Transportation In Plants And Animals

CloseThe heartbeat is the complete sequence of contraction (systole) and relaxation (diastole) of the heart chambers. Each heartbeat pumps blood into the arteries. An adult human heart beats about 60 to 100 times per minute at rest. The heartbeat is controlled by the sinoatrial node, often called the natural pacemaker.

ClosePulse is the rhythmic expansion and contraction of arterial walls caused by the pressure wave generated when the left ventricle pumps blood into the aorta. The pulse can be felt at various points on the body, such as the wrist (radial artery) or neck (carotid artery). The pulse rate equals the heart rate.

CloseBlood pressure is the pressure exerted by circulating blood on the walls of arteries, veins, and capillaries. It is highest in arteries and lowest in veins. Blood pressure is measured in millimeters of mercury (mm Hg) and is recorded as two numbers: systolic pressure (during heart contraction) over diastolic pressure (during heart relaxation).

CloseSystolic pressure is the pressure in the arteries when the ventricles contract and pump blood out of the heart. It is the higher number in a blood pressure reading. Normal systolic pressure for a healthy adult is around 120 mm Hg. It reflects the force of blood against artery walls during heartbeats.

CloseDiastolic pressure is the pressure in the arteries when the ventricles relax and the heart fills with blood. It is the lower number in a blood pressure reading. Normal diastolic pressure for a healthy adult is around 80 mm Hg. It represents the constant pressure in arteries between heartbeats.

CloseThe ideal normal blood pressure for an adult is about 120 mm Hg systolic and 80 mm Hg diastolic, written as 120/80 mm Hg. Readings below 90/60 mm Hg are considered low blood pressure (hypotension), while readings consistently above 130/80 mm Hg may indicate high blood pressure (hypertension).

CloseExcretion is the biological process by which organisms remove harmful metabolic wastes from their bodies. These wastes include carbon dioxide, urea, uric acid, ammonia, excess water, and salts. Excretion is essential because accumulation of wastes can damage cells and lead to death. Different organs are involved in excretion.

CloseOxygen is not a waste product; it is essential for cellular respiration. The main excretory products in humans are carbon dioxide (from lungs), urea (from kidneys), excess water and salts (from kidneys and skin), and bile pigments (from liver). Oxygen is taken in, not removed as waste.

CloseSmall aquatic animals have a large surface area to volume ratio. Their body surface is thin and in direct contact with surrounding water. Ammonia (their main waste) and carbon dioxide diffuse directly out through the cell membrane or body surface into the water. They do not need complex excretory organs.

CloseFreshwater unicellular organisms like Amoeba constantly take in water by osmosis because their cytoplasm is more concentrated than the surrounding water. The contractile vacuole collects this excess water and actively pumps it out of the cell. This prevents the cell from bursting. It is a form of excretion.

CloseThe lungs excrete carbon dioxide, which is a waste product of cellular respiration. When we exhale, carbon dioxide diffuses from the blood into the alveoli of the lungs and is then expelled. The lungs also excrete small amounts of water vapor. Without this excretion, blood pH would become dangerously acidic.

CloseSweat glands in the skin produce sweat, which contains water, sodium chloride (salt), and small amounts of urea and lactic acid. When sweat evaporates, it cools the body, but the process also removes these wastes. On a hot day, the skin can excrete several liters of water and significant amounts of salt.

CloseThe large intestine forms and stores feces, which consists mainly of undigested food, bacteria, water, and some excretory products. Bile pigments (from breakdown of hemoglobin) are excreted in feces, giving it its brown color. However, the large intestine is primarily for defecation, not for metabolic waste excretion.

CloseThe liver performs several excretory functions. It converts toxic ammonia (from protein breakdown) into less toxic urea, which is then sent to the kidneys. The liver also produces bile, which contains bilirubin (a waste product from old red blood cells). Bile pigments are excreted into the small intestine and leave the body in feces.

CloseHumans are ureotelic animals, meaning they excrete urea as their main nitrogenous waste. Urea is produced in the liver from ammonia (which is highly toxic) through the urea cycle. Urea is less toxic and requires less water for excretion than ammonia. About 25-30 grams of urea are excreted daily in urine.

CloseThe nephron is the microscopic structural and functional unit of the kidney. Each human kidney contains about 1 to 1.5 million nephrons. Each nephron consists of a glomerulus (filtering unit) and a renal tubule (where reabsorption and secretion occur). Nephrons filter blood and produce urine.

CloseEach kidney has a ureter, a muscular tube about 25-30 cm long in humans. Urine produced in the kidneys drains into the renal pelvis and then moves down the ureters to the urinary bladder by peristaltic contractions. The ureters have valves at their entrance to the bladder to prevent backflow of urine.

CloseThe urinary bladder is a hollow, muscular, and elastic organ located in the pelvis. It stores urine produced by the kidneys. In an adult, the bladder can hold approximately 400-600 mL of urine comfortably, though it can stretch to hold more. When it becomes full, nerve signals trigger the urge to urinate.

