Cellular Respiration, Nutrition, and Human Body Systems
Cellular Respiration and Energy Production
Nutrients contribute to the fuel for cell energy. Cells use this energy to perform their functions. Cellular respiration occurs in the mitochondria. Glucose is the nutrient most commonly used. There are three phenomena in this process:
- Consumption of oxygen, whose presence is necessary for combustion
- Release of energy, used by cells
- Production of carbon dioxide and water
The useful energy contained in nutrients are chemical substances. This energy is called chemical energy. Cellular respiration releases the chemical energy contained in nutrients. That energy is transformed in the cells into three forms of energy:
- Mechanical: for muscle contraction
- Chemical: to produce new molecules
- Thermal: to maintain body temperature between 36 and 37 degrees Celsius, independent of ambient temperature
Caloric Value of Nutrients
One gram of lipid provides double the energy of one gram of protein or carbohydrates. One kilocalorie (kcal) is equal to 4.2 kilojoules (kJ).
Nutrient | kJ | kcal |
---|---|---|
1 g protein | 17 | 4 |
1 g carbohydrate | 17 | 4 |
1 g lipid | 38 | 9 |
Dietary Recommendations
In a balanced diet, carbohydrates should provide 55% of the energy, lipids 30%, and proteins the remaining 15%.
Basal metabolism is the amount of energy a person needs at rest, after fasting for 12 hours, without being subjected to extreme temperatures.
- Teenagers: Females need approximately 10,000 kJ; Males need approximately 12,600 kJ.
- Adults: Females need approximately 8,300 kJ; Males need approximately 10,800 kJ.
- Elderly: Females need approximately 5,800 kJ; Males need approximately 5,800 kJ.
Factors influencing energy needs include physical activity, environmental temperature, cell activity, sex, and age.
An adult with appropriate weight for their sex and age has their energy needs covered if their weight remains stable. Malnutrition refers to inadequate nutrition due to either poor nutrition or excessive food consumption.
Malnutrition and Eating Disorders
Malnutrition occurs when the amount of food is insufficient to cover the body’s energy needs, often seen in countries experiencing extreme poverty.
Deficiency diseases, also common in impoverished countries, result from consuming enough food but lacking certain vitamins, such as in the case of beriberi.
Anorexia is characterized by an intense fear of gaining weight and a distorted body image, leading to physical and physiological deterioration. Excessive exercise can also contribute and may lead to death.
Bulimia involves eating large amounts of food and then inducing vomiting to prevent weight gain.
Obesity results from ingesting large amounts of energy-rich foods (carbohydrates and fats). Sedentary lifestyles cause these nutrients to accumulate as fat.
The Respiratory System
The respiratory system is responsible for circulating air between the organism and the external environment. It consists of the airways and the lungs, which are lodged in the thoracic cavity.
Airways
The airways are conduits for circulating air. There are two types:
- Upper airways: nose, pharynx, and larynx
- Lower airways: trachea, bronchi, and bronchioles, which end in the alveoli
The nose and mouth are the entry points for air into the respiratory system. From there, the air passes into the pharynx, a cavity shared with the digestive system. After this point, the air travels through a path separate from food.
- Larynx: Funnel-shaped with hard cartilage walls, palpable in the anterior neck. It houses the vocal cords, which vibrate with airflow.
- Trachea: A flexible tube always open to airflow, thanks to cartilage rings in its walls.
- Bronchi and Bronchioles: Similar to the trachea, these tubes branch like a tree. They initially branch into two bronchi, which further subdivide into finer bronchioles.
Lungs
The lungs are two organs located in the thoracic cavity, protected by the ribs. They have a conical shape with a slightly concave base. They are elastic and have a spongy mass. They rest on the diaphragm, a dome-shaped muscle separating the thoracic cavity from the abdominal cavity.
Pulmonary Alveoli
Pulmonary alveoli are small pockets with very thin walls at the end of the finest bronchioles. They are surrounded by many capillaries.
Gas exchange occurs between atmospheric air and blood in the alveoli. The alveoli are well-suited for this due to their large surface area, thin walls, and being surrounded by numerous capillaries.
