Prasanna

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Types of Muscles and its Uses

Muscles are specialized tissues which are derived from the embryonic mesoderm. They are made of cells called myocytes and constitute 40 – 50 percent of body weight in an adult. These cells are bound together by a connective tissue to form a muscular tissue. The muscles are classified into three types, namely skeletal, visceral and cardiac muscles.

The three main types of muscle include skeletal, smooth and cardiac. The brain, nerves and skeletal muscles work together to cause movement this is collectively known as the neuromuscular system.

The 3 types of muscle tissue are cardiac, smooth, and skeletal. Cardiac muscle cells are located in the walls of the heart, appear striated, and are under involuntary control.

Comparison of Types

• Skeletal muscle
• Smooth muscle
• Cardiac muscle
• Smooth muscle
• Cardiac muscle

Muscle is one of the four primary tissue types of the body, and the body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle.

In the body, there are three types of muscle: skeletal (striated), smooth, and cardiac. Skeletal Muscle. Skeletal muscle, attached to bones, is responsible for skeletal movements.

• Smooth Muscle
• Cardiac Muscle

The strongest muscle based on its weight is the masseter. With all muscles of the jaw working together it can close the teeth with a force as great as 55 pounds (25 kilograms) on the incisors or 200 pounds (90.7 kilograms) on the molars.

The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction.

Muscle size increases when a person continually challenges the muscles to deal with higher levels of resistance or weight. Muscle hypertrophy occurs when the fibers of the muscles sustain damage or injury. The body repairs damaged fibers by fusing them, which increases the mass and size of the muscles.

Skeletal muscles are voluntary muscles under the control of the somatic nervous system. The other types of muscle are cardiac muscle which is also striated, and smooth muscle which is non-striated; both of these types of muscle are involuntary.

Depending on the amount of microscopic muscle damage from any given workout, your muscle cells can take anywhere from one to several days to grow back bigger and stronger than before, which is why most experts don’t recommend working the same muscle group on back-to-back days, he says.

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Types of Movement in Human Body

The different types of movements that occur in the cells of our body are amoeboid, ciliary, flagellar and muscular movement. Amoeboid movement – Cells such as macrophages exhibit amoeboid movement for engulfing pathogens by pseudopodia formed by the streaming movement of the cytoplasm.

Ciliary Movement:

This type of movement occurs in the respiratory passages and genital tracts which are lined by ciliated epithelial cells.

Flagellar Movement:

This type of movement occurs in the cells which are having flagella or whip-like motile organelle. The sperm cells show flagellar movement.

Muscular Movement:

The movement of hands, legs, jaws, tongue are caused by the contraction and relaxation of the muscle which is termed as the muscular movement.

The different types of movement that are permitted at each joint are described below.

• Flexion – bending a joint.
• Extension – straightening a joint.
• Abduction – movement away from the midline of the body.
• Adduction – movement towards the midline of the body.
• Circumduction – this is where the limb moves in a circle.

In the world of mechanics, there are four basic types of motion. These four are rotary, oscillating, linear and reciprocating.

Flexibility is extending and contracting the muscle tissues, joints, and ligaments into a greater range of motion accepted by the nervous system.

Mobility is neuromuscular active control of the range of motion within the muscle tissue, joints, and ligaments.

• Strength
• Power
• Endurance
• Stability

Body movement involves a complex cascade transforming neural signals to depolarization of myofibres, binding of individual myosin and actin filaments in the sarcomeres leading to myofibre contraction, and myofibre cross-linking transmitting force throughout muscle groups and into the skeletal system via their tendinous.

Muscles move body parts by contracting and then relaxing. Muscles can pull bones, but they can’t push them back to the original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint.

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Process of Haemodialysis and its Kidney Transplantation

Malfunctioning of the kidneys can lead to accumalation of urea and other toxic substances, leading to kidney failure. In such patients toxic urea can be removed from the blood by a process called haemodialysis. A dialyzing machine or an artificial kidney is connected to the patient’s body.

A dialyzing machine consists of a long cellulose tube surrounded by the dialysing fluid in a water bath. The patient’s blood is drawn from a conveinent artery and pumped into the dialysing unit after adding an anticoagulant like heparin.