CloseThe urethra is a thin tube that connects the urinary bladder to the external opening. In males, the urethra is longer (about 20 cm) and also carries semen; in females, it is shorter (about 4 cm) and only carries urine. Sphincter muscles control the release of urine through the urethra.

CloseA healthy adult produces about 1 to 1.8 liters of urine per day, depending on fluid intake, diet, temperature, and physical activity. The minimum amount needed to excrete waste products is about 500 mL per day. Urine output less than 400 mL per day is called oliguria, and less than 50 mL is called anuria, both indicating kidney problems.

CloseDialysis is a medical procedure that performs the function of healthy kidneys when they fail. It removes excess water, urea, creatinine, and other toxins from the blood using a machine and a semipermeable membrane. The two main types are hemodialysis (blood is filtered outside the body) and peritoneal dialysis (using the abdominal lining).

CloseThe dialyzer, also called an artificial kidney, contains thousands of hollow fibers with semipermeable membranes. Blood flows through these fibers while a dialysis fluid (dialysate) flows on the outside. Wastes diffuse from the blood into the dialysate, while useful substances like glucose and electrolytes are kept in the blood.

CloseThe glomerulus is a tiny ball of capillaries inside Bowman’s capsule. Blood pressure forces water, urea, glucose, salts, and other small molecules from the blood into Bowman’s capsule. This process is called ultrafiltration. Blood cells and large proteins remain in the blood because they are too large to pass through the filtration slits.

CloseAfter filtration, the filtrate passes through the renal tubule. In the proximal convoluted tubule, about 65% of water, all glucose, amino acids, and many ions are reabsorbed back into the blood. Glucose is completely reabsorbed in healthy individuals; its presence in urine indicates diabetes. Reabsorption is an active process requiring energy.

CloseUrea is the primary nitrogenous waste in human urine, making up about 50% of the total dissolved solids. It is produced in the liver from ammonia and carbon dioxide. Normal urine contains about 20-35 grams of urea per day. Uric acid (from nucleic acid breakdown) and creatinine (from muscle metabolism) are present in smaller amounts.

CloseUrochrome is a yellow pigment produced from the breakdown of hemoglobin (via bilirubin). It gives urine its characteristic pale yellow to amber color. The color can change with hydration: dark yellow urine indicates concentrated urine (less water), while nearly colorless urine indicates overhydration. Certain foods and drugs can also change urine color.

CloseFish are ammonotelic, meaning they excrete ammonia directly. Ammonia is highly toxic but very soluble in water. Fish excrete ammonia through their gills directly into the surrounding water, where it dilutes rapidly. This requires large amounts of water, which is not a problem for aquatic animals. Humans convert ammonia to urea to save water.

CloseBirds and reptiles are uricotelic, excreting uric acid as a white paste. Uric acid is not very toxic and requires very little water to be removed. This is an adaptation for animals with eggs (uric acid does not harm the developing embryo) and for those living in dry environments. Birds do not have a urinary bladder to store liquid urine.

CloseIn diabetes mellitus, blood glucose levels become very high (hyperglycemia). The nephrons cannot reabsorb all the glucose from the filtrate because the transport proteins are saturated. Excess glucose then appears in the urine (glucosuria). This is a common diagnostic sign of diabetes. Normally, urine contains no detectable glucose.

CloseUremia (or uremic syndrome) occurs when the kidneys fail to filter waste products properly. Urea, creatinine, and other toxins accumulate in the blood. Symptoms include fatigue, nausea, loss of appetite, confusion, and eventually coma. Dialysis or kidney transplant is required to treat severe uremia.

CloseThe medulla oblongata, located in the brainstem, contains the cardiac center that regulates heart rate. It receives signals from sensors (baroreceptors and chemoreceptors) and sends instructions through the autonomic nervous system to speed up or slow down the heart. This control is involuntary, meaning we do not consciously control our heart rate.

CloseDuring exercise, active muscles use more oxygen for cellular respiration and produce more carbon dioxide. The medulla oblongata detects increased carbon dioxide and decreased oxygen in blood and sends signals to increase heart rate and breathing rate. This delivers more oxygen to muscles and removes wastes faster.

CloseUrine formed in the kidneys collects in the renal pelvis. It then flows down each ureter to the urinary bladder for storage. When the bladder contracts during urination, urine passes through the urethra to the outside of the body. The urethra is the final tube. Valves prevent backflow from bladder to ureters.

CloseOsmoregulation is the active regulation of the osmotic pressure of body fluids to maintain water and salt balance. The kidneys adjust the concentration of urine: when you are dehydrated, they produce concentrated (dark) urine; when you have drunk excess water, they produce dilute (pale) urine. This maintains a constant internal environment (homeostasis).

