Q.19. Write notes on the following:
(a) Liver and its functions (2015)
(b) Heart beat and factors influencing it (2012)
Related Question -
Q. Write short note on Heart beat. (2015)
Ans. The liver, hepar, is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion. The liver is necessary for survival; there is currently no way to compensate for the absence of liver function in the long term, although new liver dialysis techniques can be used in the short term.
This organ plays a major role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production, and detoxification. It lies below the diaphragm in the abdominal-pelvic region of the abdomen. It produces bile, an alkaline compound which aids in digestion via the emulsification of lipids. The liver’s highly specialized tissues regulate a wide variety of high-volume biochemical reactions, including the synthesis and breakdown of small and complex molecules, many of which are necessary for normal vital functions.
The central area where the common bile duct, hepatic portal vein, and hepatic artery proper enter is the hilum or “porta hepatis”. The duct, vein, and artery divide into left and right branches, and the portions of the liver supplied by these branches constitute the functional left and right lobes.
The functional lobes are separated by an imaginary plane (historically called Cantle’s line) joining the gallbladder fossa to the inferior vena cava. The plane separates the liver into the true right and left lobes. The middle hepatic vein also demarcates the true right and left lobes. The right lobe is further divided into an anterior and posterior segment by the right hepatic vein. The left lobe is divided into the medial and lateral segments by the left hepatic vein. The fissure for the ligamentum teres also separates the medial and lateral segments. The medial segment is also called the quadrate lobe. In the widely used Couinaud (or “French”) system, the functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein. The caudate lobe is a separate structure which receives blood flow from both the right- and left-sided vascular branches.
Other functions
· The liver stores a multitude of substances, including glucose (in the form of glycogen), vitamin A (1–2 years’ supply), vitamin D (1–4 months’ supply), vitamin B12 (1–3 years’ supply), vitamin K, iron, and copper.
· The liver is responsible for immunological effects—the reticuloendothelial system of the liver contains many immunologically active cells, acting as a ‘sieve’ for antigens carried to it via the portal system.
· The liver produces albumin, the major osmolar component of blood serum.
· The liver synthesizes angiotensinogen, a hormone that is responsible for raising the blood pressure when activated by renin, an enzyme that is released when the kidney senses low blood pressure.
1 linker Leberlappen, 2 rechter Leberlappen, 3 Schwanzlappen, 4 quadratischer Leberlappen, 5 Leberpforte mit Leberarterie und Pfortader, 6 Leberlymphknoten, 7 Gallenblase
(ii) Heart Beat: -
Heart beats are the noises generated by the beating heart and the resultant flow of blood through it (specifically, the turbulence created when the heart valves snap shut). In cardiac auscultation, an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart to a trained observer.
In healthy adults, there are two normal heart sounds often described as a lub and a dub (or dup), that occur in sequence with each heartbeat. These are the first heart sound (S1) and second heart sound (S2), produced by the closing of the AV valves and semilunar valves respectively. In addition to these normal sounds, a variety of other sounds may be present including heart murmurs, adventitious sounds, and gallop rhythms S3 and S4.
Heart murmurs are generated by turbulent flow of blood, which may occur inside or outside the heart. Murmurs may be physiological (benign) or pathological (abnormal). Abnormal murmurs can be caused by stenosis restricting the opening of a heart valve, resulting in turbulence as blood flows through it. Abnormal murmurs may also occur with valvular insufficiency (or regurgitation), which allows backflow of blood when the incompetent valve closes with only partial effectiveness. Different murmurs are audible in different parts of the cardiac cycle, depending on the cause of the murmur.
A human heart beats approximately 45 million times per year, but this can vary based on factors such as age, gender and physical activity level. According to the American Heart Association, a normal heart rate can range between 50 and 100 beats per minute. However, a resting heart rate under 80 beats per minute is considered optimal. Your heart rate has large variability and can change frequently throughout the day. Here are six primary factors that influence heart rate.
(i) Body Temperature -When your body temperature changes, so does your heart rate. This is one of the thermoregulatory changes that occur to prevent the body’s core temperature of 98.6 degrees Farhenheit from increasing or decreasing. Heart rate increases when heat is gained by the body such as in hot climates and during exercise in order to transfer more heat away from the body. When the body loses heat such as in cold weather or a cold shower, heart rate decreases to preserve core temperature.