The tiny pores in the dialysis tube allows small molecules such as glucose, salts and urea to enter into the water bath, whereas blood cells and protein molecules do not enter these pores. This stage is similar to the filtration process in the glomerulus.

The dialysing liquid in the water bath consists of solution of salt and sugar in correct proportion in order to prevent loss of glucose and essential salts from the blood. The cleared blood is then pumped back to the body through a vein Figure 8.10.

Kidney Transplantation

It is the ultimate method for correction of acute renal failures. This involves transfer of healthy kidney from one person (donor) to another person with kidney failure. The donated kidney may be taken from a healthy person who is declared brain dead or from sibling or close relatives to minimise the chances of rejection by the immune system of the host. Immunosuppressive drugs are usually administered to the patient to avoid tissue rejection.

Haemodialysis is a way of replacing some of the functions of your kidney, if your kidneys have failed, by using a machine to filter and clean your blood. Blood is pumped out of your body to the machine where it is passed through a series of tiny tubes, in an ‘artificial kidney’ or ‘dialyser’.

In hemodialysis, blood is removed from the body and filtered through a man-made membrane called a dialyzer, or artificial kidney, and then the filtered blood is returned to the body. The average person has about 10 to 12 pints of blood; during dialysis only one pint (about two cups) is outside of the body at a time.

There are three different types of dialysis. Hemodialysis. Hemodialysis is the most common type of dialysis. Peritoneal dialysis. Peritoneal dialysis involves surgery to implant a peritoneal dialysis (PD) catheter into your abdomen. Continuous renal replacement therapy (CRRT).

When your kidneys fail, dialysis keeps your body in balance by: removing waste, salt and extra water to prevent them from building up in the body. keeping a safe level of certain chemicals in your blood, such as potassium, sodium and bicarbonate helping to control blood pressure.

Hemodialysis is a procedure where a dialysis machine and a special filter called an artificial kidney, or a dialyzer, are used to clean your blood. To get your blood into the dialyzer, the doctor needs to make an access, or entrance, into your blood vessels. This is done with minor surgery, usually to your arm.

The Benefits of Hemodialysis Include:

• Nurses perform treatments for the patient.
• Regular contact with other hemodialysis patients and staff.
• Patients usually only have three treatments per week; giving them four days off.
• No equipment or supplies have to be kept at home.
• In an emergency, medical help is available quickly.

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Disorders Related to the Excretory System

Urinary Tract Infection

Female’s urethra is very short and its external opening is close to the anal opening, hence improper toilet habits can easily carry faecal bacteria into the urethra. The urethral mucosa is continuous with the urinary tract and the inflammation of the urethra (urethritis) can ascend the tract to cause bladder inflammation (cystitis) or even renal inflammation (pyelitis or pyelonephritis).

Symptoms include dysuria (painful urination), urinary urgency, fever and sometimes cloudy or blood tinged urine. When the kidneys are inflammed, back pain and severe headache often occur. Most urinary tract infections can be treated by antibiotics.

Renal Failure (Kidney Failure)

Failure of the kidneys to excrete wastes may lead to accumulation of urea with marked reduction in the urine output. Renal failure are of two types, Acute and chronic renal failure. In acute renal failure the kidney stops its function abruptly, but there are chances for recovery of kidney functions. In chronic renal failure there is a progressive loss of function of the nephrons which gradually decreases the function of kidneys.

Uremia

Uremia is characterized by increase in urea and other non-protein nitrogenous substances like uric acid and creatinine in blood. Normal urea level in human blood is about 17-30mg/100mL of blood. The urea concentration rises as 10 times of normal levels during chronic renal failure.

Renal Calculi

Kidney stone or calculi, also called renal stone or nephrolithiasis, is the formation of hard stone like masses in the renal tubules of renal pelvis. It is mainly due to the accumulation of soluble crystals of salts of sodium oxalates and certain phosphates.

This result in severe pain called “renal colic pain” and can cause scars in the kidneys. Renal stones can be removed by techniques like pyleothotomy or lithotripsy.

Glomerulonephritis

It is also called Bright’s disease and is characterized by inflammation of the glomeruli of both kidneys and is usually due to poststreptococcal infection that occurs in children. Symptoms are haematuria, proteinuria, salt and water retention, oligouria, hypertension and pulmonary oedema.