CloseA sphygmomanometer consists of an inflatable cuff, a pressure gauge (mercury or aneroid), and a stethoscope or electronic sensor. The cuff is placed around the upper arm and inflated to temporarily stop blood flow. As the cuff is deflated, the clinician listens for Korotkoff sounds to determine systolic and diastolic pressures.

CloseWhile the average urge to urinate occurs when the bladder contains about 300-400 mL, the bladder can stretch considerably. The maximum capacity of a healthy adult bladder is about 800 to 1000 mL (1 liter). Stretching beyond this can cause discomfort and potential damage. Frequent overstretching can weaken bladder muscles.

CloseThe dialysate has a composition similar to normal blood plasma except it contains no urea or other waste products. This creates a concentration gradient. Wastes (urea, creatinine) diffuse from the blood into the dialysate. At the same time, glucose and essential electrolytes are kept in the blood or added if needed. The dialysate is continuously refreshed.

CloseProtein digestion occurs in the stomach and small intestine, not in the kidneys. The kidneys have many functions: excreting urea and toxins, regulating water and salt balance, maintaining blood pH, producing the hormone erythropoietin (stimulates RBC production), and activating vitamin D. They also help regulate blood pressure through the renin-angiotensin system.

ClosePulse can be felt at any superficial artery that lies over a bone. Common sites include the radial artery (wrist, most common), carotid artery (neck, used in emergencies), brachial artery (inside elbow), femoral artery (groin), and dorsalis pedis (foot). Each site is useful in different clinical situations.

CloseHypertension is a chronic medical condition where blood pressure is consistently elevated. It is often called the “silent killer” because it has no symptoms but can lead to heart attack, stroke, kidney failure, and other complications. Lifestyle changes (diet, exercise, reduced salt) and medications can control it. Normal is 120/80; 130/80 or higher is considered hypertension.

CloseHypotension is abnormally low blood pressure. It may cause dizziness, fainting, blurred vision, and fatigue. Causes include dehydration, blood loss, certain medications, or heart problems. Some athletes naturally have low blood pressure without symptoms. Severe hypotension can be life-threatening because organs may not receive enough oxygen.

CloseBlood enters the glomerulus through the afferent arteriole (wider) and leaves through the efferent arteriole (narrower). The narrower efferent arteriole creates high pressure inside the glomerulus, which forces filtration. After leaving the glomerulus, the efferent arteriole branches into peritubular capillaries that surround the renal tubule for reabsorption.

CloseNormally, urine contains no detectable protein (albumin). The glomerulus prevents large molecules like proteins and blood cells from passing into the filtrate. Presence of protein in urine (proteinuria) indicates kidney damage, such as in glomerulonephritis or diabetic nephropathy. Temporary proteinuria can occur after heavy exercise.

CloseNewborn babies have a much faster heart rate than adults, typically 100 to 160 beats per minute. This is because they have a smaller heart and a higher metabolic rate relative to body size. The heart rate gradually decreases during childhood, reaching adult rates (60-100 bpm) by adolescence. Fever and crying can increase a baby’s heart rate further.

CloseMicturition, also called urination, is the process of releasing urine from the urinary bladder. When the bladder contains about 300-400 mL of urine, stretch receptors send signals to the spinal cord and brain, creating the urge to urinate. The brain can voluntarily delay urination by keeping the external urethral sphincter closed.

CloseThe collecting duct receives filtrate from several nephrons. As it passes through the medulla of the kidney, water is reabsorbed (under the influence of ADH hormone), concentrating the urine. The final concentrated urine then drains into the renal pelvis and then into the ureter. Without the collecting duct, humans could not produce concentrated urine.

CloseADH (also called vasopressin) is produced in the hypothalamus and released from the pituitary gland. When the body is dehydrated, ADH increases water reabsorption in the collecting ducts, producing concentrated urine. When excess water is drunk, ADH decreases, producing dilute urine. Alcohol inhibits ADH, causing increased urine output and dehydration.

CloseThe renal artery branches directly from the aorta and carries oxygenated blood (along with dissolved waste products like urea) to the kidney for filtration. After the kidney filters the blood and removes wastes, the cleaned blood leaves through the renal vein (which carries deoxygenated blood back to the inferior vena cava and heart).

CloseUric acid is a white, paste-like waste that is almost insoluble in water. Excreting it saves water, which is important for birds and reptiles living in dry habitats. Additionally, developing embryos inside eggs cannot eliminate liquid waste; uric acid crystallizes harmlessly and remains in the eggshell. This adaptation is crucial for reproduction on land.

CloseComplete kidney failure is fatal without medical intervention. Without dialysis or a kidney transplant, urea, creatinine, and other toxins build up in the blood (uremia), causing nausea, seizures, coma, and death. Electrolyte imbalances and fluid overload also occur. No other organ can fully replace the filtering function of the kidneys. Death typically occurs within 1-2 weeks.