In the alveoli, oxygen passes from air to blood by simple diffusion. Carbon dioxide moves in the opposite direction by the same mechanism. Nitrogen remains at equal concentrations.
Air leaving the lungs contains approximately 78% N2, 16% O2, 4.5% CO2, and slightly more water vapor.
Respiratory Illnesses
Upper Respiratory Tract Infections (URTIs): Range from mild to severe, including the common cold and flu.
Lower Respiratory Tract Infections (LRTIs): If in the ducts, they manifest as bronchitis; if in the lung tissue, they manifest as pneumonia.
Effects of Smoking
Chronic Bronchitis: Irritants in tobacco smoke cause excessive mucus secretion, clogging the respiratory cilia. It also destroys the cilia that line these pathways and help keep them clean. The cough associated with chronic bronchitis is an attempt to clear the clogged passages.
Lung Cancer: Results from uncontrolled growth of malignant cells in the lungs. Tobacco use also contributes to the development of other tumors, such as those in the larynx, esophagus, and bladder.
Respiratory Health Recommendations
- Inhale through the nose to filter and warm the air.
- Avoid staying in crowded and poorly ventilated indoor spaces.
- Cover your mouth and nose when coughing or sneezing.
- Use tissues to contain respiratory secretions and discard them in the trash after use.
The Urinary System
The urinary system eliminates waste substances from the cells. Urine is a yellow, transparent liquid containing 95% water and 5% dissolved substances. These substances are also present in the blood, but in smaller proportions. Urea, a waste product from protein degradation in cells, is found in higher concentrations in urine than in plasma.
Urine has a composition similar to blood plasma but with a higher concentration of waste substances like urea.
Kidneys
The kidneys are two bean-shaped organs located on either side of the spine. They are responsible for urine formation. Internally, they have three parts:
- Cortex: The outer part, granular in appearance
- Medulla: Pyramid-shaped zone
- Renal Pelvis: Contains blood vessels that enter and leave the kidney through their openings (renal artery and vein)
Bladder
The bladder collects urine, which is continuously produced by the kidneys and transported by the ureters. It is extensible and can hold a variable amount of urine (250 to 500 cm3). When it contracts, the urge to urinate arises.
Ureters
The ureters are two thin tubes that collect urine produced in each kidney.
Urethra
The urethra is a tube that carries urine from the bladder to the outside.
Nephron Function
Blood flowing through the capillaries is filtered in the glomerulus. Then, in the tubule, water, salts, glucose, and waste products like urea are reabsorbed. Excess salts are collected by the peritubular capillaries. Water and glucose are reabsorbed, leaving concentrated urea and excess salts, which form urine.
The nephron’s components include the glomerulus, capsule, peritubular capillaries, tubule, and collecting duct.
Blood is composed of cells (red blood cells, white blood cells, platelets) and fluids (blood plasma). Blood plasma contains water with dissolved molecules, including urea, salts, glucose, lipids, and proteins.
Kidney Functions and Homeostasis
The kidneys perform a dual function: they help cleanse the blood of wastes (excretion) and control the amount of water and salts it contains.
Homeostasis is a set of mechanisms by which all living things tend to achieve stability in the properties of their internal environment.
Besides the kidneys, other organs involved in homeostasis include:
- Lungs: Regulate oxygen and carbon dioxide levels in the blood.
- Liver: Regulates blood glucose levels.
- Skin: Besides being an excretory organ, it helps regulate body temperature.
- Brain: Acts as a controller of homeostatic processes.
Urinary System Disorders
- Infections: Inflammation of the bladder (cystitis) causes discomfort when urinating (pain, itching, burning).
- Stone Formation: Renal colic, caused by the accumulation of salts, forming stones or sand.
Urinary System Health Recommendations
- Drink in moderation, especially meat and seafood.
- Avoid excessive salt intake, such as from sausages, to reduce urea production.
- Drink plenty of water (approximately 2 liters per day for adults).
Body Mass Index (BMI)
BMI is calculated as weight (in kilograms) divided by height (in meters) squared.
- Less than 20: Underweight
- 20-25: Normal weight
- 25-30: Overweight
- 30-35: Moderately obese
- Over 35: Obese