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Role of Other Organs in Excretion

Apart from kidneys, organs such as lungs, liver and skin help to remove wastes. Our lungs remove large quantities of carbon dioxide (18 L/day) and significant quantities of water every day. Liver secretes bile containing substances like, bilirubin and biliverdin, cholesterol, steroid hormones, vitamins and drugs which are excreted out along with the digestive wastes.

Sweat and sebaceous glands in the skin eliminate certain wastes through their secretions. Sweat produced by the sweat glands primarily helps to cool the body and secondarily excretes Na⁺ and Cl^–, small quantities of urea and lactate.

Sebaceous glands eliminate certain substances like sterols, hydrocarbons and waxes through sebum that provides a protective oily covering for the skin. Small quantities of nitrogenous wastes are also excreted through saliva.

Kidneys play a major role in the process of excretion in humans. Kidneys help in the elimination of wastes from the body in the form of urine. Apart from kidneys, organs like lungs, liver, skin and sebaceous glands help in excretion.

The excretory system in humans consists mainly of the kidneys and bladder. The kidneys filter urea and other waste products from the blood, which are then added to the urine within the bladder. Other organs, such as the liver, process toxins but put their wastes back into the blood.

Excretory Organs. Organs of excretion include the skin, liver, large intestine, lungs, and kidneys (see the figure below). Together, these organs make up the excretory system. They all excrete wastes, but they don’t work together in the same way that organs do in most other body systems. The appendix is a vestigial organ that has no role to play in excretion.

The liver regulates most chemical levels in the blood and excretes a product called bile. This helps carry away waste products from the liver. Production of bile, which helps carry away waste and break down fats in the small intestine during digestion. Production of certain proteins for blood plasma.

These chemical reactions produce waste products such as carbon dioxide, water, salts, urea and uric acid. Accumulation of these wastes beyond a level inside the body is harmful to the body. The excretory organs remove these wastes. This process of removal of metabolic waste from the body is known as excretion.

Humans have two kidneys and each kidney is supplied with blood from the renal artery. The kidneys remove from the blood the nitrogenous wastes such as urea, as well as salts and excess water, and excrete them in the form of urine.

Role of Liver in Excretion:

Liver converts the amino acids present in blood into ammonia and pyruvic acid. Pyruvic acid gets oxidized to release energy and ammonia gets converted into urea. Kidney helps in the filtration of the urea and urea gets excreted in the form of urine.

Certain waste and harmful substances are formed during the functioning of body cells. When these toxic materials are not removed from the body, they get mixed with blood and can damage the cells of the body. The removal of such poisonous waste materials is therefore necessary.

Skin has an important role in excretion in man . So Skin is important to clean our body by the process of excretion. Lungs release Carbon dioxide (CO₂) which helps in the process of respiration and purifies blood. Intestine helps in excretion of food digested in stomach and in duodenum.

Excretion, the process by which animals rid themselves of waste products and of the nitrogenous by-products of metabolism. Through excretion organisms control osmotic pressure the balance between inorganic ions and water and maintain acid-base balance.

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The Physiology of Micturition Definition and its Uses

The process of release of urine from the bladder is called micturition or urination. Urine formed by the nephrons is ultimately carried to the urinary bladder where it is stored till it receives a voluntary signal from the central nervous system. The stretch receptors present in the urinary bladder are stimulated when it gets filled with urine.

Stretching of the urinary bladder stimulates the CNS via the sensory neurons of the parasympathetic nervous system and brings about contraction of the bladder. Simultaneously, somatic motor neurons induce the sphincters to close. Smooth muscles contracts resulting in the opening of the internal sphincters passively and relaxing the external sphincter.

When the stimulatory and inhibitory controls exceed the threshold, the sphincter opens and the urine is expelled out. An adult human on an average excretes 1 to 1.5 L of urine per day. The urine formed is a yellow coloured watery fluid which is slightly acidic in nature (pH 6.0), Changes in diet may cause pH to vary between 4.5 to 8.0 and has a characteristic odour. The yellow colour of the urine is due to the presence of a pigment, urochrome.

