional,the heart loses its ability to initiate these rhythmic impulses,and consequently,the cardiac muscles will not contract in a coordinated manner.

(C) The brain receives a significant portion of the cardiac output to maintain its high metabolic demands.
On average,the brain receives approximately $750 \, ml$ of blood per minute in a healthy adult.
This represents about $15\%$ of the total cardiac output.

(C) When irregularity in the heart rhythm occurs,the normal heart rhythm can be restored and maintained by surgically implanting an artificial pacemaker. This device sends out small electrical impulses to stimulate the heart muscle to contract at a regular rate.

(D) Systole refers to the contraction of the heart chambers.
It includes atrial systole,which is the contraction of the atria that propels blood into the ventricles.
It also includes ventricular systole,which is the contraction of the ventricles that expels blood into the aorta and pulmonary artery.

(C) Cardiac muscles are specialized muscles found only in the heart.
They are $Involuntary$ in nature, meaning they function without conscious control.
They exhibit $Striated$ (striped) appearance due to the arrangement of actin and myosin filaments, similar to skeletal muscles.
Therefore, cardiac muscles are classified as $Involuntary$ $Striated$ muscles.

(A) The heart is myogenic,meaning its contraction is initiated by a specialized nodal tissue.
This nodal tissue consists of specialized cardiac muscle fibres known as the $SA$ node,$AV$ node,bundle of $His$,and $Purkinje$ fibres.
Among the given options,$Purkinje$ fibres are the specialized cardiac muscle fibres that conduct electrical impulses through the ventricles to coordinate contraction.
Therefore,the correct option is $A$.

(D) Papillary muscles are specialized muscles located in the ventricles of the mammalian heart. They attach to the cusps of the atrioventricular valves (mitral and tricuspid valves) via the chordae tendineae. Their primary function is to prevent the inversion or prolapse of these valves into the atria during ventricular systole,thereby ensuring unidirectional blood flow. Therefore,the correct option is $(d)$.

(C) The $Bicuspid$ valve,also known as the $Mitral$ valve,is the most frequently damaged heart valve in clinical practice. This is largely due to its location on the left side of the heart,where it is subjected to higher pressure loads compared to the valves on the right side of the heart. Conditions such as rheumatic heart disease and mitral valve prolapse are common causes of damage to this valve.

(D) The systemic aorta (or simply the aorta) is the main artery that carries oxygenated blood from the heart to the rest of the body.
It originates from the $Left \text{ ventricle}$ of the heart.
When the left ventricle contracts, oxygenated blood is pumped through the aortic valve into the systemic aorta, from where it is distributed to all systemic tissues.

(B) In the human circulatory system, the $Pulmonary$ artery is unique because it is the only artery that carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation.
All other arteries in the systemic circulation carry oxygenated blood.
Conversely, the $Pulmonary$ vein carries oxygenated blood from the lungs to the left atrium of the heart.
Therefore, the correct option is $B$.

(D) The heartbeat is myogenic in nature. The sequence of conduction is as follows:
$1$. The impulse originates in the $SA$ (Sino-Atrial) node,which acts as the pacemaker.
$2$. From the $SA$ node,the impulse travels to the $AV$ (Atrio-Ventricular) node.
$3$. From the $AV$ node,it passes through the Bundle of $His$ (Atrioventricular bundle).
$4$. Finally,it spreads through the Purkinje fibers to the ventricular musculature,causing contraction.
Thus,the correct sequence is: $SA$ node $\rightarrow$ $AV$ node $\rightarrow$ Bundle of $His$ $\rightarrow$ Purkinje fibers.

(A) Angiology is the medical specialty that studies the diseases of the circulatory system and the lymphatic system. $William \ Harvey$ is considered the father of Angiology because he was the first to accurately describe the systemic circulation and properties of blood being pumped to the body by the heart.

(A) The heart is myogenic,meaning its rhythmic contraction is initiated by a specialized nodal tissue. The $SA$ (Sinoatrial) node is known as the pacemaker of the heart because it generates the maximum number of action potentials ($70-75$ per minute) and is responsible for initiating and maintaining the rhythmic contractile activity of the heart at a rate of approximately $72$ beats per minute.

(D) The coronary arteries are a pair of arteries that branch off from the base of the aorta.
They are responsible for supplying oxygenated blood to the cardiac muscle (myocardium) of the heart itself.
This blood supply is essential for the continuous contraction and relaxation of the heart muscle.

(D) The human heart is a myogenic organ composed of cardiac muscle. It consists of four chambers: two atria (right and left) and two ventricles (right and left). The sinus venosus is a structure found in the hearts of lower vertebrates like fish and amphibians,which acts as a pacemaker. In the human heart,the sinus venosus is incorporated into the wall of the right atrium during embryonic development to form the sinoatrial $(SA)$ node. Therefore,the human heart does not possess a distinct sinus venosus.

(C) The heart is enclosed by a double-walled membranous bag known as the $Pericardium$.
This structure consists of an outer fibrous layer and an inner serous layer.
The $Pericardium$ protects the heart,anchors it within the chest cavity,and prevents overfilling with blood.