Fundamentals of Biomedical Engineering

1.The kidneys are a pair of excretory organs situated on the posterior wall of the abdomen just below the diaphragm, one on each side of the vertebral column. They remove waste products of metabolism, the excess of water and the excess of salts from the bloods. They also maintain pH value. Each kidney is bean shaped. Each kidney is about 11 cm long, 6 cm broad and 3 cm thick. The left kidney is a little lengthier and narrower than the right kidney. The kidney is about 150 gm in normal adult. The kidneys are also called renes from which the deriative renal and nephron have been derived. The red corpuscles of the blood supple oxygen to the tissues of the kidney. In return the kidneys remove waste products from the blood plasma and regulate the composition of blood plasma.

1.Each kidney consists of one to three million of tiny functional units which are called nephrons. Each nephron consists of a cluster of capillary loop which is called the glomerulus which opens into a collecting tubule. The renal arteries carry blood from the aorta into the glomerular capillary tuft through arterioles. The blood pressure in the glomerulus capillary tuft is about 70 to 90 mm of Hg. The flow of blood is controlled by the arterioles by the amount of contraction. Due to the pressure the waste water and salt in the plasma of the blood

pass through the thin walls of the capillaries into the glomerulus, from where they move into the tubule. The glomerulus filtrate a larger quantity of fluid, about 180 litres per day which consists mainly of water and other substance besides the body waste. A large

amount of water and other substance are reabsorbed by kidney tubules and waste which is called urine (about 1 to 1.5 litres per day) is passed to bladder through ureter. The total blood flow through the kidneys is about 1200 millilitre per min while extracellular fluid (fluid outside cells) is about 15 litres out of total body fluid of 40 litre which means that intra cellular fluid volume is 25 litres (fluid inside the cells). The blood plasma and extra-cellular fluid are in equilibrium which ensures that the amount

of blood equivalent to extra-cellular fluid can pass through the kidneys once every 15 mins. Hence the composition of blood plasma and extra cellular fluid is closely regulated by the kidneys. Special aspects of blood flow through the nephrons–.

(a)The glomerular capillary tuff has high blood pressure which helps in filtering.

(b)Low pressure in the peritubular capillary which permits fluid being absorbed continually into the capillaries.

2.Uremia is urine in blood which is a renal malfunction. In acute renal failure, urine formation stops as kidneys fail to perform excretory or regulatory function on the

blood. The renal failure results in changes in the body fluid due to the progressive decrease in the number of functioning nephrons. Due to decrease in number of

KIDNEY AND BLOOD FLOW

functional nephrons, the clearance of urea, creatinine and other metabolic waste products in the plasma of the blood decreases which is called reduction in the glomerular filteration rate (GFR). The kidneys become less effective as regulatory organs. Uremia is the clinical state resulting from renal failure. Uremia affects other organs of the body as certain substances that accumulate in the blood are toxic. The artificial kidney (Dialyzer) is used which is a mechanical device to remove the accumulated waste products in the blood.

THE ARTIFICIAL KIDNEY (DIALYZER)

1.The artificial kidney is a dialyzing unit which operates outside the patient’s own body. It receives the blood from the cannulated artery of the patient through a plastic tube. The dialysate consists of electrolyte solutions of desirable composition. The dialysis occurs across a membrane of cellophone. After dialysis, the dialyzed blood is fed to an appropriate vein of the patient through a tube. The dialyzing membrane has small

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preforation (diameter of about 5×10–9 m) and waste products of the blood are able to pass through the membrane into the dialysate fluid because of the existence of a concentration gradient across the membrane. The movement of waste products from the blood to the dialysate results in clearing of the blood and dialysate with waste products is discarded. To speed up the dialysis either a positive pressure is applied to the blood compartment or a negative pressure is created in the dialysate compartment.

W aste Products

Principle of Dialysis

11.Artificial kidney is also called ---------------

(a) Analyzer (b) Dialyzer

12.The dialyzing membrane has small ---------

(a) charge (b) perforation

13.Due to existence of the concentration gradient across the membrane, the waste products are able to pass through the

14.To speed up the dialysis either a --------

pressure is applied to the blood compartment or a -------- pressure is created in the dialysate compartment (a) positive, negative (b) negative, positive

15.The composition of the blood plasma and

16. The blood pressure in the glomerulus

18.A large amount of water and other substance of the filtrate are reabsorbed by kidney ----

------ (a) tubules (b) ureter

19.The kidneys function on the blood----------

to remove waste products and to regulate composition (a) corpuscles (b) plasma

INTRODUCTION

1.Prosthesis is a fabricated substitute for a missing part of the body as a limb, heart valve, eyes and tooth. Cybernetics is the study of self organizing machines and mechanical brains. The emphasis is to develop prosthetic devices for human enhancement. Prosthetics are hot area of research. Artificial hands and legs give wearers a better quality of life. Degenerative retinal diseases result in the death of the rods and cones (the cells responsible for light detection). The scientists are working on ways to restore functional sight to those who have become blind through disease. The bionic eye system is made of a 3 mm chip implanted into the retina and a pair of virtualreality style goggle containing a video camera. The goggles convert the video pictures into an infrared image. Dextra is an artificial hand system which is being developed. It can control up to three fingers by recording the movement of muscles in the remaining part of the arm as a person thinks about moving his hand. Robotic devices are also being developed to help the handicapped and also to enhance the strength of a normal person. The Berkeley lower extremity exokeleton (Bleek) is a device which is being developed.

It can calculate how to distribute weight so that wearer feels little or none of it. A soldier who can carry huge loads without getting tired would be more useful on any battle field. A Fireman who needs to climb stairs with heavy equipment or a rescue worker who needs to take supplies into areas where vehicles can not go are other applications of Bleek.

GAIT ANALYSIS

1.Human ambulation or gait is one of the basic need of independent functioning. It is commonly affected by other disease processes or injury. The terminology used to describe gait is :–

(a) Gait Cycle: It commences when the heel of the reference extremity contacts the ground and ends when the heel of the same extremity contacts ground again. The gait cycle consists of two periods of stance, two periods of swing and two periods of double support.

(b) Stance phase: It is the interval inwhich the foot of the reference extremity is in contact with the ground. For example, when we consider the right lower extremity as reference extremity, the left lower extermity is in swing phase while

the right lower extremity is in stance phase. A single gait cycle contains right and left stance. Stance phase constitutes 60% of the gait cycle.

(c) Swing phase: It is the interval inwhich the foot of the reference extremity does not contact the ground. Therefore a single gait cycle contains right and left swing phase. The swing phase constitutes 40% of the gait cycle.

(d) Double support phase: It is the interval in which body weight is transferred from one foot to the other and both right

and left feet are in contact with the ground at the same line. There are two double support phases in a gait cycle.

(e) Stride: Two steps consisting of a right step and a left step comprises a stride. Step length is the distance from the point of heel strike of one extermity to the point of heel strike of the second extremity. Stride length is the distance from the point of heel strike of one extremity to the point of heel strike of the same extremity.