On an average, 25-30 gms of urea is excreted per day. Various metabolic disorders can affect the composition of urine. Analysis of urine helps in clinical diagnosis of various metabolic disorders and the malfunctioning of the kidneys. For example the presence of glucose (glucosuria) and ketone bodies (ketonuria) in the urine are indications of diabetes mellitus.

The exact cause of micturition syncope isn’t fully understood. But it may be related to opening (vasodilation) of the blood vessels that occurs when getting up and standing at the toilet or that occurs at the rapid emptying of a full bladder. This is thought to result in a sudden drop in blood pressure.

Micturition involves the simultaneous coordinated contraction of the bladder detrusor muscle, which is controlled by parasympathetic (cholinergic) nerves, and the relaxation of the bladder neck and sphincter, which are controlled by sympathetic (α-adrenergic) nerves.

Micturition syncope causes more than 8 percent of all episodes of fainting. People who experience it are more prone to fainting under other circumstances, too. Micturition syncope occurs more often in men. It often happens after using the bathroom in the middle of the night or first thing in the morning.

The pons is a major relay center between the brain and the bladder. The mechanical process of urination is coordinated by the pons in the area known as the pontine micturition center (PMC). The conscious sensations associated with bladder activity are transmitted to the pons from the cerebral cortex.

Introduction. Micturition is the process of eliminating water and electrolytes from the urinary system, commonly known as urinating. It has two discrete phases: the storage/continence phase, when urine is stored in the bladder; and the voiding phase, where urine is released through the urethra.

Micturition is the process by which the urine from the urinary bladder is excreted. This reflex stimulates the urge to pass out urine. To discharge urine, the urethral sphincter relaxes and the smooth muscles of the bladder contract. This forces the urine out from the bladder.

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Regulation of Kidney Function

ADH and Diabetes Insipidus

The functioning of kidneys is efficiently monitored and regulated by hormonal feedback control mechanism involving the hypothalamus, juxta glomerular apparatus and to a certain extent the heart. Osmoreceptors in the hypothalamus are activated by changes in the blood volume, body fluid volume and ionic concentration.

When there is excessive loss of fluid from the body or when there is an increase in the blood pressure, the osmoreceptors of the hypothalamus respond by stimulating the neurohypophysis to secrete the antidiuretic hormone (ADH) or vasopressin (a positive feedback). ADH facilitates reabsorption of water by increasing the number of aquaporins on the cell surface membrane of the distal convoluted tubule and collecting duct.

This increase in aquaporins causes the movement of water from the lumen into the interstitial cells, thereby preventing excess loss of water by diuresis. When you drink excess amounts of your favourite juice, osmoreceptors of the hypothalamus is no longer stimulated and the release of ADH is suppressed from the neurohypophysis (negative feedback) and the aquaporins of the collecting ducts move into the cytoplasm.

This makes the collecting ducts impermeable to water and the excess fluid flows down the collecting duct without any water loss. Hence dilute urine is produced to maintain the blood volume. Vasopressin secretion is controlled by positive and negative feedback mechanism.

Defects in ADH receptors or inability to secrete ADH leads to a condition called diabetes insipidus, characterized by excessive thirst and excretion of large quantities of dilute urine resulting in dehydration and fall in blood pressure.

Renin Angiotensin

Juxta glomerular apparatus (JGA) is a specialized tissue in the afferent arteriole of the nephron that consists of macula densa and granular cells. The macula densa cells sense distal tubular flow and affect afferent arteriole diameter, whereas the granular cells secrete an enzyme called renin. A fall in glomerular blood flow, glomerular blood pressure and glomerular filtration rate, can atctivate JG cells to release renin which converts a plasma protein, angiotensinogen (synthesized in the liver) to angiotensin I.

Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II. Angiotensin II stimulates Na⁺ reabsorption in the proximal convoluted tubule by vasoconstriction of the blood vessels and increases the glomerular blood pressure.

Angiotensin II acts at different sites such as heart, kidney, brain, adrenal cortex and blood vessels. It stimulates adrenal cortex to secrete aldosterone that causes reabsorption of Na⁺, K⁺ excretion and absorption of water from the distal convoluted tubule and collecting duct.

This increases the glomerular blood pressure and glomerular filtration rate. This complex mechanism is generally known as Renin-AngiotensinAldosterone System (RAAS). Figure 8.9 shows the schematic representation of the various hormones in the regulation of body fluid concentration.