(ii) Eating - After you eat a meal, your heart rate increases to aid with digestion. More blood is directed toward the gastrointestinal tract to process the food. When larger quantities of food are consumed, heart rate may be increased for a longer period of time compared to after eating a small meal or snack. Heart rate can rise above 100 beats per minute, reaching a tachycardic rate due to the effects of eating.
(iii) Exercise - During exercise, your heart rate goes up to facilitate the increased demand for oxygen and carbon dioxide removal to and from the muscles. Heart rate can increase two to three times above resting heart rate depending on the intensity and duration of exercise. Exercising on a regular basis can reduce your resting heart rate and is considered a healthy and beneficial adaptation. Drink water before, during and after exercise to prevent dehydration. Being dehydrated can increase your heart rate and place more stress on the heart.
(iv) Age - As you age, your resting and daily average heart rate does not change significantly. However, your maximum heart rate decreases as you get older due to the physiological effects of aging, such as telomere shortening and associated deconditioning. Your maximum heart rate can be estimated by subtracting your age from 220.
(v) Gender - Women have higher heart rates than men during sleep and when awake. The general consensus for this difference is that women are usually smaller than men and require a faster heart beat to facilitate metabolism. Much of the size difference between men and women is due to women having a less total muscle mass. Because muscle is responsible for much of the body’s metabolism, the higher heart rates experienced by women may be a natural compensatory mechanism to turn up the metabolic rate.
(vi) Caffeine and Other Drugs - Found in coffee, teas and sodas, caffeine is a stimulant drug that influences the nervous system to increase heart rate. It mimics the effect of adrenaline, a natural hormone in the body responsible for elevating heart rate. Other stimulants such as cocaine and ephedrine work in a similar manner.
On the other hand, there are specific drugs used in lowering heart rate such as beta- and calcium channel blockers. Beta-blockers work by interfering with the receptors that adrenaline binds to, subsequently decreasing hormonal influence on heart rate. Calcium channel blockers reduce the amount of calcium that enters the heart muscle. Because calcium is needed for muscle to contract, the heart beats at a slower rate when this drug is taken.
(iii) Situated along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, including aldosterone and cortisol respectively. It is also a secondary site of androgen synthesis.
All adrenocortical hormones are synthesized from cholesterol. Cholesterol is transported into the adrenal gland. The steps up to this point occur in many steroid-producing tissues. Subsequent steps to generate aldosterone and cortisol, however, primarily occur in the adrenal cortex:
· Progesterone --> (hydroxylation at C21) --> 11-Deoxycorticosterone --> (two further hydroxylations at C11 and C18) --> Aldosterone
· Progesterone --> (hydroxylation at C17) --> 17-alpha-hydroxyprogesterone --> (hydroxylation at C21) --> 11-Deoxycortisol --> (hydroxylation at C11) --> Cortisol
The adrenal cortex produces a number of different corticosteroid hormones.
(i) Mineralocorticoids
They are produced in the zona glomerulosa. The primary mineralocorticoid is aldosterone. Its secretion is regulated by the oligopeptide angiotensin II (angiotensin II is regulated by angiotensin I, which in turn is regulated by renin). Aldosterone is secreted in response to high extracellular potassium levels, low extracellular sodium levels, and low fluid levels and blood volume. Aldosterone affects metabolism in different ways:
· It increases urinary excretion of potassium ions
· It increases interstitial levels of sodium ions
· It increases water retention and blood volume
(ii) Glucocorticoids
They are produced in the zona fasciculata. The primary glucocorticoid released by the adrenal gland in the human is cortisol and corticosterone in many other animals. Its secretion is regulated by the hormone ACTH from the anterior pituitary. Upon binding to its target, cortisol enhances metabolism in several ways:
· It stimulates the release of amino acids from the body
· It stimulates lipolysis, the breakdown of fat
· It stimulates gluconeogenesis, the production of glucose from newly-released amino acids and lipids
· It increases blood glucose levels in response to stress, by inhibiting glucose uptake into muscle and fat cells
· It strengthens cardiac muscle contractions
· It increases water retention
· It has anti-inflammatory and anti-allergic effects
Androgens
They are produced in the zona reticularis. The most important androgens include:
· Testosterone: a hormone with a wide variety of effects, ranging from enhancing muscle mass and stimulation of cell growth to the development of the secondary sex characteristics.