Atrial Natriuretic Factor

Excessive stretch of cardiac atrial cells cause an increase in blood flow to the atria of the heart and release Atrial Natriuretic Peptide or factor (ANF) travels to the kidney where it increases Na⁺ excretion and increases the blood flow to the glomerulus, acting on the afferent glomerular arterioles as a vasodilator or on efferent arterioles as a vasoconstrictor.

It decreases aldosterone release from the adrenal cortex and also decreases release of renin, thereby decreasing angiotensin II. ANF acts antagonistically to the renin – angiotensin system, aldosterone and vasopressin.

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Mechanism of Urine Formation in Human

The nitrogenous waste formed as a result of breakdown of amino acids is converted to urea in the liver by the Ornithine cycle or urea cycle (Figure 8.7).

Urine formation involves three main processes namely, glomerular fitration, tubular reabsorption and tubular secretion.

(i) Glomerular Filtration

Blood enters the kidney from the renal artery, into the glomerulus. Blood is composed of large quantities of water, colloidal proteins, sugars, salts and nitrogenous end product. The first step in urine formation is the filtration of blood that takes place in the glomerulus.

This is called glomerular filtration which is a passive process. The fluid that leaves the glomerular capillaries and enters the Bowman’s capsule is called the glomerular filtrate.

The glomerular membrane has a large surface area and is more permeable to water and small molecules present in the blood plasma. Blood enters the glomerulus faster with greater force through the afferent arteriole and leaves the glomerulus through the efferent arterioles, much slower.

This force is because of the difference in sizes between the afferent and efferent arteriole (afferent arteriole is wider than efferent arteriole) and glomerular hydrostatic pressure which is around 55mm Hg.

Kidneys produce about 180L of glomerular filtrate in 24 hours. The molecules such as water, glucose, amino acids and nitrogenous substances pass freely from the blood into the glomerulus. Molecules larger than 5nm are barred from entering the tubule.

Glomerular pressure is the chief force that pushes water and solutes out of the blood and across the filtration membrane. The glomerular blood pressure (approximately 55 mmHg) is much higher than in other capillary beds. The two opposing forces are contributed by the plasma proteins in the capillaries.

These includes, colloidal osmotic pressure (30 mmHg) and the capsular hydrostatic pressure (15 mmHg) due to the fluids in the glomerular capsule. The net filtration pressure of 10 mmHg is responsible for the renal filtration.

Net filtration Pressure = Glomerular
hydrostatic pressure – (Colloidal osmotic pressure + Capsular hydrostatic pressure).
Net filtration pressure = 55 mmHg – (30 mmHg + 15 mmHg) = 10mmHg

The effective glomerular pressure of 10 mmHg results in ultrafiltration. Glomerular filtration rate (GFR) is the volume of filtrate formed min^-1 in all nephrons (glomerulus) of both the kidneys. In adults the GFR is approximately 120-125mL/min. Blood from the glomerulus is passed out through the efferent arteriole.

The smooth muscle of the efferent arteriole contract resulting in vasoconstriction. Table 8.1 shows the relative concentrations of substances in the blood plasma and the glomerular filtrate. The glomerular filtrate is similar to blood plasma except that there are no plasma proteins.

In cortical nephrons, blood from efferent arteriole flows into peritubular capillary beds and enters the venous system carrying with it recovered solutes and water from the interstitial fluid that surrounds the tubule.

Table 8.1 Concentration of substances in the blood plasma and in the glomerular filtrate

(ii) Tubular Reabsorption

This involves movement of the filtrate back into the circulation. The volume of filtrate formed per day is around 170-180 L and the urine released is around 1.5 L per day, i.e., nearly 99% of the glomerular filtrate that has to be reabsorbed by the renal tubules as it contains certain substances needed by the body.

This process is called selective reabsorption. Reabsorption takes place by the tubular epithelial cells in different segments of the nephron either by active transport or passive transport, diffusion and osmosis.

Proximal Convoluted Tubule (PCT):

Glucose, lactate, amino acids, Na⁺ and water in the filtrate is reabsorbed in the PCT. Sodium is reabsorbed by active transport through sodium-potassium (Na⁺K⁺) pump in the PCT. Small amounts of urea and uric acid are also reabsorbed.

Descending Limb

Of Henle’s loop is permeable to water due the presence of aquaporins, but not permeable to salts. Water is lost in the descending limb, hence Na⁺ and Cl^– gets concentrated in the filtrate.

Ascending Limb of Henle’s Loop

Is impermeable to water but permeable to solutes such as Na⁺, Cl^– and K⁺.

The distal convoluted tubule recovers water and secretes potassium into the tubule. Na⁺, Cl^– and water remains in the filtrate of the DCT. Most of the reabsorption from this point is dependent on the body’s need and is regulated by hormones. Reabsorption of bicarbonate (HCO₃^–) takes place to regulate the blood pH. Homeostasis of K⁺ and Na⁺ in the blood is also regulated in this region.

Collecting Duct

Is permeable to water, secretes K⁺ (potassium ions are actively transported into the tubule) and reabsorbs Na⁺ to produce concentrated urine. The change in permeability to water is due to the presence of number of waterpermeable channels called aquaporins.

Tubular Secretion:

Substances such as H⁺, K⁺, NH₄⁺, creatinine and organic acids move into the filtrate from the peritubular capillaries into the tubular fluid. Most of the water is absorbed in the proximal convoluted tubule and Na⁺ is exchanged for water in the loop of Henle. Hypotonic fluid enters the distal convoluted tubule and substances such as urea and salts pass from peritubular blood into the cells of DCT.

The urine excreted contains both filtered and secreted substances. Once it enters the collecting duct, water is absorbed and concentrated hypertonic urine is formed. For every H⁺ secreted into the tubular filtrate, a Na⁺ is absorbed by the tubular cell.

The H⁺ secreted combines with HCO₃^–, HPO₃^– and NH₃^– and gets fixed as H₂CO₄⁺, H₂PO₄⁺ and NH₄⁺ respectively. Since H⁺ gets fixed in the fluid, reabsorption of H⁺ is prevented.

Formation of Concentrated Urine

Formation of concentrated urine is accomplished by kidneys using counter current mechanisms. The major function of Henle’s loop is to concentrate Na⁺ and Cl^–. There is low osmolarity near the cortex and high osmolarity towards the medulla.

This osmolarity in the medulla is due to the presence of the solute transporters and is maintained by the arrangement of the loop of Henle, collecting duct and vasa recta. This arrangement allows movement of solutes from the filtrate to the interstitial fluid. At the transition between the proximal convoluted tubule and the descending loop of Henle the osmolarity of the interstitial fluid is similar to that of the blood – about 300mOsm.

Ascending and Descending Limbs of Henle, Create a Counter Current Multiplier

(Interaction between flow of filtrate through the limbs of Henle’s and JMN) by active transport. Figure 8.8 (a) shows the counter current multiplier created by the long loops of Henle of the JM nephrons which creates medullary osmotic gradient.

As the fluid enters the descending limb, water moves from the lumen into the interstitial fluid and the osmolarity of interstitial fluid decreases. To counteract this dilution the region of the ascending limb actively pumps solutes from the lumen into the interstitial fluid and the osmolarity increases to about 1200mOsm in medulla. This mismatch between water and salts creates osmotic gradient in the medulla. The osmotic gradient is also due to the permeability of the collecting duct to urea.

The vasa recta, maintains the medullary osmotic gradient via counter current exchanger (the flow of blood through the ascending and descending vasa recta blood vessels) by passive transport. Figure 8.8 (b) shows counter current exchanger where the vasa recta preserves the medullary gradient while removing reabsorbed water and solutes.

This system does not produce an osmotic gradient, but protects the medulla by removal of excess salts from the interstitial fluid and removing reabsorbed water. The vasa recta leave the kidney at the junction between the cortex and medulla. The interstitial fluid at this point is iso-osmotic to the blood.

When the blood leaves the efferent arteriole and enters vasa recta the osmolarity in the medulla increases (1200mOsm) and results in passive uptake of solutes and loss of water in descending vasa recta. As the blood enters the cortex, the osmolarity in the blood decreases (300mOsm) and the blood loses solutes and gains water.