· Dihydrotestosterone (DHT): a metabolite of testosterone, and a more potent androgen than testosterone in that it binds more strongly to androgen receptors.
· Androstenedione (Andro): an androgenic steroid produced by the testes, adrenal cortex, and ovaries. While androstenediones are converted metabolically to testosterone and other androgens, they are also the parent structure of estrone.
· Dehydroepiandrosterone (DHEA): It is the primary precursor of natural estrogens. DHEA is also called dehydroisoandrosterone or dehydroandrosterone. The reticularis also produces DHEA-sulfate due to the actions of a sulfotransferase, SULT2A1.
(iv) Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same. Although the term contraction implies shortening, when referring to the muscular system, it means muscle fibers generating tension with the help of motor neurons (the terms twitch tension, twitch force, and fiber contraction are also used).
Voluntary muscle contraction is controlled by the central nervous system. The brain sends signals, in the form of action potentials, through the nervous system to the motor neuron that innervates several muscle fibers. In the case of some reflexes, the signal to contract can originate in the spinal cord through a feedback loop with the grey matter. Involuntary muscles such as the heart or smooth muscles in the gut and vascular system contract as a result of non-conscious brain activity or stimuli proceeding in the body to the muscle itself.
· Testosterone: a hormone with a wide variety of effects, ranging from enhancing muscle mass and stimulation of cell growth to the development of the secondary sex characteristics.
· Dihydrotestosterone (DHT): a metabolite of testosterone, and a more potent androgen than testosterone in that it binds more strongly to androgen receptors.
· Androstenedione (Andro): an androgenic steroid produced by the testes, adrenal cortex, and ovaries. While androstenediones are converted metabolically to testosterone and other androgens, they are also the parent structure of estrone.
· Dehydroepiandrosterone (DHEA): It is the primary precursor of natural estrogens. DHEA is also called dehydroisoandrosterone or dehydroandrosterone. The reticularis also produces DHEA-sulfate due to the actions of a sulfotransferase, SULT2A1.
(iv) Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same. Although the term contraction implies shortening, when referring to the muscular system, it means muscle fibers generating tension with the help of motor neurons (the terms twitch tension, twitch force, and fiber contraction are also used).
Voluntary muscle contraction is controlled by the central nervous system. The brain sends signals, in the form of action potentials, through the nervous system to the motor neuron that innervates several muscle fibers. In the case of some reflexes, the signal to contract can originate in the spinal cord through a feedback loop with the grey matter. Involuntary muscles such as the heart or smooth muscles in the gut and vascular system contract as a result of non-conscious brain activity or stimuli proceeding in the body to the muscle itself.
Q.20. Describe the physiological processes of reproductive system in humans. (2013)
Ans. The reproductive system includes the gonads, reproductive tract, and accessory sex glands, all of which are different in males and females. Reproduction depends upon the union of the male and female gametes (reproductive, or germ, cells), each with a half set of chromosomes, to form a new individual with a full, unique set of chromosomes. Unlike the other body system, which are essentially identical in the two sexes, the reproductive system of males and females are markedly different, befitting their different role in the reproductive process. The male and female reproductive systems are designed to enable union of genetic material from the two sexual partners, and the female system is equipped to house and nourish the offspring to the developmental point at which it can survive independently in the external environment.
The primary reproductive organs, or gonads, consists of a pair of testes in the male and a pair of ovaries in the female. In both sexes, the mature gonads perform the dual function of (1) producing gemetes (gamerogenesis), that is, spermatozoa (sperm) in the male and ova (eggs) in the female, and (2) secreting sex hormones specifically, testosterone in males and estrogen and progesterone in females. In addition to gonads, the reproductive system in each sex includes a reproductive tract encompassing a system of ducts specialized to transport or house the gametes after they are produced, plus accessory sex glands that empty their supportive secretion into these passageways. In females, the breasts are also considered accessory reproductive organs. The externally visible portions of the reproductive system are known as external genitalia.