At the final stage in collecting duct to form concentrated urine (hypertonic). Human kidneys can produce urine nearly four times concentrated than the initial filtrate formed.

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Human Excretory System – Structure of Kidney, Nephron

Structure of kidney

Excretory system in human consists of a pair of kidneys, a pair of ureters, urinary bladder and urethra (Figure. 8.2). Kidneys are reddish brown, bean shaped structures that lie in the superior lumbar region between the levels of the last thoracic and third lumber vertebra close to the dorsal inner wall of the abdominal cavity.

The right kidney is placed slightly lower than the left kidney. Each kidney weighs an average of 120-170 grams. The outer layer of the kidney is covered by three layers of supportive tissues namely, renal fascia, perirenal fat capsule and fibrous capsule.

The longitudinal section of kidney (Figure. 8.3) shows, an outer cortex, inner medulla and pelvis. The medulla is divided into a few conical tissue masses called medullary pyramids or renal pyramids. The part of cortex that extends in between the medullary pyramids is the renal columns of Bertini.

The centre of the inner concave surface of the kidney has a notch called the renal hilum, through which ureter, blood vessels and nerves innervate. Inner to the hilum is a broad funnel shaped space called the renal pelvis with projection called calyces.

The renal pelvis is continuous with the ureter once it leaves the hilum. The walls of the calyces, pelvis and ureter have smooth muscles which contracts rhythmically. The calyces collect the urine and empties into the ureter, which is stored in the urinary bladder temporarily. The urinary bladder opens into the urethra through which urine is expelled out.

Structure of a Nephron

Each kidney has nearly one million complex tubular structures called nephron (Figure 8.4). Each nephron consists of a filtering corpuscle called renal corpuscle (malpighian body) and a renal tubule. The renal tubule opens into a longer tubule called the collecting duct. The renal tubule begins with a double walled cup shaped structure called the Bowman’s capsule, which encloses a ball of capillaries that delivers fluid to the tubules, called the glomerulus.

The Bowman’s capsule and the glomerulus together constitute the renal corpuscle. The endothelium of glomerulus has many pores (fenestrae). The external parietal layer of the Bowman’s capsule is made up of simple squamous epithelium and the visceral layer is made of epithelial cells called podocytes. The podocytes end in foot processes which cling to the basement membrane of the glomerulus. The openings between the foot processes are called filtration slits.

The renal tubule continues further to form the proximal convoluted tubule [PCT] followed by a U-shaped loop of Henle (Henle’s loop) that has a thin descending and a thick ascending limb. The ascending limb continues as a highly coiled tubular region called the distal convoluted tubule [DCT].

The DCT of many nephrons open into a straight tube called collecting duct. The collecting duct runs through the medullary pyramids in the region of the pelvis. Several collecting ducts fuse to form papillary duct that delivers urine into the calyces, which opens into the renal pelvis.

In the renal tubules, PCT and DCT of the nephron are situated in the cortical region of the kidney whereas the loop of Henle is in the medullary region. In majority of nephrons, the loop of Henle is too short and extends only very little into the medulla and are called cortical nephrons. Some nephrons have very long loop of Henle that run deep into the medulla and are called juxta medullary nephrons (JMN) (Figure 8.5 a and b)

The capillary bed of the nephrons. First capillary bed of the nephron is the glomerulus and the other is the peritubular capillaries. The glomerular capillary bed is different from other capillary beds in that it is supplied by the afferent and drained by the efferent arteriole.

The efferent arteriole that comes out of the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries. The efferent arteriole serving the juxta medullary nephron forms bundles of long straight vessel called vasa recta and runs parallel to the loop of Henle. Vasa recta is absent or reduced in cortical nephrons (Figure 8.6).

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Models of Excretion Definition and Its Explanation

Excretory system helps in collecting nitrogenous waste and expelling it into the external environment. Animals have evolved different strategies to get rid of these nitrogenous wastes. Ammonia produced during amino acid breakdown is toxic hence must be excreted either as ammonia, urea or uric acid.

The type of nitrogenous end product an animal excretes depends upon the habitat of the animal. Ammonia requires large amount of water for its elimination, whereas uric acid, being the least toxic can be removed with the minimum loss of water, and urea can be stored in the body for considerable periods of time, as it is less toxic and less soluble in water than ammonia.

Animals that excrete most of its nitrogen in the form of ammonia are called ammonoteles. Many fishes, aquatic amphibians and aquatic insects are ammonotelic. In bony fishes, ammonia diffuses out across the body surface or through gill surface as ammonium ions.

Reptiles, birds, land snails and insects excrete uric acid crystals, with a minimum loss of water and are called uricoteles. In terrestrial animals, less toxic urea and uric acid are produced to conserve water. Mammals and terrestrial amphibians mainly excrete urea and are called ureoteles. Earthworms while in soil are ureoteles and when in water are ammonoteles. Figure 8.1 shows the excretory products in different groups of animals.

The animal kingdom presents a wide variety of excretory structures. Most invertebrates have a simple tubular structure in the form of primitive kidneys called protonephridia and metanephridia. Vertebrates have complex tubular organs called kidneys.

Protonephridia are excretory structures with specialized cells in the form of flame cells (cilia) in Platyhelminthes (example tapeworm) and Solenocytes (flagella) in Amphioxus. Nematodes have rennette cells, Metanephridia are the tubular excretory structures in annelids and molluscs.

Malpighian tubules are the excretory structures in most insects. Antennal glands or green glands perform excretory function in crustaceans like prawns. Vertebrate kidney differs among taxa in relation to the environmental conditions.

Nephron is the structural and functional unit of kidneys. Reptiles have reduced glomerulus or lack glomerulus and Henle’s loop and hence produce very little hypotonic urine, whereas mammalian kidneys produce concentrated (hyperosmotic) urine due to the presence of long Henle’s loop.

The Loop of Henle of the nephron has evolved to form hypertonic urine. Aglomerular kidneys of marine fishes produce little urine that is isoosmotic to the body fluid. Amphibians and fresh water fish lack Henle’s loop hence produce dilute urine (hypoosmotic).

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Cardio Pulmonary Resuscitation (CPR)

In 1956, James Elam and Peter Safar were the first to use mouth to mouth resuscitation. CPR is a life saving procedure that is done at the time of emergency conditions such as when a person’s breath or heart beat has stopped abruptly in case of drowning, electric shock or heart attack.

CPR includes rescue of breath, which is achieved by mouth to mouth breathing, to deliver oxygen to the victim’s lungs by external chest compressions which helps to circulate blood to the vital organs.

CPR must be performed within 4 to 6 minutes after cessation of breath to prevent brain damage or death. Along with CPR, defibrillation is also done. Defibrillation means a brief electric shock is given to the heart to recover the function of the heart.

Cardiopulmonary resuscitation (CPR) is an emergency procedure that combines chest compressions often with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore spontaneous blood circulation and breathing in a person who is in cardiac arrest.

5 Steps for Performing CPR

• Check the patient’s responsiveness.
• Shake the unresponsive person by the shoulders and speak loudly to them in an attempt to rouse them.
• Check their breathing and pulse.
• Administer chest compressions.
• Recheck breathing and pulse.

After every 30 chest compressions at a rate of 100 to 120 a minute, give 2 breaths. Continue with cycles of 30 chest compressions and 2 rescue breaths until they begin to recover or emergency help arrives.

Cardiopulmonary resuscitation (CPR) is a lifesaving technique. It aims to keep blood and oxygen flowing through the body when a person’s heart and breathing have stopped. CPR can be performed by any trained person. It involves external chest compressions and rescue breathing.

Types of CPR

High-Frequency Chest Compressions. This technique involves imitating hear beats by giving more chest compressions at intervals of time in high frequency. Open-Chest CPR. Open chest CPR is a procedure in which the heart is retrieved through thoracotomy. Interposed Abdominal Compression CPR.

How is CPR Performed? There are two commonly known versions of CPR: For healthcare providers and those trained: conventional CPR using chest compressions and mouth-to-mouth breathing at a ratio of 30:2 compressions-to-breaths.

CPR stands for cardiopulmonary resuscitation. It is an emergency life-saving procedure that is done when someone’s breathing or heartbeat has stopped.

The three basic parts of CPR are easily remembered as “CAB”: C for compressions, A for airway, and B for breathing. C is for compressions. Chest compressions can help the flow of blood to the heart, brain, and other organs.